SPECTROSCOPIC EVIDENCE FOR A 5.4 MINUTE ORBITAL PERIOD IN HM CANCRI
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States)
- Department of Physics, University of Warwick, Coventry, CV4 7AL (United Kingdom)
- Department of Astrophysics, Radboud University Nijmegen, P.O. Box 9010, 6500 GL, Nijmegen (Netherlands)
HM Cancri is a candidate ultracompact binary white dwarf with an apparent orbital period of only 5.4 minutes, as suggested by X-ray and optical light-curve modulations on that period, and by the absence of longer-period variability. In this Letter, we present Keck-I spectroscopy which shows clear modulation of the helium emission lines in both radial velocity and amplitude on the 5.4 minute period and no other. The data strongly suggest that the binary is emitting He I 4471 from the irradiated face of the cooler, less massive star, and He II 4686 from a ring around the more massive star. From their relative radial velocities, we measure a mass ratio q = 0.50 {+-} 0.13. We conclude that the observed 5.4 minute period almost certainly represents the orbital period of an interacting binary white dwarf. We thus confirm that HM Cnc is the shortest period binary star known: a unique test for stellar evolution theory, and one of the strongest known sources of gravitational waves for LISA.
- OSTI ID:
- 21305103
- Journal Information:
- Astrophysical Journal Letters, Vol. 711, Issue 2; Other Information: DOI: 10.1088/2041-8205/711/2/L138; Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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