[daip] Smearing calculation in JMFIT

[Vinodiran Arumugam]

Alright, thanks Leonia.

Regards,
Vinod

On Thu, 25 Feb 2010, Leonia Kogan wrote:

> I' like to wait for the AIPS group leader Eric Greisen to answer your last 
> question. He will be back from vacation this Monday.
>
> Hi   LK
>
> Vinodiran Arumugam wrote:
>> Dear Leonia,
>> 
>> Thank you for your email. The reason for wanting the know the way in which 
>> the beam shape is handled across the map (eg 0 to 90 degrees from y-axis to 
>> x-axis), is to be able to replicate the change in the fwhm and apply it to 
>> the I/Io correction for a square bandpass, in comparison to the JMFIT 
>> calculation for the peak reduction using a gaussian bandpass.
>> 
>> Is there any way of obtaining this information?
>> 
>> With thanks,
>> Vinod
>> 
>> On Thu, 25 Feb 2010, Leonia Kogan wrote:
>> 
>>> Vinodiran Arumugam wrote:
>>>> Hi,
>>>> 
>>>> I'm exploring the smearing correction applied to my data to correct for 
>>>> the reduction in peak fluxes. It would help if I could understand how 
>>>> JMFIT varies the half peak beam width (hpbw) used in the smearing 
>>>> equation (fractional bandwidth x radius in hpbw) across the map.
>>>> 
>>>> So for an elliptical beam of bmaj = 1.82, bmin = 1.63 and bpa = -3deg, 
>>>> how is the hpbw varied to use 1.82 at the nothern/southern most point and 
>>>> 1.63 at the eastern/western most point? What function of position and 
>>>> major/minor axis is used to calculate the bandwidth smearing?
>>>> 
>>>> Thank you,
>>>> Vinod
>>>> 
>>>> _______________________________________________
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>>>> Daip at listmgr.cv.nrao.edu
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>>> Hi Vinod,
>>> 
>>> I have spent a time this morning looking into the codes of JMFIT.
>>> Now I am ready to discuss the smearing in JMFIT.
>>> 
>>> 1. JMFIT uses the clean beam given at the header of the image.
>>> 2. This clean beam is smeared by a Gaussian in the radial direction 
>>> proportional to the radius from the pointing position (center) times 
>>> BWSMEAR. Typically BMSWEAR is the ratio of freq channel width to the 
>>> central frequency
>>> 3. All found Gaussian components are deconvolved using the relevant found 
>>> new clean beam. Different clean beam is used for different components.
>>> 4. You do not need to think about the beam shape at different place of the 
>>> map. JMFIT takes care about this.
>>> 
>>> I hope it will help
>>> 
>>> Leonid Kogan
>>> 
>>> 
>>> 
>>> 
>> 
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