Astronomy and Astrophysics, volume 610A, 30-30 (2018/2-1)
Open clusters. III. Fundamental parameters of B stars in NGC 6087, NGC 6250, NGC 6383, and NGC 6530 B-type stars with circumstellar envelopes.
AIDELMAN Y., CIDALE L.S., ZOREC J. and PANEI J.A.
Abstract (from CDS):
Context. Stellar physical properties of star clusters are poorly known and the cluster parameters are often very uncertain.
Methods. 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. 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 inspected the Balmer discontinuity to provide evidence for the presence of circumstellar disks and identify Be star candidates. We used an additional set of high-resolution spectra in the Hα region to confirm the Be nature of these stars.
Results. We provide Teff, logg, Mv, Mbol, 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 11 open clusters studied along this series of three papers, we report 6 new Be stars, 4 blue straggler candidates, and 15 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 (<40Myr). Another maximum of Be stars is observed at the spectral type B6-B8 in open clusters older than 40Myr, 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 increase of stars with circumstellar envelopes with cluster age. The Be phenomenon reaches its maximum in clusters of intermediate age (10-40Myr) and the number of B stars with circumstellar envelopes (Be plus Bdd stars) is also high for the older clusters (40-100Myr).
© ESO 2018
open clusters and associations: individual: NGC 6087 - open clusters and associations: individual: NGC 6250 - open clusters and associations: individual: NGC 6383 - open clusters and associations: individual: NGC 6530 - stars: fundamental parameters - stars: emission-line
VizieR on-line data:
<Available at CDS (J/A+A/610/A30): table1.dat table2.dat tables9-16.dat>
Status at CDS:
// Objects in title, abstract, text, figures, and all or part of small table(s) being processed in SIMBAD.
Table 7 NGC 3114 079 is a probable misprint for NGC 3114 47.
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