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Issue A&A Volume 375, Number 2, August IV 2001 Page(s) 411 - 418 Section Formation, structure and evolution of stars DOI 10.1051/0004-6361:20010840

A&A 375, 411-418 (2001)
DOI: 10.1051/0004-6361:20010840

Projection effects in the spectra of early-type pulsating stars

P. Montañés Rodriguez and C. S. Jeffery

Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK
    e-mail: pmr@star.arm.ac.uk, csj@star.arm.ac.uk

(Received 13 July 2000 / Accepted 7 June 2001 )

Abstract
The relation between the surface velocity of a pulsating star in the star's inertial frame and the apparent expansion velocity measured by a remote observer has been classically formulated in terms of a projection factor p. This factor depends on the relative limb darkening in continuum and spectral lines and may therefore be a function of composition. We have computed synthetic spectra to investigate the behaviour of p and, indeed, of the apparent line profile for radially pulsating stars over a range of temperature and gravity with hydrogen-rich and hydrogen-poor atmospheres. We have subsequently derived values of p suitable for the interpretation of velocity measurements of pulsating early type stars. Effective temperature has the most important influence on p: a change of 10 000 K in introduces a change of 2-3 per cent with important consequences for measurements of stellar radii to an accuracy .

Key words: stars: early-type -- stars: pulsations -- stars: atmospheres

Offprint request: P. Montañés Rodriguez, pmr@star.arm.ac.uk

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