Discovery of a Weak CN Spectral Absorption Feature in Red Supergiant Stars in the Andromeda (M31) and Triangulum (M33) Galaxies
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| Main Authors: | , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Guhathakurta, Puragra Filho, Douglas Grion Bhattacharya, Antara R. Cullinane, Lara R. Dalcanton, Julianne J. Gilbert, Karoline M. Girardi, Leo Kamath, Anika Kirby, Evan N. Maheshwari, Arya Marigo, Paola Masegian, Alexandra Quirk, Amanda C. N. Raikar, Rachel Rinehart V, Stanley M. Rodriguez, Caelum J. Williams, Benjamin F. |
| author_facet | Guhathakurta, Puragra Filho, Douglas Grion Bhattacharya, Antara R. Cullinane, Lara R. Dalcanton, Julianne J. Gilbert, Karoline M. Girardi, Leo Kamath, Anika Kirby, Evan N. Maheshwari, Arya Marigo, Paola Masegian, Alexandra Quirk, Amanda C. N. Raikar, Rachel Rinehart V, Stanley M. Rodriguez, Caelum J. Williams, Benjamin F. |
| contents | Using Keck DEIMOS spectra of stars in the Andromeda (M31) and Triangulum (M33) galaxies, selected from the large multi-band (near ultraviolet, visible light, and near infrared) Hubble Space Telescope surveys PHAT and PHATTER, respectively, we have identified a subset of stars that contain a previously unnoticed weak spectral absorption feature around 8000 Angstrom (0.8 micron). This absorption feature appears to be associated with the cyanogen (CN) molecule. Strong CN spectral absorption is a standard feature of carbon stars, which are thought to be intermediate mass (2-3 ~ M_sun) stars with C/O > 1 in the thermally-pulsating asymptotic giant branch phase of stellar evolution. However, the stars that are the focus of this paper are characterized by a weak version of this CN spectral absorption feature in a spectrum that is otherwise dominated by normal O-rich spectral absorption lines such as TiO and/or the Ca near infrared triplet. We have dubbed these stars "weak CN" stars. We present an automated method for identifying weak CN stars in M31 and M33, and examine their photometric properties in relation to model isochrones and stellar tracks. We find that weak CN stars tend to be fairly localized in color-magnitude space, and appear to be red supergiant stars with masses ranging from 5-10 M_sun, overall lifetimes of about 40-50 Myr, and currently in the core He burning phase of stellar evolution. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_04291 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Discovery of a Weak CN Spectral Absorption Feature in Red Supergiant Stars in the Andromeda (M31) and Triangulum (M33) Galaxies Guhathakurta, Puragra Filho, Douglas Grion Bhattacharya, Antara R. Cullinane, Lara R. Dalcanton, Julianne J. Gilbert, Karoline M. Girardi, Leo Kamath, Anika Kirby, Evan N. Maheshwari, Arya Marigo, Paola Masegian, Alexandra Quirk, Amanda C. N. Raikar, Rachel Rinehart V, Stanley M. Rodriguez, Caelum J. Williams, Benjamin F. Solar and Stellar Astrophysics Astrophysics of Galaxies Using Keck DEIMOS spectra of stars in the Andromeda (M31) and Triangulum (M33) galaxies, selected from the large multi-band (near ultraviolet, visible light, and near infrared) Hubble Space Telescope surveys PHAT and PHATTER, respectively, we have identified a subset of stars that contain a previously unnoticed weak spectral absorption feature around 8000 Angstrom (0.8 micron). This absorption feature appears to be associated with the cyanogen (CN) molecule. Strong CN spectral absorption is a standard feature of carbon stars, which are thought to be intermediate mass (2-3 ~ M_sun) stars with C/O > 1 in the thermally-pulsating asymptotic giant branch phase of stellar evolution. However, the stars that are the focus of this paper are characterized by a weak version of this CN spectral absorption feature in a spectrum that is otherwise dominated by normal O-rich spectral absorption lines such as TiO and/or the Ca near infrared triplet. We have dubbed these stars "weak CN" stars. We present an automated method for identifying weak CN stars in M31 and M33, and examine their photometric properties in relation to model isochrones and stellar tracks. We find that weak CN stars tend to be fairly localized in color-magnitude space, and appear to be red supergiant stars with masses ranging from 5-10 M_sun, overall lifetimes of about 40-50 Myr, and currently in the core He burning phase of stellar evolution. |
| title | Discovery of a Weak CN Spectral Absorption Feature in Red Supergiant Stars in the Andromeda (M31) and Triangulum (M33) Galaxies |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2504.04291 |