Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997mnras.286..447d&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 286, Issue 2, pp. 447-462.
Astronomy and Astrophysics
Astronomy
17
Binaries: Close, Stars: Individual: V795 Her (Pg 1711+336), Novae, Cataclysmic Variables
Scientific paper
The optical emission-line properties of the nova-like cataclysmic variable V795 Her are studied using high-resolution Isaac Newton Telescope [Intermediate Dispersion Spectrograph (IDS) and Faint-Object Spectrograph (FOS)] data secured during 1994 June. The observed Balmer and He emission lines, and He i lambda4471 absorption, modulate on the 2.6-h orbital period of this system. The detailed nature of these changes is complex, however, with the incidence of separate low- and high-velocity fluctuations. Low-intensity `S'-wave features are apparent in the blue and red outer wings of the Balmer lines, extending to ~+/-1600 km s^-1. These phased changes are seen as two synchronized components with net blueshift and redshift. The Balmer profiles are also affected by absorption which dominates during the first part of the cycle. We propose an empirical interpretation of this behaviour in terms of a single broad emission feature which follows a high-velocity `S' wave, plus a superimposed, sympathetically phased, absorption component. The associated physical interpretation is that of a gas stream (seen in absorption) that overflows the outer accretion disc and re-impacts on the inner disc regions. The `double-peaked' inner cores of the Balmer lines have relatively fixed central velocities, and do not reveal an obvious `S'-wave variation. This inner-core emission likely arises from material located in the outer regions of the accretion disc. An ~10 per cent variation is present in the continuum flux of V795 Her, restricted to less than 25 per cent of the system orbit. We find some correspondence between the overall optical emission changes and those found by us in the UV resonance lines of V795 Her in a separate study based on Hubble Space Telescope data. We discuss our observational results in terms of magnetic white dwarf and disc-overflow gas stream scenarios. Constraints are presented that argue against recently proposed models for V795 Her which invoke channelled accretion columns flowing on to a synchronously rotating white dwarf. Disc-overflow model simulations are presented which quantitatively account for several of the observed dynamical properties of V795 Her. There remain some discrepancies, however, which call for a more detailed physical model.
Dickinson R. J.
Hellier Coel
Horne Keith
King Andrew R.
Prinja Raman K.
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