Using the Very Large Telescope (VLT), an international team of astronomers conducted a spectroscopic study of a young open star cluster NGC 3293. The results of the study, published July 26 in arXiv’s pre-print repository, shed more light. the properties and chemical composition of this cluster.
Open clusters (OCs), formed from the same giant molecular cloud, are groups of stars loosely bound together by gravity. More than 1,000 of them have been discovered in the Milky Way so far, and scientists are still looking for more, hoping to find a variety of these stellar groups. Expanding the list of known galactics open clusters and studying them in detail could be crucial to improving our understanding of the formation and evolution of our galaxy.
Discovered in 1751, NGC 3293 (also known as the Gem Nebula) is a young (about 12 million years old) open TROS in the Carina Nebula, about 8,400 light-years from Earth. It is one of the most populous stellar aggregates in the Carina Nebula region and contains dozens of relatively undeveloped early B stars, along with some blue and red supergiants.
Although many photometric observations of NGC 3293 have been made, few spectroscopic studies of this cluster have been performed to date. Therefore, a group of astronomers led by Thierry Morel from the University of Liège in Belgium performed a spectroscopic analysis of NGC 3293, mainly to investigate the properties of its stellar B-type population in terms of spectral variability, chemical abundances and rotational speeds.
“We present a homogeneous analysis of the Galactic open cluster NGC 3293 based on GES [Gaia-ESO public survey] and FS VLT-FLAMES observations of approximately 160 B-type candidate members covering a wide range of physical properties. To our knowledge, it is the most comprehensive spectroscopic study of this cluster to date,” the researchers explained.
The study found that NGC 3293 has a Gauss-like velocity distribution of stars with peaks around 200-250 km/s. It turned out that most of the stars in the cluster appear to be rotating at about 50 to 60% of their critical speed. However, significantly lower spin rates were observed for more massive cluster members.
The age of NGC 3293 was estimated to be about 20 million years, so the cluster is older than previously thought. This means that NGC 3293 appears to be the oldest stellar aggregate in the Carina Nebula complex. The new result is based on a realistic distribution of spin rates and a detailed star-to-star correction for the effect of star rotation, while the old value was obtained from photometric studies using non-rotating isochrones.
The chemical analysis found that NGC 3293 contains no objects exposing nuclear-processed material to their surface, despite the fact that most of them are fast rotators. This may be due to the fact that most of the members of this cluster are most likely low-mass B dwarfs. The study also acknowledged the lack of highly nitrogen-enriched stars in NGC 3293, as only the two brightest B-type members of this cluster provide any evidence of mild nitrogen enrichment.
T. Morel et al, The Gaia-ESO survey: A spectroscopic study of the young open cluster NGC 3293. arXiv:2207.12792v1 [astro-ph.SR], arxiv.org/abs/2207.12792
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