Examine image

We use the SAOImage program ds9 here. Typical settings to see the entire image are:

Use Block=1 Zoom=4 to see faint sources at full resolution. The left button sets cursor markers, middle button resets field center, and right button adjusts color settings. Region Shape=circle can mark sources Shape=text can show source names, Shape=line can set scale bar. Edit Preferences=WCS can change units of RA/Dec. Print under the File menu can save desired image to disk in .ps format, or send to -Pcolor445 for hard copy.
As ACIS is an imaging spectrometer, we often want color images where the color represents X-ray energy, not intensity. It has proved difficult to produce aesthetically attractive energy-colored images. Following is a recipe by P. Broos based on IDL/function_2d.
  1. Construct three FITS images with different energy ranges to drive the red, green and blue colors in an RGB color palette. This can be done using CIAO dmcopy or FTOOL fselect. We assume they have astrometry keywords (e.g. CRVAL1) in their FITS headers, have exactly the same dimensions, and are precisely coaligned. See alignment recipes if this is not the case. Let's call the three FITS files A, B and C.
  2. In IDL, use the interactive environment function_2d to crop, rebin and recolor the images until you are pleased.
    3. and similarly for B and C. Pat suggests choosing a greyscale and recording the min/max levels for each image.
  3. In function_2d, click on Analysis --> RGB Image to bring up the tool true_color_image.pro. Adjust the scaling of the RB and B components, either with the mouse or using the Edit menu. Add titles and choose 1-1 aspect if desired.
  4. Print a color Postscript file (higher quality) or save a GIF file (lower quality).
Note 1: If you have two rather than three images, you can try the Hue-(saturation)-Value model in function_2d/true_color_image. For example, you could use the ratio A/B as the Hue component and A as the Value component.
Note 2: March 2000 release of ds9 version 1.8.7.7 has a number of improvmenets including improved contouring, printing of mouse coordinates, improved FITS header usage, improved color support, a new Examine Mode, and most importantly, capabilities of plotting RA/Dec coordinate grids.
An analogous procedure based on event lists rather than images is possible using IDL Event Browser. See Pat Broos for advice.