Instabilities in Accretion Discs and the Outbursts of Dwarf Novae Retake of Safing

Details Instabilities in Accretion Discs and the Outbursts of Dwarf Novae Retake of Safing Instabilities in Accretion Discs and the Outbursts of Dwarf Novae Retake of Safing

Jul 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991hst..prop.3820h&link_type=abstract

HST Proposal ID #3820

Computer Science

Hst Proposal Id #3820

Scientific paper

We will use the HST with the FOS to observe eclipses of a dwarf nova at 5 epochs in the quiescent period between outbursts. From the eclipse data we will determine the secular evolution of the white dwarf, the accretion disc, and the bright spot. This evidence will be a clean test of the two competing theories for the instability which triggers dwarf nova outbursts. In the disc instability model the transition of the disc from a cool to hot state triggers the outburst, whereas in the red star instability model the cool binary companion transfers a short burst of material into the disc which then becomes brighter. During quiescence the disc instability model predicts an increasing accretion rate and hence an increasing ultraviolet flux, whereas the red star model predicts a decreasing accretion rate and ultraviolet flux. Therefore the variation of the ultraviolet flux with time will distinguish which of the two current models is correct. Only the HST is able to resolve the rapid variations seen in an eclipsing dwarf nova, and therefore determine the ultraviolet flux from the accretion disc. The observations that we propose will also probe the nature of the boundary layer between the disc and the white dwarf, a region too small and hot to be well constrained by any previous observations. In particular, we will measure the extent of heating of the white dwarf by the boundary layer, and the cooling

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