HST Primer for Cycle 22

7.4	Hubble Source Catalogs (HSC)

As described in Section 7.3, the HLA produces source lists for tens of thousands of HST images. The Hubble Source Catalog (HSC) combines these single, visit-based WFC3, ACS, and WFPC2 source lists into a single Master Catalog, hence providing entry into the field of database astronomy. Searches that would require months or years to perform in the past can in many cases be done in seconds with the HSC. This resource may be used to support a wide range of new archival proposals, a few potential examples of which are listed below.

Version 1 of the HSC was released in February 2015, and Version 2 is scheduled to be released February 2016. The HSC can be used to support exploratory projects that might be considered for Archival Research (AR) proposals for HST. A journal-level publication describing the HSC, quality of the data, and potential for doing science has been written and will be available when Version 2 is released. A FAQ describing most aspects of the HSC is available. The matching algorithms used by the HSC are described in Budavari & Lubow, 2012.

The HSC can be accessed in a variety of ways. For most cases, the best method will be the MAST Discovery Portal (DP). This Virtual Observatory (VO)-based tool provides easy yet powerful access for searches involving 10,000 sources or less. It provides footprints, object selection filtering, and interactive displays. For larger queries, a powerful CASJobs (CAS = Catalog Archive Server) capability is available¹. This resource is based on the Sloan Digital Sky Survey (SDSS) tool², providing similar support into the world of database astronomy.

Below is a list of some of the types of projects that might make particularly good use of this new resource.

•	Variable stars, galaxies, calibrations, etc., identified using HST’s ~25 year baseline. Note: a project to construct a Hubble Variable Catalog is underway, headed by the National Observatory of Athens.

•	Astrometric properties: proper motions, cluster kinematics, KBOs, etc.

•	Extremely large data sets: e.g., creating CMDs based on the ~ 4000 HST observations of the LMC.

•	Cross-matching with other catalogs: SDSS, 2MASS, spectral catalogs, etc.

•	Object properties: star clusters and associations, colors, elongations, etc.

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Photo-Zs

A third method of access is via the HSC homepage. This provides the most flexibility for very detailed queries.

A word of caution is in order, however. Unlike SDSS, with a uniform set of filters and all-sky coverage over a substantial part of the sphere, the Hubble database consists of tiny pieces of sky using three different cameras and hundreds of filters. Potential users should pay special attention to the Five Things You Should Know About the HSC webpage. Detailed use cases are available to guide users in common ways to make use of the HSC and to avoid common pitfalls.