Far-Infrared Properties of M Dwarfs

We report the mid- and far-infrared properties of nearby M dwarfs. Spitzer MIPS measurements were obtained for a sample of 62 stars at 24 mu m, with subsamples of 41 and 20 stars observed at 70 and 160 mu m, respectively. We compare the results with current models of M star photospheres and look for indications of circumstellar dust in the form of significant deviations of K-[24 mu m] colors and 70 pm/24 mu m flux ratios from the average M star values. At 24 mu m, all 62 of the targets were detected; 70 mu m detections were achieved for 20 targets in the subsample observed, and no detections were seen in the 160 mu m subsample. No clear far-infrared excesses were detected in our sample. The average far-infrared excess relative to the photospheric emission of the M stars is at least 4 times smaller than the similar average for a sample of solar-type stars. However, this limit allows the average fractional infrared luminosity in the M-star sample to be similar to that for more massive stars. We have also set low limits (10 super(-4) to 10 super(-9) M [unk] depending on location) for the maximum mass of dust possible around our stars.