Astronomers find new family of atypical red giants in the Milky Way galaxy

An international team of astrophysicists, led by Universidad Católica del Norte (UCN) astronomer Dr. José Fernández-Trincado, identified a new population of red giant stars with chemical anomalies in our galaxy. The researchers used data obtained with the du Pont telescope at Las Campanas Observatory and Apache Point Observatory.

The Milky Way is populated by a large number of stellar conglomerates or globular clusters, many of which remain unexplored. The research identified 42 stars scattered in the disk, halo, and galactic bulge with chemical patterns totally different from the rest of the star field.

This new family of red giants possess atmospheric properties very identical to ordinary Milky Way stars in terms of surface temperatures, surface gravity, and iron content. However, they show atmospheres highly enriched in nitrogen and aluminum, high levels of which are not present in the galaxy's typical red giants.

Astronomer Dr. José Fernández-Trincado explains that their characteristics indicate that these stars were not born with the galactic disk, but originated in other environments similar to those formed in stellar conglomerates. "What we found was basically a needle in a haystack. These stars give us an indication that - in the early past of galaxy formation - there were violent events that destroyed globular clusters and where these stars were detached, they were debris or the first blocks of that destruction. We have found the traces that the early or primordial galaxy was a "cannibal"; it fed on the stellar material of those other systems in which they were gravitationally bound," describes the astronomer.

These new near-infrared observations made it possible to penetrate the dense columns of interstellar gas and dust to capture the atmospheres of the red giants in great detail. The researchers analyzed data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) advanced spectrograph, a mapping of the sky that complements data from the Sloan Foundation Telescope at Apache Point Observatory (USA) and the Irénée du Pont telescope at Las Campanas Observatory (Chile); creating a view of the entire Milky Way thanks to the combination of both hemispheres of the planet.

"These stars are potential candidates for being the remains of ancient globular clusters that died out in the high metallicity regime (metallicity levels typical of all the stars that form the disk of the galaxy), which were completely destroyed by the Milky Way -when it was still young- approximately 10 billion years ago", emphasizes Fernández-Trincado.

The stellar characteristics obtained in this research, in which also participated the astronomer Dr. Christian Moni Bidin of the UCN, provide clues to formulate the scenarios of the initial assembly of our galaxy.

This study, published under the title "APOGEE-2 Discovery of a Large Population of Relatively High-metallicity Globular Cluster Debris" in the scientific journal The Astrophysical Journal Letters, was led by the astrophysicist Dr. José G. Fernández-Trincado and counted with the international collaboration of astronomers Timothy Beers, Anna Queiroz, Cristina Chiappini, Dante Minniti, Beatriz Barbuy, Steven Majewski, Mario Ortigoza-Urdaneta, Christian Moni Bidin, Annie Robin, Edmundo Moreno, Leonardo Chaves-Velasquez, Sandro Villanova, Richard Lane, Kaike Pan and Dmitry Bizyaev.

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