HD 45314: a new<i>γ</i> Cassiopeiae analog among Oe stars

Rauw, Grégor; Nazé, Yaël; Spano, M.; Morel, Thierry; ud‐Doula, Asif

doi:10.1051/0004-6361/201321774

Cited by 17 publications

(28 citation statements)

References 31 publications

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“…Indeed, their spectrum is characterized by the presence of a very hot plasma, around 10-20 keV, as we observe. This hot component is often accompanied by lower temperature plasma (Smith et al 2004;Lopes de Oliveira et al 2006, 2010Torrejón et al 2012), but not always (Rauw et al 2013). Also, iron abundance is found to be subsolar for such objects (e.g., Lopes de Oliveira et al 2007).…”

Section: Spectral Characteristicsmentioning

confidence: 99%

π Aquarii is another γ Cassiopeiae object

Nazé

Rauw

Cazorla

2017

A&A

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The γ Cas category is a subgroup of Be stars displaying a strong, hard, and variable thermal X-ray emission. An XMM-Newton observation of π Aqr reveals spectral and temporal characteristics that clearly make this Be star another member of the γ Cas category. Furthermore, π Aqr is a binary but, contrary to γ Cas, the nature of the companion to the Be star is known; it is a non-degenerate (stellar) object and its small separation from the Be star does not leave much room for a putative compact object close to the Be disk. This renders the accretion scenario difficult to apply in this system, and, hence, this discovery favors a disk-related origin for the γ Cas phenomenon.

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Section: Spectral Characteristicsmentioning

confidence: 99%

π Aquarii is another γ Cassiopeiae object

Nazé

Rauw

Cazorla

2017

A&A

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“…The first observation took place in April 2012 (ObsID 0670080301), when the star was in an intermediate emission state (EW(Hα) = −22.3 Å). This observation led to the discovery of the γ Cas nature of HD 45314 (Rauw et al, 2013). In March 2016, when the level of the Be-like emission lines reached a historical minimum, we triggered a target of opportunity (ToO) observation (ObsID 0760220601, see Table 1).…”

Section: Observationsmentioning

confidence: 99%

“…In particular, no campaign was ever obtained as the disk was dissipating, though this would provide a most critical test for any scenario aiming at explaining the γ Cas phenomenon. In this context, we discuss here a new set of observations of the Oe star HD 45314 (= PZ Gem), which was previously found to be a member of the class of γ Cas stars (Rauw et al, 2013). With an O9e -O9.7e spectral type, HD 45314 has the earliest spectral type among the currently-known sample of γ Cas stars.…”

Section: Introductionmentioning

confidence: 98%

Intriguing X-ray and optical variations of the γ Cassiopeiae analog HD 45314

Rauw

Nazé

Smith

et al. 2018

A&A

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Context. A growing number of Be and Oe stars, named the γ Cas stars, are known for their unusually hard and intense X-ray emission. This emission could either trace accretion by a compact companion or magnetic interaction between the star and its decretion disk. Aims. To test these scenarios, we carried out a detailed optical monitoring of HD 45314, the hottest member of the class of γ Cas stars, along with dedicated X-ray observations on specific dates. Methods. High-resolution optical spectra were taken to monitor the emission lines formed in the disk, while X-ray spectroscopy was obtained at epochs when the optical spectrum of the Oe star was displaying peculiar properties. Results. Over the last four years, HD 45314 has entered a phase of spectacular variations. The optical emission lines have undergone important morphology and intensity changes including transitions between single-and multiple-peaked emission lines as well as shell events, and phases of (partial) disk dissipation. Photometric variations are found to be anti-correlated with the equivalent width of the Hα emission. Whilst the star preserved its hard and bright X-ray emission during the shell phase, the X-ray spectrum during the phase of (partial) disk dissipation was significantly softer and weaker. Conclusions. The observed behaviour of HD 45314 suggests a direct association between the level of X-ray emission and the amount of material simultaneously present in the Oe disk as expected in the magnetic star-disk interaction scenario.

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“…Berghoefer et al 1997;Sana et al 2006), while VFTS 399 is orders of magnitude brighter, with log(L x /L bol ) ∼ 0.3−4 × 10 −4 in the observations reported above, while the emission is of a non-thermal nature. These properties also exclude membership of the class of X-ray bright and variable γ Cas-like OeBe stars, for which a high temperature thermal spectrum and log(L x /L bol ) ∼ 10 −6 are expected (Smith et al 2012;Rauw et al 2013). Likewise, the peak X-ray luminosity of VFTS 399 is two orders of magnitude greater than that found for Of?p stars and the subset of strongly magnetic O-type stars which, in turn, are X-ray over-luminous with respect to the wider population of massive stars (cf.…”

Section: Understanding the X-ray Emissionmentioning

confidence: 90%

The VLT-FLAMES Tarantula survey

Clark

Bartlett

Broos

et al. 2015

A&A

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Context. The stellar population of the 30 Doradus star-forming region in the Large Magellanic Cloud contains a subset of apparently single, rapidly rotating O-type stars. The physical processes leading to the formation of this cohort are currently uncertain. Aims. One member of this group, the late O-type star VFTS 399, is found to be unexpectedly X-ray bright for its bolometric luminosity − in this study we aim to determine its physical nature and the cause of this behaviour. Methods. To accomplish this we performed a time-resolved analysis of optical, infrared and X-ray observations. Results. We found VFTS 399 to be an aperiodic photometric variable with an apparent near-IR excess. Its optical spectrum demonstrates complex emission profiles in the lower Balmer series and select He i lines − taken together these suggest an OeBe classification.The highly variable X-ray luminosity is too great to be produced by a single star, while the hard, non-thermal nature suggests the presence of an accreting relativistic companion. Finally, the detection of periodic modulation of the X-ray lightcurve is most naturally explained under the assumption that the accretor is a neutron star. Conclusions. VFTS 399 appears to be the first high-mass X-ray binary identified within 30 Dor, sharing many observational characteristics with classical Be X-ray binaries. Comparison of the current properties of VFTS 399 to binary-evolution models suggests a progenitor mass 25 M for the putative neutron star, which may host a magnetic field comparable in strength to those of magnetars. VFTS 399 is now the second member of the cohort of rapidly rotating "single" O-type stars in 30 Dor to show evidence of binary interaction resulting in spin-up, suggesting that this may be a viable evolutionary pathway for the formation of a subset of this stellar population.

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HD 45314: a newγ Cassiopeiae analog among Oe stars

Cited by 17 publications

References 31 publications

π Aquarii is another γ Cassiopeiae object

π Aquarii is another γ Cassiopeiae object

Intriguing X-ray and optical variations of the γ Cassiopeiae analog HD 45314

The VLT-FLAMES Tarantula survey

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