Meixner, M. ; Riebel, D. ; Groenewegen, M. ; Whitelock, P. ; Feast, M. ; Cook, K. ; Whitney, B. ; Ita, Y. ; Hora, J. ; Boyer, M. ; Sargent, B. ; Srinivasan, S. ; Kemper, C. ; Cioni, M.-R. ; van Loon, J. ; Babler, B. ; Churchwell, E. ; Cohen, M. ; Fraser, O. ; Marengo, M. ; Matsunaga, N. ; Matsuura, M. ; Meade, M. ; Otsuka, M. ; Vijh, U. ; Wood, P. ; Woods, P.

published in Spitzer Proposal, pp. 70020 (2010)

Abstract: Using data from the Spitzer Surveys of the Large Magellanic Cloud (LMC) and Small Magellanic cloud (SMC): Surveying the Agents of Galaxy Evolution (SAGE), we have been able to classify candidate asymptotic giant branch (AGB) star populations, estimate their mass-loss rates based on infrared excesses and derive infrared period-luminosity (P-L) relationships from a sample of ~30,000 stars. However, the intrinsic variability of these sources, especially at 3.6 and 4.5 microns, which sample the peak of the SEDs, causes our estimates of the mass-loss rate to be uncertain by a factor of ~2, and produces a scatter of ± 1 mag in the period-luminosity relationship at these wavelengths. We propose to obtain 4 additional epochs of data at both 3.6 and 4.5 microns for ~6100 and ~1500 AGB variable stars in the bar regions of the LMC and Small Magellanic Cloud (SMC), respectively. These data will provide, for the first time, precise (+/- 0.05 mag) mean magnitudes at the crucial peak of the SED for these sources. This accuracy will allow us to use radiative transfer modeling to reduce the uncertainty in our estimates of the mass-loss rate by a factor of ~2, and the scatter in the P-L relationship by a factor of ~20. The reduced scatter will make the P-L relationship of AGB stars a viable distance indicator for future IR missions, such as JWST. The proposed survey area overlaps deliberately with the OGLE-III, SuperMacho, and IRSF variability surveys of the LMC and SMC, adding to the legacy value of our proposed variability study.

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