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Title:
V795 Her: an SW Sex star in the period gap?
Authors:
Casares, J.; Martinez-Pais, I. G.; Marsh, T. R.; Charles, P. A.; Lazaro, C.
Affiliation:
AA(University of Oxford, Department of Physics, Nuclear Physics Laboratory, Keble Road, Oxford OX1 3RH, UK ), AB(Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain ), AC(Department of Physics, The University of Southampton, Southampton SO17 5BJ, UK ), AD(University of Oxford, Department of Physics, Nuclear Physics Laboratory, Keble Road, Oxford OX1 3RH, UK ), AE(Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain )
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 278, Issue 1, pp. 219-235. (MNRAS Homepage)
Publication Date:
01/1996
Origin:
MNRAS
MNRAS Keywords:
ACCRETION, ACCRETION DISCS, BINARIES: CLOSE, BINARIES: SPECTROSCOPIC, STARS: INDIVIDUAL: V795 HER, NOVAE, CATACLYSMIC VARIABLES
Bibliographic Code:
1996MNRAS.278..219C

Abstract

We present optical photometry and spectroscopy of the nova-like variable V795 Her. The emission lines exhibit an extremely complex structure consisting of several time-variable emission and absorption components. We confirm the spectroscopic modulation of 0.1082d which we attribute to the orbital period of the system. The equivalent widths (EWs) of all the emission lines are strongly modulated on this period, showing a pronounced minimum around phase 0.5. We associate this minimum with the transit of an absorption feature which drives dramatic line changes, seen as transient double peaks and PCygni type profiles. The absorption depth grows with the excitation level in Balmer and HeI lines, but both the HeII lambda4686 and the metallic lines (e.g. CII lambda4267 and the Bowen blend) are entirely in emission. The centroid of the Hα emission (which is contaminated very little by the absorption feature) is delayed by 83 deg with respect to the high-excitation lines. We assume that the latter trace the orbital motion of the primary, enabling us to define an absolute zero-phase. High-velocity S-waves are clearly observed in all Balmer lines, with amplitudes of about 1750 km s^-1 and maximum redshift at about phase 0. However, our high-resolution spectra suggest that these can be separated into two phased components, with gamma-velocities of ~+/-750 km s^-1 and K~1000 km s^-1, probably formed in accretion columns on the white dwarf. In addition, the HI cores exhibit the presence of low-velocity (K=268 km s^-1) S-waves, roughly phased with their high-amplitude partners. On the other hand, our R-band photometry is dominated by flickering with no evidence for modulation with the orbital period nor the previously reported 0.1165-d periodicity. Based on the spectral properties, we propose that V795 Her is a new SW Sex star, observed at intermediate inclination. The complex behaviour of V795 Her can be qualitatively explained invoking an intermediate polar scenario with a synchronously rotating white dwarf.

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