ESPaDOnS: an Echelle SpectroPolarimetric Device
for the Observation of Stars at CFHT

Engineering

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 [image]
  • guiding on a nearby star [image]
  • 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:
  • 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) [graph]
  • it does not introduce spurious polarization
  • it does not reduce the flux very significantly
Replacement parts to make the ADC mechanism more robust were found and installed for the 2d engineering run.
• Data was successfully obtained in the 3 modes (polarimetry, spectroscopy star+sky [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 re-glued.
• 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 collected.
• 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 expected.
• 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 investigated.

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