How to use Virtual Observatory tools with ctools?

What you will learn

You will learn how to interact with the Virtual Observatory tools Aladin for image display and Topcat for display of tables such as event lists.

Several ctools can interact with Virtual Observatory tools such as Aladin or Topcat for the visualisation and exploration of the analysis results.

Let’s take the example of generating a sky map, as explained before. Start with launching the Aladin application on your desktop:

../../../_images/howto_vo_aladin_before.png

Aladin application after start-up

Then use ctskymap to create a sky map and specify publish=yes as argument after the tool name:

$ ctskymap publish=yes
Input event list or observation definition XML file [events.fits] obs_selected.xml
Coordinate system (CEL - celestial, GAL - galactic) (CEL|GAL) [CEL] GAL
Projection method (AIT|AZP|CAR|GLS|MER|MOL|SFL|SIN|STG|TAN) [CAR]
First coordinate of image center in degrees (RA or galactic l) (0-360) [83.63] 0.0
Second coordinate of image center in degrees (DEC or galactic b) (-90-90) [22.01] 0.0
Image scale (in degrees/pixel) [0.02]
Size of the X axis in pixels [200] 400
Size of the Y axis in pixels [200] 400
Lower energy limit (TeV) [0.1]
Upper energy limit (TeV) [100.0]
Background subtraction method (NONE|IRF|RING) [NONE]
Output skymap file [skymap.fits]

Once ctskymap has terminated, the resulting sky map will automatically appear in the Aladin application (see below).

../../../_images/howto_vo_aladin_after.png

Aladin application after ctskymap finished execution

You can then overlay sky maps obtained at other wavelengths for comparison or objects extracted from a catalogue. In the example below we show the overlay of the Fermi/LAT 3FGL catalogue catalogue which allows us to identify Src001 with a Fermi/LAT source at the Galactic centre.

../../../_images/howto_vo_aladin_catalog.png

Overlay of the Fermi/LAT 3FGL catalogue over the sky map

Another example is the display of an event list using Topcat. Start with launching the Topcat application on your desktop:

../../../_images/howto_vo_topcat_before.png

Topcat application after start-up

Then run ctselect for event selection and specify publish=yes as argument after the tool name:

$ ctselect publish=yes
Input event list or observation definition XML file [events.fits] selected_gps_baseline_110380.fits
Radius of ROI around pointing or specified RA/DEC (degrees) (0-180) [3.0] NONE
Start time (UTC string, JD, MJD or MET in seconds) [NONE]
Lower energy limit (TeV) [0.1] 0.2
Upper energy limit (TeV) [100.0] 50.0
Output event list or observation definition XML file [selected_events.fits]

Once ctselect has terminated, the resulting event list will automatically appear in the Topcat application (see below).

../../../_images/howto_vo_topcat_after.png

Topcat application after ctselect finished execution

You can now open the 3-dimensional display tab and visualise the data in a coordinate system that is spanned by Right Ascension, Declination and energy (see below).

../../../_images/howto_vo_topcat_scatter.png

Display of event list in 3-dimensional representation

Below the list of tools and scripts that interact with Virtual Observatory tools.

Tool or script Object VO tool (example)
cslightcrv Table Topcat
csresmap Image Aladin
csspec Table Topcat
csviscube Image Aladin
ctbin Image Aladin
ctbkgcube Image Aladin
ctcubemask Image Aladin
ctexpcube Image Aladin
ctmapcube Image Aladin
ctmodel Image Aladin
ctobssim Table Topcat
ctphase Table Topcat
ctprob Table Topcat
ctselect Table Topcat
ctskymap Image Aladin
cttsmap Image Aladin