Related papers: WZ Sagittae - an old dwarf nova
We argue that the quiescent value of the viscosity parameter of the accretion disc in WZ Sge may be alpha_{cold}~0.01, in agreement with estimates of alpha_{cold} for other dwarf novae. Assuming the white dwarf in WZ Sge to be magnetic, we…
We examine the light curve of the July-August 2001 superoutburst of WZ Sagittae. During the decline from maximum light the locally defined decay time increases from ~4 d/mag to ~12 d/mag over the first ~15 d of the ~25 d superoutburst, as…
Numerical simulations suggest that merging double white dwarfs (WDs) may produce a newborn neutron star surrounded by a fossil disk. We investigate the evolution of the fossil disk following the coalescence of double WDs. We demonstrate…
We report the results of a worldwide campaign to observe WZ Sagittae during its 2001 superoutburst. After a 23-year slumber at V=15.5, the star rose within 2 days to a peak brightness of 8.2, and showed a main eruption lasting 25 days. The…
We show that if the inner regions of accretion discs in quiescent dwarf nova systems are removed by magnetic disruption or evaporated by siphon flows, the remaining disc is globally stable for mass transfer rates $\lta 10^{15}$ g s$^{-1}$.…
Dwarf novae are semi-detached binaries, where a white dwarf accretes material from a cool main-sequence companion via an accretion disk, and are known for their intermittent outbursts, making them key systems for studying accretion physics.…
We find a dimming during optical quiescence of the cataclysmic variable WZ Sge by about half a magnitude between superoutbursts. We connect the dimming with the development of a cavity in the inner part of the accretion disk. We suggest…
Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured…
WZ Sge-type stars are an extreme subclass of dwarf novae characterised by very rare, large-amplitude superoutbursts. Within the disc instability model (DIM), such events are explained as being triggered by enhanced mass transfer from the…
Diversity of the X-ray observations of dwarf nova are still not fully understood. I review the X-ray spectral characteristics of dwarf novae during the quiescence in general explained by cooling flow models and the outburst spectra that…
We present a model for the dwarf nova WZ Sge which does not require assuming unusually and unexplained low values of the viscosity alpha-parameter during exceptionally long quiescent states of this system. We propose that the inner parts of…
WZ Sagittae is the prototype object of a subclass of dwarf novae, with rare and long (super)outbursts, in which a white dwarf primary accretes matter from a low mass companion. High-energy observations offer the possibility of a better…
We have analysed a series of Suzaku data and one dataset of XMM-Newton of the SU UMa type dwarf nova VW Hyi in optical quiescence. The observed spectra in the 0.2-10 keV band are moderately well represented by multi-temperature thermal…
V Sagittae shows quasi-periodic optical high (soft X-ray off) and low (soft X-ray on) states with the total period of ~300 days. A binary model is presented to explain orbital light curves both for the high and low states as well as the…
We present an analysis of CCD photometric observations of the eclipsing novalike cataclysmic variable DW UMa obtained in two different luminosity states: high and intermediate. The star presents eclipses with very different depth: ~1.2 mag…
We use recent observations of high-redshift galaxies to study the evolution of galactic disks over the redshift range 0<z<1. The data are inconsistent with models in which disks were already assembled at z=1 and have evolved only in…
The 2001 outburst of WZ Sagittae has shown the most compelling evidence yet for an enhancement of the mass transfer rate from the donor star during a dwarf nova outburst in the form of hot-spot brightening. I show that even in this extreme…
We discuss the possibility of observing the transient formation event of an accretion disk from the tidal destruction process of an asteroid near a white dwarf (WD). This scenario is commonly proposed as the explanation for dusty disks…
We present a broadband X-ray study ($\sim$\,0.3-50 keV) of the dwarf nova SS Cyg highlighting the changes in the accretion during two phases, the quiescence and the outburst states. The investigation was based on simultaneous observations…
We present the last HST/STIS E140M FUV spectrum (1150-1725A) of the dwarf nova (DN) WZ Sge, obtained in July 2004, 3 years following the early superoutburst of July 2001. Single white dwarf (WD) synthetic spectral fits (log{g}=8.5) to the…