KVN and VERA Array (KaVA)

KaVA Guideline for Data Analysis

1. Documentations of KaVA data analysis

Note that the AIPS Cookbook is a useful general guide for calibration and imaging of VLBI data.
http://www.aips.nrao.edu/cook.html : AIPS Cookbook

Hands-on analysis documentation of VLBI data is available in the following URL.

Several documentations related the KaVA data analysis would be helpful.

2. Tips for KaVA data analysis

For some parts of data analysis, KaVA would require special treatment as below :

2.1 Amplitude calibration

For amplitude calibration of KaVA data, KaVA provides the ANTAB files to PIs. The ANTAB file contains the gain curves for each antenna, and system temperature taken during the observation. You will obtain the TY and GC tables, loading the ANTAB file by running the AIPS task "ANTAB".

2.2 Parallactic angle correction

Time variation of a parallactic angle of a source occurs for the receiving system mounted in an azimuth-elevation mounted telescope and generates a phase rotation. This phase rotation can be corrected with the AIPS task "CLCOR" with the adverb of OPCODE='PANG'. In the case of VERA antenna, the field rotator in the receiving room fixes the parallactic angle, and therefore it is not necessary to run "CLCOR" for VERA antennas. But, you have to do this correction for the KVN antennas.

2.3 Editing the AN table

The doppler velocity shifts due to the earth's rotation and its motion within the solar system and towards the local standard of rest can be corrected using the AIPS task "CVEL". When the ARRNAM keyword in the AN table is "VLBA", then "CVEL" assumes that all data have been fringe-rotated to the centre of the Earth and determine the velocity correction accordingly. KaVA follows the VLBA and fringe rotates to the Earth center. Thus, the ARRNAM keyword in the AN table has to be "VLBA". Please run the task "TABED" and give "VLBA" to the ARRNAME keyword in the AN table.

2.4 Gibbs ringing effects around a bright and narrow spectral line

KaVA contains comparatively-short baselines (~300 km) as a VLBI array, and various Gibbs ringing effects could sometimes be seen in the case of the bright narrow spectral features. It is strongly recommended to smooth such spectral features when you correct the velocity shifts, by running the AIPS task "CVEL" with the adverb of APARM(9)>1.

Figures : Water maser lines in Orion KL in the Tamna-Ulsan baseline

r10105a_bf_cvl: Before CVEL

r10105a_aft_cvl_nosmooth: After CVEL with APARM(9)=0 (no smoothing)

r10105a_aft_cvl_smooth: After CVEL with APARM(9)=2 (smoothing)

KASI logo image

KaVA ( KVN and VERA Array )