[daip] Smearing calculation in JMFIT

[Vinodiran Arumugam]

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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> 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
>
>
>
>