ESPaDOnS: an Echelle
for the Observation of
Stars at CFHT
ESPaDOnS has its own acquisition and guiding camera
There are 3 ways to guide when observing with ESPaDOnS:
- By default, the ESPaDOnS guider is used, and controlled by the
- If the science target is too faint (fainter than about magnitude
12.0) for the ESPaDOnS guider, or if the ESPaDOnS guider has
difficulties doing a good guiding (for whatever reason), it is possible
to do Cass guiding with a star offset from the science target; this is
under OA control.
- If neither ESPaDOnS guiding or Cass guiding is satisfactory (eg,
there are dec oscillations and the star is not kept in the hole),
guiding can be performed manually by the observer, by stopping all
guiding, and using the Guider Control button "Center Star" to re-center
the target every 30-60 seconds.
The rest of this page documents the ESPaDOnS guider.
At the entrance of the polarimeter module, there is a tilted mirror
[photo] that reflects the light of the
field into the guiding camera, located on the side of the
polarimeter. At the center of this tilted mirror are the star and sky
The field of view is about 100 arcsec. The shortest exposure time is
0.5 seconds. A neutral density filter can be used to attenuate the light
of bright stars; the setting for the neutral density filter is on the
same window as for the guider control.
As shown on the Guider window of the GUI, the acquisition and guiding
camera can be used 4 ways:
- as an acquisition camera that shows the field of view, with
integration times that can be changed to suit the brightness of
the target; when going on a target, this is usually the first
mode used for the guider, to find and center the target of interest
- as a guiding camera, calculating the guiding corrections
needed, but without sending corrections to the telescope; this
mode can used to see if the guiding is stable
- as a guiding camera, sending guiding corrections to the
It is possible to guide on the target (which is in the star hole)
or on a nearby target (offset guiding with the Cassegrain guiding camera)
[image]. This is done by defining the
position of the guiding zone (represented by a dashed circle in the 2
previous images), using the GUI.
If for some reason the ESPaDOnS guider does not work well, it is
possible to use the Cassegrain guiding camera. The ESPaDOnS camera can
then be used in acquisition mode only, while the guiding is taken care
of by the Cass camera.
Back to ESPaDOnS's page
This CFHT Web page is maintained by Nadine Manset (manset