A representative sample of Be stars

Barnsley, R. M.; Steele, I. A.

doi:10.1051/0004-6361/201220419

Cited by 21 publications

(19 citation statements)

References 24 publications

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“…Among early and mid Be stars, 15% and 9% of the objects respectively, have W1-W2 between 0.05 and 0.15, which points towards the finding that the formation of small short lived disks (perhaps from outbursts) is more common among early type stars, in agreement with other authors (e.g. Hubert & Floquet 1998;Barnsley & Steele 2013;Labadie-Bartz et al 2017).…”

Section: Discussionsupporting

confidence: 90%

Quiescent and Active Phases in Be Stars: A WISE Snapshot of Young Galactic Open Clusters

Granada

Jones

Sigut

et al. 2018

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Through the modelling of near-infrared photometry of star plus disk systems with the codes bedisk/beray, we successfully describe the WISE photometric characteristics of Be stars in five young open clusters, NGC 663, NGC 869, NGC 884, NGC 3766 and NGC 4755, broadly studied in the literature. WISE photometry allows previously known Be stars to be detected and to find new Be candidates which could be confirmed spectroscopically. The location of Be stars in the WISE colour-magnitude diagram, separates them in two groups; active (Be stars hosting a developed circumstellar disk) and quiescent objects (Be stars in a diskless phase), and this way, we can explore how often stars are observed in these different stages. The variability observed in most active variable Be stars is compatible with a disk dissipation phase. We find that 50 percent of Be stars in the studied open clusters are in an active phase. We can interpret this as Be stars having a developed circumstellar disk half of the time. The location of Be stars with a developed disk in the CMD require mass loss rates in agreement with values recently reported in the literature. For these objects, we expect to have a tight relation between the equivalent width of the Hα line and the mass of the disk, if the inclination is known. Also, near-infrared photometry of Be stars in stellar clusters has the potential of being useful to test whether there is a preferential viewing angle.

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Section: Discussionsupporting

confidence: 90%

Quiescent and Active Phases in Be Stars: A WISE Snapshot of Young Galactic Open Clusters

Granada

Jones

Sigut

et al. 2018

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“…However, recent observations by Shokry et al (2018) have demonstrated that, with the help of high-quality spectral line profiles, weak Hα emission can be detected in many more late B-type stars than previously thought. The variability of their emission lines seems to be much slower and reach lower amplitudes than displayed by many early-type Be stars (Barnsley & Steele 2013). Photospheric line-profile variability is also much less pronounced in late-type Be stars (Baade 1989b).…”

Section: Introductionmentioning

confidence: 92%

Short-term variability and mass loss in Be stars

Borre

Pigulski²,

Rivinius³

et al. 2018

A&A

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Context. In early-type Be stars, groups of nonradial pulsation (NRP) modes with numerically related frequencies may be instrumental for the release of excess angular momentum through mass-ejection events. Difference and sum/harmonic frequencies often form additional groups. Aims. The purpose of this study is to find out whether a similar frequency pattern occurs in the cooler third-magnitude B7-8 IIIe shell star ν Pup. Methods. Time-series analyses were performed of space photometry with BRITE-Constellation (2015, 2016/17, and 2017/18), SMEI (2003-2011), and Hipparcos (1989-1993. Two IUE SWP and 27 optical echelle spectra spanning 20 years were retrieved from various archives.Results. The optical spectra exhibit no anomalies or well-defined variabilities. A magnetic field was not detected. All three photometry satellites recorded variability near 0.656 c/d which is resolved into three features separated by ∼0.0021 c/d. Their first harmonics and two combination frequencies form a second group, whose features are similarly spaced by 0.0021 c/d. The frequency spacing is very nearly but not exactly equidistant. Variability near 0.0021 c/d was not detected. The long-term frequency stability could be used to derive meaningful constraints on the properties of a putative companion star. The IUE spectra do not reveal the presence of a hot subluminous secondary. Conclusions. ν Pup is another Be star exhibiting an NRP variability pattern with long-term constancy and underlining the importance of combination frequencies and frequency groups. This star is a good target for efforts to identify an effectively single Be star.Article published by EDP Sciences A145, page 1 of 16 A&A 620, A145 (2018)

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“…These are extreme values for classical Be stars. Only two objects among more than 50 Be stars monitored by Barnsley & Steele (2013) have ever shown comparable values. In addition, six other Be stars have been identified in the slitless fields, namely stars 40, 78, 84, 92, 213 (this latter without a 2MASS counterpart) and 389.…”

Section: Referencementioning

confidence: 98%

NGC 3105: a young open cluster with low metallicity

Alonso-Santiago

Tobarra

Negueruela

et al. 2018

A&A

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Context. NGC 3105 is a young open cluster hosting blue, yellow and red supergiants. This rare combination makes it an excellent laboratory to constrain evolutionary models of high-mass stars. It is poorly studied and fundamental parameters such as its age or distance are not well defined. Aims. We intend to characterize in an accurate way the cluster as well as its evolved stars, for which we derive for the first time atmospheric parameters and chemical abundances. Methods. We performed a complete analysis combining U BVR photometry with spectroscopy. We obtained spectra with classification purposes for 14 blue stars and high-resolution spectroscopy for an in-depth analysis of the six other evolved stars. Results. We identify 126 B-type likely members within a radius of 2.7±0.6 arcmin, which implies an initial mass, M cl ≈4 100 M . We find a distance of 7.2±0.7 kpc for NGC 3105, placing it at R GC =10.0±1.2 kpc. Isochrone fitting supports an age of 28±6 Ma, implying masses around 9.5 M for the supergiants. A high fraction of Be stars (≈25%) is found at the top of the main sequence down to spectral type b3. From the spectral analysis we estimate for the cluster an average v rad =+46.9 ± 0.9 km s −1 and a low metallicity, [Fe/H]=−0.29±0.22. We also have determined, for the first time, chemical abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved stars. The chemical composition of the cluster is consistent with that of the Galactic thin disc. An overabundance of Ba is found, supporting the enhanced s-process. Conclusions. NGC 3105 has a low metallicity for its Galactocentric distance, comparable to typical LMC stars. It is a valuable spiral tracer in a very distant region of the Carina-Sagittarius spiral arm, a poorly known part of the Galaxy. As one of the few Galactic clusters containing blue, yellow and red supergiants, it is massive enough to serve as a testbed for theoretical evolutionary models close to the boundary between intermediate and high-mass stars.

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A representative sample of Be stars

Cited by 21 publications

References 24 publications

Quiescent and Active Phases in Be Stars: A WISE Snapshot of Young Galactic Open Clusters

Quiescent and Active Phases in Be Stars: A WISE Snapshot of Young Galactic Open Clusters

Short-term variability and mass loss in Be stars

NGC 3105: a young open cluster with low metallicity

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