Astronomy Seminar

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Date/Time:Friday, 29 Aug 2014 at 4:10 pm
Location:3 Physics
Contact:Steve Kawaler, Physics and Astronomy
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Infrared variability in the Small Magellanic Cloud using data from Spitzer Space Telescope (Elizabeth Polsdorfer, Iowa State University)

We present our results and source list of variable sources in the Small Magellanic Cloud (SMC). The data are taken from "Surveying the Agents of Galaxy Evolution in the Tidally­ Stripped, Low Metallicity SMC" (SAGE-­SMC) and the Spitzer Survey of the Small Magellanic Cloud (S3MC), taken over three different epochs separated in time from each other by several months to a year. S3MC and SAGE-­SMC cover a region of ~4 deg and ~30 deg, respectively, with data taken from the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) aboard the Spitzer Space Telescope. Thermal infrared variable sources are identified using a combination of the IRAC 3.6, 4.5, 5.8 and 8.0 micron bands and the MIPS 24 micron bands. An error­-weighted flux difference between three intervals of data is used to assess the variability. Of the 8 million sources in the SAGE catalog, we identify ~800 that meet our variability criteria of at least 3? in two neighboring Spitzer bands. We matched the 800 variables to catalogs in the literature of typically variable ­type stars including several evolved stellar types, YSOs and background galaxies. Carbon-­rich AGB stars make up the majority (61%) of our variable sources, with about a third of all sources being also classified as extreme AGB stars. We find small, but significant populations of oxygen-­rich AGB (8.6%), red supergiant (2.8%) and red giant branch stars (<1%). Our survey also includes matches to the literature on Cepheid variable stars (8.6%), young­-stellar objects (5.8%), background galaxies (1.2%) and early type stars (2.8%).