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GMOS-N Hamamatsu Array

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The upgraded GMOS-N detector array consists of three ~ 2048 x 4176 Hamamatsu chips of two different types arranged in a row. The central CCD (CCDg) has an enhanced response between ~450 and 650 nm compared to the left- and right-most CCDs (CCDr and CCDb, which probe the red and blue end of the spectral dispersion). CCDr and CCDb are both of the same type and have an enhanced response below ~450 nm and above ~650 nm. In the ITC, the central CCD is referred to as "HSC", while the two outer CCDs are referred to as "BB". The Hamamatsu detector array  has the same orientation as the previous e2v deep depletion array and continues to support Nod-and-Shuffle mode. The expected QE of the GMOS-N Hamamatsu CCDs compared to the previous e2v deep depletion devices is shown in the plot below. See the Status and Availability webpage for more details.


Comparison of the expected QE for the GMOS-N Hamamatsu and e2v dd detectors  



First results from the commissioning of the GMOS-N Hamamatsu detectors were presented as a poster at the AAS summer meeting 2017 in Austin, Texas: 


[First results from the commissioning of the GMOS-N Hamamatsu detectors]


The table below summarizes some of the Hamamatsu detector/controller characteristics

Array Hamamatsu
Pixel format 6278 x 4176 pixels (mosaiced)
Array layout Three 2048 x 4176 chips in a row with 67 pix = 1.005 mm gaps(*)
Pixel size 15 microns square; 0.0807 arcsec/pixel
Spectral Response approx 0.36 to 1.03 microns 
Bias level Bias Image
Flat field response Example flat
Readout time 1x1: characterization ongoing   2x2: characterization ongoing
Chip ref no. BI13-20-4k-1 BI12-09-4k-2 BI13-18-4k-2
Dark current ~3 e-/hr/pix ~3 e-/hr/pix ~3 e-/hr/pix
Full Well ~129000 e- ~123000 e- ~125000 e-
Fringing at 900nm < 1% ~ 2% < 1%

(*) Due to bright columns on either side of the chip gaps, the effective gap size, not usable for science, is 80 pix = 1.200 mm.


Read-noise and Gain Values

The table below gives gain/read-noise values for the GMOS-N Hamamatsu CCDs. The values are averaged over all 12 amps.  


Readout Gain Resulting average
rate level Gain (e-/ADU) noise (e- rms)
Slow Low 1.63 4.14
Fast Low 1.96 6.27
Fast High 5.11 8.69


Slow Read / Low Gain is the primary mode for science use. Fast Read / Low Gain may be of use, for example, with acquisition observations or for time resolved observations. Fast Read / High Gain is expected to be used primarily for very bright targets.



The linearity is better than 99.5% up to the full well values given in the Table above. (In the standard slow/low readout mode, the limit of the analog-to-digital converter will be reached before the full well depth.)


Cosmic hit rate 

The cosmic ray hit rate is higher on the Hamamatsu CCDs - about 2.6 times more pixels are affected by cosmic rays, as compared to the previous E2Vs. As for GMOS-S, it is recommended to keep individual exposure times <=1200 s.