Astronomers investigate chemical composition of multiple stellar populations in NGC 2808

Utilizing ESO’s Very Massive Telescope (VLT) and the Hubble House Telescope (HST), astronomers have inspected the globular cluster NGC 2808. Outcomes of the examine, revealed December 2 on the arXiv pre-print repository, shed extra mild on the chemical composition of a number of stellar populations on this cluster.

Globular clusters (GCs) are collections of tightly certain stars orbiting galaxies. Astronomers understand them as pure laboratories enabling research on the evolution of stars and galaxies. Specifically, globular clusters might assist researchers higher perceive the formation historical past and evolution of early kind galaxies, because the origin of GCs appears to be intently linked to intervals of intense star formation.

At a distance of about 31,300 light years, NGC 2808 is a Galactic GC within the constellation Carina. The cluster is estimated to be 10.2 billion years outdated, has a mass of roughly 742,000 solar lots, and its metallicity is at a degree of -1.14. Earlier observations of NGC 2808 have discovered that it hosts a minimum of three stellar populations.

A group of astronomers, led by Marília Gabriela Carlos of the College of Padua in Italy, determined to conduct a full chemical characterization of the distinct stellar populations in NGC 2808. For this objective they used VLT’s FLAMES/GIRAFFE spectrograph, in addition to HST’s two devices: the Utraviolet and Visible Channel of the Large Area Digicam 3 (UVIS/WFC3), and the Large Area Channel of the Superior Digicam for Surveys (WFC/ACS).

Pseudo two-color diagrams or chromosome maps (ChM) of NGC 2808 present that the cluster hosts 5 totally different stellar populations (designated from A to E). Excessive-resolution spectra from FLAMES/GIRAFFE allowed the astronomers to research 70 pink large department (RGB) and seven asymptotic large department (AGB) stars. They decided their stellar parameters and abundances for six parts: carbon, nitrogen, oxygen, aluminum, nickel and iron.

Usually, the analysis discovered that the sunshine parts of the investigated stars range from one stellar inhabitants to a different. The utmost inside elemental variations vary from about 0.7 dex in carbon, to 1.1 dex in nitrogen, and aluminum, and as much as greater than 1.3 dex in oxygen. In the case of the iron peak parts, they present negligible variation between the totally different populations. These outcomes are typical for a number of stellar populations within the pattern of recognized globular clusters.

Furthermore, the examine discovered that the celebrities from populations A and B have usually decrease content material of aluminum and nitrogen in distinction with larger abundances of oxygen and carbon. It turned out that whereas aluminum and nitrogen abundances grow to be step by step larger for populations C and D, reaching their highest values in inhabitants E, the abundances of oxygen and carbon grow to be systematically decrease. It was added that D and E are essentially the most helium-enriched populations and they don’t present important variations in mild parts.

The researchers famous that their observations detected one AGB star, designated N2808_2_9_wf, that’s strongly depleted in oxygen (per being helium-rich) and extremely enhanced in aluminum, which challenges present stellar evolution fashions.

“Our discovery, along with earlier spectroscopic proof of an AGB star related to the inhabitants D demonstrates that stars with excessive helium abundances can evolve into AGB. An identical conclusion comes from the ChMs of AGB stars, which reveals distinct populations of AGB stars which might be related to inhabitants D and presumably population E. These findings appear in distinction with the predictions of evolutionary fashions of the helium-rich stars, which ought to skip the AGB phase,” the authors of the paper defined.

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