The galactic mass injection from cool stellar winds of the 1 to 2.5 stars in the solar neighbourhood

¹ University of Sussex, Astronomy Centre, Falmer, Brighton BN1 9QJ, UK
² Technische Universität Berlin, Inst. f. Astronomie u. Astrophysik, Sekr. PN 8-1, Hardenbergstr. 36, 10623 Berlin, Germany

Corresponding author: K.-P. Schröder, kps@star.cpes.susx.ac.uk

Received: 20 December 1999
Accepted: 16 November 2000

Abstract

We have computed synthetic stellar samples and HR diagrams on the basis of a fine-meshed, consistent grid of evolution tracks for given IMF and SFR(t). In order to model the galactic disk stellar component (single stars only) and to derive its IMF and apparent SFR(t), we selected the synthetic sample which is the best fit to the observed distribution of single stars in the solar neighbourhood HR diagram (complete for pc, , based on Hipparcos data). Most giants of this synthetic sample fall in the range of M_i = 1 to 2.5 . Stellar evolution on the tip-AGB has been computed by adopting, time-step by time-step, the mass-loss rates predicted by very detailed dust-driven, pulsating wind models for carbon-rich stars. This mass-loss description causes the natural development of superwinds. Their properties are in agreement with the range of measured masses and expansion velocities of PNe, i.e. a total mass of between 0.25 and 0.65 has been ejected over the final 30 thousand years. For the preceeding mass-loss on the AGB and RGB, we use a semi-empirical approach, i.e., a re-calibrated Reimers mass-loss which yields an RGB mass-loss (for ) consistent with the formation of horizontal branch stars. Combining these approaches, we obtain a consistent grid of mass-loss histories in the mass range of to . By increasing the number of stars in our synthetic solar neighbourhood stellar sample by a factor of thousand, we have been able to compute a detailed, present-day, synthetic reference sample of galactic disk RGB and AGB giant stars, together with their mass-loss. The results are in good agreement with observations of cool giant stellar mass-loss, as well as with the estimated space density of carbon stars. Finally, we discuss the relative collective yields of the RGB, AGB and tip-AGB stellar mass-loss as contributions to the galactic disk mass re-injection.