Volume 620, December 2018
|Number of page(s)||17|
|Section||Stellar structure and evolution|
|Published online||11 December 2018|
Physical properties of AM CVn stars: New insights from Gaia DR2⋆
Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK
2 Department of Physics, University of Warwick, Coventry CV4 7AL, UK
3 Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106, USA
4 Department of Physics, University of California, Santa Barbara, CA 93106, USA
5 Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
6 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
7 Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
8 Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands
9 Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
10 Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
11 Inter-University Institute for Data Intensive Astronomy, Department of Astronomy, University of Cape Town, Private Bag X3 Rondebosch 7701, South Africa
12 Department of Physics, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand
Accepted: 14 October 2018
AM CVn binaries are hydrogen deficient compact binaries with an orbital period in the 5–65 min range and are predicted to be strong sources of persistent gravitational wave radiation. Using Gaia Data Release 2, we present the parallaxes and proper motions of 41 out of the 56 known systems. Compared to the parallax determined using the HST Fine Guidance Sensor we find that the archetype star, AM CVn, is significantly closer than previously thought. This resolves the high luminosity and mass accretion rate which models had difficulty in explaining. Using Pan-STARRS1 data we determine the absolute magnitude of the AM CVn stars. There is some evidence that donor stars have a higher mass and radius than expected for white dwarfs or that the donors are not white dwarfs. Using the distances to the known AM CVn stars we find strong evidence that a large population of AM CVn stars has yet to be discovered. As this value sets the background to the gravitational wave signal of LISA this is of wide interest. We determine the mass transfer rate for 15 AM CVn stars and find that the majority has a rate significantly greater than expected from standard models. This is further evidence that the donor star has a greater size than expected.
Key words: accretion, accretion disks / stars: distances / white dwarfs
Photometry of AM CVn stars is also available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A141
© ESO 2018
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