Mapping the core of the Tarantula Nebula with VLT-MUSE

II. The spectroscopic Hertzsprung-Russell diagram of OB stars in NGC 2070^⋆,⋆⋆

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: ncastro@aip.de
² Department of Physics & Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK
³ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁴ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG Northern Ireland, UK
⁵ LMU München, Universitätssternwarte Scheinerstr. 1, 81679 München, Germany
⁶ Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
⁸ Centro de Astrobiología CSIC-INTA, Crtra. de Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁹ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 7630355, Santiago, Chile

Received: 27 November 2020
Accepted: 27 January 2021

Abstract

We present the spectroscopic analysis of 333 OB-type stars extracted from VLT-MUSE observations of the central 30 × 30 pc of NGC 2070 in the Tarantula Nebula on the Large Magellanic Cloud, the majority of which are analysed for the first time. The distribution of stars in the spectroscopic Hertzsprung-Russell diagram (sHRD) shows 281 stars in the main sequence. We find two groups in the main sequence, with estimated ages of 2.1 ± 0.8 and 6.2 ± 2 Myr. A subgroup of 52 stars is apparently beyond the main sequence phase, which we consider to be due to emission-type objects and/or significant nebular contamination affecting the analysis. As in previous studies, stellar masses derived from the sHRD are systematically larger than those obtained from the conventional HRD, with the differences being largest for the most massive stars. Additionally, we do not find any trend between the estimated projected rotational velocity and evolution in the sHRD. The projected rotational velocity distribution presents a tail of fast rotators that resembles findings in the wider population of 30 Doradus. We use published spectral types to calibrate the He Iλ4921/He IIλ5411 equivalent-width ratio as a classification diagnostic for early-type main sequence stars when the classical blue-visible region is not observed. Our model-atmosphere analyses demonstrate that the resulting calibration is well correlated with effective temperature.