CFHT, Instruments, QSO, ESPaDOnS

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

A Franco-Canadian project

managed by
Jean-François Donati,
Claude Catala and
John Landstreet

Reduction of Classical data
Classical Observing with ESPaDOnS ESPaDOnS in Queued Service Observing Mode
Characteristics and Performances Other relevant documents

ESPaDOnS is a bench-mounted high-resolution echelle spectrograph and spectropolarimeter
which was designed to obtain a complete optical spectrum (from 370 to 1,050 nm)
in a single exposure
with a resolving power of about 68,000 (in spectropolarimetric and 'object+sky' spectroscopic mode)
and up to 81,000 (in 'object only' spectroscopic mode).

Latest news (Updated Dec 2017)
    Around May 24, the surface of the Olapa detector was contaminated by a thin coat of an unknown material. The contamination caused the appearances of bright and dark, small, patches, most easily seen on flats (using a histogram scale), at a low level of 10-30 ADUs. The total area affected was low. As far as we can see, observations did not suffer and data reduction took out (flat-fielded) most if not all of the artefacts. The contamination lasted from May to early December.

    The photo at left shows how the detector appeared in late August. The contamination looks much worse on this photograph than on scientific exposures. The ds9 image at right shows a few of the brightest splotched, which were seen in and between spectral orders.

    The contamination occured when ESPaDOnS suffered a loss of cooling power around May 24. The detector was warmed up to room temperature, the system checked and recharged with coolant, and the detector was pumped and cooled again. However, cooling likely started while the vacuum was still a bit high, causing contaminants to be deposited on the detector. The artefacts on the images were only discovered during the August 2017 run. Observations had been performed during the May/June run without any detectable effect on the data reduction. The August data also did not seem to suffer from those artefacts. Since calibrations are taken daily, data reduction removed (flat-fielded) most if not all the patches.

    The detector was warmed up and pumped before the September run. Data taken that run did not show any splotches at the center of the chip as before, however, a few faint features could be seen at the short edges of the chip (at the edges of the spectral orders). The same features remained during the Oct/Nov run.

    The detector was warmed up at a higher temperature and pumped again in December. Cosmetically, the surface of the detector looks much better now, which hopefully indicates that all remnants of the contaminant have been removed.


    The current crosstalk has been below 1% since Fall of 2009

    This was accomplished by fabricating a triplet with a new design, new materials, and a new mechanical mount not using any glue at all, and by also installing a new ADC (Atmospheric Dispersion Corrector) whose prisms also are not held with glue either. Results of on-sky tests performed with these 2 new optical devices show a total crosstalk below 1%.

    DateNov 2009Dec 2009Jan 2010 Mar 2010Aug 2010Jul 2011Jun 2012 May 2013Sep 2014Jul 2015 Jun 2016Nov 2017
    Xtalk0.70%0.46%0.59% 0.40%0.55%0.3%0.47%0.3% 0.16%0.44% 0.35%0.1%

    Some of the crosstalk left, along with its variation, is due to the Atmospheric Dispersion Corrector. This complex optical device probably still exhibits stress birefringence, and since its configuration changes as function of time (as a function of the telescope's position), this small stress birefringence introduces a small level of variable crosstalk.

    Crosstalk is the contamination of one Stokes parameter (one type of polarization) by another Stokes parameter. For example, a linear polarization of 10% "leaks" and a small signal of 0.5% is recorded in circular polarization, alghouth there should not be any. In ESPaDOnS, crosstalk is caused by stress birefringence in a triplet lens and in the ADC, and is usually temperature dependendent.

    The triplet lens used between June 18 2005 and February 2006 showed birefringence, with about 7% of Stokes V (circular polarization) ending up in Stokes Q and Stokes U. The cross-talk produces spurious continuum polarization, which does not affect most programs because ESPaDOnS is best used to measure polarization in lines and not in the continuum (measurement of continuum polarization with ESPaDOnS is very difficult as the instrument was not designed to do that).

    The next triplet, installed in June 2006, had cross-talk around 2-3% (linear to circular, and vice-versa).

    An improved triplet (with new optical design and new materials) installed in Oct 2008 initially showed low cross-talk, which unfortunately increased into 2009 (up to about 4% in June 2009). It is thought that curing glue was the cause. During the summer of 2009, it was also discovered that the ADC (Atmospheric Dispersion Corrector) also introduces a large amount of cross-talk.

    Please see the ESPaDOnS known technical issues page for more details related to the first investigations of the crosstalk.


    The 2015 SF2A proceedings include an update about ESPaDOnS and recent improvements ("News from the CFHT/ESPaDOnS spectropolarimeter", Moutou, Malo, Manset, Selliez-Vandernotte, Desrochers):


    All ESPaDOnS data, taken in either Classical or QSO mode, are available as processed files at CADC. See all Espadons news for more details.


    See all Espadons news for more details.


    Since Semester 2008A, ESPaDOnS is offered in Queued Service Observing only. PIs who want to submit Proposals should consult the ESPaDOnS in QSO Mode web page. See all Espadons news for more details.


    Between Jan and Jun 2005, there was a 1.0mag drop in efficiency (damaged main fiber bundle). Between Jun 2005 and Jun 2006, the drop in efficiency was 0.4mag (spare fiber bundle). New fibers and connectors were installed in Jun 2006. See all Espadons news for more details.


    Please note the following:

    BEFORE July 2005
    (with the script real_time_esprit)
    invert the sign of V and Q
    the sign for U is OK
    AFTER July 2005
    (with the script libre_esprit
    or with Upena)
    invert the sign of U
    the signs for V and Q are OK


    Contemplating continuum polarization? Please consult the FAQ before you make any proposal. ESPaDOnS was not designed to do continuum polarization very well. See details on the Continuum Polarization page.

  10. If you have any question or concern, please contact the Support Astronomer Nadine Manset (manset -=at=-

Characteristics and Performances [top]

The engineering that took place in September 2004 was very successful. A brief summary includes a few figures and graphs. In November and December 2004, commissioning took place, with average weather conditions.

For official information and numbers, please see the official ESPaDOnS webpage. [top]

Other relevant documents [top]
  1. Photos
    1. ESPaDOnS arriving at the summit (July 2004)
    2. ESPaDOnS at CFHT (August 2004)
  2. Documents
    1. Development Responsibilities List
  3. Various presentations made at CFHT (newest first)
    1. Board of Directors, December 2004 [HTML, best with IE]
    2. Science Advisory Committee, November 2004, [PDF file | HTML, best with IE]
    3. Board of Directors, December 2003 [JPG slides]
    4. Science Advisory Committee, November 2003 [JPG slides]
    5. Science Advisory Committee, November 2002 [JPG slides]
    6. Science Advisory Committee, November 2001 [Gif and PS slides]
    7. Board of Directors, December 2000 [Gif and PS slides]
  4. Posters
    1. CASCA 2006 [PDF]
    2. CFHT Users' Meeting 2007 [PDF]
  5. Courses
    1. Graduate level short course on ESPaDOnS [PDF]
This CFHT Web page is maintained by Nadine Manset (manset -=AT=-