2008ApJ...683..813G

We have mapped the η Chamaeleontis young stellar association in the far-infrared with the Multiband Imaging Photometer for Spitzer (MIPS) on the Spitzer Space Telescope. All 16 members within the map region were detected at 24 µm, along with five members at 70 µm and two at 160 µm. Ten stars show far-infrared excess emission indicating the presence of circumstellar disks; six of these have central clearings as evidenced by the onset of excess emission at λ>5 µm. No new infrared-excess sources are identified among the 113 2MASS field stars with 24 µm photometry but not seen as X-ray sources, indicating that membership lists derived from X-ray surveys are reasonably complete. Circumstellar disks in the η Cha association span the range from 10^–1 to 10^–4 in their fractional infrared luminosity, with a median L_d/L_* of 0.04. The presence of optically thick, optically thin, and intermediate optical depth disks within the same stellar group, in combination with the large fraction of disks with inner holes, indicates that the η Cha association represents a crucial stage in circumstellar disk evolution.