ON THE INITIAL-FINAL MASS RELATION AND MAXIMUM MASS OF WHITE-DWARF PROGENITORS

The four white dwarfs (WDs) discovered in the young open cluster NGC 2 516 are crucial in defining the shape of the initial-final mass relati on (IFMR) and upper mass limit for CVD progenitors (M-wd). The cluster metallicity has been recently determined as [M/H] = -0.32 +/- 0.06, w hich is found to decrease the previously derived WD progenitor masses by 1.0-1.7 M.. The new progenitor masses are consistent with M-wd of o nly 5-6 M., which is confirmed by integrating an extrapolated cluster mass function. The results disagree with the 8-M. upper limit containe d in the frequently used semi-empirical IFMR of Weidemann, but are now in agreement with evolutionary models with moderate core overshoot. I t is suggested that beyond an initial mass of 3 M., the IFMR may follo w the relationship between initial mass and the core mass at the start of the thermally pulsating asymptotic giant branch, implying very eff icient mass loss. According to these evolutionary models, non-degenera te carbon burning is possible in the cores of stars with initial mass < 6M., so a similar M-wd means there should be few carbon deflagration supernovae. However, decreasing M-wd from 8 to 5-6 M. would significa ntly increase the expected numbers of core-collapse supernovae.