The Cosmic Origins Spectrograph,1 COS, will be installed in the Hubble Space Telescope (HST) during the next
servicing mission. This will be the most sensitive ultraviolet spectrograph ever flown aboard the HST.
The calibration pipeline (CALCOS), written in Python, has been developed by the Space Telescope Science
Institute (STScI) to support the calibration of HST/COS data. As with other HST pipelines, CALCOS uses an
association table 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 designed with a common underlying structure for processing far ultraviolet (FUV) and near
ultraviolet (NUV) channels which, respectively, use a cross delay line and a Multi Anode Microchannel Array
(MAMA) detector. The pipeline basics and channel dependent specifics are presented. The generation and
application of the current reference files, derived from ground-based calibration data, is described, along with
the pipeline verification process and results.
The CALCOS calibration includes pulse-height filtering and geometric correction for the FUV channel; flat-field,
deadtime, and Doppler correction for both channels. Methods for obtaining an accurate wavelength calibra-tion
using the on-board spectral line lamp are described. The instrument sensitivity is applied to the background
corrected spectrum to produce the final flux calibrated spectrum.
Bias and Dark reference files are part of the basic reduction of the CCD data taken by the Space Telescope
Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). At STScI, the STIS team has been
creating these reference files using the Bias and Dark Pipeline. This pipeline system starts with automatic
retrieval of bias and dark exposures from the HST archive after they have been ingested. After data retrieval,
a number of automatic scripts is executed in a manner compatible with the OPUS pipeline architecture. We
encourage any group looking to streamline a stepwise calibration process to look into this software.