This is a description of the current version 4 of the Hubble Source Catalog.
You may still access HSC version 3 and the documentation for the older versions HSC version 2 and HSC version 1.
Version 4 of the
Hubble Source Catalog
The Hubble Source Catalog (HSC) is designed to optimize science from the Hubble Space Telescope by combining the tens of thousands of visit-based source lists in the Hubble Advanced Products (HAP) and Hubble Legacy Archive (HLA) into a single master catalog.
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Recent Updates
2026 June 30: The new version 4 of the HSC is released! HSC version 4 is based primarily on data from the Hubble Advanced Products and includes 8 years of new Hubble observations acquired since the creation of HSCv3. This version of the catalog has improved astrometry (with Gaia DR3 calibrations for 88% of the images), better photometry for ACS/WFC and WFC3/UVIS, and improved instrument calibrations. See the Highlights from version 4 below and the HSCv4 FAQ for more details. - Coming soon: An update is underway to allow the HSC notebooks to run using either HSCv4 or HSCv3.
- Coming soon: An update is underway to allow the HSC notebooks to run using either HSCv4 or HSCv3.
- 2025 May 7: See the MAST Notebook Repository for updated versions of all the HSC Jupyter notebooks.
2019 September 24: The Hubble Catalog of Variables (HCV), a major new High-Level Science Product derived from the HSC, was released. The HCV is the first homogeneous catalog of variable sources found in the HSC. It includes variable stars in our Galaxy and nearby galaxies, as well as transients and variable active galactic nuclei. The HCV contains 84,428 candidate variable sources (out of 3.7 million HSC sources that were searched for variability) with V <= 27 mag; for 11,115 of them the variability is detected in more than one filter. The number of data points in a light curve range from 5 to 120, and the time baseline ranges from under a day to over 15 years. The released data includes both variable objects and objects identified as "constant".
The HCV was created from HSCv3 in a 4 year ESA-funded project at the National Observatory of Athens (PI: Alceste Bonanos). It is available for download via the HLSP page and is also fully integrated with the MAST user interfaces for the HSC, including the HSC CasJobs and VO TAP database query interfaces and the MAST catalogs simple form interface and query API. There are Python Jupyter notebooks available that show how to access the data in scripts. The ESAC Science Data Centre has created the HCV Explorer, a new online web tool to access, visualize, and interactively explore the HCV.
Note that the HCV includes improved magnitudes with local corrections for objects that were searched for variability (those with at least 5 epochs available in some HST filter), so this data may also be useful for projects that are not primarily focused on variability. See the HCV journal paper (Bonanos et al., 2019, A&A, 630, A92) for more details on the project.
2019 August 15: A new search interface for the HSC was released as part of the MAST catalogs access tools. This interface allows searching multiple tables and releases of the HSC in a single web form. Searches can optionally be filtered by catalog parameters (such as magnitudes and available filters). An API can be used for scripted queries of the catalogs, and a Python Jupyter notebook shows some examples demonstrating the use of the API for simple and complex queries.- 2019 June 26: HSC version 3.1 was released. It adds to the current HSC version 3.0 by providing proper motions of over 400,000 objects in the augmented Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) HST field. This field is within a few degrees of the Galactic center, and most of the stars belong to the Galactic bulge. The field has been observed by ACS and WFC3 with a time baseline as long as 12 years. The proper motion information is available in the form of database tables within the HSCv3 context of the STScI CasJobs interface. The data can be readily queried by means of SQL through that interface. In addition, we provide a Python Jupyter notebook that shows how to access CasJobs via a script. The notebook provides statistical information about the photometry and proper motions and includes some science use cases. More details are found here.
- 2018 July 5: HSC version 3 was released. It includes many improvements in the photometry and astrometry along with a significant increase in the number of objects and measurements.
Highlights from Version 4
- HSCv4 has 35% more Hubble visits compared with the HSCv3 release in 2018. ACS and WFC3 data that were public as of 2026 March 17 are included. There are 37% more ACS/WFC images, 2.25 times as many WFC3/UVIS images, and 48% more WFC3/IR images than the HSCv3 catalog. The WFPC2 images and catalogs from the HLA are still being used for the new release and have not changed. (There have of course been no new WFPC2 data added since WFPC2 was removed from Hubble in 2009.)
- HSCv4 has improved photometric quality in the source lists for ACS/WFC and WFC3/UVIS. This is due mainly to better alignment of exposures and filters in the HAP image processing. Improved geometric distortion models for the instruments have likely also helped. See the HSCv4 Photometry page for more details.
- The astrometric calibration is significantly better than HSCv3. Astrometry is now based on the Gaia DR3 catalog. 88% of the source lists have been matched to Gaia DR3, and an additional 8% have been matched to the PS1 catalog (which has also been recalibrated using Gaia DR3: see Lubow et al. 2021 and White et al. 2022). Half of the 4% of source lists without external reference catalog matches still have cross-matches to other HSC source lists, which improves the relative astrometry. Improved geometric calibration of the instruments have also led to astrometric improvements within fields. See the HSCv4 Astrometry page for more details.
- Cross-matching tables are available between HSCv4 and HSCv3 to facilitate transitioning research projects between the two catalog versions.
Properties of the HSC
The HSC v4 contains members of the ACS/WFC, WFC3/UVIS and WFC3/IR HAP segment catalog source lists along with WFPC2 source lists from HLA DR10 (data release 10). The absolute astrometry is calibrated using Gaia DR3, Pan-STARRS, SDSS, and 2MASS as the astrometric backbone for initial corrections. (SDSS and 2MASS are rarely used.) Then a cross-matching process adjusts the relative astrometry of overlapping images so as to minimize positional offsets between closely aligned sources in different images. After these corrections, the astrometric residuals of cross-matched sources are significantly reduced, with median errors less than 8 mas. See the new page describing HSCv4 Astrometry for many more details. In addition, the catalog includes source non-detections. The cross-matching algorithms and the properties of the initial (Beta 0.1) catalog are described in Budavari & Lubow (2012), and the Version 1 catalog is described in Whitmore et al. (2016).
Five things you should know about the HSC
1. Detailed Use Cases are available, although many of these are still in the process of being updated for HSCv4.
2. Sky coverage can be very non-uniform (unlike surveys such as SDSS) due to the highly variable HST observing patterns.
3. Current WFPC2, ACS/WFC and WFC3 source lists are of variable quality. In particular, the WFPC2 source lists are of poorer quality than the ACS and WFC3 source lists.
4. The default is to show all HSC objects. This may include a large number of artifacts. You can request NumImages > 1 (or more) to filter out many artifacts.
5. The default is to use aperture magnitudes (mag_aper2) from the photutils segment catalog (in the ABMAG system) . You can request mag_auto if desired.
Interfaces
MAST is in a transitional state where several interfaces are being reinvented, leading to complexities. The table below outlines which interfaces are available for which versions of the HSC. For HSCv4, only the CasJobs interface is supported at this time. We expect the TAP interface to be available soon, and also are working on HSC support in the new Catalogs Search interface.
| Interface | HSC versions available | Tables available (for the available versions) | Deprecation status | Notes |
|---|---|---|---|---|
| v4, v3, v2, v1 | All tables | TBD | MAST CasJobs permits you to run large and complex queries, expressed in the Structured Query Language (SQL). Note that it is not difficult to run CasJobs queries from a Python script. See the Python Jupyter notebook developed for HSC v3.1 and the Hubble Catalog of Variables notebook for examples. New examples using HSCv4 are coming soon. | |
| VO-TAP | v3, v2, and coming soon for v4 | Selected high-priority tables; more coming soon | Long-term support (v4 and v3) | The HSC TAP service provides database query access to several HSC tables through the Virtual Observatory Table Access Protocol (VO-TAP), as part of MAST's VO-TAP service. There is a Python Jupyter notebook that demonstrates how to query the HSC databases using VO-TAP. The VO-TAP endpoint is:
|
| Catalogs Search | Coming soon: likely v4 and v3 | Selected high-priority tables; more coming soon | Long-term support (v4 and v3) | Coming soon! |
v3, v2 | Selected high-priority tables | Deprecation planned in favor of new Catalogs Search | The Catalogs.MAST interface provides a simple but powerful search interface for the HSC and other catalogs (including Pan-STARRS). It includes a user interface for searches at a sky position with optional filtering by catalog parameters and customization of the columns. It also incorporates an API for scripted queries of the catalogs.
| |
| v3, v2 | Selected high-priority tables | Deprecation planned eventually in favor of new Multi-Mission Search | The MAST Discovery Portal provides a one-stop web access to a wide variety of astronomical data. Select "Hubble Source Catalog v3" in the Select Collection dropdown menu, enter your search target, click Search, and you are on your way. Please try the Use Case Using the Discovery Portal to Query the HSC. |
Current Limitations of HSCv4
- The quality of the WFC3/IR photometry is poorer in HSCv4 than for HSCv3 because the HAP WFC3/IR images are drizzled using larger pixels (0.1285 arcsec for HAP vs. 0.09 arcsec for the HLA products). A change to the HAP data products to use a finer pixel scale is being considered as a future improvement. See the HSCv4 Photometry page for details.
- About 30% of the ACS/WFC, WFC3, and WFPC2 images are not included in the catalog due to image quality and other issues (e.g., moving targets, grism observations, cosmic ray contamination, etc.)
- About 4% of the source lists in the HSC do not have an astrometric correction from an external catalog (e.g. Gaia DR3 or Pan-STARRS). 2% of source lists could also not be cross-matched to other HST images to generate better relative astrometry. (Note this is improved from HSCv3, where 3.2% of source lists had no cross-matches.)
- About 8% of the sources are detected in a single image and are not cross-matched with sources in other visits or in other filters from the same visit. Such single sources are more likely to be spurious but nonetheless are included in the catalog. (Note that many Hubble fields have only a single observation, which precludes cross-matching.) WFPC2 sources have a larger fraction of single-image detections: nearly 30% of WFPC2 sources are detected in only 1 image. That was true in HSCv3 as well.
Help and Acknowledgment
More detailed information can be found on the Frequently Asked Questions page. Several Use Cases are available to give you step by step instructions, although many of these are still in the process of being updated for HSCv4.
We are interested in your feedback. If you have questions, or items to bring to our attention, please send them to archive help (archive@stsci.edu).
HSC Data Use Policy:
The HSC is based on data from the Hubble Legacy Archive (HLA). Refereed publications making use of the HSC should therefore include this footnote in the acknowledgements:
Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESAC/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).
Authors are also asked to acknowledge the "Hubble Source Catalog" in the text of the paper, and consider a reference to the Whitmore et al. (2016) paper describing the HSC.