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 Legacy Archive (HLA)
single master catalog.
Version 3 was released on 2018 July 5 and includes
many improvements in the photometry and astrometry along with a significant increase in the
number of objects and measurements.
Highlights from Version 3 include:
25% more ACS/WFC images and more than twice as many
WFC3 images compared with the HSC v2 release. ACS and WFC3 data that were public as of 2017 October 1 are included.
See notes on the HLA DR10 data release and on the
current HLA holdings for details.
Improved photometric quality in the source lists due both to the alignment algorithm used to match exposures and filters in the HLA
image processing and to improved algorithms for Source Extractor photometry (particularly near the edges of images).
The scatter in magnitudes is measured using the median absolute deviation (MAD) of the differences
from the median magnitude. This is more robust and less sensitive to outliers than the RMS used in
Cross-matching between HSC sources and spectroscopic COS, STIS, FOS, and GHRS observations.
The HSC v3 contains members of the
WFPC2, ACS/WFC, WFC3/UVIS and WFC3/IR
source lists from HLA version DR10 (data release 10). The cross-matching process involves adjusting the relative astrometry
of overlapping images so as to minimize positional offsets between
closely aligned sources in different images. After correction, the
astrometric residuals of cross-matched sources are significantly
reduced, with median errors less than 8 mas.
The absolute astrometry is calibrated using Gaia DR1, Pan-STARRS, SDSS, and 2MASS as the astrometric backbone for initial corrections.
In addition, the catalog includes source nondetections. 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).
There are currently four ways to access the HSC as described below. We are working towards having these interfaces consolidated into one primary interface, the MAST Discovery Portal.
The HSC Summary Search Form displays a single row entry for each object, as
defined by a set of detections that have been cross-matched and
hence are believed to be a single object. Median values for
magnitudes, positions, and other relevant parameters are provided.
The HSC Detailed Search Form displays an entry for each separate
detection (or nondetection if nothing is found at that position)
using all the relevant Hubble observations for a given object (i.e., different
filters, detectors, separate visits).
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 mag_aper2 Source Extractor values for
magnitudes (in the ABMAG system) . You can request mag_auto if desired.
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 6% of the source lists (white-light images) in the HSC do not have an astrometric correction
from either an external catalog (e.g. Gaia) or from overlapping HST images. (Note this is much improved from the
About 19% of the sources could not be cross-matched with sources in other visits.
Such single sources are nonetheless included in the catalog.
We are interested in your feedback. If you have questions, or items to
bring to our attention, please send them to: archive help.
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.