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Published April 1, 2016 | Submitted + Published
Journal Article Open

UVES and X-Shooter spectroscopy of the emission line AM CVn systems GP Com and V396 Hya

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 K_(spike) = 11.7 ± 0.3 km s^(−1) for GP Com and K_(spike) = 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 n_e ≃ 5 × 10^(15) 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 M_(Jupiter) for GP Com and 6.1–30.5 M_(Jupiter) for V396 Hya. We find an upper limit for the rotational velocity of the accretor of v_(rot) < 46 km s^(−1) for GP Com and v_(rot) < 59 km s^(−1) for V396 Hya which excludes a fast rotating accretor in both systems.

Additional Information

© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society Accepted 2016 January 12. Received 2016 January 8; in original form 2015 November 25. First published online February 4, 2016. TK acknowledges support by the Netherlands Research School for Astronomy (NOVA). TRM and DS acknowledge the support from the Science and Technology Facilities Council (STFC), ST/L00733, during the course of this work. We thank Simon Jeffery for useful discussion on the spectral features. Based on observations made with ESO telescopes at the Paranal Observatory under programme ID 69.D-0562(A), 084.D-0814(A).

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Published - Kupfer,T.etal.pdf

Submitted - 1601.02841v1.pdf

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August 20, 2023
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