[mmaimcal] Minutes

[Al Wootten]

MMA Imaging and Calibration Group

Minutes for meeting Mon, 26 October 1998 at 11am ET.

Date: Monday, 26 October, 1998

Time: 11:00 am EST (9:00 am Socorro, 9:00 am Tucson)

Phone: (804)296-7082 (CV SoundStation Premier Conference phone).

Past minutes, etc on MMA Imaging and Calibration Division Page
http://www.cv.nrao.edu/~awootten/mmaimcal/mmaimcal.html

Agenda

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Experience from the BIMA Key Project on Galaxies: SD/interferometer
addition, relative pointing calibration, relative amplitude calibration, and
miscellaneous deconvolution issues (Helfer)

The project specifically includes combination of 12m OTF maps and BIMA maps
of galaxies. Sault's mosmem and related routines in miriad are used. A
number of problems were discussed involving: * use of gaussian to
approximate 12m beam, and problems associated with that; weighting of SD
data; * dealing with decorrelation in the BIMA data (using SD model for M51
selfcal didn't work); * reported renewed interest in getting more accurate
BIMA autocorrelation data which is currently limited by: bad and temporally
variable data, not OTF mode, non-nutating secondary, variation of total
power with 3s refrigerator power cycle, etc.

Query from Webber: How much aliasing from out of band lines in a digitally
filtered band can we tolerate scientifically? Is 25db acceptable?

Rejection was 23 db on the non-digitally-filtered HySpec, and is about 20db
or larger for the other sideband in current receivers. After the meeting,
Turner reasoned that he would like to be able to observe 10 mK lines near
OMC1, whose strongest line (CO) is 70K or so. This suggests 40db of
rejection would certainly be best.

New image in Image Gallery:

                  [HiZ CO Starburst] CO in a HiZ Starburst

                                   Caption

We discussed how best to attach captions to images. There seemed to be
general agreement that the pictures should lead one to a separate WWW page
with the picture and caption on one page.

MAC meeting: Plans

This was deferred pending the second generation of a meeting plan.

Report from the JCMT/CSO interferometer 183 GHz radiometer phase correcting
experiment (Yun)

FIRST FRINGES AT 690 GHz! Yun reported that the interferometer had
successfully obtained fringes at this highest frequency yet. He stayed for 5
or the ten days in the run to watch the operation of the 183 GHz phase
correction radiometer system, working with Martina Wiedner and others. He
described numerous instrumental and weather problems which have prevented
this system from working as planned in the past.

One problem emphasized by Wiedner was that one had to have a good
atmospheric model to interpret the data--the temperature and pressure of the
water layer must be well known. In fact, they are not. One approach might be
to use more channels to sample the atmospheric line than the three currently
employed. This will ameliorate the problem but not solve it completely. This
problem exists, less seriously perhaps, at 22 GHz also.

These devices are about 40 x 30 x 30 cm and could be made smaller. On the
MMA, some of the systems present in the JCMT/CSO devices may not be needed.
For example, the Welch/Bock calibration system could alleviate some of the
calibration bits.

The Chajnantor system has a single instrument working. There is no phase
lock loop, which is not serious if the LO is stable enough compared to the
bandwidth of the sampling spectral channels.

Since the JCMT/CSO goal of obtaining fringes at 690 GHz appears to have been
reached, and demand for a single baseline interferometer may not be
sufficient to keep it operational, the future of this system is unassured.
Reportedly the SMA (which also reported first fringes this week, at
Haystack) has no plans for a similar instrument. While both Woody and
Staguhn have expressed interest in such a system, operation at the low
altitudes of BIMA or OVRO is not practical. This is viewed as a problem for
the MMA project. However, in the larger LMA context, the Europeans (the UK
built and operates the JCMT/CSO system; OSO the Chajnantor system) will
pursue this project. At the Division Heads meeting, Napier reported that the
current baseline antenna design has a Cassegrain hole big enough for a 22
GHz beam waist, should such a system be needed on the MMA. It would not,
however, fit in the current baseline dewar.

At the University of Virginia, Alan Boss gave a lecture Tuesday on
Extrasolar Planets. He pointed out the problem with the Pollack/Bodenheimer
accretion scenario timescale for the formation of giant planets. He noted
that the collapse model which he proposed will produce giant planets on
shorter (106) yr timescales. The capability of the MMA was discussed after
the talk. The planets should be just as observable, but more rarely
observed, by the MMA. A survey could favor one model over the other, on the
basis of the statistics of observation. The Keck interferometer or SIM could
in principle do this, but since the giant planets form more quickly in the
collapse scenario, observations would be more difficult in the highly
obscured infrared portion of the spectrum. Advantage: MMA.

Action Items 26Oct98

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URSI Meeting (Radford)

Radford reported that one presentation slot is open.

Travel

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T. Helfer:07Oct-17Oct (Green Bank/UMD), 20-22 Nov (Chi) 26Nov-09Dec
(Tenerife)

A. Wootten: 13Oct-15Oct (U. Md.) 20-22 Nov (Chi)

J. Mangum: 20-22 Nov (Chi)

S. Radford: 20-22 Nov (Chi)