The spectra energy distribution and nature of the symbiotic system AS 296 in outburst.

Photometry at 0.36-5 microns is reported for the symbiotic star AS 296 about 2 months after the onset of the first recorded novalike outburst. Analysis of published preoutburst photometry provides evidence for the presence of an accreting white dwarf of high luminosity. This information, together with the new observations, is used to eliminate various mechanisms suggested for outbursts in symbiotic objects. It is shown that hydrogen burning of accreted material can produce the white dwarf luminosity during quiescence. The outburst is then the result of a thermonuclear runaway in the unburnt material.