NEW DEBRIS DISK CANDIDATES AROUND 49 NEARBY STARS

Abstract

We present 49 new candidate debris disks that were detected around nearby stars with the Spitzer Space Telescope using the Multiband Imaging Photometer (MIPS) at 24 μm (MIPS24) and 70 μm (MIPS70). The survey sample was composed of stars within 25 pc of the Sun that were not previously observed by any other MIPS survey. Only stars with V < 9 were selected, corresponding to spectral types earlier than M0. MIPS24 integration times were chosen to detect the stellar photosphere at 10σ levels or better. MIPS70 observations were designed to detect excess infrared emission from any star in the MIPS70 sample with a disk as luminous at that around epsilon Eridani. The resulting sample included over 436 nearby stars that were observed with both MIPS24 and MIPS70, plus an additional 198 observed only with MIPS24. Debris disk candidates were defined as targets where excess emission was detected at 3σ levels or greater, and the ratio of observed flux density to expected photosphere emission was three standard deviations or more above the mean value for the sample. The detection rate implied by the resulting 29 MIPS24 candidates is 4.6%. A detection rate of 4.8% is implied by 21 MIPS70 candidates. The distribution of spectral types for stars identified as candidates resembles that of the general sample and yields strong evidence that debris-disk occurrence does not decrease for K dwarfs. Modeling of non-uniform sensitivity in the sample is required to interpret quantitative estimates of the overall detection frequency and will be presented in a future work.