Observations detect hundreds of possible supergiant stars in two nearby galaxies

04 Nov 2024, 14:31 by Tomasz Nowakowski

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Left: Spatial distribution of supergiant candidates of M33 Herschel SPIRE 250 µm image. Right: Image of the southwestern corner of M33 in Galex NUV band. The white dashed box highlights an extended substructure from M33's disk, where three supergiant candidates are distributed. Credit: Wu et al., 2024.

Using the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), Chinese astronomers have identified nearly 300 candidate supergiant stars in the Andromeda and Triangulum galaxies. The finding was reported in a research paper published October 25 on the pre-print server arXiv.

Supergiants are evolved high-mass stars, larger and more luminous than main-sequence stars. Studying such objects is crucial for improving our understanding of stellar evolution; however, their observation is complicated due to the fact that they are relatively far away, tend to be born in binary or multiple systems, and are associated with dense clouds of interstellar material.

In particular, systematic research and studies of supergiants in the Local Group of galaxies could be essential to collect important clues in order to constrain theoretical models of stellar evolution. However, although significant progress has been made in searching for supergiants in nearby Local Group galaxies, their census is still not complete.

Now, a team of astronomers led by Hao Wu of Peking University in Beijing, China, has published the results of a new study that may greatly expand the list of known supergiants in the Milky Way's neighborhood. They conducted a systematic identification of supergiants in two Local Group galaxies: Messier 31 (Andromeda galaxy) and Messier 33 (Triangulum galaxy).

All in all, based on the dataset from LAMOST's data release 10 (DR10) Wu's team identified 199 supergiant stars in the Andromeda galaxy and 84 in the Triangulum galaxy. The astronomers noted that about 84% of the supergiant candidates in Andromeda have successfully passed through two independent selection criteria, indicating a high level of credibility as true supergiant members of this galaxy. When it comes to the Triangulum galaxy, this number is lower—approximately 67%.

According to the paper, the sample of identified candidates in the Andromeda galaxy consists of 134 yellow supergiants (YSGs), 62 blue supergiants (BSGs) and three red supergiants (RSGs). In the Triangulum galaxy, the researchers identified 53 YSGs, 28 BSGs and also three RSGs.

The most massive supergiant among the highly probable member stars in both galaxies turned out to be the one in Andromeda, designated LAMOST J0043+4124. The mass of this star was estimated to be over 40 solar masses.

Summing up the results, the authors of the paper underlined the importance of their newly published study.

"So far, this is one of the largest supergiant samples of M31/M33 with full optical wavelength coverage. This sample is valuable for understanding the star formation and stellar evolution under different environments," the scientists concluded.

More information: Hao Wu et al, The LAMOST Spectroscopic Survey of Supergiants in M31 and M33, arXiv (2024). DOI: 10.48550/arxiv.2410.19447

Journal information: arXiv