Soft X-ray observations of the early B giants Formula and Formula CMa

Drew, J. E.; Denby, M.; Hoare, M. G.

doi:10.1093/mnras/266.4.917

Cited by 36 publications

(32 citation statements)

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“…Perhaps of more relevance is the fact that the same conclusion was reached for some late O-type dwarfs in the SMC having mass-loss rates comparable to what is anticipated for β Cephei stars (Ṁ down to 10 −9 -10 −10 M yr −1 ; Bouret et al 2003). A very weak wind was derived for the most evolved star in our sample, β CMa, from soft X-ray observations:Ṁ = 6 × 10 −9 M yr −1 (Drew et al 1994).…”

Section: Neglect Of Stellar Windssupporting

confidence: 86%

Abundance analysis of prime B-type targets for asteroseismology

Morel¹,

Butler

Aerts

et al. 2006

A&A

157

222

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Seismic modelling of the β Cephei stars promises major advances in our understanding of the physics of early B-type stars on (or close to) the main sequence. However, a precise knowledge of their physical parameters and metallicity is a prerequisite for correct mode identification and inferences regarding their internal structure. Here we present the results of a detailed NLTE abundance study of nine prime targets for theoretical modelling: γ Peg, δ Cet, ν Eri, β CMa, ξ 1 CMa, V836 Cen, V2052 Oph, β Cep and DD (12) Lac (hereafter 12 Lac). The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S and Fe. Our curve-of-growth abundance analysis is based on a large number of time-resolved, high-resolution optical spectra covering in most cases the entire oscillation cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four stars, three of which have severe constraints on their equatorial rotational velocity, ΩR, from seismic or line-profile variation studies: β Cep (ΩR ∼ 26 km s −1 ), V2052 Oph (ΩR ∼ 56 km s −1 ), δ Cet (ΩR < 28 km s −1 ) and ξ 1 CMa (ΩR sin i < ∼ 10 km s −1 ). The existence of core-processed material at the surface of such largely unevolved, slowly-rotating objects is not predicted by current evolutionary models including rotation. We draw attention to the fact that three stars in this subsample have a detected magnetic field and briefly discuss recent theoretical work pointing to the occurrence of diffusion effects in β Cephei stars possibly capable of altering the nitrogen surface abundance. On the other hand, the abundances of all the other chemical elements considered are, within the errors, indistinguishable from the values found for OB dwarfs in the solar neighbourhood. Despite the mild nitrogen excess observed in some objects, we thus find no evidence for a significantly higher photospheric metal content in the studied β Cephei stars compared to non-pulsating B-type stars of similar characteristics.

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Section: Neglect Of Stellar Windssupporting

confidence: 86%

Abundance analysis of prime B-type targets for asteroseismology

Morel¹,

Butler

Aerts

et al. 2006

A&A

157

222

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“…While this is likely to be valid for the wind of a star like ζ Pup (see e.g. discussion by Hillier et al 1993), the assumption will eventually become invalid as the density declines (Drew, Hoare & Denby 1994;Martins et al 2005b;Lucy 2012). Recently Huenemoerder et al (2012) showed that the X-ray emission from μ Columbae originated in the wind, and required a hot gas component with a mass-loss rate in excess of that inferred from analysis of UV lines.…”

Section: Line Force Momentum Equation and Implicationsmentioning

confidence: 98%

No breakdown of the radiatively driven wind theory in low-metallicity environments★†

Bouret¹,

Lanz²,

Hillier³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We present a spectroscopic analysis of Hubble Space Telescope/Cosmic Origins Spectrograph observations of three massive stars in the low metallicity dwarf galaxies IC 1613 and WLM. These stars, were previously observed with Very Large Telescope (VLT)/X-shooter by Tramper et al., who claimed that their mass-loss rates are higher than expected from theoretical predictions for the underlying metallicity. A comparison of the far ultraviolet (FUV) spectra with those of stars of similar spectral types/luminosity classes in the Galaxy, and the Magellanic Clouds provides a direct, model-independent check of the mass-loss-metallicity relation. Then, a quantitative spectroscopic analysis is carried out using the non-LTE (NLTE) stellar atmosphere code CMFGEN. We derive the photospheric and wind characteristics, benefiting from a much better sensitivity of the FUV lines to wind properties than Hα. Iron and CNO abundances are measured, providing an independent check of the stellar metallicity. The spectroscopic analysis indicates that Z/Z = 1/5, similar to a Small Magellanic Cloud-type environment, and higher than usually quoted for IC 1613 and WLM. The mass-loss rates are smaller than the empirical ones by Tramper et al., and those predicted by the widely used theoretical recipe by Vink et al. On the other hand, we show that the empirical, FUV-based, mass-loss rates are in good agreement with those derived from mass fluxes computed by Lucy. We do not concur with Tramper et al. that there is a breakdown in the mass-loss-metallicity relation.

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“…Importantly, these work ratios Q are calculated from models that include X‐ray emission in the ionization balance. Drew, Hoare & Denby (1994) highlighted the effect that X‐ray emission may have on the wind velocity and mass‐loss rate. They suggest that ionization by X‐rays may change the ionization structure in the inner part of the wind, thus reducing the total radiative acceleration and consequently the mass‐loss rate.…”

Section: Stellar Windsmentioning

confidence: 99%

Early magnetic B-type stars: X-ray emission and wind properties

Oskinova¹,

Todt²,

Ignace³

et al. 2011

Monthly Notices of the Royal Astronomical Society

108

144

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We present a comprehensive study of X-ray emission and wind properties of massive magnetic early B-type stars. Dedicated XMM-Newton observations were obtained for three stars xi1 CMa, V2052 Oph, and zeta Cas. We report the first detection of X-ray emission from V2052 Oph and zeta Cas. The observations show that the X-ray spectra of our program stars are quite soft. We compile the complete sample of early B-type stars with detected magnetic fields to date and existing X-ray measurements, in order to study whether the X-ray emission can be used as a general proxy for stellar magnetism. We find that hard and strong X-ray emission does not necessarily correlate with the presence of a magnetic field. We analyze the UV spectra of five non-supergiant B stars with magnetic fields by means of non-LTE iron-blanketed model atmospheres. The latter are calculated with the PoWR code, which treats the photosphere as well as the the wind, and also accounts for X-rays. Our models accurately fit the stellar photospheric spectra in the optical and the UV. The parameters of X-ray emission, temperature and flux are included in the model in accordance with observations. We confirm the earlier findings that the filling factors of X-ray emitting material are very high. Our analysis reveals that the magnetic early type B stars studied here have weak winds. The mass-loss rates are significantly lower than predicted by hydrodynamically consistent models. We find that, although the X-rays strongly affect the ionization structure of the wind, this effect is not sufficient in reducing the total radiative acceleration. When the X-rays are accounted for at the intensity and temperatures observed, there is still sufficient radiative acceleration to drive stronger mass-loss than we empirically infer from the UV spectral lines. (abridged)Comment: 20 pages, accepted by MNRA

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Soft X-ray observations of the early B giants Formula and Formula CMa

Cited by 36 publications

References 0 publications

Abundance analysis of prime B-type targets for asteroseismology

Abundance analysis of prime B-type targets for asteroseismology

No breakdown of the radiatively driven wind theory in low-metallicity environments★†

Early magnetic B-type stars: X-ray emission and wind properties

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