Detection of Additional Be+sdO Systems from IUE Spectroscopy

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

doi:10.3847/1538-4357/aaa4b8

Cited by 100 publications

(176 citation statements)

References 55 publications

(59 reference statements)

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“…The occurrence of the RBF in our models is a genuine binary-evolution effect and does not depend on the choice of initial rotation rates. The effectiveness of accretion-induced spin-up in nature is demonstrated by the observed group of Be/X-ray binaries, which are understood as rapidly rotating B stars that have accreted from the progenitors of neutron star companions (Wang et al 2018). We therefore identify our RBF models, which all rotate extremely rapidly (see Fig.…”

Section: Comparison To Observed Star Clustersmentioning

confidence: 99%

Effects of Close Binary Evolution on the Main-sequence Morphology of Young Star Clusters

Wang

Langer

Schootemeijer

et al. 2020

ApJL

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Star clusters are the building blocks of galaxies. They are composed of stars of nearly equal age and chemical composition, allowing us to use them as chronometers and as testbeds for gauging stellar evolution. It has become clear recently that massive stars are formed preferentially in close binaries, in which mass transfer will drastically change the evolution of the stars. This is expected to leave a significant imprint in the distribution of cluster stars in the Hertzsprung-Russell diagram. Our results, based on a dense model grid of more than 50,000 detailed binary-evolution calculations, indeed show several distinct, coeval main-sequence (MS) components, most notably an extended MS turnoff region, and a group of near-critical rotating stars that is spread over a large luminosity range on the red side of the classical MS. We comprehensively demonstrate the time evolution of the features in an animation, and we derive analytic expressions to describe these features. We find quantitative agreement with results based on recent photometric and spectroscopic observations. We conclude that while other factors may also be at play, binary evolution has a major impact on the MS morphology of young star clusters.

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Section: Comparison To Observed Star Clustersmentioning

confidence: 99%

Effects of Close Binary Evolution on the Main-sequence Morphology of Young Star Clusters

Wang

Langer

Schootemeijer

et al. 2020

ApJL

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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 disk had a strongly asymmetric structure the nature of which could not be firmly established. Wang et al (2018) did not detect the signature of an sdO companion in International Ultraviolet Explorer (IUE) UV spectra.…”

Section: Bz Crumentioning

confidence: 96%

“…In stars with only a few scattered UV spectra, crosscorrelations of the observations with model spectra have been used to identify additional sdO companions and candidates (Wang et al 2018). As explained in Sects.…”

Section: Sdo Starsmentioning

confidence: 99%

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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 Additional Be+sdO Systems from IUE Spectroscopy

Cited by 100 publications

References 55 publications

Effects of Close Binary Evolution on the Main-sequence Morphology of Young Star Clusters

Effects of Close Binary Evolution on the Main-sequence Morphology of Young Star Clusters

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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