[mmaimcal] Q-band on ALMA

[Mark Holdaway]

> 
> 
> just to put some numbers on the relative sensitivity for extended
> sources, you can write this like:
> 
>          / Bmax(VLA)  \ 2
> r = p * | -----------  | 
>          \ Bmax(ALMA) /
> 
> where Bmax(VLA) is the max baseline in the smallest configuration for
> the VLA (D-config has Bmax(VLA) ~ 1 km), Bmax(ALMA) is the analagous
> number for ALMA (compact array has Bmax(ALMA) ~ 200 m), and p is the
> ratio of the point source sensitivities.  so, the brightness temp.
> sensitivity for ALMA in the compact configuration will be about a
> factor of 30 better than the VLA in the D-config.  this is a big
> improvement.
> 

I would look at this differently, comparing the sensitivities at the
same resolution.  To do that, you need to taper away much of the VLA,
but you come out with a factor much less than 30.


> i also agree with frazer's other points, though it's not clear to me
> how large the fraction of time is when the array will be 'unusable' at
> 3mm...
> 

The phase stability will usually be the limiting factor, even with fast
switching or radiometric phase calibration (David Woody gave me an
optimistic equation to estimate residual phase errors in the radiometric
case).  And yes, there is plenty of time when the array is unuable at 3mm.  
I don't have the numbers in front of me, but I recall its like 5% totally
unusable, 10% usable only at Q band, etc.

	-Mark