Spectroscopy of the present extraordinary bright outburst phase of the LMC S DOR variable R 127.

Abstract

We observed the S Dor variable R 127 in 1986, August 22, when it was the visually brightest star of the LMC at high dispersion in the optical range with CASPEC. We discuss this echelle spectrogram together with spectra taken at earlier epochs with the same instrument to study the spectral evolution of R 127 during outburst. In addition a high dispersion IUE-LWP spectrum was taken in 1986, April 17. The spectra are compared to spectroscopic data obtained for S Dor during a similar bright outburst phase. The IUE spectra of both stars are characterized by copious singly ionized metallic lines. Their edge velocity is increasing with decreasing excitation potential which is interpreted by a slowly accelerated dense cool wind in both stars. The same acceleration mechanism as in S Dor appears to be present. Also during outburst phases the mass loss does not occur continuously but rather by discrete shell ejection. An observed fast component (ν_exp_ = 260 km s^-1^) is ascribed to the ejection of a shell during the early phases of the outburst when R 127 is supposed to have been similar to P Cygni. Various S Dor variables with different minimum characteristics show during outburst quite similar spectra. It is suggested that this is due to the same physical conditions in the pseudo-photospheres of these stars during outburst.