The Hubble Legacy Archive - Open for Business

The Hubble Legacy Archive (HLA) is an augmentation of the Hubble Space Telescope (HST) data archive service. The goal is to optimize the science coming from the telescope by providing better browsing capabilities and easy access to enhanced products. The project is a collaboration between the Space Telescope Science Institute (STScI), the European Coordinating Facility (ST-ECF) and the Canadian Astronomy Data Centre (CADC). One of the primary goals of the project is to make HST data VO (Virtual Observatory) compatible.

Some of the primary enhancements for image data include:

1. Putting the data online for immediate access
2. Adding a footprint service to make it easier to browse and download images
3. Providing more extensive "composite images" (e.g., stacked, color, mosaics)
4. Improving absolute astrometry (i.e., from ~ 1-2" to ~ 0.3") when there is sufficient overlap with the Guide Star Catalog 2 (GSC2)
5. Developing source lists

We are currently in the Early Data Release phase of the project (e.g., the HLA includes ~25% of the ACS data), with the more formal Data Release-1 planned for the Fall. The user interface system is still somewhat rudimentary, hence we warn users that they might run into some rough edges. We would appreciate your help in testing the system and providing feedback by sending us a quick e-mail with any problems or provide us suggestions. This will help us prioritize our work so that we spend our effort on the most important modifications.

The URL to access the HLA is: http://hla.stsci.edu.

As part of this Early Data Release, ST-ECF is providing a sample of NICMOS grism extractions (~ 10 % of the available G141 data) http://hla.stecf.org/archive/hla/. Please see the article in the July 2006 ST-ECF Newsletter for more information about this project.

Here are a few HLA essentials. Please consult the HLA HELP page (especially the FAQ) for more details.

HLA ESSENTIALS

The current HLA data release has the following limitations:

• The HLA only runs using FIREFOX or a compatible browser.

• The HLA currently contains only ~25 % of the ACS data (mainly data from 2002 - 2003). The data can be viewed in one of three ways:
  • INVENTORY, a tabular format
  • IMAGES, an array of preview images and an interactive quick-look display
  • FOOTPRINTS, an outline of the detector field of view overlaid on a DSS image.

  Screen Shot showing inventory table	Screen Shot showing images page	Screen Shot showing footprints page
  Click on images to see full-sized screen shot

• Most WFPC2 (prior to September 2006) and STIS (prior to August 2004) observations are shown in the FOOTPRINTS, but the data are not contained in the HLA database. Hence they will not show up in the INVENTORY or IMAGES. These data can be retrieved from MAST in the normal manner.

• Only non-proprietary ACS data taken BEFORE JANUARY 1, 2006 is currently (July, 2007) included in the HLA.

The HLA images are combined using the multi-drizzle software which is used in the normal HST calibration pipeline. Some of the differences are that we improve the absolute astrometry when possible by cross-correlating with the GSC2 catalog (this is possible for ~ 80 % of the images), we align the image with north up to make comparison with other datasets easier, and we combine some datasets that the normal HST pipeline does not (e.g., when POS TARGs are used to dither the observations). Two source lists are provided for many images. The first uses DAOPHOT, which is best for finding point-like sources. The second uses SEXTRACTOR, which is best for extended sources. Note that these are general use source lists; researchers will generaly need to make their own catalogs to optimize the particular science they are interested in.

HLA Source List Overlaid on M101

Future enhancements to the HLA include:

1. providing "ACS-like" products for the WFPC2 (e.g., cosmic-ray rejected, multi-drizzle combined images;) the Canadian Astronomy Data Centre is taking the lead in developing these products
2. providing similar products for NICMOS, and STIS imaging
3. providing spectroscopic data and quick look tools.

Thanks for helping us exercise the system. We are looking forward to your feedback.