X-ray observations of symbiotic stars.

X-ray observations of 19 symbiotic stars made with the imaging proportional counter onboard the Einstein Observatory are reported. Three of the sources, HM Sge, V 1016 Cyg and RR Tel, were detected as soft X-ray sources, with blackbody temperatures of about 1,000,000 K or less. The symbiotic stars detected as X-ray sources are all noted to have undergone slow-nova outbursts in historic times, and to have X-ray luminosities, scaled according to the visible magnitude, decreasing with time since the outbursts. Results support a model of slow novae as representing thermonuclear events on white dwarfs accreting matter from M giants companions, while the symbiotic stars in their steady states are powered by the accretion process alone.