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

3. The evidence for mass-loss from 1944 to 1978

The early outburst data of RR Tel, obtained from the ground, are not absolutely calibrated, and Thackeray (1977) warns us even about the relative calibration. Mayall (1949) describes the spectrum from which she derived the F-type character as "The only spectra available are of short dispersion with the star at maximum brightness, and are too burned out to classify". Thus, we can at best hope for qualitative information. According to Thackeray (1950) spectra taken in June 1949 showed "pure absorption apparently supergiant F type with H and K three times as intense as H ". Spectra taken in September and October 1949 show a change to a "rich bright line spectrum superposed on a continuous background in which no absorption is measurable". Also Pottasch & Varsavsky (1960) report a qualitative change: in May 1949 the spectrum was entirely in absorption, corresponding to that of an early F star, whereas in August 1950 it was practically all in emission. On subsequent spectra violet displaced absorption in He I lines was seen. Pottasch & Varsavsky (1960) give displacements corresponding to -430 km/s in October 1949, and -510 km/s in August 1950. Thackeray (1953) gives -685 km/s for 1951, and -865 km/s for 1952. Thackeray (1953) also reports that by 1952 He II is very broad and much stronger than in 1951. Thackeray and Webster (1974) show the profiles of He II 4686. Their half widths correspond to 480 km/s in 1951-52, 700 km/s in 1953, 1100 km/s in 1955-56, and to 1300 km/s in 1958 and 1960. When discussing his spectroscopic results from 1951 to 1973, Thackeray (1977) states that no P Cyg absorption had been detected since 1952. Schmutz (1996) finds that the combination of a diminishing He I P Cygni feature and a growing broad He II emission is exactly what is expected from a mass losing star with increasing effective temperature.

He II 4686 in emission is no proof of a stellar wind. We need to distinguish between the broad stellar wind lines and the narrow nebular emission, a distinction which is obvious when looking at the profiles of He II 4686 shown in Thackeray and Webster (1974). The change in the profiles, including N III , shows that in 1955 narrower components developed on top of a broad underlying feature, and that already in 1955 the broad emission began to decline relative to the continuum.

We conclude that the outburst of 1944 produced an extended atmosphere around the white dwarf. For 1949 Mürset & Nussbaumer (1994) give a radius of and K. There is no indication of mass-loss for that period. The spectral change in the autumn of 1949 signaled the emergence of a substantial stellar wind with terminal velocities increasing from km/s in 1949 to km/s in 1960. There is no indication that it had disappeared in 1973 which is the date of the last entry of Thackeray's (1977) RR Tel publication. However, he comments about the intensity of He II 4686: "A steady increase occurred up to 1960 and thereafter there appears to have been a slow decline". The published observational data do not permit to calculate the mass-loss for this period.

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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