by A team of Italian astronomers has recently conducted high-resolution spectroscopic observations of Messier 39, a young open cluster located in the constellation Cygnus. The results of their study, featured in a paper published on the pre-print server arXiv, provide valuable insights into the cluster’s chemical composition.
Open clusters (OCs) are groups of stars that are loosely bound to each other and formed from the same giant molecular cloud. In the Milky Way alone, over 1,000 OCs have been discovered, and scientists continue to search for more in order to better understand the formation and evolution of our galaxy.
Messier 39, also known as M39 or NGC 7092, is a relatively young open cluster located approximately 1,000 light years away. With a linear tidal radius of 28 light years and a mass of around 232 solar masses, this cluster is estimated to be around 280 million years old.
Despite its discovery almost three centuries ago, Messier 39 has not been subject to high-resolution spectroscopy until now, leaving its chemical composition a mystery. Therefore, a team of astronomers led by Javier Alonso-Santiago from the Catania Astrophysical Observatory in Italy decided to conduct detailed observations of this cluster using the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere spectrograph (HARPS-N) and the Fiber-fed Echelle Spectrograph (FIES).
The researchers began by identifying 260 likely members of Messier 39 within a 250 arcminute radius around the nominal cluster center. Among these members, it was discovered that three were double-lined spectroscopic binary systems, while no evolved stars were found within the sample. By analyzing the spatial distribution of these members, the distance to Messier 39 was estimated to be approximately 980 light years.
Next, the astronomers measured the radial and projected rotational velocities of the stars in their sample. They discovered that most of the stars had rotational velocities ranging from -6 to -3 km/s, with a mean radial velocity for Messier 39 calculated to be -5.46 km/s. The team also estimated the extinction and atmospheric parameters of these stars.
The chemical analysis of the nine coolest stars in the sample (with effective temperatures below 7,100 K) revealed abundances for 21 elements. It was found that Messier 39 has a solar-like metallicity (0.04 dex) and that the investigated stars possess a chemical composition similar to that of the sun.
However, the researchers noted that sodium exhibited a lower abundance in the studied sample, while sulfur and heavier elements, particularly barium, displayed higher values. Furthermore, it was observed that Messier 39 exhibits solar-like mean ratios for alpha elements and iron-peak elements to iron, with a slightly overabundant ratio for neutron-capture elements.
Based on these findings, the scientists concluded that the chemical composition of Messier 39 is fully compatible with that of the Galactic thin disk. This study provides valuable insights into the formation and evolution of open clusters within our galaxy, contributing to a deeper understanding of the cosmos.
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