[daip] Smearing calculation in JMFIT

[Leonia Kogan]

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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