Astron. Astrophys. 339, 183-186 (1998)

4. The continuum spectra of the sources

In Figs. 3 and 4 we show the continuum spectra of the observed sources. The straight line is a fit to the data points in the form

which reflects the contribution from free-free emission and from two dust-continuum-emission components. The parameters of the spectral fit are given in Table 4 for in units of 100 GHz. The observations listed in Table 3 have been put into reasonable bins and are shown as filled dots. The uncertainty of the curves shown in the figure (especially in the short submm-range) can be estimated by comparing the flux densities at a given frequency observed with different resolutions. For both sources such data are available from the JCMT at 384 GHz and in the 860 GHz range, where the published peak flux densities at a given frequency vary by factors of 1.2-1.5 depending on the aperture. After applying the corrections to the peak flux data, the corrected flux densities plotted in Figs. 3 and 4 nearly merge and the differences become comparable or smaller than the internal observational errors. We think that this is a good indicator that the applied procedure works properly.

Fig. 1. Broadband 1.2 mm dust continuum map of W 3(OH) observed with the IRAM 7-channel bolometer array. Contour levels are: -0.65, 0.65, 1.3, 2, 3, 4, 5, 6 Jy/beam.

Fig. 2. Broadband 1.2 mm map of K 3-50A. Contour levels are: -0.15, 0.15, 0.3, 0.45, 0.6, 0.9, 1.2, 1.6, 2, 3, 4, 5, 6 Jy/beam The North-Eastern extension is K 3-50B (e.g. Salter et al. 1989)

Fig. 3. The mm-to-submm continuum spectrum of the HII Region W 3(OH). The filled points are binned data listed in Table 3. Open circles are measurements by Sandell (1994) and the open triangles are data points from Altenhoff et al. (1994) at 250 GHz and from Chini et al. (1986) at 850 GHz. All the data have been multiplied following Eq. (1) and the procedure described in the text. The solid line is the fit to the observed points after Eq. (2) and the dotted lines are the contributions from one free-free and two dust components. The parameters of the fit are given in Table 4

Fig. 4. The mm-to-submm continuum spectrum of K 3-50A. The symbols are the same as in Fig. 3.

Table 3. List of measured flux densities

For a calibration check, it is necessary to get the flux of one of the sources for a given frequency and beam size. This is simply done by calculating the integrated flux of the source using the parameters given in Table 4 and then to scale down the calculated flux according to

Table 4. Fit parameters

© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998
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