Keck Interferometer Modes and Sensitivities

Summary Information

The table below summarizes the basic capabilities and sensitivity limits for each mode and instrument configuration. This table was last updated for sensitivity numbers on Aug. 10, 2011.

Please refer to the links below for complete details and additional sub-system (AO & angle tracking) limits.

Spectral Resolution and
Point Source Limiting Magnitude for Science Camera
H4:   H < 9.0 (200 Hz frame rate)
K5:   K < 10.3 (100 Hz frame rate)
K10: K < 9.8 (100 Hz frame rate)
K42: K < 7.6 (100 Hz frame rate)
note: if the seeing requires a faster rate of 200Hz, the limits are 0.5 mag brighter
L10:  L < 6.0 (100 Hz frame rate)
shared risk
Split-Pupil K/L
L10: L < 4.8 (100 Hz frame rate)
and one of the following:
K5 or K10 or K42 or H4, with 1.2 mag brighter limits that the standard configurations above.
note: shared risk and available only during NULLING runs.

Self-Phase Referenced (ASTRA-SPR) K K330: 4.45 < K < 7.8
note: fringe tracking at 250 Hz and longer integrations (1Hz typical) on spectrally dispersed output
Dual-Field Phase Referenced (ASTRA-DFPR) K K < 14 (long integrations).
note: shared risk.
Astrometry (ASTRA-Astrometry) K
K < 14 (long integrations).
note: shared risk.

N < 2.7 (2.4 Jy)  best performance.
N < 3.0 (1.7 Jy) sensitivity limit.

Updates for Semester 2012B:

  • The Keck Interferometer is not available.

Sub-System Limits

Modes and Configurations: Detailed Information

Additional Important Information

  • Zenith angle limits:
    • 50 deg zenith angle maximum.
    • 3 deg radius around zenith excluded, performance may start degrading within 5 deg of zenith.
  • Delay lines and Sky Coverage:
    • continuous (fast delay lines - FDL): +/- 15 m (+/- 13 m for NULLING).
    • quasi-static (long delay lines - LDL): +/- 70 m (+/- 65 m for NULLING).
    • The total delay is calculated by summing the FDL and LDL values. For an object at zenith, the delay is approx. -40 m, which means that targets with high and low declinations can not be observed with a single LDL position at all hour angles.
    • We recommend using getCal to determine detailed coverage for specific objects.
    • Up to 4 different long delay line positions can be used in a single night for the V2 modes.
    • Up to 3 different long delay line positions can be used in a single night for the NULLING mode.
    • Relocation of the LDLs takes about 15 min.
    • Relocation of the LDLs should only be done between complete calibrator-target clusters.
  • KI baseline:
    • physical length: 85 m.
    • orientation: 38 degrees East of North.
  • Spatial resolution: ultimately depends on the calibration accuracy; however a useful reference is the fringe spacing (wavelength/baseline):
    • H (1.65 um): 4.0 mas.
    • K (2.18 um): 5.3 mas.
    • L (3.8 um): 9.2 mas.
    • N (8.5 um): 21 mas.
  • Field-of-view (FOV, set by single mode fiber or pinhole):
    • H-band: ~35 mas.
    • K-band: ~45 mas.
    • L-band: ~80 mas.
    • N-band: ~450 mas.
  • Camera gains:
    • K band fringe tracker & science camera (FATCAT): 0.26 dn/electron.
    • L band fringe tracker & science camera: 0.065 dn/electron.
  • The first 30 mins after the telescope domes are opened may be needed for interferometer set-up: no science observations are guaranteed during this time.
  • Return to the KI Support page