ISO-LWS mapping observations of the Serpens molecular cloud core are
presented. The spectral range is 50 - 200 micron and the map size is 8' X 8'.
These observations suffer from severe source confusion at FIR wavelengths and
we employ a Maximum Likelihood Method for the spectro-spatial deconvolution.
The strong and fairly isolated source SMM1 FIRS1 presented a test case, whose
modelled spectral energy distribution (SED), within observational errors, is
identical to the observed one. The model results for the other infrared and
submillimetre sources are therefore likely to represent their correct SEDs.
Simulations demonstrating the reliability and potential of the developed method
support this view. For the majority of sources the peak of the SEDs is found
within the spectral range of the LWS and derived temperatures are generally
higher (>30K) than have been found by earlier deconvolution attempts using IRAS
data. SMM sizes are found to be only a few arcsec in diameter. In addition, the
SMMs are generally optically thick even at LWS wavelengths. Self-consistent
radiative transfer calculations indicates that the SMMs are optically thick out
to even longer wavelengths. Models were calculated for five sources, for which
sufficient data were available, viz. SMM 1, 2, 3, 4 and 9. These models are
optically thick out to millimetre wavelengths (wavelength of unit optical depth
900 to 1400 micron). Envelope masses for these SMMs are in the range 2-6 Msun,
which is of course considerably more massive than estimates based on the
optically thin assumption. The luminosities are in the range 10-70 Lsun,
suggesting the formation of low-mass to intermediate mass stars, so that the
existence of such massive envelopes argues for extreme youth of the SMMs in the
Serpens cloud core.Comment: 17 pages, 21 figures, accepted for publication in A&
