Astronomers from the Aryabhatta Research Institute of Observational Sciences (ARIES) and India’s Physical Research Laboratory report the detection of 57 variable stars in the field of the open cluster NGC 381. The discovery was detailed in a paper published December 19 in the arXiv preprint server.

Open Clusters (OCs), formed from the same giant molecular cloud, are groups of stars loosely gravitationally bound to each other. So far, more than 1,000 of them have been discovered in the Milky Way, and scientists are still looking for more, hoping to find a variety of these stellar groupings. Expanding the list of known galactic OCs and studying them in detail could be crucial to improving our understanding of the formation and evolution of our galaxy. Detecting and studying variable stars, especially in OC environments, could offer important insights into aspects of stellar structure and evolution. It could also be useful for advancing our knowledge of the distance scale of the universe.

Located about 3,700 light-years away in the constellation Cassiopeia, NGC 381 (also known as Collinder 10) is an intermediate-age (about 447 million years old) scattered open cluster with a radius of about 15 light-years and a mass about 32.4 solar masses. Although several studies of NGC 381 have been conducted, very little is still known about its variable star content. That’s why a team of astronomers led by Jayanand Maurya of ARIES conducted the first study of the variability of NGC 381 and its surroundings. For this purpose, they employed the 1.3m Devasthal Fast Optical Telescope (DFOT) in India.

“We extensively observed the region of the open cluster NGC 381 in bands V and I for the study of variability. The region was observed using the DFOT 1.3m telescope equipped with a 2k × 2k CCD which has a large field of view of ∼18′ × 18′ suitable for searching for variability. Data was collected on 27 nights over a period of more than a year, from October 1, 2017 to January 14, 2019,” the researchers explained. As a result, the team identified a total of 57 periodic variable stars in the field of NGC 381, five of which turned out to be cluster members.Astronomers classified these variables based on the shape of their light curves, period, amplitude, and location on Hertzsprung-Russell (HR) diagrams.

According to the study, 10 of the 57 identified variables are eclipsing binary: eight of the WUMa (EW) type and two of the Algol (EA) type. Also in the sample are 15 rotational variable stars and two pulsating variables, one of the Delta Scuti type and one of the Gamma Doradus type. The remaining 30 variables could not be classified into any particular type; therefore, the researchers called them “miscellaneous type variables.” The authors of the article added that more time series data complemented by a spectroscopic study are needed to characterize these variables.

More information: Jayanand Maurya et al, Investigating stellar variability in the region of the open cluster NGC 381, arXiv (2022). DOI: 10.48550/arxiv.2212.09386