Theoretical models of star formation make predictions about the density and velocity structure of the envelopes surrounding isolated , low-mass young stars .
This paper tests such models through high quality submillimeter continuum imaging of four embedded young stellar objects in Taurus and previously obtained molecular-line data .
Observations carried out with the Submillimeter Continuum Bolometer Array on the James Clerk Maxwell Telescope at 850 and 450 \mu m of L1489 IRS , L1535 IRS , L1527 IRS , and TMC 1 reveal \sim 2000 AU elongated structures embedded in extended envelopes .
The density distribution in these envelopes is equally well fit by a radial power-law of index p = 1.0 –2.0 or with a collapse model such as that of Shu ( 1997 : ApJ , 214 , 488 ) .
This inside-out collapse model predicts ^ { 13 } CO , C ^ { 18 } O , HCO ^ { + } , and H ^ { 13 } CO ^ { + } line profiles which closely match observed spectra toward three of our four sources .
This shows that the inside-out collapse model offers a good description of YSO envelopes , but also that reliable constraints on its parameters require independent measurements of the density and the velocity structure , e.g. , through continuum and line observations .
For the remaining source , L1489 IRS , we find that a model consisting of a 2000 AU radius , rotating , disk-like structure better describes the data .
Possibly , this source is in transition between the embedded Class I and the optically revealed T Tauri phases .
The spectral index of the dust emissivity decreases from \beta = 1.5 –2.0 in the extended envelope to 1.0 \pm 0.2 in the central peaks , indicating grain growth or high optical depth on small scales .
The observations of L1527 IRS reveal warm ( \gtrsim 30 K ) material outlining , and presumably heated by , its bipolar outflow .
This material comprises \lesssim 0.2 M _ { \odot } , comparable to the amount of swept-up CO but only 10 % of the total envelope mass .
Two apparently starless cores are found at \sim 10 , 000 AU from L1489 IRS and L1535 IRS .
They are cold , 10–15 K , contain 0.5–3.0 M _ { \odot } , and have flat density distributions characterized by a Gaussian of \sim 10 , 000 AU FWHM .
The proximity of these cores shows that star formation in truly isolated cores is rare even in Taurus .