The calibration pipeline, calcos
, has been developed by the Space Telescope Science Institute (STScI) to support the calibration of HST
/COS data. Although the COS pipeline benefits from the design heritage of previous HST
instruments and of the Far Ultraviolet Spectroscopic Explorer (FUSE), the calcos
modules are tailored specifically to the COS instrument and based on data reduction algorithms defined by the COS Instrument Definition Team (IDT). As with other HST
uses an association table (the _asn
files) to specify the data files to be included, and employs header keywords to specify the calibration steps to be performed and the reference files to be used. Calcos
is written in Python, which enables the pipeline and users to take advantage of an extremely productive, open-source, easy-to-read scripting language, with many libraries for data reduction and analysis. Calcos
is in the stsci_python
package, which is available for download from STScI:
is designed with a common underlying structure for processing FUV and NUV channels which, respectively, use a cross delay line (XDL) and a Multi Anode Microchannel Array (MAMA) detector. The calcos
calibration pipeline includes pulse-height filtering and geometric correction for the FUV channel, and flat-field, deadtime, and Doppler correction for both channels. It includes methods for obtaining an accurate wavelength calibration by using the onboard spectral line lamps. A background subtracted spectrum is produced and the instrument sensitivity is applied to create the final flux calibrated spectrum.
There are two basic types of raw data files: TIME-TAG
photon lists and ACCUM
images of the detector. In general, calcos
must convert these into one dimensional calibrated flux and wavelength arrays. Calcos
must be able to perform different types of calibration processes to accommodate the different input types.
See Chapter 2
for the naming conventions of the various input, temporary, and output calibrated files.