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

Larsson, B.; Liseau, R.; Men'schikov, A. B.; Olofsson, G.; Caux, E.; Ceccarelli, C.; Lorenzotti, D.; Molinari, S.; Nisini, B.; Nordh, L.; Saraceno, P.; Sibille, F.; Spinoglio, L. and White, G. J. (2000). The ISO-LWS map of the Serpens cloud core. I. The SEDs of the IR/SMM sources. Astronomy & Astrophysics, 363 pp. 253–268.



ISO-LWS mapping observations of the Serpens molecular cloud core are presented. The spectral range is 50 - 200 μm 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 SMM 1/FIRS 1 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.

It is found that some sources do not exhibit significant FIR emission and others are most likely not pointlike at long wavelengths. In contrast, the SEDs of a number of SMMs are well fit by modified single-temperature blackbodies 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 derived temperatures are generally higher (≥ 30 K) 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, i.e. estimated λ (τ=1) are in the range 160-270 μm.

The Rayleigh-Jeans tails are less steep than expected for optically thin dust emission. This indicates that the SMMs are optically thick out to longer wavelengths than previously assumed, an assertion confirmed by self-consistent radiative transfer calculations. 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 1 400 μm). Envelope masses for these SMMs are in the range 2-6 M, which is of course considerably more massive than estimates based on the optically thin assumption. The luminosities are in the range 10-70 L, 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.

Finally, we present, for the first time, the full infrared SEDs for the outburst source DEOS, both at high and low intensity states.

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