Tip-AGB stellar evolution in the presence of a pulsating, dust-induced ``superwind"

Details Tip-AGB stellar evolution in the presence of a pulsating, dust-induced ``superwind" Tip-AGB stellar evolution in the presence of a pulsating, dust-induced ``superwind"

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...349..898s&link_type=abstract

Astronomy and Astrophysics, v.349, p.898-906 (1999)

Astronomy and Astrophysics

Astrophysics

55

Stars: Carbon, Stars: Circumstellar Matter, Stars: Evolution, Stars: Interiors, Stars: Late-Type, Stars: Mass-Loss

Scientific paper

We present selected ``superwind" mass-loss histories and the related tip-AGB stellar evolution models, which have been computed according to the characteristics of a dust-induced, carbon-rich wind, and which include several recent improvements as compared to Schröder et al. (1998). We discuss the (initial) stellar mass-range of 1 to 2.5 Msun, with a nearly solar composition (X=0.28, Y=0.70, Z=0.02). In each time-step, mass-loss rates are used, which are consistent with the actual stellar parameters, and which are based on our pulsating, dust-induced wind models for carbon-rich stars (Fleischer et al. 1992), including a detailed and consistent treatment of dust formation, radiative transfer and radiative wind acceleration. The resulting ``superwind" mass-loss rates reach 2 to 3* 10(-5) Msun yr(-1) . For this reason, they become an influential factor of tip-AGB stellar evolution - but also vice versa, since our mass-loss rates vary strongly with effective temperature (dot {M} ~ T_eff(-8) (roughly), see Arndt et al. 1997), reflecting the temperature sensitivity of the dust formation process on a macroscopic scale. With all tip-AGB models of an initial stellar mass Mi >~ 1.3 Msun we find superwinds with a total mass outflow of 0.26 to >~ 0.55 Msun during their final 3* 10(4) yrs, just as required for PN-formation. Furthermore, a thermal pulse leads to a very short (100 to 200 yrs) interruption of the ``superwind" of these models. A critical (Eddington-like) luminosity Lc is required for the radiation driven wind models, which our evolution models fail to reach for Mi <~ 1.1 Msun. With slightly larger stellar masses, L_tAGB is near Lc and thermal pulses can trigger very short ``superwind" bursts, as already pointed out by Schröder et al. (1998). We find good agreement between our improved models and the mass-loss characteristics of the thin CO shells found by Olofsson et al. (1990, 1993, 1996, 1998) around some carbon-rich Mira stars.

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