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

Abstract

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 (Paper IV), a reanalysis of the total flux variations (cf. Paper II) 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 (∼0.18 M ). The best estimate for the dimensions of V652 Her averaged over the pulsation cycle is given by: T eff = 22 930 ± 10 K and log g = 3.46 ± 0.05 (ionization equilibrium), T eff = 20 950 ± 70 K (total flux method), R = 2.31 ± 0.02 R , L = 919 ± 14 L , M = 0.59 ± 0.18 M 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 M .

Stark Widths of Ar II Spectral Lines in the Atmospheres of Subdwarf B Stars

“…In order to study the importance of Stark broadening in the atmospheric conditions of subdwarf B stars, we have compared Stark and Doppler widths for Ar II ( 3 P) 3d 4 D 5/2 -( 3 P) 4p 4 P o 3/2 (λ = 4371.33 Å) spectral lines. We used the atmospheric models of Jeffery et al [27] which are plane-parallel line-blanketed model atmospheres for hot stars in local thermal, radiative and hydrostatic equilibrium. The considered atmospheres have the following composition: 0.001 helium, 0.99741 hydrogen and 0.00047 carbon and nitrogen.…”

An Analysis of Ultraviolet Spectra of Extreme Helium Stars and New Clues to Their Origins

“…The Stark broadening and radiative broadening coefficients, if available, are mostly taken from the Vienna Atomic Line Database. 4 The data for computing He i profiles are the same as in Jeffery et al (2001), except for the He i line at 6678 8, for which the g f-values and electron broadening coefficients are from Kurucz's database. The line-broadening coefficients are not available for the He i line at 2652.8 8.…”

Stark broadening tables for the helium I 492.2 line

“…The shape analysis of the 492.2 line was used to obtain information on He abundances (Leone & Lanzafame 1998;Castelli & Hubrig 2004;Lyubimkov et al 2004;Catanzaro 2008), He stratification (Catanzaro 2008) or radial velocities (Jeffery et al 2001). Owing to a lack of available information, some authors were in some cases only able to use line widths obtained from approximate models (Castelli & Hubrig 2004) instead of using the full profiles for comparison with the experimental data, though several authors already pointed out the better results obtained by comparing the full theoretical and experimental profiles instead of using only the line widths (Leckrone 1971).…”

“…Owing to a lack of available information, some authors were in some cases only able to use line widths obtained from approximate models (Castelli & Hubrig 2004) instead of using the full profiles for comparison with the experimental data, though several authors already pointed out the better results obtained by comparing the full theoretical and experimental profiles instead of using only the line widths (Leckrone 1971). Other authors using full profiles for comparison with experimental data employed old calculations (Heasley & Wolff 1981;Jeffery et al 2001) to include the influence of Stark broadening in the profiles. The discrepancies in those and other comparisons neccessitated more advances in line broadening calculations of the He I 492.2 nm line (Lyubimkov et al 2004;Castelli & Hubrig 2004).…”