Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...547..840s&link_type=abstract
The Astrophysical Journal, Volume 547, Issue 2, pp. 840-861.
Astronomy and Astrophysics
Astronomy
22
Stars: Circumstellar Matter, Ism: Clouds, Ism: Molecules, Stars: Formation, Stars: Pre-Main-Sequence
Scientific paper
A dense gas survey was carried out toward 10 low-mass embedded young sources in Taurus with the Nobeyama Millimeter Array (NMA) to investigate protostellar evolution. All the sources were observed in the H13CO+(J=1-0) line, a high-density tracer. Significant H13CO+ emission (>=4.5 σ) was detected toward six of them. The H13CO+ emission is distributed roughly perpendicular to the molecular outflow axes, indicating that the H13CO+ line traces the dense envelopes associated with the central stars. The sizes and masses of the dense envelopes are estimated to be (1-7)×103 AU and 0.01-0.2 Msolar, respectively. The 10 sources are divided into the following three classes based on their H13CO+ intensities of the NMA maps, and their properties are studied using our own and other available data. Class A sources have H13CO+ emission centered on the star with its elongation perpendicular to the molecular outflow axes. These sources also have dense outflowing gas and centrally condensed parent cores. Class B sources have H13CO+ emission near the source positions and dense outflowing gas. The parent cores around class B sources, however, have a shallower density profile. Class C sources have neither H13CO+ emission nor wing emission in dense gas tracers. From these properties, we conclude that low-mass protostars evolve from class A, B to C sources by dissipating their parent cloud cores, which is consistent with the widely accepted ideas of star formation. In addition, these observational data suggest that significant dispersion of a parent core by a molecular outflow and main accretion phase ends at the early protostellar phase. Six of the 10 sources are detected in continuum emission at 87 GHz. The intensities of the H13CO+ emission do not correlate with the flux densities at 87 GHz. This is because our continuum maps trace compact disks on a 102 AU scale and not dense gas on a 103-4 AU scale.
Kawabe Ryo
Kitamura Yoshimi
Saito Masao
Sunada Kazuyoshi
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