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Combining observational techniques to constrain convection in evolved massive star models

Published online by Cambridge University Press:  23 January 2015

C. Georgy ,
H. Saio  and
G. Meynet
C. Georgy
Affiliation:
Astrophysics group, Lennard-Jones Laboratories, EPSAM, Keele University, Staffordshire ST5 5BG, UK email: c.georgy@keele.ac.uk
H. Saio
Affiliation:
Astronomical Institute, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
G. Meynet
Affiliation:
Geneva Observatory, University of Geneva, Maillettes 51, CH-1290 Versoix, Switzerland
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Abstract

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Recent stellar evolution computations indicate that massive stars in the range ~ 20-30 M⊙ are located in the blue supergiant (BSG) region of the Hertzsprung-Russell diagram at two different stages of their life: immediately after the main sequence (MS, group 1) and during a blueward evolution after the red supergiant phase (group 2). From the observation of the pulsationnal properties of a subgroup of variable BSGs (α Cyg variables), one can deduce that these stars belongs to group 2. It is however difficult to simultaneously fit the observed surface abundances and gravity for these stars, and this allows to constrain the physical processes of chemical species transport in massive stars. We will show here that the surface abundances are extremely sensitive to the physics of convection, particularly the location of the intermediate convective shell that appears at the ignition of the hydrogen shell burning after the MS. Our results show that the use of the Ledoux criterion to determine the convective regions in the stellar models leads to a better fit of the surface abundances for α Cyg variables than the Schwarzschild one.

Keywords

stars: abundances–stars: early-type–stars: evolution–stars: mass loss–stars: oscillations

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