Indian astronomers explore open cluster NGC 6940 with AstroSat

Using the AstroSat spacecraft, astronomers from the Birla Institute of Technology and Science in Pilani, India, studied a nearby open cluster NGC 6940. Results of the observation campaign, published December 21 on the pre-print. arXivshed further light on the stellar properties and populations of this cluster.

Open clusters (OC), formed from the same giant molecular cloud, are groups of a few dozen to a few hundred stars weakly gravitationally bound to each other. To date, more than 1,000 OCs have been identified in the Milky Way. The detailed study of these stellar groupings could prove essential to improve our understanding of the formation and evolution of our galaxy.

Discovered in 1784, NGC 6940 (also known as Melotte 232) is an open cluster located in the constellation Vulpecula, at a distance of approximately 2,500 light years. The age of the cluster is estimated at 720 million years and its metallicity is close to the sun.

Previous observations of NGC 6940 revealed that it hosts several populations of exotic stars, apart from normal single and binary stars, such as blue stragglers (BSS), blue prowlers (BL), yellow stragglers ( YSS) and red clusters (RC). ) stars. However, although many studies on this OC have been carried out, these exotic stars have not yet been studied in depth.

Recently, astronomers Anju Panthi and Kaushar Vaidya used AstroSat’s Ultraviolet Imaging Telescope (UVIT) to take a closer look at NGC 6940, with the primary goal of gathering more information about its exotic stellar content. They also used data from ESA’s Gaia satellite to identify cluster members.

“This cluster was observed with the Ultraviolet Imaging Telescope (UVIT) on board AstroSat, which has the ability to detect exotic objects and their hot companions when combined with other multi-length data from wave,” the researchers explained.

In total, astronomers identified 492 members of NGC 6940, and 16 of them turned out to be exotic stars. In particular, they found 11 candidate blue stars, two yellow lagging stars, two red clump stars, and one blue lagging star.

Additionally, three BL candidates were found to most likely have white dwarfs as preferred companions. Both YSS stars have sdB stars as likely companions and one of the identified RC stars has a white dwarf companion.

According to the study, NGC 6940 shows signs of massive segregation, suggesting that dynamic evolution has occurred within the cluster. Massive single stars exhibit the highest degree of segregation, followed by binary main sequence (MS) populations of equal mass, and then low-mass single stars.

Additionally, observations revealed the presence of an extended main sequence stopping function (eMSTO) in NGC 6940. Astronomers speculate that the age distribution of stars is one of the factors contributing to the observed eMSTO . However, they do not exclude the possibility that the effect of stellar rotation and dust absorption contributes.

The paper’s authors also estimated the core radius of NGC 6940, which was calculated to be 9.8 arc minutes, and its tidal radius was measured to be 37.5 arc minutes.

© 2023 Science X Network