Gretchen R. Greene

The Second-Generation Guide Star Catalog: Description and Properties

The Guide Star Catalog II (GSC-II) is an all-sky database of objects derived from the uncompressed Digitized Sky Surveys that the Space Telescope Science Institute has created from the Palomar and UK Schmidt survey plates and made available to the community. Like its predecessor (GSC-I), the GSC-II was primarily created to provide guide star information and observation planning support for Hubble Space Telescope. This version, however, is already employed at some of the ground-based new-technology telescopes such as GEMINI, VLT, and TNG, and will also be used to provide support for the James Webb Space Telescope (JWST) and GAIA space missions as well as the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, one of the major ongoing scientific projects in China. Two catalogs have already been extracted from the GSC-II database and released to the astronomical community. A magnitude-limited (RF = 18.0) version, GSC2.2, was distributed soon after its production in 2001, while the GSC2.3 release has been available for general access since 2007. The GSC2.3 catalog described in this paper contains astrometry, photometry, and classification for 945,592,683 objects down to the magnitude limit of the plates. Positions are tied to the International Celestial Reference System; for stellar sources, the all-sky average absolute error per coordinate ranges from 02 to 028 depending on magnitude. When dealing with extended objects, astrometric errors are 20% worse in the case of galaxies and approximately a factor of 2 worse for blended images. Stellar photometry is determined to 0.13-0.22 mag as a function of magnitude and photographic passbands (RF , BJ , IN ). Outside of the galactic plane, stellar classification is reliable to at least 90% confidence for magnitudes brighter than RF = 19.5, and the catalog is complete to RF = 20.

Independent detector testing laboratory and the NGST detector characterization project

The Independent Detector Testing Laboratory (IDTL) has been established by the Space Telescope Science Institute (STScI) and the Johns Hopkins University (JHU), and it will assist the Next Generation Space Telescope (NGST) mission in choosing and operating the best near-infrared detectors. The NGST is the centerpiece of the NASA Office of Space Science theme, the Astronomical Search for Origins, and the highest priority astronomy project for the next decade, according to the National Academy of Science. NGST will need to have the sensitivity to see the first light in the Universe to determine how galaxies formed in the web of dark matter that existed when the Universe was in its infancy (z ~10-20). To achieve this goal, the NGST Project must pursue an aggressive technology program and advance infrared detectors to performance levels beyond what is now possible. As part of this program, NASA has selected the IDTL to verify comparative performance between prototype NGST detectors developed by Rockwell Scientific (HgCdTe) and Raytheon (InSb). The IDTL is charged with obtaining an independent assessment of the ability of these two competing technologies to achieve the demanding specifications of the NGST program within the 0.6-5 μm bandpass and in an ultra-low background (<0.01 e-/s/pixel) environment. We describe the NGST Detector Characterization Project that is being performed in the IDTL. In this project, we will measure first-order detector parameters, i.e. dark current, read noise, QE, intra-pixel sensitivity, linearity, as functions of temperature, well size, and operational mode.

The GSC-I and GSC-II Databases: An Object-Oriented Approach

The original GSC-I (Jenkner et al. 1990) which contains 25 million entries and requires approximately 1GB of storage was at the edge of technological capability at the time catalogue construction began in 1984. At that time, a custom coded database was built since the relational databases of the era were unsuited to the HST-specific access requirements. A second generation GSC is now being constructed (Lasker et al. 1995), with an estimated 10 billion entries and a size of 2 Terabytes. The current generation of object-oriented database (OODB) systems are more suited to the needs of large astronomical catalogues and are being adopted by many large-scale projects. In a joint effort between the Space Telescope Science Institute and Osservatorio Astronomico di Torino, we are currently designing such an OODB for the Guide Star Catalogues and are implementing a prototype using the GSC-I data.

Building archives in the virtual observatory era

Broad support for Virtual Observatory (VO) standards by astronomical archives is critical for the success of the VO as a research platform. Indeed, a number of effective data discovery, visualization, and integration tools have been created which rely on this broad support. Thus, to an archive, the motivation for supporting VO standards is strong. However, we are now seeing a growing trend among archive developers towards leveraging VO standards and technologies not just to provide interoperability with the VO, but also to support an archives internal needs and the needs of the archives primary user base. We examine the motivation for choosing VO technologies for implementing an archives functionality and list several current examples, including from the Hubble Legacy Archive, NASA HEASARC, NOAO, and NRAO. We will also speculate on the effect that VO will have on some of the ambitious observatory projects planned for the near future.

The GSC-II catalog release GSC 2.3: description and properties

The GSC 2.3 is a current catalog release extracted from the Guide Star Catalog II database, which is maintained at the Space Telescope Science Institute in Baltimore, USA. The catalog contains astrometry, multi-band photometry ( B J , R J , I N ) and star/non-star classification for 945,592,683 objects down to the magnitude limit of the survey plates. We review the performance of stellar parameters, anticipating the improvements in astrometric accuracy foreseen by its recalibration with the newly available catalog in the UCAC series.

Ultra-Low Background Operation of Near-Infrared Detectors Using Reference Pixels for NGST

The Next Generation Space Telescope (NGST) Project is developing a new generation of near-infrared (NIR; λ=0.6-5 μm) array detectors optimized for ultra-low space-based backgrounds. NASA has selected the Independent Detector Testing Laboratory (IDTL) at the Space Telescope Science Institute (STScI) and the Johns Hopkins University to assist in testing and characterizing NGSTs near-infrared detectors. In the IDTL, we have begun to explore how reference pixels might be used to calibrate infrared array data. Here we report some early results from these studies. Results to date are very encouraging, particularly with regard to techniques using temporal or spatial averaging to compute low-noise reference levels before making row-by-row reference pixel corrections. We explored the effectiveness of four potential calibration strategies using a shorting resistor installed where the detector would normally mount and are currently validating the techniques presented here using candidate NGST detectors.

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

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.

JWST science data products

Science data products for James Webb Space Telescope (JWST) ©observations will be generated by the Data Management Subsystem (DMS) within the JWST Science and Operations Center (S&OC) at the Space Telescope Science Institute (STScI). Data processing pipelines within the DMS will produce uncalibrated and calibrated exposure files, as well as higher level data products that result from combined exposures, such as mosaic images. Information to support the science observations, for example data from engineering telemetry, proposer inputs, and observation planning will be captured and incorporated into the science data products. All files will be generated in Flexible Image Transport System (FITS) format. The data products will be made available through the Mikulski Archive for Space Telescopes (MAST) and adhere to International Virtual Observatory Alliance (IVOA) standard data protocols.