KI V² H, K and L band accuracy and precision

This page details the visibility accuracy and precision for measurements made with KI.

The accuracy of the visibility measurements was determined by performing a series of observations of binaries with known orbital parameters and comparing the absolute value of the measurements to the predicted visibility values. The details of these tests are given in the recommended settings and flux bias memos.

These 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 scatter within a cluster is often better than this level (0.01 to 0.02 for bright sources) but for determinations of angular size and comparisons between nights, the 0.03 bias applies.

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. Over narrow spectral features, differential phase measurements have been demonstrated to about 1 deg rms (or equivalently, for unresolved objects, 16 microarcsec sky offset), per single visit (120 sec of data), and for stars near the sensitivity limit. However, differential phase slopes or curvatures across the band are dominated by instrument effects (mainly the continuously changing differential optical paths in air), and therefore these broad features are not likely to contain astrophysical information.

The accuracy of the visibility measurements at L-band has not yet been definitely measured.

Return to the KI V2 sensitivity page.