This page contains KI sensitivity and instrument details for proposal and observation planning for V2 observations. In the V2 mode the main data product is the normalized visibility amplitude squared for a given source. Integrations on the target source and calibrators are interleaved in time, where each integration comprises fringe tracking data and all necessary calibrations. See the data overview for more details on the data.
Updates for 2009B call for proposals: Two new modes of visibility observing are available for shared-risk science in 2009B - self-phase referencing (V2-SPR) and L-band. The sensitivity values given below are based on current performance for these modes and while every effort will be made to perform proposed science observations, no guarantees are made for shared-risk observing.
The V2 mode is open for proposals from all Keck users (UC, Caltech, UH, NASA and NOAO TACs). The sensitivity values below are based on past interferometer performance in good weather. The interferometer performance degrades substantially in poor seeing.
Visibility mode verification tests have shown a 0.03 systematic bias in the squared visibility at H and K bands. Users should not assume measurements of absolute visibility to better than this level. The spectral channel-to-channel relative visibility systematic has been measured at 0.02 in squared visibility for the 4 and 5 channels modes and 0.01 for the 10 and 42 channels modes. See the flux bias memo for more details.
For the V2-SPR mode (330 channels), the channel-to-channel performance is expected to be 0.02. The expected absolute visibility-square accuracy based on preliminary measurements is 0.05. Differential phase measurements have been demonstrated to ~6 deg.
The limits below apply to unresolved targets.
As KI is a fringe-tracking interferometers, all targets and calibrators must exceed a threshold visibility to be observable. The limits given above are appropriate for unresolved (i.e. point-like) sources. If the target is resolved, the instrument sensitivity decreases as shown in the table below. Targets can not be larger than 4.5 mas diameter at K band or 3.3 mas diameter at H band. Please contact NExScI if you have questions about the observability of potential targets.
The table below gives the reduction in sensitivity (X given in magnitudes) for a given source diameter.
|X K_mag||Diameter (mas)||X H_mag||Diameter (mas)|
|0.00||< 1||0.00||< 0.7|
Up to different 4 long delay line positions can be used in a single night. The long delay lines take 15 minutes to re-position and align and should be changed only between groups of targets and calibrators. The timing gui in getCal plots the detailed coverage for a given LDL position.
For sources at the sensitivity limit of one of the sub-systems, the efficiency is generally closer to 4 scans per hour.
The first 30 minutes after the domes open may be necessary for interferometer set-up and no science observations are guaranteed during this time.
K-band u-v Coverage (as a function of declination):