- CIRSI


Cambridge Infra-Red Survey Instrument

Technical Characteristics and Other Background Information

Array Type:
Rockwell 1024 x 1024 pixel HgCdTe HAWAII array [Rockwell]

Pixel size:
18.5um

Geometric data:

  • Active Area per Array; 18.944mm x 18.944mm
  • Detector Spacing(nominal); 17.056mm/922 pixels

    Wavelength range:
    Detector: 0.8 um - 2.5 um (CIRSI, phase 1 will not work beyond 1.9um)

    Quantum efficiency:
    60% at 1.0um, 60% at 0.8 um [QE curve(provided by Rockwell)]

    Operational Temperature:

  • Cooled by Liquid Nitrogen(77.4K; 195.8C)
  • normal operation is with chips 5-10degrees LN ie 87K or 186C.

    Filters: Available and planned Filter Set

    CIRSI+PATT Telescopes: Image scale and field of view

    Telescope and Focus Diameter
    (m)     		um/" "/pixel fov
    (single array)     		Contiguous field
    for 4 exposures     		Exposures
    per degree     		Survey Power
    WHT
    Prime f/2.8     		4.2m 57.0 0.32 5.5' x 5.5' 20.9' x 20.9' 30.9 0.42
    INT
    Prime f/3.3     		2.5m 40.486 0.457 7.80' x 7.80' 29.64' x 29.64' 16.4 0.29
    AAT
    Prime f/3.3     		3.9m 63.5 0.29 4.9' x 4.9' 18.6' x 18.6' 39.4 0.28
    Notes:
    (1) assumes 10% overlap on all exposures. (2) Survey Power is the product of the collecting area in m^2 times the field of view in degrees, neglecting any losses due to beam obstruction or the hole in the primary

    Other Telescope NIR camera combinations:

    Telescope and Focus - - "/pixel fov
    (single array)     		Exposures
    per degree     		Survey
    Power
    Keck 10.0m Cass NIRC InSb 256x256 0.15 0.64'x 0.64' 8800 0.0089
    VLT 8.2m Cass ISAAC MCT 1024x1024 0.15 2.5'x 2.5' 576 0.09
    WHT 4.2m Cass f/11 INGRID MCT 1024x1024 0.25 4.27' x 4.27' 197 0.07
    WHT 4.2m Nas f/11 WHIRCAM InSb 256x256 0.24 1.02' x 1.02' 3400 0.0040
    UKIRT
    3.9m Cass f/?     		IRCAM3 InSb 256x256 0.29 1.22' x 1.22' 2400 0.0027
    UKIRT
    3.9m Cass f/?     		UFTI MCT 1024x1024 0.09 1.54' x 1.54 ' 1526 0.0043
    CFHT 3.6m Cass QUIRC MCT 1024x1024 0.15 2.56'x2.56' 550 0.0185
    ESO NTT SOFI MCT 1024x1024 0.14 2.9' x 2.9' 428 0.02
    HST 2.4m Cass NICMOS MCT 256x256 0.04-0.20 - - -
    Notes:
    (1) Survey Power is the product of the collecting area in m^2 times the field of view in degrees, neglecting any losses due to beam obstruction or the hole in the primary

    Filter wheel:

    8 available slots ie 6 filters in addition to clear and opaque

    Filter options:

    The currently available filters are listed here

    The Gemini project has produced a list of [ filters and specifications ] for IR filters. The Gemini J filter is of interest since it is narrow than the standard J cutting out more of the OH absorption features. As a result the sky background is reduced. The potential gain needs to be investigated since the photon rate from the objects of interest is reduced.

    Filter Central wavelenth
    or Bandpass
    (um)     		FWHM
    (um or %)     		Transmission
    Peak
    (%)     		Comment
    Z 0.92 0.14 75 -
    J 1.25 0.28 75 -
    H 1.65 0.30 75 -
    K 1.95-?.?? - - red cut will depend
    on background
    HeI 1.083 1% 75 depends on interest
    Pa-gamma 1.094 1% 75 depends on interest
    OII 1.237 1% 75 depends on interest
    Pa-beta 1.282 1% 75 depends on interest
    FeII 1.644 1% 75 depends on interest
    NB-J 1.25 1% 75 survey
    NB-H 1.64 1% 75 survey

    Notes:
    (1) precise wavelengths for NB-J and NB-H will depend on sky lines and scientific requirments.

    Sky Brightness

    Note in J and H the sky is predominantly due to OH lines and factors of 3 variations in a single night are not uncommon in H, so that values below should not be necessarily interpreted to mean a particular site OR instrument is worse than another.

    Telescope Instrument J H Ks K reference
    CFHT RedEye 16.0 14.5 - 13.2 CFHT Redeye manual
    UoH 88' - 16.1 14.4 - 13.3 CFHT Redeye manual
    Palomar 60' - 15.8 14.1 13.6 - Murphy et al, PASP, 107, 1234 1995
    OCIW 100' - 15.9 14.0 11.8 - Persson et al, PASP, 104, 204 1992
    WHT WHIRCAM 15.6 13.9 - - Shaun Hughes, priv comm (Feb 97)
    Calar Alto 3.5m MAGIC 16.0 13.9 13.0 12.2 WWW
    Calar Alto 3.5m OMEGA 15.1 13.1 12.7 11.9 WWW
    ESO 2.2m IRAC-2 15.0-16.5 12.8-14.3 12.0-13.5 11.2-13.0 WWW
    ESO 3.5m NTT SOFI 16.0 14.3 13.0 - WWW
    CTIO 3.95m CCOB 14.6 13.6 12.6 11.9 WWW

    Sensitivity

    Below we tabulated the sensitivity of various camera systems in terms of the measured photon rate in electrons per second. Note that one actually measures Analogue to Digigal Units(ADUs) or counts. The units are Billions of electrons/second from zeroth magnitude object or 1000 of electrons/second for a 15th magnitude star. Taking the value at 15th magnitude is convenent for J and H since this is then detected count rate from the sky. When computing the count/rate per pixel do not forget to include the conversion from magnitudes/arc sec^2 to magnitudes/pixel.

    Telescope Instrument J H Ks K reference
    Calar Alto 3.5m MAGIC 8.2 7.7 5.8 5.3 WWW
    Calar Alto 3.5m OMEGA 12.7 9.4 10.1 9.4 WWW
    CTIO 3.95m CCOB 3.6 3.8 2.5 2.9 WWW

    CIRSI Sensitivity:

    Use the Exposure Time Calculator which is available here

    Effective Wavelengths and Zero-points for Photometric Bands

    Band Lambda DLambda NICMOS handbook - - - - - - - -
    Fo[Jy]
    (CIT)     		Fo[Jy]
    (UKIRT)     		Beckwith
    (1976)     		Wamsteker
    (198n)     		Koornneef
    (198n)     		Campins et al
    (1985)     		Bessell and Brett
    (1988)     		van def Bliek et al(1996) adopted AB
    V 0.55 0.80 3540 3540 - - - - 3600 - 3540 0.03
    z 0.92 0.15 - - - - - - - - 2190 0.55
    J 1.25 0.25 1670 1600 - 1650 1635 1622 1570 1680 1625 0.88
    H 1.65 0.30 980 1020 980 1070 1090 1055 1020 1070 1040 1.36
    K 2.2 0.4 620 657 620 673 665 65 636 664 650 1.87
    L 3.4 - 280 290 280 269 277 283 281 - 288 -
    L' 3.74 - - 252 - - - - 235 260 250 -
    M 4.8 - 150 163 150 158 164 167 154 167 160 -
    N 10.1 - 37 39 37 - - - - 43.5 - -
    Q 20.0 - 10 10 10 - - - - 12.3 - -
    1 Jy= 10**-23 ergs cm-2 Hz-1 = 10**-26 W m-2 Hz-1 1 Jansky (Jy) is defined as 10-26Wm-2Hz-1
    2 AB=-2.5log(Fnu) -48.60
    3 Note that whilst Vega is defined has having zero colour in the Vega based magnitude system it has a magnitude of V=0.03 for the above normalisation

    Observing Issues

    Published by Richard McMahon rgm@ast.cam.ac.uk
    Last modified: Sat Jun 12 11:55:36 1999