DS9: the Chandra X-ray Telescope Image Processor
Hands On Universe TRA Conference,
Williams Bay, WI, August 18, 2005 

the Chandra X-ray telescope

    high-resolution (0.5 arcsec/pixel),  large area, 0.1 - 10 kev energy range (10 - 0.1 nm)

the ds9 software (runs under Win, Mac, Unix)

    downloading and installing the software
 
    opening the software and connecting to a Chandra server:
       under Analysis, select Virtual Observatory
       click in the Rutgers/MIT Server box (any box is OK); wait until color is green
       load the Cas A image by clicking on Cas A link
       (Cas A is a remnant of a type II supernova that exploded in 1670?; 10,000 c-yrs distant) 
       to set proxy host and port: under Edit, select Preferences > http .... ; type in proxy info
       to save proxy host preferences: under Edit select Preferences > Save Preferences

the data

    the Chandra telescope records the energy (equivalent to wavelength), time of arrival, 
        and position of each photon
    the X,Y Image numbers show the cursor/pixel location relative to the bottom left corner
    the FK5 a, d numbers show the right ascension, declination location of the image
    under Analysis, select Display Coordinate Grid
    the Value number shows the photon count at the cursor/pixel location
    under Analysis, select Pixel Table; it displays the Value numbers in surrounding pixels
    [Student Activities with Cas A: given the distance and age, determine the angular size,
        linear size, and expansion speed]

changing the display

    click the Color box, then the he sub-box
    click the Scale box
        click consecutively on these sub-boxes: log; sqrt; hist equ; linear; squared
        they emphasize (respectively):
        faintest regions; medium faint; medium; medium bright; bright
    left-clicking on the image creates a Region for Analysis
    to remove Regions: click on the Region box, then on the delall box 
                                         OR click on the Region, press Delete key

contrast & bias

 contrast is the rate of change of color with color level;
    at low contrast, color changes gradually with changing pixel values, 
        whereas at high contrast color varies rapidly with changing pixel values
    contrast is adjusted by dragging the right mouse button vertically in the display window

 bias is the offset added to the pixel values before the color map is applied
    at low bias, low pixel values will show; at high bias, only the high pixel values will show
    bias is adjusted by dragging the right mouse button horizontally in the display window

spectra

    create a Region (left click) at X,Y Physical pixels (4050,4100)
    (Regions can be moved: click on the Region, then click&drag with left mouse) 
    (Regions can be resized: click on the Region, then click&drag on corner tabs)
    under Analysis, under Chandra Ed Analysis Tools, select Quick Energy Spectrum Plot
    in the pop-up window, zoom in on spectrum by creating a box using click/drag/click; 
        right click to return to previous plot; more display options under View
    create another Region by at X,Y (4530,4175) and obtain a spectrum 
    note differences in emission-line strengths in spectra of the two Regions
    identifying lines in spectra: spectra of supernova remnants
    [student activities with supernova remnants:  Tycho's SNR  ds9 SNR assessment]

image info

    return to suzuki.rutgers.edu page; back arrow to the Chandra Ed
    load Cen X-3; do not delete the Regions
    Cen X-3 is a binary system (2.1 day period) consisting of a pulsar and an O6III star 
    under File, select Display Fits Header
    find observation date and time, duration of observation, time resolution (1.34104 s)

light curves & periodicities

    under Analysis, under Chandra Ed Analysis Tools, select FTOOLS/Light Curve; click OK 
    zoom in on light curve by creating a box using click/drag/click; right click to go back
    zoom until graph displays about 100 seconds of time; estimate the (pulsar) period; 
    under Analysis, under Chandra Ed Analysis Tools, select FTOOLS/Power Spectrum; click OK 
    (this command does a fast Fourier Transform on the data to search for periodicities)
    note peak at frequency .208 s^-1 ; convert to period
    click/drag/click to expand that region of the graph; why is there a range of periodicities?   
    [Student Activities with Cen X3: determine the orbital speed and size from the pulsar period
        variation; determine the mass of the companion]

x-ray vs. optical views 

    return to suzuki.rutgers.edu page; back arrow to Chandra Ed images; load the Coma image;
    Coma is a cluster of galaxies 400 M light years distant; image shows intergalactic gas
    select b for Color; select sqrt for Scale
    under Color, select Colormap Parameters; select  1.1 for the Contrast and 0.4 for the Bias 
    to retrieve the corresponding optical view:
    under Frame, select Tile Frames
    under Analysis, select DSS server; click Retrieve in the pop-up box
    After the optical image loads, click on the x-ray image
    under Frame, select Match Frames > WCS 
    under Frame, select Lock Crosshairs > WCS
    under Edit, select Crosshairs
    click&drag the crosshairs to see which positions in the two images match
    [Student Activities with Coma: determine the temperature & luminosity of the cluster gas]