Confirmation of a Supernova candidate (based on the EuroVO-AIDA WP5 case, developed by G. Iafrate and M. Ramella, expanded by E. Hatziminaoglou)

Uses Aladin and TOPCAT

Confirming a supernova candidate on an image taken by the Col Druscie Remote Observatory Supernovae Search (CROSS) programme; looking for other Supernovae in the field.

• launch Aladin and TOPCAT; make sure they "see" each other (the Aladin little antenna should be emitting, and the Aladin logo should appear in the TOPCAT main window)







• load in Aladin the local image of NGC6946 (ngc6946.fit) taken by the Col Druscie Remote Observatory Supernovae Search (CROSS) programme
• to make the image clearer, modify the pixel distribution ("pixel" button, 3rd from the bottom in the vertical tool bar, right next to the image window -> Contrast - Log)
  • you can change the colour map but again selecting "pixel" and then Color map
• the image has no astrometric calibration; this becomes obvious by placing the cursor anywhere on the image: the "Location" field at the top of the main window will state the lack of astrometric calibration. The calibration can be done from within Aladin
  • open the Server Selector by clicking on the Open File button
  • set the "Target" name (NGC6946) and "Submit"
  • the response will appear in the form of a table in the Server selector window
  • click on the image of your choice (tip: do not select large images!) and "Submit"
  • the selected image should now appear in the main Aladin window
  • we now need to overplot a catalogue on the newly loaded image in order to accurately pick up the coordinates of the stars we will use to perform the astrometric calibration
  • open the Server Selector by clicking on Open File (in case you have closed it) and click on "Surveys" under "Catalogue Servers"
  • chose a catalogue (2MASS point source catalogue (PSC), USNO or GSC2 are good choices) and "Submit"; the catalogue should now appear on top of the calibrated image but not on top of the local (uncalibrated) image
  • if the symbols are too small (dots), highlight the catalogue plane and edit its properties ("prop"); select e.g. circle, rhomb or square and "Apply"
  • place both images (calibrated and non-calibrated) side by side by splitting the display window in two panels (click on the corresponding option at the bottom left of the display window - multiview)
  • highlight the non-calibrated image plane and select the properties button "prop", 2nd from the bottom(or right-click on the image and select "Properties ...")
  • in the Astrometric Reduction section select New and select by matching stars
  • activate the cells under "x y" position (by clicking on them) and click on a few (5-6) stars on the uncalibrated image and their corresponding counterpart in the calibrated image, altenating between the two images; the position of the stars on the calibrated image should appear as coordinates under hh mm ss +dd mm ss ; after selecting a sufficient number of stars (5-6) click Create
• if everything went according to plan, the catalogue you loeade before (2MASS, USNO etc) should now appear on top of the previously uncalibrated image
• return to single view mode (showing one single image in the main Aladin window)
• you should be viewing something like this:

  
  

• in order to identify the supernova, unselect the catalogue you used for the calibration and superpose the two images: change the transparency of the POSSII or 2MASS image by sliding bar appearing on the image logo to the right

  
  

• "tag" the supernova (6th button from the top)
• 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
• now look for known supernovae in the same field
  • load Simbad from the Server Selector, apply no filter
  • clicking on either of the object, 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 - try it
  • to see immediately the SNe, highlight the Simbad plane and click on the column named OTYPE
  • the corresponding histogram (objects grouped per type) will appear in the little graphic window below the stacks; move the mouse over each bar to see the corresponding objects highlighted in the main Aladin window
  • send the Simbad plane to TOPCAT
  • view the Simbad table selecting View -> Table Data
  • view the column metadata selecting View -> Column Info
  • place the cursor on any Simbad identification on the main Aladin window and see how the relevant column is highlighted in the TOPCAT Table Data
  • create the SN sub-sample as follows:
    • click on Display row subset -> Define new subset using algebraic expression as equals(OTYPE,"SN")
    • OR (if you don't know the syntax for the algebraic expression) display the column metadata; 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; 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
• select other images taken in other wavebands and different epochs
• try to create an RGB image ( "rgb") from three images of your choice
• draw contours ( "cont") on any of the image