THE ACS NEARBY GALAXY SURVEY TREASURY. IX. CONSTRAINING ASYMPTOTIC GIANT BRANCH EVOLUTION WITH OLD METAL-POOR GALAXIES

By L. Girardi, B. Williams, K. Gilbert, P. Rosenfield, J. J. Dalcanton, P. Marigo, M. Boyer, A. Dolphin, D. Weisz, J. Melbourne and 3 more. 2010

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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☉, ). 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/23a3c35063b55fbf0824a884615bf36086b0ec9f

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THE STAR FORMATION HISTORIES OF LOCAL GROUP DWARF GALAXIES. I. HUBBLE SPACE TELESCOPE/WIDE FIELD PLANETARY CAMERA 2 OBSERVATIONS (2014, methodology): “…the following parameters for the SFH solutions: a Kroupa IMF (Kroupa 2001), a binary star fraction of 0.35 with the mass of the secondary drawn from a uniform distribution of mass ratios, and the Padova stellar evolution models of (Girardi et al. 2010), with mass limits ranging from 0.15 to 120 M .”
Making Galaxies in a Cosmological Context: The Need for Early Stellar Feedback (2012, methodology): “The one dimensional, face-on surface brightness profiles were constructed using the stellar population models from Girardi et al. (2010).”
SOPHIE velocimetry of Kepler transit candidates VII. A false-positive rate of 35% for Kepler close-in giant candidates (2012, methodology): “We modeled a binary scenario using stellar atmosphere models of Castelli & Kurucz (2004), light-curve models from JKTEBOP (Southworth 2008) and evolution stracks from Marigo et al. (2008) and Girardi et al. (2010).”
MESA ISOCHRONES AND STELLAR TRACKS (MIST). I. SOLAR-SCALED MODELS (2016, background): “…the models against optical and NIR photometry and spectroscopy of the AGB population in nearby galaxies, including the Magnellanic Clouds, dwarf spheroidals, and spirals (e.g., Marigo & Girardi 2001, 2007; Girardi & Marigo 2007; Girardi et al. 2010; Boyer et al. 2011; Rosenfield et al. 2014).”
A CATALOG OF BULGE, DISK, AND TOTAL STELLAR MASS ESTIMATES FOR THE SLOAN DIGITAL SKY SURVEY (2013, background): “Girardi et al. (2010) show that the evolutionary tracks of Marigo & Girardi (2007) may overestimate the frequency of AGB stars by factors of 3–7, naively suggesting that at Δ log L of −0.3 to −0.8 may be necessary to match the observed data, within the range of the FSPS calibration.”
A NEW GENERATION OF PARSEC-COLIBRI STELLAR ISOCHRONES INCLUDING THE TP-AGB PHASE (2017, methodology): “PARSEC tracks PARSEC (the PAdova and tRieste Stellar Evolutionary Code) represents a deeply-revised version of the Padova code used in many popular sets of isochrones (e.g. in Bertelli et al. 1994; Girardi et al. 2000, 2010; Marigo et al. 2008).”
THE MILKY WAY HAS NO DISTINCT THICK DISK (2011, methodology): “In order to turn this number density N(R0; [Fe/H], [α/Fe]) into a stellar mass we use stellar isochrones in the SDSS photometric system (Girardi et al. 2004; Marigo et al. 2008; Girardi et al. 2010)6 to model the mass M(g−r, τ, [Fe/H]) as a function of color g−r, age τ , and metallicity [Fe/H].”
Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, result): “Examination of the data presented in this Section suggests that the ratio is probably no larger than ∼ 5-10%, being thus consistent with data from other old metal-poor stellar populations (see, e.g., Girardi et al. 2010, for a discussion).”
The Romulus cosmological simulations: a physical approach to the formation, dynamics and accretion models of SMBHs (2016, methodology): “Colors from stellar emission are calculated using tables generated from population synthesis models using http://stev.oapd.inaf.it/cgi-bin/cmd (Marigo et al. 2008; Girardi et al. 2010).”
THE ACS NEARBY GALAXY SURVEY TREASURY. VIII. THE GLOBAL STAR FORMATION HISTORIES OF 60 DWARF GALAXIES IN THE LOCAL VOLUME (2011, methodology): “However, broad uncertainties in the AGB models (e.g., Girardi et al. 2010; Marigo et al. 2010) make the precise age for the drop in dSph SFRs and the degree of synchronization uncertain.”