Year: 2019
Type: article
Abstract: M subdwarfs are low-metallicity M dwarfs that typically inhabit the halo population of the Galaxy. Metallicity controls the opacity of stellar atmospheres; in metal-poor stars, hydrostatic equilibrium is reached at a smaller radius, leading to smaller radii for a given effective temperature. We compile a sample of 88 stars that span spectral classes K7 to M6 and include stars with metallicity classes from solar-metallicity dwarf stars to the lowest metallicity ultra subdwarfs to test how metallicity changes the stellar radius. We fit models to Palomar Double Spectrograph (DBSP) optical spectra to derive effective temperatures (T eff) and we measure bolometric luminosities (L bol) by combining broad wavelength-coverage photometry with Gaia parallaxes. Radii are then computed by combining the T eff and L bol using the Stefan–Boltzman law. We find that for a given temperature, ultra subdwarfs can be as much as five times smaller than their solar-metallicity counterparts. We present color-radius and color-surface brightness relations that extend down to [Fe/H] of −2.0 dex, in order to aid the radius determination of M subdwarfs, which will be especially important for the WFIRST exoplanetary microlensing survey.
Source: The Astronomical Journal
Authors: Aurora Y. Kesseli, J. Davy Kirkpatrick, Sergio B. Fajardo-Acosta, Matthew T. Penny, B. Scott Gaudi, Mark Veyette, Patricia C. Boeshaar, Calen B. Henderson, Michael C. Cushing, Sebastiano Calchi-Novati, Y. Shvartzvald, Philip S. Muirhead
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Funders: National Science Foundation, Smithsonian Institution, U.S. Department of Energy, National Aeronautics and Space Administration, Alfred P. Sloan Foundation, Gordon and Betty Moore Foundation, Yale University, Carnegie Institution of Washington, Vanderbilt University, Ohio State University, California Institute of Technology, University of Utah, University of Washington, Johns Hopkins University, Carnegie Mellon University, University of Notre Dame, University of Portsmouth, New Mexico State University, Space Telescope Science Institute, European Space Agency, York University, University of Oxford, Queen's University Belfast, Durham University, Queen's University, Ministério da Ciência, Tecnologia e Inovação, National Central University, Universidad Nacional Autónoma de México, Eötvös Loránd Tudományegyetem, Max-Planck-Institut für Astrophysik, Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Canarias, Office of Science, Jet Propulsion Laboratory, University of California, Los Angeles, University of Colorado Boulder, Smithsonian Astrophysical Observatory, Science Mission Directorate, Leibniz-Gemeinschaft, Planetary Science Division, Lawrence Berkeley National Laboratory, Los Alamos National Laboratory
OpenAlex ID: W2897275667