[daip] Re: be026a (fwd)

Wed May 24 04:42:11 EDT 2006

Hello, I am not sure that AIP is the right adress for my question, but
I got no answer trying to contact the data analysists. Maybe you are
able to help me?
Regards, Dieter Engels 

---------- Forwarded message ----------
Date: Thu, 18 May 2006 15:33:19 +0200 (CEST)
From: Dieter Engels <st2b102 at hs.uni-hamburg.de>
Reply-To: dengels at hs.uni-hamburg.de
To: Data Analysts <analysts at aoc.nrao.edu>
Subject: Re: be026a

Dear colleagues, I have a question to the observation BE026A (June 2003)
made with the VLBA. 

http://www.vlba.nrao.edu/astro/VOBS/astronomy/jun03/be026a/

The file header of the raw data set is

AIPS 1: Image=MULTI     (UV)         Filename=BE026A      .UVDATA.   1
AIPS 1: Telescope=VLBA               Receiver=VLBA
AIPS 1: Observer=BE026               User #=   29
AIPS 1: Observ. date=15-JUN-2003     Map date=09-MAY-2006
AIPS 1: # visibilities    351556     Sort order  TB
AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  TIME1  BASELINE
AIPS 1:            SOURCE  FREQSEL  INTTIM  GATEID  CORR-ID  WEIGHT
AIPS 1:            SCALE
AIPS 1: ----------------------------------------------------------------
AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
AIPS 1: COMPLEX      1   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: STOKES       1  -1.0000000E+00       1.00 -1.0000000E+00    0.00
AIPS 1: FREQ       512   2.2234200E+10       1.00  3.1250000E+04    0.00
AIPS 1: IF           2   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: RA           1    00 00 00.000       1.00       0.000000    0.00
AIPS 1: DEC          1    00 00 00.000       1.00       0.000000    0.00
AIPS 1: ----------------------------------------------------------------
AIPS 1: Coordinate equinox 2000.00
AIPS 1: Rest freq  22235.081         Vel type: OPTICAL wrt LSR
AIPS 1: Alt ref. value -6.60000E+04  wrt pixel  257.00

1) If I apply VLBAFIX the header is rewritten giving STOKES=2 and IF=1,
creating a new dataset called FXPOL
I am not sure that in this case it makes sense to apply VLBAFIX.

2) Later I set the velocity -66 km/s to pixel 257 with SETJY
   making
   AIPS 1: Alt ref. value -6.60000E+04  wrt pixel  257.00

3) After calibration I splitted the target IRAS 19135+2131 from the
   UV-Dataset using SPLIT. The header of the resulting file is

AIPS 1: Image=19135+21  (UV)         Filename=19135+2131  .EXTCAL.   2
AIPS 1: Telescope=VLBA               Receiver=VLBA
AIPS 1: Observer=BE026               User #=   29
AIPS 1: Observ. date=15-JUN-2003     Map date=15-MAY-2006
AIPS 1: # visibilities    229358     Sort order  TB
AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  TIME1  BASELINE
AIPS 1:            INTTIM  GATEID  CORR-ID  WEIGHT  SCALE
AIPS 1: ----------------------------------------------------------------
AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
AIPS 1: COMPLEX      1   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: STOKES       2  -1.0000000E+00       1.00 -1.0000000E+00    0.00
AIPS 1: FREQ       512   2.2234200E+10       1.00  3.1250000E+04    0.00
AIPS 1: IF           1   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: RA           1    19 15 35.369       1.00       3600.000    0.00
AIPS 1: DEC          1    21 36 33.133       1.00       3600.000    0.00
AIPS 1: ----------------------------------------------------------------
AIPS 1: Coordinate equinox 2000.00
AIPS 1: Rest freq  22235.081         Vel type: RADIO   wrt LSR
AIPS 1: Alt ref. value  4.18521E+04  wrt pixel  257.00

The velocity assigned to channel 257 was changed unadvertendly to 41.852 
km/s,
where (41.85 - -66) / 0.42 = 256, where 0.42 is the velocity resolution
correponding to the frequency resolution 3.1250000E+04 m/s. I could not
fix this problem, except for using ALTDEF.

What happened there?  

4) Working on the VLBAFIXed dataset FXPOL I had two pseudo polarizations
   LL and RR, in which the data apparently looked slightly different. 
   Thats  probably because they are from different IFs?

Can you help me to clarify how the data is organized in this case?

Dieter Engels 

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Dieter Engels                          e-mail:    dengels at hs.uni-hamburg.de
Hamburger Sternwarte        Internet: http://www.hs.uni-hamburg.de/~st2b102
Gojenbergsweg 112                                Skype:       dieter.engels
D-21029 Hamburg                                    Tel:    49-40-42891 4136
Germany                                            Fax:    49-40-42891 4198
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