Open clusters

Aidelman, Yael Judith; Cidale, L. S.; Zorec, J.; Panei, J. A.

doi:10.1051/0004-6361/201730995

Cited by 23 publications

(47 citation statements)

References 92 publications

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“…Our work suggests that some Be stars can be produced as a result of core contraction and surface rotational acceleration due to efficient AM transport. This single star scenario, proposed by Maeder & Meynet (2001), also explains the higher abundance of Be stars in slightly aged populations (older than 10 Myr) and stars near the TAMS (Keller, Bessell & Da Costa 2000;Aidelman et al 2018), because more envelope spin-up occurs as stars age and evolve toward the TAMS. Additionally, the larger abundance of Be stars in low-metallicity environments (Peters et al 2019 and references therein) is naturally explained by the smaller mass/AM loss through winds (rather than having to appeal to larger rotation rates at birth), allowing more stars to reach their breakup rotation rate.…”

Section: The Be Star Phenomenonmentioning

confidence: 83%

Centrifugally driven mass-loss and outbursts of massive stars

Zhao

Fuller

2020

Monthly Notices of the Royal Astronomical Society

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Rotation and mass-loss are crucially interlinked properties of massive stars, strongly affecting their evolution and ultimate fate. Massive stars rotating near their break-up limit shed mass centrifugally, creating Be stars with circumstellar discs and possibly driving outbursts. Using the mesa stellar evolution code, we examine the effects of efficient angular momentum transport on the main-sequence and post-main-sequence rotational evolution of massive stars. In rapid rotators, angular momentum transported from the contracting core to the expanding envelope can spin-up the surface layers past the break-up rate, particularly for stars near (or beyond) the end of the main-sequence and in low-metallicity environments. We also demonstrate that centrifugal instabilities could arise in rapidly rotating massive stars, potentially triggering the S Doradus outbursts observed in luminous blue variable stars. Prior mass accretion from a binary companion increases both the likelihood and the intensity of centrifugal mass-loss. We discuss implications for massive stellar evolution, Be stars, and luminous blue variables.

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Section: The Be Star Phenomenonmentioning

confidence: 83%

Centrifugally driven mass-loss and outbursts of massive stars

Zhao

Fuller

2020

Monthly Notices of the Royal Astronomical Society

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“…The rapid rotation that characterizes Bn stars, the occasional appearance of some emission in the Balmer lines (at least in Hα), and the presence of signatures for some sBD are motivate us to think that Bn and Be probably belong to the same class of objects. Some attempts to show a possible correlation between fastrotating late B-type stars and Be stars based on the presence of a sBD were discussed by Aidelman et al (2018) in open clusters.…”

Section: Bn Starsmentioning

confidence: 99%

“…Contrarily, in the diagrams where the parameters were corrected for rotational effects, we see that Bn stars can have age ratios 0.2 (t/t MS ) Bn 0.8 if M/M 4, whereas they have 0.0 (t/t MS ) Bn 0.2 for masses M/M 5. According to Aidelman et al (2018), the Be phenomenon is observed along the whole MS, and appears on average at an earlier age in massive stars than in the less massive stars. Thus, the possibility that the most massive Bn stars display the Be phenomenon at any time should not be excluded.…”

Section: Distribution Of Stellar Ages In Our Samplementioning

confidence: 99%

Be and Bn stars: Balmer discontinuity and stellar-class relationship

Cochetti

Zorec

Cidale

et al. 2020

A&A

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Context. A significant number of Be stars show a second Balmer discontinuity (sBD) attributed to an extended circumstellar envelope (CE). The fast rotational velocity of Be stars undoubtedly plays a significant role in the formation of the CE. However, Bn stars, which are also B-type rapidly rotating stars, do not all present clear evidence of being surrounded by circumstellar material. Aims. We aim to characterize the populations of Be and Bn stars, and discuss the appearance of the sBD as a function of the stellar parameters. We expect to find new indices characterizing the properties of CEs in Be stars and properties relating Be and Bn stars. Methods. We obtained low-and high-resolution spectra of a sample of Be and Bn stars, derived stellar parameters, characterized the sBD, and measured the emission in the Hα line. Results. Correlations of the aspect and intensity of the sBD and the emission in the Hα line with the stellar parameters and the Vsin i are presented. Some Bn stars exhibit the sBD in absorption, which may indicate the presence of rather dense CEs. Six Bn stars show emission in the Hα line, so they are reclassified as Be stars. The sBD in emission appears in Be stars with Vsin i 250 km s −1 , and in absorption in both Be and Bn stars with Vsin i 50 km s −1 . Low-mass Be and Bn stars share the same region in the Hertzsprung-Russell diagram. The distributions of rotational to critical velocity ratios of Be and Bn stars corresponding to the current stellar evolutionary stage are similar, while distributions inferred for the zero-age main sequence have different skewness. Conclusions. We found emission in the Hα line and signs of a CE in some Bn stars, which motivated us to think that Bn and Be stars probably belong to the same population. It should be noted that some of the most massive Bn stars could display the Be phenomenon at any time. The similarities found among Be and Bn stars deserve to be more deeply pursued.

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“…There is only one study based on CCD photometry with UBVRI data performed by Sagar & Cannon (1997). We refer the reader to the very recent study of Aidelman et al (2018) for a complete compilation of the parameters of the cluster determined by different authors, using different data and techniques.…”

Section: Ngc 6087mentioning

confidence: 99%

Astrometric and photometric study of Dias 4, Dias 6, and other five open clusters using ground-based and Gaia DR2 data

Dias

Monteiro

Lépine

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present a study of 7 southern open clusters based on UBVRI CCD photomety (Johnsons-Cousins system) and Gaia DR2 data. Dias 4, Dias 6 and four other clusters had UBVRI photometric observations determined for the first time. From the observational UBVRI data we obtained photometric membership probability estimates and, using the proper motions from the UCAC5 catalog, we also determined the kinematic membership. From Gaia DR2 astrometric data we determine the stellar membership using proper motions and parallaxes, taking into account the full covariance matrix. For both independent sets of data and membership we apply our non subjective multidimensional global optimization tool to fit theoretical isochrones to determine the distance, age, reddening, metallicity and binary fraction of the clusters. The results of the mean proper motions, distances and ages are in agreement, but the ones obtained from Gaia DR2 data are more precise in both membership selection and estimated parameters. In the case of NGC 6087, the Cepheid S Nor, member of the open cluster, was used to obtain an independent distance estimate, confirming the one determined by our fitting method. We also report a serendipitous discovery of two new clusters in the extended field near what was originally Dias 4. 1 The latest version (3.5) can be accessed on line at https:// wilton.unifei.edu.br/ocdb/.has contributed in this topic through membership probability estimates from both photometric (Monteiro et al. 2017) and proper motion data (Dias et al. 2014(Dias et al. , 2018. In this study we show how the solution of this question evolved in the era of the Gaia mission (Gaia Collaboration et al. 2018a).The open clusters investigated in the present study were selected from DAML02 with the aim to provide a set of homogeneous UBVRI data and parameters determined from them in a non subjective isochrone-fitting approach. For all the clusters studied here, except for NGC 6087, these are the first results based on UBVRI data. The cluster NGC 6087 was observed in this run because the Cepheid S Nor, member of the cluster, allows us to obtain an independent check of the distance estimate by our isochrone fit method.Despite the fact that several of the clusters investigated in the present work had previous determinations of distances and ages, important corrections were needed given the discrepancies between results obtained by different works using different methods, as discussed by Netopil et al. (2015).

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Open clusters

Cited by 23 publications

References 92 publications

Centrifugally driven mass-loss and outbursts of massive stars

Centrifugally driven mass-loss and outbursts of massive stars

Be and Bn stars: Balmer discontinuity and stellar-class relationship

Astrometric and photometric study of Dias 4, Dias 6, and other five open clusters using ground-based and Gaia DR2 data

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