Detection of the Circumstellar Disk Associated with 2MASS J0820-8003 in
  the eta Cha Cluster
  The Nearby Young Moving Groups (NYMGs) of stars are ideal for the study of
evolution circumstellar disks in which planets may form because their ages
range from a few Myr to about 100 Myr, about the same as the interval over
which planets are thought to form. Their stars are distributed over large
regions of the sky. Hence, the Wide Field Infrared Survey Explorer (WISE) which
scanned the entire sky in four bands from 3.4 to 22.1 mu provides a database
well-suited for the study of members of the NYMGs, particularly those
identified after the eras of the IRAS and Spitzer observatories. We report our
study of the stars in the epsilon and eta Cha, TW Hya, beta Pic, Tuc-Hor, and
AB Dor NYMGs. The WISE Preliminary Release Source Catalog, which covers 57% of
the sky, contains data for 64% of the stars in our search lists. WISE detected
the 11.6 and 22.1 mu emission of all the previously known disks except for the
coldest one, AU Mic. WISE detected no disks in the Tuc-Hor and AB Dor groups,
the two oldest in our sample; the frequency of disks detected by WISE decreases
rapidly with age of the group. WISE detected a circumstellar disk associated
with 2M J0820-8003, a pre-main sequence star with episodic accretion in the ~ 6
Myr old eta Cha cluster. The inner radius of the disk extends close to the
star, ~0.02 AU and its luminosity is about a tenth that of the star. The
episodic accretion is probably powered by the circumstellar disk discussed
here.
