The evolution and lifetimes of thermally pulsating asymptotic giant branch (TP-AGB) stars suffer from significant uncertainties. In this work, we analyze the numbers and luminosity functions of TP-AGB stars in six quiescent, low metallicity ([Fe/H] ≲ -0.86) galaxies taken from the ACS Nearby Galaxy Survey Treasury sample, using Hubble Space Telescope (HST) photometry in both optical and near-infrared filters. The galaxies contain over 1000 TP-AGB stars (at least 60 per field). We compare the observed TP-AGB luminosity functions and relative numbers of TP-AGB and red giant branch (RGB) stars, N TP-AGB/N RGB, to models generated from different suites of TP-AGB evolutionary tracks after adopting star formation histories derived from the HST deep optical observations. We test various mass-loss prescriptions that differ in their treatments of mass loss before the onset of dust-driven winds (pre-dust). These comparisons confirm that pre-dust mass loss is important, since models that neglect pre-dust mass loss fail to explain the observed N TP-AGB/N RGB ratio or the luminosity functions. In contrast, models with more efficient pre-dust mass loss produce results consistent with observations. We find that for [Fe/H] ≲ -0.86, lower mass TP-AGB stars (M ≲ 1 M ) must have lifetimes of ∼0.5 Myr and higher masses (M ≲ 3 M ) must have lifetimes ≲ 1.2 Myr. In addition, assuming our best-fitting mass-loss prescription, we show that the third dredge-up has no significant effect on TP-AGB lifetimes in this mass and metallicity range. © 2014. The American Astronomical Society. All rights reserved..
|Titolo:||Evolution of Thermally Pulsing Asymptotic Giant Branch Stars. IV. Constraining Mass Loss and Lifetimes of Low Mass, Low Metallicity AGB Stars|
|Autori:||Rosenfield, P.; Marigo, P.; Girardi, L.; Dalcanton, J. J.; Bressan, A.; Gullieuszik, M.; Weisz, D.; Williams, B. F.; Dolphin, A.; Aringer, B.|
|Rivista:||THE ASTROPHYSICAL JOURNAL|
|Data di pubblicazione:||2014|
|Digital Object Identifier (DOI):||10.1088/0004-637X/790/1/22|
|Appare nelle tipologie:||1.1 Journal article|