I adopt the following general recipe for the detection of infall and the subsequent detailed study of candidate protostars:

• Map optically thick density tracers - HCO+, CS using millimeter and submillimeter single dish telescopes like:
  • FCRAO
  • HHT
  • CSO
  • JCMT
• From optically thick maps:
  • Asymmetric Blue Line signature
  • Blue-bulge signature
• Optically thin tracer - in conjunction with thick isotope, derive optical depth profile
• CO Outflow
  • Rotational axis and outflow direction
  • Effect of outflow on HCO+, CS line profiles
• Effect of Angular Resolution on Observations. Observe same transition at different resolutions.
• Millimeter interferometer studies of blue-bulge at high angular resolution
• FCRAO observations to make large scale maps. Study envelope structure and extent of outflow
• N₂H+ observations to derive v_LSR of source.

• Survey and detailed study of selected list of low-mass and high-mass protostellar regions for the blue-bulge infall signature. [Collaborators: Gerald Moriarty-Schieven (JCMT), Chris Walker (UA), Harold Butner (HHT)].
• Search for episodic outflows [Collaborators: Ron Snell UMass].
• Observational study of triggered star-formation [Collaborators: Chris DeVries and Ron Snell UMass].

In a recently published paper, we presented the first detection of the theoretically predicted blue-bulge signature of infall. Shown below is the detection of the blue-bulge in multiple transitions:

IRAS 16293 Centroid Velocity Maps showing the ``Blue-Bulge'' Infall Signature. In all four panels, the centroid velocities only in the linecore (2 to 6 km/s) are shown. The central 40" × 40" is shown. In all four panels, the positions of the two VLA sources detected by Wootten (1989) are marked in the maps with stars. The velocity of the ambient cloud (4 km/s) has been subtracted in the maps. Blueshifted velocities are shown in dashed blue contours, and redshifted velocities are shown in solid red contours. It can be seen that in the central regions, blueshifted velocities bulge into what would otherwise be the redshifted half of the rotational axis. (a) Contour map of the centroid velocities in the line core of the CSO CS J=5-4 emission toward IRAS 16293. Contour levels are -0.5 to 0.5 km/s, in steps of 0.08 km/s. (b) Contour map of the centroid velocities in the line core of the HHT HCO+ J=3-2 emission. Contour levels are -0.8 to 1 km/s, in steps of 0.07 km/s. (c) Contour map of the centroid velocities in the line core of the CSO CS J=7-6 emission toward IRAS 16293. Contour levels are -0.6 to 0.6 km/s, in steps of 0.1 km/s. (d) Contour map of the centroid velocities in the line core of the JCMT HCO+ J=4-3 emission toward IRAS 1629 3. Contour levels are -0.7 to 0.7 km/s, in steps of 0.1 km/s.

Accretion processes and molecular outflows seem to be an integral part of star formation. Molecular outflows are believed to be driven by accretion in the protostellar disk. Due to the small physical scales and large obscuration, accretion processes cannot presently be observed easily. However, because of the believed accretion-outflow connection, the more extended molecular outflows can provide a convenient time-history of accretion activity onto the underlying YSO. Indeed, using CSO, BIMA and NRAO 12m observations of CO, I have found evidence for multiple outbursts from the Cepheus A molecular outflow (see Narayanan and Walker 1996).

Past Observational Projects