B stars seen at high resolution by <i>XMM</i>-<i>Newton</i>

Cazorla, Constantin; Nazé, Yaël

doi:10.1051/0004-6361/201731562

Cited by 8 publications

(4 citation statements)

References 82 publications

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“…Further evidence for a direct connection between the photospheric conditions and the X-ray emission comes from the detection of X-ray pulsations in (at least) two stars of the class of β Cep pulsators: ξ 1 CMa [100] and β CMa [12]. These X-ray pulsations (at the ∼ 10% level, see Fig.…”

Section: Earthmentioning

confidence: 95%

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X-ray emission of massive stars and their winds

Rauw¹

2022

Preprint

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Most types of massive stars display X-ray emission that is strongly affected by the properties of their stellar winds. Single non-magnetic OB stars have an X-ray luminosity that scales with their bolometric luminosity and their emission is thought to arise from a distribution of wind-embedded shocks. The lack of significant short-term stochastic variability indicates that the winds consist of a large number of independent fragments. Detailed investigations of temporal variability unveiled a connection between the photosphere and the wind: well-studied O-type stars exhibit a ∼ 10% modulation of their emission on timescales consistent with their rotation period, and a few early B-type pulsators display ∼ 10% modulations of their X-ray flux with the same period as their photospheric pulsations. Unlike OB stars, their evolved descendants (Wolf-Rayet stars and Luminous Blue Variables) lack a well-defined relation between their X-ray and bolometric luminosities, and several subcategories of objects remain undetected. These properties most likely stem from the combined effects of wind optical depth and wind velocity. Magnetic OB stars display an enhanced X-ray emission which is frequently modulated by the rotation of the star. These properties are well explained by the magnetically confined wind shock model and an oblique magnetic rotator configuration. Some massive binaries display phase-dependent excess emission arising from the collision between the winds of the binary components. Yet, the majority of the massive binaries do not show evidence for such an emission, probably as a consequence of radiative cooling of the shock-heated plasma. Finally, a growing subset of the Be stars, the so-called γ Cas stars, feature an unusually hard and strong thermal X-ray emission that varies in a complicated manner over a wide range of timescales. Several scenarios have been proposed to explain these properties, but the origin of the γ Cas phenomenon remains currently one of the major unsolved puzzles in stellar X-ray astrophysics.

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Section: Earthmentioning

confidence: 95%

“…The top panel illustrates the Hipparcos photometry, retaining only points with uncertainties of less than 0.005 mag, folded with the 6.03 h pulsation period [150]. The bottom panel illustrates the EPIC count rate from XMM-Newton revolution 2814 folded with the same period and zero point [12].…”

Section: Earthmentioning

confidence: 99%

X-ray emission of massive stars and their winds

Rauw¹

2022

Preprint

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“…However, as all LDI models thus far have been computed for stars with mass-loss rates well above 10 −8 M /yr, it remains to be investigated how LDIgenerated shocks develop in the weak-wind regime. Indeed, although previous LDI models have been successful in explaining X-ray emission from dense O-supergiants (Feldmeier et al 1997), X-ray observations of late O-type stars (Huenemoerder et al 2012;Doyle et al 2017) and early B-type stars (Cazorla & Nazé 2017) do seem to indicate that these winds might have larger portions of hot gas embedded in them.…”

Section: Introductionmentioning

confidence: 99%

Shock-heated radiation-driven outflows as a solution to the weak-wind problem of late O-type stars

Lagae

Driessen

Hennicker

et al. 2021

A&A

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Context. Radiation-driven mass loss is key to our understanding of massive-star evolution. However, for low-luminosity O-type stars there are big discrepancies between theoretically predicted and empirically derived mass-loss rates (called the weak-wind problem). Aims. We compute radiation-line-driven wind models of a typical weak-wind star to determine its temperature structure and the corresponding impact on ultra-violet (UV) line formation. Methods. We carried out hydrodynamic simulations of the line-deshadowing instability (LDI) for a weak-wind star in the Galaxy. Subsequently, we used this LDI model as input in a short-characteristics radiative transfer code to compute synthetic UV line profiles. Results. We find that the line-driven weak wind is significantly shock heated to high temperatures and is unable to cool down efficiently. This results in a complex temperature structure where more than half of the wind volume has temperatures significantly higher than the stellar effective temperature. Therefore, a substantial portion of the weak wind will be more ionised, resulting in a reduction of the UV line opacity and therefore in weaker line profiles for a given mass-loss rate. Quantifying this, we find that weak-wind mass-loss rates derived from unsaturated UV lines could be underestimated by a factor of between 10 and 100 if the high-temperature gas is not properly taken into account in the spectroscopic analysis. This offers a tentative basic explanation for the weak-wind problem: line-driven weak winds are not really weaker than theoretically expected, but rather a large portion of their wind volume is much hotter than the stellar effective temperature.

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“…Fewer investigations have sought to frame massive stars in terms of an X-ray classification based on high-resolution spectral data. Certainly, there have been efforts to group highresolution data in relation to stellar winds (Oskinova et al 2006;Waldron & Cassinelli 2007;Cazorla & Nazé 2017), magnetic stars (Oskinova et al 2011b;Nazé et al 2014;, or studies of individual colliding-wind binaries, such as η Carinae, WR 147, WR 140, WR 48a, and WR 25 (Corcoran et al 2001;Pollock et al 2005;Zhekov & Park 2010;Zhekov et al 2014;Pradhan et al 2021). Walborn et al (2009) explored trends for massive stars based on Chandra grating spectra and found a trend of X-ray hardness correlated with spectral subtype in O and early-B stars, indicating a correlation between X-ray plasma temperature and stellar effective temperature.…”

Section: Introductionmentioning

confidence: 99%

Survey of X-Rays from Massive Stars Observed at High Spectral Resolution with Chandra

Pradhan,

Huenemoerder,

Ignace

et al. 2023

ApJ

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Identifying trends between observational data and the range of physical parameters of massive stars is a critical step to the still-elusive full understanding of the source, structure, and evolution of X-ray emission from the stellar winds, requiring a substantial sample size and systematic analysis methods. As of 2022, the Chandra data archive contains 37 high-resolution spectra of O, B, and WR stars, observed with the Chandra/HETGS, and of sufficient quality to fit the continua and emission-line profiles. Using a systematic approach to the data analysis, we explore morphological trends in the line profiles (i.e., O, Ne, Mg, and Si) and find that the centroid offsets of resolved lines versus wavelength can be separated in three empirically defined groups based on the amount of line broadening and centroid offset. Using Fe xvii (15.01, 17.05 Å) and Ne x α (12.13 Å) lines, which are prevalent among the sample stars, we find a well-correlated linear trend of increasing Full Width Half Maximum with faster wind terminal velocity. The H-like/He-like total line flux ratio for strong lines displays different trends with spectral class depending on ion species. Some of the sources in our sample have peculiar properties (e.g., magnetic and γ Cas-analog stars) and we find that these sources stand out as outliers from more regular trends. Finally, our spectral analysis is presented summarily in terms of X-ray spectral energy distributions in specific luminosity for each source, including tables of line identifications and fluxes.

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B stars seen at high resolution by XMM-Newton

Cited by 8 publications

References 82 publications

X-ray emission of massive stars and their winds

X-ray emission of massive stars and their winds

Shock-heated radiation-driven outflows as a solution to the weak-wind problem of late O-type stars

Survey of X-Rays from Massive Stars Observed at High Spectral Resolution with Chandra

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