Completion of a SCUBA Survey of Lynds Dark Clouds and Implications for Low-mass Star Formation

Details Completion of a SCUBA Survey of Lynds Dark Clouds and Implications for Low-mass Star Formation Completion of a SCUBA Survey of Lynds Dark Clouds and Implications for Low-mass Star Formation

Nov 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aj....124.2756v&link_type=abstract

The Astronomical Journal, Volume 124, Issue 5, pp. 2756-2789.

Astronomy and Astrophysics

Astronomy

76

Ism: Clouds, Stars: Formation, Stars: Pre-Main-Sequence

Scientific paper

We have carried out a survey of optically selected dark clouds using the bolometer array SCUBA on the James Clerk Maxwell Telescope at λ=850 μm. The survey covers a total of 0.5 deg2 and is unbiased with reference to cloud size, star formation activity, and the presence of infrared emission. Several new protostars and starless cores have been discovered; the protostars are confirmed through the detection of their accompanying outflows in CO (2-1) emission. The survey is believed to be complete for Class 0 and Class I protostars, and yields two important results regarding the lifetimes of these phases. First, the ratio of Class 0 to Class I protostars in the sample is roughly unity, very different from the 1:10 ratio that has previously been observed for the ρ Ophiuchi star-forming region. Assuming star formation to be a homogeneous process in the dark clouds, this implies that the Class 0 lifetime is similar to the Class I phase, which from infrared surveys has been established to be ~2×105 yr. It also suggests there is no rapid initial accretion phase in Class 0 objects. A burst of triggered star formation some ~105 yr ago can explain the earlier results for ρ Ophiuchus. Second, the number of starless cores is approximately twice that of the total number of protostars, indicating a starless core lifetime of ~8×105 yr. These starless cores are therefore very short lived, surviving only two or three free-fall times. This result suggests that, on size scales of ~104 AU at least, the dynamical evolution of starless cores is probably not controlled by magnetic processes.

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