Chemical abundances from inversions of stellar spectra: Analysis of solar-type stars with homogeneous and static model atmospheres

Spectra of late-type stars are usually analyzed with static model atmospher es in local thermodynamic equilibrium (LTE) and a homogeneous plane-paralle l or spherically symmetric geometry. The energy balance requires particular attention, as two elements that are particularly difficult to model play a n important role: line blanketing and convection. Inversion techniques are able to bypass the difficulties of a detailed description of the energy bal ance. Assuming that the atmosphere is in hydrostatic equilibrium and LTE, i t is possible to constrain its structure from spectroscopic observations. A mong the most serious approximations still implicit in the method is a stat ic and homogeneous geometry. In this paper, we take advantage of a realisti c three-dimensional radiative hydrodynamical simulation of the solar surfac e to check the systematic errors incurred by an inversion assuming a plane- parallel horizontally-homogeneous atmosphere. The thermal structure recover ed resembles the spatial and time average of the three-dimensional atmosphe re. Furthermore, the abundances retrieved are typically within 10% (0.04 de x) of the abundances used to construct the simulation. The application to a fairly complete data set from the solar spectrum provides further confiden ce in previous analyses of the solar composition. There is only a narrow ra nge of one-dimensional thermal structures able to Dt the absorption lines i n the spectrum of the Sun. With our carefully selected data set, random err ors are about a factor of 2 smaller than systematic errors. A small number of strong metal lines can provide very reliable results. We foresee no majo r difficulties in applying the technique to other similar stars, and obtain ing similar accuracies, using spectra with lambda/delta lambda similar to 5 x10(4) and a signal-to-noise ratio as low as 30.