The young massive SMC cluster NGC 330 seen by MUSE

Abstract

Context. A majority of massive stars are part of binary systems, a large fraction of which will inevitably interact during their lives. Binary-interaction products (BiPs), i.e. stars affected by such interaction, are expected to be commonly present in stellar populations. BiPs are thus a crucial ingredient in the understanding of stellar evolution. Aims. We aim to identify and characterize a statistically significant sample of BiPs by studying clusters of 10 − 40 Myr, an age at which binary population models predict the abundance of BiPs to be highest. One example of such a cluster is NGC 330 in the Small Magellanic Cloud. Methods. Using MUSE WFM-AO observations of NGC 330, we resolve the dense cluster core for the first time and are able to extract spectra of its entire massive star population. We develop an automated spectral classification scheme based on the equivalent widths of spectral lines in the red part of the spectrum. Results. We characterize the massive star content of the core of NGC 330 which contains more than 200 B stars, two O stars, 6 A-type supergiants and 11 red supergiants. We find a lower limit on the Be star fraction of 32 ± 3% in the whole sample. It increases to at least 46 ± 10% when only considering stars brighter than V = 17 mag. We estimate an age of the cluster core between 35 and 40 Myr and a total cluster mass of 88 +17 −18 × 10 3 M . Conclusions. We find that the population in the cluster core is different than the population in the outskirts: while the stellar content in the core appears to be older than the stars in the outskirts, the Be star fraction and the observed binary fraction are significantly higher. Furthermore, we detect several BiP candidates that will be subject of future studies.

Effects of Close Binary Evolution on the Main-sequence Morphology of Young Star Clusters

“…3), as Be stars (Pols et al 1991). Recent photometric and spectroscopic results show that a significant fraction of the MS stars in young clusters ( ∼ < 100 Myr) within two to three magnitudes below the turnoff are Be stars (Milone et al 2018;Bodensteiner et al 2019). As demonstrated by our animation (Fig.…”

“…Recently, photometric studies using the Hubble Space Telescope revealed that the MS of young and intermediate age star clusters (14-600 Myr) in the Magellanic Clouds and in the Galaxy is split into two distinct MSs, as well as an extended MS turnoff region (D'Antona et al 2017;Milone et al 2018;Li et al 2019, and references therein). Furthermore, the young clusters show distinct groups of emission-line stars, extending more than two magnitudes below the turnoff (Milone et al 2018), most of which are spectroscopically identified as Be stars (Bodensteiner et al 2019).…”

A naked-eye triple system with a nonaccreting black hole in the inner binary

“…This is not completely implausible: If Be stars owe their rapid rotation to spin-up by mass overflow from a now underluminous companion (e.g., Langer et al 2020a, and references therein) a resulting rejuvenation of the outer Be star is one possible explanation. Some blue stragglers in open clusters have been reported to show Hα in emission and may be classical Be stars (Aidelman et al 2018;Bodensteiner et al 2020).…”

MUSE crowded field 3D spectroscopy in NGC 300 II. Quantitative spectroscopy of BA-type supergiants

“…The first surveys of the massive star populations in nearby galaxies have already started with MUSE. Demonstrations were made for dense star clusters in the LMC (Castro et al 2018(Castro et al , 2021 and SMC (Bodensteiner et al 2020), and for wider fields in the Sculptor Group galaxies NGC 300 (Roth et al 2018, henceforth Paper I) and NGC7793 (Wofford et al 2020).…”