Using NASA’s Kepler spacecraft and ESA’s Gaia probe, an international team of astronomers conducted an astronomical survey of six massive stars in the open star cluster NGC 6866. The study, presented August 24 on the preprint server arXiv, sheds more light on the properties of these massive stars and of the cluster itself. Open star clusters (OCs), formed from the same massive molecular cloud, are groups of stars weakly bound together by gravity. To date, more than 1,000 of them have been discovered in the Milky Way, and scientists are always looking for more in the hope of finding many of these star groups. Expanding the list of known open galaxy clusters and studying them in detail could be important for improving our understanding of the formation and evolution of our galaxy.
Discovered in 1783, NGC 6866 (also known as OCL 183) is a relatively young OC (estimated between 480 and 780 million years old) in the constellation Swan, at a distance of about 3,900 light-years. However, although the cluster has been known for more than two centuries, many of its properties, including its age, remain uncertain. This is why a team of astronomers led by Karsten Brogaard from the University of Bologna in Italy decided to identify and study the pulsating giant members of the open star cluster NGC 6866, using them. to limit cluster characteristics. To this end, they analyzed the results of Gaia’s Data Release 3 (DR3) and the photometric light curves from the Kepler spacecraft. “We identified the six colossal members of NGC 6866 through photometric, specific motion and parallax from Gaia measurements and spectroscopic documentation. These are combined with asteroid seismic measurements that we obtained from photometric data from the Kepler mission to five stars,” the researchers explain.
Astronomers have selected and studied six massive stars in the helium core combustion (HeCB) stage, namely: KIC 8461659, KIC 8329894, KIC 8395903, KIC 8264549, KIC 7991875 and KIC 8264592. All of these stars have similar effective temperatures, to some extent. is 5100K. The study found that the six giant planets have an average radius of about 10.1 times the radius of the Sun and an average mass of about 2.8 times the mass of the Sun. The astronomers point out that the stars studied are therefore significantly smaller than predicted by current one-dimensional stellar models. According to the newspaper, the six stars will be between 443 and 580 million years old. By comparing all the collected data with the stellar model concurrency, the age of NGC 6866 was estimated to be 430 million years, so the cluster turned out to be younger than previously thought.