[daip] Question about ZEMAN

[Bill Cotton]

Eric,
    Fiddling the parameters a bit did cause it to do more of what I 
expected.
Thanks,
Bill
On 12/01/2016 11:39 AM, Eric Greisen wrote:
> On 12/01/2016 02:41 AM, Bill Cotton wrote:
>> Eric,
>>
>>     I've been trying to run ZEMAN on some maser data and don't
>> understand the results, see attached.  The data in question has been
>> calibrated using a technique assuming the Stokes V integrated over the
>> spectra of all sources in the field is zero.  The Stokes V spectrum in
>> this plot is essentially unchanged from that calibration.  My
>> understanding of ZEMAN was that it tries on a pixel basis to decompose
>> the Stokes V spectrum into a symmetric part ("instrumental
>> polarization") and an antisymmetric part ("Zeeman").  My expectation for
>> the corrected Stokes V spectrum was a straight line.
>>
>>     I ran ZEMAN with optype='2SID' and did not need to do Gaussian
>> fitting as the masers are all spatially separated with symmetric
>> spectra. I ran ZEMAN in batch mode. The field contained a larger number
>> of masers but I only gave it the region around this one cluster of
>> masers and the spectrum is of the brightest.  I also don't fully
>> understand the output images (dooutput=7) as the names are not quite
>> what is in the HELP file and looking at them didn't help much. "FIELD1"
>> contains only 0s and a few blanks, DFELD1 is mostly largish numbers (few
>> 10's) except where there is maser emission where the values are closer
>> to 1.  Is there some threshold of significance below which ZEMAN does
>> nothing?
>>
>> Thanks,
>>
>> Bill
>>
>
> The output classes have to be what is said in the help (since the .FOR 
> matches) except that uncertainty images are also written (DGAIN, DFELDn).
>
> The operation is only performed on pixels for which 3 consecutive 
> channels have brightness > FLUX.
>
> Try running it interactively to start with - this may give you a 
> better feel for what it does.  The spectrum you sent looks like it did 
> nothing at this pixel.  If the interactive thing does not show this 
> pixel then it did not access it.  The ZE table attached to the Vpol 
> image is instructive also - use RPARM in PRTAB to select the desired 
> pixel region to examine.
>
> Eric
>
>