Carbon Stars from Gaia Data Release 3 and the Space Density of Dwarf Carbon Stars
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1.
Clarkson University
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2.
University of California, Santa Cruz
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3.
Harvard-Smithsonian Center for Astrophysics
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4.
Wellesley College
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5.
California Institute of Technology
Abstract
Carbon stars (with atmospheric C/O > 1) range widely in temperature and luminosity, from low-mass dwarfs to asymptotic giant branch (AGB) stars. The main-sequence dwarf carbon (dC) stars have inherited carbon-rich material from an AGB companion, which has since transitioned to a white dwarf. The dC stars are far more common than C giants, but no reliable estimates of the dC space density have been published to date. We present results from an all-sky survey for carbon stars using the low-resolution XP spectra from Gaia Data Release 3. We developed and measured a set of spectral indices contrasting C2 and CN molecular band strengths in carbon stars against common absorption features found in normal (C/O < 1) stars, such as Ca i, TiO, and Balmer lines. We combined these indices with the XP spectral coefficients as inputs to supervised machine learning algorithms trained on a vetted sample of known C stars from LAMOST. We describe the selection of the carbon candidate sample and provide a catalog of 43,574 candidates dominated by cool C giants in the Magellanic Clouds and at low Galactic latitude in the Milky Way. We report the confirmation of candidate C stars using intermediate-resolution (R ∼ 1800) optical spectroscopy from the Fred Lawrence Whipple Observatory and provide estimates of the sample purity and completeness. From a carefully vetted sample of over 600 dCs, we measure their local space density to be ρ₀ = 1.96_(−0.12)^(+0.14)×10⁻⁶ pc⁻³ (about one dC in every local disk volume of radius 50 pc), with a relatively large disk scale height of H_z = 856₋₄₃⁺⁴⁹pc.
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
B.R. was supported for this work by the National Aeronautics and Space Administration through Chandra Award Numbers GO0-21003X and GO1-22004X issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration, under contract NAS8-03060. Additional support for observations made with the NASA/ESA Hubble Space Telescope was provided under program number GO-16392, provided by NASA through a grant from STScI, which is operated by AURA, Inc., under NASA contract NAS 5-26555.
We are grateful for the Vizier service (F. Ochsenbein et al. 2000), which we accessed for numerous purposes during this study. This research made use of the SIMBAD database, operated at CDS, Strasbourg, France (M. Wenger et al. 2000)
This study made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
This study made use of the Python package GaiaXPy, developed and maintained by members of the Gaia Data Processing and Analysis Consortium (DPAC), and, in particular, Coordination Unit 5 (CU5) and the Data Processing Centre located at the Institute of Astronomy, Cambridge, UK (DPCI).
Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions.
SDSS-IV acknowledges support and resources from the Center for High Performance Computing at the University of Utah. The SDSS website is https://www.sdss.org/.
SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration, including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, Center for Astrophysics ∣ Harvard & Smithsonian, the Chilean Participation Group, the French Participation Group, Instituto de Astrofìsica de Canarias, the Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo, the Korean Participation Group, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatories of China, New Mexico State University, New York University, University of Notre Dame, Observatário Nacional/MCTI, the Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University.
Facilities
Gaia - , LAMOST - .
Software References
Astropy (Astropy Collaboration et al. 2013, 2018), Matplotlib (J. D. Hunter 2007), Numpy (C. R. Harris et al. 2020), Scikit-Learn (F. Pedregosa et al. 2011), Scipy (P. Virtanen et al. 2020), TOPCAT (M. B. Taylor 2005).
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Additional details
- Alternative title
- Carbon Stars From Gaia DR3 and the Space Density of Dwarf Carbon Stars
- National Aeronautics and Space Administration
- GO0-21003X
- National Aeronautics and Space Administration
- GO1-22004X
- Smithsonian Astrophysical Observatory
- National Aeronautics and Space Administration
- NAS8-03060
- Space Telescope Science Institute
- National Aeronautics and Space Administration
- NAS 5-26555
- Accepted
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2025-01-27
- Available
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2025-03-28Published
- Caltech groups
- Division of Physics, Mathematics and Astronomy (PMA)
- Publication Status
- Published