Producing Colour Temperature Maps

 The task of producing colour temperature maps contains at least three separate problems:

1.

Producing two images with similar resolution from two different wavebands.

2.

Subtracting a suitable background from each image.

3.

Calculating the temperature at each pixel.

The first step can be accomplished using the following recipe:

• Create two images from the two separate wavebands as normal (see section ).
• Use each image to generate simulated CRDD, using application SIMCRDD. The input CRDD files (which are used to define the position and PSF for each sample) should be for the other waveband. For instance, if the two wavebands are 60 and 100 $\mu$m, then the 60 $\mu$m image should be sampled at positions defined by the 100 $\mu$m CRDD files, and likewise the 100 $\mu$m image should be sampled at positions defined by the 60 $\mu$m CRDD files.
• The CRDD files generated by SIMCRDD should be mapped using MAPCRDD. The resulting images should have similar resolution.
• The images created by MAPCRDD will have inappropriate wavebands stored within them (the stored wavebands will be those of the CRDD files used to define sample positions when creating simulated data). Application SETIMAGE should be used to correct this.

Having created two surface brightness images with similar resolution, the facilities of KAPPA should be used to remove an appropriate background from each image, leaving only the flux for which the temperature is required.

Having done that, the IRAS90 application COLTEMP can be used to produce a colour temperature map and an optical depth map from the two surface brightness maps (a greybody source spectrum is assumed, with a user-specified emissivity spectral index, $\beta$).

An example of a procedure which goes through the entire process of producing a colour temperature map from two sets of ``raw'' CRDD files is described in appendix .