Mapping the core of the Tarantula Nebula with VLT-MUSE II. The spectroscopic Hertzsprung-Russell diagram of OB stars in NGC 2070

TL;DR

This study provides a detailed spectroscopic analysis of 333 OB stars in NGC 2070, revealing their distribution in the Hertzsprung-Russell diagram, stellar ages, and rotational velocities, with implications for understanding massive star evolution.

Contribution

First spectroscopic Hertzsprung-Russell diagram of OB stars in NGC 2070, offering new insights into their ages, masses, and rotational properties using VLT-MUSE data.

Findings

Identified two main stellar populations with ages ~2.1 and ~6.2 Myr.

Detected a subgroup of stars beyond the main sequence likely due to emission or nebular effects.

Calibrated a spectral diagnostic for early-type stars based on He I/He II line ratios.

Abstract

We present the spectroscopic analysis of 333 OB-type stars extracted from VLT-MUSE observations of the central 30 x 30 pc of NGC 2070 in the Tarantula Nebula on the Large Magellanic Cloud, the majority of which are analysed for the 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$\pm$0.8 and 6.2$\pm$2 Myr. A subgroup of 52 stars is apparently beyond the main sequence phase, which we consider to be due to emission-type objects and/or significant nebular contamination affecting the analysis. As in previous studies, stellar masses derived from the sHRD are systematically larger than those obtained from the conventional HRD, with the differences being largest for the most massive stars. Additionally, we do not find any trend between the estimated projected rotational velocity and evolution in the sHRD. The projected rotational velocity distribution presents a tail of fast rotators that resembles findings in the wider population of 30 Doradus. We use published spectral types to calibrate the HeI$\lambda$4921/HeII$\lambda$5411 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.