The ISO-LWS map of the Serpens cloud core I. The SEDs of the IR/SMM sources

Iso-Lws mapping observations of the Serpens molecular cloud core are presen ted. The spectral range is 50 - 200 mum 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. T he strong and fairly isolated source SMM 1/FIRS 1 presented a test case, wh ose modelled spectral energy distribution (SED), within observational error s, is identical to the observed one. The model results for the other infrar ed and submillimetre sources are therefore likely to represent their correc t SEDs. Simulations demonstrating the reliability and potential of the deve loped method support this view. It is found that some sources do not exhibit significant FIR emission and o thers are most likely not pointlike at long wavelengths. In contrast, the S EDs of a number of SMMs are well fit by modified single-temperature blackbo dies over the entire accessible spectral range. For the majority of sources the peak of the SEDs is found within the spectral range of the Lws and der ived temperatures are generally higher (greater than or equal to 30 K) than have been found by earlier deconvolution attempts using IRAS data. SMM siz es are found to be only a few arcsec in diameter. In addition, the SMMs are generally optically thick even at Lws wavelengths, i.e. estimated lambda(t au = 1) are in the range 160-270 mum. The Rayleigh-Jeans tails are less steep than expected for optically thin du st emission. This indicates that the SMMs are optically thick out to longer wavelengths than previously assumed, an assertion confirmed by self-consis tent radiative transfer calculations. Models were calculated for five sourc es, for which sufficient data were available, viz. SMM 1, 2, 3, 4 and 9. Th ese models are optically thick out to millimetre wavelengths (wavelength of unit optical depth 900 to 1 400 mum). Envelope masses for these SMMs are i n the range 2-6 M., which is of course considerably more massive than estim ates based on the optically thin assumption. The luminosities are in the ra nge 10-70 L., suggesting the formation of low-mass to intermediate mass sta rs, so that the existence of such massive envelopes argues for extreme yout h of the SMMs in the Serpens cloud core. Finally, we present, for the first time, the full infrared SEDs for the out burst source DEOS, both at high and low intensity states.