Detection of the Ultraviolet Spectrum of the Hot Subdwarf Companion of 60 Cygni (B1 Ve) from a Survey of IUE Spectra of Be Stars

Wang, Luqian; Gies, Douglas R.; Peters, Geraldine J.

doi:10.3847/1538-4357/aa740a

Cited by 54 publications

(62 citation statements)

References 44 publications

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“…Under favorable circumstances, the photospheric spectral signatures of hot sdOB companions can be directly detected in the far-UV domain, observable from space by, e.g., the International Ultraviolet Explorer (IUE) and the Hubble Space Telescope (HST). To date, five CBe+sdOB binaries have been confirmed using this method, namely ϕ Per (Thaller et al 1995), FY CMa (Peters et al 2008), 59 Cyg (Peters et al 2013), HR 2142 (Peters et al 2016), and 60 Cyg (Wang et al 2017). Using the same method, eight more were classified as candidate Be+sdOB binaries and four more as potential candidates (Wang et al 2018).…”

Section: Binarity Among Cbesmentioning

confidence: 99%

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Prevalence of SED Turndown among Classical Be Stars: Are All Be Stars Close Binaries?

Klement

Carciofi

Rivinius

et al. 2019

ApJ

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Rapid rotation is a fundamental characteristic of classical Be stars and a crucial property allowing for the formation of their circumstellar disks. Past evolution in a mass and angular momentum transferring binary system offers a plausible solution to how Be stars attained their fast rotation. Although the subdwarf remnants of mass donors in such systems should exist in abundance, only a few have been confirmed due to tight observational constraints. An indirect method of detecting otherwise hidden companions is offered by their effect on the outer parts of Be star disks, which are expected to be disrupted or truncated. In the context of the IR and radio continuum excess radiation originating in the disk, the disk truncation can be revealed by a turndown in the spectral energy distribution due to reduced radio flux levels. In this work we search for signs of spectral turndown in a sample of 57 classical Be stars with radio data, 2 Klement et al.which include new data for 23 stars and the longest wavelength detections so far (λ ≈ 10 cm) for 2 stars. We confidently detect the turndown for all 26 stars with sufficient data coverage (20 of which are not known to have close binary companions). For the remaining 31 stars, data are inconclusive as to whether the turndown is present or not. The analysis suggests that many if not all Be stars have close companions influencing their outer disks. If confirmed to be subdwarf companions, the mass transfer spin-up scenario might explain the existence of the vast majority of classical Be stars.

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Section: Binarity Among Cbesmentioning

confidence: 99%

“…HR 8053 -60 Cyg. The signature of an sdOB companion has been directly detected in the observed UV spectra (Wang et al 2017). The spectroscopic binary orbit was derived from RV variations of emission wings of the Hα line by Koubský et al (2000).…”

Section: A Known Binaries In the Samplementioning

confidence: 99%

Prevalence of SED Turndown among Classical Be Stars: Are All Be Stars Close Binaries?

Klement

Carciofi

Rivinius

et al. 2019

ApJ

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“…If the system remains bound, an excess in UV or hard X-ray flux may indicate the presence of a compact companion like in the case of subdwarf companions (see e.g. Gies et al 1998;Wang et al 2017Wang et al , 2018) and X-ray binaries (Verbunt 1993;Reig 2011). In star clusters, mass-gainers and mergers are expected to appear younger than their sibling stars, i.e.…”

Section: Introductionmentioning

confidence: 99%

The young massive SMC cluster NGC 330 seen by MUSE

Bodensteiner

Sana

Mahy

et al. 2020

A&A

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Context. A majority of massive stars are part of binary systems, a large fraction of which will inevitably interact during their lives. Binary-interaction products (BiPs), i.e. stars affected by such interaction, are expected to be commonly present in stellar populations. BiPs are thus a crucial ingredient in the understanding of stellar evolution. Aims. We aim to identify and characterize a statistically significant sample of BiPs by studying clusters of 10 − 40 Myr, an age at which binary population models predict the abundance of BiPs to be highest. One example of such a cluster is NGC 330 in the Small Magellanic Cloud. Methods. Using MUSE WFM-AO observations of NGC 330, we resolve the dense cluster core for the first time and are able to extract spectra of its entire massive star population. We develop an automated spectral classification scheme based on the equivalent widths of spectral lines in the red part of the spectrum. Results. We characterize the massive star content of the core of NGC 330 which contains more than 200 B stars, two O stars, 6 A-type supergiants and 11 red supergiants. We find a lower limit on the Be star fraction of 32 ± 3% in the whole sample. It increases to at least 46 ± 10% when only considering stars brighter than V = 17 mag. We estimate an age of the cluster core between 35 and 40 Myr and a total cluster mass of 88 +17 −18 × 10 3 M . Conclusions. We find that the population in the cluster core is different than the population in the outskirts: while the stellar content in the core appears to be older than the stars in the outskirts, the Be star fraction and the observed binary fraction are significantly higher. Furthermore, we detect several BiP candidates that will be subject of future studies.

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“…The strength of this emission follows the long-term variability of the overall emission strength. As for γ Cas, the cross-correlation technique of Wang et al (2017) did not detect the companion to this hot and broad-lined star. Nazé et al (2017) put forward the argument that the secondary in the π Aqr system is not a compact object itself and that no such third body is likely to be in a closer orbit than the secondary.…”

Section: π Aqrmentioning

confidence: 80%

“…Sometimes it is even asked whether all Be stars have highly evolved companions (e.g., Wang et al 2017), making their Betypical rapid rotation the result of mass transfer from their progenitors (cf. Introduction).…”

Section: Observations Of Binary Be Starsmentioning

confidence: 99%

γCas stars: Normal Be stars with discs impacted by the wind of a helium-star companion?

Langer

Baade

Bodensteiner

et al. 2020

A&A

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γ Cas stars are a ∼1% minority among classical Be stars with hard (≥5-10 keV) but only moderately strong continuous thermal X-ray flux and mostly very early-B spectral type. The X-ray flux has been suggested to originate from matter accelerated via magnetic diskstar interaction, by a rapidly rotating neutron star (NS) companion via the propeller effect, or by accretion onto a white dwarf (WD) companion. In view of the growing number of identified γ Cas stars and the only imperfect matches between these suggestions and the observations, alternative models should be pursued. Two of the three best-observed γ Cas stars, γ Cas itself and π Aqr, have a low-mass companion with low optical flux; interferometry of BZ Cru is inconclusive. Binary-evolution models are examined for their ability to produce such systems. The OB+He-star stage of post-mass transfer binaries, which is otherwise observationally unaccounted, can potentially reproduce many observed properties of γ Cas stars. The interaction of the fast wind of helium stars with the circumstellar disk and/or with the wind of Be stars may give rise to the production of hard X-rays. While not modelling this process, it is shown that the energy budget is favourable, and that the wind velocities may lead to hard X-rays as observed in γ Cas stars. Furthermore, the observed number of these objects appears to be consistent with the evolutionary models. Within the Be+He-star binary model, the Be stars in γ-Cas stars are conventional classical Be stars. They are encompassed by O-star+Wolf-Rayet systems towards higher mass, where no stable Be decretion disks exist, and by Be+sdO systems at lower mass where the sdO winds may be too weak to cause the γ Cas phenomenon. In decreasing order of the helium-star mass, the descendants could be Be+black-hole, Be+NS or Be+WD binaries. The interaction between the helium-star wind and the disk may provide new diagnostics of the outer disk.

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Detection of the Ultraviolet Spectrum of the Hot Subdwarf Companion of 60 Cygni (B1 Ve) from a Survey of IUE Spectra of Be Stars

Cited by 54 publications

References 44 publications

Prevalence of SED Turndown among Classical Be Stars: Are All Be Stars Close Binaries?

Prevalence of SED Turndown among Classical Be Stars: Are All Be Stars Close Binaries?

The young massive SMC cluster NGC 330 seen by MUSE

γCas stars: Normal Be stars with discs impacted by the wind of a helium-star companion?

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