ESPaDOnS: an Echelle
for the Observation of
Stars at CFHT
The first engineering nights (Sept. 2/3 and 3/4) were very
successful! First light occurred around 10pm without any major
technical problem. The second engineering run (Sept. 23/24 and 24/25)
was a little less successful, mainly because of communications problems
caused by a virus in CFHT's network. Here is a summary of
accomplishments and issues remaining as of Jan 2005:
- Acquisition and guiding work
- Guiding works in both modes:
- guiding on the science target, on the ring of light seen
outside of the aperture hole
- guiding on a nearby star
- guiding under bad seeing conditions (over 1 arcsec - 2d
engineering run) also works, although it is more difficult
- Cassegrain guiding works too (if for some reason the ESPaDOnS
guiding camera cannot be used for guiding)
- Although the guiding camera doesn't seem to see as faint as
advertized by the manufacturer, stars magnitude 14-15 can be seen easily
with 0.5 second exposures, and guiding was successfully conducted on
targets mag~14-15 with exposure times of 3 seconds.
- The ADC (Atmospheric Dispersion Corrector) works:
Replacement parts to make the ADC mechanism more robust were found and
installed for the 2d engineering run.
- it corrects for atmospheric dispersion every 30 seconds, as
seen on images on the guider (stars round), and also as measured on
spectra (more flux at red wavelengths)
- it does not introduce spurious polarization
- it does not reduce the flux very significantly
- Data was successfully obtained in the 3 modes (polarimetry,
[right on this figure],
high resolution spectroscopy on star only
[left on this figure]). The
expected polarimetric signatures were seen on selected targets.
- The half-wave rhomb that exhibited stress birefringence in the
cold (Run #1) was re-glued and tested (Run #2) and works much better
now. However, the quarter-wave rhomb now seems to suffer from variable
retardance at different temperatures... One quarter-wave rhomb has been
- The intermittent noise problem seen on the detector was fixed (it
was due to the camera focus motor).
- The APD (avalanche photodiode) used for the Exposure Meter works.
- The data reduction software, Libre-ESpRIT, has been used on all data
- Communication with the Telescope Control System works very well
(guiding, telescope position, FITS headers...)
- The throughput for the instrument is within 0.5mag of what is
- Work continues for the GUI, the Observer's Manual, and the
preparation of Libre-ESpRIT for the first observers.
- Some servos need to be re-tuned.
- An unexpected cross-talk from circular to linear polarization is being
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This CFHT Web page is maintained by Nadine Manset (manset