[daip] Regarding VLA " First sky survey" catalogue with 946432 sources.

[Prabhakar]

Thanks for your response. I read the paper(publ. in 1995 &1996) regarding
First sky survey.
But one doubts is still remained, the 3rd question that i mentioned not
cleared. How could i contact to prof. BECKER,? I google but, not found any
mail. could you provide me some access(mail)?

Thanks a lot.


Regards
Prabhakar
Msc-phd student
IIT kanpur(INDIA)



> On 05/21/2019 02:44 AM, Prabhakar wrote:
>> Dear sir,
>>
>> I am Msc-PhD student at IIT Kanpur(Indian Institute of Technology,
>> Kanpur)
>> (INDIA), in the Department of Physics. I am doing some project work
>> using
>> VLA, First sky survey" catalogue with 946432 sources. I have some
>> queries
>> regarding this catalogue.Please let me know the reason behind the quires
>> that I am mentioning below:
>>
>> 1. I saw around 170000 sources with both Bmaj and Bmin zero and around
>> 3lakhs sources with Bmaj non zero but still Bmin zero. What it implies!
>>
>> 2. Through my work I have noticed when I plotted a histogram of position
>> angle(PA), it appeared most of the sources with PA 90 deg. and even more
>> sources with PA 0 and 180 deg. What it implies!
>>
>> 3.** As for extended sources ratio of peak_flux/flux_inte.  would be
>> less
>> than 1 or close to 0.9. But most of the sources with its ratio greater
>> than 1. How is it possible? If yes, then What it implies!
>>
>> 4** I want very random data, with PA  random distribute. Is there any
>> bias
>> or limitations on these data, let me know, please.
>> I will be very grateful for your response to these issues.
>> Thank you
>>
>> Regards
>> Prabhakar
>> Msc-phd student
>> IIT kanpur(INDIA)
>>
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>
> My previous reply was based on the assumption that the authors of FIRST
> used AIPS for the fitting.  It is quite likely that they did not.
> Nonetheless, the issue of deconvolution is always present.  If the fit
> values do not resemble the Clean beam due to noise etc then the
> deconvolution will produce improper solutions.  The authors may also
> have chosen to change insignificant values of Bmaj and Bmin to 0.
>
> The observations in FIRST were short snapshots with the VLA.  As such,
> the center part of the dirty beam is always elliptical with the long
> axis NS for southerly sources.  This may well bias the fit PAs toward EW
> (i.e. 90).  AIPS does not give the answers you see in question 3 which
> also suggests that the authors used their own software for the fitting.
>
> If you restrict your study to sources of higher S/N (i.e. >=10) you may
> find a more random distribution of things.
>
> These questions should really be directed not to NRAO but to the primary
> author Bob Becker.  I believe he has retired but is still publishing.
>
> Eric Greisen
>
>