Armagh Observatory Preprint Series No. ???

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Time-resolved spectral analysis of the pulsating helium star V652 Her.

Authors: C.S. Jeffery, V.M. Woolf, D.L. Pollacco

Journal: 2001, A&A in press

Abstract. A series of 59 moderate-resolution high signal-to-noise spectra of the pulsating helium star V652 Her covering 1.06 pulsation cycles was obtained with the William Herschel Telescope. These have been supplemented by archival ultraviolet and visual spectrophotometry and used to make a time-dependent study of the properties of V652 Her throughout the pulsation cycle. This study includes the following features:

• the most precise radial velocity curve for V652 Her measured so far,
• new software for the automatic measurement of effective temperature, surface gravity and projected rotation velocities from moderate-resolution spectra,
• self-consistent high-precision measurements of effective temperature and surface gravity around the pulsation cycle,
• a demonstration of excessive line-broadening at minimum radius and evidence for a pulsation-driven shock front,
• a new method for the direct measurement of the radius of a pulsating star using radial velocity and surface gravity measurements alone,
• new software for the automatic measurement of chemical abundances and microturbulent velocity,
• updated chemical abundances for V652 Her compared with previous work (Jeffery et al. 1999),
• a reanalysis of the total flux variations (cf. Lynas-Gray et al. 1984) in good agreement with previous work, and
• revised measurements of the stellar mass and radius which are similar to recent results for another pulsating helium star, BX Cir.

Masses measured without reference to the ultraviolet fluxes turn out to be unphysically low ($\sim0.18\Msolar$). The best estimate for the dimensions of V652 Her averaged over the pulsation cycle is given by:

• <Teff> = 22 930 ± 10 K and
• <log g>=3.46 ± 0.05 (ionization equilibrium),
• <Teff>=20 950 ± 70 K (total flux method),
• <R>=2.31 ± 0.02 Rsun,
• <L>=919 ± 14 Lsun,
• M=0.59 ± 0.18 Msun and
• d=1.70 ± 0.02 kpc.

Two significant problems were encountered. The line-blanketed hydrogen-deficient model atmospheres used yield effective temperatures from the optical spectrum (ionization equilibrium) and visual and UV photometry (bolometric flux) that are inconsistent. Secondly, the IUE spectra are poorly distributed in phase and have low signal-to-noise. These problems may introduce systematic errors of up to 0.1 Msun.

Keywords: stars: fundamental parameters -- stars: abundances -- stars: helium -- stars: individual (V652 Her) -- stars: pulsation -- techniques: spectroscopic

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