WHIRCAM

WHIRCAM has been superceded by INGRID, and is no longer available as a common-user instrument. The notes below supplement the main instrument manual . See also the WHIRCAM software page .

Useful numbers

CHIP:       SBRC InSb array 256*256 30-micron pixels
SCALE:      .24"/pix -> 61"
            .08"/pix (MARTINI) -> 20" 
            .05"/pix (MARTINI) -> 13"
READOUT:    0.12  sec (256*256) 
            0.036 sec (128*128) 
            0.012 sec (64*64)
            4 readouts, each reads every 4th column
READNOISE:  40 e- (ND STARE), 55 e- (STARE)
SATURATION: 10000 (ND STARE), 38000 (STARE) (p.16)
            (saturation, but non-linear 1%  3000 counts ND STARE
                                       10% 17000 counts ND STARE)
            (defined by well capacity pixels, not A/D dyn range)
DARK:       1e-/sec, but thermal leaks -> 10 e-/sec
GAIN:       6e-/ADU
BAD COLS:   (54,256) -> (55,81) (hot pixels plot p.6 of manual)
RESET LEVEL ("BIAS"):  
            22000 counts even cols, 30000 odd cols, hence striped 
            appearance 
            (made different so that they saturate at similar levels)
FLATFIELD:  varies on tiemscale ~ hours



                             J         H         Ks        L

Wavelength (microns)        1.28      1.67      2.20     3.42

Bandpass (microns)           .3        .3        .3       .06

Extinction (1 airmass)       .10       .11       .07

Throughput (empirical)       .16       .17       .17
  (atm + tel + instr) 
  (MARTINI halves it)
Throughput (theoretical)     .22       .22       .22

QE                           .8        .8        .8

Photons/sec mag = 0
  (=6 * counts/sec)         9.2e9     4.9e9     3.0e9 
  (deduced from 15% throughput quoted in the manual, value for H was
   confirmed 9/97)

Sky mag/arcsec**2          15.6      13.9      11.4
  Compared with UKIRT:     same      same      1 mag
                                               brighter
  Due to:                  --- sky lines ---   --- sky + tel ---

Sky photons/sec ~         120       500      2800

Longest integration (sec)
  with ND-STARE ~         500       120        20        < 1 
  (sky saturation)
  
mag -> S:N = 5 with
  100 sec in .8" seeing    19.6      18.2      17.1             (p.24)

Saturation mag 0.12 sec
  if seeing = 0.5"          8.6       8.4       7.8

Min exp time for sky noise
  to be > readout noise     3         1         0.5

WHIRCAM history (some of)

930106
Roche et al meeting at RGO re using old IRCAM on WHT
940629
Hughes' report on possible uses of WHIRCAM at other focal stations
9410
Optics delivered to Oxford
950209
First commissioning run on WHT
950612
Final commissioning run on WHT (VSD/Roche/JMB)
950906
First scheduled WHIRCAM observing
960704
First commissioning run at Cassegrain (VSD/KMD)
961121
WHIRCAM failed while on Cassegrain rotator (see 9710)
9611
WHIRCAM opened up, charred wires and broken contacts found
970324
Array tested by SBRC, found OK, returned to ING
9704
WHIRCAM back on telescope, sensitive to light
970613
Used successfully for observing by Perez et al
970818
Dichroic badly scratched, probably while WHIRCAM off GHRIL table
970724
VSD reports H, K throughputs a factor of 4 down
970807
J, H, K throughputs/nominal = 0.12, 0.70, 0.41 (CRB)
970824
J, H, K throughputs/nominal = 0.47, 0.95, 0.70 (CRB)
970905
Cold-head motor shaft snapped
970914
H, K throughputs/nominal about 0.7 (CRB)
971020
QE instability cured by replacement of reamp power supply (PCM)
9710
9611 failure probably traced to loose nut floating around in the preamp power supply (PCM)
980208
Readout noise twice nominal, no cure in sight
9802
Filter wheel not positioning, new motorcode installed (PCM)
980507
Readout noise now only 30% above nominal (CRB)
980701
Dark current 2000 e- counts/sec. WHIRCAM was opened up, and a bolt on the heat shield was tightened. Dark current back to few e-/sec on 980704. Readout noise still above nominal.
981027
Readout noise high: 89 (STARE), 69 (ND STARE). Dark current 4



Chris Benn (crb@ing.iac.es)

1999 Dec 28