|
Документ взят из кэша поисковой машины. Адрес
оригинального документа
: http://vega.inp.nsk.su/catalogs/gsc-description.php3
Дата изменения: Unknown Дата индексирования: Mon Oct 1 19:42:13 2012 Кодировка: Поисковые слова: п п п п п п п п п п п п п п п п п п |
I/220 The HST Guide Star Catalog (Lasker+ 1992) ================================================================================ The Guide Star Catalog Version 1.1 - An all-sky astrometric and photometric catalog to support the operation of the Hubble Space TelescopeThe Guide Star Catalog Version 1.0 is described in a series of papers: I. Astronomical foundations and image processing Lasker B.M., Sturch C.R., McLean B.J., Russell J.L., Jenkner H., Shara M.M. =1990AJ.....99.2019L II. Photometric and astrometric models and solutions Russell J.L., Lasker B.M., McLean B.J., Sturch C.R., Jenkner H. =1990AJ.....99.2059R III. Production, database organization, and population statistics Jenkner H., Lasker B.M., Sturch C.R., McLean B.J., Shara M.M., Russell J.L. =1990AJ.....99.2082J ================================================================================ ADC_Keywords: Surveys ; Positional data Abstract: The Guide Star Catalog (GSC), which has been constructed to support the operational need of the Hubble Space Telescope contains nearly 19 million objects brighter than sixteenth magnitude, of which more than 15 million are classified as stars. This catalog provides positions and magnitudes for these stars. Introduction: The original version of this catalog, GSC 1.0, is described in a series of papers: Lasker et al. (1990); Russell et al. (1990); and Jenkner et al. (1990); hereafter referred to as Papers I, II, and III. Additions and corrections made in GSC 1.1 address: incompleteness, misnomers, artifacts, and other errors due to the overexposure of the brighter stars on the Schmidt plates, the identification of blends likely to have been incorrectly resolved, the incorporation of errata reported by the user-community or identified by the analysis of HST operational problems. Among the primary authors of the GSC 1.0 and the associated systems, the scientific responsibilities were divided as follows: Helmut Jenkner, system coordination and overall design; Barry M. Lasker, astrophysics and photometry; Brian J. McLean, algorithmic analysis and systems development; Jane L. Russell, astrometry; Michael M. Shara, system management; and Conrad R. Sturch , production management and quality control. GSC 1.1 analysis and production were performed primarily by Jesse B. Doggett, Daniel Egret, Brian J. McLean, and Conrad R. Sturch. Helmut Jenkner is on assignment from the European Space Agency; Jane L. Russell is currently affiliated with the Applied Research Corporation, Landover, MD; and Conrad R. Sturch is with the Astronomy Programs, Computer Sciences Corporation at Space Telescope Science Institute. Daniel Egret is affiliated with Observatoire de Strasbourg, France. Astronomical and Algorithmic Foundation: As described in Paper I, the GSC is primarily based on an all-sky, single epoch, single passband collection of Schmidt plates. For centers at +6 degree s and north, a 1982 epoch "Quick V" survey was obtained by the Palomar Observatory, while for southern fields, materials from the UK SERC J survey (epoch approximately 1975) and its equatorial extension (epoch approximately 1982) were used. In addition, over 100 short- exposure plates were taken with the Palomar Oschin and UK Schmidt telescopes to cover complex regions including the southern Milky Way, the Magellanic Clouds, and M31. These northern, southern, and supplemental plates hereafter are referred to as N, S, and X plates, respectively. The plates were digitized into 14000-square rasters at 25 um sample intervals using modified PDS microdensitometers. The sky-background was modeled with a bi-dimensional cubic spline approximation to the modal level. Then an object finder, based on locating connected pixels at a certain threshold above the background, was used to obtain, for each plate, a list of positions, sizes, intensities, and related descriptive parameters. Images with multiple peaks were deblended by an algorithm based on correlations against a library of stellar images. The identified objects were classified as stars or non-stars by an interactive multivariate Bayesian classifier that used image features from the object-detection steps and was started from a small set of objects visually identified on each plate. Comparison of classifications from multiply catalogued objects in the plate overlap areas shows that the purity of objects classified as stars is typically 97 percent. Photometric and Astrometric Calibrations: The GSC calibrations were obtained on a plate-by-plate basis by polynomial modeling against the photometric and astrometric reference catalogs. Photometry is available in the natural systems defined by the individual plates in the GSC collection (generally J or V), and the calibrations are done using B, V standards from the Guide Star Photometric Catalog (Lasker, Sturch, et al. 1988). In Paper II the overall quality of the photometry near the standard stars was estimated from the fits and other tests to be 0.15 mag (one sigma, averaged over all plates), while the quality far from the sequences was estimated from the all-sky plate-to-plate agreement and from comparisons with independent photometric surveys to be about 0.3 mag (one sigma), with about 10% of the errors being greater than 0.5 mag. Additionally, Ratnatunga's (1990) comparison of the GSC against totally independent J-band photographic photometry for three southern fields (20 sq deg area) for 12.5 < J < 15.5 shows agreement at the 0.1-0.2 mag level. Astrometry, at equinox J2000, is available at the epochs of the individual plates used in the GSC; and the reductions to the reference catalogs (AGK3, SAOC, or CPC, depending on the declination zone) use third order expansions of the modeled plate and telescope effects. The fits to the reference catalogs lie in the range 0.5" to 0.9", and most of this is attributable to errors in the reference catalogs, to centroiding errors on the relatively large images of the reference stars, and to unmodeled astrometric effects. Paper II reported estimates of the overall external astrometric error, produced by comparisons of independently measured positions, in the range 0.2" to 0.8" (per coordinate), depending on the areas of the plate and the sky. Then from a more extensive analysis against the Carlsberg Automatic Meridian Circle data, Taff et al. (1990) found that GSC absolute positional errors from plate center to edge vary from 0.5" to 1.1" in the north and from 1.0" to 1.6" in the south, and that relative errors at half-degree separations range from 0.33" to 0.76" depending upon hemisphere and magnitude. Production, Database, Organization, and Population Statistics: Paper III describes the software system used to produce the GSC. It consisted of a set of (primarily non-interactive) image-processing and calibration programs interconnected by a set of pipeline files and supported by databases organized on a plate-by-plate basis. A set of utility programs was also provided to support quality control and to correct operational problems. Object names are of the form GSC rrrrr nnnnn, where the first field specifies an internal region number and the second is an ordinal within it. For objects catalogued from more than one photographic plate, an entry was made from each image; and all entries for the same object were given the same unique name. Paper III also reviews the database for compiling statistics of objects with multiple entries and the details of the organization and structure of the GSC, including the provisions for assigning unique names, for cataloguing objects lying in the plate overlap regions, for rapidly indexing positions against regions, and for recovering the original plate measurements. The separate count statistics for stellar and non-stellar objects on a plate-by-plate basis are provided in the supporting tables. User Interfaces, Utilities, and Astronomical Applications: The all-sky collection of Schmidt plates that were digitized, archived to optical disc, and processed to generate the Guide Star Catalog (GSC) constitute a general image resource for astronomical research. This data set, combined with the computing environment provided by the Guide Star Astrometric Support Package (GASP), major elements of which are exported within the Space Telescope Science Data Analysis System, provides random access to a digital image in any part of the sky. The GASP environment also supports access to the GSC and to other major astronomical catalogs. The GASP is part of the STScI SDAS package which, together with IRAF, can be obtained through the STScI World Wide Web pages. Revisions in GSC 1.1: The GSC 1.1 activities performed to address a number of known problems in GSC 1.0 are summarized here and described in detail in the text file for this revision, rev_1_1.tbl. Two concerns related to the brighter stars arise from the heavily overexposed images on the Schmidt plates used in the GSC, namely an incompleteness and a reduced precision. Both are addressed in the domain V < 7.5 by the use of data from the INCA Data Base (Turon et al. 1992; Jahreiss et al. 1992; Grenon et al. 1992) in the Tycho Input Catalog (TIC; Egret et al. 1992). Such entries are designated by the plate identifier +056 in GSC 1.1. The limit of V < 7.5 preserves the original GSC data for objects that were used in the GSC 1.0 astrometric calibration. Naming errors occur when objects catalogued from more than one photographic plate have positional errors sufficiently large that cross-matching of the overlapping plate areas is done incorrectly. The most significant known instances of this in GSC 1.0 were associated with overexposed (and therefore badly centroided) images of the brighter stars. A search around the positions of the INCA stars facilitated the identification of these naming errors, which were then removed in GSC 1.1. GSC 1.0 contains many pairs of objects (from single plates) with separations significantly smaller than the expected resolution of the catalog, which Garnavich (1991), based on a study of four northern plates, estimates at ~ 10" for 8.0 < V < 14.0. Visual inspection shows that these are generally blends that have been properly resolved, but then affected by a centroider defect that made the separations artificially small. Such components of blends with incorrect separations are given a classification of 2 (blend; cf. the text file for a full listing of the codes). For stars with V < 8, image-processing artifacts near the diffraction spikes exist in GSC 1.0. In GSC 1.1, potential artifacts were identified by use of a purely geometrical criterion (proximity of the object to the spike), and were assigned a classification of 5. Small areas around southern stars brighter than V ~ 3 are not processed from the Schmidt plates and were left blank in GSC 1.0. For these, GSC 1.1 contains entries from supplemental astrograph plates taken with the Gran Prisma Objectif (GPO) telescope on La Silla, and the astrograph at the Black Birch Observatory (BBO) in Blenheim, New Zealand. Because of their smaller fields, the photometric and astrometric calibrations of data from most GPO and a few BBO plates were performed against nearby GSC entries based on the Schmidt plates. The details for these plates are given in the file bright.plt. A number of specific errors in GSC 1.0 have been identified by the user-community and by analyses of HST operational problems. These generally involve naming errors, plate flaws, misclassifications, and multiple stars; most are individually corrected in GSC 1.1. Also, the photometric error parameter in GSC 1.1 is now correctly described by equation (3) in Paper II; i.e., the erratum of footnote 5 therein is no longer pertinent. Organization of the data files: The Guide Star Catalog is subdivided into regions that are bounded by small circles of right ascension and great circles of declination, and that are numbered consecutively from 0001 to 9537. Data for each region are stored as separate files; these files are contained in directories, each of which subtends a 7.5 degree zone of declination. File regions.dat gives the vertices (in J2000 coordinates) for each of the 9537 catalog regions. The requirement for efficient random access to small areas of the sky (e.g., circles 0.5 to 1.0 degrees in diameter) underlies the adopted catalog organization, which divides the sky into large regions, approximately 7.5 deg in size, which are then subdivided into small regions on the basis of their expected individual stellar populations; each small region corresponds to one file of the GSC. The parameters are selected such that small regions nominally contain 2000 objects; and since the regions are defined entirely by celestial geometry, any area can be accessed by reference to a small number of regions identifiable with simple logic. The details of this scheme are given in Paper III. The declination boundaries of the large regions are small circles of right ascension taken at 7.5 deg intervals beginning at declination +90 deg. Each of these declination bands is subdivided in right ascension by segments of great circles of declination spaced at intervals of 360/N deg, where N is the nearest integer to 48/cos(DEC_0), DEC_0 being the center of the declination band. There are 732 large regions in the GSC. Finally each large region is divided into small regions by the segments of N great circles of declination, uniformly spaced in right ascension, and by N small circles of right ascension, uniformly spaced in declination. The values of N range from 2 near the galactic poles to 4 in the plane, and there are 9537 small regions in the GSC. Large region numbers are numbered first (most rapidly) by right ascension, beginning with the regions whose southwest corner is at RA = 0 and DEC = 0, then proceeding north by bands of declination, until the polar zone is counted; then the process continues symmetrically in the south, beginning at the northwest corner of the region at RA= 0 and DEC = 0. Small regions are numbered in the same manner, except that the count goes through all the small regions of a large region before proceeding to the small regions of the next large region. The right ascension and declination limits of each of the 9537 small regions, in J2000 coordinates, are given in the table an ASCII version of this table is given in regions.dat. The user is cautioned that, according to the nomenclature convention explained in Paper III, maintenance procedures may result in an object being located up to a few seconds outside the tabulated geometric boundaries of its regions; therefore, a commensurate expansion of search areas is often appropriate in determining the catalog regions to be used. However, this version (1) of the GSC does not contain any occurrences of overlapping region boundaries. All data files (i.e., with the exception of this ReadMe file and the directory files) except regions.dat are in FITS (Flexible Image Transport System; Greisen et al. 1981; Wells et al. 1981; Grosbol et al. 1988; and Jahreiss et al. 1992) table format. The root directory contains the following files: ReadMe - this file GSC - Directory for the binary compressed version of the GSC (300Mbytes) TABLES - Directory for GSC supporting tables. regions.dat - The corners of each small region. Directory GSC contains a compact version of the Guide Star Catalogue (details in the README file of this GSC directory), and includes directories for the 7.5 degree zones in declination; these directories in turn contain the GSC region files in a compacted format (usable on any architecture with the provided programs, see the README file therein), with file identifiers of the form nnnn.GSC, where nnnn is the 4-digit decimal region number, with leading zeroes used as required to fill the field. The directories are named as follows: Directory Declination Region From To From To ------------------------------------------ N0000 +00D 00' +07D 30' 0001 0593 N0730 +07D 30' +15D 00' 0594 1177 N1500 +15D 00 +22D 30' 1178 1728 N2230 +22D 30' +30D 00' 1729 2258 N3000 +30D 00' +37D 30' 2259 2780 N3730 +37D 30' +45D 00' 2781 3245 N4500 +45D 00' +52D 30' 3246 3651 N5230 +52D 30' +60D 00' 3652 4013 N6000 +60D 00' +67D 30' 4014 4293 N6730 +67D 30' +75D 00' 4294 4491 N7500 +75D 00' +82D 30' 4492 4614 N8230 +82D 30' +90D 00' 4615 4662 S0000 -00D 00' -07D 30' 4663 5259 S0730 -07D 30' -15D 00' 5260 5837 S1500 -15D 00' -22D 30' 5838 6411 S2230 -22D 30' -30D 00' 6412 6988 S3000 -30D 00' -37D 30' 6989 7522 S3730 -37D 30' -45D 00' 7523 8021 S4500 -45D 00' -52D 30' 8022 8463 S5230 -52D 30' -60D 00' 8464 8839 S6000 -60D 00' -67D 30' 8840 9133 S6730 -67D 30' -75D 00' 9134 9345 S7500 -75D 00' -82D 30' 9346 9489 S8230 -82D 30' -90D 00' 9490 9537 ------------------------------------------ File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file regions.dat 47 9537 The corners of each small region bright.plt 18 98 Details of the plates for bright stars out.sam 63 100 Sample output (out of 25,258,765 positions) TABLES/* . 15 FITS GSC supporting tables GSC/* . . Compact version of GSC (for DOS and Unix) -------------------------------------------------------------------------------- File Summary (FITS files in the directory TABLES): -------------------------------------------------------------------------------- comments.tbl Introduction and general comments. rev_1_1.tbl Comments on GSC 1.1 revisions. plates.tbl Information on the plates used in the GSC. process.tbl Image processing parameters. astr_cal.tbl Parameters of astrometric calibrations. phot_cal.tbl Parameters of photometric calibrations. c_up_pop.tbl Catalog update population statistics. st_pop.tbl Population statistics for stars. ns_pop.tbl Population statistics for non-stars. regions.tbl Boundaries of GSC regions. c_re_pop.tbl GSC region population statistics. lg_reg_x.tbl Index to large regions. sm_reg_x.tbl Index to small regions. xref_p2r.tbl Cross-reference table, plates to regions. xref_r2p.tbl Cross-reference table, regions to plates. -------------------------------------------------------------------------------- Byte-by-byte Description of file: regions.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 I5 --- num Number of region 7- 8 I2 h RA0h Low limit of right ascension, hours (J2000) 10-11 I2 min RA0m Low limit of right ascension, minutes (J2000) 13-17 F5.2 s RA0s Low limit of right ascension, seconds (J2000) 19-20 I2 h RA1h High limit of right ascension, hours (J2000) 22-23 I2 min RA1m High limit of right ascension, minutes (J2000) 25-29 F5.2 s RA1s High limit of right ascension, seconds (J2000) 31 A1 --- DE0- Low limit of declination, sign (J2000) 32-33 I2 deg DE0d Low limit of declination, degrees (J2000) 35-38 F4.1 arcmin DE0m Low limit of declination, minutes (J2000) 40 A1 --- DE1- High limit of declination, sign (J2000) 41-42 I2 deg DE1d High limit of declination, degrees (J2000) 44-47 F4.1 arcmin DE1m High limit of declination, minutes (J2000) -------------------------------------------------------------------------------- Byte-by-byte Description of file: bright.plt -------------------------------------------------------------------------------- Bytes Format Units Label Explanation -------------------------------------------------------------------------------- 1- 4 A4 --- plate PPD plate identification 7- 8 A2 --- region PPD plate region identification 11-18 F8.3 yr ep Mid exposure of PPD plate ------------------------------------------------------------------------------- Byte-by-byte Description of file: out.sam -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 10 I10 --- GSC *GSC designation 12- 20 F9.5 deg RAdeg Right ascention in J2000, epoch of plate 22- 30 F9.5 deg DEdeg Declination in J2000, epoch of plate 33- 36 F4.1 arcsec PosErr Mean error on position 38- 42 F5.2 mag Pmag photographic magnitude (see n_Pmag) 44- 47 F4.2 mag e_Pmag photographic magnitude 49- 50 I2 --- n_Pmag *[0,18] Coded passbland for magnitude 52 I1 --- Class [0,3] Class of object (0=star; 3=non-stellar) 54- 61 F8.3 yr Epoch Epoch of position 63 A1 --- Mult [TF] True if multiple object / False otherwise -------------------------------------------------------------------------------- Note on GSC: the GSC Identification is made of a plate number (5 digits) and star number on the plate (5 digits); note that, in the literature, a dash separates generally the two parts. Note on n_Pmag: the number designates the following combination of emulsion and filter: magband emulsion filter ------- -------- -------- 0 IIIaJ GG395 1 IIaD W12 4 (bright star) 6 IIaD GG495 8 103aE Red Plex 10 IIaD GG495 11 103aO GG400 18 IIIaJ GG385 ------- -------- -------- -------------------------------------------------------------------------------- Acknowledgements: The primary authors would like to thank the large number of persons who have participated in the Guide Star Selection System and the Guide Star Catalog developments over the past years. In addition to the many people previously acknowledged, they would like to thank the following who made contributions in GSC 1.1: by collaboration in merging INCA data into GSC 1.1: Daniel Egret and the Hipparcos INCA and Tycho groups; for providing astrograph plates for southern bright stars: Geoffrey Douglass, Robert Harrington, G. Monderen, and Otto Richter; by contributing to the GSC 1.0 error discussion or by reporting specific errors in GSC 1.0: Beatrice Bucciarelli, Daniel Egret, Holland Ford, Peter Garnavich, Roberto Gilmozzi, Roberta Humphreys, Mario Lattanzi, William Owen, Barry Rappaport, Kavan Ratnatunga, Larry Taff, Patrick Wallace, Fred Walter, and Archibald Warnock; for pre-mastering the CD-ROMs: Ian Evans; o and by making essential contributions to the project's infra- structure: Ian Evans; and by making essential contributions to the project's infrastructure: Marian Iannuzzi, Greg McLeskey, Dave Paradise, Don Stevens-Rayburn, and Patty Trovinger. Finally, special thanks are due to Riccardo Giacconi, Director of the Space Telescope Science Institute, for his vision and continuing support of this project. The Guide Star Catalog is partially based on data obtained at Palomar Observatory, operated by the California Institute of Technology; at the UK Schmidt Telescope, operated by the UK Science and Engineering Research Council and by the Anglo-Australia n Observatory; at the Cerro Tololo Inter-American Observatory and the Sacramento Peak Observatory, both operated by the Association of Universities for Research in Astronomy, Inc., under contract to the National Science Foundation; and at the Mount Lemmon Observatory, operated by the University of Arizona. The two CD-ROMS from which this catalog was copied contain the Guide Star Catalog - Version 1.1, with an issue date of 1 August 1992. The Guide Star Catalog (GSC) was prepared by the Space Telescope Science Institute (ST ScI), 3700 San Martin Drive, Baltimore, MD 21218, USA. ST ScI is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under contract with the National Aeronautics and Space Administration (NASA). The Astronomical Data Centers (ADCs) thank the Space Telescope Science Institute and the Association of Universities for Research in Astronomy for permission to archive this catalog. This document is the README.TXT file for this catalog slightly reformatted to be consistent with the format used by the ADCs with a few additions from other STScI publications and the addition of the regions.dat from the FITS file. References: Egret, D., Didelon, P., McLean, B. J., Russell, J. L., and Turon, C., Tycho Input Catalog - Cross-matching the Guide Star Catalog with the Hipparcos INCA Data Base, Astron. Astrophys., 258, 217-212 (1992). (1992A&A...258..217E ; Catalog ) Garnavich, P., The Stellar Angular Correlation, Clues to Wide Binary Star Properties, dissertation, University of Washington (1991). Greisen, E. W., Harten, R. H., An Extension of FITS for Groups of Small Arrays of Data, Astron. Astrophys. Suppl. Ser., 44, 371-374 (1981). Grenon, M., Mermilliod, M., Mermilliod, J. C., The Hipparcos Input Catalogue. III. Photometry, Astron. Astrophys., 258, 88-93 (1992). Grosbol, P., Harten, R. H., Greisen, E. W., Wells, D. C., Generalized Extensions and Blocking Factors for FITS, Astron. Astrophys. Suppl. Ser., 73, 359-364 (1988). Harten, R. H., Grosbol, P., Greisen, E. W., Wells, D. C., The FITS Tables Extension; Astron. Astrophys. Suppl. Ser., 73, 365-372 (1988). Jahreiss, H., Requieme, Y., Argue, A. N., Dommanget, J., Rousseau, M., Lederle, T., Le Poole, R. S., Mazurier, J. M., Morrison, L. V., Nys, O., Penston, M. J., Perie, J. P., Prevot, L., Tucholke, H. J., de Vegt, C., The Hipparcos Input Catalogue. II. Astrometric Data; Astron. Astrophys., 258, 82-87 (1992). Jenkner, H., Lasker, B. M., Sturch, C. R., McLean, B. J., Shara, M. M., Russell, J. L., The Guide Star Catalog. III. Production, Database Organization, and Population Statistics, Astron. J., 99, 2081-2154 (1990). Lasker, B. M., Sturch, C. R., Lopez, C., Mallama, A. D., McLaughlin, S. F., Russell, J. L., Wisniewski, W. Z., Gillespie, B. A., Jenkner, H., Siciliano, E. D., Kenny, D., Baumert, J. H., Goldberg, A. M., Henry, G. W., Kemper, E., Siegel, M. J., The Guide Star Photometric Catalog. I., Astrophys. J. Suppl., 68, 1-90 (1988). (1988ApJS...68....1L ; Catalog ) Lasker, B. M., Sturch, C. R., McLean, B. J., Russell, J. L., Jenkner, H., Shara, M. M., The Guide Star Catalog. I. Astronomical and Algorithmic Foundations; Astron. J., 99, 2019-2058 (1990). Ratnatunga, K. U., Comparison of GSC Photometry in Three Southern Fields; Astron. J., 100, 280-290 (1990AJ....100..280R) Russell, J. L., Lasker, B. M., McLean, B. J., Sturch, C. R., Jenkner, H., The Guide Star Catalog. II. Photometric and Astrometric Calibrations; Astron. J., 99, 2059-2081 (1990). Taff, L. G., Lattanzi, M. G., Bucciarelli, B., Two Successful Techniques for Schmidt Plate Astrometry; Astrophys. J., 358, 359-369 (1990). Taff, L. G., Lattanzi, M. G., Bucciarelli, B., Gilmozzi, R., McLean, B. J., Jenkner, H., Laidler, V. G., Lasker, B. M., Shara, M. M., Sturch, C. R., Some Comments on the Astrometric Properties of the Guide Star Catalog; Astrophys. J., 353, L45-L48 (1990). Turon, C., Gomez, A., Crifo, F., Creze, M., Perryman, M. A. C., Morin, D., Arenou, F., Nicolet, B., Chareton, M., Egret, D., The Hipparcos Input Catalogue. I. Star Selection; Astron. Astrophys., 258, 74-81 (1992). Wells, D. C., Greisen, E. W., Harten, R. H., FITS - A Flexible Image Transport System; Astron. Astrophys. Suppl. Ser., 44, 363-370 (1981). ================================================================================ (End) Nancy G. Roman/Gail L. Schneider [SSDOO/ADC] 22-Feb-1996