Spitzer Far-Infrared Detections of Cold Circumstellar Disks

Observations at 70 microns with the Spitzer Space Telescope have detectedseveral stellar systems within 65 pc of the Sun. Of 18 presumably young systemsdetected in this study, as many as 15 have 70-micron emission in excess of thatexpected from their stellar photospheres. Five of the systems with excesses aremembers of the Tucanae Association. The 70-micron excesses range from a factorof ~2 to nearly 30 times the expected photospheric emission from these stars.In contrast to the 70-micron properties of these systems, there is evidence foran emission excess at 24 microns for only HD 3003, confirming previous resultsfor this star. The lack of a strong 24-micron excess in most of these systemssuggests that the circumstellar dust producing the IR excesses is relativelycool (T_dust < 150 K) and that there is little IR-emitting material within theinner few AU of the primary stars. Many of these systems lie close enough toEarth that the distribution of the dust producing the IR excesses might beimaged in scattered light at optical and near-IR wavelengths.Comment: Accepted for publication in The Astrophysical Journal Letters; 5 pages, 2 tables, 2 figure