Here we present a new particle-mesh galactic N-body code that uses the full multigrid algorithm for solving the modified Poisson equation of the quasi-linear formulation of modified Newtonian dynamics (QUMOND). A novel approach for handling the boundary conditions using a refinement strategy is implemented and the accuracy of the code is compared with analytical solutions of Kuzmin discs. We then employ the code to compute the predicted rotation curves for a sample of five spiral galaxies from the THINGS sample. We generated static N-body realizations of the galaxies according to their stellar and gaseous surface densities and allowed their distances, mass-to-light ratios (M/L values) and both the stellar and gas scale-heights to vary in order to estimate the best-fitting parameters. We found that NGC 3621, NGC 3521 and DDO 154 are well fitted by MOND using expected values of the distance and M/L. NGC 2403 required a moderately larger M/L than expected and NGC 2903 required a substantially larger value. The surprising result was that the scale-height of the dominant baryonic component was well constrained by the rotation curves: the gas scale-height for DDO 154 and the stellar scale-height for the others. In fact, if the suggested stellar scale-height (one-fifth the stellar scale-length) was used in the case of NGC 3621 and NGC 3521 it would not be possible to produce a good fit to the inner rotation curve. For each of the four stellar dominated galaxies, we calculated the vertical velocity dispersions which we found to be, on the whole, quite typical compared with observed stellar vertical velocity dispersions of face-on spirals. We conclude that modelling the gas scale-heights of the gas-rich dwarf spiral galaxies will be vital in order to make precise conclusions about MOND.

In preparation for the High Efficiency and Resolution Multi-Element Spectrograph (HERMES) chemical tagging survey of about a million Galactic FGK stars, we estimate the number of independent dimensions of the space defined by the stellar chemical element abundances [X/Fe]. This leads to a way to study the origin of elements from observed chemical abundances using principal component analysis. We explore abundances in several environments, including solar neighbourhood thin/thick disc stars, halo metal-poor stars, globular clusters, open clusters, the Large Magellanic Cloud and the Fornax dwarf spheroidal galaxy. By studying solar-neighbourhood stars, we confirm the universality of the r-process that tends to produce [neutron-capture elements/Fe] in a constant ratio. We find that, especially at low metallicity, the production of r-process elements is likely to be associated with the production of α-elements. This may support the core-collapse supernovae as the r-process site. We also verify the overabundances of light s-process elements at low metallicity, and find that the relative contribution decreases at higher metallicity, which suggests that this lighter elements primary process may be associated with massive stars. We also verify the contribution from the s-process in low-mass asymptotic giant branch (AGB) stars at high metallicity. Our analysis reveals two types of core-collapse supernovae: one produces mainly α-elements, the other produces both α-elements and Fe-peak elements with a large enhancement of heavy Fe-peak elements which may be the contribution from hypernovae. Excluding light elements that may be subject to internal mixing, K and Cu, we find that the [X/Fe] chemical abundance space in the solar neighbourhood has about six independent dimensions both at low metallicity (−3.5 ≲ [Fe/H] ≲−2) and high metallicity ([Fe/H] ≳−1). However the dimensions come from very different origins in these two cases. The extra contribution from low-mass AGB stars at high metallicity compensates the dimension loss due to the homogenization of the core-collapse supernovae ejecta. Including the extra dimensions from [Fe/H], K, Cu and the light elements, the number of independent dimensions of the [X/Fe]+[Fe/H] chemical space in the solar neighbourhood for HERMES is about eight to nine. Comparing fainter galaxies and the solar neighbourhood, we find that the chemical space for fainter galaxies such as Fornax and the Large Magellanic Cloud has a higher dimensionality. This is consistent with the slower star formation history of fainter galaxies. We find that open clusters have more chemical space dimensions than the nearby metal-rich field stars. This suggests that a survey of stars in a larger Galactic volume than the solar neighbourhood may show about one more dimension in its chemical abundance space.

In 2004, the cosmic background radiation (CBR) temperature T_γ(CN) determined from interstellar CN absorption spectra was found to be 50 ± 20 mK higher than the COBE bolometer measured value. It was proposed that this was due, at least in part, to an error in the evaluation of the rotational components of the oscillator strengths of the rovibronic transitions corresponding to the CN B ²Σ⁺–X ²Σ⁺(0 − 0), R(0), R(1) and P(1) lines. Corrections to the standard Hönl–London (HL) rotational line intensity factors used were determined. New data on interstellar CN absorption show that T_γ(CN) is 29 ± 2 mK greater than the latest value of the cosmological CBR temperature, T_γ(COBE) = 2.72548 ± 0.00057 K. These new results and CN fluorescence lifetime data are shown to give similar derived values for improved HL corrections as well as providing further evidence for the intramolecular coupling between the relevant B ²Σ⁺ state rotational levels and close-lying levels of the A ²Π state which invalidates the standard HL factors. Revised HL factors may be required in future T_γ(CN) measurements, in particular in high-redshift sites, which cannot be studied by bolometric means.

We study the possibility for constraining the topology of the Universe by means of the matched circles statistic applied to polarized cosmic microwave background (CMB) anisotropy maps. The advantages of using the CMB polarization maps in studies of the topology over simply analysing the temperature data as has been done to date are clearly demonstrated. We test our algorithm to search for pairs of matched circles on simulated CMB maps for a universe with the topology of a 3-torus. It is found that the noise levels of both Planck and next generation CMB experiment data are no longer prohibitive and should be low enough to enable the use of the polarization maps for such studies. For such experiments, the minimum radius of the back-to-back matched circles which can be detected is determined. We also show that the polarization generated after reionization does not have an impact on the detectability of the matched circles.

We address the cosmological evolution of violent gravitational instability in high-redshift, massive, star-forming galactic discs. To this aim, we integrate in time the equations of mass and energy conservation under self-regulated instability of a two-component disc of gas and stars. The disc is assumed to be continuously fed by cold gas at the average cosmological rate. The gas forms stars and is partly driven away by stellar feedback. The gas and stars flow inward through the disc to a central bulge due to torques that drive angular momentum outwards. The gravitational energy released by the mass inflow down the gravitational potential gradient drives the disc turbulence that maintains the disc unstable with a Toomre instability parameter Q∼ 1, compensating for the dissipative losses of the gas turbulence and raising the stellar velocity dispersion. We follow the velocity dispersion of stars and gas as they heat and cool, respectively, and search for disc ‘stabilization’, to be marked by a low gas velocity dispersion comparable to the speed of sound ∼10 km s⁻¹. We vary the model parameters that characterize the accreted gas fraction, turbulence dissipation rate, star formation rate and stellar feedback. We find that as long as the gas input roughly follows the average cosmological rate, the disc instability is a robust phenomenon at high redshift till z∼ 1, driven by the high surface density and high gas fraction due to the intense cosmological accretion. For a broad range of model parameter values, the discs tend to ‘stabilize’ at z∼ 0–0.5 as they become dominated by hot stars. When the model parameters are pushed to extreme values, the discs may stabilize as early as z∼ 2, with the gas loss by strong outflows serving as the dominant stabilizing factor.

The flux-ratio anomalies observed in multiply lensed quasar images are most plausibly explained as the result of perturbing structures superposed on the underlying smooth matter distribution of the primary lens. The cold dark matter cosmological model predicts that a large number of substructures should survive inside larger haloes but, surprisingly, this population alone has been shown to be insufficient to explain the observed distribution of the flux ratios of quasars’ multiple images. Other haloes (and their subhaloes) projected along the line of sight to the primary lens have been considered as additional sources of perturbation. In this work, we use ray tracing through the Millennium II simulation to investigate the importance of projection effects due to haloes and subhaloes of mass m > 10⁸ h⁻¹  M_⊙ and extend our analysis to lower masses, m≥ 10⁶ h⁻¹  M_⊙, using Monte Carlo halo distributions. We find that the magnitude of the violation depends strongly on the density profile and concentration of the intervening haloes, but clustering plays only a minor role. For a typical lensing geometry (lens at a redshift of 0.6 and source at a redshift of 2), background haloes (behind the main lens) are more likely to cause a violation than foreground haloes. We conclude that line-of-sight structures can be as important as intrinsic substructures in causing flux-ratio anomalies. The combined effect of perturbing structures within the lens and along the line of sight in the Λ cold dark matter (ΛCDM) universe results in a cusp-violation probability of 20–30 per cent. This alleviates the discrepancy between models and current data, but a larger observational sample is required for a stronger test of the theory.

We have collated multiplicity data for five clusters (Taurus, Chamaeleon I, Ophiuchus, IC 348 and the Orion Nebula Cluster). We have applied the same mass ratio (flux ratios of ΔK≤ 2.5) and primary mass cuts (∼0.1–3.0 M_⊙) to each cluster and therefore have directly comparable binary statistics for all five clusters in the separation range 62–620 au, and for Taurus, Chamaeleon I and Ophiuchus in the range 18–830 au. We find that the trend of decreasing binary fraction with cluster density is solely due to the high binary fraction of Taurus; the other clusters show no obvious trend over a factor of nearly 20 in density.

With N-body simulations, we attempt to find a set of initial conditions that are able to reproduce the density, morphology and binary fractions of all five clusters. Only an initially clumpy (fractal) distribution with an initial total binary fraction of 73 per cent (17 per cent in the range 62–620 au) is able to reproduce all of the observations (albeit not very satisfactorily). Therefore, if star formation is universal, then the initial conditions must be clumpy and with a high (but not 100 per cent) binary fraction. This could suggest that most stars, including M dwarfs, form in binaries.

We investigate the form and evolution of the X-ray luminosity–temperature (L_X–kT) relation of a sample of 114 galaxy clusters observed with Chandra at 0.1 < z < 1.3. The clusters were divided into subsamples based on their X-ray morphology or whether they host strong cool cores. We find that when the core regions are excluded, the most relaxed clusters (or those with the strongest cool cores) follow an L_X–kT relation with a slope that agrees well with simple self-similar expectations. This is supported by an analysis of the gas density profiles of the systems, which shows self-similar behaviour of the gas profiles of the relaxed clusters outside the core regions. By comparing our data with clusters in the Representative XMM-Newton Cluster Structure Survey (REXCESS) sample, which extends to lower masses, we find evidence that the self-similar behaviour of even the most relaxed clusters breaks at around 3.5   keV. By contrast, the L_X–kT slopes of the subsamples of unrelaxed systems (or those without strong cool cores) are significantly steeper than the self-similar model, with lower mass systems appearing less luminous and higher mass systems appearing more luminous than the self-similar relation. We argue that these results are consistent with a model of non-gravitational energy input in clusters that combines central heating with entropy enhancements from merger shocks. Such enhancements could extend the impact of central energy input to larger radii in unrelaxed clusters, as suggested by our data. We also examine the evolution of the L_X–kT relation, and find that while the data appear inconsistent with simple self-similar evolution, the differences can be plausibly explained by selection bias, and thus we find no reason to rule out self-similar evolution. We show that the fraction of cool core clusters in our (non-representative) sample decreases at z > 0.5 and discuss the effect of this on measurements of the evolution in the L_X–kT relation.

Common models of blazars and gamma-ray bursts assume that the plasma underlying the observed phenomenology is magnetized to some extent. Within this context, radiative signatures of dissipation of kinetic and conversion of magnetic energy in internal shocks of relativistic magnetized outflows are studied. We model internal shocks as being caused by collisions of homogeneous plasma shells. We compute the flow state after the shell interaction by solving Riemann problems at the contact surface between the colliding shells, and then compute the emission from the resulting shocks. Under the assumption of a constant flow luminosity, we find that there is a clear difference between the models where both shells are weakly magnetized (σ≲ 10⁻²) and those where, at least, one shell has σ≳ 10⁻². We obtain that the radiative efficiency is largest for models in which, regardless of the ordering, one shell is weakly and the other strongly magnetized. Substantial differences between weakly and strongly magnetized shell collisions are observed in the inverse-Compton part of the spectrum, as well as in the optical, X-ray and 1-GeV light curves. We propose a way to distinguish observationally between weakly magnetized and strongly magnetized internal shocks by comparing the maximum frequency of the inverse-Compton part and synchrotron part of the spectrum to the ratio of the inverse-Compton to synchrotron fluence. Finally, our results suggest that low-frequency peaked blazars (LBL) may correspond to barely magnetized flows, while high-frequency peaked blazars (HBL) could correspond to moderately magnetized ones. Indeed, by comparing with actual blazar observations, we conclude that the magnetization of typical blazars is σ≲ 0.01 for the internal shock model to be valid in these sources.

The Schönberg–Chandrasekhar (SC) limit is a well-established result in the understanding of stellar evolution. It provides an estimate of the point at which an evolved isothermal core embedded in an extended envelope begins to contract. We investigate contours of constant fractional mass in terms of homology invariant variables U and V and find that the SC limit exists because the isothermal core solution does not intersect all of the contours for an envelope with polytropic index 3. We find that this analysis also applies to similar limits in the literature including the inner mass limit for polytropic models of quasi-stars. Consequently, any core solution that does not intersect all of the fractional mass contours exhibits an associated limit and we identify several relevant cases where this is so. We show that a composite polytrope is at a fractional core mass limit when its core solution touches but does not cross the contour of the corresponding fractional core mass. We apply this test to realistic models of helium stars and find that stars typically expand when their cores are near a mass limit. Furthermore, it appears that stars that evolve into giants have always first exceeded an SC-like limit.

We investigate for the first time the effects of a warm dark matter (WDM) power spectrum on the statistical properties of galaxies using a semi-analytic model of galaxy formation. The WDM spectrum we adopt as a reference case is suppressed – compared to the standard cold dark matter (CDM) case – below a cut-off scale ≈1 Mpc corresponding (for thermal relic WDM particles) to a mass m_X= 0.75 keV. This ensures consistency with present bounds provided by the microwave background Wilkinson Microwave Anisotropy Probe data and by the comparison of hydrodynamical N-body simulations with observed Lyman-α forest. We run our fiducial semi-analytic model with such a WDM spectrum to derive galaxy luminosity functions (in B, UV and K bands) and the stellar mass distributions over a wide range of cosmic epochs, to compare with recent observations and with the results in the CDM case. The predicted colour distribution of galaxies in the WDM model is also checked against the data. When compared with the standard CDM case, the luminosity and stellar mass distributions we obtain assuming a WDM spectrum are characterized by (i) flattening of the faint-end slope and (ii) sharpening of the cut-off at the bright end for z≲ 0.8. We discuss how the former result is directly related to the smaller number of low-mass haloes collapsing in the WDM scenario, while the latter is related to the smaller number of satellite galaxies accumulating in massive haloes at a low redshift, thus suppressing the accretion of small lumps on the central, massive galaxies. These results shows how adopting a WDM power spectrum may contribute to solving two major problems of CDM galaxy formation scenarios, namely, the excess of predicted faint (low-mass) galaxies at low and – most of all – high redshifts, and the excess of bright (massive) galaxies at low redshifts.

In this paper we consider the detection of compact sources in maps of the cosmic microwave background radiation following the philosophy behind the Mexican hat wavelet family (MHWn) of linear filters. We present a new analytical filter, the biparametric adaptive filter (BAF), that is able to adapt itself to the statistical properties of the background as well as to the profile of the compact sources, maximizing the amplification and improving the detection process. We have tested the performance of this filter using realistic simulations of the microwave sky between 30 and 857 GHz as observed by the Planck satellite, where complex backgrounds can be found. We demonstrate that doing a local analysis on flat patches allows one to find a combination of the optimal scale of the filter R and the index of the filter g that will produce a global maximum in the amplification, enhancing the signal-to-noise ratio (SNR) of the detected sources in the filtered map and improving the total number of detections above a threshold. We conclude that the new filter is able to improve the overall performance of the MHW2, increasing the SNR of the detections and, therefore, the number of detections above a 5σ threshold. The improvement of the new filter in terms of SNR is particularly important in the vicinity of the Galactic plane and in the presence of strong Galactic emission. Finally, we compare the sources detected by each method and find that the new filter is able to detect more new sources than the MHW2 at all frequencies and in clean regions of the sky. The BAF is also less affected by spurious detections, associated with compact structures in the vicinity of the Galactic plane.

We present a statistical framework which can be used to determine the contribution of an unresolved population of pulsars to the gamma-ray background. This formalism is based on the joint analysis of photon time series over extended regions of the sky. We demonstrate the robustness of this technique in controlled simulations of pulsar populations, and show that the Fermi Gamma-ray Space Telescope can be used to detect a pulsar contribution as small as 0.1 per cent of the gamma-ray background. This technique is sensitive to pulsar populations with photon fluxes greater than ∼10⁻¹⁰ cm⁻² s⁻¹. The framework is extensible to arbitrarily complex searches for periodicity and can therefore be tailored to specific applications such as all-sky surveys and studies of the Galactic Centre and globular clusters.

Recent observations reveal that spectral breaks at ∼GeV are commonly present in Galactic γ-ray supernova remnants (SNRs) interacting with molecular clouds and that most of them have a spectral (E²dF/dE) ‘platform’ extending from the break to lower energies. In Paper I, we developed an accumulative diffusion model by considering an accumulation of the diffusive protons escaping from the shock front throughout the history of the SNR expansion. In this paper, we improve the model by incorporating the finite volume of molecular clouds, demonstrate the model dependence on particle diffusion parameters and cloud size, and apply it to nine interacting SNRs (W28, W41, W44, W49B, W51C, Cygnus Loop, IC443, CTB 37A and G349.7+0.2). This refined model naturally explains the GeV spectral breaks and, in particular, the ‘platforms’, together with available TeV data. We find that the index of the diffusion coefficient δ is in the range 0.5–0.7, similar to the Galactic averaged value, and the diffusion coefficient for cosmic rays around the SNRs is essentially two orders of magnitude lower than the Galactic average (χ∼ 0.01), which is a good indication for the suppression of cosmic-ray diffusion near SNRs.

We present recent Hubble Space Telescope observations of the inner filament of Centaurus A, using the new Wide Field Camera 3 (WFC3) F225W, F657N and F814W filters. We find a young stellar population near the south-west tip of the filament. Combining the WFC3 data set with archival Advanced Camera for Surveys (ACS) F606W observations, we are able to constrain the ages of these stars to ≲10 Myr, with best-fitting ages of 1–4 Myr. No further recent star formation is found along the filament.

Based on the location and age of this stellar population, and the fact that there is no radio lobe or jet activity near the star formation, we propose an updated explanation for the origin of the inner filament. Sutherland et al. suggested that radio jet-induced shocks can drive the observed optical line emission. We argue that such shocks can naturally arise due to a weak cocoon-driven bow shock (rather than from the radio jet directly), propagating through the diffuse interstellar medium from a location near the inner northern radio lobe. The shock can overrun a molecular cloud, triggering star formation in the dense molecular cores. Ablation and shock heating of the diffuse gas then give rise to the observed optical line and X-ray emission. Deeper X-ray observations should show more diffuse emission along the filament.

We calculate the angular power spectrum of galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 7 by using a quadratic estimation method with Karhunen–Loéve compression. The primary data sample includes over 18 million galaxies covering more than 5700 deg² after masking areas with bright objects, reddening greater than 0.2 mag and seeing of more than 1.5 arcsec. We test for systematic effects by calculating the angular power spectrum by SDSS stripe and find that these measurements are minimally affected by seeing and reddening. We calculate the angular power spectrum for ℓ≤ 200 multipoles by using 40 bandpowers for the full sample, and ℓ≤ 1000 multipoles using 50 bandpowers for individual stripes. We also calculate the angular power spectrum for this sample separated into 3 mag bins with mean redshifts of z= 0.171, 0.217 and 0.261 to examine the evolution of the angular power spectrum. We determine the theoretical linear angular power spectrum by projecting the 3D power spectrum to two dimensions for a basic comparison to our observational results. By minimizing the χ² fit between these data and the theoretical linear angular power spectrum we measure a loosely constrained fit of with a linear bias of b= 0.94 ± 0.04.

A sample of 18 286 radio-loud active galactic nuclei (AGN) is presented, constructed by combining the seventh data release of the Sloan Digital Sky Survey with the NRAO (National Radio Astronomy Observatory) VLA (Very Large Array) Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty centimetres (FIRST) survey. Using this sample, the differences between radio galaxies of ‘high-excitation’ (‘quasar-mode’; hereafer HERG) and ‘low-excitation’ (‘radio-mode’; LERG) are investigated. A primary difference between the two radio source classes is the distinct nature of the Eddington-scaled accretion rate on to their central black holes: HERGs typically have accretion rates between one per cent and 10 per cent of their Eddington rate, whereas LERGs predominately accrete at a rate below one per cent Eddington. This is consistent with models whereby the population dichotomy is caused by a switch between radiatively efficient and radiatively inefficient accretion modes at low accretion rates. Local radio luminosity functions are derived separately for the two populations, for the first time, showing that although LERGs dominate at low radio luminosity and HERGs begin to take over at L_1.4 GHz∼ 10²⁶ W Hz⁻¹, examples of both classes are found at all radio luminosities. Using the V/V_max test it is shown that the two populations show differential cosmic evolution at fixed radio luminosity: HERGs evolve strongly at all radio luminosities, while LERGs show weak or no evolution. This suggests that the luminosity dependence of the evolution previously seen in the radio luminosity function is driven, at least in part, by the changing relative contributions of these two populations with luminosity. The host galaxies of the radio sources are also distinct: HERGs are typically of lower stellar mass, with lower black hole masses, bluer colours, lower concentration indices and less pronounced 4000 Å breaks indicating younger stellar populations. Even if samples are matched in radio luminosity and stellar and black hole masses, significant differences still remain between the accretion rates, stellar populations and structural properties of the host galaxies of the two radio source classes. These results offer strong support to the developing picture of radio-loud AGN in which HERGs are fuelled at high rates through radiatively efficient standard accretion discs by cold gas, perhaps brought in through mergers and interactions, while LERGs are fuelled via radiatively inefficient flows at low accretion rates. In this picture, the gas supplying the LERGs is frequently associated with the hot X-ray haloes surrounding massive galaxies, groups and clusters, as part of a radio-AGN feedback loop.

We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The Sydney-AAO (Australian Astronomical Observatory) Multi-object IFS (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles (‘hexabundles’) to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly fused multi-mode fibres with reduced cladding and yields a 75 per cent filling factor. Each fibre core diameter subtends 1.6 arcsec on the sky and each hexabundle has a field of view of 15 arcsec diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R=λ/δλ≈ 1700–13 000) over the optical spectrum (3700–9500 Å). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z≈ 0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially resolved spectroscopic surveys of 10⁴–10⁵ galaxies.

We take a sample of 24 elliptical and lenticular galaxies previously analysed by the SAURON project using three integral dynamical models created with Schwarzschild method, and re-analyse them using the made-to-measure (M2M) method of dynamical modelling. We obtain good agreement between the two methods in determining the dynamical mass-to-light ratios (M/L values) for the galaxies with over 80 per cent of ratios differing by <10 per cent and over 95 per cent differing by <20 per cent. We show that . For the global velocity dispersion anisotropy parameter δ, we find similar values but with fewer of the M2M models tangentially anisotropic by comparison with their SAURON Schwarzschild counterparts. Our investigation is the largest comparative application of the M2M method to date.

Stochastic heating of small grains is often mentioned as a primary cause of large infrared (IR) fluxes from star-forming galaxies, for example, at 24 m. If the mechanism does work at a galaxy-wide scale, it should show up at smaller scales as well. We calculate temperature probability density distributions within a model protostellar core for four dust components: large silicate and graphite grains, small graphite grains, and polycyclic aromatic hydrocarbon particles. The corresponding spectral energy distributions are calculated and compared with observations of a representative IR dark cloud core. We show that stochastic heating, induced by the standard interstellar radiation field, cannot explain high mid-IR emission towards the centre of the core. In order to reproduce the observed emission from the core projected centre, in particular, at 24 m, we need to increase the ambient radiation field by a factor of about 70. However, the model with enhanced radiation field predicts even higher intensities at the core periphery, giving it a ring-like appearance, which is not observed. We discuss possible implications of this finding and also discuss the role of other non-radiative dust heating processes.

We describe the internal photometric calibration of the Deep Lens Survey, which consists of five widely separated fields observed by two different observatories. Adopting the global linear least-squares (‘ubercal’) approach developed for the Sloan Digital Sky Survey (SDSS), we derive flat-field corrections for all observing runs, which indicate that the original sky flats were non-uniform by up to 0.13 mag peak-to-valley in z band, and by up to half of that amount in BVR. We show that the application of these corrections reduces spatial non-uniformities in corrected exposures to the 0.01–0.02 mag level. We conclude with some lessons learned in applying ubercal to a survey structured very differently from SDSS, with isolated fields, multiple observatories and shift-and-stare rather than drift-scan imaging. Although the size of the error caused by using sky or dome flats is instrument and wavelength dependent, users of wide-field cameras should not assume that it is small. Pipeline developers should facilitate routine application of this procedure, and surveys should include it in their plans from the outset.

We present measurements of the mean mid-infrared to submillimetre flux densities of massive (M_★≳ 10¹¹ M_⊙) galaxies at redshifts 1.7 < z < 2.9, obtained by stacking positions of known objects taken from the GOODS NICMOS Survey (GNS) catalogue on maps at 24 m (Spitzer/MIPS); 70, 100 and 160 m (Herschel/PACS); 250, 350 and 500 m (BLAST); and 870 m (LABOCA). A modified blackbody spectrum fit to the stacked flux densities indicates a median [interquartile] star formation rate (SFR) of SFR = 63[48, 81] M_⊙ yr⁻¹. We note that not properly accounting for correlations between bands when fitting stacked data can significantly bias the result. The galaxies are divided into two groups, disc-like and spheroid-like, according to their Sérsic indices, n. We find evidence that most of the star formation is occurring in n≤ 2 (disc-like) galaxies, with median [interquartile] SFR = 122[100, 150] M_⊙ yr⁻¹, while there are indications that the n > 2 (spheroid-like) population may be forming stars at a median [interquartile] SFR = 14[9, 20] M_⊙ yr⁻¹, if at all. Finally, we show that star formation is a plausible mechanism for size evolution in this population as a whole, but find only marginal evidence that it is what drives the expansion of the spheroid-like galaxies.

We analyse the possibilities of detection of hypothetical exoplanets in co-orbital motion from synthetic radial velocity (RV) signals, taking into account different types of stable planar configurations, orbital eccentricities and mass ratios. For each nominal solution corresponding to small-amplitude oscillations around the periodic solution, we generate a series of synthetic RV curves mimicking the stellar motion around the barycentre of the system. We then fit the data sets obtained assuming three possible different orbital architectures: (a) two planets in co-orbital motion, (b) two planets in a 2/1 mean-motion resonance (MMR) and (c) a single planet. We compare the resulting residuals and the estimated orbital parameters.

For synthetic data sets covering only a few orbital periods, we find that the discrete RV signal generated by a co-orbital configuration could be easily confused with other configurations/systems, and in many cases the best orbital fit corresponds to either a single planet or two bodies in a 2/1 resonance. However, most of the incorrect identifications are associated with dynamically unstable solutions.

We also compare the orbital parameters obtained with two different fitting strategies: a simultaneous fit of two planets and a nested multi-Keplerian model. We find that, even for data sets covering over 10 orbital periods, the nested models can yield incorrect orbital configurations (sometimes close to fictitious MMRs) that are nevertheless dynamically stable and with orbital eccentricities lower than the correct nominal solutions.

Finally, we discuss plausible mechanisms for the formation of co-orbital configurations, by the interaction between two giant planets and an inner cavity in the gas disc. For equal-mass planets, both Lagrangian and anti-Lagrangian configurations can be obtained from same initial condition depending on final time of integration.

We present a detailed study of the active eclipsing binary V455 Cygni (V455 Cyg), based on spectroscopic and photometric data from the 1.25-m and 0.6-m telescopes at the Crimean SAI Observatory and the 0.6-m telescope at the Maidanak Observatory, collected in the period from 2000 to 2010.

Spectroscopic evidence and the shape of the light curves suggest the existence of a geometrically and optically thick accretion disc around the more massive and hotter gainer. We used a model of the binary system based on the Roche geometry and including the accretion disc with active regions to estimate the orbital and physical parameters of the components of V455 Cyg. Our model fits the observations very well for all individual passband light curves.

The evident seasonal changes in the shape of the light curves, including prominent variations in the depth of the eclipses, can be explained by the changes in the parameters of the accretion disc and the active regions of the disc, arising in turn from a variable rate of mass transfer.

In this paper, we propose a new integral representation for reconstructing the surface density of matter in the flat discs of spiral galaxies. The surface density is expressed through the observed rotation velocity curves of visible matter in the discs of spiral galaxies. The new integral representation is not based on the quadrature of special functions. The solution that is found is used to process and analyse observational data from several spiral galaxies. The new integral representation can be used to more accurately estimate the amount of dark matter in spiral galaxies.

The scattering of small bodies by planets is an important dynamical process in planetary systems. In this paper, we present an analytical model to describe this process using the simplifying assumption that each particle’s dynamics are dominated by a single planet at a time. As such the scattering process can be considered as a series of three-body problems during each of which the Tisserand parameter with respect to the relevant planet is conserved. This constrains the orbital parameter space into which a particle can be scattered. Such arguments have previously been applied to the process by which comets are scattered to the inner Solar system from the Kuiper belt. Our analysis generalizes this for an arbitrary planetary system. For particles scattered from an outer belt directly along a chain of planets, based on the initial value of the Tisserand parameter, we find that it is possible to (i) determine which planets can eject the particles from the system; (ii) define a minimum stellar distance to which particles can be scattered; and (iii) constrain a range of particle inclinations (and hence the disc height) at different distances. Applying this to the Solar system, we determine that the planets are close to optimally separated for scattering particles between them. Concerning warm dust found around stars that also have Kuiper belt analogues, we show that, if there is to be a dynamical link between the outer and inner regions, then certain architectures for the intervening planetary system are incapable of producing the observations. We speculate that the diversity in observed levels of warm dust may reflect the diversity of planetary system architectures. Furthermore, we show that for certain planetary systems, comets can be scattered from an outer belt, or with fewer constraints, from an Oort cloud analogue, on to star-grazing orbits, in support of a planetary origin to the metal pollution and dustiness of some nearby white dwarfs. In order to make more concrete conclusions regarding scattering processes in such systems, it is necessary to consider not only the orbits available to scattered particles, but also the probability that such particles are scattered on to the different possible orbits.

A new, transient ultraluminous X-ray source (ULX) was recently discovered by Chandra in M31 with a luminosity at ∼5 × 10³⁹ erg s⁻¹. Here we analyse a series of five subsequent XMM–Newton observations. These show a steady decline in X-ray luminosity over 1.5 months, from 1.8 × 10³⁹ to 0.6 × 10³⁹ erg s⁻¹, giving an observed e-fold time-scale of ∼40 d. This is similar to the decay time-scales seen in multiple soft X-ray transients in our own Galaxy, supporting the interpretation of this ULX as a stellar mass black hole in a low-mass X-ray binary (LMXB), accreting at super-Eddington rates. This is further supported by the lack of detection of an O/B star in quiescence and the spectral behaviour of the XMM–Newton data being dominated by a disc-like component rather than the power law expected from a sub-Eddington intermediate-mass black hole.

These data give the best sequence of high Eddington fraction spectra ever assembled due to the combination of low absorption column to M31 and well-calibrated bandpass down to 0.3 keV of XMM–Newton in full frame mode. The spectra can be roughly described by our best current disc model, BHSPEC, assuming a 10 M_⊙ black hole with best-fitting spin ∼0.4, declining from L/L_Edd= 0.75 to 0.25. However, the data are better described by a two-component model, where the disc emission is significantly affected by advection, and with an additional low-temperature Comptonization component at high energies which becomes more important at high luminosities. This could simply indicate the limitations of our current disc models, though changes in the energy-dependent variability also weakly supports a two-component interpretation of the data.

Irrespective of the detailed interpretation of the spectral properties, these data support the presence of accretion on to a stellar mass black hole in a LMXB accreting in the Eddington regime. This allows an unambiguous connection of this object, and, by extension, similar low-luminosity ULXs, to ‘standard’ X-ray binaries.

Using William Herschel Telescope (WHT) Optically Adaptive System for Imaging Spectroscopy (OASIS) integral field unit observations, we report the discovery of a thin plume of ionized gas extending from the brightest cluster galaxy (BCG) in Abell 2146 to the subcluster X-ray cool core which is offset from the BCG by ∼37 kpc. The plume is greater than 15 kpc long and less than 3 kpc wide. This plume is unique in that the cluster it is situated in is currently undergoing a major galaxy cluster merger. The BCG is unusually located behind the X-ray shock front and in the wake of the ram-pressure-stripped X-ray cool core, and evidence for recent disruption to the BCG is observed. We examine the gas and stellar morphology, the gas kinematics of the BCG and their relation to the X-ray gas. We propose that a causal link between the ionized gas plume and the offset X-ray cool core provides the simplest explanation for the formation of the plume. An interaction or merger between the BCG and another cluster galaxy is probably the cause of the offset.

We present a study of the Fundamental Plane (FP) for a sample of 71 dwarf galaxies in the core of the Coma cluster in the magnitude range −21 < M_I < −15. Taking advantage of the high-resolution DEIMOS spectrograph on Keck II for measuring the internal velocity dispersion of galaxies and high-resolution imaging of the Hubble Space Telescope (HST)/ACS, which allows an accurate surface brightness modelling, we extend the FP of galaxies to luminosities of ∼1 mag fainter than all the previous studies of the FP in the Coma cluster. We find that the scatter about the FP depends on the faint-end luminosity cut-off, such that the scatter increases for fainter galaxies. The residual from the FP correlates with the galaxy colour, with bluer galaxies showing larger residuals from the FP.

We find M/L ∝ M^{−0.15±0.22} in the F814W band, indicating that in faint dwarf ellipticals, the M/L ratio is insensitive to the mass. We find that less massive dwarf ellipticals are bluer than their brighter counterparts, possibly indicating ongoing star formation activity. Although tidal encounters and harassment can play a part in removing stars and dark matter from the galaxy, we believe that the dominant effect will be the stellar wind associated with the star formation, which will remove material from the galaxy, resulting in larger M/L ratios. We attribute the deviation of a number of faint blue dwarfs from the FP of brighter ellipticals to this effect.

We also study other scaling relations involving galaxy photometric properties including the Photometric Plane. We show that compared to the FP, the scatter about the Photometric Plane is smaller at the faint end.

We present the study of a large sample of early-type dwarf galaxies in the Coma cluster observed with DEIMOS on the Keck II to determine their internal velocity dispersion. We focus on a subsample of 41 member dwarf elliptical galaxies for which the velocity dispersion can be reliably measured, 26 of which were studied for the first time. The magnitude range of our sample is −21 < M_R < −15 mag.

This paper (Paper I) focuses on the measurement of the velocity dispersion and their error estimates. The measurements were performed using penalized pixel fitting (ppxf) and using the calcium triplet absorption lines. We use Monte Carlo bootstrapping to study various sources of uncertainty in our measurements, namely statistical uncertainty, template mismatch and other systematics. We find that the main source of uncertainty is the template mismatch effect which is reduced by using templates with a range of spectral types.

Combining our measurements with those from the literature, we study the Faber–Jackson relation (L∝σ^α) and find that the slope of the relation is α= 1.99 ± 0.14 for galaxies brighter than M_R≃−16 mag. A comprehensive analysis of the results combined with the photometric properties of these galaxies is reported in Paper II.

This paper presents further results from our spectroscopic study of the globular cluster (GC) system of the group elliptical NGC 3923. From observations made with the GMOS instrument on the Gemini South Telescope, an additional 50 GC and ultra-compact dwarf (UCD) candidates have been spectroscopically confirmed as members of the NGC 3923 system. When the recessional velocities of these GCs are combined with the 29 GC velocities reported previously, a total sample of 79 GC/UCD velocities is produced. This sample extends to over 6 arcmin (> 6 R_e∼ 30 kpc) from the centre of NGC 3923 and is used to study the dynamics of the GC system and the dark matter content of NGC 3923. It is found that the GC system of NGC 3923 displays no appreciable rotation, and that the projected velocity dispersion is constant with radius within the uncertainties. The velocity dispersion profiles of the integrated light and GC system of NGC 3923 are indistinguishable over the region in which they overlap. We find some evidence that the diffuse light and GCs of NGC 3923 have radially biased orbits within ∼130 arcsec. The application of axisymmetric orbit-based models to the GC and integrated light velocity dispersion profiles demonstrates that a significant increase in the mass-to-light ratio (from M/L_V= 8 to 26) at large galactocentric radii is required to explain this observation. We therefore confirm the presence of a dark matter halo in NGC 3923. We find that dark matter comprises 17.5 per cent of the mass within 1 R_e, 41.2 per cent within 2 R_e and 75.6 per cent within the radius of our last kinematic tracer at 6.9 R_e. The total dynamical mass within this radius is found to be M_⊙. In common with other studies of large ellipticals, we find that our derived dynamical mass profile is consistently higher than that derived by X-ray observations, by a factor of around 2.

The association reaction S + CO OCS + hν has been identified as being particularly important for the prediction of gas-phase OCS abundances by chemical models of dark clouds. We performed detailed ab initio calculations for this process in addition to undertaking an extensive review of the neutral–neutral reactions involving this species which might be important in such environments. The rate constant for this association reaction was estimated to be several orders of magnitude smaller than the one present in current astrochemical data bases. The new rate for this reaction and the introduction of other processes, notably OH + CS OCS + H and C + OCS CO + CS, dramatically change the OCS gas-phase abundance predicted by chemical models for dark clouds. The disagreement with observations in TMC-1 (CP) and L134N (N) suggests that OCS may be formed on grain surfaces as is the case for methanol. The observation of solid OCS on interstellar ices supports this hypothesis.

We discuss chemical enrichments of ∼4000 Sloan Digital Sky Survey early-type galaxies using as tracers a large variety of element abundance ratios, namely [C/Fe], [N/Fe], [O/Fe], [Mg/Fe], [Ca/Fe] and [Ti/Fe]. We utilize the stellar population models of absorption line indices from Thomas, Maraston & Johansson which are based on the MILES stellar library. We confirm previous results of increasing age, [Z/H] and [O/Fe] ratios (most often represented by [α/Fe] in the literature) with velocity dispersion. We further derive identical correlations with velocity dispersion for the abundance ratios [O/Fe], [Mg/Fe] and [C/Fe], implying that C/Mg and C/O are close to solar values. This sets a lower limit on the formation time-scales and starburst components of early-type galaxies to ∼0.4 Gyr, which is the lifetime of a 3 M_⊙ star, since the full C enrichment must be reached. [N/Fe] correlates with velocity dispersion, but offset to lower values and with a steeper slope compared to the other element ratios. We do not find any environmental dependencies for the abundances of C and N, contrary to previous reports in the literature. [Fe/H] does not correlate with velocity dispersion over the entire parameter range covered, but for fixed age we find a steep trend for the [Fe/H]–σ relation. This trend is weaker than the analogous for total metallicity (which also shows steeper trends at fixed age) owing to the lower Fe contribution from Type Ia supernova (SN Ia) for more massive early-type galaxies. We find [Ca/Fe] ratios that are close to solar values over the entire velocity dispersion range covered. Tentative, due to large scatter, the results for [Ti/Fe] indicate that Ti follows the trends of Ca. This implies a significant contribution from SN Ia to the enrichment of heavy α-elements and puts strong constraints on supernova nucleosynthesis and models of galactic chemical evolution.

Recent observation of the tidally excited stellar oscillations in the main-sequence binary KOI-54 by the Kepler satellite provides a unique opportunity for studying dynamical tides in eccentric binary systems. We develop a general theory of tidal excitation of oscillation modes of rotating binary stars and apply our theory to tidally excited gravity modes (g-modes) in KOI-54. The strongest observed oscillations, which occur at 90 and 91 times the orbital frequency, are likely due to prograde m= 2 modes (relative to the stellar spin axis) locked in resonance with the orbit. The remaining flux oscillations with frequencies that are integer multiples of the orbital frequency are likely due to nearly resonant m= 0 g-modes; such axisymmetric modes generate larger flux variations compared to the m= 2 modes, assuming that the spin inclination angle of the star is comparable to the orbital inclination angle. We examine the process of resonance mode locking under the combined effects of dynamical tides on the stellar spin and orbit and the intrinsic stellar spindown. We show that KOI-54 can naturally evolve into a state in which at least one m= 2 mode is locked in resonance with the orbital frequency. Our analysis provides an explanation for the fact that only oscillations with frequencies less than 90–100 times the orbital frequency are observed. We have also found evidence from the published Kepler result that three-mode non-linear coupling occurs in the KOI-54 system. We suggest that such non-linear mode coupling may explain the observed oscillations that are not harmonics of the orbital frequency.

We have recently developed an extended merger-tree model that efficiently follows hierarchical evolution of galaxy clusters and provides a quantitative description of both their dark matter and gas properties. We employed this diagnostic tool to calculate the thermal Sunyaev–Zel’dovich power spectrum and cluster number counts, accounting explicitly for uncertainties in the relevant statistical and intrinsic cluster properties, such as the halo mass function and the gas equation of state. Results of these calculations are compared with those obtained from a direct analytic treatment and from hydrodynamical simulations. We show that under certain assumptions on the gas mass fraction our results are consistent with the latest South Pole Telescope measurement. Our approach can be particularly useful in predicting cluster number counts and their dependence on cluster and cosmological parameters.

We propose a new and highly model-independent test of cosmic acceleration by comparing observations of the baryon acoustic oscillation (BAO) scale at low and intermediate redshifts: we derive a new inequality relating BAO observables at two distinct redshifts, which must be satisfied for any reasonable homogeneous non-accelerating model, but is violated by models similar to Λ cold dark matter, due to acceleration in the recent past. This test is fully independent of the theory of gravity (general relativity or otherwise), the Friedmann equations, cosmic microwave background and supernova observations: the test assumes only the cosmological principle, and that the length-scale of the BAO feature is fixed in comoving coordinates. Given realistic medium-term observations from the Baryon Oscillation Spectroscopic Survey, this test is expected to exclude all homogeneous non-accelerating models at ∼4σ significance, and can reach with next-generation surveys.

A complete sample of bright Swift gamma-ray bursts (GRBs) have been recently selected by Salvaterra et al. The sample has a high level of completeness in redshift (90 per cent). We derive here the intrinsic absorbing X-ray column densities of these GRBs making use of the Swift/X-ray Telescope data. This distribution has a mean value of log (N_H/cm⁻²) = 21.7 ± 0.5. This value is consistent with the distribution of the column densities derived from the total sample of GRBs with redshift. We find a mild increase in the intrinsic column density with redshift. This can be interpreted as due to the contribution of intervening systems along the line of sight. Making use of the spectral index connecting optical and X-ray fluxes at 11 h (β_OX), we investigate the relation between the intrinsic column density and the GRB ‘darkness’. We find that there is a very tight correlation between dark GRBs and high X-ray column densities. This clearly indicates that the dark GRBs are formed in a metal-rich environment where dust must be present.

We present observations of a large-scale disc of neutral hydrogen (H i) in the nearby Fanaroff–Riley type I (FR I) radio galaxy NGC 3801 with the Westerbork Synthesis Radio Telescope. The H i disc (34 kpc in diameter and with ) is aligned with the radio jet axis. This makes NGC 3801 an ideal system for investigating the evolution of a small radio source through its host galaxy’s cold interstellar medium (ISM). The large-scale H i disc is perpendicular to a known inner CO disc and dust lane. We argue that the formation history of the large-scale H i disc is in agreement with earlier speculation that NGC 3801 was involved in a past gas-rich galaxy–galaxy merger (although other formation histories are discussed). The fact that NGC 3801 is located in an environment of several H i-rich companions, and shows indications of ongoing interaction with the nearby companion NGC 3802, strengthens this possibility. The large amounts of ambient cold ISM, combined with X-ray results by Croston, Kraft & Hardcastle on the presence of overpressured radio jets and evidence for an obscuring torus, are properties that are generally not, or no longer, associated with more evolved FR I radio sources. We do show, however, that the H i properties of NGC 3801 are comparable to those of a significant fraction of nearby low-power compact radio sources, suggesting that studies of NGC 3801 may reveal important insight into a more general phase in the evolution of at least a significant fraction of nearby radio galaxies.

During stellar core collapse, which eventually leads to a supernova explosion, the stalled shock is unstable due to the standing accretion shock instability (SASI). This instability induces large-scale non-spherical oscillations of the shock, which have crucial consequences on the dynamics and the geometry of the explosion. While the existence of this instability has been firmly established, its physical origin remains somewhat uncertain. Two mechanisms have indeed been proposed to explain its linear growth. The first is an advective–acoustic cycle, where the instability results from the interplay between advected perturbations (entropy and vorticity) and an acoustic wave. The second mechanism is purely acoustic and assumes that the shock is able to amplify trapped acoustic waves. Several arguments favouring the advective–acoustic cycle have already been proposed; however, none was entirely conclusive for realistic flow parameters. In this paper we give two new arguments which unambiguously show that the instability is not purely acoustic and should be attributed to the advective–acoustic cycle. First, we extract a radial propagation time-scale by comparing the frequencies of several unstable harmonics that differ only by their radial structure. The extracted time matches the advective–acoustic time but strongly disagrees with a purely acoustic interpretation. Secondly, we present a method to compute purely acoustic modes by artificially removing advected perturbations below the shock. All these purely acoustic modes are found to be stable, showing that the advected wave is essential to the instability mechanism.

The importance of rotational transition rates in the analysis of cold interstellar clouds is well known. We present results, for temperatures ranging from 5 to 80 K, for the hyperfine-resolved rotational transitions of DCO⁺ induced by collision with helium. Since the isotopic substitution is not expected to introduce significant changes, close-coupling calculations are based on a potential energy surface obtained for He–HCO⁺ and checked by accurate pressure broadening and shift measurements. The well-grounded assumption that deuterium nuclear spin is not affected by the collisions allowed us to obtain the hyperfine-resolved transition matrix elements as a sum of spin-free transition matrix elements, which account for collision dynamics, multiplied by purely geometrical factors, which account for the hyperfine dependence. The temperature dependence of the rates is weak for downward transitions j→j′, j′ < j, while for upward transitions (j′ > j) it can be large due to the need of energy to be transferred from translation to rotation. The dependence of the rates on j and j′ and hyperfine propensities is discussed. The rates for quasi-elastic purely hyperfine transitions j, F→jF′ are also obtained.

We have compared the oxygen and nitrogen abundances derived from global emission-line Sloan Digital Sky Survey (SDSS) spectra of galaxies using (1) the T_e method and (2) two recent strong-line calibrations: the ON and NS calibrations. Using the T_e method, anomalously high N/O abundance ratios have been found in some SDSS galaxies. To investigate this, we have Monte Carlo simulated the global spectra of composite nebulae by a mix of spectra of individual components, based on spectra of well-studied H ii regions in nearby galaxies. We found that the T_e method results in an underestimated oxygen abundance (and hence in an overestimated nitrogen-to-oxygen ratio) if H ii regions with different physical properties contribute to the global spectrum of composite nebulae. This effect is somewhat similar to the small-scale temperature fluctuations in H ii regions discussed by Peimbert. Our work thus suggests that the high T_e-based N/O abundance ratios found in SDSS galaxies may not be real. However, such an effect is not expected to be present in dwarf galaxies since they generally have a uniform chemical composition. The ON and NS calibrations give O and N abundances in composite nebulae which agree with the mean luminosity-weighted abundances of their components to within ∼0.2 dex.

High-precision cosmology with weak gravitational lensing requires a precise measure of the point spread function across the imaging data where the accuracy to which high spatial frequency variation can be modelled is limited by the stellar number density across the field. We analyse dense stellar fields imaged at the Canada–France–Hawaii Telescope to quantify the degree of high spatial frequency variation in ground-based imaging point spread functions and compare our results to models of atmospheric turbulence. The data show an anisotropic turbulence pattern with an orientation independent of the wind direction and wind speed. We find the amplitude of the high spatial frequencies to decrease with increasing exposure time as t^−1/2, and find a negligibly small atmospheric contribution to the point spread function ellipticity variation for exposure times t > 180 s. For future surveys analysing shorter exposure data, this anisotropic turbulence will need to be taken into account as the amplitude of the correlated atmospheric distortions becomes comparable to a cosmological lensing signal on scales less than ∼10 arcmin. This effect could be mitigated, however, by correlating galaxy shear measured on exposures imaged with a time separation greater than 50 s, for which we find the spatial turbulence patterns to be uncorrelated.

In this work we investigate the multivariate statistical description of the matter distribution in the non-linear regime. We introduce the multivariate Edgeworth expansion of the lognormal distribution to model the cosmological matter field. Such a technique could be useful to generate and reconstruct three-dimensional non-linear cosmological density fields with the information of higher order correlation functions. We explicitly calculate the expansion up to third order in perturbation theory making use of the multivariate Hermite polynomials up to sixth order. The probability distribution function for the matter field includes at this level the two-point, the three-point and the four-point correlation functions. We use the hierarchical model to formulate the higher order correlation functions based on combinations of the two-point correlation function. This permits us to find compact expressions for the skewness and kurtosis terms of the expanded lognormal field which can be efficiently computed. The method is, however, flexible to incorporate arbitrary higher order correlation functions which have analytical expressions. The applications of such a technique can be especially useful to perform weak-lensing or neutral hydrogen 21-cm line tomography, as well as to directly use the galaxy distribution or the Lyman α forest to study structure formation.

We extend the two-dimensional Cartesian shapelet formalism to d-dimensions. Concentrating on the three-dimensional case, we derive shapelet-based equations for the mass, centroid, root mean square radius, and components of the quadrupole moment and moment of inertia tensors. Using cosmological N-body simulations as an application domain, we show that three-dimensional shapelets can be used to replicate the complex sub-structure of dark matter haloes and demonstrate the basis of an automated classification scheme for halo shapes. We investigate the shapelet decomposition process from an algorithmic viewpoint, and consider opportunities for accelerating the computation of shapelet-based representations using graphics processing units.

I briefly review the flatness problem within the context of classical cosmology and examine some of the debate in the literature with regard to its definition and even the question whether it exists. I then present some new calculations for cosmological models which will collapse in the future; together with previous work by others for models which will expand forever, this allows one to examine the flatness problem quantitatively for all cosmological models. This leads to the conclusion that the flatness problem does not exist, not only for the cosmological models corresponding to the currently popular values of λ₀ and Ω₀ but indeed for all Friedmann–Lemaître models.

We conduct Bayesian model inferences from the observed K-band luminosity function of galaxies in the local Universe, using the semi-analytic model (SAM) of galaxy formation introduced in Lu et al. The prior distributions for the 14 free parameters include a large range of possible models. We find that some of the free parameters, e.g. the characteristic scales for quenching star formation in both high-mass and low-mass haloes, are already tightly constrained by the single data set. The posterior distribution includes the model parameters adopted in other SAMs. By marginalizing over the posterior distribution, we make predictions that include the full inferential uncertainties for the colour–magnitude relation, the Tully–Fisher relation, the conditional stellar mass function of galaxies in haloes of different masses, the H i mass function, the redshift evolution of the stellar mass function of galaxies and the global star formation history. Using posterior predictive checking with the available observational results, we find that the model family (i) predicts a Tully–Fisher relation that is curved; (ii) significantly overpredicts the satellite fraction; (iii) vastly overpredicts the H i mass function; (iv) predicts high-z stellar mass functions that have too many low-mass galaxies and too few high-mass ones and (v) predicts a redshift evolution of the stellar mass density and the star formation history that are in moderate disagreement. These results suggest that some important processes are still missing in the current model family, and we discuss a number of possible solutions to solve the discrepancies, such as interactions between galaxies and dark matter haloes, tidal stripping, the bimodal accretion of gas, preheating and a redshift-dependent initial mass function.

In this paper, we consider a new mechanism for stopping the inward migration of a low-mass planet embedded in a gaseous protoplanetary disc. It operates when a low-mass planet (for example a super-Earth) encounters outgoing density waves excited by another source in the disc. This source could be a gas giant in an orbit interior to that of the low-mass planet. As the super-Earth passes through the wave field, angular momentum is transferred to the disc material and then communicated to the planet through co-orbital dynamics, with the consequence that its inward migration can be halted or even reversed.

We illustrate how the mechanism we consider works in a variety of different physical conditions employing global two-dimensional hydrodynamical calculations. We confirm our results by performing local shearing box simulations in which the super-Earth interacts with density waves excited by an independent harmonically varying potential. Finally, we discuss the constraints arising from the process considered here, on formation scenarios for systems containing a giant planet and lower mass planet in an outer orbit with a 2:1 commensurability such as GJ 876.

We examine the gas and stellar metallicities in a sample of H ii galaxies from the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of H ii galaxy spectra to date.

We eliminated all spectra with an insufficient signal-to-noise ratio, without strong emission lines and without the [O ii] λ3727 Å line, which is necessary for the determination of the gas metallicity. This excludes galaxies with redshift ≲ 0.033. Our final sample contains ∼700 spectra of H ii galaxies.

Through emission line strength calibrations and a detailed stellar population analysis employing evolutionary stellar synthesis methods, which we already used in previous works, we determined the metallicities of both the gas and the stellar content of these galaxies.

We find that in H ii galaxies up to stellar masses of 5 × 10⁹ M_⊙, enrichment mechanisms do not vary with galactic mass, being the same for low- and high-mass galaxies on average. They do seem to present a greater variety at the high-mass end, though, indicating a more complex assembly history for high-mass galaxies. In around 23 per cent of our H ii galaxies, we find a metallicity decrease over the last few Gyr. Our results favour galaxy evolution models featuring constantly infalling low-metallicity clouds that retain part of the galactic winds. Above 5 × 10⁹ M_⊙ stellar mass, the retention of high-metallicity gas by the galaxies’ gravitational potential dominates.

We present a detailed analysis of the neutral hydrogen kinematics of 12 nearby dwarf irregular galaxies observed as part of the Local Volume H i Survey conducted at the Australia Telescope Compact Array. For each galaxy we measure the disc parameters (inclination, position angle) and the H i rotation curve. Six galaxies in our sample (AM 0605−341, Argo Dwarf, ESO 059−G001, ESO 137−G018, ESO 174−G?001 and ESO 308−G022) have their atomic hydrogen distribution studied for the first time. AM 0605−341 was found to have an extension of redshifted H i which we propose is due to a tidal interaction with NGC 2188. There is evidence that ESO 215−G?009 has extraplanar H i gas. We also compare the global galaxy properties, in particular the integrated H i flux density and velocity widths of the observed H i spectra, with the results from the low angular resolution H i Parkes All Sky Survey. We discuss under what circumstances the 21 cm emission-line profile can accurately predict the galaxies rotation velocity, an observational parameter crucial to study the classical and baryonic Tully–Fisher relations.

We present an extension to the short-characteristic ray-tracing and non-equilibrium photoionization code C²-Ray. The new version includes the effects of helium and improved multifrequency heating. The motivation for this work is to be able to deal with harder ionizing spectra, such as from quasar-like sources during cosmic reionization. We review the basic algorithmic ingredients of C²-Ray before describing the changes implemented, which include a treatment of the full on-the-spot (OTS) approximation, secondary ionization, and multifrequency photoionization and heating. We performed a series of tests against equilibrium solutions from cloudy as well as comparisons to the hydrogen-only solutions by C²-Ray in the extensive cosmological radiative transfer code comparison project. We show that the full, coupled OTS approximation is more accurate than the simplified, uncoupled one. We find that also with helium and a multifrequency setup, long time-steps (up to ∼ 10 per cent of the recombination time) still give accurate results for the ionization fractions. On the other hand, accurate results for the temperature set strong constraints on the time-step. The details of these constraints depend, however, on the optical depth of the cells. We use the new version of the code to confirm that the assumption made in many reionization simulations, namely that helium is singly ionized everywhere where hydrogen is, is indeed valid when the sources have stellar-like spectra.

We present resolved Herschel images of a circumbinary debris disc in the 99 Herculis system. The primary is a late F-type star. The binary orbit is well characterized and we conclude that the disc is misaligned with the binary plane. Two different models can explain the observed structure. The first model is a ring of polar orbits that move in a plane perpendicular to the binary pericentre direction. We favour this interpretation because it includes the effect of secular perturbations and the disc can survive for Gyr time-scales. The second model is a misaligned ring. Because there is an ambiguity in the orientation of the ring, which could be reflected in the sky plane, this ring either has near-polar orbits similar to the first model or has a 30° misalignment. The misaligned ring, interpreted as the result of a recent collision, is shown to be implausible from constraints on the collisional and dynamical evolution. Because disc+star systems with separations similar to 99 Herculis should form coplanar, possible formation scenarios involve either a close stellar encounter or binary exchange in the presence of circumstellar and/or circumbinary discs. Discovery and characterization of systems like 99 Herculis will help understand processes that result in planetary system misalignment around both single and multiple stars.

It is theoretically expected that a supermassive black hole (SMBH) in the centre of a typical nearby galaxy disrupts a solar-type star every ∼10⁵ yr, resulting in a bright flare lasting for months. Sgr A*, the resident SMBH of the Milky Way, produces (by comparison) tiny flares that last only hours but occur daily. Here we explore the possibility that these flares could be produced by disruption of smaller bodies – asteroids. We show that asteroids passing within an au of Sgr A* could be split into smaller fragments which then vaporize by bodily friction with the tenuous quiescent gas accretion flow on to Sgr A*. The ensuing shocks and plasma instabilities may create a transient population of very hot electrons invoked in several currently popular models for Sgr A* flares, thus producing the required spectra. We estimate that asteroids larger than ∼10 km in size are needed to power the observed flares, with the maximum possible luminosity of the order of 10³⁹ erg s⁻¹. Assuming that the asteroid population per parent star in the central parsec of the Milky Way is not too dissimilar from that around stars in the solar neighbourhood, we estimate the asteroid disruption rates, and the distribution of the expected luminosities, finding a reasonable agreement with the observations. We also note that planets may be tidally disrupted by Sgr A* as well, also very infrequently. We speculate that one such disruption may explain the putative increase in Sgr A* luminosity ∼100 yr ago.

We present optical spectroscopy of MWC 656 and MWC 148, the proposed optical counterparts of the γ-ray sources AGL J2241+4454 and HESS J0632+057, respectively. The main parameters of the Hα emission line [equivalent width (EW), full width at half-maximum and centroid velocity] in these stars are modulated on the proposed orbital periods of 60.37 and 321 d, respectively. These modulations are likely produced by the resonant interaction of the Be discs with compact stars in eccentric orbits. We also present radial velocity curves of the optical stars folded on the above periods and obtain the first orbital elements of the two γ-ray sources, thus confirming their binary nature. Our orbital solution supports eccentricities e∼ 0.4 and 0.83 ± 0.08 for MWC 656 and MWC 148, respectively. Furthermore, our orbital elements imply that the X-ray outbursts in HESS J0632+057/MWC 148 are delayed ∼0.3 orbital phases after periastron passage, similar to the case of LS I +61 303. In addition, the optical photometric light-curve maxima in AGL J2241+4454/MWC 656 occur ∼0.25 phases passed periastron, similar to what is seen in LS I +61 303. We also find that the orbital eccentricity is correlated with the orbital period for the known γ-ray binaries. This is explained by the fact that small stellar separations are required for the efficient triggering of very high energy radiation. Another correlation between the EW of Hα and orbital period is also observed, similar to the case of Be/X-ray binaries. These correlations are useful to provide estimates of the key orbital parameters P_orb and e from the Hα line in future Be γ-ray binary candidates.

V 393 Scorpii is a bright Galactic Double Periodic Variable showing a long photometric cycle of ≈253 d. We present new VIJK photometric time series for V 393 Scorpii along with the analysis of All Sky Automated Survey (ASAS) V-band photometry. We disentangled all light curves into the orbital and long-cycle components. The ASAS V-band orbital light curve was modelled with two stellar components plus a circumprimary optically thick disc assuming a semi-detached configuration. We present the results of this calculation, giving physical parameters for the stars and the disc, along with general system dimensions. Our results are in close agreement with those previously found by Mennickent et al. from infrared (IR) spectroscopy and the modelling of the spectral energy distribution. The stability of the orbital light curve suggests that the stellar plus disc configuration remains stable during the long cycle. Therefore, the long cycle should be produced by an additional variable and not-eclipsed emitting structure. We discuss the evolutionary stage of the system finding the best match with one of the evolutionary models of van Rensbergen et al. According to these models, the system is found to be after an episode of fast mass exchange that transferred 4 M_⊙ from the donor to the gainer in a period of 400 000 years. We argue that a significant fraction of this mass has not been accreted by the gainer but remains in an optically thick massive (∼2 M_⊙) disc-like surrounding pseudo-photosphere whose luminosity is not driven by viscosity but probably by reprocessed stellar radiation. Finally, we provide the result of our search for Galactic Double Periodic Variables and briefly discuss the outliers β Lyr and RX Cas.

The first high-resolution (R∼ 50 000) optical spectrum of the B-type star, LS III +52°24, identified as the optical counterpart of the hot post-asymptotic giant branch (post-AGB) candidate IRAS 22023+5249 (I22023) is presented. We report the detailed identifications of the observed absorption and emission features in the full wavelength range (4290–9015 Å) as well as the atmospheric parameters and photospheric abundances (under the local thermodynamic equilibrium approximation) for the first time. The nebular parameters (T_e, N_e) are also derived. We estimate T_eff= 24 000 K, log g= 3.0 and ξ_t= 7 km s⁻¹, and the derived abundances indicate a slightly metal-deficient evolved star with C/O < 1. The observed P-Cygni profiles of hydrogen and helium clearly indicate ongoing post-AGB mass-loss. The presence of [N ii] and [S ii] lines and the non-detection of [O iii] indicate that photoionization has just started. The observed spectral features, large heliocentric radial velocity, atmospheric parameters and chemical composition indicate that I22023 is an evolved post-AGB star belonging to the old disc population. The derived nebular parameters (T_e= 7000 K, N_e= 1.2 × 10⁴ cm⁻³) also suggest that I22023 may be evolving into a compact, young low-excitation planetary nebula. Our optical spectroscopic analysis together with the recent Spitzer detection of double-dust chemistry (the simultaneous presence of carbonaceous molecules and amorphous silicates) in I22023 and other B-type post-AGB candidates may point to a binary system with a dusty disc as the stellar origin common to the hot post-AGB stars with O-rich central stars.

We present a detailed analysis of the X-ray spectrum of the Seyfert 2 galaxy NGC 454E, belonging to the interacting system NGC 454. Observations performed with Suzaku, XMM–Newton and Swift allowed us to detect a dramatic change in the curvature of the 2–10 keV spectrum, revealing a significant variation of the absorbing column density along the line of sight (from ∼ 1 × 10²⁴ cm⁻² to ∼ 1 × 10²³ cm⁻²). Consequently, we propose this source as a new member of the class of ‘changing look’ active galactic nuclei (AGN), i.e. AGN that have been observed both in Compton thin (N_H= 10²³  cm⁻²) and reflection-dominated states (Compton thick, N_H > 10²⁴  cm⁻²). Due to the quite long time lag (six months) between the Suzaku and XMM–Newton observations, we cannot infer the possible location of the obscuring material causing the observed variability. In the 6–7 keV range, the XMM–Newton observation also shows a clear signature of the presence of an ionized absorber. Since this feature is not detected during the Suzaku observation (despite its detectability), the simplest interpretation is that the ionized absorber is also variable; its location is estimated to be within ∼ 10⁻³ pc from the central black hole, probably much closer in than the rather neutral absorber.

The ratio of the Fe abundance in the photosphere to that in coronal flare plasmas is determined by X-ray lines within the complex at 6.7 keV (1.9 Å) emitted during flares. The line complex includes the He-like Fe (Fe xxv) resonance line w (6.70 keV) and Fe Kα lines (6.39 and 6.40 keV), the latter being primarily formed by the fluorescence of photospheric material by X-rays from the hot flare plasma. The ratio of the Fe Kα lines to the Fe xxvw depends on the ratio of the photospheric to flare Fe abundance, heliocentric angle θ of the flare and the temperature T_e of the flaring plasma. Using high-resolution spectra from X-ray spectrometers on the P78-1 and Solar Maximum Mission spacecraft, the Fe abundance in flares is estimated to be 1.6 ± 0.5 and 2.0 ± 0.3 times the photospheric Fe abundance, the P78-1 value being preferred as it is more directly determined. This enhancement is consistent with results from X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft, but is significantly less than a factor of 4 as in previous work.

Over the last 40 years, the ¹²C +¹²C fusion reaction has been the subject of considerable experimental efforts to constrain uncertainties at temperatures relevant for stellar nucleosynthesis. Recent studies have indicated that the reaction rate may be higher than that currently used in stellar models. In order to investigate the effect of an enhanced carbon-burning rate on massive star structure and nucleosynthesis, new stellar evolution models and their yields are presented exploring the impact of three different ¹²C +¹²C reaction rates. Non-rotating stellar models considering five different initial masses, 15, 20, 25, 32 and 60 M_⊙, at solar metallicity, were generated using the Geneva Stellar Evolution Code (genec) and were later post-processed with the NuGrid Multi-zone Post-Processing Network tool (mppnp). A dynamic nuclear reaction network of ∼1100 isotopes was used to track the s-process nucleosynthesis. An enhanced ¹²C +¹²C reaction rate causes core carbon burning to be ignited more promptly and at lower temperature. This reduces the neutrino losses, which increases the core carbon-burning lifetime. An increased carbon-burning rate also increases the upper initial mass limit for which a star exhibits a convective carbon core (rather than a radiative one). Carbon-shell burning is also affected, with fewer convective-shell episodes and convection zones that tend to be larger in mass. Consequently, the chance of an overlap between the ashes of carbon-core burning and the following carbon shell convection zones is increased, which can cause a portion of the ashes of carbon-core burning to be included in the carbon shell. Therefore, during the supernova explosion, the ejecta will be enriched by s-process nuclides synthesized from the carbon-core s-process. The yields were used to estimate the weak s-process component in order to compare with the Solar system abundance distribution. The enhanced rate models were found to produce a significant proportion of Kr, Sr, Y, Zr, Mo, Ru, Pd and Cd in the weak component, which is primarily the signature of the carbon-core s-process. Consequently, it is shown that the production of isotopes in the Kr–Sr region can be used to constrain the ¹²C +¹²C rate using the current branching ratio for α- and p-exit channels.

In this paper, we study the wind accretion on to a rotating black hole in a close binary system that harbours a young massive star. It is shown that the angular momentum of the accreted stellar wind material is not sufficient for the formation of an accretion disc. However, in the conditions considered, the Blanford–Znajek mechanism can be activated, and thus powerful jets can be launched in the direction of the rotation axis of the black hole. Importantly, no observational signatures of accretion, as are typically seen from the thermal X-ray emission of accretion discs, are expected in the suggested scenario. Here, the properties of the generated jet are studied numerically in the framework of a two-dimensional general relativity magnetohydrodynamical approach. Because of the accumulation of the magnetic flux at the black hole horizon, the jet power is expected to be modulated on a subsecond time-scale. Although the intervals between the jet active phases depend on the magnetic flux that escapes from the black hole horizon (which can be modelled self-consistently only using a three-dimensional code), a general estimate of the averaged jet power is obtained. It is shown that for the black hole rotation, expected in a stellar binary system (the dimensionless rotation parameter a= 0.5), approximately 5 per cent of the accreted rest energy can be channelled into the jets. In the case of the faster rotation of the black hole, the efficiency is expected to be significantly higher (e.g. for the dimensionless rotation parameter a= 0.95, the jet carries approximately 20 per cent of the accreted rest energy). In the specific case of the gamma-ray binary system LS 5039, the obtained jet luminosity can be responsible for the observed GeV radiation if Doppler boosting is invoked, which can enhance the apparent flux from the system.

Here we present the results of various approaches to measure accurate colours and photometric redshifts (photo-z) from wide-field imaging data. We use data from the Canada–France–Hawaii Telescope Legacy Survey which have been re-processed by the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS) team in order to carry out a number of weak gravitational lensing studies. An emphasis is put on the correction of systematic effects in the photo-z arising from the different point spread functions (PSFs) in the five optical bands. Different ways of correcting these effects are discussed and the resulting photo-z accuracies are quantified by comparing the photo-z to large spectroscopic redshift (spec-z) data sets. Careful homogenization of the PSF between bands leads to increased overall accuracy of photo-z. The gain is particularly pronounced at fainter magnitudes where galaxies are smaller and flux measurements are affected more by PSF effects. We discuss ways of defining more secure subsamples of galaxies as well as a shape- and colour-based star–galaxy separation method, and we present redshift distributions for different magnitude limits. We also study possible re-calibrations of the photometric zero-points (ZPs) with the help of galaxies with known spec-z. We find that if PSF effects are properly taken into account, a re-calibration of the ZPs becomes much less important suggesting that previous such re-calibrations described in the literature could in fact be mostly corrections for PSF effects rather than corrections for real inaccuracies in the ZPs. The implications of this finding for future surveys like the Kilo Degree Survey (KiDS), Dark Energy Survey (DES), Large Synoptic Survey Telescope or Euclid are mixed. On the one hand, ZP re-calibrations with spec-z values might not be as accurate as previously thought. On the other hand, careful PSF homogenization might provide a way out and yield accurate, homogeneous photometry without the need for full spectroscopic coverage. This is the first paper in a series describing the technical aspects of CFHTLenS.

Multifrequency radio continuum observations (1.4–22 GHz) of a sample of reddened quasi-stellar objects (QSOs) are presented. We find a high incidence (13/16) of radio spectral properties, such as low-frequency turnovers, high-frequency spectral breaks or steep power-law slopes, similar to those observed in powerful compact steep spectrum (CSS) and gigahertz-peaked spectrum (GPS) sources. The radio data are consistent with relatively young radio jets with synchrotron ages  yr. This calculation is limited by the lack of high-resolution (milliarcsec) radio observations. For the one source in the sample that such data are available a much younger radio age is determined, ≲ 2 × 10³ yr, similar to those of GPS/CSS sources. These findings are consistent with claims that reddened QSOs are young systems captured at the first stages of the growth of their supermassive black holes. It also suggests that expanding radio lobes may be an important feedback mode at the early stages of the evolution of active galactic nuclei.

Hu 1-2 is a planetary nebula that contains an isolated knot located north-west of the main nebula, which could be related to a collimated outflow. We present a subarcsecond Hα+[N ii] image and a high-resolution, long-slit spectrum of Hu 1-2 that allow us to identify the south-eastern counterpart of the north-western knot and to establish their high-velocity (>340 km s⁻¹), collimated bipolar outflow nature. The detection of the north-western knot in Palomar Observatory Sky Atlas (POSS) red plates allows us to carry out a proper motion analysis by combining three POSS red plates and two narrow-band Hα+[N ii] CCD images, with a time baseline of ≃57 yr. A proper motion of 20 ± 6 mas yr⁻¹ along position angle 312°± 15° and a dynamical age of 1375 yr are obtained for the bipolar outflow. The measured proper motion and the spatio-kinematical properties of the bipolar outflow yield a lower limit of 2.7 kpc for the distance to Hu 1-2.

This paper reports follow-up photometric and spectroscopic observations, including warm Spitzer IRAC photometry of seven white dwarfs from the SDSS with apparent excess flux in UKIDSS K-band observations. Six of the science targets were selected from 16 785 DA star candidates identified either spectroscopically or photometrically within SDSS DR7, spatially cross-correlated with HK detections in UKIDSS DR8. Thus, the selection criteria are completely independent of stellar mass, effective temperature above 8000 K and the presence (or absence) of atmospheric metals. The infrared fluxes of one target are compatible with a spatially unresolved late M or early L-type companion, while three stars exhibit excess emissions consistent with warm circumstellar dust. These latter targets have spectral energy distributions similar to known dusty white dwarfs with high fractional infrared luminosities (thus the K-band excesses). Optical spectroscopy reveals the stars with disc-like excesses are polluted with heavy elements, denoting the ongoing accretion of circumstellar material. One of the discs exhibits a gaseous component – the fourth reported to date – and orbits a relatively cool star, indicating the gas is produced via collisions as opposed to sublimation, supporting the picture of a recent event. The resulting statistics yield a lower limit of 0.8 per cent for the fraction dust discs at DA-type white dwarfs with cooling ages less than 1 Gyr. Two overall results are noteworthy: (i) all stars whose excess infrared emission is consistent with dust are metal rich and (ii) no stars warmer than 25 000 K are found to have this type of excess, despite sufficient sensitivity.

Spiral density wave theory attempts to describe the spiral pattern in spiral galaxies in terms of a long-lived wave structure with a constant pattern speed in order to avoid the winding dilemma. The pattern is consequently a rigidly rotating, long-lived feature. We run N-body simulations of a giant disc galaxy consisting of a pure stellar disc and a static dark matter halo, and find that the spiral arms are transient features whose pattern speeds decrease with radius in such a way that the pattern speed is almost equal to the rotation curve of the galaxy. We trace particle motion around the spiral arms. We show that particles from behind and in front of the spiral arm are drawn towards and join the arm. Particles move along the arm in the radial direction and we find a clear trend that they migrate towards the outer (inner) radii on the trailing (leading) side of the arm. Our simulations demonstrate that because the spiral arm feature is corotating, the particles continue to be accelerated (decelerated) by the spiral arm for long periods, which leads to strong and efficient migration, at all radii in the disc.

We constrain the properties of cluster haloes by performing likelihood analysis using lensing shear and flexion data. We test our analysis using two mock cluster haloes: an isothermal ellipsoid (SIE) model and a more realistic elliptical Navarro–Frenk–White model. For both haloes, we find that flexion is more sensitive to the halo ellipticity than shear. The introduction of flexion information significantly improves the constraints on halo ellipticity, orientation and mass. We also point out that there is a degeneracy between the mass and the ellipticity of SIE models in the lensing signal.

We propose a scenario where blazars are classified into flat-spectrum radio quasars (FSRQs), BL Lacertae (BL Lac) objects, low-synchrotron, or high-synchrotron peaked objects according to a varying mix of the Doppler-boosted radiation from the jet, the emission from the accretion disc, the broad-line region, and the light from the host galaxy. In this framework, the peak energy of the synchrotron power () in blazars is independent of source type and radio luminosity. We test this new approach, which builds upon unified schemes, using extensive Monte Carlo simulations, and show that it can provide simple answers to a number of long-standing issues, including, amongst others, the different cosmological evolution of BL Lac objects selected in the radio and X-ray bands, the larger values observed in BL Lac objects, the fact that high-synchrotron peaked blazars are always of BL Lac type, and the existence of FSRQ–BL Lac transition objects. Objects so far classified as BL Lac objects on the basis of their observed weak, or undetectable, emission lines are of two physically different classes: intrinsically weak lined objects, more common in X-ray-selected samples, and heavily diluted broad-lined sources, more frequent in radio-selected samples, which explains some of the confusion in the literature. We also show that strong selection effects are the main cause of the diversity observed in radio and X-ray samples, and that the correlation between luminosity and , which led to the proposal of the ‘blazar sequence’, is also a selection effect arising from the comparison between shallow radio and X-ray surveys, and to the fact that high-–high-radio-power objects have never been considered because their redshift is not measurable.

We present new ages and abundance measurements for the pre-main-sequence star PZ Telescopii (more commonly known as PZ Tel). PZ Tel was recently found to host a young and low-mass companion. Such companions, whether they are brown dwarfs or planetary systems, can attain benchmark status by detailed study of the properties of the primary, and then evolutionary and bulk characteristics can be inferred for the companion. Using Fibre-fed Extended Range Optical Spectrograph spectra, we have measured atomic abundances (e.g. Fe and Li) and chromospheric activity for PZ Tel and used these to obtain the metallicity and age estimates for the companion. We have also determined the age independently using the latest evolutionary models. We find PZ Tel A to be a rapidly rotating (v sin i= 73 ± 5  km s⁻¹), approximately solar metallicity star [log N(Fe) =−4.37 ± 0.06 dex or [Fe/H] = 0.05 ± 0.20 dex]. We measure a non-local thermodynamic equilibrium lithium abundance of log N(Li) = 3.1 ± 0.1 dex, which from depletion models gives rise to an age of 7 Myr for the system. Our measured chromospheric activity ( of −4.12) returns an age of 26 ± 2 Myr, as does fitting pre-main-sequence evolutionary tracks (τ_evol= 22 ± 3 Myr), both of these are in disagreement with the lithium age. We speculate on reasons for this difference and introduce new models for lithium depletion that incorporate both rotation and magnetic field effects. We also synthesize solar, metal-poor and metal-rich substellar evolutionary models to better determine the bulk properties of PZ Tel B, showing that PZ Tel B is probably more massive than previous estimates, meaning the companion is not a giant exoplanet, even though a planetary-like formation origin can go some way to describing the distribution of benchmark binaries currently known. We show how PZ Tel B compares to other currently known age and metallicity benchmark systems and try to empirically test the effects of dust opacity as a function of metallicity on the near-infrared colours of brown dwarfs. Current models suggest that in the near-infrared observations are more sensitive to low-mass companions orbiting more metal rich stars. We also look for trends between infrared photometry and metallicity amongst a growing population of substellar benchmark objects, and identify the need for more data in mass–age–metallicity parameter space.

The gravitational stability of a disc with gaseous and stellar components is studied in the linear regime when the gaseous component is turbulent. A phenomenological approach is adopted to describe the turbulence, in which both the effective surface density and the velocity dispersion of the gaseous component are scale-dependent as power-law functions of the wavenumber of the perturbations. In addition, the stellar component, which interacts gravitationally with the gas, is considered as a fluid. We calculate growth rates of the perturbations, and find that in most cases the stability of the disc depends strongly on the existence of the stars and on the exponents of the functions for describing the turbulence. Our analysis suggests that the conventional gas and star threshold is not adequate for analysing the stability of two-component discs when turbulence is considered.

We present the fourth portion of a Galactic plane survey of methanol masers at 6668 MHz, spanning the longitude range 186°–330°. We report 207 maser detections, 89 new to the survey. This completes the southern sky part of the methanol multibeam survey and includes a large proportion of new sources, 43 per cent. We also include results from blind observations of the Orion–Monoceros star-forming region, formally outside the latitude range of the methanol multibeam survey; only the four previously known methanol emitting sites were detected, of which we present new positions and spectra for masers at Orion A (south) and Orion B, obtained with the Multi-Element Radio Linked Interferometer Network (MERLIN) array.

We present a narrow-band Very Large Telescope/Focal Reduced Low-dispersion Spectrograph #1 imaging survey of the SAB(rs)cd spiral galaxy NGC 5068, located at a distance of 5.45 Mpc, from which 160 candidate Wolf–Rayet sources have been identified, of which 59 cases possess statistically significant λ4686 excesses. Follow-up Gemini Multi-Object Spectrograph spectroscopy of 64 candidates, representing 40 per cent of the complete photometric catalogue, confirms Wolf–Rayet signatures in 30 instances, corresponding to a 47 per cent success rate. 21 out of 22 statistically significant photometric sources are spectroscopically confirmed. Nebular emission detected in 30 per cent of the Wolf–Rayet candidates spectrally observed, which enable a re-assessment of the metallicity gradient in NGC 5068. A central metallicity of log (O/H) + 12 ∼ 8.74 is obtained, declining to 8.23 at R₂₅. We combine our spectroscopy with archival Hα images of NGC 5068 to estimate a current star formation rate of , and provide a catalogue of the 28 brightest H ii regions from our own continuum subtracted Hα images, of which ∼17 qualify as giant H ii regions. Spectroscopically, we identify 24 WC- and 18 WN-type Wolf–Rayet stars within 30 sources since emission-line fluxes indicate multiple Wolf–Rayet stars in several cases. We estimate an additional ∼66 Wolf–Rayet stars from the remaining photometric candidates, although sensitivity limits will lead to an incomplete census of visually faint WN stars, from which we estimate a global population of ∼170 Wolf–Rayet stars. Based on the Hα-derived O star population of NGC 5068 and N(WR)/N(O) ∼ 0.03, representative of the Large Magellanic Cloud, we would expect a larger Wolf–Rayet population of 270 stars. Finally, we have compared the spatial distribution of spectroscopically confirmed WN and WC stars with Sloan Digital Sky Survey derived supernovae, and find both WN and WC stars to be most consistent with the parent population of Type Ib supernovae.

We study the amount and distribution of dark matter substructures within dark matter haloes, using a large set of high-resolution simulations ranging from group-size to cluster-size haloes, and carried out within a cosmological model consistent with Wilkinson Microwave Anisotropy Probe (WMAP) 7-year data. In particular, we study how the measured properties of subhaloes vary as a function of the parent halo mass, the physical properties of the parent halo and redshift. The fraction of halo mass in substructures increases with increasing mass: it is of the order of 5 per cent for haloes with M₂₀₀∼ 10¹³  M_⊙ and of the order of 10 per cent for the most massive haloes in our sample, with M₂₀₀∼ 10¹⁵  M_⊙. There is, however, a very large halo-to-halo scatter that can be explained only in part by a range of halo physical properties, e.g. concentration. At a given halo mass, less concentrated haloes contain significantly larger fractions of mass in substructures because of the reduced strength of tidal disruption. Most of the substructure mass is located at the outskirts of the parent haloes, in relatively few massive subhaloes. This mass segregation appears to become stronger at increasing redshift, and should reflect into a more significant mass segregation of the galaxy population at different cosmic epochs. When haloes are accreted on to larger structures, their mass is significantly reduced by tidal stripping. Haloes that are more massive at the time of accretion (these should host more luminous galaxies) are brought closer to the centre on shorter time-scales by dynamical friction, and therefore suffer a more significant stripping. The halo merger rate depends strongly on the environment with substructure in more massive haloes suffering more important mergers than their counterparts residing in less massive systems. This should translate into a different morphological mix for haloes of different mass.

We investigate the emission of active galactic nucleus (AGN) dusty tori in infrared domain. Following theoretical predictions derived from hydrodynamical simulations, we model the dusty torus as a 3D two-phase medium with high-density clumps and low-density medium filling the space between the clumps. Spectral energy distributions (SEDs) and images of the torus at different wavelengths are obtained using the 3D Monte Carlo radiative transfer code skirt. Our approach of generating clumpy structure allows us to model the tori with single clumps, complex structures of merged clumps or interconnected sponge-like structure. A corresponding set of clumps-only models and models with smooth dust distribution is calculated for comparison. We found that dust distribution, optical depth, clump size and their actual arrangement in the innermost region all have an impact on the shape of near- and mid-infrared SED. The 10-μm silicate feature can be suppressed for some parameters, but models with smooth dust distribution are also able to produce a wide range of silicate feature strength. Finally, we find that having the dust distributed in a two-phase medium might offer a natural solution to the lack of emission in near-infrared, compared to observed data, which affects clumpy models currently available in the literature.

The supermassive black hole candidate at the centre of M87 drives an ultra-relativistic jet visible on kiloparsec scales, and its large mass and relative proximity allow for event horizon scale imaging with very long baseline interferometry at millimetre wavelengths (mm-VLBI). Recently, relativistic magnetohydrodynamic simulations of black hole accretion flows have proven capable of launching magnetically dominated jets. We construct time-dependent disc/jet models of the innermost portion of the M87 nucleus by performing relativistic radiative transfer calculations from one such simulation. We identify two types of models, jet-dominated or disc/jet, that can explain the spectral properties of M87, and use them to make predictions for current and future mm-VLBI observations. The Gaussian source size for the favoured sky orientation and inclination from observations of the large-scale jet is as (≃4–6 Schwarzschild radii) on current mm-VLBI telescopes, very similar to existing observations of Sgr A*. The black hole shadow, direct evidence for an event horizon, should be visible in future measurements using baselines between Hawaii and Mexico. Both models exhibit variability at millimetre wavelengths with factor of ≃2 amplitudes on year time-scales. For the low inclination of M87, the counter-jet dominates the event horizon scale millimetre wavelength emission from the jet-forming region.

Thermonuclear explosions may arise in binary star systems in which a carbon–oxygen (CO) white dwarf (WD) accretes helium-rich material from a companion star. If the accretion rate allows a sufficiently large mass of helium to accumulate prior to ignition of nuclear burning, the helium surface layer may detonate, giving rise to an astrophysical transient. Detonation of the accreted helium layer generates shock waves that propagate into the underlying CO WD. This might directly ignite a detonation of the CO WD at its surface (an edge-lit secondary detonation) or compress the core of the WD sufficiently to trigger a CO detonation near the centre. If either of these ignition mechanisms works, the two detonations (helium and CO) can then release sufficient energy to completely unbind the WD. These ‘double-detonation’ scenarios for thermonuclear explosion of WDs have previously been investigated as a potential channel for the production of Type Ia supernovae from WDs of ∼ 1  M_⊙. Here we extend our 2D studies of the double-detonation model to significantly less massive CO WDs, the explosion of which could produce fainter, more rapidly evolving transients. We investigate the feasibility of triggering a secondary core detonation by shock convergence in low-mass CO WDs and the observable consequences of such a detonation. Our results suggest that core detonation is probable, even for the lowest CO core masses that are likely to be realized in nature. To quantify the observable signatures of core detonation, we compute spectra and light curves for models in which either an edge-lit or compression-triggered CO detonation is assumed to occur. We compare these to synthetic observables for models in which no CO detonation was allowed to occur. If significant shock compression of the CO WD occurs prior to detonation, explosion of the CO WD can produce a sufficiently large mass of radioactive iron-group nuclei to significantly affect the light curves. In particular, this can lead to relatively slow post-maximum decline. If the secondary detonation is edge-lit, however, the CO WD explosion primarily yields intermediate-mass elements that affect the observables more subtly. In this case, near-infrared observations and detailed spectroscopic analysis would be needed to determine whether a core detonation occurred. We comment on the implications of our results for understanding peculiar astrophysical transients including SN 2002bj, SN 2010X and SN 2005E.

In a quadruply imaged lens system, the angular distribution of images around the lens centre is completely described by three relative angles. We show empirically that in the three-dimensional space of these angles, spanning 180°× 180°× 90°, quads from simple twofold symmetric lenses of arbitrary radial density profile and arbitrary radially dependent ellipticity or external shear define a nearly invariant two-dimensional surface. We give a fitting formula for the surface using the SIS+elliptical lensing potential. Various circularly symmetric mass distributions with shear up to γ∼ 0.4 deviate from it by typically an rmsof ∼01, while elliptical mass distributions with ellipticity of up to e∼ 0.4 deviate from it by rms ∼15. The existence of a near-invariant surface gives a new insight into the lensing theory and provides a framework for studying quads. It also allows one to gain information about the lens mass distribution from the image positions alone, without any recourse to mass modelling. As an illustration, we show that about 3/4 of observed galaxy-lens quads do not belong to this surface within observational error, and so require additional external shear or substructure to be modelled adequately.

We present an analysis of Spitzer IRAC (3.6–8 μm) and MIPS (24 μm) imaging of members of the 16 Myr old open cluster NGC 1960 (M36). Models of terrestrial planet formation indicate that rocky planets are likely to achieve their final masses at around 10–30 Myr, and thus this cluster is at an interesting epoch for planet formation. We find 21 B–F5 type stars and 14 F6–K9 type stars which have 24 μm excess emission, and thus determine that >30 per cent of B–F5 type stars and >23 per cent of F6–K9 type stars in this cluster have 24 μm excess emission. These excess frequencies are similar to those observed in other clusters of similar age. Three early-type stars have excesses at near-infrared wavelengths. Analysis of their spectral energy distributions confirms that these are true debris discs and not remnant primordial or transitional discs. None of the 61 Sun-like stars has confirmed near-infrared excess, and we can place a limit on the frequency of 8 μm excess emission around Sun-like stars of <7 per cent. All of the detected excesses are consistent with emission from debris discs and are not primordial.

We present the structure of the 3D ideal magnetohydrodynamics pulsar magnetosphere to a radius 10 times that of the light cylinder, a distance about an order of magnitude larger than any previous such numerical treatment. Its overall structure exhibits a stable, smooth, well-defined undulating current sheet which approaches the kinematic split monopole solution of Bogovalov only after a careful introduction of diffusivity even in the highest resolution simulations. It also exhibits an intriguing spiral region at the crossing of two zero-charge surfaces on the current sheet, which shows a destabilizing behaviour more prominent in higher resolution simulations. We discuss the possibility that this region is physically (and not numerically) unstable. Finally, we present the spiral pulsar antenna radiation pattern.

We present the first statistical study of X-ray cavities in distant clusters of galaxies (z > 0.3). With the aim of providing further insight into how active galactic nucleus (AGN) feedback operates at higher redshift, we have analysed the Chandra X-ray observations of the MAssive Cluster Survey (MACS) and searched for surface brightness depressions associated with the brightest cluster galaxy (BCG). The MACS sample consists of the most X-ray luminous clusters within 0.3 ≤z≤ 0.7 (median L_{X, RASS}= 7 × 10⁴⁴ erg s⁻¹), and out of 76 clusters, we find 13 with ‘clear’ cavities and seven with ‘potential’ cavities (detection rate ∼25 per cent). Most of the clusters in which we find cavities have a short central cooling time below 3–5 Gyr, consistent with the idea that cavities sit predominantly in cool core clusters. We also find no evidence for evolution in any of the cavity properties with redshift, up to z∼ 0.6. The cavities of powerful outbursts are not larger (or smaller) at higher redshift, and are not able to rise to further (or lesser) distances from the nucleus. The energetics of these outbursts also remain the same. This suggests that extreme ‘radio mode’ feedback (L_mech > 10⁴⁴ erg s⁻¹) starts to operate as early as 7–8 Gyr after the big bang and shows no sign of evolution since then. In other words, AGNs lying at the centre of clusters are able to operate at early times with extreme mechanical powers, and have been operating in such a way for at least the past 5 Gyr.

Radio observations of galaxy clusters show that the intracluster medium is permeated by magnetic fields. The origin and evolution of these cosmological magnetic fields is currently not well understood, and so their impact on the dynamics of structure formation is not known. Numerical simulations are required to gain a greater understanding and produce predictions for the next generation of radio telescopes. We present the galactic chemodynamics smoothed particle magnetohydrodynamics (SPMHD) code (gcmhd+), which is an MHD implementation for the cosmological smoothed particle hydrodynamics code gcd+. The results of 1D, 2D and 3D tests are presented and the performance of the code is shown relative to the athena grid code. gcmhd+ shows good agreement with the reference solutions produced by athena. The code is then used to simulate the formation of a galaxy cluster with a simple primordial magnetic field embedded in the gas. A homogeneous seed field of 3.5 × 10⁻¹¹ G is amplified by a factor of 10³ during the formation of the cluster. The results show good agreement with the profiles found in other magnetic cluster simulations of similar resolution.

We reformulate the adiabatic inflow–outflow solution (ADIOS) model for radiatively inefficient accretion flows, treating the inflow and outflow zones on an equal footing. For purely adiabatic flows (i.e. with no radiative losses), we show that the mass flux in each zone must satisfy with n= 1, in contrast to previous work in which 0 < n < 1 is a free parameter but in rough agreement with numerical simulations. We also demonstrate that the resulting two-zone ADIOS models are not dynamically self-consistent without the introduction of an energy source close in to the central regions of the flow; we identify this with the energy liberated by accretion. We explore the parameter space of non-radiative models and show that both powerful winds and gentle breezes are possible. When small radiative losses (with fixed efficiency) are included, any centrally injected energy flux is radiated away and the system reverts to a power-law behaviour with n≲ 1, where n falls in a small range determined by the fractional level of radiative losses. We also present an ADIOS model for hypercritical (super-Eddington) disc accretion, in which the radiative losses are closely related to the flow geometry. We suggest that hyperaccretion can lead to either winds or breezes.

We use 500 pc resolution cosmological simulations of a Virgo-like galaxy cluster to study the properties of the brightest cluster galaxy (BCG) that forms at the centre of the halo. We compared two simulations; one incorporating only supernova feedback and a second that also includes prescriptions for black hole growth and the resulting active galactic nucleus (AGN) feedback from gas accretion. As previous work has shown, with supernova feedback alone we are unable to reproduce any of the observed properties of massive cluster ellipticals. The resulting BCG rotates quickly, has a high Sérsic index, a strong mass excess in the centre and a total central density profile falling more steeply than isothermal. Furthermore, it is far too efficient at converting most of the available baryons into stars which is strongly constrained by abundance matching. With a treatment of black hole dynamics and AGN feedback the BCG properties are in good agreement with data: they rotate slowly, have a cored surface density profile, a flat or rising velocity dispersion profile and a low stellar mass fraction. The AGN provides a new mechanism to create cores in luminous elliptical galaxies; the core expands due to the combined effects of heating from dynamical friction of sinking massive black holes and AGN feedback that ejects gaseous material from the central regions.

We present results from an analysis of stellar population parameters for 7132 galaxies in the 6dF Galaxy Survey Fundamental Plane (FP) sample. We bin the galaxies along the axes, v₁, v₂ and v₃, of the tri-variate Gaussian to which we have fitted the galaxy distribution in effective radius, surface brightness and central velocity dispersion (FP space), and compute median values of stellar age, [Fe/H], [Z/H] and [α/Fe]. We determine the directions of the vectors in FP space along which each of the binned stellar population parameters vary most strongly. In contrast to previous work, we find stellar population trends not just with velocity dispersion and FP residual, but with radius and surface brightness as well. The most remarkable finding is that the stellar population parameters vary through the plane (v₁ direction) and across the plane (v₃ direction), but show no variation at all along the plane (v₂ direction). The v₂ direction in FP space roughly corresponds to ‘luminosity density’. We interpret a galaxy’s position along this vector as being closely tied to its merger history, such that early-type galaxies with lower luminosity density are more likely to have undergone major mergers. This conclusion is reinforced by an examination of the simulations of Kobayashi, which show clear trends of merger history with v₂.

The desorption characteristics of molecules on interstellar dust grains are important for modelling the behaviour of molecules in icy mantles and, critically, in describing the solid–gas interface. In this study, a series of laboratory experiments exploring the desorption of three small molecules from three astrophysically relevant surfaces is presented. The desorption of CO, O₂ and CO₂ at both submonolayer and multilayer coverages was investigated from non-porous water, crystalline water and silicate surfaces. Experimental data were modelled using the Polanyi–Wigner equation to produce a mathematical description of the desorption of each molecular species from each type of surface, uniquely describing both the monolayer and multilayer desorption in a single combined model. The implications of desorption behaviour over astrophysically relevant time-scales are discussed.

In this paper, we investigate the action of solar wind on an arbitrarily shaped interplanetary dust particle. The final relativistically covariant equation of motion of the particle also contains the change of the particle’s mass. The non-radial solar wind velocity vector is also included. The covariant equation of motion reduces to the Poynting–Robertson effect in the limiting case when a spherical particle is treated, when the speed of the incident solar wind corpuscles tends to the speed of light and when the corpuscles spread radially from the Sun. The results of quantum mechanics have to be incorporated into the physical considerations, in order to obtain the limiting case.

If the solar wind affects the motion of a spherical interplanetary dust particle, then . Here, p′_in and p′_out are the incoming and outgoing radiation momenta (per unit time), respectively, measured in the proper frame of reference of the particle, and and are the solar wind pressure and the total scattering cross-sections, respectively.

An analytical solution of the derived equation of motion yields a qualitative behaviour consistent with numerical calculations. This also holds if we consider a decrease of the particle’s mass. Using numerical integration of the derived equation of motion, we confirm our analytical result that the non-radial solar wind (with a constant value of angle between the radial direction and the direction of the solar wind velocity) causes outspiralling of the dust particle from the Sun for large values of the particle’s semimajor axis. The non-radial solar wind also increases the time the particle spirals towards the Sun. If we consider the periodical variability of the solar wind with the solar cycle, then there are resonances between the particle’s orbital period and the period of the solar cycle.

The precision of radial velocity (RV) measurements depends on the precision attained on the wavelength calibration. One of the available options is to use atmospheric lines as a natural, freely available wavelength reference. Figueira et al. measured the RV of O₂ lines using High Accuracy Radial velocity Planet Searcher (HARPS) and showed that the scatter was only of ∼10 m s⁻¹ over a time-scale of 6 yr. Using a simple but physically motivated empirical model, they demonstrated a precision of 2 m s⁻¹, roughly twice the average photon noise contribution. In this paper, we take advantage of a unique opportunity to confirm the sensitivity of the telluric absorption lines’ RV to different atmospheric and observing conditions by means of contemporaneous in situ wind measurements. This opportunity is a result of the work done during site testing and characterization for the European Extremely Large Telescope (E-ELT). The HARPS spectrograph was used to monitor telluric standards while contemporaneous atmospheric data were collected using radiosondes. We quantitatively compare the information recovered by the two independent approaches.

The RV model fitting yielded results similar to that of Figueira et al., with lower wind magnitude values and varied wind direction. The probes confirmed the average low wind magnitude and suggested that the average wind direction is a function of time as well. However, these results are affected by large uncertainty bars that probably result from a complex wind structure as a function of height. The two approaches deliver the same results in what concerns wind magnitude and agree on wind direction when fitting is done in segments of a couple of hours. Statistical tests show that the model provides a good description of the data on all time-scales, being always preferable to not fitting any atmospheric variation. The smaller the time-scale on which the fitting can be performed (down to a couple of hours), the better the description of the real physical parameters is. We then conclude that the two methods deliver compatible results, down to better than 5 m s⁻¹ and less than twice the estimated photon noise contribution on O₂ lines’ RV measurement. However, we cannot rule out that parameters α and γ (dependence on airmass and zero-point, respectively) have a dependence on time or exhibit some cross-talk with other parameters, an issue suggested by some of the results.

We have obtained high-resolution optical spectroscopy of 10 reddened O-type stars with Ultraviolet and Visual Echelle Spectrograph at Very Large Telescope to search for interstellar bands of the naphthalene cation (C₁₀H₈⁺) in the intervening clouds. No absorption features were detected near the laboratory strongest band of this cation at 6707 Å except for star HD 125241 (O9 I). Additional bands in the optical spectrum of this star appear to be consistent with other transitions of this cation. Under the assumption that the bands are caused by naphthalene cations, we derive a column density = (1.2 ± 0.3) × 10 ¹³ cm⁻² similar to the column density claimed in the Perseus complex star Cernis 52. The strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797 Å suggests the presence of a σ-type cloud in the line of sight of HD 125241.

We study the time evolution of a rotating, axisymmetric, viscous accretion flow around black holes using a grid-based finite difference method. We use the Shakura–Sunyaev viscosity prescription. However, we compare with the results obtained when all the three independent components of the viscous stress are kept. We show that the centrifugal pressure supported shocks became weaker with the inclusion of viscosity. The shock is formed farther out when the viscosity is increased. When the viscosity is above a critical value, the shock disappears altogether and the flow becomes subsonic and Keplerian everywhere except in a region close to the horizon, where it remains supersonic. We also find that as the viscosity is increased, the amount of outflowing matter in the wind is decreased to less than a percentage of the inflow matter. Since the post-shock region could act as a reservoir of hot electrons or the so-called ‘Compton cloud’, the size of which changes with viscosity, the spectral properties are expected to depend on viscosity strongly: the harder states are dominated by low angular momentum and the low-viscosity flow with significant outflows while the softer states are dominated by the high-viscosity Keplerian flow having very few outflows.

The effects of a protostellar outflow on the star formation in a single cloud core are investigated by three-dimensional resistive magnetohydrodynamic (MHD) simulations. Starting from the pre-stellar cloud core, the star formation process is calculated until the end of the main accretion phase. In the calculations, the mass of the pre-stellar cloud is parametrized. During the star formation, the protostellar outflow is driven by the circumstellar disc. The outflow extends also in the transverse direction until its width becomes comparable to the initial cloud scale, and thus the outflow has a wide opening angle of ≳40°. As a result, the protostellar outflow sweeps up a large fraction of the infalling material and ejects it into the interstellar space. The outflow can eject at most over half of the host cloud mass, significantly decreasing the star formation efficiency. The outflow power is stronger in clouds with a greater initial mass. Thus, the protostellar outflow effectively suppresses the star formation efficiency in a massive cloud. The outflow weakens significantly and disappears in several free-fall time-scales of the initial cloud after the cloud begins to collapse. The natal pre-stellar core influences the lifetime and size of the outflow. At the end of the main accretion phase, a massive circumstellar disc comparable in mass to the protostar remains. Calculations show that ∼26–54 per cent of the initial cloud mass is converted into the protostar and ∼8–40 per cent remains in the circumstellar disc, while ∼8–49 per cent can be ejected into the interstellar space by the protostellar outflow. Therefore, the protostellar outflow can decrease the star formation efficiency to ∼50 per cent at the maximum.

We present a detailed study of the largest sample of intervening O vi systems in the redshift range 1.9 ≤z≤ 3.1 detected in high-resolution (R∼ 45 000) spectra of 18 bright quasi-stellar objects observed with Very Large Telescope/Ultraviolet and Visible Echelle Spectrograph. Based on Voigt profile and apparent optical depth analysis we find that (i) the Doppler parameters of the O vi absorption are usually broader than those of C iv, (ii) the column density distribution of O vi is steeper than that of C iv, (iii) line spread (δv) of the O vi and C iv is strongly correlated (at 5.3σ level) with δv(O vi) being systematically larger than δv(C iv) and (iv) δv(O vi) and δv(C iv) are also correlated (at >5σ level) with their respective column densities and with N(H i) (3 and 4.5σ, respectively). The median column densities of H i, O vi and C iv are found to be higher when low ions are present. N(C iv) and N(H i) are strongly correlated (at 4.3σ level). However, no significant correlation is found between N(O vi) and N(H i). These findings favour the idea that C iv and O vi absorption originate from different phases of a correlated structure and systems with large velocity spread is probably associated with overdense regions. The velocity offset between optical depth weighted redshifts of C iv and O vi absorption is found to be in the range 0 ≤|Δv(O vi–C iv)|≤ 48 km s⁻¹ with a median value of 8 km s⁻¹.

We do not find any evidence for the ratios N(O vi)/N(H i), N(O vi)/N(C iv) and N(C iv)/N(H i) to evolve with z over the redshift range considered here. However, a lack of systems with high N(O vi)/N(H i) ratio (i.e. ≥−0.5 dex) for z > 2.5 is noticeable. Similar trend is also seen for the N(C iv)/N(H i) ratio. We compare the properties of O vi systems in our sample with that of low-redshift (z < 0.5) samples from the literature and find that (i) the O vi components at low z are systematically wider than at high z with an enhanced non-thermal contribution to their b parameter, (ii) the slope of the column density distribution functions for high and low z is consistent, (iii) the range in gas temperature estimated from a subsample of well-aligned absorbers is similar at both high and low z and (iv) for N(O vi) > 10^13.7 cm⁻², estimated in our high-z sample, is very similar to low-z estimations.

Microquasars are expected to emit high-energy γ-rays owing to their general similarities to γ-ray-emitting blazars (evidence of relativistic jets, non-thermal radio to X-ray emission). In fact, the first source of this type, Cyg X-3, has recently been unambiguously discovered by satellite telescopes. We study the features of the γ-ray radiation produced in these sources by relativistic electrons accelerated in the inner part of the jet. The electrons initiate an inverse Compton e^± pair cascade in the radiation field of the accretion disc. Owing to the anisotropy of the accretion disc radiation field, the spectra of γ-rays show a strong dependence on the observation angle, the location of the emission region within the jet, and the details of the acceleration process. As an example, we test our model with observations of the microquasar Cyg X-3, which has recently been reported as a transient GeV γ-ray source by the Agile and Fermi observatories. Satisfactory descriptions of the γ-ray spectra observed from Cyg X-3 are obtained in the case of injection of electrons in the inner part of the jet (located within 300 inner disc radius from the jet base), provided that the observer is located at a relatively small angle to the jet axis.

Type II quasars are luminous active galactic nuclei with the optical spectra of type II Seyfert galaxies, and their central regions are obscured by large amounts of gas and dust. In this paper, we present Spitzer spectra of eight type II quasars using infrared photometric observations. It is found that almost all the sources in this paper show features of polycyclic aromatic hydrocarbon and silicate in absorption, which indicate strong star formation activities. All the sources show significant highly ionized atomic emission features, such as [Ne v] and/or [S iv], in the mid-infrared, which indicate that their properties are similar to those of type I Seyfert galaxies. Furthermore, our results reveal that, similar to type II Seyfert galaxies, there might be two types of type II quasar: the ‘true’ type II quasars and those that have the properties of Seyfert I galaxies in the infrared. Therefore, the classifications of quasars that are based only on their optical spectra are not perfect if their infrared properties are considered.

The seismological dynamics of magnetars are largely determined by a strong hydromagnetic coupling between the solid crust and the fluid core. In this paper, we set up a ‘spectral’ computational framework in which the magnetar’s motion is decomposed into a series of basis functions that are associated with the crust and core vibrational eigenmodes. A general relativistic formalism is presented for evaluation of the core Alfvén modes in the magnetic flux coordinates, as well for eigenmode computation of a strongly magnetized crust of finite thickness. By considering coupling of the crustal modes to the continuum of Alfvén modes in the core, we construct a fully relativistic dynamical model of the magnetar which allows: (i) fast and long simulations without numerical dissipation; and (ii) very fine sampling of the stellar structure. We find that the presence of strong magnetic field in the crust results in localizing of some high-frequency crustal elastomagnetic modes with the radial number n≥ 1 to the regions of the crust where the field is nearly horizontal. While the hydromagnetic coupling of these localized modes to the Alfvén continuum in the core is reduced, their energy is drained on a time-scale of ≪1 s. Therefore, the puzzle of quasi-periodic oscillations with frequencies larger than 600 Hz still stands.

The characterization of the atomic and molecular hydrogen content of high-redshift galaxies is a major observational challenge that will be addressed over the coming years with a new generation of radio telescopes. We investigate this important issue by considering the states of hydrogen across a range of structures within high-resolution cosmological hydrodynamical simulations. In addition, our simulations allow us to investigate the sensitivity of our results to numerical resolution and to sub-grid baryonic physics (especially feedback from supernovae and active galactic nuclei). We find that the most significant uncertainty in modelling the neutral hydrogen distribution arises from our need to model a self-shielding correction in moderate density regions. Future simulations incorporating radiative transfer schemes will be vital to improve on our empirical self-shielding threshold. Irrespective of the exact nature of the threshold, we find that while the atomic hydrogen mass function evolves only mildly from redshift two to zero, the molecular hydrogen mass function increases with increasing redshift, especially at the high-mass end. Interestingly, the weak evolution of the neutral hydrogen mass function is insensitive to the feedback scheme utilized, but the opposite is true for the molecular gas, which is more closely associated with the star formation in the simulations.

We propose a new hypothesis for the origin of protoplanetary discs with large inner holes (or gaps), so-called transition discs. Our gas disc model takes into account layered accretion, in which poorly ionized low-viscosity dead zones are sandwiched by high-viscosity surface layers, and photoevaporative winds induced by X-rays from the central stars. We find that a gap opens at a radius outside a dead zone, if the mass-loss rate due to photoevaporative winds exceeds the mass accretion rate in the dead zone region. Since the dead zone survives even after the gap opens, mass accretion on to the central star continues for a long time. This model can reproduce large gap sizes and high mass accretion rates seen in observed transition discs.

Cosmic shear has been identified as the method with the most potential to constrain dark energy. To capitalize on this potential, it is necessary to measure galaxy shapes with great accuracy, which in turn requires a detailed model for the image blurring by the telescope and atmosphere, the point spread function (PSF). In general, the PSF varies with wavelength and therefore the PSF integrated over an observing filter depends on the spectrum of the object. For a typical galaxy the spectrum varies across the galaxy image, thus the PSF depends on the position within the image. We estimate the bias on the shear due to such colour gradients by modelling galaxies using two co-centred, co-elliptical Sérsic profiles, each with a different spectrum. We estimate the effect of ignoring colour gradients and find the shear bias from a single galaxy can be very large depending on the properties of the galaxy. We find that halving the filter width reduces the shear bias by a factor of about 5. We show that, to the first order, tomographic cosmic shear two point statistics depend on the mean shear bias over the galaxy population at a given redshift. For a single broad filter, and averaging over a small galaxy catalogue from Simard et al., we find a mean shear bias which is subdominant to the predicted statistical errors for future cosmic shear surveys. However, the true mean shear bias may exceed the statistical errors, depending on how accurately the catalogue represents the observed distribution of galaxies in the cosmic shear survey. We then investigate the bias on the shear for two-filter imaging and find that the bias is reduced by at least an order of magnitude. Lastly, we find that it is possible to calibrate galaxies for which colour gradients were ignored using two-filter imaging of a fair sample of noisy galaxies, if the galaxy model is known. For a signal-to-noise ratio of 25 the number of galaxies required in each tomographic redshift bin is of the order of 10⁴.

Recent measurements of cosmic ray spectra of several individual nuclear species by the CREAM, TRACER and ATIC experiments indicate a change in the spectral index of the power laws at TeV energies. Possible explanations among others include non-linear diffusive shock acceleration of cosmic rays, different cosmic ray propagation properties at higher and lower energies in the Galaxy and the presence of nearby sources. In this paper, we show that if supernova remnants are the main sources of cosmic rays in our Galaxy, the effect of the nearby remnants can be responsible for the observed spectral changes. Using a rigidity-dependent escape of cosmic rays from the supernova remnants, we explain the apparent observed property that the hardening of the helium spectrum occurs at relatively lower energies as compared to the protons and also that the spectral hardening does not persist beyond ∼(20–30) TeV energies.

The main aim of this paper is the first detailed analysis of multiple system V2083 Cyg, to reveal its basic physical properties. The system was studied using the methods of light-curve and radial-velocity curve analysis, together with interferometric data from the visual pair obtained during the last century. It was found that the close subsystem contains two very similar stars of spectral type A7–8. Moreover, a third body is orbiting around this pair with a period of about 177 yr. Due to the discrepancy in the total mass derived with the two methods, the possibility arises that the third body is perhaps also a binary, or some object with lower luminosity but higher mass than a normal main-sequence star. Another explanation is that the Hipparcos value of parallax is incorrect and the system is much closer to the Sun.

We analyse a high-resolution spectrum of the A3m star HD 27411. We compare abundances derived from atlas9 model atmospheres with those using the more computationally intensive atlas12 code. We found very little differences in the abundances, suggesting that atlas9 can be used for moderate chemical peculiarity. Our abundances agree well with the predictions of diffusion theory, though for some elements it was necessary to calculate line profiles in non-thermodynamic equilibrium to obtain agreement. We investigate the effective temperatures and luminosities of Am/Fm stars using synthetic Strömgren indices derived from calculated spectra with the atmospheric abundances of HD 27411. We find that the effective temperatures of Am/Fm stars derived from Strömgren photometry are reliable, but the luminosities are probably too low. Caution is required when deriving the reddening of these stars owing to line blanketing effects. A comparison of the relative proportions of pulsating and non-pulsating Am stars with δ Scuti stars shows quite clearly that there is no significant decrease of helium in the driving zone, contrary to current models of diffusion.