We propose deep CAM imaging of two high density cores in the archetypal
quiescent cloud TMC-1. Such imaging will yield the actual density
distribution of the cloud cores and the possible presence of first-
protostars. Our recent experience with deep CAM imaging at 7 microns
in the L183 dark cloud has shown that it is possible to detect absorption
(see Fig. 1) by the very high density protostellar core regions,
n_H2~ 10^6 cm-3, where CAM dust absorption is the ONLY reliable density
tracer. What we observe in L183 may represent a very early shortlived
phase in the birth of a star. These results motivated us to apply for
discretionary time for a high sensitivity study of TMC-1, which is the most
thoroughly observed and modelled dense molecular cloud to date and contains
two dense cores which may be in a similar/later stage of star formation.
TMC-1 is also a well observed cloud with ISO. It is part of a large ISOCAM
guaranteed time mapping programme by LNORDH et al. (SURVEY_2), however
their sensitivity is far too low to detect any absorption such as we have
seen in L183, and to detect low-luminosity so-called "class -I" (Boss
& Yorke 1995) first-protostars which lie between precollapse clouds and
the class 0 protostars. We propose deep rasters of much smaller regions
using microscanning and will approach the highest sensitivity achievable
with ISO, up to a factor of 10 better than that achievable in the project
of Nordh et al. Since TMC-1 is the prime testing object for astrochemical
models, such a deep investigation is highly warranted.
Deep high resolution dust absorption maps of the two cores at 7 microns
in CAM LW2 would give a direct and independent estimate of the density
distribution in this cloud. In addition we want to investigate if TMC-1 is
truly quiescent by observing it at 15 microns in CAM LW3 which is sensitive
to cold low-luminosity protostars. Due to the proximity of TMC-1 and the
excellent sensitivity of ISO, we should be able to detect any point-like
object for which the luminosity is higher than 10^-5 Lsun with ISOCAM. In
case of a detection, this will be the first observation of a true protostar.