1.1 Archive Overview

All HST data files are stored in the Barbara A. Mikulski Archive for Space Telescopes (MAST; https://archive.stsci.edu/). HST Guaranteed Time Observers (GTOs), Guest Observers (GOs), and Archival Researchers can retrieve data in one of the following ways:

Note that users may need to disable pop-up blockers when downloading data from the MAST Portal.

Users requiring alternative means of data retrieval or access to large volumes of data from MAST are encouraged to contact the MAST Help Desk (web: https://masthelp.stsci.edu/; e-mail: archive@stsci.edu) for assistance.

All science data retrieved from MAST, regardless of the method used, will be in FITS (Flexible Image Transport System) format. Further information on HST file formats is presented in Chapter 3.

HST data in MAST may be either available to the public or have exclusive access (formerly called "proprietary") privileges. Users wishing to retrieve exclusive access data must have the appropriate My Space Telescope (MyST; https://profile.stsci.edu/) account permissions granted by the Principal Investigator (PI) of the program. As of Cycle 25, exclusive access privileges are automatically granted to PIs.

Non-exclusive access data in MAST can be retrieved electronically either by registered MyST account users or anonymously. All calibration observations as well as observations made as part of GO parallel programs are immediately public. All observations made as part of a Treasury Program will either be immediately public or have only a brief proprietary period. The High-Level Science Products (HLSPs) in MAST also contain several sets of publicly available and fully reduced HST data such as the Ultra Deep Field (UDF) and the GEMS survey data (see Section 1.2.2 for more information about HLSPs).

When accessing data via the MAST Portal or the staging disk, the archive recommends retrieving compressed data to shorten the retrieval time without any significant information loss.

1.1.1 Archive Processing

MAST contains all observations ever made by HST and a catalog that describes the data. Each time a user makes a data request, MAST delivers data that have been processed with the best available reference files from the Calibration Reference Data System (CRDS; http://hst-crds.stsci.edu/). Calibrated data from all HST instruments are stored in a static form for retrieval. When changes are made to active instrument (ACS1, COS, STIS, or WFC3) data pipelines and/or reference files, all affected observations are reprocessed. User requests for data from observations in the reprocessing queue will increase the reprocessing priority of the observations requested.

Requests for data in the reprocessing queue increase the reprocessing priority, but do not guarantee that the reprocessed data will be delivered to the user. If in doubt, users can check the DATE keyword in the FITS header to find when the file was last updated. Users can also reprocess data themselves using the latest versions of the relevant instrument calibration pipeline and reference files. For more information on how to reprocess data, please see the appropriate chapter of the data handbook for your instrument.

Table 1.1 Active HST Instruments

Advanced Camera for Surveys (ACS1)Wide Field Channel (WFC), Solar Blind Channel (SBC)
Cosmic Origins Spectrograph (COS)FUV Channel, NUV Channel
Space Telescope Imaging Spectrograph (STIS)CCD, NUV-MAMA, FUV-MAMA
Wide Field Camera 3 (WFC3)UV/Visible Channel (UVIS), Infrared Channel (IR)

Data from HST legacy instruments are preserved in a static form, and there are no plans to regularly reprocess these data. In this context, legacy instruments include the ACS High Resolution Channel (ACS/HRC), Faint Object Camera (FOC), Faint Object Spectrograph (FOS), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Near Infrared Camera and Multi-Object Spectrometer (NICMOS), Wide-Field Planetary Camera 1 (WF/PC-1), and Wide-Field Planetary Camera 2 (WFPC2). For ACS/HRC, FOC, FOS, GHRS, NICMOS, and WFPC2, no further improvements in the calibration for these instruments are expected. The user is provided with a copy of the raw and final calibrated data from the archive once a request is made. For HSP and WF/PC-1, no calibration has been done nor is any planned. Once raw data from these instruments are retrieved from MAST, they need to be calibrated locally by users.

1.1.2 Archive Registration (MyST)

MAST authentication is performed using a MyST account. From their MyST account, observing program PIs can view a list of accepted observing proposals and control access rights to exclusive access data for other users. Users accessing public data do not need to register for a MyST account. To make a new MyST account, or to update information in an already existing account, please visit https://profile.stsci.edu/. Users requiring a password reset can contact the HST Help Desk for assistance.

1.1.3 Archive Documentation and Help

The MAST Portal provides a wealth of useful information for data retrieval. Investigators expecting to work regularly with HST and other datasets supported by MAST should ensure they are subscribed to the MAST electronic newsletter for information regarding updates to the data archive. Users with a MyST account are registered for the MAST newsletter by default, and can verify their subscription status in the "Manage Subscriptions" menu in their MyST account. Questions about MAST should be directed to the MAST Help Desk either via the web portal or via e-mail to archive@stsci.edu.

1The ACS High Resolution Channel (ACS/HRC) is no longer operational after Servicing Mission 4. The Wide-Field Channel (WFC) and Solar Blind Channel (SBC) are available for observing.