Astronomers identify 19 new Wolf-Rayet stars in Andromeda Galaxy

Wolf-Rayet (WR) stars are not only hot, bright, and massive. They are also in an advanced stage of evolution, losing mass at an incredible rate.
Mrigakshi Dixit
Representational image of luminous, hot star Wolf-Rayet 124.
Representational image of luminous, hot star Wolf-Rayet 124.

NASA, ESA, CSA, STScI, Webb ERO Production Team 

While surveying the neighboring Andromeda galaxy, astronomers discovered a new batch of Wolf-Rayet stars. 

Some huge stars in galaxies may develop into Wolf-Rayet stars before going supernova. That’s why, Wolf-Rayet stars are intriguing candidates for studying the universe's evolution. 

By definition, Wolf-Rayet (WR) stars are hot, bright, and massive stars that are in an advanced stage of evolution and shedding mass at an incredibly high rate. 

The catchy name is taken from two astronomers, Charles-Joseph-Étienne Wolf and Georges-Antoine-Pons Rayet, who first categorized this type of star in 1867.

In a recent survey, astronomers Kathryn F. Neugent of the Harvard-Smithsonian Center for Astrophysics (CfA) and Philip Massey of the Lowell Observatory discovered roughly 19 such stars using the Lowell Discovery Telescope (LDT) in Arizona.

This is not the first time such stars have been identified in Andromeda. Over a hundred of them have been discovered in the galaxies out there, most of which come from the Milky Way.

The discovery of a new batch 

Astronomers detected 19 new stars using a Large Monolithic Imager (LMI) equipped on this telescope.

"Our improved imaging data and spectroscopic follow-up confirmed 19 new WRs across three small fields in M31 [Andromeda galaxy]," mentioned the paper, which has been uploaded to the preprint server. 

At first, the team identified 30 potential WR candidates in late 2021. The team went on to conduct a detailed spectroscopic analysis in 2022 using the 6.5-m MMT telescope, which is operated by the Multiple Mirror Telescope Observatory (MMTO). 

This subsequent observation confirmed the presence of 19 Wolf-Rayet stars among the 30 candidates. 

According to the study, the newly discovered WRs in the Andromeda galaxy are significantly dimmer compared to previously identified ones. Reportedly, the newly-identified WR stars were not noticed in the previous Andromeda galaxy-wide survey owing to a lack of observational sensitivity. 

The authors believe numerous more Wolf-Rayet stars in the Andromeda galaxy are waiting to be identified. 

One challenge is that WRs are only concentrated near their birthplaces rather than elsewhere in the galaxy. As a result, astrophysicists must first pinpoint such regions to locate more similar stars in our neighboring galaxy. 

The findings have been uploaded to the pre-print server arXiv.

Study abstract:

The evolved massive star populations of the Local Group galaxies are generally thought to be well-understood. However, recent work suggested that the Wolf-Rayet (WR) content of M31 may have been underestimated. We, therefore, began a pilot project to search for new WRs in M31 and re-examine the completeness of our previous WR survey finished almost a decade prior. Our improved imaging data and spectroscopic follow-up confirmed 19 new WRs across three small fields in M31. These newly discovered WRs are generally fainter than the previously known sample due to slightly increased reddening as opposed to intrinsic faintness. From these findings, we estimate that there are another ~60 WRs left to be discovered in M31; however, the overall ratio of WN-type (nitrogen-rich) to WC-type (carbon-rich) WRs remains unchanged with our latest additions to the M31 WR census. We are in the process of extending this pilot WR survey to include the rest of M31, and a more complete population will be detailed in our future work.

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