### 24 Importing regions of the HST GSC

The Hubble Space Telescope Guide Star Catalog (GSC, see Section 2, above) is divided into some 9537 regions and each region is held as a separate FITS table file. These FITS tables can be read directly by CURSA. However, there is a CURSA utility to convert them to a more convenient format. I recommend that you use it to convert a region before accessing the region with other CURSA applications. The utility generates a new version of the region with the following changes:

• the units of the Right Ascension and Declination are changed from degrees to radians and the UNITS attributes set so that CURSA can format the coordinates as sexagesimal values for display,
• the region is sorted into ascending Declination order so that (fast) range selections can be performed on it.

In order to convert a GSC region simply type:

catgscin

The amount of textual information written to the output catalogue is controlled using the command line mechanism described in Section 10.1. You then answer the following prompt.

CATIN
Enter the name of the input GSC region.

Here ‘CATIN’ is the name of the corresponding ADAM parameter name, which appears at the start of the prompt line. The original version of the region is not overwritten, but rather a new catalogue containing the modified version is created.

GSC regions have names of the form region_number.gsc (where region_number is an integer number). The converted region is written to a file called gscregion_number.FIT. Thus, for example, the converted version of region 5828.gsc would appear as file gsc5828.FIT.