Title: The relationship between initial and final mass of white dwarfs: breaking a paradigm and new constraints on stellar evolution
Speaker: Paola Marigo
Affiliation: University of Padova
Time: Thursday 13 January 2022, 1400 to 1500
Location: online at https://uu-se.zoom.us/j/62091586806 (Zoom meeting ID: 620 9158 6806)
Abstract:
The initial-final mass relation (IFMR) of white dwarfs plays an important role across astrophysics. It sets stringent constraints to the contribution from low- and intermediate-mass stars to the chemical enrichment and integrated light of galaxies. In a recent analysis of a few carbon-oxygen white dwarfs in old open clusters of the Milky Way we identified a kink in the initial-final mass relation (IFMR), located over a range of initial masses, 1.65 ≲ Mi/Msun ≲ 2.10, which unexpectedly interrupts the commonly assumed monotonic trend. The kink's peak in white dwarf mass of about 0.70-0.75 Msun is produced by stars with Mi ≈ 1.8-1.9 Msun, whereas these final masses are typically associated to Mi~3-3.5 Msun. We interpret the kink as the fingerprint of carbon star formation and the modest outflows produced as long the carbon excess remains too low to produce dust grains in sufficient amounts. Under these conditions the mass of the carbon-oxygen core can grow more than is generally predicted by stellar models. A new systematic follow-up investigation, based on GAIA DR2 and EDR3, of evolved giants belonging to open clusters of known age allows us to identify 19 TP-AGB stars including 12 C stars, 3 S stars and 4 M stars. By combining observations and models, for each star we derive the initial mass, Mi, of the progenitor, the bolometric luminosity L, the present-day dust mass-loss rate, the period and mode of pulsation, and the current core mass, Mc. We place the estimated (Mi, Mc) of the TP-AGB stars on the IFMR diagram: the comparison strikingly reveals the presence of optically visible carbon stars just below the IFMR kink with Mc ~ 0.70 Msun and low mass-loss rates. The implications of this intriguing result are discussed.