Space Telescope Science Institute
COS Data Handbook 2.00
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COS Data Handbook > Chapter 2: COS Data Files > 2.1 Overview

Raw COS telescope data are processed through the STScI OPUS pipeline. The OPUS pipeline first processes the data through Generic Conversion, where the data bits from individual exposures are unpacked and combined into files containing raw, uncalibrated data. Next, the data are processed through the COS calibration pipeline, calcos, which performs image and spectroscopic reduction to produce output files that can be used directly for scientific analysis (see Chapter 3 for a more detailed description of the COS calibration pipeline). Finally, the data are ingested into the Hubble Data Archive (HDA) through the Data Archive and Distribution System (DADS). This system populates a database containing header keywords which is accessible to users via the Multimission Archive at STScI (MAST). The data (both calibrated and uncalibrated) are then available for distribution by MAST to the user.
When COS data are requested from the HDA, they go through “On The Fly Reprocessing” (OTFR) which provides the best calibrated products by reprocessing the raw telemetry files “on-the-fly” each time data are requested. OTFR reprocessing uses the latest software versions and reference files available. The re-processed data are then distributed to the requestor.
The calibration reference files (e.g. flat fields, bad pixel tables) are also available from the HST Data Archive for users to download. Since reference files are frequently updated, OTFR may use different reference files depending on the date of reprocessing. In the event of an updated reference file or calibration software, users may re-calibrate their data in one of two ways. Once the updated reference files are released, the preferred method is for the user to re-retrieve the data from the HDA and let OTFR recalibrate the data with the default settings. Alternatively, the user can reprocess the data at home through calcos using the most recent reference files and software code (see “Run Calcos” in Section 3.6.1). The second option will not include any changes in the data due to Generic Conversion updates, but will allow a customized calibration through the use of modified reference files or keyword switches. Also, the user will need to manually edit the header keywords stating which reference files should be used by calcos (Table 2.18, and Section 3.6.1).
Once you have retrieved your data, you will need to understand:

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