Testing Protostellar Collapse Theory through Extinction Mapping

The identification of collapsing protostars remains a ``holy grail'' of star formation studies. The best collapse candidate is generally recognized to be B335, an isolated round globule containing a deeply embedded low luminosity young stellar object {detected only at Lambda>60 Mum}. In an influential study, Zhou et al. {1993} observed a variety of trace molecules in B335 and showed that detailed radiative transfer models based on the velocity and density fields of the ``inside-out'' collapse theory developed by Shu {1977} reproduced the spectra extremely well. Here we propose to use NICMOS to obtain near-infrared photometry of background stars shining through B335, to measure the density field in a way that suffers from none of the problems inherent in molecular line work {abundances, opacities, unknown collision rates, etc.}. Ground based data show that the projected reddening distribution at large radii {>30''} is in good agreement with an npropto r^-2 density profile. Deeper observations using NICMOS will probe into higher extinctions and smaller radii and show directly if the density field has relaxed to the npropto r^-1.5 form predicted for collapse. The proposed observations take advantage of the high sensitivity of NICMOS to sample the B335 infall zone to equivalent visual extinctions of 50 magnitudes or more, a regime that simply cannot be probed from the ground.