SEARCH

SEARCH BY CITATION

Keywords:

  • stars: abundances;
  • stars: evolution;
  • stars: fundamental parameters;
  • stars: late-type

ABSTRACT

We describe the procedure to determine effective temperatures, rotational velocities, microturbulent velocities and chemical abundances in the atmospheres of Sun-like stars. We use independent determinations of iron abundances using the fits to the observed Fe i and Fe ii atomic absorption lines. We choose the best solution from the fits to these spectral features for the model atmosphere that provides the best confidence in the determined log N(Fe), Vt and v sin i. Computations were performed in the framework of local thermodynamic equilibrium. Blending effects were accounted for explicitly. First, we compute the abundance of iron for a set of adopted microturbulent velocities. In some cases, a few points of log N(Fe i) = log N(Fe ii) can be found. To determine the most self-consistent effective temperature and microturbulent velocity in any star’s atmosphere, we used an additional constraint where we minimize the dependence of the derived abundances of Fe i and Fe ii on the excitation potential of the corresponding lines. Using this procedure we analyse the spectra of the Sun and two well-known solar-type stars, HD 1835 and HD 10700, to determine their abundances, microturbulent velocity and rotational velocity. Our approach allows us to determine self-consistent values for the effective temperatures, abundances, Vt and v sin i. For the Sun, we obtain the best agreement for a model atmosphere of Teff/log g/[Fe/H] = 5777/4.44/0.0, iron abundances and microturbulent velocities of log N(Fe) = 4.44, Vt= 0.75 km s−1, for the Fe i lines, and log N(Fe) =−4.47 and Vt= 1.5 km s−1 for the Fe ii lines. Furthermore, abundances of other elements obtained from the fits of their absorption features agree well enough (±0.1 dex) with the known values for the Sun. We determined a rotational velocity of v sin i= 1.6 ± 0.3 km s−1 for the spectrum of the Sun as a star. For HD 1835, the self-consistent solution for Fe i and Fe ii lines log N(Fe) =+0.2 was obtained with a model atmosphere of 5807/4.47/+0.2 and microturbulent velocity of Vt= 0.75 km s−1, and leads to v sin i= 7.2 ± 0.5 km s−1. For HD 10700, the self-consistent solution log N(Fe) =−4.93 was obtained using a model atmosphere of 5383/4.59/−0.6 and microturbulent velocity of Vt= 0.5 km s−1. The Fe i and Fe ii lines give rise to a v sin i= 2.4 ± 0.4 km s−1. Using Teff found from the ionization equilibrium parameters for all three stars, we found abundances of a number of other elements: Ti, Ni, Ca, Si and Cr. We show that uncertainties in the adopted values of Teff of 100 K and Vt of 0.5 km s−1 change the abundances of elements up to 0.1 and 0.2 dex, respectively. Galactic abundance variations can generally be larger than this measurement precision and therefore we can study abundance variations throughout the Galaxy.