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

Granada, A.; Jones, C. E.; Sigut, T. A. A.; Semaan, T.; Georgy, Cyril; Meynet, Georges; Ekström, Sylvia

doi:10.3847/1538-3881/aa9f1d

Cited by 8 publications

(4 citation statements)

References 74 publications

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“…Given these numbers, we estimate that at a given epoch ∼ 75% of HMXBs (BeXBs) are active. Although this is in general agreement with the fraction of active Be stars identified in open Galactic clusters ranging from 50-75% (Fabregat 2003;McSwain & Gies 2005;Granada et al 2018), we point out that it is actually a lower limit of the overall OBe population. This is because our selection criteria for OBe stars are conservative and this photometric approach is not sensitive to OBe stars with relatively faint Hα emission.…”

Section: Resultssupporting

confidence: 88%

Clarifying the population of HMXBs in the Small Magellanic Cloud

et al. 2018

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Almost all confirmed optical counterparts of HMXBs in the SMC are OB stars with equatorial decretion disks (OBe). These sources emit strongly in Balmer lines and standout when imaged through narrow-band Hα imaging. The lack of secure counterparts for a significant fraction of the HMXBs motivated us to search for more. Using the catalogs for OB/OBe stars (Maravelias et al. 2017) and for HMXBs (Haberl & Sturm 2016) we detect 70 optical counterparts (out of 104 covered by our survey). We provide the first identification of the optical counterpart to the source XTEJ0050-731. We verify that 17 previously uncertain optical counterparts are indeed the proper matches. Regarding 52 confirmed HMXBs (known optical counterparts with Hα emission), we detect 39 as OBe and another 13 as OB stars. This allows a direct estimation of the fraction of active OBe stars in HMXBs that show Hα emission at a given epoch to be at least ∼ 75% of their total HMXB population.

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Section: Resultssupporting

confidence: 88%

Clarifying the population of HMXBs in the Small Magellanic Cloud

et al. 2018

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“…We found 22 ± 2% (100/452 cluster and field Be stars; Table 5) of Be stars experienced a disk-loss or disk-renewal episode within 1 year, which is lower than the composite mean of 51 ±7% (23/45 Be stars) reported by the smaller McSwain et al (2009) study, although these transient rates do technically agree within 3σ of the quoted errors. The rate of disk-loss episodes that we observe across our entire sample (∼13%; Table 5) is similar to the fraction of dissipating or small disks inferred from the IR photometric study of Granada et al (2018). We do caution that Be stars have been found to vary over periods of many years, and our one-year survey may not have captured the full transition period for many of these stars.…”

Section: Discussion 41 Variabilitysupporting

confidence: 70%

“…45 Be stars distributed across 7 clusters; McSwain et al 2008McSwain et al , 2009, revealing a wide dispersion in the observed rate of transients spanning a wide range of time-scales (0±18% -75±22%, with a composite mean of 51 ±7%; McSwain et al 2009). Granada et al (2018) characterized the IR color variability and location in IR CMD and 2-CD space of a sample of Be stars in open clusters to infer that ∼9-15% of their sample of Be stars had a dissipating or small disk. Larger volume surveys have quantified that longterm variations (LTVs) in the R-band occur over many years in 37% (81/217) of Be stars (Labadie-Bartz et al 2017).…”

Section: Cluster Versus Field Be Starsmentioning

confidence: 99%

The Hubble Space Telescope Advanced Camera for Surveys Emission Line Survey of Andromeda. I. Classical Be Stars

Peters¹,

Wisniewski²,

Williams³

et al. 2020

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We present results from a 2-epoch HST Hα emission line survey of the Andromeda Galaxy that overlaps the footprint of the Panchromatic Hubble Andromeda Treasury (PHAT) survey. We find 552 (542) classical Be stars and 8429 (8556) normal B-type stars in epoch # 1 (epoch # 2), yielding an overall fractional Be content of 6.15% ±0.26% (5.96% ±0.25%). The fractional Be content decreased with spectral sub-type from ∼23.6% ±2.0% (∼23.9% ±2.0%) for B0-type stars to ∼3.1% ±0.34% (∼3.4% ±0.35%) for B8-type stars in epoch # 1 (epoch # 2). We observe a clear population of cluster Be stars at early fractional main sequence lifetimes, indicating that a subset of Be stars emerge onto the ZAMS as rapid rotators. Be stars are 2.8x rarer in M31 for the earliest sub-types compared to the SMC, confirming that the fractional Be content decreases in significantly more metal rich environments (like the Milky Way and M31). However, M31 does not follow a clear trend of Be fraction decreasing with metallicity compared to the Milky Way, which may reflect that the Be phenomenon is enhanced with evolutionary age. The rate of disk-loss or disk-regeneration episodes we observe, 22% ± 2% yr −1 , is similar to that observed for seven other Galactic clusters reported in the literature, assuming these latter transient fractions scale by a linear rate. The similar number of disk-loss events (57) as disk-renewal events (43) was unexpected since disk dissipation time-scales can be ∼2x the typical time-scales for disk build-up phases.

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“…Members of an open cluster (OC) are thought to be born in almost the same molecular cloud, with similar ages and chemical abundances, and all have nearly the same distance to Earth (Lada et al 1993;Friel 1995). Owing to such properties, the OC serves as an ideal laboratory for the establishment of the theory of stellar structure and evolution (Evans et al 2009;Granada et al 2018). In addition, various types of variable stars in open clusters provide an extra tool for studying the fundamental stellar parameters and the internal structure that otherwise cannot be seen directly.…”

Section: Introductionmentioning

confidence: 99%

Variable Stars in the 50BiN Open Cluster Survey. III. NGC 884

Wang,

Nie,

Wang

et al. 2024

Res. Astron. Astrophys.

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Open clusters are the basic building blocks that serve as an the laboratory for the study of young stellar populations in the Milky Way. Variable stars in open clusters provide a unique way to accurately probe the internal structure, temporal and dynamical evolutionary stages of individual stars and the host cluster. The most powerful tool for such studies is time-domain photometric observations. This paper follows the route of our previous work, concentrating on a photometric search for variable stars in NGC 884. The target cluster is the companion of NGC 869, forming the well-known double cluster system that is gravitationally bound. From the observation run in November 2016, a total of 9247 B-band CCD images and 8218 V-band CCD images were obtained. We detected a total of 15 stars with variability in visual brightness, including 5 Be stars, 3 eclipsing binaries, and 7 of unknown type. Two new variable stars were discovered in this work. We also compared the variable star content of NGC 884 with its companion NGC 869.

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

Cited by 8 publications

References 74 publications

Clarifying the population of HMXBs in the Small Magellanic Cloud

Clarifying the population of HMXBs in the Small Magellanic Cloud

The Hubble Space Telescope Advanced Camera for Surveys Emission Line Survey of Andromeda. I. Classical Be Stars

Variable Stars in the 50BiN Open Cluster Survey. III. NGC 884

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