Development of the astronomical image archive and catalog database for production of GSC-II

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Abstract

The Catalogs and Surveys Branch (CASB) of the Space Telescope Science Institute (STScI), in collaboration with a number of international astronomical institutions, is continuing with the development and creation of an archive of digitized images, and an associated catalog of stars and galaxies which cover the entire sky. These data are being made available to the astronomical community to support telescope operations and research projects.

Introduction

An important part of observational astronomy has historically been the creation of catalogs to support the operation of telescopes and their observing programs. An astronomical catalog typically contains parameters that characterize celestial objects such as position, brightness, and type of object. Modern astronomical telescopes are becoming increasingly complex and expensive to construct and operate, which demands that we optimize observing efficiency in order to maximize the scientific return of the investment. The original need for more complete all-sky catalogs was highlighted by the pointing requirements of the Hubble Space Telescope (HST). This required the construction of a catalog of 15 million stars, about 10 times larger than previously existing catalogs, down to a brightness level of 15th magnitude or 10000× fainter than stars visible to the naked eye.

The basic technique involved was to obtain photographic plates covering the entire sky, digitize these, and use image-processing techniques to identify and measure all of the stars down to the desired brightness limit. The detected objects were then stored in a custom coded database, since the relational databases of the era were unsuited to the HST-specific access requirements. This database required 1GB of storage and was at the edge of technological capability at the time catalog construction begun in 1984. A description of this catalog, GSC-I, is published as a set of three papers [1], [2], [3]. In addition to the HST, this catalog was published and quickly became established in the operations of almost every observatory and astronomical satellite.

The original goals were merely to create a catalog to point the HST. However, it quickly became clear that having access to digital images would greatly benefit not only HST operations but also the entire astronomical community. With this in mind, it was decided to develop an image archive, which would facilitate user access to these data. These images have now been distributed to the community and placed on-line at a number of institutions around the world. The availability of these images has revolutionized observational astronomical research and telescope operations.

Today, astronomers require even larger catalogs to operate ground-based telescopes and space observatories that are either under construction or being planned. As the next generation of large-aperture, new-technology telescopes becomes available, there are increasing demands for catalogs containing fainter objects to support remote or queue-scheduling capabilities. In addition, many of these telescopes have active optics, and efficient operations require convenient access to many stars within a small field of view near the target for tip/tilt corrections and for dynamic maintenance of collimation. The precision requirements of these new telescopes means that in addition to many more objects, the positions, brightness, colors and motions must also be accurately determined. Similarly, the availability of images taken at different wavelength is of immense value for astronomical research purposes.

Section snippets

Project overview

Our overall goal is to produce digitized images of the entire sky in different optical wavelengths along with an accurate catalog of celestial objects. These data will then be made available to international astronomical observatories for telescope operations and to the astronomical community for research purposes. This will be done both by media distribution and web access to on-line archives and databases.

COMPASS database

The primary responsibility for the development and implementation of the GSC-II database lies with STScI, but there is significant development work in collaboration with the Osservatorio Astronomico di Torino, which is leading the Italian portion of this consortium. One of the early strategic decisions was to purchase commercial database software. Despite the limited resources and budget for the project, one of the lessons learned from GSC-I was that development and maintenance costs for a

User access

At STScI, DSS images and GSC-I catalog retrieval are available by a Web interface (Fig. 4). We are in the planning stages for extending this to directly access the GSC-II COMPASS database for catalog queries. These data can be analyzed and visualized with the standard community tools such as IRAF. Several other institutions have provided similar access to the distributed data sets, one such example is the European Southern Observatory (ESO) SkyCat Tool [7]. SkyCat is a software tool that allows

Production system

The system is split into three major parts. The plate digitization and image-processing are running on Digital Alpha systems running OpenVMS. This part of our pipeline contains a great deal of legacy fortran and C code that is specifically designed to run on VMS systems due to their robustness, reliability and real-time features. It is the most intensive operational procedure of the project because of the heavy costs in hardware and time to complete each task. When we started implementing the

Summary

The GSC-II project is one of the first large-scale astronomical archives in production. With the advancement in computer hardware and technology to support not only archive development, but also the potential to network these archives, large-scale astronomical research that was never before possible can be performed within a time frame of months. For more information on the project, several Web pages can be viewed at HYPERLINK http://www-gsss.stsci.edu/casbhome.html, //www-gsss.stsci.edu/casbhome.html

Gretchen Greene received her MS in Applied Physics from John Hopkins University in 1990 and has worked in a number of diverse engineering fields from medical analysis to sonar design. Since joining the Catalogs and Surveys Branch at Space Telescope Science Institute in 1992 she has been responsible for the optical design and construction of the scanning microdensitometers and the object-oriented astronomical database for construction of the second Guide Star Catalog. Her other interests include

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Gretchen Greene received her MS in Applied Physics from John Hopkins University in 1990 and has worked in a number of diverse engineering fields from medical analysis to sonar design. Since joining the Catalogs and Surveys Branch at Space Telescope Science Institute in 1992 she has been responsible for the optical design and construction of the scanning microdensitometers and the object-oriented astronomical database for construction of the second Guide Star Catalog. Her other interests include large-scale archive interoperability.

Brian McLean received his PhD in Astronomy from St. Andrews University, Scotland in 1981 and following a post-doctoral position at Queen’s University, Canada, moved to the Space Telescope Science Institute in 1984. Whilst retaining a strong interest in instrumentation, most of his work has been in the field of astronomical surveys. This has ranged from the discovery of radio emission from contact binary systems to involvement in all-sky X-ray surveys as well as the Digitized Sky Surveys and Guide Star Catalogues.

Barry M. Lasker, BS 1961 Yale, Physics, and PhD 1965, Princeton, Astrophysical Sciences, was on the staff of Cerro Tololo Inter-American Observatory through the 1970s and then in 1981 moved to his current position at the Space Telescope Science Institute. His major projects have included the Guide Star Catalogs and the Digitized Sky Surveys described in this paper, as well as investigations on the interstellar media of nearby galaxies.

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