Abstract
The determination of photospheric abundances in late-type stars from spectroscopic observations is a well-established field, built on solid theoretical foundations. Improving those foundations to refine the accuracy of the inferred abundances has proven challenging, but progress has been made. In parallel, developments on instrumentation, chiefly regarding multi-object spectroscopy, have been spectacular, and a number of projects are collecting large numbers of observations for stars across the Milky Way and nearby galaxies, promising important advances in our understanding of galaxy formation and evolution. After providing a brief description of the basic physics and input data involved in the analysis of stellar spectra, a review is made of the analysis steps, and the available tools to cope with large observational efforts. The paper closes with a quick overview of relevant ongoing and planned spectroscopic surveys, and highlights of recent research on photospheric abundances.
Highlights
Page 3 of 40 1 metals of the Milky Way in the chemical compositions of intermediate and low-mass stars that were born at different times
Line strengths are heavily influenced by temperature, which dictates the relative populations of the energy levels, and somewhat by pressure, which has an impact on ionization and molecular equilibrium, and through collisional broadening
This paper aims to explain the motivation for our excitement about stellar spectroscopy, and as an overview of the procedures involved in the analysis of stellar spectra, in particular the derivation of chemical compositions of stars
Summary
Page 3 of 40 1 metals of the Milky Way in the chemical compositions of intermediate and low-mass stars that were born at different times. The chemical mixtures found in the surfaces of main-sequence stars, essentially undisturbed by the nuclear reactions going on deep in the interior, sample the chemistry of the gas in the interstellar medium from which they formed. Stars preserve those samples for us to study. The distribution of escaping photons reflects the state of the gas in the stellar atmosphere. To model a stellar atmosphere we need to know how much energy flows through it, σ Te4ff , where σ is the Stefan–Boltzmann constant, the surface gravity of the star, g = G M/R2, and its chemical composition. Bound–bound transitions within discrete energy levels in atoms and molecules block the light at specific wavelengths, at which the increased opacity shifts the optical depth scale outwards, to cooler
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