Gecko's Web Page
Gecko's Web Page
| 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=- cfht.hawaii.edu).
Gecko traditional users can use ESPaDOnS instead for many (but not all!) of their programs.
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)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:
| EEV1 | EEV2 | MIT2 | |
|---|---|---|---|
| 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% |
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).
Observer's
Corner
NOAO Comparison Arc
Spectral Atlases Very useful 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=- cfht.hawaii.edu).
For Real Gecko Nuts...
Tiny
gecko is 'world's smallest'... from the BBC News
Gecko...
from britannica.com
Gecko... from
Wikipedia.com
