aXedrizzle

The "traditional" aXe redcution scheme until version 1.3 produces a spectrum for each object in each science image. ACS data sets, however, usually consist of several images with small dithers between them. The approach of co-adding the 1D spectra from each image to get a deep, combined spectrum has disadvantages:

• The spectral data is rebinned twice, once during the individual spectral extraction and once when combining the individual 1D spectra
• The weighting scheme to flag bad pixels and exclude cosmics is very complex
• Low level information on the cross dispersion profile is lost when only the 1D spectra are combined to a deep spectrum

With aXedrizzle we implemented in aXe-1.4 a new reductions scheme to circumwent these drawbacks. In this scheme all the individual 2D spectra of an object are coadded to a single, deep 2D spectrum. Then the deep 1D spectrum is extracted from this combined 2D spectral image. The combination of the individual 2D spectrum is done with the "drizzle" [1] software within PyRAF/IRAF. The advantages of this technique are:

• Regridding to a constant wavelength scale and cross-dispersion scale is achieved in a single step
• Bad pixels, cosmics and different exposure times are correctly handled
• Only one linear rebinning step is required to produce a 2D spectrum
• The combined 2D spectra can be viewed to detect any problems

Figure 2 gives a schematic overview on aXedrizzle. More information and discussion on aXedrizzle is in the aXe User Manual and in [2], [3].

Figure 2: An overview on aXedrizzle

References

[1]Fruchter, A. S., Hook, R. N., 2002, PASP, 114, p.144
[2] Kümmel, M., Walsh, J. R., Larsen, S. S., Hook, R., 2004, ``Drizzling and the aXe Slitless Spectra Extraction Software'', ST-ECF Newsletter 36, p.10-12
[3]Kümmel, M., Walsh, J. R., Larsen, S. S., 2004, The HUDF HRC Parallels: From the Pixels to the World Wide Web, ADA III Meeting 2004

 

Maintained by Martin Kümmel <mkuemmel@eso.org>