Open clusters. I. Fundamental parameters of B stars in NGC 3766 and NGC 4755.

AIDELMAN, YAEL; CIDALE, LYDIA; ZOREC, JUAN; ARIAS, MARÍA LAURA

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2012 vol. 544 p. 1 - 18

0004-6361

Context. Spectroscopic investigations of galactic open clusters are scarce and limited to a reduced sample of cluster members.Aims. We intend to perform a complete study of the physical parameters of two galactic clusters as well as of their individual members.Methods. To carry out this study, we use the BCD (Barbier-Chalonge-Divan) spectrophotometric system, which is based on the study of theBalmer discontinuity and is independent of interstellar and circumstellar extinction. Additional physical properties are derived from the lineprofiles (FWHM) and stellar evolution models.Results. We analyze low resolution spectra around the Balmer discontinuity for both normal B-type and Be stars in two open clusters: NGC3766 and NGC 4755. We determine the stellar fundamental parameters, such as: effective temperatures, surface gravities, spectral types, luminosityclasses, absolute and bolometric magnitudes and color gradient excesses. The stellar rotation velocity is also determined. Complementaryinformation, mainly, stellar mass, age and radius of the star population are calculated using stellar evolution models. In some cases, the stellarfundamental parameters have been derived for the first time. The obtained results allow us also to determine the reddening, age and distance tothe clusters.Conclusions. The cluster parameters obtained through the BCD method are in very good agreement with those derived from classical methodsbased on photometric data. The BCD system provides also physical properties of the star members. From this study, we are able to test the wellbehavior of Mbol(λ1, D)-calibrations and detect systematic discrepancies between log g estimates from model atmospheres and those derivedfrom stellar evolution models. In order to improve our knowledge on the formation and evolution of the clusters, further statistical studies onthe initial mass luminosity and angular momentum distributions should be addressed. Therefore, the BCD spectrophotometric system could bea powerful tool to study far galactic and extragalactic clusters with the large telescope generation and the multi-object technique.