Cannot specify position angle of Gaussian taper in invert

[abutler]

Hi Mark, Jamie:

I'm trying to taper the visibilities in my 1.1-3.1 GHz data to achieve the same beam size across 471 pointings. However, invert only contains a "fwhm" parameter, and not a "pa" parameter (like restor and convol do). I've tried using the fwhm parameter without being able to specify the position angle, but it simply doesn't give me the beam size I want. For example, one of the beam sizes I've been testing is fwhm=4.911,2.983 pa=13.68. I want to taper it so that it is fwhm=5.39,4.21 pa=0. I calculate the FWHM of the Gaussian taper on each axis to be FWHM_RA=SQRT(4.21^2 - 2.983^2) = 2.971 and FWHM_Dec = SQRT(5.39^2 - 4.911^2) = 2.221. After tapering, the resulting beam is fwhm=5.685,3.951 pa=25.03. Even if I project the FWHM of the original beam onto the RA and Dec axes so that it's "aligned" with the Gaussian I taper with, I still get fwhm=5.869,3.961 pa=21.32, which is not what I'm after. The only way to be able to achieve the beam shape and orientation I want is to specify the position angle of the Gaussian that I taper the visibilities with (in addition to the fwhm).

I know CASA has this capability, so would it be possible to add the pa option into invert in Miriad? I would greatly appreciate it.

Cheers,
Andrew

[Mark.Wieringa]

Hi Andrew,

I will have a look at this later this week, it looks possible but will need careful testing to keep existing scripts working correctly.
I'll let you know when I have something to try.

Cheers,

Mark

[Mark.Wieringa]

Hi Andrew,

I've added position angle to the fwhm parameter in invert. I've done some testing and all looks well to me, but let me know if you notice anything odd.

The new version should be available with mirsync after tonight's update and in the tar file late Thursday night.

Cheers,

Mark

[abutler]

Thanks Mark! I'll let you know if I find anything unexpected.

Cheers,
Andrew