Variations on a theme: the puzzling behaviour of Schulte 12

Nazé, Yaël; Rauw, Grégor; Czesla, S.; Mahy, L.; Campos, F.

doi:10.1051/0004-6361/201935141

Cited by 14 publications

(13 citation statements)

References 95 publications

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“…For Schulte 12, the threshold that we adopt does not select that star as potential binary system. A period of 108 days has been reported from spectroscopy and X-rays by Nazé et al (2019). This points out that this period might be associated with another phenomenon than binarity as suggested by these authors.…”

Section: Multiplicity Criteriasupporting

confidence: 57%

Multiplicity of Galactic luminous blue variable stars

Mahy

Lanthermann

Hutsemékers

et al. 2021

A&A

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Context. Luminous blue variables (LBVs) are characterised by strong photometric and spectroscopic variability. They are thought to be in a transitory phase between O-type stars on the main sequence and the Wolf-Rayet stage. Recent studies also evoked the possibility that they might be formed through binary interaction. Only a few are known in binary systems so far, but their multiplicity fraction is still uncertain. Aims. We derive the binary fraction of the Galactic LBV population. We combine multi-epoch spectroscopy and long-baseline interferometry to probe separations from 0.1 to 120 mas around confirmed and candidate LBVs. Methods. We used a cross-correlation technique to measure the radial velocities of these objects. We identified spectroscopic binaries through significant radial velocity variability with an amplitude larger than 35 km s−1. We also investigated the observational biases to take them into account when we established the intrinsic binary fraction. We used CANDID to detect interferometric companions, derive their flux fractions, and their positions on the sky. Results. From the multi-epoch spectroscopy, we derive an observed spectroscopic binary fraction of 26−10+16%. Considering period and mass ratio ranges from log(Porb) = 0 − 3 (i.e. from 1 to 1000 days), q = 0.1 − 1.0, and a representative set of orbital parameter distributions, we find a bias-corrected binary fraction of 62−24+38%. Based on data of the interferometric campaign, we detect a binary fraction of 70 ± 9% at projected separations between 1 and 120 mas. Based on the derived primary diameters and considering the distances of these objects, we measure for the first time the exact radii of Galactic LBVs to be between 100 and 650 R⊙. This means that it is unlikely that short-period systems are included among LBV-like stars. Conclusions. This analysis shows for the first time that the binary fraction in the Galactic LBV population is large. If they form through single-star evolution, their orbit must be large initially. If they form through a binary channel, the implication is that either massive stars in short binary systems must undergo a phase of fully non-conservative mass transfer to be able to sufficiently widen the orbit to form an LBV, or that LBVs form through merging in initially binary or triple systems. Interferometric follow-up would provide the distributions of orbital parameters at more advanced stages and would serve to quantitatively test the binary evolution in massive stars.

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Section: Multiplicity Criteriasupporting

confidence: 57%

Multiplicity of Galactic luminous blue variable stars

Mahy

Lanthermann

Hutsemékers

et al. 2021

A&A

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“…The final spectra (about ten for each star) display typical signal-to-noise ratios of 150-200. Within IRAF, a further correction was made for eliminating telluric lines around H and He 5876Å in the optical (template of Hinkle et al 2000), as well as around 1 m and 1.28 m in the near-IR (template as in Nazé et al 2019b). Sky emission lines near 1.56 m were also eliminated, using the data from the sky fiber.…”

Section: Carmenesmentioning

confidence: 99%

Velocity monitoring of γ Cas stars reveals their binarity status

Nazé

Rauw

Czesla

et al. 2022

Monthly Notices of the Royal Astronomical Society

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The binary status of γ Cas stars has been discussed while theoretically examining the origin of their peculiar X-ray emission. However, except in two cases, no systematic radial velocity monitoring of these stars had been undertaken yet to clarify their status. We now fill this gap using TIGRE, CARMENES, and UVES high-resolution spectroscopy. Velocities were determined for 16 stars, revealing shifts and/or changes in line profiles. The orbit of six new binaries could be determined: the long periods (80–120 d) and small velocity amplitudes (5–7 km s−1) suggest low mass companions (0.6–1 M⊙). The properties of the known γ Cas binaries appear similar to those of other Be systems, with no clear-cut separation between them. One of the new systems is a candidate for a rare case of quadruple system involving a Be star. Five additional γ Cas stars display velocity variations compatible with the presence of companions, but no orbital solution could yet be formally established for them hence they only receive the status of “binary candidate”.

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“…The former is a 5.5 yr highly eccentric colliding wind binary, indicating that its X-ray emission most probably arises from the wind interaction rather than inside the wind of the LBV [91,113]. As to Schulte 12, this star displays a bright (log L x /L bol = −6.1) and hard (kT ∼ 2 keV) emission [131,13] that was shown to undergo a 108 day modulation which is reminiscent of a colliding wind binary [84]. Yet, the optical spectra and photometry of this star do not vary as regularly as the X-ray data, but rather undergo variations on timescales of 50 -100 days, which are more likely to result from pulsations.…”

Section: Evolved Massive Starsmentioning

confidence: 85%

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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Variations on a theme: the puzzling behaviour of Schulte 12

Cited by 14 publications

References 95 publications

Multiplicity of Galactic luminous blue variable stars

Multiplicity of Galactic luminous blue variable stars

Velocity monitoring of γ Cas stars reveals their binarity status

X-ray emission of massive stars and their winds

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