Rainfall from Protostellar Envelopes onto Protoplanetary Disks


First Author:
Dan Watson
Email: dmw AT pas.rochester.edu
University of Rochester
Department of Physics and Astronomy, University of Rochester
Rochester, NY 14627 USA
Coauthors:
Puravankara, Manoj, University of Rochester
Sheehan, Patrick, University of Rochester
Allen, Lori, Center for Astrophysics
Bergin, Edwin, University of Michigan
Calvet, Nuria, University of Michigan
Forrest, William, University of Rochester
Furlan, Elise, Jet Propulsion Laboratory
Hartmann, Lee, University of Michigan
Houck, James, Cornell University
Maret, Sebastien, l'Observatoire de Grenoble
Megeath, S. Thomas, University of Toledo
Melnick, Gary, Center for Astrophysics
Najita, Joan, National Optical Astronomy Observatory
Neufeld, David, Johns Hopkins University

Abstract

Class 0 protostars, the youngest type of young stellar objects, show many signs of rapid development from their initial, spheroidal configurations. They are therefore studied intensively for details of the formation and nature of the dense cores within protostellar envelopes. At millimeter wavelengths, kinematic signatures of envelope collapse have been observed in several such objects. These objects and many more Class 0s also show evidence of strong high-velocity bipolar outflows. The long-sought link between these two flows and the central protostar -- the embedded protoplanetary disk -- has recently been discovered in observations with the Spitzer Space Telescope's Infrared Spectrograph. We have detected rich emission spectra of water vapor, at wavelengths 20-37 microns, in ten Class 0 objects in the NGC 1333, Orion A and Chamaeleon II clouds. The observations indicate directly the presence of extremely dense, warm gas from regions of Solar-system dimension. Models based upon vigorous infall onto a disk, in the form of a plane-parallel disk-accretion shock, reproduce the observed spectra well. More complex models will enable precise constraints to be placed on the structure and stability of the youngest protoplanetary disks. The observations also show directly that water arrives in protoplanetary disks as a warm vapor rather than ice, thus erasing any chemical signature of this material's interstellar origins.
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