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 May 31, 2012)
  1. Classical data processed and available at CADC

    In 2011 and 2012, CFHT undertook a small project to reduce all the ESPaDOnS data that had been taken over the first 3 years of ESPaDOnS, under Classical mode. Until then, only raw (unprocessed) data were available at CADC, and were then of limited use.

    Processed data are now available to any registered user from the CADC query pages for CFHT data and CFHT data, advanced search.

    The query can be made by instrument or target name, for example.

    Important information regarding the processed data available, their format, and the reduction can be found in the Processed classical ESPaDOnS data page.

  2. New detector and new Exposure time Calculator starting with 11A
    Starting in 11A, CFHT uses a new deep-depletion e2v device called Olapa. Olapa has exquisite cosmetics and much less red fringing than EEV1. Another major difference is that the QE in the red is about twice as high as with EEV1.

    YOU WILL GET TWICE A MUCH FLUX IN THE RED compared to EEV1, and even a bit more flux in the blue too! To help PIs deal with the change, CFHT has prepared a Olapa-ready Exposure Time Calculator: New ETC for ESPaDOnS and Olapa

    This new ETC is based on the one for EEV1, which was created by JF Donati. The interface and presentation are very similar.

    The current crosstalk is finally below 1%!

    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 2014
    Xtalk0.70%0.46%0.59% 0.40%0.55%0.3%0.47%0.3% 0.16%

    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.

    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.

    Classical Observers (Semesters up to and including 2007B) can consult the ESPaDOnS in Classical Mode webpage.

    Thanks to the new fibers and connectors intalled in June 2006, the efficiency of ESPaDOnS has increased, and the flux is higher. The throughput is now at the best level we have ever seen (the level of the commissioning period of late 2004).

    The drop of efficiency was roughly 1.0mag for the period Jan-June 2005 total (with respect to the inital and best throughput values measured on the sky). Between June 2005 and February 2006, the spare spare fiber bundle has exhibiting a 0.4mag loss of flux (again with respect to the best throughput measured on the sky).

    Please see the ESPaDOnS known technical issues page 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.

  8. 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=-