3.1 Mikulski Archive for Space Telescopes - MAST

ACS data requests are processed with the Mikulski Archive for Space Telescopes (MAST) pipeline. It provides users with calibrated data that are created using the best available reference files and latest software upgrades.

STScI's calibration pipeline consists of two main software systems: the "Data Management System" (DMS) and the "Data Archive and Distribution System" (DADS).

Raw spacecraft telemetry data from the Goddard Space Flight Center are transmitted to STScI in the form of POD files that are stored in the HST Archive. MAST processing begins with the POD files when DMS runs a step called Generic Conversion to extract and create uncalibrated "raw" data. During this step, the Calibration Reference Database System (CRDS), where all calibration reference files are stored, is queried to determine the most current reference files for the observation's configuration and date. DMS then calibrates the raw data using calacs, with the best-available reference images and tables from the CRDS. These calibrated data, along with other requested data products, are sent to the user. See Chapter 1 of the Introduction to the HST Data Handbooks for more information about retrieving data from the Archive.

ACS Wide Field Channel (WFC) CCD dark, CTE-corrected dark, bias and sink-pixel reference files are delivered to CRDS following each ACS WFC anneal. Users who receive their data shortly after an observation was executed are advised to wait a few more weeks for the best-suited reference files (usually the darks) to become available in CRDS. At that point, the data could be re-retrieved from the Archive or manually recalibrated using the new reference files. To check if reference files have been updated, compare the names of the reference files in the image header with those listed as the recommended reference files for a particular dataset in MAST HST Data Search or via the CRDS Best References tool website. There is also a command line tool to retrieve the best references for a dataset, crds bestrefs, which is demonstrated in the acs_reduction.ipynb notebook on github. For dated ACS products, it is often more convenient to retrieve freshly-calibrated data from the Archive before beginning data analysis. Users who choose to rerun calacs on raw data should consult the ACS Reference Files web page and retrieve reference files from the CRDS web page or MAST (See Section 3.5 for information about running calacs). A full example of an ACS WFC image reduction with relevant code is provided in the acs_reduction.ipynb notebook on github.