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VO-Day ... in Tour

Use Case 1

Confirmation of a Supernova candidate

(based on the EuroVO-AIDA WP5 case, developed by G. Iafrate and M. Ramella)

Uses Aladin and TOPCAT.

Confirming a supernova candidate on an image taken by the Col Druscie Remote Observatory Supernovae Search (CROSS) programme

  • launch Aladin
  • load alocal image of NGC 6946 (taken by the “Col Druscie Remote Observatory Supernovae Search, CROSS, programme)
    • click “open” icon and use the “File” tab in the “Server selector” window (or via File-> Open local file... from the menu)
    • improve image visualization modifying the pixel distribution
      • click the "pixel" button, 3rd from the bottom in the vertical tool bar, right next to the display window (or Image -> Pixel contrast & map... from the menu, having the image plane selected)
      • use “Sqrt” for Contrast
      • play with the cursors of the transfer function plot
  • the image has no astrometric calibration, calibrate it from within Aladin
    • select a calibrated image either from the Aladin Image Server (or from all VO, e.g. 2MASS; do not select large images!)
      • choose “Aladin images” tab in the “Server selector” window
      • use “ngc6946” as “Target” (leave “Search cone” field as is)
      • select one of the results (e.g. the POSSII F-DSS2 13’x13’)
      • click “Submit” if you ticked its left box, or “Load” from the “Data info frame” if you selected it
    • select a reference catalogue from the Catalogue Servers (e.g. 2MASS, USNO)
    • place both images (calibrated and non-calibrated) side by side by splitting the Aladin display window in two panels (click on the corresponding icon at the bottom left of the display window or choose “View -> 2 panels” from the menu)
    • select “Properties...” right-clicking on the non-calibrated image plane
    • in the “Astrometrical Reduction” section click “New” and select the “by matching stars” tab
      • alternate a click on a star from the non-calibrated image to one on the corrisponding star on the calibrated one (cells in the tab should automatically highlight), use catalogue stars overlaing the catalogue to the calibrated image to obtain more precise positions
      • non-calibrated coordinates should be copied in the “x y” position column, calibrated ones in the “hh mm ss +dd mm ss” one; use at least 3 or 4 stars
      • click “Create” (eventually also “Apply” and close the 2 windows, main Aladin one will suffice)
  • the local image is now calibrated and can be superposed on the POSSII (or other) image in order to identify the Supernova
    • return to “1 panel” view (via menu or bottom icons)
    • select/highlight the newly calibrated image plane to display it
    • a small rectangular cursor should appear on the bottom side of the POSSII (or other) image plane: drag it left/right to change image transparency in the superposition;
    • (as an alternative use a blinking image association using the “assoc” icon in the left vertical toolbar and using the 2 images to create a new blinking plane)
    • identify the SN (there are 9 of them in the image, maybe the easiest to detect is at the bottom of the image near coordinates 20:34:45 +60:05:57, look at “location” field above the image display)
  • (alternative) try to identify the supernova by running SExtractor on the 2MASS image (Load -> SExtractor, select the 2MASS image in "image reference") and overplot the resulting catalogue on the local image on which you are trying to identify the supernova)
  • "tag" the supernova: use the “tag” icon in the vertical toolbar and click on it
  • measure the distance from the centre of the galaxy, by clicking on the "dist" icon, 4th from the top of the vertical tool bar: then click on the centre of the galaxy and without releasing the mouse button, drag the pointer all the way to the supernova; the distance is displayed on the main window
  • check for other SNe in the same galaxy
    • select "Simbad" from the Server Selector, apply "- no filter -" and "Submit"
    • filter the new Simbad plane
      • (with the Simbad plane selected) click the "filter" icon in the vertical toolbar
      • chosse the "Advanced Mode" tab
      • define: $[src.class]="SN" {draw red square} (the SNe will appear in red)
      • Apply and/or Export; a new plane with the filtered source has now been created
    • clicking on either of the objects displayed by the catalog, the available information will appear in tabular form at the bottom of the Aladin window, linking directly to the Simbad query results on your browser
  • (alternative) search for SNe in VizieR (and other, using the "all VO" button catalogues)
  • launch Topcat
  • send the Simbad plane to TOPCAT
    • select the Simbad plane and right-click it
    • choose "Broadcast selected tables to..." -> topcat
  • create the SN sub-sample as follows
    • menu "Views -> Row Subset -> Define new subset" using algebraic expression: "equals(OTYPE,"SN")"
    • OR (if you don't know the syntax for the algebraic expression)
      • display the column metadata (6th icon)
      • highlight the OTYPE column
      • rank the table based on the selected column by clicking on one of the yellow arrows at the top of the column metadata window
      • display the table (4th icon)
      • select the rows with OTYPE=SN
      • define a new sub-set including the selected rows only by clicking on the upper left button of the display table window
  • broadcast the SN subset back to Aladin
    • in Topcat main window select the subset from the "Row Subsets" dropdown
    • menu "Interop -> Send table to... -> aladin
  • overlay subset result on image to identify the SN in the image
  • look for e.g. X-ray (or other wavelengths) counterparts
    • in Topcat create new subsets using keywords or OTYPE as detailed for the SN subset before


Last update: 2009-11-26