Chilean researchers investigate chemical composition of spherical cluster NGC 6553

Using the Very Large Telescope (VLT), Chilean astronomers performed a chemical analysis of a sample of stars in the spherical cluster NGC 6553. Results of this study, available in an article published on March 12 on the arXiv pre-print server, sheds more light on the chemical composition of this group.

Globular clusters (GCs) are collections of strongly bound stars orbiting galaxies. Astronomers consider them to be natural laboratories that allow studies of the evolution of stars and galaxies. In particular, spherical clusters can help researchers better understand the formation history and evolution of early types of galaxies, as the origin of GCs is closely linked to periods of intense star formation.

NGC 6553 is approximately 19,500 light-years away and is a metal-rich GC in the bulge of the Milky Way. The group is about 13 billion years old and has a mass of about 235,000 solar masses. Although several studies have been conducted on NGC 6553, little is known about its chemical composition.

A team of astronomers, led by Carolina Montecinos of the University of Concepción, Chile, has now conducted a chemical analysis of NGC 6553 on a sample of more than 100 giant stars, examining the data mainly from the FLAMES / GIRAFFE spectrograph on VLT. The study was supplemented by results from VISTA Variables in the Vía Láctea (VVV) survey Data Release 2 (DR2) of ESA’s Gaia satellite.

“In this work, we realized a chemical analysis of the hump spherical cluster NGC 6553 into a sample of 116 giant stars, both in the horizontal branch and a giant branch, using the FLAMES / GIRAFFE spectrograph. (…) Then we realized a comparison between NGC 6553 and other nearby spherical spherical clusters, as well as with other galaxies spherical clusters and field stars from the hump, the disk and the halo of the Milky Way, ‘the researchers in the newspaper written.

The study found that the stars studied in NGC 6553 show the abundance of five alpha elements – oxygen, magnesium, silicon, calcium and titanium. This is consistent with all GCs in the Milky Way’s hump, as it also has a similar abundance of alpha elements.

Furthermore, a vertical anticoloration of sodium oxygen has been identified as there is a distribution in sodium but the variation in oxygen is minimal. Such anti-cholera occurs in other clusters of the galactic hump.

Furthermore, the research did not find an intrinsic variation in the content of alpha and iron peak elements. The astronomers have noted that this is consistent with the trend of galactic humpback stars, indicating a similar origin and evolution.

The average iron content of the sample stars in NGC 6553 was found to be -0.1. However, the study did not detect any significant distribution in the iron content.

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