GeRT Data Reduction Recipes

Welcome to the Germaninium Reprocessing Tools (GeRT) Recipes page.

This website contains step-by-step recipes for using GeRT to reduce 70 and 160 micron data taken by the MIPS Instrument on board the Spitzer Space Telescope.

GeRT Recipes:

Correct a poor stimflash calibration in MIPS 70 data	In this recipe, we use the GeRT to correct for a poor stimflash calibration in 70 micron photometry observations, before running MOPEX to create the final mosaic. For those users who are not interested in diffuse extended emission, such as the ISM, this recipe then continues in a filtering step.
Filter MIPS 70 BCD frames for extended targets	This recipe describes how to use the GeRT to filter your MIPS-70 BCD frames for extended targets, e.g. galaxies. WARNING: users who are interested in extended background emission such as the ISM should *not* filter their data, as this type of emission is removed during the process. The filtered BCDs (*fbcd.fits) downloaded from the archive and created automatically with the GeRT are optimised for point sources only. Users wishing to analyse data of extended sources must either work on the non-filtered BCD frames (*_bcd.fits), or filter the BCDs with different parameters. This demonstration follows on from a previous recipe: Correcting for Bad Stim Flash Calibration in MIPS-70 data, using the same data set. We assume that you have worked through the previous recipe before beginning this one.
Recover mildly saturated sources in MIPS 70 data	This recipe describes how to use the GeRT to recover mildly saturated sources in your MIPS-70 data. MIPS BCDs are created from the raw data cubes by calculating the slopes of the data ramps for each pixel. For more information about this, see the MIPS Data Handbook and Gordon et al. 2005. Normally the BCDs use at least 4 samples to calculate the slope of the ramp, but if the pixel in question saturates before the last of these 4 samples, the pixel is flagged and masked in the BCD frame. The GeRT can be adjusted to re-make the BCDs using fewer samples, so, for example, pixels that are saturated at 4 samples, but not at 3, are recovered. The GeRT can generate BCDs using as few as 2 samples. WARNING: changing the number of samples used to calculate the slope of the data ramp will affect the calibration of the data. You must read the 70 micron calibration paper (Gordon et al. 2007, PASP, 119, 1019) if you intend to use the GeRT to recover saturated pixels in your scientific data. Obviously there are limits to the correction - pixels that are saturated before the second sample in the data ramps cannot be recovered, and so the GeRT can only work in cases of mild saturation. Here we describe how to re-create the BCDs using only 2 data samples to calculate the slope of the data ramp, so recovering the flux information from pixels that are mildly saturated in the postBCD image.

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