The fine structure of the proper motion in a solar active region. The contour lines represent the boundaries to the penumbra and to the umbra (see L. Beauregard et al., this issue, p. 125) (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

As was demonstrated in earlier studies, turbulence can result in a negative contribution to the effective mean magnetic pressure, which, in turn, can cause a large-scale instability. In this study, hydromagnetic mean-field modelling is performed for an isothermally stratified layer in the presence of a horizontal magnetic field. The negative effective magnetic pressure instability (NEMPI) is comprehensively investigated. It is shown that, if the effect of turbulence on the mean magnetic tension force vanishes, which is consistent with results from direct numerical simulations of forced turbulence, the fastest growing eigenmodes of NEMPI are two-dimensional. The growth rate is found to depend on a parameter β_* characterizing the turbulent contribution of the effective mean magnetic pressure for moderately strong mean magnetic fields. A fit formula is proposed that gives the growth rate as a function of turbulent kinematic viscosity, turbulent magnetic diffusivity, the density scale height, and the parameter β_*. The strength of the imposed magnetic field does not explicitly enter provided the location of the vertical boundaries are chosen such that the maximum of the eigenmode of NEMPI fits into the domain. The formation of sunspots and solar active regions is discussed as possible applications of NEMPI (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A fully autonomous data reduction pipeline has been developed for FRODOSpec, an optical fibre-fed integral field spectrograph currently in use at the Liverpool Telescope. This paper details the process required for the reduction of data taken using an integral field spectrograph and presents an overview of the computational methods implemented to create the pipeline. Analysis of errors and possible future enhancements are also discussed (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Comet C/1853 E1 (Secchi) has a hyperbolic orbit with eccentricity 1.01060 and perihelion outside of the Earth's orbit. Integrating the orbit with barycentric coordinates backwards to 50000 AU, the approximate edge of the Oort cloud, shows that the orbit remains hyperbolic. This is still true even if plutoids additional to Pluto are included in the integration. Nor does including Galactic tidal and disc effects and possible nongravitational forces change the orbit to a high eccentricity ellipse. Although certain factors, such as unknown massive plutoids, gravitational effects by interstellar gas clouds, or unmodelled nongravitational forces operating on the comet, could change this situation, the tentative conclusion that the origin of this comet is extrasolar remains the one most consistent with the observations (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Horizontal proper motions were measured with local correlation tracking (LCT) techniques in active region NOAA 11158 on 2011 February 15 at a time when a major (X2.2) solar flare occurred. The measurements are based on continuum images and magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The observed shear flows along the polarity inversion line were rather weak (a few 100 m s^–1). The counter-streaming region shifted toward the north after the flare. A small circular area with flow speeds of up to 1.2 km s^–1 appeared after the flare near a region of rapid penumbral decay. The LCT signal in this region was provided by small-scale photospheric brigthenings, which were associated with fast traveling moving magnetic features. Umbral strengthening and rapid penumbral decay was observed after the flare. Both phenomena were closely tied to kernels of white-light flare emission. The white-light flare only lasted for about 15 min and peaked 4 min earlier than the X-ray flux. In comparison to other major flares, the X2.2 flare in active region NOAA 11158 only produced diminutive photospheric signatures (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The Praesepe cluster contains a number of δ Sct and γ Dor pulsators. Asteroseismology of cluster stars is simplified by the common distance, age and stellar abundances. Since asteroseismology requires a large number of known frequencies, the small pulsation amplitudes of these stars require space satellite campaigns. The present study utilizes photometric MOST satellite measurements in order to determine the pulsation frequencies of two evolved (EP Cnc, BT Cnc) and two main-sequence (BS Cnc, HD 73872) δ Sct stars in the Praesepe cluster. The frequency analysis of the 2008 and 2009 data detected up to 34 frequencies per star with most amplitudes in the submillimag range. In BS Cnc, two modes showed strong amplitude variability between 2008 and 2009. The frequencies ranged from 0.76 to 41.7 cd^–1. After considering the different evolutionary states and mean stellar densities of these four stars, the differences and large ranges in frequency remain (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present the analysis of 20 years of time-series BV photometry of the SB1 RS CVn binary HD 89546. The system's yearly mean V brightness, the B – V color index, the photometric period, and the light curve amplitude all show clear cyclic variability with an ≈9-year time scale. We also find some evidence for brightness variability on a time scale longer than the 20-year time span of our observations, perhaps indicating a longer cycle analogous to the solar Gleissberg cycle. We estimate the unspotted V magnitude of HD 89546 to be 7.^m154, which is ≈0.^m2 brighter than the observed maximum brightness. Spot modelling of the system shows that spot temperature variations affect the observed B – V color as well as the V brightness. Two active longitudes are observed, centered around 180° and 360° longitude on the G9 III primary, each covering a longitude range of 120°. Furthermore, two inactive longitude zones are seen spanning only 60° between the two active longitudes. The longitudinal distribution of the spots exhibits no strong cyclic variability but does show rapid jumps of 120° that look like the flip-flop phenomenon. We estimate the differential rotation coefficient of the star as k = 0.086 by considering the range of observed photometric period variations and assumed latitudinal spot variations over 45° (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A dual étalon Fabry-Pérot spectrometer called DEFPOS has been used for observing physical properties of HII regions and planetary nebulae since May 2007 (Aksaker et al. 2009, 2011; Şahan et al. 2009; Şahan 2011). In this study, the Hα measurements of the HII region NGC 1499 (California Nebula) have been investigated with a 4′ circular field of view over a 200 km s^–1 (4.4 Å) spectral window. These measurements provide information about the densities, line widths, and radial velocities of the surrounding NGC 1499 nebula. The intensities, the radial velocities and the line widths of the Hα emission line vary from 397.75 R to 1044.14 R, –4.88 km s^–1 to –1.02 km s^–1, and 36.72 km s^–1 to 42.81 km s^–1, respectively (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This article discusses the interstellar extinction curve in the visible and the value of the ratio of absolute to selective extinction R_V = A_V/E (B – V). It is concluded that the visible extinction curve is likely to be linear in the visible and that indirect estimates of R_V from tentative determinations of A_V or from infrared and UV observations are questionable. There is currently no evidence of any variation of R_V with direction. If R_V is close to 3, as it has been inferred from mid-infrared data, starlight in the visible is extinguished by a factor F /F₀ = (2.5 e^–2μm/λ)^{E (B –V)}. But if the visible wavelength range alone is considered, 4 appears as its most natural and probable value and F /F₀ = e^{–2E (B –V)/λ} (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Observational data in the BVRI bands of the variable BL Lacertae object S5 0716+714 are discussed from the point of view of its power spectral distribution (PSD). A model of the type P (f) = βf^–1 [1 + (f /δ)^α–1]^–1 + γ is fitted to the data for four null hypothesis and the Bayesian p parameter for the fits is calculated. Spectral slopes with values ranging from 1.083 to 2.65 are obtained, with medium values for each band of = 2.028, = 1.809, = 1.932 and = 1.54 respectively. These values confirm conclusions of previous studies, namely that the source is turbulent. Two disk models, the standard prescription of the Shakura-Sunyaev disk and magnetized disks exhibiting magneto-rotational instabilities, were discussed. We found that it is unlikely that they explain this set of observational data (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Existing photometry for NGC 2264 tied to the Johnson & Morgan (1953) UBV system is reexamined and, in the case of the original observations by Walker (1956), reanalyzed in order to generate a homogeneous data set for cluster stars. Color terms and a Balmer discontinuity effect in Walker's observations were detected and corrected, and the homogenized data were used in a new assessment of the cluster reddening, distance, and age. Average values of E_{B – V} = 0.075 ± 0.003 s.e. and V₀ –M_V = 9.45 ± 0.03 s.e. (d = 777 ± 12 pc) are obtained, in conjunction with an inferred cluster age of ∼5.5 × 10⁶ yr from pre-main-sequence members and the location of the evolved, luminous, O7 V((f)) dwarf S Mon relative to the ZAMS. The cluster main sequence also contains gaps that may have a dynamical origin. The dust responsible for the initial reddening towards NGC 2264 is no more than 465 pc distant, and there are numerous, reddened and unreddened, late-type stars along the line of sight that are difficult to separate from cluster members by standard techniques, except for a small subset of stars on the far side of the cluster embedded in its gas and dust and background B-type ZAMS members of Mon OB2. A compilation of likely NGC 2264 members is presented. Only 3 of the 4 stars recently examined by asteroseismology appear to be likely cluster members. NGC 2264 is also noted to be a double cluster, which has not been mentioned previously in the literature (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The Pioneer anomaly is one of the most important problems in modern physics. The observed blueshift of the Doppler signals coming back from the space probes Pioneer 10 and 11 is interpreted as being due to an anomalous acceleration a_p = (8.74 ± 1.33) × 10^–8 cm s^–2 towards the Sun. In this paper the blueshift is explained by the frequency shifts of the receivers. These frequency shifts result from an increase in elementary particle masses in time, the rate of increase being tied up with the present-day Hubble parameter H₀. The result is that the seeming acceleration a_p is the product of H₀ and the velocity of light. Taking new physics into consideration, this paper presents a new explanation of the Pioneer anomaly based on the assumption that the Universe is eternal and infinite without expansion or contraction (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We describe here the possible discovery of a portrait of Galileo Galilei in his youth. The painting is not signed and the identification is mainly physiognomic. In fact, the face reveals clear resemblance to Domenico Tintoretto's portrait and to Giuseppe Calendi's engraving derived from a lost portrait made by Santi di Tito in 1601. Along with the portraits by Tintoretto, Furini, Leoni, Passignano, and Sustermans this could be another portrait of Galileo made al naturale, but, unlike the others, it depicts the scientist before he reached fame. Galileo looks rather young, at age of about 20–25 years. His eyes in the portrait are clear and the expression intense and appealing. From Galileo's correspondence we know of a portrait made by his friend Ludovico Cigoli. Rather interesting, though admittedly quite improbable, is the possibility of a self-portrait whose existence is mentioned in the first biography of Galileo by Salusbury in 1664 (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)