The Ga II Lines in the Red Spectrum of Ap-Stars

Details The Ga II Lines in the Red Spectrum of Ap-Stars The Ga II Lines in the Red Spectrum of Ap-Stars

May 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...272..465l&link_type=abstract

Astronomy and Astrophysics, Vol.272, NO. 2/MAYII, P. 465, 1993

Astronomy and Astrophysics

Astrophysics

27

Stars: Abundance, Stars: Atmospheres, Stars: Chemically Peculiar, Stars: Variables, Stars: Fundamental Parameters

Scientific paper

We report first observations of the Ga II λ633.4 line in the red spectrum of Ap stars. This line is present in the spectrum of 16 out of 45 Ap stars of our sample, translating to large gallium overabundances. While most HgMn stars are gallium-rich, we have observed strong gallium lines in several magnetic stars. We have derived LTE abundances from this line after reviewing all needed atomic data and stellar parameters. In particular, a new calibration of the Geneva photometry for the effective temperature of the magnetic Ap stars is presented. LTE abundances arc compared to previous analyses of the ultraviolet resonance lines, and they arc about 1 dex larger. This large discrepancy might possibly be explained by departures from LTE or by the stratification of gallium predicted by the radiative diffusion theory. We present the variations of the Ga II line strength during the rotation period of three magnetic Ap stars; from the variations of silicon and of the longitudinal component of the magnetic field it appears that gallium accumulates around magnetic poles. Moreover, we suggest that secular changes in the gallium surface abundance on time-scales of about 1-2 108 yr might explain why some Ap HgMn stars arc not gallium-rich.

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