skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Detecting the companions and ellipsoidal variations of RS CVn primaries. I. σ Geminorum

Journal Article · · Astrophysical Journal
; ; ; ;  [1]; ; ;  [2];  [3]; ; ;  [4];  [5]; ; ; ; ;  [6];  [7]
  1. Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States)
  2. Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37209 (United States)
  3. FNRS, Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles (ULB) (Belgium)
  4. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  5. School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom)
  6. Center for High Angular Resolution Astronomy, Georgia State University, Mount Wilson, CA 91023 (United States)
  7. Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, FI-21500 Piikkiö (Finland)

To measure the properties of both components of the RS Canum Venaticorum binary σ Geminorum (σ Gem), we directly detect the faint companion, measure the orbit, obtain model-independent masses and evolutionary histories, detect ellipsoidal variations of the primary caused by the gravity of the companion, and measure gravity darkening. We detect the companion with interferometric observations obtained with the Michigan InfraRed Combiner at Georgia State University’s Center for High Angular Resolution Astronomy Array with a primary-to-secondary H-band flux ratio of 270 ± 70. A radial velocity curve of the companion was obtained with spectra from the Tillinghast Reflector Echelle Spectrograph on the 1.5 m Tillinghast Reflector at Fred Lawrence Whipple Observatory. We additionally use new observations from the Tennessee State University Automated Spectroscopic and Photometric Telescopes (AST and APT, respectively). From our orbit, we determine model-independent masses of the components (M{sub 1}=1.28±0.07 M{sub ⊙}, M{sub 2}=0.73±0.03 M{sub ⊙}), and estimate a system age of 5∓1 Gyr. An average of the 27 year APT light curve of σ Gem folded over the orbital period (P=19.6027±0.0005 days) reveals a quasi-sinusoidal signature, which has previously been attributed to active longitudes 180° apart on the surface of σ Gem. With the component masses, diameters, and orbit, we find that the predicted light curve for ellipsoidal variations due to the primary star partially filling its Roche lobe potential matches well with the observed average light curve, offering a compelling alternative explanation to the active longitudes hypothesis. Measuring gravity darkening from the light curve gives β<0.1, a value slightly lower than that expected from recent theory.

OSTI ID:
22882980
Journal Information:
Astrophysical Journal, Vol. 807, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
Country of Publication:
United Kingdom
Language:
English