Seminar: How accurately can we determine effective temperature and why do we care?

From the perspective of observational stellar astrophysics, the effective temperature (Teff) is likely the parameter of highest relevance because it is the one that most influences the determination of other stellar parameters. Outcomes of widely used methods, such as “the excitation and ionization equilibrium of Fe lines” and “photometric Teff-relations”, become less accurate when applied to stars less similar to the Sun; e.g. metal-poor stars, red giants, and Carbon-Enhanced Metal-poor (CEMP). Quasi-direct Teff, inferred by interferometric measurements of stellar angular diameter, is recognized to be the closest to accurate, and therefore it has been used to calibrate spectroscopic methods in large surveys. However, interferometry is limited to the closest stars, which naturally excludes metal-poor stars of the Galaxy halo. The fitting of Balmer line profiles is a powerful alternative to derive accurate and precise Teff for most F-, G-, and K-type stars with decent quality spectra (e.g. resolution R ~ 30000 and signal-to-noise S/N ~ 100, or better). However, it has been largely avoided (likely) because of the difficulty of systematizing a proper normalization algorithm. In this talk I will show that, by optimizing data reduction procedures and combining spectroscopic methods, it is possible to take full advantage of the state of the art of Balmer line synthesis. I will also briefly show one case in the context of Galactic archaeology: how accurate Teff permitted to constrain the age-metallicity relation of the Gaia-Enceladus merger hosted in the Milky Way halo.

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We shall leave for lunch at around 12:15. There will be fika after the seminar.