Fundamental parameters and granulation properties of Alpha Centauri A and B obtained from inversions of their spectra

Details Fundamental parameters and granulation properties of Alpha Centauri A and B obtained from inversions of their spectra Fundamental parameters and granulation properties of Alpha Centauri A and B obtained from inversions of their spectra

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...444..549f&link_type=abstract

Astronomy and Astrophysics, Volume 444, Issue 2, December III 2005, pp.549-559

Astronomy and Astrophysics

Astrophysics

9

Line: Profiles, Radiative Transfer, Stars: Atmospheres, Stars: Late-Type

Scientific paper

Properties of stellar granulation are obtained by inverting spectra of the late-type stars α Centauri A and B. Our inversions are based on a multi-component model of the stellar photosphere and take into account the center-to-limb variation and rotational broadening. The different atmospheric components describe the areas harboring up-, down- and horizontal flows. The inversions are constrained by fitting not only the flux profiles, but also their line bisectors, and by using a simple mass conservation scheme. The inversions return the properties of convection at the stellar surface, including the stratification of the thermodynamic parameters, as well as fundamental parameters such as the gravitational acceleration, v sin i and the element abundances. For α Cen A (G2V) the derived stratifications of the temperature and convective velocity are very similar to the Sun, while for α Cen B (K1V) we find similar up- and downflow velocities, but lower horizontal speeds and a reduced overshoot. The latter is consistent with the smaller scale height of the atmosphere, while mass conservation arguments taken with the lower horizontal speed imply that the granules on α Cen B are smaller than on the Sun. Both these properties are in good agreement with the hydrodynamic simulation of Nordlund & Dravins (1990, A&A, 228, 155). The inversions also return the fundamental parameters (T_eff, log g, abundances, v sin i, etc.) of the two stars. These values are on the whole in good agreement with literature values. Also, most of them do not strongly depend on the details of the inversion. However, importantly, the element abundances are 0.1 to 0.15 dex lower when a 2- or 3-component inversion is carried out than with a 1-component inversion.
Based on observations collected at the European Southern Observatories, La Silla, Chile.

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