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Part 1 Section Contents
Part 1: First Look Qualitative Analysis using ds9

Learning to Use the ds9 Imaging System

Part 1: First Look Qualitative Analysis using ds9

A quick list of the basic techniques of X-ray analysis:
  • look at an X-ray image using ds9 to get a qualitative feel for the data
  • use ds9 to select one or more regions of interest
  • perform quantitative analysis - spatial, spectral, or timing analysis - on the regions you have selected

In this first section you will use ds9 to make and color an image, and to look at some features.

One of the great things about Chandra is that both of its X-ray detectors can record really good position information. Because of this, the first thing we typically want to do when studying an object using Chandra data is to look at an image of the object. We call this a "qualitative" look because we are asking you to notice characteristics of the data that you can see by eye, without doing any complex numerical (quantitative) analysis.

Don't underestimate the value of taking a qualitative look at new data: the human eye is a wonderful instrument that can pick up subtle features of data, providing invaluable insights into where to look further with more quantitative methods.

Loading the Cas-A image

load Cas A image
Enlarge Image
  • To load the Chandra image of the supernova remnant Cas-A, start up the ds9 imaging system.
  • You will see a window similar to the one to the left.
  • Click on Analysis on the menu bar. You'll notice a dashed line at the top of the drop down menu. Click on this line to keep the DS9 Analysis window opened on your desktop.

ds9 analysis The DS9 Analysis window includes several quantitative analysis tools you will use at various times during the tutorial.

Choose the Virtual Observatory to access images from various sources.

tutorial For this tutorial, you will need to open the Cas-A supernova remnant image which is located on the Rutgers X-ray Analysis Server or the Chandra-Ed Archive server.

Place a checkmark in the box to the left of the Rutgers server OR the Chandra-Ed Archive server.

Enlarge Image
Load the Cas-A image from the list of images shown. (If you are connecting from Chandra-Ed Archive, you will click on: "ACIS observation of CAS A" , which is the first observation listed on the page.)
Enlarge Image
A window indicating that you have loaded the image of interest will appear.

Minimize this window so that you can load other images from the list at a later time.

Enlarge Image
When you have successfully loaded the image of Cas-A the image will appear as it does here with the following default settings:
  • grey color
  • contrast = 1
  • bias = 0.5
  • linear scale

This is the same Cas-A data set that you can load through the Activities and Images section. If the image does not load, check to make sure that you have:
  1. installed ds9
  2. started ds9 and
  3. connected to the Chandra analysis tools through the virtual observatory on the ds9 pulldown analysis menu.
If you think you missed a step, go back to the links on the top installation page and check to be sure that you have completed parts a, b and c of Step 1. If you are still having a problem, contact SAO R&D.

You will want to follow the directions in this section while working primarily in the ds9 window. We suggest that you print this section and use the printout as your reference for working in the ds9 window.

Next: Looking at an X-ray image: Contrast and Bias

Last updated: 08/26/08


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