Kupfer, T., Steeghs, D., Groot, P. J., Marsh, Tom, Nelemans, G. and Roelofs, G. H. A. (2016) UVES and X-Shooter spectroscopy of the emission line AM CVn systems GP Com and V396 Hya. Monthly Notices of the Royal Astronomical Society, 457 (2). pp. 1828-1841. doi:10.1093/mnras/stw126 ISSN 0035-8711.

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Abstract

We present time-resolved spectroscopy of the AM CVn-type binaries GP Com and V396 Hya obtained with VLT/X-Shooter and VLT/UV-Visual Echelle Spectrograph (UVES). We fully resolve the narrow central components of the dominant helium lines and determine radial velocity semi-amplitudes of Kspike = 11.7 ± 0.3 km s−1 for GP Com and Kspike = 5.8 ± 0.3 km s−1 for V396 Hya. The mean velocities of the narrow central components show variations from line to line. Compared to calculated line profiles that include Stark broadening we are able to explain the displacements, and the appearance of forbidden helium lines, by additional Stark broadening of emission in a helium plasma with an electron density ne ≃ 5 × 1015 cm−3. More than 30 nitrogen and more than 10 neon lines emission lines were detected in both systems. Additionally, 20 nitrogen absorption lines are only seen in GP Com. The radial velocity variations of these lines show the same phase and velocity amplitude as the central helium emission components. The small semi-amplitude of the central helium emission component, the consistency of phase and amplitude with the absorption components in GP Com as well as the measured Stark effect shows that the central helium emission component, the so-called central-spike, is consistent with an origin on the accreting white dwarf. We use the dynamics of the bright spot and the central-spike to constrain the binary parameters for both systems and find a donor mass of 9.6–42.8 MJupiter for GP Com and 6.1–30.5 MJupiter for V396 Hya. We find an upper limit for the rotational velocity of the accretor of vrot < 46 km s−1 for GP Com and vrot < 59 km s−1 for V396 Hya which excludes a fast rotating accretor in both systems.

Item Type:	Journal Article
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Oxford University Press
ISSN:	0035-8711
Official Date:	1 April 2016
Dates:	Date Event 1 April 2016 Published 4 February 2016 Available 12 January 2016 Accepted 8 January 2016 Submitted
Volume:	457
Number:	2
Page Range:	pp. 1828-1841
DOI:	10.1093/mnras/stw126
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
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