Mary Stuart. Eine historische Szene

Haberl, Franz P.; Hildesheimer, Wolfgang

doi:10.2307/40126177

Cited by 21 publications

(27 citation statements)

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“…ROSAT pointed observations of γ-Cas revealed a factor 3 variability of the (0.1-2.4 keV) band flux on a time scale of a few hours. However, the average PSPC count rate changed by only a factor ∼ 1.5 between all-sky survey and pointed observations (Haberl 1995). Therefore, our lower limit of 2.7 on the soft band long term variability of HD 157832 is in principle compatible with what is observed from γ-Cas, but could also indicate a much larger variation of the soft X-ray flux.…”

Section: Discussionsupporting

confidence: 63%

A Hard and Variable X-Ray Emission From the Massive Emission-Line Star Hd 157832

Oliveira¹,

Motch²

2011

ApJ

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We report the discovery with XMM-Newton of a hard-thermal (T ∼ 130 MK) and variable X-ray emission from the Be star HD 157832, a new member of the puzzling class of γ -Cas-like Be/X-ray systems. Recent optical spectroscopy reveals the presence of a large/dense circumstellar disk seen at intermediate/high inclination. With a B1.5V spectral type, HD 157832 is the coolest γ -Cas analog known. In addition, its non-detection in the ROSAT all-sky survey shows that its average soft X-ray luminosity varied by a factor larger than ∼3 over a time interval of 14 yr. These two remarkable features, "low" effective temperature, and likely high X-ray variability turn HD 157832 into a promising object for understanding the origin of the unusually high-temperature X-ray emission in these systems.

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Section: Discussionsupporting

confidence: 63%

A Hard and Variable X-Ray Emission From the Massive Emission-Line Star Hd 157832

Oliveira¹,

Motch²

2011

ApJ

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“…The nature of this companion is, however, not well constrained. The companion was speculated to be a white dwarf (Haberl 1995), a NS (e.g., Postnov et al 2017), or a He star (e.g., Langer et al 2020b). A recent study by Borre et al (2020) studied the long-term variations of the Hα profile and found indications that a spiral structure in the circumstellar decretion disk is in phase with the companion.…”

Section: B2 Binaries With Unknown Uncertain or Debated Companionsmentioning

confidence: 99%

Investigating the lack of main-sequence companions to massive Be stars

Bodensteiner

Shenar

Sana

2020

A&A

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Context. About 20% of all B-type stars are classical Be stars – stars whose spectra imply the presence of a circumstellar decretion disk. The disk phenomenon is strongly correlated with rapid rotation, the origin of which remains unclear. It may be rooted in single- or binary-star evolution. In the framework of the binary channel, the initially more massive star transfers mass and angular momentum to the original secondary, which becomes a Be star. The system then evolves into a Be binary with a post-main-sequence companion, which, depending on the companion mass, may later be disrupted in a supernova event. Hence, if the binary channel dominates the formation of Be stars, one may expect a strong lack of close Be binaries with main sequence (MS) companions. Aims. We want to test the prediction of the binary channel. Through an extensive, star-by-star review of the literature of a magnitude-limited sample of Galactic early-type Be stars, we investigate whether Be binaries with MS companions are known to exist. Methods. Our sample is constructed from the BeSS database and cross-matched with all available literature on the individual stars. Archival and amateur spectra are used to verify the existing literature when conflicting reports are found. Results. Out of an initial list of 505 Be stars, we compile a final sample of 287 Galactic Be stars earlier than B1.5 with V ≤ 12 mag. Out of those, 13 objects were reported as Be binaries with known post-MS companions (i.e., compact objects or helium stars) and 11 as binaries with unknown, uncertain or debated companions. We find no confirmed reports of Be binaries with MS companions. For the remaining 263 targets, no significant reports of multiplicity exist in the literature, implying that they are either Be binaries with faint companions, or truly single. Conclusions. The clear lack of reported MS companions to Be stars, which stands in contrast to the high number of detected B+B MS binaries, strongly supports the hypothesis that early-type Be stars are binary interaction products that spun up after mass and angular momentum transfer from a companion star. Taken at face value, our results may suggest that a large majority of the early-type Be stars have formed through binary mass-transfer.

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“…Similar to an accreting NS, WDs are expected to show hard X-ray emission powered by accretion, but at lower luminosity of 10 29−33 erg s −1 , compared to 10 34−38 erg s −1 for NSs (Waters et al 1989). Suggested candidates are γ Cas like objects (Haberl 1995;Lopes de Oliveira et al 2006). In addition, nuclear burning on the WD surface can produce super-soft X-ray emission at luminosities of 10 35−38 erg s −1 , which might be absorbed by the decretion disc in most cases, complicating the discovery of such systems (Apparao 1991).…”

Section: Introductionmentioning

confidence: 99%

A new super-soft X-ray source in the Small Magellanic Cloud: Discovery of the first Be/white dwarf system in the SMC?

Sturm

Haberl

Pietsch

et al. 2012

A&A

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Context. The Small Magellanic Cloud (SMC) hosts a large number of Be/X-ray binaries, however no Be/white dwarf system is known so far, although population synthesis calculations predict that they might be more frequent than Be/neutron star systems. Aims. XMMU J010147.5-715550 was found as a new faint super-soft X-ray source (SSS) with a likely Be star optical counterpart. We investigate the nature of this system and search for further high-absorbed candidates in the SMC. Methods. We analysed the XMM-Newton X-ray spectrum and light curve, optical photometry, and the I-band OGLE III light curve. Results. The X-ray spectrum is well represented by black-body and white dwarf atmosphere models with highly model-dependent temperature between 20 and 100 eV. The likely optical counterpart AzV 281 showed low near infrared emission during X-ray activity, followed by a brightening in the I-band afterwards. We find further candidates for high-absorbed SSSs with a blue star as counterpart. Conclusions. We discuss XMMU J010147.5-715550 as the first candidate for a Be/white dwarf binary system in the SMC.

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Mary Stuart. Eine historische Szene

Cited by 21 publications

References 0 publications

A Hard and Variable X-Ray Emission From the Massive Emission-Line Star Hd 157832

A Hard and Variable X-Ray Emission From the Massive Emission-Line Star Hd 157832

Investigating the lack of main-sequence companions to massive Be stars

A new super-soft X-ray source in the Small Magellanic Cloud: Discovery of the first Be/white dwarf system in the SMC?

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