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Session 92 - Very Young Stars, T-Tauri Stars, H-H Objects.
Oral session, Friday, January 09

[92.02] Unveiling the Disk and Envelope: A Sub-Arcsecond Survey of YSOs

L. W. Looney (U. Maryland)

We present results of the first sub-arcsecond resolution survey of YSOs in the \lambda = 2.7 millimeter continuum. The sample ranges in evolution from deeply embedded, optically invisible systems to optically visible, T Tauri systems. The observations are fully sampled spatially from 0.4" out to 50", measuring size scales in Taurus from 60 AU (proto-solar system size scales) to 7000 AU (envelope size-scales). The two orders of magnitude in spatial sampling allows us to image circumstellar disks, search for embedded binaries, and examine in detail the envelope-disk connection.

Among the optical T Tauri stars, we resolve circumstellar disks in the HL Tauri and DG Tauri systems (disk sizes of 100 AU) and the larger circumbinary disk of the binary system GG Tauri. For the embedded sources (NGC 1333 IRAS4 amp; IRAS2, IRAS 16293-2422, VLA 1623, L1448 IRS3, SVS 13, and L1551 IRS5), we find that a resolution of at least 1.5" is needed to separate the strong, extended envelope emission from the compact emission at the cores of these systems. Only when the emission is separated into these two components can one begin to model the deeply embedded YSO structure.

By combining imaging and modeling of the systems, we examine the structure of the disks and envelopes and their implications for planet formation. In particular, the circumstellar disks in the deeply, embedded systems are generally less massive and smaller than in the older systems. Since their infall rates are expected to be higher due to their more massive envelopes, either the embedded disks are more efficient at transporting mass onto the star or the masses of the disks are limited by dynamical processes. This flushing of material through the disk onto the star may impede planet formation in these younger, embedded systems.

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