On the mass-loss of PG 1159 stars

L. Koesterke1S. Dreizler2, T. Rauch3

1Institut für Physik, Astrophysik der Universität Potsdam
2Institut für Astronomie und Astrophysik der Universität Tübingen

The winds of the four PG 1159 stars NGC 7094, NGC 246, K 1-16 and RX J2117.1+3412 are investigated by means of non-LTE models for spherically expanding atmospheres. Based on the results of recent plane-parallel non-LTE analyses, several individual models with various mass-loss rates are calculated. Synthetic profiles of the C IV resonance line are compared to high resolution, high quality HST and IUE UV spectra in order to determine mass-loss rates of the stars and terminal velocities of their winds. Complex model atoms of hydrogen, helium, carbon and oxygen are taken into account. In contrast to previous studies we find from the C IV line at 1550 Å exceedingly high mass-loss rates of -7.6 < = log (M dot [Msun yr-1]) < = -6.9 which are, in case of K 1-16, only two times smaller than the mass-loss rates of [WC]-PG 1159 stars. From the comparison with theoretical predictions of line strength and terminal wind velocity it is most likely that the theory of radiation driven winds is appropriate for the PG 1159 stars. The results are discussed in the light of the evolutionary sequence [WCL]-> [WCE]-> [WC]-PG 1159 -> PG 1159 -> WD, which is suggested for hydrogen deficient post-AGB stars. Similarities between the winds of PG 1159 stars and the exceptional strong winds of [WC]-type stars lead to the assumption that the theory of radiation driven winds might also apply for [WCE] stars. Changes of ionization degrees, which might enhance the mass-loss by multi-scattering processes, are found in the atmospheres of [WCE] stars but not in the atmospheres of PG 1159 stars.

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