ESO VO Day, Tuesday 15 September 2009

Where

Council Room

Programme

• 09:00 - 09:45 Introductory talks
• 09:45 - 11:15 Use Case 1
• 11:15 - 12:00 Use Case 2
• 12:00 - 13:00 Lunch (lunch will be provided)
• 13:00 - 14:15 Use Case 2
• 14:15 - 15:00 Use Case 3
• 15:00 - 15:30 Coffee break
• 15:30 - 16:45 Use case 3
• 16:45 - 17:00 Feedback

Tutors

• Evanthia Hatziminaoglou, Paolo Padovani (ESO)
• Mark Allen (CDS)
• Mark Taylor (AstroGrid)

Introductory talks

• VO overview (PP, 15')
• A Virtual Tour of the Virtual Observatory (EH, 30')

Tools

• Aladin
• TOPCAT, STILTS
• VOSpec

Other tools you might want to have a look at (but they will not be used during the tutorials):

• VODesktop
• SPLAT-VO
• The US VO web services
• VOSED and VOSA, from the Spanish VO

For an exhaustive list of VO tools and services and their functionalities, have a look at the dedicated EURO-VO pages

USE CASES

Use Case 1: Confirming a supernova candidate (uses Aladin, TOPCAT)

• launch Aladin and TOPCAT
• load the local image (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)
  • you can change the colour map but 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
    • 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.e. 2MASS, USNO)
  • 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 (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
• the local image is now calibrated and can be superposed on the POSSII (or other) image, in order to identify the Supernova: change the transparency of the POSSII image by dragging the purple bar 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 other SNe 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
  • send the Simbad plane to TOPCAT
  • view the Simbad table selecting View -> Table Data
  • view the column metadata selecting View -> Column Info
  • place the cursos 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
  • OR you can "filter" the new Simbad plane, 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 for e.g. X-ray (or other wavelengths) counterparts: in TOPCAT: Load -> DataSources ->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 (NGC 6946) 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

Use Case 2: Searching for Data available for the bright galaxy M51 (uses Aladin, SIMBAD, VizieR, Topcat, VOSpec)

• launch Aladin, TOPCAT, VOSpec
• search for images of the bright galaxy M51 in Aladin
• open the Server Selector by clicking on the Load button, then try the various image servers:
  • the Aladin Image Server
  • explore Skyview
  • try Sloan
• select allVO; explore allVO
  • 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
• after selecting a few images, make a colour composite image using the "rgb" button, 7rd from the bottom in the vertical tool bar, right next to the image window; select the three images and "Create"
• use the multi-view windows to manage the various images you have in the 'stack'
• try the match button at the bottom of the image window to align the image for synchronized zooming
• go back to single image view and try the transparency control for viewing images overlaid on each other
• overlay as SIMBAD identifications using the SIMBAD link in the Server Selector window
  • try 'All objects' for a simple listsing of the IDs
  • click on a SIMBAD object or select a list of objects and see the details in tabular form below the image window
  • highlight the Simbad plane and click on "filter"
  • try the various filtering options (optional - open the properties'" window for the Simbad plane to see or edit the filter)
• filtering of sources can also be done interactively with TOPCAT; send the SIMBAD plane to TOPCAT (right-click on the plane in the stack, and 'Broadcast selected tables to..'
• view the table values in TOPCAT by selecting Views -> Table Data or by clicking on the 4th button from the top left
• make a plot of the positions and try the area selection tools to select a number of points in the plot, then create a subset; note how the selected subset may be transmitted back to Aladin to highlight sources from the original Simbad plane
• make a subset of the HII regions, and send the table back to Aladin using the TOPCAT Interop menu
  • place the cursor on any of the HII regions in Aladin and see how the corresponding row is highlighted in TOPCAT
• search for spectra available in the VO with the 'all VO' button in the server selector window.
• find spectra available from the Hubble Space Telescope, and view the positions of the spectra (and sometimes the spectral slit aperture) on the image; make a plane containing all the spectra positions, and cross match these with the positions of the HII regions
• start VOSpec (Web Start: http://esavo.esac.esa.int/webstart/VOSpec.jnlp) and display some of the spectra, by clicking on the spectra in the server selector window, and 'Load in -> VOSpec'.
• check VizieR for more detailed catalogues of HII emitting regions in M51; this can be done via Aladin or via the more detailed VizieR interface
• (Advanced - compile a list of bright HII regions in M51 and query VizieR with this list)

Use Case 3: Search for ULX sources and X-ray binaries in nearby (e.g. D<10 Mpc) galaxies (uses TOPCAT, Aladin)

ULXs (Ultra-Luminous X-ray sources) are X-ray sources that are less luminous than AGN but more luminous than any known stellar process (Lx > 10^39 erg/sec)

• tip: launch TOPCAT with a larger memory buffer; try java -Xmx512M -jar topcat-full.jar
• load the NED-1D galaxy catalogue (a .csv (coma-separated values) version of the catalogue can be found here: NED-1D.csv)
• the RA and Dec are in sexadecimals; convert RA, Dec to decimal: select Table Columns and then Add new sky coordinate column based on existing one; get rid of the multiple entries using the option match one, Eliminate All But First of Each Group.
• optional: apply a filter in distance (e.g. D<10 Mpc) using TOPCAT (the stricter the criterion, the smaller the number of objects!) and send the filtered nearby galaxies catalogue to Aladin
• this catalogue does not contain any information about the size of the objets; load the hyperLeda catalogue in Aladin [(VII/237) from All VizieR] (this might take a while as it contains about a million objects; place the cursor on the plane as it loads to get an idea of the number of objects still to be loaded); the catalogue is also available here) in a .gz VOTable format;
• cross-match the two catalogues and send the match back to TOPCAT; add new column with radius in arcmin: pow(10.,$diameter_column)*0.1/2
• you can now delete the hyperLEDA plane in order to save memory; then load the 2XMMi catalogue (0.2-12 keV band) in Aladin (IX/40), which gives the calibrated fluxes for sources; a copy of the 2XMMi catalogue in gzipped VOTable format can be obtained from here: 2xmmi.xml.gz)
• send it to TOPCAT and cross-correlate (match two; "Sky with Errors"; "1&2"; "All Matches") the 2XMMi with the nearby galaxies catalogue using the new radius and the X-ray position uncertainty (ePOS) as errors
• add new column with the luminosity Lx for the point like sources from the calibrated flux and distance to each galaxy, i.e. Lx = 4*pi*D^2*fx = (do the math!) 50.078+2*log10($distance_column)+log10($fx_column)
• filter those sources with Lx >= 1e39 erg/s (our ULX candidates)
• plot Lx vs cross-correlation separation: most objects are at very low offsets, therefore X-ray emission most probably comes from the nucleus; some objects are clearly off; keep those above a given separation which you can select based on the separation distribution
• send the catalogue to Aladin keeping only the X-ray coordinates
• cross-match with X-ray binaries table(s) to find the non-matches
• cross-match with quasars and/or AGN catalogue(s)
• find images of the galaxies, plot the positions of the AGN and ULX candidates; verify their separation as well as from the galaxy centre
• find existing ULX catalogues to confirm candidates