Boyer, M. ; Barmby, P. ; Bonanos, A. Z. ; Gehrz, R. D. ; Gordon, K. D. ; Groenewegen, M. ; Lagadec, E. ; Lennon, D. ; Marengo, M. ; McQuinn, K. B. W. ; Meixner, M. ; Skillman, E. D. ; Sloan, G. C. ; van Loon, J. T. ; Zijlstra, A.

published in Spitzer Proposal, pp. 80063 (2011)

Abstract: Highly evolved stars (massive stars and intermediate-mass Asymptotic Giant Branch -or AGB- stars) can become heavily enshrouded in dust. This material is ejected into the interstellar medium (ISM), driving galactic chemical evolution. The dwarf galaxies of the Local Group (LG) are ideal laboratories for studying dusty evolved stars since their stellar populations are resolvable and they span a wide range in metallicity, luminosity, star formation history, ISM content, and interaction history. The majority of known resolvable LG dwarf galaxies (d 2 Mpc) remains unobserved with IRAC or were observed with inadequate areal coverage and/or depth for detecting the dusty stellar population. We propose to complete a uniform census of LG dwarf galaxies with IRAC that is designed to detect and characterize the circumstellar dust around evolved stars, especially those obscured in optical and near-infrared surveys. The dust-producing phase is brief, so it is rare in low-luminosity dwarf galaxies. We must therefore observe a complete sample of dwarf galaxies to build equivalent statistics at each metallicity. Our immediate science goals are to (1) analyze dust content and mass loss in AGB stars, (2) generate intermediate-age star formation histories using AGB stars, (3) analyze the infrared properties of massive evolved stars, and (4) use this survey as a pathfinder for JWST science. These observations and the resulting database will leave a valuable and lasting Spitzer legacy.

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