Astron. Astrophys. 324, 281-288 (1997)

1. Introduction

Photospheres and line forming regions in solar-like stellar atmospheres lay practically on the upper part of their convective envelopes. Here metals are mainly in the form of ions due to their low ionization potentials. For this reason, small changes of the temperature structure in the stellar atmospheres caused by atmospheric inhomogeneities may strongly affect the intensity of metal absorption lines. In general, sizes and contrasts of inhomogeneities in stellar atmospheres depend on gravity , effective temperature , and metallicity µ. On the other hand, results of the convection modeling depend on the procedure used in the computations. Mixing length theory (MLT) has been widely used to compute the convective flux in 1-D model atmospheres, but this approach involves strong assumptions.

Nordlund (1984), Steffen & Gigas (1985), Gadun (1986), Steffen (1989), and Atroshchenko (1993) carried out multidimensional hydrodynamic computations of the solar convection and used these multidimensional model atmospheres for LTE computations of line profiles. Later, Bruls & Rutten (1993) performed NLTE computations of and K I 769.9 nm lines using three-dimensional (3-D) models of Stein & Nordlund (1989). Extensive LTE computations for 42 Fe I and 32 Fe II lines were carried out by Gadun (1994; see also Atroshchenko & Gadun 1994: hereafter Paper I) for two sequences of 3-D models: cool "grey" model atmospheres of Gadun (1986) and hot non-grey model atmospheres of Atroshchenko (1993). He showed that the impact of the atmospheric inhomogeneities on the abundance determination is in the range 0.03-0.04 dex for both Fe I and Fe II lines. Furthermore, the specific nature of 3-D models leads to abundance differences up to 0.1 dex for Fe I lines between 3-D and one-dimensional (1-D) models.

Recently, Gadun (1995) developed a new algorithm for the numerical simulation of convection. In the frame of his approach the radiative transfer equation is solved directly in 97 frequency intervals using the earlier ODF tables of Kurucz (1979). This scheme was used to compute a set of two-dimensional (2-D) models of the solar atmosphere (Gadun 1995; Gadun & Vorob'yov 1995; Gadun & Pikalov 1996). On the other hand, several attempts have been made to modify the MLT approach, and, recently, Kurucz (1993) implemented convective overshooting (CoOv) in his ATLAS9 program.

The aim of this paper is to investigate the dependence, in LTE, of lithium and iron lines on different treatments of the solar convection. Iron lines are widely used in astrophysics, and the study of Li I lines becomes especially important due to its implications on stellar structure and evolution models and because it has been questioned by Kurucz (1995).

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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