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

5. FIR colours of the knots

In order to visualize the spectral shape of all knots at once Fig. 4 shows the colour-diagram, where is plotted against . For each SED type a different symbol has been chosen for better identification. The types are clearly distributed on different regions in the diagram, although they do not separate completely. The colour-diagram emphasizes the gain, provided by the 175 µm data. Whereas the knots are not distinguished along the axis, the inclusion of 175 µm yields the separation of the types. is actually a colour temperature indicator.

Fig. 4. FIR colour - colour diagram: The colour is plotted against for each knot. The three SED types are indicated by different symbols: = I (cold), = II (medium), = III (warm).

The triangle in the lower left corner of Fig. 4 belongs to Knot 27, which is the nucleus of M 31 having the bluest colour and therefore being the warmest knot, as already discussed by Habing et al. (1984) and Hoernes et al. (1998). From a single modified Planck fit to the SED, its temperature is estimated at about 29 K ( -emissivity law). As the 175 µm map gives no new information for such warm dust in addition to the 60 µm and 100 µm, we exclude this source from our further discussion.

© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
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