B. A. Wilking

Cold DCO(+) cores and protostars in the warm Rho Ophiuchi cloud

The decrease of DCO(+) abundance with elevation of a clouds T(K) is used to identify a cluster of a dozen of the coldest, youngest dense cores embedded in the L1688, L1689, and L1709 clouds in the Rho Ophiuchi complex. Most of the cores in L1688 have T(K) = 12-14 K, about half that indicated by CO throughout L1688. Ten cold dust shell, protostellar IR point sources are embedded within these cores. Not every DCO(+) core contains a protostar, but every protostar with a steep spectral index is found in close association with DCO(+) emission. The rotational axes for all of the Rho Oph DCO(+) cores are parallel to the ambient magnetic field, regardless of whether a core is elongated parallel or perpendicular to the direction of the magnetic field. In the Taurus complex the ambient magnetic field is perpendicular to the axes of the major filaments and will inhibit further concentration of material. 53 refs.

A millimeter-wave spectral-line and continuum survey of cold IRAS sources

The results of a CO, millimeter-wave continuum, and radio continuum survey of a sample of 50 IRAS sources selected to have cold, bright, far-IR emission and no optical counterparts are presented. The majority of these sources are found to be associated with recent star formation as evidenced by the presence of strong CO emission and high gas column densities along the line of sight. Interferometric observations in the 2.7 mm continuum detected emission from cold dust on scales of less than 35 arcsec in 16 of 39 sources. Source sizes, dust optical depths, masses, and spatial gas densities of these compact dust structures are derived. Two broad classes of dust emission regions are identified: (1) small or unresolved dust structures characterized by high spatial gas densities and large dust optical depths, and (2) extended dust envelopes displaying relatively lower spatial gas densities and dust optical depths. 38 refs.

The circumstellar structure of IRAS 16293-2422 - (C-18)O, NH3, and CO observations

Interferometric observations of the (C-18)O and (C-12)O J = 1-0 transitions, and the NH3 (1, 1) and (2, 2) transitions toward the young far-IR source IRAS 16293-2422 are presented. The data reveal elongated gas structures which are aligned perpendicular to the axis of a bipolar outflow and to the local magnetic field direction. By combining the interferometric data with single-dish spectra of the (C-18)O and (C-17)O lines, a comprehensive model for the IRAS 16293-2422 region is developed. In this model, the compact (C-18)O line and 40 K dust emission arise from rotating material within which the central heat source is embedded. The NH3 emission is distributed in a ring with radius 3000 to 4000 AU surrounding the central disk. The dearth of ammonia emission from the (C-18)O emission region is attributed to an actual decrease in NH3 abundance. 15 refs.

High Angular Resolution Observations of Maser Kinematics Near Low Mass Young Stellar Objects

With the advent of new correlators and dedicated arrays, spectral line VLBI is entering its ascendancy as a probe of a variety of interesting astrophysical environments. One of the most interesting environments where spectroscopic VLBI techniques are valuable are the regions directly coincident with forming stars. In these sources, water maser emission is observed when the outflowing jets of material interact with the surrounding medium. Observations of these water masers dramatically reveal the innermost regions of the star formation process at or below the 1-AU scale. We have found that the water masers clearly trace the jets at these scales. The masers show space motions on the order of 60 to 100 kms −1 and form within a few AU of the exciting protostar. By observing the distributions and motions of the water masers associated with these objects, we may be able to address in greater detail the collimation mechanism of the jets seen in these protostars. In this brief poster proceeding, we provide a summary image of the water masers associated with SVS13, the driving source for the HH 7-11 objects. We have also mapped the masers associated with IRAS 16293-2422, IRAS 05413-0104, IRAS 4A and IRAS 4B, both in the NGC 1333 star forming region. For further information on these sources, please contact any of the authors directly.