Massive Star Discovery in M31 and M33 Galaxies

Using the LAMOST telescope, a group of Chinese astronomers has identified nearly 300 potential supergiant stars in the Andromeda and Triangulum galaxies, a discovery that could enhance our understanding of stellar evolution. Their study, released on October 25 via the preprint server arXiv, highlights the importance of these massive, evolved stars in improving theoretical models of how stars develop over time.

Supergiants are evolved, high-mass stars that are significantly larger and brighter than regular main-sequence stars. Although studying these stars is crucial for advancing knowledge of stellar life cycles, it is challenging because they are often located far from Earth, tend to exist in binary or multiple star systems, and are surrounded by dense interstellar clouds that obscure observation.

In the Local Group of galaxies, which includes our own Milky Way, examining supergiants in nearby galaxies like Andromeda (M31) and Triangulum (M33) can provide vital information to refine stellar evolution models. Despite progress in cataloging these stars, a complete census of supergiants in nearby galaxies has yet to be achieved.

The new study, led by Hao Wu from Peking University, presents the results of a focused survey to identify and catalog supergiants in the Andromeda and Triangulum galaxies. Using data from LAMOST's Data Release 10 (DR10), the researchers identified 199 supergiants in Andromeda and 84 in Triangulum. Of these, 84% of the Andromeda candidates met two independent selection criteria, making them highly likely to be actual supergiants, while only 67% of the candidates in Triangulum passed the same criteria.

The Andromeda sample consists of 134 yellow supergiants (YSGs), 62 blue supergiants (BSGs), and 3 red supergiants (RSGs), while in Triangulum, the counts are 53 YSGs, 28 BSGs, and 3 RSGs. The most massive supergiant star identified in both galaxies was found in Andromeda and is designated LAMOST J0043+4124, with a mass estimated to be over 40 solar masses.

This discovery is significant because it represents one of the largest samples of supergiants in the Andromeda and Triangulum galaxies with full optical wavelength coverage. The study's results are valuable for deepening our understanding of star formation and stellar evolution in different galactic environments. The findings provide new insights into how these massive stars form and evolve, contributing to a broader understanding of the life cycles of stars in the Local Group of galaxies.