Researchers are exploring the properties of globular cluster NGC 6355

The research explores the properties of globular cluster NGC 6355

F438W/F555W collect a color image from the HST WFC3 camera of NGC 6355. Credit: Souza et al., 2023.

An international team of astronomers has performed a chrono-dynamic and chemical analysis of a galactic globular cluster known as NGC 6355. The results of the study, presented in a paper published Jan. 12 on arXiv Preprint server, providing important insights into the properties and chemical composition of this group.

Globular clusters (GCs) are tightly bound groups of stars that orbit galaxies. Astronomers view them as natural laboratories that enable studies of the evolution of stars and galaxies. Especially, spherical clusters It could help researchers better understand the formation and evolution history of early galaxies, since the origin of GCs appears to be closely linked to periods of intense star formation.

At a distance of about 28,300 km light years Far from Earth, NGC 6355 (also known as GCl-63 or ESO 519-SC15) is a globular cluster in the constellation of Ophiuchus. It is a well-known group that has been studied since the 20th century. Previous observations of NGC 6355 found it to have a relatively high mass of around 101,000 solar masses, redness is at a level of 0.82 and metallicity is approximately -1.46. The absolute age of the group is estimated at 13.2 billion years.

Recently, a group of Astronomy scientists Led by Stefano O. Souza of the University of São Paulo in Brazil, he has studied NGC 6355 with the main goal of shedding more light on its history and properties.

“In the current work, we combine chemical information with the photodynamic and dynamic properties of the cluster to constrain its history. Chemical information It is based on a UVES spectrometer (Dekker et al, 2000) in FLAMES-UVES mode in the ESO-VLT, photometry on HST data, and the dynamical properties are provided by orbital integration using the McMillan (2017) galactic potential,” the researchers explained.

Overall, the team analyzed the globular cluster NGC 6355 in the context of the evolution of the galactic bulge. They performed an in-depth and careful analysis, including photometry, chemical abundances, and dynamics.

The study found that NGC 6355 has a metallicity of 1.39, confirming that it is one of the most metal-poor clusters of galactic bulges. The mean abundance ratio of alpha elements to iron in NGC 6355 was measured to be 0.37, indicating enrichment from type II supernovae. Overall, the astronomers concluded that NGC 6355’s abundance pattern is consistent with RR Lyrae stars in the bulge and well-studied in situ GCs.

The research confirmed NGC 6355 to be about 13.2 billion years old, and refined the distance as it turned out that the cluster is much closer than previously thought – about 27,800 light-years away. Furthermore, NGC 6355’s orbital parameters, and its extinction coefficient of 2.84, indicate that the cluster is currently confined within the volume of the galactic bulge.

The paper’s authors conclude that this GC appears to have originated from a major bulge ancestor, with little possibility of an ex situ origin; However, more spectral data of the cluster’s stars are needed to confirm this.

more information:
Stefano O. Souza et al., Chrono-chemodynamical analysis of globular cluster NGC 6355: the search for the building blocks of the bulge, arXiv (2023). doi: 10.48550/arxiv.2301.05227

Journal information:

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