Velocity monitoring of γ Cas stars reveals their binarity status

Nazé, Yaël; Rauw, Grégor; Czesla, S.; Smith, M. A.; Robrade, J.

doi:10.1093/mnras/stab3378

Cited by 29 publications

(40 citation statements)

References 90 publications

(115 reference statements)

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“…6). Moreover, for the TIGRE spectra, overall Hα RVs were determined by four different methods (for details, see Nazé et al 2019aNazé et al , 2022a: the first-order moment of the entire line profile, a comparison between the blue wing and the mirrored red wing 7 obtained by reversing the velocities, correlation of the line profile to a two-Gaussian function (bisector derivation at half width), and correlation of the observed profiles against the profile obtained on February 19, 2021. The results of all these measurements are displayed in the middle and bottom panels of Fig.…”

Section: Radial Velocitiesmentioning

confidence: 99%

The X-ray Emission of γ Cassiopeiae During the 2020–2021 disc eruption

Rauw

Nazé

Motch

et al. 2022

A&A

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Context. γ Cas is known for its unusually hard and intense X-ray emission. This emission could trace accretion by a compact companion, wind interaction with a hot sub-dwarf companion, or magnetic interaction between the star and its Be decretion disc. Aims. These various scenarios should lead to diverse dependences of the hard X-ray emission on disc density. To test these scenarios, we collected X-ray observations of γ Cas during an episode of enhanced disc activity that took place around January 2021. Methods. We investigate the variations in the disc properties using time series of dedicated optical spectroscopy and existing broadband photometry. Equivalent widths and peak velocity separations are measured for a number of prominent emission lines. Epochdependent Doppler maps of the Hα, Hβ, and He  λ 5876 emission lines are built to characterise the emission regions in velocity space. We analyse four XMM-Newton observations obtained between January 2021 and January 2022 at key phases of the episode of enhanced disc activity. Archival XMM-Newton, Chandra, MAXI, and RXTE-ASM data are also used to study the long-term correlation between optical and X-ray emission. Results. Optical spectroscopy unveils a clear increase in the radial extent of the emission regions during the episode of enhanced disc activity, whilst no increase in the V-band flux is recorded. Our Doppler maps do not reveal any stable feature in the disc resulting from the putative action of the companion on the outer parts of the Be disc. Whilst the hard X-ray emission is found to display the usual level and type of variability, no specific increase in the hard emission is observed in relation to the enhanced disc activity. However, at two occasions, including at the maximum disc activity, the soft X-ray emission of γ Cas is strongly attenuated, suggesting more efficient obscuration by material from a large flaring Be disc. In addition, there is a strong correlation between the long-term variations in the X-ray flux and the optical variations in the V-band photometry. Conclusions. The observed behaviour of γ Cas suggests no direct link between the properties of the outer regions of the Be disc and the hard X-ray emission, but it favours a link between the level of X-ray emission and the properties of the inner part of the Be disc. These results thus disfavour an accretion or colliding wind scenario.

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Section: Radial Velocitiesmentioning

confidence: 99%

The X-ray Emission of γ Cassiopeiae During the 2020–2021 disc eruption

Rauw

Nazé

Motch

et al. 2022

A&A

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“…Indeed, two Cas stars have long been known to lie in a binary system: Cas (Harmanec et al 2000) and Aqr (Bjorkman et al 2002). The multiplicity of other Cas analogs has been recently studied (Nazé et al 2022a). In total, orbits could be derived in eight cases (out of 25 Cas objects) and five additional stars show hints of binarity.…”

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confidence: 99%

The X-ray emission of Be+stripped star binaries★

Nazé

Rauw

Smith³

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Using observations from Chandra, Swift and XMM-Newton, we investigate the high-energy properties of all known (18) Be+sdO systems as well as 7 additional Be binaries suspected to harbour stripped stars. The observed X-ray properties are found to be similar to those observed for other Be samples. The vast majority of these systems (15 out of 25) display very faint (and soft) X-ray emission, and six others are certainly not bright X-ray sources. Only two systems display γ Cas characteristics (i.e. bright and hard X-rays), and one of them is a new detection: HD 37202 (ζ Tau). It presents an extremely hard spectrum, due to a combination of high temperature and high absorption (possibly due to its high inclination). In parallel, it may be noted that the previously reported cyclic behaviour of this Be star has disappeared in recent years. Instead, shorter cycles and symmetric line profiles are observed for the Hα line. It had been recently suggested that the peculiar X-ray emissions observed in γ Cas stars could arise from a collision between the disk of a Be star and the wind of its hot, stripped-star companion. The small fraction of γ Cas analogs in this sample, as well as the properties of the known companions of the γ Cas cases (low mass or not extremely hot, contrary to predictions), combined to the actual stripped-star and colliding-wind empirical knowledge, make the disk-wind collision an unlikely scenario to explain the γ Cas phenomenon.

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“…Over the last eight years, we have used TIGRE to monitor the optical spectra of a sample of γ Cas stars. Thanks to its robotic mode, TIGRE enabled us to collect well-sampled time series of spectra which were used to perform a systematic radial velocity monitoring of these stars (Nazé et al, 2022). This study showed that the properties of the known and newly found γ Cas binaries do not significantly differ from those of other Be binary systems and that companions are of low mass (0.6 -1 M ).…”

Section: Hot Starsmentioning

confidence: 91%

Eight years of TIGRE robotic spectroscopy: Operational experience and selected scientific results

González‐Pérez¹,

Mittag²,

Schmitt³

et al. 2022

Preprint

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TIGRE (Telescopio Internacional de Guanajuato Rob ótico Espectrosc ópico) has been operating in fully robotic mode in the Observatory La Luz (Guanajuato, Mexico) since the end of 2013. With its sole instrument, HEROS, an échelle spectrograph with a spectral resolution R∼20000, TIGRE has collected more than 48000 spectra of 1151 different sources with a total exposure time of more than 11000 hours in these eight years. Here we briefly describe the system and the upgrades performed during the last years. We present the statistics of the weather conditions at the La Luz Observatory, emphasizing the characteristics that affect the astronomical observations. We evaluate the performance and efficiency of TIGRE, both optical and operational, and describe the improvements of the system implemented to optimize the telescope's performance and meet the requirements of the astronomer in terms of timing constraints for the observations and the quality of the spectra. We describe the actions taken to slow down the optical efficiency loss due to the aging of the optical surfaces as well as the upgrades of the scheduler and the observing procedures to minimize the time lost due to interrupted observations or observations that do not reach the required quality. Finally, we highlight a few of the main scientific results obtained with TIGRE data.

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Velocity monitoring of γ Cas stars reveals their binarity status

Cited by 29 publications

References 90 publications

The X-ray Emission of γ Cassiopeiae During the 2020–2021 disc eruption

The X-ray Emission of γ Cassiopeiae During the 2020–2021 disc eruption

The X-ray emission of Be+stripped star binaries★

Eight years of TIGRE robotic spectroscopy: Operational experience and selected scientific results

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