[daip] Smearing calculation in JMFIT

[Leonia Kogan]

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