Gemini/GMOS search of massive binaries in the ionizing cluster of 30 Dor

TL;DR

This study uses Gemini GMOS observations to identify massive binary stars in 30 Doradus, revealing a high binary fraction and refining the cluster’s velocity dispersion and mass estimates, supporting its potential as a future globular cluster.

Contribution

First detection of a high binary fraction among massive stars in 30 Doradus using multi-epoch spectroscopy, leading to more accurate cluster mass estimates.

Findings

Binary candidate rate of about 50% among massive stars.

Corrected velocity dispersion of 8.3 km/s after accounting for binaries.

Cluster mass estimate of approximately 4.5×10^5 solar masses.

Abstract

If binaries are common among massive stars, it will have important consequences for the derivation of fundamental properties like the cluster age, IMF and dynamical mass. Making use of the multiplexing facilities of Gemini Multi Object Spectrograph (GMOS) we were able to investigate the presence of binary stars within the ionising cluster of 30 Doradus. From a seven epochs observing campaign at Gemini South we detect a binary candidate rate of about 50%, which is consistent with an intrinsic 100% binary rate among massive stars. We find that single epoch determinations of the velocity dispersion give values around 30 km/s . After correcting the global velocity dispersion for the binary orbital motions, the true cluster velocity dispersion is 8.3 km/s. This value implies a virial mass of about 4.5E5 Msun or 8 percent of the mass calculated using the single epoch value. The binary corrected virial mass estimate is consistent with photometric mass determinations thus suggesting that NGC 2070 is a firm candidate for a future globular cluster.