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The ACS Nearby Galaxy Survey Treasury. IX. Constraining Asymptotic Giant Branch Evolution with Old Metal-poor Galaxies

Girardi, Léo and Williams, Benjamin F. and Gilbert, Karoline M. and Rosenfield, Philip and Dalcanton, Julianne J. and Marigo, Paola and Boyer, Martha L. and Dolphin, Andrew and Weisz, Daniel R. and Melbourne, Jason and Olsen, Knut A. G. and Seth, Anil C. and Skillman, Evan (2010) The ACS Nearby Galaxy Survey Treasury. IX. Constraining Asymptotic Giant Branch Evolution with Old Metal-poor Galaxies. Astrophysical Journal, 724 (2). pp. 1030-1043. ISSN 0004-637X.

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In an attempt to constrain evolutionary models of the asymptotic giant branch (AGB) phase at the limit of low masses and low metallicities, we have examined the luminosity functions and number ratios between AGB and red giant branch (RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy Survey Treasury. This database provides Hubble Space Telescope optical photometry together with maps of completeness, photometric errors, and star formation histories for dozens of galaxies within 4 Mpc. We select 12 galaxies characterized by predominantly metal-poor populations as indicated by a very steep and blue RGB, and which do not present any indication of recent star formation in their color-magnitude diagrams. Thousands of AGB stars brighter than the tip of the RGB (TRGB) are present in the sample (between 60 and 400 per galaxy), hence, the Poisson noise has little impact in our measurements of the AGB/RGB ratio. We model the photometric data with a few sets of thermally pulsing AGB (TP-AGB) evolutionary models with different prescriptions for the mass loss. This technique allows us to set stringent constraints on the TP-AGB models of low-mass, metal-poor stars (with M < 1.5 M_⊙, [Fe/H] ≾ -1.0). Indeed, those which satisfactorily reproduce the observed AGB/RGB ratios have TP-AGB lifetimes between 1.2 and 1.8 Myr, and finish their nuclear burning lives with masses between 0.51 and 0.55 M_⊙. This is also in good agreement with recent observations of white dwarf masses in the M4 old globular cluster. These constraints can be added to those already derived from Magellanic Cloud star clusters as important mileposts in the arduous process of calibrating AGB evolutionary models.

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Olsen, Knut A. G. 0000-0002-7134-8296
Additional Information:© 2010 The American Astronomical Society. Received 2010 July 26; accepted 2010 September 23; published 2010 November 10. L.G. and P.M. acknowledge financial support from contract ASI-INAF I/016/07/0 and INAF/PRIN07 CRA B.F.W., J.J.D., P.R., and D.R.W. acknowledge financial support from HST GO-10915. K.M.G. acknowledges support from HST GO-10945. P.R. acknowledges the Achievement Rewards for College Scientists (ARCS) Fellowship. J.J.D. and P.R. were partially supported by AR-10945, GO-11718, and GO-11307. This work is based on observations made with the NASA/ ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. Support for this work was provided by NASA through grant Nos. GO-10915 and GO- 10945 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. This research has made use of the NASA/IPAC Infrared Science Archive and the NASA/IPAC Extragalactic Database (NED), which are both operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made extensive use of NASA’s Astrophysics Data System Bibliographic Services. Facilities: HST (ACS, WFPC2)
Funding AgencyGrant Number
Agenzia Spaziale Italiana-Istituto Nazionale di Astrofisica (ASI-INAF) I/016/07/0
Hubble Space Telescope (HST)GO-10915
Hubble Space Telescope (HST)GO-10945
Achievement Rewards for College Scientists (ARCS) Fellowship UNSPECIFIED
NASANAS 5-26555
Istituto Nazionale di Astrofisica (INAF)INAF/PRIN07 CRA
Subject Keywords:stars: general
Classification Code:PACS: 97.10.Cv; 97.10.Xq; 97.20.Li; 97.20.Tr; 97.10.Bt
Record Number:CaltechAUTHORS:20101223-095511767
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Official Citation:Léo, G. and et al. (2010). "The ACS Nearby Galaxy Survey Treasury. IX. Constraining Asymptotic Giant Branch Evolution with Old Metal-poor Galaxies." The Astrophysical Journal 724(2): 1030. doi: 10.1088/0004-637X/724/2/1030
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21515
Deposited By: Tony Diaz
Deposited On:12 Jan 2011 18:44
Last Modified:20 Mar 2019 18:24

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