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Astron. Astrophys. 323, 387-392 (1997)

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2. The history of the outburst

The lightcurve of Mayall (1949) shows that the outburst began in October 1944. By the end of the year the initial phase of rapid brightness increase from [FORMULA] to [FORMULA] was terminated. In the middle of 1946 it had reached [FORMULA], and in July 1949 the visual brightness began to fade (Thackeray 1950). The evolution is traced in Mürset & Nussbaumer (1994). Previous to the outburst the visual brightness was determined by the contribution of the Mira with its 387 days period. The outburst occurs on the white dwarf companion. In an initial fast expansion it led to a bloated atmosphere which according to Mayall (1949) seems to have mimicked a F type giant. She writes: "There is no evidence of a banded or nova-like spectrum, which should appear if the sudden rise in brightness was due to a superposed nova. The only features visible are strong absorption H and K, and many absorption lines in the violet, somewhat similar to an F-type star." The luminosity of the outbursting object rose to [FORMULA]. Until 1949 its temperature remained below 10 000 K. Pottasch & Varsavsky (1960) report that in the middle of 1949 the spectrum of RR Tel began to change rapidly, implying an increase in the colour temperature from 8400 K in October 1949 to 12 500 K in August 1950. It then slowly but steadily rose to attain [FORMULA] K and [FORMULA] in 1978, in 1992 the temperature was at [FORMULA] K whereas the luminosity had decreased to [FORMULA] (Jordan et al. 1994).

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998