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Using the 104-cm Sampurnanand optical telescope, Indian astronomers have performed photometric observations of an open cluster named King 6, which resulted in the detection of three new variable stars in the field of this cluster. The finding was April 25 on the arXiv pre-print 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 open clusters and studying them in detail could be crucial for improving our understanding of the formation and evolution of our galaxy.

King 6 is a Galactic open cluster at a distance of about 2,357 light years. Very little is known about this cluster as previous observations have only found that it has a color excess of 0.55, mass function slope at a level of 1.29 and its age was estimated to be some 200 million years.

That is why a team of astronomers led by Vaibhav Kumar Pandey of the Deen Dayal Upadhyaya Gorakhpur University in India decided to take a closer look at King 6. For this purpose, they employed the 104-cm Sampurnanand optical telescope. Their study was complemented by data from ESA's Gaia satellite and NASA's Transiting Exoplanet Survey Satellite (TESS).

As a result, Pandey's team identified three new variable stars, namely TIC 31624679716, TIC 31632068918, and TIC 3163212399. The newfound variables showcase variation in magnitude of approximately 0.02, 0.01, and 0.04 mag, and their periods are 46.70, 47.92, and 37.56 hours, respectively. The effective temperatures of these stars were measured to be within the range of 10,500–11,050 K.

Based on the obtained data, the astronomers classified the three stars as slow pulsating B-type (SPB) variables. In general, SPBs have periods between 0.30 and 5.0 days, while their magnitude variations are less than 0.1 mag.

Besides the detection of new variables, the study also provided more insights into the properties of King 6. It was found that the cluster has a radius of about 6.45 light years, while its tidal radius was calculated to be 10.37 light years. The distance to King 6 was measured to be 2,360 light years and its age was estimated to be 251 million years, which is generally consistent with previous findings.

Moreover, it turned out that the overall mass function slope for King 6 is approximately 0.57, therefore much less than previously thought, and the observations have found clear evidence of mass segregation within the cluster. The authors of the paper added that the relaxation time of King 6 is about six million years, which suggests that the cluster is dynamically relaxed.

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