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WHIRCAM has been superceded by INGRID, and is no longer available as a common-user instrument.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