8 Displaying an Image

This introductory recipe demonstrates displaying an image, which is the simplest use of GAIA. The image used is file ngc1275jkt.sdf, a reduced V band CCD image of the galaxy NGC 1275 obtained with the Jacobus Kapteyn Telescope (JKT) on La Palma. It was derived from observations included on the CD-ROM Astronomical Images by Jaffe[11]. However, the same data are publicly available from the ING (Isaac Newton Group) data archive maintained at the Institute of Astronomy, University of Cambridge. See URL:

For technical reasons there are some differences in the arrangement of the FITS headers in the archive and CD-ROM versions of the files but both contain identical astronomical information.

ngc1275jkt.sdf was created by reducing the raw observations using CCDPACK (see SUN/139[9]) following the recipe in SC/5[7]. The data reduction is not considered further here. The image is in the NDF data format (see Section 4 for details of the data formats available to GAIA). If you prefer you could use an image of your own rather than this one.

Assuming that you have copied all the example data files for the cookbook into your current directory (as described in Section 7, above) and configured your terminal or workstation to receive X-output, then proceed as follows.

(1)

Start GAIA by typing:

  %  gaia &

The ampersand (‘&’) is, of course, simply to run GAIA as a detached process, so that you can continue to issue Unix commands from the command line. A window displaying a start-up message should be displayed, shortly followed by the main GAIA window. If these windows do not appear then GAIA is not properly installed at your site; in the first instance seek assistance from your site manager.

(2)

Load file ngc1275jkt.sdf by clicking the File menu (leftmost of the options in the menu-bar at the top of the window), selecting Open… and using the file-picker which appears to choose the appropriate file.

(3)

The file should open, but the main display window will probably be mostly dark, with just a few white dots corresponding to the brightest parts of the image. Set some of the display options as follows:

(a)

select the range of intensities in the image to be displayed: click the Auto Cut: button (in the middle right of the control panel in the centre top of the window) and set it to 98%,

(b)

set the magnification: click the Scale: button (in the bottom left of the control panel in the centre top of the window) and set it to 1/2x,

(c)

set the colour table: click the Color Map: button (in the lower right of the control panel in the centre top of the window) and set it to heat.

The display should now look something like Figure 1.

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Figure 1: A V band CCD image of the galaxy NGC 1275. The image was obtained with the Jacobus Kapteyn Telescope (JKT) on La Palma

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(4)

You can inspect the header information associated with the image (see Section 4) by clicking on the View menu (second on the left on the menu-bar along the top of the main window) and choosing the Fits Header… option.

Note that this option will work with images in the NDF format as well as those in the FITS format (because the NDF format can contain FITS-like header information which GAIA can access).

(5)

GAIA has many other functions and options and you may want to spend a while exploring some of them. Similarly, you might also like to examine the other images included in the examples.

On-line help is available from the Help menu at the extreme right of the menu-bar at the top of the window. If you click on this menu and choose the Help topics index… item then the introductory page of the GAIA on-line help information will appear (see Figure 2). From this page you can follow hyper-links to further pages giving notes on how to perform numerous common tasks with GAIA. You are likely to find this help information very useful.

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Figure 2: The introductory GAIA help page

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(6)

When you have finished, close GAIA by clicking on the File menu and choosing the Exit option.