The Gaia-ESO survey: A spectroscopic study of the young open cluster NGC 3293^⋆,⋆⋆

¹ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Quartier Agora, Allée du 6 Août 19c, Bât. B5c, B4000 Liège, Belgium
e-mail: tmorel@uliege.be
² Centre National d’Etudes Spatiales, Toulouse, France
³ Observatoire de Genève, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁴ Sorbonne Université CNRS, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
⁵ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
⁶ Observatório Nacional/MCTIC, R. Gal. José Cristino 77, São Cristovão, 20921-400 Rio de Janeiro/RJ, Brazil
⁷ Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria
⁸ Department of Physics and Astronomy, Notre Dame University-Louaize, PO Box 72 Zouk Mikaël, Lebanon
⁹ Department of Chemistry and Physics, Saint Mary’s College, Notre Dame, IN 46556, USA
¹⁰ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹¹ Universidad de La Laguna, Dept. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹² Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
¹³ Institute of Theoretical Physics and Astronomy, Vilnius University, Sauletekio av. 3, 10257 Vilnius, Lithuania
¹⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁵ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
¹⁶ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁷ Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁸ Niels Bohr International Academy, Niels Bohr Institute, University of Copenhagen Blegdamsvej 17, 2100 Copenhagen, Denmark
¹⁹ INAF – Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
²⁰ Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
²¹ Space Science Data Center – Agenzia Spaziale Italiana, via del Politecnico, s.n.c., 00133 Roma, Italy
²² Dipartimento di Fisica e Astronomia, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy

Received: 25 May 2022
Accepted: 19 July 2022

Abstract

We present a spectroscopic analysis of the GIRAFFE and UVES data collected by the Gaia-ESO survey for the young open cluster NGC 3293. Archive spectra from the same instruments obtained in the framework of the ‘VLT-FLAMES survey of massive stars’ are also analysed. Atmospheric parameters, non-local thermodynamic equilibrium (LTE) chemical abundances for six elements (He, C, N, Ne, Mg, and Si), or variability information are reported for a total of about 160 B stars spanning a wide range in terms of spectral types (B1 to B9.5) and rotation rate (up to 350 km s⁻¹). Our analysis leads to about a five-fold increase in the number of cluster members with an abundance determination and it characterises the late B-star population in detail for the first time. We take advantage of the multi-epoch observations on various timescales and a temporal baseline, sometimes spanning ∼15 years, to detect several binary systems or intrinsically line-profile variables. A deconvolution algorithm is used to infer the current, true (deprojected) rotational velocity distribution. We find a broad, Gaussian-like distribution peaking around 200–250 km s⁻¹. Although some stars populate the high-velocity tail, most stars in the cluster appear to rotate far from critical. We discuss the chemical properties of the cluster, including the low occurrence of abundance peculiarities in the late B stars and the paucity of objects showing CN-cycle burning products at their surface. We argue that the former result can largely be explained by the inhibition of diffusion effects because of fast rotation, while the latter is generally in accord with the predictions of single-star evolutionary models under the assumption of a wide range of initial spin rates at the onset of main-sequence evolution. However, we find some evidence for a less efficient mixing in two quite rapidly rotating stars that are among the most massive objects in our sample. Finally, we obtain a cluster age of ∼20 Myr through a detailed, star-to-star correction of our results for the effect of stellar rotation (e.g., gravity darkening). This is significantly older than previous estimates from turn-off fitting that fully relied on classical, non-rotating isochrones.