Contents of: VI/111/./abstract/PANDRE_PA_DARK.abs

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==> This proposal is an extension of PANDRE.PA_PROTO and LNORDH.SURVEY_1
We propose to conduct CAM LW2 mapping observations of a broad sample of
starless dense cores (with no associated IRAS sources) located within
optically opaque spots of the sky. These cores are presumably pre-collapse
and pre-stellar in nature and provide good laboratories for studying the
initial conditions of star formation. The LW2/LW3 images of the rho Oph
main cloud (Abergel et al. 1996) obtained as part of LNORDH.SURVEY_1
demonstrate that CAM is sensitive enough to detect dense clumps in
absorption (against the diffuse mid-IR background produced by the
interstellar radiation field or arising from cloud envelopes). The high
angular resolution and high mapping speed of CAM thus offer a unique
opportunity to search for small-scale structure within a large number of
cloud cores. We have selected for study a sample of dark clouds/globules
which all have a relatively strong (> 1 MJy/sr) estimated background at
6.75 um and span a wide range of properties (e.g. morphologies,
environments). Our proposed absorption survey should bring invaluable
information on the structure of pre-stellar cores and on the process of
cloud fragmentation. It is crucial to study a large number of cores in
order to build a complete theoretical picture. Based on the rho Oph
example, we expect to discover many new pre-stellar and/or protostellar
dense clumps that we intend to study in detail at a later stage by means of
follow-up molecular-line and continuum observations with large ground-based
(sub)millimeter radiotelescopes. By comparing the column densities derived
from mid-IR extinction profiles with those estimated from mm continuum
maps, an immediate scientific return of our survey will be the relative
calibration of the uncertain dust absorptivities in the mm and the mid-IR
for a whole range of core densities.

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