ANÁLISE ESPECTROSCÓPICA DE ESTRELAS OB NA NEBULOSA DE CARINA

Abstract

Open clusters, rich in gas and dust, are excellent environment for star formation. The formation of massive stars, however, requires specific conditions, associated with the giant molecular clouds. Massive stars of spectral types O and B are luminous and young objects, being easily observed and located close to their place of birth, allowing the mapping of the present-day abundances of the Galaxy. We describe the procedures and results of a detailed spectroscopic analysis for a sample of OB stars located in 8 open clusters in the Carina Nebula, based on high-resolution spectra obtained with the FLAMES/GIRAFFE spectrograph coupled to the UT2 VLT 8 m telescope of the Gaia-ESO Public Spectroscopic Survey. Our study begins with membership analysis based on astrometric and photometric data from the Gaia Mission, as well as radial velocities measured from observed spectra. We obtained the projected rotation velocity V sini for a sample of 330 OB stars, probable members of the open clusters Trumpler 14, Trumpler 15, Trumpler 16E and 16W, Collinder 228, Collinder 232, Bochum 11 and NGC 3293, based on the widths of two lines of He i. The V sini distribution for the full sample presents an average value of 159±91kms-1 , while the average for individual cluster varies between 126±77 kms-1, for Collinder 228 and 180±84 kms-1, for NGC 3293. The V sini distribution for a subsample of B0 - B3 is bimodal. Finally, we use a semi-automatic routine based on non-NLTE model atmospheres and synthetic spectra to perform a self-consistent analysis and determine the atmospheric parameters (effective temperature, surface gravity, projected rotational velocity , microturbulence and macroturbulence) and abundances of silicon, oxygen, carbon and nitrogen for a subsample of 65 stars with V sini < ~ 100 kms-1. The stars in our sample are mainly on the main sequence, with effective temperatures between 14,000 and 33,000 K and logarithm of surface gravity between 3.00 and 4.50. The average abundances of C, N, and O are consistent with the solar value, while being slightly subsolar for Si. Our results suggest that the Carina Nebula is chemically homogeneous to within ~ 0.10 dex and the average abundances of O and Si are consistent with its radial position in the Galactic disk.