Unveiling the circumstellar envelope and disk: A subarcsecond survey of circumstellar structures

We present the results of a lambda = 2.7 mm continuum interferometric surve y of 24 young stellar objects in 11 fields. The target objects range from d eeply embedded class 0 sources to optical T Tauri sources. This is the firs t subarcsecond survey of the lambda = 2.7 mn dust continuum emission from y oung, embedded stellar systems. These multiarray observations, utilizing th e high dynamic u-nu range of the BIMA array, fully sample spatial scales ra nging from 0 ".4 to 60 ", thus allowing the first consistent comparison of dust emission structures in a variety of systems. The images show a diversi ty of structure and complexity. The optically visible T Tauri stars (DG Tau ri, HL Tauri, GG Tauri, and GM Aurigae) have continuum emission dominated b y compact (less than or equal to 1 ") circumstellar disks. In the cases of HL Tauri and DG Tauri, the disks are resolved. The more embedded near-infra red sources (SVS 13 and L1551 IRS 5) have continuum emission that is extend ed and compact. The embedded sources (L1448 IRS 3, NGC 1333 IRAS 2, NGC 133 3 IRAS 4, VLA 1623, and IRAS 16293 - 2422) have continuum emission dominate d by the extended envelope, typically greater than or equal to 85% of the e mission at lambda = 2.7 mm. In many of the deeply embedded systems, it is d ifficult to uniquely isolate the disk emission component from the envelope extending inward to AU-sized scales. Simple estimates of the circumstellar mass in the optical/infrared and embedded systems are in the ranges 0.01-0. 08 M. and 0.04-2.88 M., respectively. All of the target embedded objects ar e in multiple systems with separations on scales of similar to 30 " or less . Based on the system separation, we place the objects in three categories: separate envelope (separation greater than or equal to 6500 AU), common en velope (separation 150-3000 AU), and common disk (separation less than or e qual to 100 AU). These three groups can be linked with fragmentation events during the star formation process: separate envelopes from prompt initial fragmentation and the separate collapse of a loosely condensed cloud, commo n envelopes from fragmentation of a moderately centrally condensed spherica l system, and common disk from fragmentation of a high angular momentum cir cumstellar disk.