National Radio Astronomy Observatory                           Memo
-------------------------------------------------------------------
 Updated: 2005 September 27
 To     : VLBA users
 From   : J.M. Wrobel
 Subject: Your recent VLBA program


1. AUTOMATED CALIBRATION TRANSFER FOR VLBA CORRELATOR OUTPUT

The first phase of automated calibration transfer for data from the
VLBA correlator has been completed, and has been invoked for all
observations entered in the VLBA correlator queue after 1999 April 1.
This transfer of calibration information includes data from the 10
VLBA antennas, as well as selected information from the VLA, Green
Bank, and Effelsberg, which currently provide VLBA-style monitor data.
Significant changes to AIPS have been required to introduce
calibration transfer, so users must have a recent version of AIPS,
preferably 31DEC02 or 31DEC03.  (We strongly recommend a recent
version of 31DEC03, since it contains the latest procedures for
streamlining the calibration of VLBA data.)  Help files for a number
of AIPS tasks have been updated to reflect the new calibration
procedures.  Other documents of interest, available from
http://www.vlba.nrao.edu/astro/obscor
include (a) Automated Calibration Transfer and (b) A Step-by-Step Recipe 
for VLBA Calibration in AIPS.  The latter exists as Appendix C in the 
AIPS Cookbook which is a useful general resource. 

The calibration-transfer process relieves observers of the burden of
creating and inputting calibration files for VLBA antennas.  Instead,
this information is now provided as tables attached to the FITS data
sets output by the VLBA correlator.  The ancillary data include
antenna gain (GC table), system temperature (TY table), pulse
calibration (PC table), flags (FG table), and weather (WX table).
Wise observers will not modify these original tables, as processing
errors might then force the data to be reloaded using FITLD.
Skeptical observers can simply delete the appropriate tables created
by FITLD and generate their tables in the old manner using fetched
files (see section 2).  Please send comments to cwalker@nrao.edu, and
send bug reports to daip@nrao.edu, with a copy to cwalker@nrao.edu.

When implemented, the next phase of calibration-transfer will include
data from external antennas.

2. VLBA/VLA FILE SUMMARY SHOULD YOU NEED OR WISH TO FETCH FILES

2.1. Anonymous FTP

The session
    ftp ftp.aoc.nrao.edu      ! or 146.88.1.10
    Name: anonymous
    Password: <your e-mail address>
    ftp> cd pub
    ftp> get vlba_gains.key
    ftp> quit
fetches file `vlba_gains.key' containing VLBA zenith sensitivities and
gain curves, with an explanatory preamble.  This file is *not* needed
if you receive a distribution tape from the VLBA correlator with GC
tables attached.

2.2. File Server aspen

2.2.1. What Files Might You Want?

If `mmmyy' is a code for the month and year of the beginning of your
program (e.g., oct05) and `pppppp' is your program code (e.g.,
bw999x), then the following files are stored in directory
/home/vlbiobs/astronomy/mmmyy/pppppp:
  + pppppplog.vlba:  VLBA observing log containing comments entered
    by the array operator.  File is automatically e-mailed to
    observers whose addresses are known to VLBA operations.
  + ppppppcal.vlba.gz:  Gzipped VLBA calibration file containing
    system temperatures, flagging information, pulse cal and weather 
    station data, scan summaries, and VLBA tape recorder information
    for all available VLBA antennas (plus the VLA).  File is *not*
    needed if you receive a distribution tape from the VLBA 
    correlator with TY, FG, PC, and WX tables attached.
  + pppppptsm.XX.ps.gz:  Gzipped PostScript plots of selected data
    from file ppppppcal.vlba.gz for each available antenna with 
    station code XX = SC, HN, NL, FD, LA, PT, KP, OV, BR, MK, or Y.
  + pppppplog.y:  VLA observing log containing comments entered
    by the array operator, if VLA was used.  File is automatically 
    e-mailed to observers whose addresses are known to VLA operations.
  + ppppppcal.y.gz:  Gzipped VLA calibration file containing
    calibration information for all VLA polarizations and IFs,
    if VLA was used.  File starts with an explanatory preamble.
    File *is* needed even if you receive a distribution tape from 
    the VLBA correlator with TY, FG, PC, and WX tables attached.
  + pppppptap.vlba:  VLBA tape log made for programs not correlated
    in Socorro.  File lists VLBI tapes used.

2.2.2. Browse the File Server Aspen

Operations staff have devised a web browser to navigate the file
server, as well as view and retrieve its text and PostScript files,
gzipped or not.  This browser can be reached from
http://www.vlba.nrao.edu/astro/obscor, then click on "Browse the
Aspen File Server".

(document ends)