KI V2 -- Description of L1 Data Plots

This page describes plots produced by KvisPlots, which are used by the L1 database data display and by the real time
analysis tool used at the observatory during observing (rtKvis). For more details on some of these quantities and data
analysis methods, please refer to the additional documentation in:

Kvis manual:
http://nexsci.caltech.edu/software/Kvis/usersGuide/usersGuide.html
http://nexsci.caltech.edu/software/Kvis/usersGuide.pdf

KI V2 data memos:
http://nexsci.caltech.edu/KISupport/dataMemos/

Level 1 file descriptions:
http://nexsci.caltech.edu/software/KISupport/v2/KIV2dataProducts.shtml

Contents

  1. Wideband Incoherent V2
  2. Composite SPEC Incoherent V2
  3. Wideband coherent V2
  4. Composite SPEC coherent V2
  5. Wideband flux
  6. Composite SPEC flux
  7. Angle tracker (KAT) flux (K1 and K2)
  8. Total optical delay (m)
  9. Wideband flux RMS
  10. Wideband flux ratio (K2/K1)
  11. Wideband ratio correction
  12. Composite SPEC flux ratio (K2/K1)
  13. Composite SPEC ratio correction
  14. Phase jitter (rads)
  15. Lock breaks
  16. Fractional time locked
  17. AO flux (K1 and K2)
  18. AO rate (K1 and K2)
  19. Elevation angle (degrees)
  20. Azimuth angle (degrees)
  21. Fringe tracker (FATCAT) throughput (DN/msec/10thmag) (rtKvis only)
  22. Angle tracker (KAT) throughput  (DN/msec/10thmag) (rtKvis only)
  23. AO throughput  (DN/msec/10thmag) (rtKvis only)  
All plots represent one of the above quantities as a function of UT. In all cases, the data is plotted only for times when the FATCAT fringe tracker is locked or recording internal calibrations as part of a fringe acquisition sequence. In all cases, a data point is plotted for each average over xx secs, where xx equals the value of the blockTime parameter in the configuration file ini.params and is generally 5 seconds. All quantities representing a flux count (plots 5,6,7,8) are expressed in data number (DN) where the conversion to electrons is approximately 0.28 DN/electron.

In addition, for grism observations (spectral side dispersed over 42 pixels) rtKvis produces plots of: coherent V2, incoherent V2, flux and ratio correction as a function of wavelength.

  1. Wideband Incoherent V2

    Incoherent V2 for the FATCAT white-light (WL) pixel. This is the basic V2 measurement, and this plot is useful for a quick assesment of the V2 data quality and to determine whether or not a given object is resolved, and by how much. Unresolved calibrators should have a V2 equal to the system visibility (V2 ~ 0.6 to 0.7) and resolved objects will have lower values of V2. An estimate of the calibrated V2 can be obtained by dividing the V2 measured on a target by the V2 measured on its calibrator(s) (if the calibrator(s) are resolved, then an additional correction will be necessary).

  2. Composite SPEC Incoherent V2

    Same as (1) but based on an average of the V2 measured on the spectrometer pixels.

  3. Wideband Coherent V2

    Same as (1) but using a coherent V2 estimator. See the Kvis manual for the algorithm defining the coherent estimator.

  4. Composite SPEC Coherent V2

    Same as (3) but based on an average of the spectrometer pixels.

  5. Wideband flux

    Photon counts on the WL pixel. This plot is useful for assesing the overall flux throughput. For a given star and FATCAT frame rate, the flux trace should remain approximately constant. Large changes may indicate an alignment or weather (clouds) problem. The flux trace should scale appropriately (as long as FATCAT is below non-linear or saturation regime) with stellar magnitude (K-band or H-band, depending on which FATCAT filter is being used) and frame rate.

  6. Composite SPEC flux

    Same as (5) but for an average of the spectrometer pixels.

  7. Angle tracker flux (K1 and K2)

    Angle tracker (KAT) flux (J-band), for the Keck-1 and Keck-2 beams. 

  8. Total optical delay (m)

    Total optical delay introduced by the KI delay lines, and defined as (FDL - LDL), where FDL and LDL are the optical delays introduced by the long  delay line and the fast delay line, respectively.

  9. Wideband flux RMS

    The rms of the points within the averaging time (typically 5 seconds) normalized by the photon count. The quantity is a measure of the amplitude stability of the fringe.

  10. Wideband flux ratio (K2/K1)

    Ratio of Keck-2 beam to Keck-1 beam FATCAT Wideband fluxes.

  11. Wideband ratio correction

    The value of the correction factor that needs to be applied to the measured V2 to compensate for the loss of coherence due to flux mismatches between the Keck-1 and Keck-2 beams (for full details, see the memo on this topic in the links above).

  12. Composite SPEC flux ratio (K2/K1)

    Same as (10) but for an average of the spectrometer pixels.

  13. Composite SPEC ratio correction

    Same as (11) but for an average of the spectrometer pixels.

  14. Phase jitter (rads)

    The frame-to-frame RMS of fringe phase. This quantity will be high when the differential (between the Keck-1 and Keck-2 beams) optical path difference fluctuates significantly due to e.g. instrument vibrations and/or atmospheric piston. To the extent that it is dominated by atmospheric effects, it may used as a good indicator of seeing quality. A value of 0.8 radians or smaller is considered indicative of ``good'' conditions.

  15. Lock breaks

    The number of times the fringe tracker looses/re-acquires lock during a block integration. If greater than 1, it indicates that fringe lock was lost frequently, and therefore the observing conditions may be marginal (e.g. low V2, low flux, bad seeing, bad AO or KAT locks).

  16. Fractional time locked

    The fractional time during the block (usually 5 seconds) in which the fringe tracker was locked. A minumum threshold of 0.5 for this value is used in the standard Kvis processing.

  17. AO Flux     

    The visible flux counts (spectral sensitivity through I-band) on the AO wavefront sensors.

  18. AO rate

    The readout rate of the AO wavefron sensors (Hz).

  19. Elevation angle

    Observed object's elevation angle (degrees).

  20. Azimuth angle

    Observed object's azimuth angle (degrees).

  21. Fringe tracker throughput

    Given the flux counts being detected by the fringe tracker (FATCAT), these are the counts that would be detected per msec from a star of 10th magnitude. This normalization is useful for comparing the instrument sensitivity across nights and runs. A unusually low value may indicate an alignment problem, or clouds. A typical value is 30 dn/msec/10thmag.

  22. Angle tracker throughput

    Same as above but for the angle tracker (KAT). A typical values is 150 dn/msec/10thmag.

  23. AO throughput

    Same as above but for the AO sensor. A typical values is 50 dn/msec/10thmag.

March 2004
rev. April 2005, November 2006
R. Millan-Gabet and R. Akeson (NExScI)