Abundance analysis of roAp stars. IV. HD24712

Details Abundance analysis of roAp stars. IV. HD24712 Abundance analysis of roAp stars. IV. HD24712

Nov 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...327.1137r&link_type=abstract

Astronomy and Astrophysics, v.327, p.1137-1146 (1997)

Astronomy and Astrophysics

Astrophysics

55

Stars: Abundances, Chemically Peculiar, Magnetic Field, Oscillations, Pulsations, Individual: Hd24712

Scientific paper

We present the first abundance analysis of the rapidly oscillating chemically peculiar star HD24712, and determine a T_eff,=7250K, log {g},=4.3, and xi_t ,=1kms(-1) . Microturbulence seems to be entirely simulated by a magnetic field with a polar field strength of 4.4kG and of dipolar structure, both of which are supported by our polarimetric observations. Rotation of HD24712 and a spotty surface distribution of the elements result in different mean abundances for different (magnetic) phases. Our results do not support the hypothesis of a monotonic correlation between the amplitude of abundance variations and the atomic number Z, and we present arguments in favour of one of the rotation periods (Prot=12\fd 4610) discussed in the literature. Rare earth elements are the most overabundant elements relative to the sun, and they have the largest abundance amplitude during a rotation cycle; only Mg has a larger amplitude. For HD24712 we find a clear overabundance of Co while most of the other iron peak elements are underabundant. A comparison of the abundance pattern with the other three roAp stars analyzed so far by us concludes the paper. A systematic difference between surface gravities obtained from spectroscopy and from both asteroseismology and evolutionary tracks is found for the roAp stars HD 24712, alpha Cir, and gamma Equ. Based on observations obtained with the Canada-France-Hawaii telescope, operated by the National Research Council of Canada, the Centre Centre National de la Recherche Scientifique de France, and the University of Hawaii, and on observations obtained at CARSO, Las Campanas, Chile

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