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Chapter 36
Calibrating and Recalibrating GHRS Data

In This Chapter...

Pipeline Calibration Process / 36-2
Calibration Steps Explained / 36-2
Recalibrating GHRS Data / 36-13

This chapter explains what happens to GHRS observations when they are processed through the calibration pipeline-the Routine Science Data Processing (RSDP) system at STScI. You should always recalibrate GHRS observations to exploit the latest and best information available. The recalibration task, calhrs, is the same as the software used in RSDP, so you will need to know how it works. The distinction between "calibration" and "recalibration" is partly artificial, but by "recalibration" we mean applying calhrs data to observations of your choice in a way that you control. Recalibration can also include some tasks that RSDP could not do, such as applying an improved wavelength calibration or accounting for background counts in a different way.

The GHRS calibration task calhrs, part of STSDAS, was developed and is maintained at STScI. For the GHRS, the calibration process assigns flux and wavelength values to each raw data point. In addition, calhrs corrects for non-uniformity in diode response and for diodes that have been turned off (dead diodes). calhrs produces, as output, the calibrated spectrum, wavelength solution, error estimates, and data quality images. The calibration software used in the RSDP pipeline to calibrate GHRS observations is the same software used within the -calhrs task. The calhrs task can be found within the STSDAS hst_calib package. We will emphasize here the calibration steps themselves, deferring a discussion of error and uncertainty to the next chapter.



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