Carbon- and oxygen-rich stars in MaStar: identification and classification

Lewis Hill, Claudia Maraston*, Daniel Thomas, Renbin Yan, Yanping Chen, Guy S. Stringfellow, Richard R. Lane, José G. Fernández-Trincado

*Corresponding author for this work

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Carbon- and Oxygen-rich stars populating the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase of stellar evolution are relevant contributors to the spectra of ∼1 Gyr old populations. Atmosphere models for these types are uncertain, due to complex molecules and mass-loss effects. Empirical spectra are then crucial, but samples are small due to the short (∼3 Myr) TP-AGB lifetime. Here we exploit the vastness of the MaNGA Stellar library MaStar (∼60 000 spectra) to identify C and O-rich type stars. We define an optical colour selection with cuts of (g - r) > 2 and (g - i) < 1.55(g - r) - 0.07, calibrated with known C- and O-rich spectra. This identifies C- and O-rich stars along clean, separated sequences. An analogue selection is found in V, R, I bands. Our equation identifies C-rich and O-rich spectra with predictive performance metric F1-scores of 0.72 and 0.74 (over 1), respectively. We finally identify 41 C- and 87 O-rich type AGB stars in MaStar, 5 and 49 of which do not have a SIMBAD counterpart. We also detect a sample of non-AGB, dwarf C-stars. We further design a fitting procedure to classify the spectra into broad spectral types, by using as fitting templates empirical C- and O-rich spectra. We find remarkably good fits for the majority of candidates and categorize them into C- and O-rich bins following existing classifications, which correlate to effective temperature. Our selection models can be applied to large photometric surveys (e.g. Euclid, Rubin). The classified spectra will facilitate future evolutionary population synthesis models.

Original languageEnglish
Pages (from-to)1534-1549
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date17 Apr 2024
Publication statusPublished - 1 May 2024


  • galaxies: stellar content
  • stars: AGB and post-AGB galaxies
  • stars: carbon
  • stars: fundamental parameters stars: statistics
  • surveys

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