Madrid

ESAC VO School

19 - 20 October 2010

European Space Astronomy Centre (ESAC)
ESA, Villafranca del Castillo, Madrid, Spain
ESAVO Portal

Use Case 4: Confirmation of a Supernova candidate

Uses Aladin, TOPCAT and VOSpec.

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; looking for available spectra of these Supernovae or of other objects in the field.

  • launch Aladin, TOPCAT and VOSpec
  • load into Aladin the local image of NGC6946 (ngc6946.fit) taken by the Col Druscie Remote Observatory Supernovae Search (CROSS) programme, File -> Open local file.
  • 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)
    • you can change the colour map by again selecting "pixel" and then Color map
  • the image has no astrometric calibration; the calibration can be done from within Aladin
    • open the Server Selector by clicking on the Load button
    • select allVO; explore allVO for NGC6946
      • tick off Catalogues and Spectra and open the Server list (click on "Detailed list ...")
      • 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 ( "SUBMIT")
    • the response will appear in the form of a tree in the Server selector window
    • pick the image of your choice ( tip: do not select large images!)
    • select a reference catalogue from the Catalogue Servers (e.g. 2MASS, USNO): Go back to the Server selector window (click the Open icon), on the right hand side of this window select Surveys, under the Catalog servers. Highlight 2MASS-PSC and "Submit". Do the same for the USNO-B1 catalog.
    • 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 select Edit -> Properties).
    • in the Astrometric Reduction section select New and select by matching stars
    • activate the cells under the "x y" position (by clicking on them) and click on a star in the uncalibrated image; then select the corresponding star in the calibrated image after activating the cells under hh mm ss +dd mm ss. Repeat this for a few stars (3-4) and then click Create
  • the local image is now calibrated and can be superposed on the POSSII (or other) image, in order to identify the Supernova: go back to single view mode (showing one single image in the main Aladin window) and change the transparency of the POSSII 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 "assoc" icon, 6th from the bottom)
  • "tag" the supernova (6th button from the top)
  • further steps:
    • 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 more SNe and other interesting objects in the same galaxy: 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 (or Views -> Row Subsets) -> Define new subset using algebraic expression (or Subsets -> New subset) 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 (or select Subsets -> Subset From Selected Rows).
    • OR you can click on "filter" within Aladin (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/or Export; a new plane with the filtered source has now been created
    • OR search for SNe in VizieR (and other, using the allVO button) catalogues
    • select other images taken in other wavebands and different epochs
    • look in catalogs for e.g. X-ray (or other wavelengths) counterparts: in TOPCAT: Load -> DataSources ->Cone Search , or VO -> Cone Search.
    • in the "Keywords" field type your constraints (e.g. x-rays, 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, send them to Aladin, check them against the images, improvise!
  • other things to try with Aladin:
    • draw contours ( "cont") 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 ( "rgb") from three images of your choice
  • look for available spectra in the field: one can look either for available spectra of particular sources or make a larger search around the centre of the galaxy, encompassing the entire field covered by our image
    • in VOSpec:
      • put the name of the Object (NGC6946) in the Target field and the size of the search radius in the Size field (0.2) and click "Query"
      • in the Server Selector window open the SSA Services tree and select the services to search, or tick the 'Select All SSA' box below. Click "Query". This will return results from all the SSAP servers available in the VO and they will be listed, by service, within the Spectra List region in the main VOSpec window.
      • select spectra from any (more than one is possible) resource and click on "Retrieve"; all selected spectra will be displayed
      • by clicking the Tree/Table view (icon on the right of the upper tool bar) the returned SSAP servers can be displayed in a table or a tree view
      • Hint: check the spectra are all from the same object by looking at the metadata fields: name, distance, etc.
      • select one spectrum from the list and visualise it; try zooming in and out; try fitting lines; familiarise yourself with the various functionalities
    • OR: Click the "Open" icon in Aladin and in the server selector choose "all VO"
      • type NGC6946 into the target field, choose a search radius of 14', tick only the "spectra" server option and click "Submit"
      • mouse over collapsed server results looking at the Aladin image display to see what positions the spectra refer to (one or more "S"s should appear there
      • click over a result and from the "Data Info Frame" click "Load in..." VOSpec to display the spectrum there.
      • use the line fitting functionalities in VOSpec, explore the tool