Studies of symbiotic stars. VI. The eclipsing symbiotic nova AS 338.

The nature and evolution of AS 338 is investigated. An extensive new set of photometric and spectrophotometric/UE, optical and IR data is presented, covering the period 1962-1991. It is found that AS 338 is a symbiotic nova that entered the outburst phase in late 1981. The outburst, far to be concluded, has been large in amplitude and of long duration: the very low decline rate (an average of 0.0009 mag/d in the last 9 yr) suggest a total duration greater than 20 yr. The outbursting component is eclipsed every 434.1 d by the cool giant companion and detailed eclipse profiles have been recorded. It is found that AS 338 is composed by an M 5 (+/- 0.5) III and a companion which was very hot (Teff greater than 100,000 K), luminous and compact during quiescence and that closely resembled an accreting white dwarf without a detectable accretion disk. The distance is 3.5 kpc and the reddening amounts to 0.7. During the outburst, which has been a TNR event in the WD accreted envelope and which developed in nondegenerate conditions, the companion expanded to about 27 solar radii, raised the luminosity to 2000 solar luminosities, and lowered the temperature to about 7450 K, with no mass being ejected.