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 ] \lesssim - 0.86 ) galaxies taken from the ANGST sample , using 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 RGB stars , N _ { TP - AGB } / N _ { RGB } , to models generated from different suites of TP-AGB evolutionary tracks after adopting star formation histories ( SFH ) 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 ] \lesssim - 0.86 , lower mass TP-AGB stars ( M \lesssim 1 \mbox { $M _ { \odot } $ } ) must have lifetimes of \sim 0.5 Myr and higher masses ( M \lesssim 3 \mbox { $M _ { \odot } $ } ) must have lifetimes \lesssim 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 .