A New Approach to Identifying Red Supergiant Stars in Metal-poor Galaxies: A Case Study of NGC 6822
A complete sample of red supergiant (RSG) stars is important for studying their properties. Identifying RSGs in extragalactic fields first requires removing the Galactic foreground dwarfs. The color–color diagram (CCD) method, specifically using r − z / z − H and J − H / H − K , has proven successfu...
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IOP Publishing
2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ada1d4 |
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| author | Zhi-wen Li Ming Yang Biwei Jiang Yi Ren |
| author_facet | Zhi-wen Li Ming Yang Biwei Jiang Yi Ren |
| author_sort | Zhi-wen Li |
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| description | A complete sample of red supergiant (RSG) stars is important for studying their properties. Identifying RSGs in extragalactic fields first requires removing the Galactic foreground dwarfs. The color–color diagram (CCD) method, specifically using r − z / z − H and J − H / H − K , has proven successful in several studies. However, in metal-poor galaxies, faint RSGs will mix into the dwarf branch in the CCD and would be removed, leading to an incomplete RSG sample. This work attempts to improve the CCD method in combination with the Gaia astrometric measurement to remove foreground contamination in order to construct a complete RSG sample in metal-poor galaxies. The empirical regions of RSGs in both CCDs are defined and modified by fitting the locations of RSGs in galaxies with a range of metallicity. The metal-poor galaxy NGC 6822 is taken as a case study for its low metallicity ([Fe/H] ≈ −1.0) and moderate distance (about 500 kpc). In the complete sample, we identify 1184 RSG, 1559 oxygen-rich AGB (O-AGBs), 1075 carbon-rich AGB (C-AGBs), and 140 extreme AGB (x-AGBs) candidates, with a contamination rate of approximately 20.5%, 9.7%, 6.8%, and 5.0%, respectively. We also present a pure sample, containing only the sources away from the dwarf branch, which includes 843 RSG, 1519 O-AGB, 1059 C-AGB, and 140 x-AGB candidates, with a contamination rate of approximately 6.5%, 8.8%, 6.1%, and 5.0%, respectively. About 600 and 450 RSG candidates are newly identified in the complete and pure samples, respectively, compared to the previous RSG sample in NGC 6822. |
| format | Article |
| id | doaj-art-ee498d97b52b44adbe13a7a5539aae2a |
| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-ee498d97b52b44adbe13a7a5539aae2a2025-01-28T07:57:43ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01979220810.3847/1538-4357/ada1d4A New Approach to Identifying Red Supergiant Stars in Metal-poor Galaxies: A Case Study of NGC 6822Zhi-wen Li0https://orcid.org/0009-0003-3321-6393Ming Yang1https://orcid.org/0000-0001-8247-4936Biwei Jiang2https://orcid.org/0000-0003-3168-2617Yi Ren3https://orcid.org/0000-0003-1218-8699Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University , Beijing 102206, People’s Republic of China; School of Physics and Astronomy, Beijing Normal University , Beijing 100875, People’s Republic of ChinaKey Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences , Beijing 100101, People’s Republic of ChinaInstitute for Frontiers in Astronomy and Astrophysics, Beijing Normal University , Beijing 102206, People’s Republic of China; School of Physics and Astronomy, Beijing Normal University , Beijing 100875, People’s Republic of ChinaDepartment of Astronomy, College of Physics and Electronic Engineering, Qilu Normal University , Jinan 250200, People’s Republic of ChinaA complete sample of red supergiant (RSG) stars is important for studying their properties. Identifying RSGs in extragalactic fields first requires removing the Galactic foreground dwarfs. The color–color diagram (CCD) method, specifically using r − z / z − H and J − H / H − K , has proven successful in several studies. However, in metal-poor galaxies, faint RSGs will mix into the dwarf branch in the CCD and would be removed, leading to an incomplete RSG sample. This work attempts to improve the CCD method in combination with the Gaia astrometric measurement to remove foreground contamination in order to construct a complete RSG sample in metal-poor galaxies. The empirical regions of RSGs in both CCDs are defined and modified by fitting the locations of RSGs in galaxies with a range of metallicity. The metal-poor galaxy NGC 6822 is taken as a case study for its low metallicity ([Fe/H] ≈ −1.0) and moderate distance (about 500 kpc). In the complete sample, we identify 1184 RSG, 1559 oxygen-rich AGB (O-AGBs), 1075 carbon-rich AGB (C-AGBs), and 140 extreme AGB (x-AGBs) candidates, with a contamination rate of approximately 20.5%, 9.7%, 6.8%, and 5.0%, respectively. We also present a pure sample, containing only the sources away from the dwarf branch, which includes 843 RSG, 1519 O-AGB, 1059 C-AGB, and 140 x-AGB candidates, with a contamination rate of approximately 6.5%, 8.8%, 6.1%, and 5.0%, respectively. About 600 and 450 RSG candidates are newly identified in the complete and pure samples, respectively, compared to the previous RSG sample in NGC 6822.https://doi.org/10.3847/1538-4357/ada1d4Red supergiant starsEvolved starsStellar classificationAsymptotic giant branch stars |
| spellingShingle | Zhi-wen Li Ming Yang Biwei Jiang Yi Ren A New Approach to Identifying Red Supergiant Stars in Metal-poor Galaxies: A Case Study of NGC 6822 The Astrophysical Journal Red supergiant stars Evolved stars Stellar classification Asymptotic giant branch stars |
| title | A New Approach to Identifying Red Supergiant Stars in Metal-poor Galaxies: A Case Study of NGC 6822 |
| title_full | A New Approach to Identifying Red Supergiant Stars in Metal-poor Galaxies: A Case Study of NGC 6822 |
| title_fullStr | A New Approach to Identifying Red Supergiant Stars in Metal-poor Galaxies: A Case Study of NGC 6822 |
| title_full_unstemmed | A New Approach to Identifying Red Supergiant Stars in Metal-poor Galaxies: A Case Study of NGC 6822 |
| title_short | A New Approach to Identifying Red Supergiant Stars in Metal-poor Galaxies: A Case Study of NGC 6822 |
| title_sort | new approach to identifying red supergiant stars in metal poor galaxies a case study of ngc 6822 |
| topic | Red supergiant stars Evolved stars Stellar classification Asymptotic giant branch stars |
| url | https://doi.org/10.3847/1538-4357/ada1d4 |
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