Calibration Data

Data necessary to perform accurate calibration for the VLBA are supplied as part of the correlator output files, and will appear as extension tables within the AIPS datasets created by task FITLD. These tables include GC (gain), TY (system temperature), and WX (weather) tables for amplitude calibration, PC (pulse-cal) tables for system phase calibration, and FG (flag) tables for editing.

For non-VLBA stations, some or all of these tables may be missing, since relevant measurements are not available at the time of correlation. For example, for the HSA, GC and TY information is available for most stations, except that calibration of the phased VLA requires additional information about the flux density of at least one source. Flag (FG) tables for non-VLBA stations generally are absent or only partially complete, lacking information about antenna off-source times. However, the "flag" file that is written by program SCHED (Walker 2011) is quite good at predicting the on-source times for HSA stations. In using this file as an input to AIPS task UVFLG, it is recommended that all entries for the ten VLBA stations be deleted. The FG table supplied with the correlator output files includes the actual on-source times for these antennas, obtained directly from VLBA monitor data. For further information on applying calibrations, see Appendix C of the AIPS Cookbook (NRAO staff, 2006) or the relevant AIPS HELP files.