CFHT, Instruments, Spectroscopy, Gecko: The Coudé f/4 Spectrograph

Gecko's Web Page

* * * N E W S * * *

(Updated Feb. 13, 2007)

Gecko is no longer offered to the CFHT communities.

Starting with Semester 2007B, Gecko is no longer offered at CFHT. The instrument has not been dismantled, as it is an asset of the Corporation. Any comment on this situation can be addressed to CFHT's Executive Director, Christian Veillet (veillet -=at=-

Gecko traditional users can use ESPaDOnS instead for many (but not all!) of their programs.

* * * A B S T R A C T * * *

The CFHT coudé spectrograph, commonly referred to as Gecko, is an echelle spectrograph that has been optimized for use with a single spectral order (between 5 and 18) from the 316 groove/mm echellette mosaic. Its spectral resolving power R can go up to 120,000.

Gecko is used with CAFE, the CAssegrain Fiber Environment (a fiber optic link between a Cassegrain module and the Coudé room), and provides a spectral coverage from 3700-3800Å (or even down to 3500Å depending on the number of photons required) to about 1 micron (depending on the detector used). See the throughput measurements table for numbers. Note that following a Science Advisory Committee recommendation, the Gecko+UV train has been decommissioned and observations below 3500Å are no longer possible.

Order sorting is achieved with interference filters or by one of three variable grisms. An image slicer is used to optimize the throughput of the instrument. To minimize traffic into and out of the inner coudé room, the entire spectrograph can be operated remotely from the control room.

A "fiber agitator" (which agitates the optical fiber with an amplitude of 1 mm and a frequency of 30 Hz) has been installed to prevent modal noise and the S/N degradation associated with it. Flat field correction seems to be better than with the coudé mirror train.

A throughput measurements table for Gecko + CAFE and a Help file containing guidelines and a FAQ are available to help observers plan their proposals and observations (updated October 2003).

What's new
Updated March 31 2004
User's Manual
and other documents.
Observer's Corner Gecko Nuts

What's New (2004/03)
(well, not much)

A new web page now contains information, guidelines and answers to Frequently Asked Questions to help observers complete their Observer Preparation Form and decide which configuration they would like to use.

The throughput measurements table for Gecko + CAFE has been updated with measurements taken with MIT2. This table can help observers estimate integration times or S/N. Observers have to remember that many factors will influence the final throughput measurement: sky condition, guiding or declination oscillation, optical fiber installed (main/spare), optics for the spectrograph (RED/UV), wavelength and its position in the order, spectral order, filter or grism, QE of CCD...

Detectors offered with Gecko. Starting in 2004B, Gecko is offered with MIT2 only. EEV1 is now dedicated to ESPaDOnS.

The MIT2 chip can only be used with Gecko because it has a lot of bad columns; the small Gecko raster can be squeezed in between bad sections of the chip. There are some low level charge injection features (~4 ADUs above the bias of ~3914 ADUs) that are removed when biases are subtracted. According to the QE curves we have, MIT2 is much less sensitive in the blue than EEV chips, and a little bit more sensitive in the red. MIT2 does not show fringing in the red like the EEV chips.

Here is a comparison of all the CCDs ever used with Gecko:

Size (px X px) 2048 X 4608 2048 X 4608 2048 X 4096
Pixel size (microns) 13.5 13.5 15
Gain (e/ADU) 1.802 1.339 1.191
Noise (e) 3.143 3.990 7.686
Full well (e) 100000 80000  
CTE 0.999994 0.99995  
Readout Time 15 sec 30 sec 30 sec
QE at 350nm 42.0% 46.9% < 5%
QE at 400nm 74.5% 86.2% 30%
QE at 500nm 82.2% 96.9% 68%
QE at 650nm 78.0% 88.5% 92%
QE at 900nm 26.6% 30.3% 62%

Climb up, little Gecko!

User's Manual

A Web version of the Manual is available. Updated October 2003.

Articles about CAFE in the CFHT Bulletins #41 (page 14: PS, PDF) and #42 (pages 32-33: PS, PDF).

Climb up, little Gecko!

Observer's Corner

NOAO Comparison Arc Spectral Atlases Very useful atlas.

Gecko Coude Atlas

LOG SHEETS: Page 1 (PS - PDF) and Page 2 (PS - PDF). Updated October 2003.

Gecko Filters
Note 1: Filters for which the status says 'Poor' or 'Bad' should only be used if there is no other suitable choice. (The status comes from a visual inspection of the filter.)
Note 2: Filter #1519 should not be used, because it is fringing.

Gecko's detector: MIT2
(Informations about the previous detectors used, EEV1 and EEV2,are still available.)

Memo for the Observers (cookbook): PS - PDF, updated September 2006.

Please! Fill in the CFHT Observing Report at the end of your run. We cannot improve the instrument, the observing environment, the support offered to the observers etc. if we do not get feedback from the people we wish to serve. Any other comment may also be sent by email to the support astronomer (manset -=AT=-

Climb up, little Gecko!

For Real Gecko Nuts...
...or really cloudy nights...

Leaping Lizards Home Page

Global Gecko Association

Tiny gecko is 'world's smallest'... from the BBC News

Gecko... from

Gecko... from

Climb up, little Gecko!
Send comments to: manset -=AT=-
Copyright © 2004-2006. CFHT Corporation. All rights reserved.