The HI shells of the Small Magellanic Cloud

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The HI shells of the Small Magellanic Cloud

• Using filters on a catalog to visualize the shell
  characteristics (size, position and velocity)

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• Start Aladin (either at http//aladin.u-strasbg.fr
  /Aladin or with the standalone software installed
  on your machine)
• Click on the Load button

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• Choose the SkyView folder
• Type SMC in the target box
• Choose IRAS 100 micron in the Surveys scrolling
  list
• Press the SUBMIT button

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• You get the IRAS ISSA 100 microns plate in the
  image display
• We will now superpose a catalog of HI shells on it

5

• Press the Load button
• Choose the Vizier Catalogs folder on the right
• Type shells in the free text zone
• Press SUBMIT
• The catalog of Staveley-Smith et al. 1997 is
  found
• Click on it and press SUBMIT

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• In the display window, the catalog is overlaid to
  the IRAS image
• Each point represents the center of an HI shell
  but we would like to draw the shells themself. To
  do that, we will use the Filter tool
• By selecting one point, you have access to the
  informations available in the catalog in the
  lowest part of the window. By moving the mouse on
  the different columns, you can see the
  corresponding UCD for each column.
• Click on the Filter button

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• Write the following expression in the filter
  definition box
• This filters draws a circle which radius is
  proportionnal to the extension radius of the
  shell (EXTENSION_RAD) and wich colour scales with
  the heliocentric velocity of the bubble
  (VELOC_HC) (between 120 and 200 km/s) with a
  rainbow palette.
• For more informations on the filters syntax,
  please press the Help on Syntax button or get the
  manual.
• Press Apply.

draw rainbow(VELOC_HC,120,200)
circle(EXTENSION_RAD)
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• We can now observe the distribution of the HI
  shells with their position, size and velocities.
  Note the colour view of the velocity gradient of
  the Small Magellanic Cloud.