Confirmation of a Supernova candidate

(based on the EuroVO-AIDA WP5 case, developed by G. Iafrate and M. Ramella, expanded by E. Hatziminaoglou. The original version can be found here)

Uses Aladin and TOPCAT.

The goal of this tutorial is to look for a supernova candidate on an image taken by the Col Druscie Remote Observatory Supernovae Search (CROSS) program and look for other Supernovae in the field.

Starting...

• launch Aladin and TOPCAT
• load the local image of NGC6946 (ngc6946.fit) taken by the Col Druscie Remote Observatory Supernovae Search (CROSS) program
  • File -> Load local file
• to make the image clearer, modify the distribution of pixel intensities ( button, 3rd from the bottom in the vertical tool bar, right next to the image window)
  • change the contrast -> check "sqrt"
  • adjust the transfer function moving the three triangles

Astrometric Calibration of an image

• the image has no astrometric calibration. It means that in the local image of ngc6946 there is no information on the celestial coordinates. The calibration can be done within Aladin, comparing our image with a calibrated image and identifying the same objects (3 or 4 stars) in both images.
  • open the Server Selector by clicking on the Load button ()
  • select allVO ( ); explore allVO resources for NGC6946
    • target NGC6946, filed 14'
    • tick off and and open the Server list (click on )
    • the button marked next to each *Registry* will give information about the Registry
    • you can Filter the resources
    • select a few resources (e.g. Aladin image server) and fire the query ( )
    • the response will appear in the form of a tree in the Server selector window
    • images from the Aladin image server can also be found through the "Aladin image" tab on left side of the server selector
    • pick the image of your choice (e.g, POSSI E-DSS1 14.2' cutout, tip: do not select large images!)
  • select a reference catalogue from the Catalogue Servers (e.g. 2MASS, USNO) either from the AllVO menu or from the Surveys tabon the right.
  • place both images (calibrated and non-calibrated) side by side by splitting the Aladin 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 (or right-click on the image and select "Properties ...")
  • in the Astrometric Reduction section select "New" and "by matching stars"
  • activate the cells under "x y" position (by clicking on them) and click on a few (3-4) stars on the uncalibrated image; then select the corresponding stars on the calibrated image after activating the cells under hh mm ss +dd mm ss and then click Create
  • 

Identifying the supernova candidate

• the local image is now calibrated and can be superposed on the POSSI (or other) image, in order to identify the Supernova:
  • go back to single view mode (showing one single image in the main Aladin window)
  • change the transparency of the POSSI image by sliding bar appearing on the image logo to the right
  • OR associate the two images (this can be done by clicking on the icon)
  • find and "tag" the supernova ( icon)
• To confirm that the apparent supernova we have just found is really a supernova, we also have to check that it does not appear in images taken in other wavelengths. We will check POSS II IR and BLUE.
  • Open the server selector, switch to the Aladin Images tab and submit POSS II J (optical B) and POSS II N (optical I) images.
  • These two further images are loaded in the Aladin plane stack, repeat the same procedure as before in order to compare our image with them.
  • Note that the supernova does not appear in any of these images, so it could be really a supernova!

Further steps:

• measure the distance from the centre of the galaxy
  • click on the icon
  • 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 more SNe and other interesting objects in the same galaxy:
  • load from the Server Selector
  • 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 select all the objects in the field (drag and drop the mouse creating a rectangle around the galaxy), highlight the Simbad plane and click on the column named OTYPE
  • the corresponding histogram (objects grouped per type) of selected objects 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
• interact between TOPCAT and Aladin:
  • send the Simbad plane to TOPCAT
    • right click on the SIMBAD plane
    • select Broadcast selected table to -> topcat
  • in TOPCAT, view the Simbad table by selecting in the Menu Views -> Table Data or by pressing on the button
  • view the column metadata selecting Views -> Column Info or by pressing the button
  • in Aladin, place the cursor on any Simbad identification on the main Aladin window and see how the relevant row is highlighted in the TOPCAT Table Data
  • in TOPCAT, create the SN sub-sample as follows:
    • click on Display row subset () -> Define new subset using algebraic expression () with the expression: 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()
    • OR, in Aladin, you can click on (make sure the Simbad plane is highlighted) -> advanced mode and define: $[src.class]="SN" {draw red square} (the SNe will appear in red); Apply and Export; a new plane with the filtered source has now been created
    • OR, in Aladin, you can search for SNe in VizieR catalogs (in theserver selector switch to tab or use the button where you will also find other catalogs)
• select other images taken in other wavebands and different epochs
  • look for e.g. X-ray (or other wavelengths) counterparts: in TOPCAT: Load () ->Cone Search()
  • in the "Keywords" field type your constraints (e.g. x-ray, radio, gamma, supernovae) and select the resources to be queried
  • put the objects name (NGC6946) in the "Object Name" field and query
  • cross-correlate () the resulting catalogues with the one(s) already loaded in TOPCAT,
    • if necessesary, add new coordinate columns to the Simbad table, based on the existing ones, in order to covert hh:mm:ss to decimal degrees. Views -> column info -> columns -> new sky coordinates columns
  • send the new matched catalogue to Aladin with SAMP (), check them against the images, improvise!
  • other things to try with Aladin:
    • draw contours () on any of the image
    • activate the Simbad automatic pointer (from the "Tools" menu), place the pointer on any object of the image
    • try to create an RGB image () from three images of your choice

-- GiuliaIafrate - 2011-03-14