Gaia-ESO survey: Massive stars in the Carina Nebula

I. A new census of OB stars^⋆

¹ Departamento de Física Aplicada, Universidad de Alicante, 03690 San Vicente del Raspeig, Alicante, Spain
e-mail: sara.rb@ua.es
² Astrophysics Group, Keele University, Keele, ST5 5BG Staffordshire, UK
³ Centro de Astrobiología (CAB), CSIC-INTA, Campus ESAC, 28692 Villanueva de la Cañada, Madrid, Spain
⁴ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁶ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
⁷ School of Architecture, Universidad Europea de Canarias, Tenerife, Spain
⁸ ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁹ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août, 19c Bât B5c, 4000 Liège, Belgium
¹⁰ Departamento de Astrofísica y Física de la Atmósfera, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹¹ Instituto de Astronomía y Física del Espacio, UBA-CONICET. CC 67, Suc. 28, 1428 Buenos Aires, Argentina
¹² Instituto de Astrofísica de Andalucía (IAA), CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁴ Niels Bohr International Academy, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark
¹⁵ Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá di Padova, Vicolo Osservatorio 3, 35122 Padova, Italy
¹⁶ Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
¹⁷ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
¹⁸ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK

Received: 31 October 2022
Accepted: 18 January 2023

Abstract

Context. The Carina Nebula is one of the major massive star-forming regions in the Galaxy. Its relatively nearby distance (2.35 kpc) makes it an ideal laboratory for the study of massive star formation, structure, and evolution, both for individual stars and stellar systems. Thanks to the high-quality spectra provided by the Gaia-ESO survey and the LiLiMaRlin library, as well as Gaia EDR3 astrometry, a detailed and homogeneous spectroscopic characterization of its massive stellar content can be carried out.

Aims. Our main objective is to spectroscopically characterize all massive members of the Carina Nebula in the Gaia-ESO survey footprint to provide an updated census of massive stars in the region and an updated estimate of the binary fraction of O stars.

Methods. We performed accurate spectral classification using an interactive code that compares spectra with spectral libraries of OB standard stars, as well as line-based classic methods. We calculated membership using our own algorithm based on Gaia EDR3 astrometry. To check the correlation between the spectroscopic n-qualifier and the rotational velocity, we used a semi-automated tool for the line-broadening characterization of OB stars based on a combined Fourier transform and goodness-of-fit methodology.

Results. The Gaia-ESO survey sample of massive OB stars in the Carina Nebula consists of 234 stars. The addition of brighter sources from the Galactic O-Star Spectroscopic Survey and additional sources from the literature allows us to create the most complete census of massive OB stars so far in the region. It contains a total of 316 stars, with 18 of them in the background and 4 in the foreground. Of the 294 stellar systems in Car OB1, 74 are of O type, 214 are of nonsupergiant B type, and 6 are of WR or nonO supergiant (II to Ia) spectral class. We identify 20 spectroscopic binary systems with an O-star primary, of which 6 are reported for the first time, and another 18 with a B-star primary, of which 13 are new detections. The average observed double-lined binary fraction of O-type stars in the surveyed region is 0.35, which represents a lower limit. We find a good correlation between the spectroscopic n-qualifier and the projected rotational velocity of the stars. The fraction of candidate runaways among the stars with and without the n-qualifier is 4.4% and 2.4%, respectively, although nonresolved double-lined binaries could be contaminating the sample of fast rotators.