The M33 varjable star population revealed by Spitzer

K. B.W. McQuinn, Charles E. Woodward, S. P. Willner, E. F. Polomski, R. D. Gehrz, Roberta M. Humphreys, Jacco Th Van Loon, M. L.N. Ashby, K. Eicher, G. G. Fazio

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We analyze five epochs of Spitzer Space Telescope Infrared Array Camera (IRAC) observations of the nearby spiral galaxy M33. Each epoch covered nearly a square degree at 3.6,4.5, and 8.0 μm. The point-source catalog from the full data set contains 37,650 stars. The stars have luminosities characteristic of the asymptotic giant branch and can be separated into oxygen-rich and carbon-rich populations by their [3.6] - [4.5] colors. The [3.6] - [8.0] colors indicate that over 80% of the stars detected at 8.0 μm have dust shells. Photometric comparison of epochs using conservative criteria yields a catalog of 2923 variable stars. These variables are most likely long-period variables amid an evolved stellar population. At least one-third of the identified carbon stars are variable.

Original languageEnglish (US)
Pages (from-to)850-861
Number of pages12
JournalAstrophysical Journal
Issue number2 I
StatePublished - Aug 1 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: individual (M33)
  • Galaxies: stellar content
  • Infrared: stars
  • Stars: AGB and post-AGB
  • Stars: Variables: other

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    McQuinn, K. B. W., Woodward, C. E., Willner, S. P., Polomski, E. F., Gehrz, R. D., Humphreys, R. M., Van Loon, J. T., Ashby, M. L. N., Eicher, K., & Fazio, G. G. (2007). The M33 varjable star population revealed by Spitzer. Astrophysical Journal, 664(2 I), 850-861.