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Astron. Astrophys. 355, 308-314 (2000)

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On the effective temperatures, surface gravities, and optical region fluxes of the CP stars

S.J. Adelman 1,2 and K.E. Rayle 1

1 Department of Physics, The Citadel, 171 Moultrie Street, Charleston, SC 29409, United States of America
2 Guest Investigator, Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 W. Saanich Drive, Victoria BC, V8X 4M6 Canada

Received 12 August 1999 / Accepted 16 December 1999

Abstract

We determined effective temperatures and surface gravities for 17 magnetic Chemically Peculiar (mCP) stars by comparing optical region spectrophotometry and H[FORMULA] profiles with the predictions of ATLAS9 model atmospheres. Although solar composition models can fit the energy distributions of the normal and many Mercury-Manganese stars, they cannot match the optical energy distributions of the mCP stars, especially the [FORMULA]5200 broad, continuum regions. The role of metallicity and microturbulence to provide appropriate energy distributions which fit those observed for the mCP stars is investigated. Using metal-rich models with the opacity distribution functions for microturbulent velocities of 4 and 8 km s-1, their [FORMULA]5200 broad, continuum features are often fit as part of this process. For some stars it is impossible to fit simultaneously both this feature and the line blanketing in the H[FORMULA] region. This suggests that this continuum feature is produced by elements other than those which contribute most of the general line blanketing. A systematic difference in the temperatures found by the photometric and spectrophotometric approaches is discovered for the hotter mCP stars. An investigation of 10 Mercury-Manganese stars shows a similar effect. This may be due to the photospheric compositions becoming less solar with increasing temperature.

Key words: stars: chemically peculiar – stars: fundamental parameters

Send offprint requests to: S.J. Adelman (adelmans@citadel.edu)

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© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000
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