Non-linear radial pulsation models for extreme helium stars: application to V652 Her (BD + 13 3224)

Woolf

Pollacco

2001

A&A

115

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 .

“…Models with R = 2 R and M = 0.7 M now reproduce the pulsational properties of V652 Her (Fadeyev & Lynas-Gray 1996) very well.…”

Section: Introductionmentioning

confidence: 64%

Section: Which Is the Correct Mass?mentioning

confidence: 99%

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

Woolf

Pollacco

2001

A&A

115

“…Non-linear analyses of V652 Her have been previously carried out by Fadeyev & Lynas Gray (1996), providing radial velocity and luminosity curves for 0.72 M models in good agreement with observational data. They also studied the variations of velocity and luminosity amplitudes within the instability strip, finding that the boundaries are close to those proposed by Saio (1995).…”

Section: Introductionmentioning

confidence: 82%

“…3). One model (11) was computed for direct comparison with that of Fadeyev & Lynas-Gray (1996). This model has the same stellar parameters as the model they consider to be in best agreement with observations at the time, i.e.…”

Section: Modelsmentioning

confidence: 99%

Non-linear radial pulsation models for the early-type helium stars V652 Her and BX Cir

Montañés-Rodŕıguez

2002

A&A

Abstract. We report new non-linear pulsation models of the helium stars V652 Her and BX Cir. Linear theory has previously shown their pulsations to be due to iron-group bump instability. Recent high-resolution spectroscopic observations have provided high-precision measurements of their radial velocity curves and of their radii. Their masses remain less well determined. A hydrodynamic code including recent OPAL opacity data has been used to construct the models. These are compared with the observational data. In particular, we attempt to reproduce accurately the observed radial velocity and luminosity curves. The results impose additional constraints on those stellar dimensions, including mass, which remain poorly determined by observation. Final results show a model for V652 Her which reproduce the observed velocity and luminosity curves with 0.7 M and 23 400 K. For BX Cir, the mass must lie between 0.50 and 0.38 M if the temperature is in the range 22 400-24 000 K. However, the luminosity of the models is smaller than that measured directly by a factor of two.

“…However, the development of improved opacities for the Sun and other stars and the discovery of additional opacity from iron group elements at ≈ 2 × 10 5 K (Rogers & Iglesias 1992;Seaton et al 1994) provided an explanation; pulsation driving is provided through the classical κ-mechanism (Saio 1993). Non-linear calculations subsequently reproduced the period, light and velocity curves with satisfactory precision (Fadeyev & Lynas-Gray 1996;Montañés Rodríguez & Jeffery 2002).…”

Section: Introductionmentioning

confidence: 96%

Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation★

Monthly Notices of the Royal Astronomical Society

Kurtz

Shibahashi

et al. 2015

High resolution spectroscopy with the Subaru High Dispersion Spectrograph, and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652 Her. Swift provides the best relative ultraviolet photometry obtained to date, but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths. Subaru has provided high spectral and high temporal resolution spectroscopy over 6 pulsation cycles (and eight radius minima). These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth. They show that the photosphere is compressed radially by a factor of at least two at minimum radius, that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 km s −1 (depending how measured) and at least ten times the local sound speed. The strong acceleration at minimum radius is demonstrated in individual line profiles; those formed deepest in the photosphere show a jump discontinuity of over 70 km s −1 on a timescale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius. These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra.