A Graphical Tool for Pointing the Hubble Space Telescope and Displaying Star Catalogs

James McCartney, William Jefferys and Barbara McArthur
Department of Astronomy
University of Texas at Austin


Pickles is a Macintosh program that was first developed by the HST Astrometry Team as a tool for determining pointings and rolls of the Hubble Space Telescope when desired target and guide stars were in the fine guidance sensor "pickles". Over time, it has become a much more sophisticated tool, and now includes apertures for all the Hubble science instruments, the ability to add user-defined apertures and the ability to display an 8° x 8° (HST Fixed Head Star Tracker) window.


1. Technical Description

Pickles is a standard Macintosh application, written in C using an object-oriented discipline.


2. Functional Operation

Pickles can manipulate the star position data graphically through the use of menus, key commands and mouse actions. The star position data can be read from ASCII files and stars can also be added manually in the program by the user. The Fixed Head Star Tracker Catalog is also available, which is a very complete compilation of many catalogs. Numerous CD-ROM catalogs can be read, including the STSCI Guide Star Catalog and the SAO, ACRS 1 and 2 and the AGK3 catalogs from the NASA Goddard Space Flight Center's "Selected Astronomical Catalogs ".

There is dynamic control over the view of the Pickle window. The apertures can be centered on stars or on specified positions. The telescope pointing, roll and date(including automatic determination of the zero roll date) can be chosen, and the application knows about the Sun and Moon position and HST constraints on Sun and Moon distance for any date. The star field and telescope can be viewed at any rotation (and that rotation can be constrained by a user specified increment) and at several different magnifications, ranging from 0.5 to 240x. A magnitude limit can be set so that faint stars are not displayed and stars can be made invisible by user selection. There are several coordinate systems available, including: equatorial, screen, theta A & B, Phi-Rho, Star Selector Encoder , and Pickle X & Y; The units available decimal degrees, radians, pi radians, hours/minutes/seconds, and degrees/minutes/seconds.

Pickles creates an ASCII file that contains the star positions that are displayed in the graphical window. It has a header with pickle-specific information, and the stars' numbers, positions and magnitudes are recorded in columnar list form. There is a provision for additional user-defined columnar data output. The star positions can be recorded in any of the available coordinate systems, and can be sorted by user-defined criteria.


3. Extended uses

Pickles can bring up a window that shows the 8°x8° field of view of the HST FHST. Most commands that work in the normal Pickles view are disabled in the FHST view. You can select stars, make them invisible, change the date, save the list of stars as a file. Whenever the FHST window is visible, any changes made to the pointing in the Pickles window will be reflected in the FHST view.


Because of its ability to extract and display star positions from CD ROM catalogs, Pickles is also being used in other astronomical projects. It is an excellent program for making finder charts. Pickles is a powerful, easy-to-use tool for visualization of star positions for any purpose.


4. Distribution

Pickles can be obtained via anonymous ftp from clyde.as.utexas.edu (internet address = Login as anonymous, use your local login name as your password. It is located in the ./pub/pickles directory.

Additional files are also available from the ftp site including the Aperture Setup file for Pickles, and several catalogs. Make sure that version 5.0.2 of ISO 9660 File Access is used when reading CD-ROM catalogs. All files ending with the extension ".hqx" have been encoded by BinHex. All files with "sit" included in their name are archives that have been compressed by StuffIt. Pickles may also be obtained on request from the authors.


This software was developed under NASA Contract NAS8-32906and NAS5-29285, the support of which is gratefully acknowledged.