[alma-config] Re: Keto's message

[Min Yun]

I would add to Bryan's point that the brightness sensitivity is
addressed by the most compact configuration, and it is not nearly
as important for the intermediate configurations as they are 
providing the range of intermediate resolutions needed.  Since the debate
over the zoom spiral versus double-ring/donut configuration only
concerns the intermediate resolution cases, the brightness sensitivity
issue is not a strong one -- as Stephane points out, you can always
get the lower resolution (higher brightness sensitivity) data, but 
I don't know of any way you can gain factor of 2 in resolution without
making the array bigger.  I would strongly argue that the scientific 
impact of a factor of 2 in resolution is far greater than whether one
compromises 10 or 20% in sensitivity by tapering (if ever needed).



					-- Min

> Received: from cv3.cv.nrao.edu (cv3.cv.nrao.edu [192.33.115.2]) by 
zia.aoc.NRAO.EDU (8.9.3/8.9.3) with ESMTP id IAA22711; Thu, 16 Mar 2000 08:25:27 
-0700 (MST)
> Received: from kochab.cv.nrao.edu (kochab.cv.nrao.edu [192.33.115.108]) by 
cv3.cv.nrao.edu (8.9.3/8.9.3/CV-SOL-3.0) with ESMTP id KAA10415; Thu, 16 Mar 
2000 10:25:21 -0500 (EST)
> Received: (from majordom at localhost) by kochab.cv.nrao.edu 
(8.9.3/8.9.3/CV-SOL-3.0) id KAA22476 for alma-config-spinner; Thu, 16 Mar 2000 
10:25:08 -0500 (EST)
> Received: from zia.aoc.NRAO.EDU (zia.aoc.nrao.edu [146.88.1.4]) by 
kochab.cv.nrao.edu (8.9.3/8.9.3/CV-SOL-3.0) with ESMTP id KAA22471 for 
<alma-config at kochab.cv.nrao.edu>; Thu, 16 Mar 2000 10:25:04 -0500 (EST)
> Received: from paso.aoc.nrao.edu (paso [146.88.1.12]) by zia.aoc.NRAO.EDU 
(8.9.3/8.9.3) with ESMTP id IAA22627; Thu, 16 Mar 2000 08:24:40 -0700 (MST)
> Received: (from bbutler at localhost) by paso.aoc.nrao.edu (8.7.3/8.6.10) id 
IAA24287; Thu, 16 Mar 2000 08:24:34 -0700 (MST)
> Date: Thu, 16 Mar 2000 08:24:34 -0700 (MST)
> From: Bryan Butler <bbutler at aoc.nrao.edu>
> Message-Id: <200003161524.IAA24287 at paso.aoc.nrao.edu>
> To: alma-config at zia.aoc.NRAO.EDU, guillote at iram.fr
> Subject: Re: [alma-config] Re: Keto's message
> X-Sun-Charset: US-ASCII
> Sender: owner-alma-config at kochab.cv.nrao.edu
> Precedence: bulk
> Mime-Version: 1.0
> Content-Type: text/plain; charset=us-ascii
> Content-Length: 1265
> 
> 
> 
> stephane wrote:
> 
> > 
> > 1) The spiral array must 2 times larger than the ring to achieve same
> >    angular resolution
> >         True: but so what ? What we should compare is the brightness
> >               sensitivity at a given angular resolution, not the apparent 
> >               size of the array (i.e. the maximum baseline)
> > 
> 
> to which i reply:
> 
> this would be fine if we were talking about putting the array in a place
> which had unlimited real estate - a very large flat plain, for instance.
> this, however, is definitely not the case, and we are presented with some
> very real topographic obstacles.  
> 
> so, we can ask the question: 
> 
>    given a fixed physical size limit, what flavor of array would you design 
then?
> 
> well, if you want the full resolution afforded by that fixed physical
> size, then you would end up with a design like the rings/donuts.  if, 
> however, you are willing to live with a resolution which is only half of
> that achievable from that maximum size, then you might likely end up with
> something somewhat more centrally condensed (like the zoom spiral).
> 
> now, if you can come up with a ring/donut which has nearly as good an imaging
> capability as the more condensed spiral, and that has twice the resolution,
> which would you choose?
> 
> 	-bryan