A Spectroscopic Survey of Metal-poor OB Stars in Local Dwarf Galaxy NGC 3109
As JWST uncovers increasingly strong evidence that metal-poor, massive stars in early galaxies dominated reionization, observational constraints on the properties of such stars are more relevant than ever before. However, spectra of individual O- and B-type stars are rare at the relevant metalliciti...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/adc923 |
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| author | Abby Mintz O. Grace Telford Evan N. Kirby John Chisholm Kristen B. W. McQuinn Danielle A. Berg |
| author_facet | Abby Mintz O. Grace Telford Evan N. Kirby John Chisholm Kristen B. W. McQuinn Danielle A. Berg |
| author_sort | Abby Mintz |
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| description | As JWST uncovers increasingly strong evidence that metal-poor, massive stars in early galaxies dominated reionization, observational constraints on the properties of such stars are more relevant than ever before. However, spectra of individual O- and B-type stars are rare at the relevant metallicities (≲0.2 Z _⊙ ), leaving models of stellar evolution and ionizing flux poorly constrained by data in this regime. We present new medium-resolution ( R ∼ 4000) optical spectra of 17 OB stars in the local low-metallicity (0.12 Z _⊙ ) dwarf galaxy NGC 3109. We assign spectral types to the stars and present new criteria for selecting O stars using optical and near-UV photometry from Hubble Space Telescope imaging. We fit the spectra and photometry with grids of stellar atmosphere models to measure stellar temperatures, surface gravities, luminosities, radii, and masses. We find evidence of strong mass loss via radiation-driven stellar winds in two O stars, one of which is the hottest, youngest, and most massive star confirmed in the host galaxy to date. Though its spectrum does not meet conventional Wolf–Rayet spectral classification criteria, this metal-poor O5 If star produces strong He ii λ 4686 emission, and its evolutionary status is ambiguous. This work nearly doubles the number of OB stars with measured parameters in NGC 3109, including 12 stars with no previously reported parameters, five with no published spectroscopy, and four binary candidates. This large sample of OB stellar parameters provides a new observational testbed to constrain the stellar astrophysics that drove cosmic reionization and influenced the evolution of the earliest galaxies. |
| format | Article |
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| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-b6529fd08e7f456987a69a730b44843e2025-08-20T01:52:38ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01985215010.3847/1538-4357/adc923A Spectroscopic Survey of Metal-poor OB Stars in Local Dwarf Galaxy NGC 3109Abby Mintz0https://orcid.org/0000-0002-9816-9300O. Grace Telford1https://orcid.org/0000-0003-4122-7749Evan N. Kirby2https://orcid.org/0000-0001-6196-5162John Chisholm3https://orcid.org/0000-0002-0302-2577Kristen B. W. McQuinn4https://orcid.org/0000-0001-5538-2614Danielle A. Berg5https://orcid.org/0000-0002-4153-053XDepartment of Astrophysical Sciences, Princeton University , 4 Ivy Lane, Princeton, NJ 08544, USA ; abby.mintz@princeton.eduDepartment of Astrophysical Sciences, Princeton University , 4 Ivy Lane, Princeton, NJ 08544, USA ; abby.mintz@princeton.edu; The Observatories of the Carnegie Institution for Science , 813 Santa Barbara Street, Pasadena, CA 91101, USA; Department of Physics and Astronomy, Rutgers University , 136 Frelinghuysen Road, Piscataway, NJ 08854, USADepartment of Physics and Astronomy, University of Notre Dame , 225 Nieuwland Science Hall, Notre Dame, IN 46556, USADepartment of Astronomy, The University of Texas at Austin , 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USADepartment of Physics and Astronomy, Rutgers University , 136 Frelinghuysen Road, Piscataway, NJ 08854, USA; Space Telescope Science Institute , 3700 San Martin Drive, Baltimore, MD 21218, USADepartment of Astronomy, The University of Texas at Austin , 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USAAs JWST uncovers increasingly strong evidence that metal-poor, massive stars in early galaxies dominated reionization, observational constraints on the properties of such stars are more relevant than ever before. However, spectra of individual O- and B-type stars are rare at the relevant metallicities (≲0.2 Z _⊙ ), leaving models of stellar evolution and ionizing flux poorly constrained by data in this regime. We present new medium-resolution ( R ∼ 4000) optical spectra of 17 OB stars in the local low-metallicity (0.12 Z _⊙ ) dwarf galaxy NGC 3109. We assign spectral types to the stars and present new criteria for selecting O stars using optical and near-UV photometry from Hubble Space Telescope imaging. We fit the spectra and photometry with grids of stellar atmosphere models to measure stellar temperatures, surface gravities, luminosities, radii, and masses. We find evidence of strong mass loss via radiation-driven stellar winds in two O stars, one of which is the hottest, youngest, and most massive star confirmed in the host galaxy to date. Though its spectrum does not meet conventional Wolf–Rayet spectral classification criteria, this metal-poor O5 If star produces strong He ii λ 4686 emission, and its evolutionary status is ambiguous. This work nearly doubles the number of OB stars with measured parameters in NGC 3109, including 12 stars with no previously reported parameters, five with no published spectroscopy, and four binary candidates. This large sample of OB stellar parameters provides a new observational testbed to constrain the stellar astrophysics that drove cosmic reionization and influenced the evolution of the earliest galaxies.https://doi.org/10.3847/1538-4357/adc923OB starsMassive starsEarly-type starsStellar windsStellar atmospheres |
| spellingShingle | Abby Mintz O. Grace Telford Evan N. Kirby John Chisholm Kristen B. W. McQuinn Danielle A. Berg A Spectroscopic Survey of Metal-poor OB Stars in Local Dwarf Galaxy NGC 3109 The Astrophysical Journal OB stars Massive stars Early-type stars Stellar winds Stellar atmospheres |
| title | A Spectroscopic Survey of Metal-poor OB Stars in Local Dwarf Galaxy NGC 3109 |
| title_full | A Spectroscopic Survey of Metal-poor OB Stars in Local Dwarf Galaxy NGC 3109 |
| title_fullStr | A Spectroscopic Survey of Metal-poor OB Stars in Local Dwarf Galaxy NGC 3109 |
| title_full_unstemmed | A Spectroscopic Survey of Metal-poor OB Stars in Local Dwarf Galaxy NGC 3109 |
| title_short | A Spectroscopic Survey of Metal-poor OB Stars in Local Dwarf Galaxy NGC 3109 |
| title_sort | spectroscopic survey of metal poor ob stars in local dwarf galaxy ngc 3109 |
| topic | OB stars Massive stars Early-type stars Stellar winds Stellar atmospheres |
| url | https://doi.org/10.3847/1538-4357/adc923 |
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