Hydrodynamic models for <i>β</i>Cephei variables

Фокин, А. Б.; Mathias, P.; Chapellier, E.; Gillet, Denis; Nardetto, N.

doi:10.1051/0004-6361:20040418

Cited by 23 publications

(25 citation statements)

References 12 publications

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“…In addition, radiative transfer is considered in the outer layers to produce a realistic atmosphere model. The derived quantities have been found to be in good agreement with observations for different classes of pulsators such as RR Lyrae , RV Tauri (Fokin 2001), post-AGB (Jeannin et al 1997), BL Herculis (Fokin & Gillet 1994) and more recently β Cephei stars (Fokin et al 2004). In particular, this model has already been used in the case of δ Cep (Fokin et al 1996).…”

Section: This Worksupporting

confidence: 76%

Self consistent modelling of the projection factor for interferometric distance determination

Nardetto¹,

Фокин

Mourard³

et al. 2004

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Abstract. The distance of galactic Cepheids can be derived through the interferometric Baade-Wesselink method. The interferometric measurements lead to angular diameter estimations over the whole pulsation period, while the stellar radius variations can be deduced from the integration of the pulsation velocity. The latter is linked to the observational velocity deduced from line profiles by the so-called projection factor p. The knowledge of p is currently an important limiting factor for this method of distance determination. A self-consistent and time-dependent model of the star δ Cep is computed in order to study the dynamical structure of its atmosphere together with the induced line profile. Different kinds of radial and pulsation velocities are then derived. In particular, we compile a suitable average value for the projection factor related to different observational techniques, such as spectrometry, and spectral-line or wide-band interferometry. We show that the impact on the average projection factor and consequently on the final distance deduced from this method is of the order of 6%. We also study the impact of a constant or variable p-factor on the Cepheid distance determination. We conclude on this last point that if the average value of the projection factor is correct, then the influence of the time dependence is not significant as the error in the final distance is of the order of 0.2%.

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Section: This Worksupporting

confidence: 76%

Self consistent modelling of the projection factor for interferometric distance determination

Nardetto¹,

Фокин

Mourard³

et al. 2004

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“…Therefore, as already observed in other stars undergoing strong non linear motions (see e.g. Fokin et al 2004), irregularities are present in the shock intensity, due to an atmospheric time relaxation that is longer than the pulsation period. Thus, the shock is not self similar from one cycle to the next.…”

Section: Two Shocks Per Pulsation Period?supporting

confidence: 65%

“…While 2 shocks per pulsation periods are not very rare (Fokin et al 2004 for β Cephei stars, Fokin 1992 for RR Lyrae stars), such a phenomenon has not been reported yet for classical Cepheid stars. In addition, the already detected second shock in the β Cephei star BW Vul and in RR Lyrae stars occurs normally during the stellar contraction, not during the expansion.…”

Section: Origin Of the Third Componentmentioning

confidence: 94%

Multiple shock waves in the atmosphere of the Cepheid X Sagittarii?

Mathias¹,

Gillet²,

Фокин³

et al. 2006

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Context. Shock waves in Cepheids have often been invoked, both from observational and theoretical points of view. However, classical shock wave signatures, such as emission or line doubling, have hardly been detected. Aims. In this paper, we suggest that our spectra of the classical Cepheid X Sgr can be interpreted by means of the passage of 2 shock waves per pulsation period. Methods. We study new, high-resolution (120 000) spectra of X Sgr that show very complicated patterns within metallic lines. Results. Spectra show up to 3 components in most of the lines of the spectra during most of the pulsation cycle. These components seem to follow a pulsation motion. In the blue wing, the appearance of a new component is observed twice per pulsation period, which can be interpreted by 2 consecutive shock waves, one being apparently related to the classical κ-mechanism at work in these stars. The origin of the second shock is still unclear. Conclusions. X Sgr is an exceptional Cepheid according to its observed multi-components behaviour. Additional observations are requested in order to establish the eventual effect of the binary orbit on the pulsation motion.

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“…This would help the future development of the hydrodynamical codes of pulsating stars (e.g. Fokin et al 2004), as well as of stellar interior models.…”

Section: Discussionmentioning

confidence: 99%

“…The radial-velocity variations of this star were first detected by Frost (1902). Five frequencies have been derived from a long-term spectroscopic study of β Cep, two of which were identified as a radial and non radial mode (Telting et al 1997).…”

Section: Introductionmentioning

confidence: 99%

An investigation of the close environment ofβCephei with the VEGA/CHARA interferometer

Nardetto¹,

Mourard²,

Tallon–Bosc

et al. 2010

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Context. High-precision interferometric measurements of pulsating stars help to characterize their close environment. In 1974, a close companion was discovered around the pulsating star β Cep using the speckle interferometry technique, and features at the limit of resolution (20 milli-arcsec or mas) of the instrument were mentioned that may be due to circumstellar material. β Cep has a magnetic field that might be responsible for a spherical shell or ring-like structure around the star as described by the MHD models. Aims. Using the visible recombiner VEGA installed on the CHARA long-baseline interferometer at Mt. Wilson, we aim to determine the angular diameter of β Cep and resolve its close environment with a spatial resolution up to 1 mas level. Methods. Medium spectral resolution (R = 6000) observations of β Cep were secured with the VEGA instrument over the years 2008 and 2009. These observations were performed with the S1S2 (30 m) and W1W2 (100 m) baselines of the array. Results. We investigated several models to reproduce our observations. A large-scale structure of a few mas is clearly detected around the star with a typical flux relative contribution of 0.23 ± 0.02. Our best model is a co-rotational geometrical thin ring around the star as predicted by magnetically-confined wind shock models. The ring inner diameter is 8.2 ± 0.8 mas and the width is 0.6 ± 0.7 mas. The orientation of the rotation axis on the plane of the sky is PA = 60 ± 1 deg, while the best fit of the mean angular diameter of β Cep gives Φ UD [V] = 0.22 ± 0.05 mas. Our data are compatible with the predicted position of the close companion of β Cep. Conclusions. These results bring additional constraints on the fundamental parameters and on the future MHD and asteroseismological models of the star.

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Hydrodynamic models for βCephei variables

Cited by 23 publications

References 12 publications

Self consistent modelling of the projection factor for interferometric distance determination

Self consistent modelling of the projection factor for interferometric distance determination

Multiple shock waves in the atmosphere of the Cepheid X Sagittarii?

An investigation of the close environment ofβCephei with the VEGA/CHARA interferometer

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