Young Stellar Associations Cleanup: A Deep Circumstellar Disk Census at Ages 8-12 Myrs

Details Young Stellar Associations Cleanup: A Deep Circumstellar Disk Census at Ages 8-12 Myrs Young Stellar Associations Cleanup: A Deep Circumstellar Disk Census at Ages 8-12 Myrs

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50316r&link_type=abstract

Spitzer Proposal ID #50316

Physics

Scientific paper

The transformation of primordial protoplanetary disks into optically thin debris disks takes place very early in a star's life. The youngest debris disks are therefore of great interest for disk evolution studies, as their properties can define the mechanisms and timescales for planet formation. In the age range 8-12 Myrs, three nearby young stellar associations are crucial to these studies: eta Chamaeleontis, TW Hydrae, and beta Pictoris. Spitzer/MIPS studies of these groups have found that both optically thick and thin disks are present at 8 Myrs, but only optically thin disks at 12 Myrs. Disk inner holes, diagnosed by the presence of 70 micron excess and absence of 24 micron excess, are found so far in only the beta Pictoris group. Disk fractions of 30-50% have been measured at 24 microns down to the photospheric limit. However, at 70 microns, the existing data are relatively shallow, probing to only to 3-20 times the photospheric limit, and providing a lower limit to the disk fraction > 30%. We propose to obtain much deeper measurements (10 cycles of 70 micron photometry) for 37 members of these groups not yet detected at 70 microns, and which are found in regions of low to medium background emission, In addition, we include 24 micron observations for two eta Cha members that fell outside the scan map region in the original study. The results of this program will allow an assessment of the frequency of disks down to Ld/Lstar ~0.0002 across the full membership of these young associations, thereby consolidating the Spitzer science legacy for early disk evolution.

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