1,482 research outputs found
The boundary layer of VW Hyi in quiescence
In this letter, we suggest that the missing boundary layer luminosity of
dwarf novae in quiescence is released mainly in the ultraviolet (UV) as the
second component commonly identified in the far ultraviolet (FUV) as the
"accretion belt".
We present the well-studied SU UMa-type system VW Hyi in detail as a
prototype for such a scenario. We consider detailed multiwavelength
observations and in particular the recent FUSE observations of VW Hyi which
confirm the presence of a second component (the "accretion belt") in the FUV
spectrum of VW Hyi in quiescence. The temperature (50,000K) and rotational
velocity (> 3,000km/s) of this second FUV component are entirely consistent
with the optically thick region (tau = 1) located just at the outer edge of
optically thin boundary layer in the simulations of Popham (1999).
This second component contributes 20% of the FUV flux, therefore implying a
boundary layer luminosity: , while the theory (Klu\'zniak 1987) predicts, for the
rotation rate of VW Hyi's WD, . The remaining
accretion energy () is apparently advected into the star as
expected for optically thin advection dominated boundary layers. This scenario
is consistent with the recent simultaneous X-ray and UV observations of VW Hyi
by (Pandel, C\'ordova & Howell 2003), from which we deduced here that the alpha
viscosity parameter in the boundary layer region must be as small as .Comment: 4 page
Orbital phase dependent IUE spectra of the nova like binary II Arietis
Nine low dispersion IUE spectra of the nova like binary TT Ari over its 3h17m orbital period were obtained. Four short wave spectra and five long wave spectra exhibit marked changes in line strength and continuum shape with orbital phase. The short wave spectra show the presence in absorption of C III, Lyman alpha, SiIII, NV, SiIV, CIV, HeII, AlIII, and NIV. The CIV shows a P Cygni profile on two of the spectra. Implications of these spectra for the nature of nova like variables are discussed
Visible-band and IUE observations of mu Sagittarii
H alpha and U band photometry and IUE spectra of the binary system mu Sagittarii are discussed. An estimate of mass-loss is made from the observed P Cygni profiles. There are indications of pulsation in the supergiant B8 component
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