Cas-A remnant with horizontal cut at position 4158, 4398. You should notice as you move your mouse around the image that data represented by this graph remains unchanged as long as your mouse remains in the same horizontal row of pixels. See for yourself by using the arrow left, right, up and down buttons on the keyboard.
	Cas-A remnant with vertical cut at position 4158, 4398. You should notice as you move your mouse around the image that data represented by this graph remains unchanged as long as your mouse remains in the same vertical column of pixels.

To remove the graphs, pull down the analysis menu and click to deselect the items.

Pixel value table

Pull down the analysis menu and click on the pixel table. A new window will be activated that displays pixel values in a 6x6 pixel area around the mouse position. Now move the mouse around the image window. Notice how the pixel table display changes. This pixel table gives a small scale view of the data. It is especially useful when used in conjunction with the magnification window in the upper right corner (which shows a blown up version of the data under the current mouse position).

To remove the pixel value table, close the window using the button in the upper left corner.

Display contours

Iso-intensity contours are connected lines drawn on the image through pixels of equal value. (The root "iso" comes from the Greek meaning "equal". We are talking here about marking out lines of equal pixel intensity on an image, just as a topographical map marks out lines of equal elevation.) These are useful for indicating large-scale features of an image. The analysis menu has an option to overlay iso-intensity contours on the image. You can choose the number of contours to generate, as well as the smoothness of the contour lines. If you select the display contours option first, it will display whatever setting has been left on the contours parameters menu. To chose the contour parameters click on that line and the menu will appear. Change the values as you wish and push both the generate and apply buttons, in that order, and wait for the new contour parameters to be drawn on the image.

To remove contours, deselect the "Display contours" option on the analysis menu.

Display coordinate grid

Pull down the analysis menu and click on display coordinate grid menu option. A grid of astronomical sky coordinates will be displayed over the image. This is useful for reminding yourself where in the sky your object is located. This feature is especially useful when looking at areas of the sky with multiple sources, like the deep surveys, or areas where it is important to be able to pick out a particular source in an area where sources are close together.

Summary

There are, of course, other features in ds9 that will help you get a "qualitative" feel for your x-ray data so that you can begin to notice interesting features that you will want to analyze quantitatively. Don't be afraid to try things out! A detailed manual of ds9 features is on-line at the ds9 homepage.

Part 3: Learning ds9, Starting Quantitative Analysis [next] [back]



Last updated: 7/20/04