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:

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).

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.

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:

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).

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).

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