Previous: Instrument calibration
Up: Instrument calibration
Next: Ring images
Previous Page: Instrument calibration
Next Page: Ring images

Phasemap cubes

Raw TAURUS datacubes have the property that the surfaces of constant wavelength are parabaloids of revolution rather than planes. Before the data can be sensibly analysed it must be rebinned so that the surfaces of constant wavelength are datacube planes. This is the process of phase calibration. FIGARO software is available to carry out this process, and is described in some detail in the manual TAURUS data and how to reduce it by Jim Lewis and Steve Unger.

In order to use this software, a phasemap calibration cube will be required. This is a 3D observation of an arc line of known wavelength, using the same datacube parameters as the observation cubes, and is used to define the precise form of the parabaloid of revolution. The calibration cube should be taken at a wavelength close to that of the observation. Table 11 lists some useful calibration lines obtained using the CuNe lamp, and lists the filters required to isolate these lines. I usually use the 6598 Å line as the principal calibration line for observations at H and the lines close to 5033 Å as the principal calibration lines for observations close to [OIII].

If time permits, try to observe more than one calibration line for each observation. This may not always be possible, since each cube will take about an hour to acquire. It is not so imnportant when a single filter transmits 2 or 3 well separated lines, as is the case for the 5033 filter.

Try to set up the etalon scanning so that the ring produced by the principal calibration line is just appearing at the first plane of the cube. As you scan through the cube, this ring will then appear to grow in size until it disappears off the edge of the field. Towards the end of the scan it will reappear. Having the same line twice in the same datacube, in adjacent orders, makes it possible accurately to determnine the free spectral range.