Astronomers study the chemical composition of stellar populations in NGC 2808

(ORDO NEWS) — Using ESO’s Very Large Telescope (VLT) and the Hubble Space Telescope (HST), astronomers have studied the globular cluster NGC 2808.

The results of the study, shed light on the chemical composition of the stellar populations in this cluster.

The globular cluster NGC 2808 lies about 31,300 light-years away in the constellation Carina.

The cluster is estimated to be 10.2 billion years old, has a mass of approximately 742,000 solar masses, and has a metallicity of -1.14.

A group of astronomers from the University of Padua in Italy decided to study the chemical composition of the stellar populations located in NGC 2808.

The researchers found that the cluster contains five distinct stellar populations (labeled A through E).

The high-resolution spectra allowed astronomers to study 70 red giant branch (RGB) stars and 7 asymptotic giant branch (AGB) stars.

Scientists have determined the stellar parameters and the abundance of six elements: carbon, nitrogen, oxygen, aluminum, nickel and iron.

The study showed that the maximum internal vibrations of the elements range from about 0.7 dex in carbon to 1.1 dex in nitrogen and aluminum, and to more than 1.3 dex in oxygen.

When it comes to iron peak elements, they show little variation between different populations.

According to the study, stars from populations A and B tend to have lower aluminum and nitrogen abundances and higher oxygen and carbon abundances.

It turned out that while the content of aluminum and nitrogen gradually increases in populations C and D, reaching its highest values ​​in population E, the content of oxygen and carbon systematically decreases.

Also populations D and E are the most helium enriched populations and they do not show significant differences in light elements.

The researchers noted that the observations revealed one AGB star, designated N2808_2_9_wf, which is highly oxygen depleted (consistent with being rich in helium) and highly enriched in aluminum, challenging current models of stellar evolution.

According to the study, this discovery, along with previous spectroscopic data on the AGB star associated with the D population, demonstrates that helium-rich stars can evolve into AGBs.

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