Physical parameters of IPHAS-selected classical Be stars

Gkouvelis, Leonardos; Fabregat, J.; Zorec, J.; Steeghs, D.; Drew, J. E.; Raddi, R.; Wright, N. J.; Drake, J. J.

doi:10.1051/0004-6361/201527090

Cited by 24 publications

(26 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Since the extra emission or absorption in the continuum spectrum produced by the CE detected as a sBD cannot come from circumstellar layers situated too far from the central star, our statistical inferences suggest that the CEs must have high enough vertical optical depths in these regions; this is very similar to suggestions made sometime ago by Arias et al (2006) and Zorec et al (2007a) to account for the presence of Fe ii emission lines originating in CE layers that are near the central star. The rather significant vertical height of CE layers near the star is also supported by the fact that rarely the sBD appears at wavelengths that are larger than the theoretical limit of Balmer lines series, λ3648 Å (Divan 1979;Zorec & Briot 1991;Moujtahid et al 1999;Gkouvelis et al 2016), where the electron density of the CE layers close to the central star cannot be larger than some N e ∼ 10 13 cm −3 . Otherwise the sBD would heavily encroach upon the first or photospheric BD, phenomenon that was exceptionally observed during some emission phases.…”

Section: Second Balmer Discontinuity and The Inclination Angle Of Thementioning

confidence: 87%

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

Cochetti

Zorec

Cidale

et al. 2020

A&A

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Second Balmer Discontinuity and The Inclination Angle Of Thementioning

confidence: 87%

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

Cochetti

Zorec

Cidale

et al. 2020

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…For this project, a list of Be stars is required first of all. Many catalogs of such stars exist, but some are too old to account for recent discoveries and their source content can be found in more recent catalogs, while others are incomplete in terms of sky coverage (they are specific to a region of the sky, e.g., Mennickent et al 2002) or contain only candidates, with some contamination by non-Be stars (e.g., following Gkouvelis et al 2016, only 70% of candidates in Witham et al 2008 truly are Be stars). Although some recent papers provide a few newly discovered objects (e.g., Li et al 2018) 1 , we restricted our analysis to a single global catalog to preserve the homogeneity of our sample, and we finally decided to use the Be Star Spectra (BeSS) catalog, which is recent and "as complete as possible" (Neiner et al 2011).…”

Section: Samplementioning

confidence: 99%

Hot stars observed by XMM-Newton

Nazé

Motch

2018

A&A

View full text Add to dashboard Cite

We perform a survey of Oe and Be stars in the X-ray range. To this aim, we cross-correlated XMM-Newton and Chandra catalogs of X-ray sources with a list of Be stars, finding 84 matches in total. Of these, 51 objects had enough counts for a spectral analysis. This paper provides the derived X-ray properties (X-ray luminosities, and whenever possible, hardness ratios, plasma temperatures, and variability assessment) of this largest ever sample of Oe and Be stars. The targets display a wide range in luminosity and hardness. In particular, the significant presence of very bright and hard sources is atypical for X-ray surveys of OB stars. Several types of sources are identified. A subset of stars display the typical characteristics of O-stars, magnetic OB stars, or pre-main-sequence (PMS) objects: their Be nature does not seem to play an important role. However, another subset comprises γ Cas analogs, which are responsible for the luminous and hard detections. Our sample contains seven known γ Cas analogs, but we also identify eight new γ Cas analogs and one γ Cas candidate. This nearly doubles the sample of such stars.

show abstract

“…Moujtahid et al (1998Moujtahid et al ( , 1999 and Gkouvelis et al (2016) estimated these effects and obtained that…”

Section: Comments On the Balmer Discontinuity Of Be Starsmentioning

confidence: 99%

Open clusters

Aidelman

Cidale

Zorec

et al. 2018

A&A

Self Cite

View full text Add to dashboard Cite

Context. Stellar physical properties of star clusters are poorly known and the cluster parameters are often quite uncertain. Aims. Our goals are to perform a spectrophotometric study of the B star population in open clusters to derive accurate stellar parameters, search for the presence of circumstellar envelopes and discuss the characteristics of these stars. Methods. The BCD spectrophotometric system is a powerful method to obtain stellar fundamental parameters from direct measurements of the Balmer discontinuity. To this end, we wrote the interactive code MIDE3700. The BCD parameters can also be used to infer the main properties of open clusters: distance modulus, color excess and age. Furthermore, we inspect the aspect of the Balmer discontinuity to put in evidence the presence of circumstellar disks and identify Be-star candidates. An additional set of high resolution spectra, in the Hα region, is used to confirm the Be nature of these stars. Results. In this work we provide T eff , log g, M v , M bol and spectral types for a sample of 68 stars in the field of the open clusters NGC 6087, NGC 6250, NGC 6383, and NGC 6530, as well as the cluster distances, ages and reddening. Then, based on a sample of 230 B stars in the direction of the eleven open clusters studied along these three series of papers, we report new six Be stars, four blue straggler candidates, and fifteen B type stars (called Bdd) with a double Balmer discontinuity which indicates the presence of circumstellar envelopes. We discuss the distribution of the fraction of B, Be and Bdd star cluster members per spectral subtype. The majority of the Be stars are dwarfs and present a maximum at the spectral type B2-B4 in young and intermediate-age open clusters (< 40 Myr). Another maximum of Be stars is observed at the spectral type B6-B8 in open clusters older than 40 Myr, where the population of Bdd stars also becomes relevant. The Bdd stars seem to be in a "passive" emission phase. Conclusions. Our results support previous statements that the Be phenomenon is present along the whole main sequence band and occurs in very different evolutionary states. We find clear evidence of an enhance of stars with circumstellar envelopes with cluster age. The Be phenomenon reaches it maximum in clusters of intermediate-age (10 − 40 Myr) and the number of B stars with circumstellar envelopes (Be plus Bdd stars) keeps also high for the older clusters (40 − 100 Myr).

show abstract

Physical parameters of IPHAS-selected classical Be stars

Cited by 24 publications

References 38 publications

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

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

Hot stars observed by XMM-Newton

Open clusters

Contact Info

Product

Resources

About