Introduction derivation of stellar physical parameters

It is generally of importance in observational stellar astronomy to precisely establish the parameters of stars (e.g. atmospheric parameters such as Teff, log g, vt, [Fe/H] for constructing model atmospheres; or fundamental stellar parameters such as M or age that are closely related to the current status of a star), the typical derivation processes of which are schematically depicted in Figure 32.1.

An accurate determination of surface chemical abundances is particularly important in the study of metal-rich stars since they may hold the key to the origin of metal-richness (e.g. the "primordial versus acquired" controversy regarding the tendency of planet-host stars to be metal-rich). Above all, unlike metal-poor stars, the precision in the abundance determination should be a vital factor in this case, since the extent of the chemical peculiarity is rather delicate (typically the enrichment is of the order of ~0.2-0.4dex at most), which in turn leads to the strong necessity of knowing the parameters of atmospheric models precisely.

atmospheric parameters (7"eff, log g, elemental abundances atmospheric parameters (7"eff, log g, colors/spectra w elemental abundances

[model-atmosphere theory, line-formation theory]

_SED modeling, spectrum modeling_

bolometric correction photometric magnitude parallax (e.g. Hipparcos) /| L (bolometric luminosity)

[stellar-evolution theory]

modeling of stellar interior/envelope and its time variation age, mass, radius,...

Figure 32.1. A schematic overview for the derivation of stellar physical parameters.

There are various ways of deriving the stellar atmospheric parameters necessary for constructing model atmospheres; for example, the determination of Teff may be implemented by using colors, Balmer-line profiles, the requirement of excitation equilibrium, line-depth ratios, etc.; while log g may be obtained via the direct method (from M and R), the requirement of ionization equilibrium, or the fitting of strong-line wings.

Among these, the traditionally well-known spectroscopic method using the strengths of Fe i and Fe 11 lines (Takeda et al. 2002) may be preferable in the context of the abundance determination, because the necessary parameters can be derived only from the "same" spectrum as that from which the abundances are to be derived. In this approach, however, the condition of LTE (i.e. application of the Saha-Boltzmann equation for computing level populations) is usually assumed, which greatly simplifies the problem. Hence, its practical validity (though it is surely unrealistic from a strict point of view) should be crucial for this spectro-scopic method of parameter determination.

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