Astron. Astrophys. 363, 917-925 (2000)

3. Spectral energy distributions (SEDs)

Since the 12 and 25 µm are dominated by a different kind of dust (small transiently heated grains, according to Désert et al. 1990 and Dwek et al. 1997), which does not show up at 175 µm, we concentrate on the 60 - 175 µm SEDs. They show a continuous range of shapes. For the purpose of recognising trends we have binned the SEDs into three different types, an example for each is given in Fig. 3. The spectra of type I show a rising flux density with increasing wavelength in a steep slope without any curvature. This indicates a very low temperature, since the maximum of any Planck curve is barely reached at 175 µm. Type II is the most common case, still with a monotonous rising flux density, but with a clear curvature. Type III contains those spectra where the flux density reaches a maximum value within the observed spectral range.

Fig. 3. SEDs of three typical knots: type I = cold (left), II = medium (middle), III = warm (right). The flux errors are smaller than the symbol sizes. The lines indicate modified Planck curves (emissivity ).

The comparison with the temperature of the cold dust component (Sect. 4) shows in fact that the SED types are well correlated to this temperature. Hence we get an unbiased definition of the types by using K ( I), 17 K K ( II), K ( III). The type of each individual source is indicated in Column (8) of Table 1.

© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
helpdesk@link.springer.de