From awootten at NRAO.EDU Tue Sep 5 15:01:32 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Tue, 5 Sep 2000 15:01:32 -0400 (EDT) Subject: [asac] Message from John Richer Message-ID: <200009051901.PAA19797@polaris.cv.nrao.edu> Dear SAC members, A proposal to develop 183 GHz radiometer prototypes for ALMA has been submitted to the ALMA project; this is essentially a response to the recommendations of the Leiden meeting. We will discuss the details of the proposal at the meeting in Berkeley, and I attach it here in uuencoded form for those of you who wish to read it beforehand. I've also placed it in PS and Word format at http://www.mrao.cam.ac.uk/~jsr/wvrprop.ps http://www.mrao.cam.ac.uk/~jsr/wvrprop.doc See you all in Berkeley, Regards, John -- John Richer Astrophysics Group, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE Tel: +44-1223-337246 Fax: +44-1223-354599 http://www.mrao.cam.ac.uk/~jsr/ From awootten at NRAO.EDU Tue Sep 5 15:03:29 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Tue, 5 Sep 2000 15:03:29 -0400 (EDT) Subject: [asac] ACA Document from Jack Welch Message-ID: <200009051903.PAA19855@polaris.cv.nrao.edu> Dear ASAC Members: Jack Welch has written a document 'Choices of Antenna Size and Number for the Atacama Compact Array.' He has set up an html file that you can read it from. The address is astro.berkeley.edu/~welch and the name of the file is ACA.ps. It is a post script file. Clear skies, Al +--------------------------------------------------------+ | Alwyn Wootten (http://www.cv.nrao.edu/~awootten/) | | Project Scientist, Atacama Large Millimeter Array/US | | Astronomer, National Radio Astronomy Observatory | | 520 Edgemont Road, Charlottesville, VA 22903-2475, USA | | (804)-296-0329 voice Help us build The ALMA| | (804)-296-0278 FAX {> {> {> {> | +----------------------------------^-----^-----^-----^---+ From awootten at NRAO.EDU Tue Sep 5 15:05:25 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Tue, 5 Sep 2000 15:05:25 -0400 (EDT) Subject: [asac] Receiver Issues Message-ID: <200009051905.PAA19984@polaris.cv.nrao.edu> Hi Al, please find a short note of John Payne and myself about some receiver issues for the next ASAC meeting. Wolfgang --------------D680328472E4E14C96C868EC Content-Type: text/plain; charset=us-ascii; name="ASAC Issues.txt" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="ASAC Issues.txt" ALMA Receiver Issues ================= For the attention of the ASAC 5 September 2000, W. Wild and J. Payne We would like to ask the ASAC to comment on the following issues which are of great importance for the further progress of the receiver design. Receiver calibration ------------------------ There seem to be different opinions regarding the inclusion of a cold load or not in the receiver optics design. The design has reached a point where a clear decision cannot be further delayed without delaying the receiver program. At the receiver groups request, two ALMA memos have been written concerning the receiver calibration system (memo # 321 by R. Plambeck, and memo # 318 by J. Mangum). R. Plambeck concludes that cold loads are not worth the complexity. We would like to have the ASAC's opinion whether a cold load is required to meet the scientific goals of the array. Receiver specifications ---------------------------- A new draft version of the receiver specifications (draft 1.4) has been released, taking into account many comments of the ASAC and other groups. We would like to know if the ASAC considers these specification adequate. In particular, we would like some reassurance that the specifications on polarization (3.2) are adequate. It is planned that J. Payne and W. Wild phone in to the ASAC meeting. From awootten at NRAO.EDU Wed Sep 6 14:47:41 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Wed, 6 Sep 2000 14:47:41 -0400 (EDT) Subject: [asac] Attendance at ASAC Message-ID: <200009061847.OAA23629@polaris.cv.nrao.edu> A final (?) agenda is at http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacberkeleyagenda.html A Power Point projector will be available, as well as VuGraph projector. The phone in session will be held in a smaller room; it may be necessary to restrict attendance at that session. Between the guest list at the Duval, and information people have sent to me, I believe the following people are coming to the ASAC meeting. If you know of someone who is coming who is not on this list, please let me know, as our goal is a fed and happy ASAC, not a gaunt hungry ASAC! Baars Bachiller Blake Baars Booth Baudry Blitz Bronfman Brown Chikada Cox Crutcher van Dishoeck Emerson Evans Fukui Guilloteau Gurwell Hasegawa Ishiguro Kawabe Kurz Mangum Menten Morita Okumura Richer Walmsley Welch Wilson Woody Wootten de Vos Yun I am unsure whether Shaver, Scoville, Nakai or Yamamoto will come. Thanks! Clear skies, Al +--------------------------------------------------------+ | Alwyn Wootten (http://www.cv.nrao.edu/~awootten/) | | Project Scientist, Atacama Large Millimeter Array/US | | Astronomer, National Radio Astronomy Observatory | | 520 Edgemont Road, Charlottesville, VA 22903-2475, USA | | (804)-296-0329 voice Help us build The ALMA| | (804)-296-0278 FAX {> {> {> {> | +----------------------------------^-----^-----^-----^---+ From awootten at NRAO.EDU Thu Sep 7 10:09:59 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Thu, 7 Sep 2000 10:09:59 -0400 (EDT) Subject: [asac] forwarded message from Larry D'Addario Message-ID: <200009071409.KAA14900@polaris.cv.nrao.edu> N. B. two versions of the document "Proposal for ALMA Front End Optics"; please collect the most recent one. Folks, The report "Proposal for ALMA Front End Optics" has been slightly updated since Jennifer distributed John's announcement of its availability on Sep-05. If you have the version dated 2000-Sep-04, then there have been a couple of small corrections to the text. If you have the version dated 2000-Sep-05, then there have been no further substantive changes, but Fig 1 and Fig 2 have had the hand-drawn sketches replaced with better-quality line drawings and the PDF file has become about 30% of its previous size. The current version can be obtained from the same URL as before: http://www.tuc.nrao.edu/~ldaddari/almaOptics.pdf We are aware of some minor errors in the tables of the Appendices, and of the need for some additional clarifications and explanations. But in the interest of stability we will avoid any substantative changes until next week. Comments and questions are welcome at any time. --Larry From awootten at NRAO.EDU Fri Sep 8 07:19:09 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Fri, 8 Sep 2000 07:19:09 -0400 (EDT) Subject: [asac] forwarded message from Sachiko Okumura Message-ID: <200009081119.HAA10854@polaris.cv.nrao.edu> Dear ASAC Members and others, A NEW PDF document about the Japanese future correlator is available now at the agenda site. Copies will be available at the meeting, but you may also obtain the document at the blinking 'NEW' on the agenda page under Correlator documents. Please see: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacberkeleyagenda.html or obtain the document directly at http://www.cv.nrao.edu/~awootten/mmaimcal/asac/HPFXforE-ALMA.pdf See you soon, Al +--------------------------------------------------------+ | Alwyn Wootten (http://www.cv.nrao.edu/~awootten/) | | Project Scientist, Atacama Large Millimeter Array/US | | Astronomer, National Radio Astronomy Observatory | | 520 Edgemont Road, Charlottesville, VA 22903-2475, USA | | (804)-296-0329 voice Help us build The ALMA| | (804)-296-0278 FAX {> {> {> {> | +----------------------------------^-----^-----^-----^---+ From kmenten at mpifr-bonn.mpg.de Fri Sep 15 08:14:45 2000 From: kmenten at mpifr-bonn.mpg.de (Karl Menten) Date: Fri, 15 Sep 2000 14:14:45 +0200 (MEST) Subject: [asac] Writing Assignments Message-ID: Dear ASAC members, I am expecting your contributions to the Berkeley ASAC minutes by next Wednesday, September 20. The following is to remind you of the writing assignments. The idea is that for each topic the first-named person should take the responsibility for getting the assigment completed and sending it to me. Before that, he should solicit and include input from the other people listed under that topic, and if neccessary from other parties as well. --- * Enhanced ALMA, ACA --- N. Evans, P. Cox * Correlator --- R. Bachiller, S. Guilloteau, A. Wootten * Calibration --- J. Welch, J. Richer, S. Guilloteau, J. Mangum * Configurations --- M.-S. Yun, R. Booth * Site --- A. Wootten * Polarization --- R. Crutcher * Receivers --- E. van Dishoeck, G. Blake, M. Walmsley, D. Woody (7 mm band) * Water Vapor Radiometer --- J. Welch Waiting for your contribution, Cheers, Karl ----------------------------------------------------------------------------- Dr. Karl M. Menten (kmenten at mpifr-bonn.mpg.de) Max-Planck-Institut fuer Radioastronomie Auf dem Huegel 69, D-53121 Bonn, Germany Tel.: +49 (0)228-525297 * Fax: +49 (0)228-525435 From awootten at NRAO.EDU Wed Sep 20 15:53:59 2000 From: awootten at NRAO.EDU (Al Wootten) Date: Wed, 20 Sep 2000 15:53:59 -0400 (EDT) Subject: [asac] The ALMA site Message-ID: <200009201953.PAA12248@polaris.cv.nrao.edu> Dear ASAC Members and others: Richard Hills sent the following note to the ASAC list but it bounced to me as a submission from a non-member, so I forward it to you. It concerns some of the issues which Leo Bronfman relayed to us from Tony Readhead concerning his impressions of Chajnantor after a year of observing there. As we discussed this at the ASAC meeting, I have prepended comments, mostly from our discussion at the meeting. The site is unimproved and access can be difficult. Anyone visiting the site should be familiar with the ALMA Safety Rules and follow them. Improvements to the site will commence soon after construction funding is secured. Site Data Collection The CBI group report 46% usable time during the Altiplanic Winter and 60% during other seasons. Time was lost owing to cloud, snow and high winds. Richard states that 'there is no doubt that weather conditions on the site have been considerably worse for the last year or two than during the period when the original site testing was done.' Our monitoring suggests, as I reported at the ASAC meeting, that this year is average among the years we have monitored the weather at the site. What is different is that this year we have accounts from astronomers attempting to observe at a hostile and unimproved site. The CBI logbooks convey valuable data which is not available from the suite of instruments we have monitoring weather, opacity and turbulence at the site. We anticipate assessing this data, and that from the Japanese experience at the ASTE site, as we move toward ALMA construction. I must take issue with a point that Richard cites as an explanation for the site failing to come up to expectations: that the site test equipment is solar powered and therefore shuts down if there are extended periods of cloudiness. There are three suites of solar powered equipment running the ALMA/US, the ALMA/EU and the LMSA instrumentation. The ALMA/US equipment is adequately powered to continue through periods of stormy weather and has failed only a very few times during the past years; this solar power operates the 225 GHz taumeter and the ALMA/US interferometer. We obtain and include in the reductions all data taken during stormy weather. The ALMA/EU power supply has been unreliable, perhaps because of inadequate capacity.; data has been lost from the equipment operated by that supply including the 183 GHz radiometers. Of course, there are periods of time when various pieces of equipment fail for various reasons and owing to the remoteness of the site it can take some time to effect repairs; I presented Radford's assessment of the amount of time each of the fundamental instruments was working to the ASAC and noted that the taumeter at either the ALMA/US site or the LMSA site or more often both ran at all times over the past season. Transparency We do collect cloud cover information from the onsite camera as well as solar insolation monitors which refer only to the daytime. Infrared cameras would measure cloud cover at night; however they are costly (>$20K per unit) and require liquid nitrogen and personal attention, an impracticality at the moment. Cheaper options are available. However, we do measure 225 GHz transparency and operate the interferometer to measure atmospheric stability through all times of day and night We have decided that these are the most important quantities to measure, because these are the quantities that affect the performance of ALMA. Access As Richard points out, access to the Chajnantor site can be a problem. This will be a lesser problem for ALMA, as a great deal of improvement of access is part of the construction plan, as Richard relates from his conversation with Daniel Hofstadt. Until that improvement occurs, however, operations on the Chajnantor site may be difficult, as they are presently for the CBI group. Chajnantor and Pampa la Bola Richard anecdotally compares Chajnantor with Pampa la Bola. Data from ALMA Memo 322 which I reported to the ASAC gives useful numbers for a quantitative comparison. The solar insolation data suggest that there is very little difference in daytime cloud cover between the two sites. If the CBI and ASTE operations overlap, visual data will be an important complement to the insolation data. The memo details seasonal and diurnal variations in wind at the two sites. The median wind velocity is in fact somewhat higher at Pampa la Bola. Pampa la Bola is now easier to access, but ALMA site development will address this problem; some control over access may be desirable and this is easier to accomplish for the Chajnantor site. Transparency is better at Chajnantor by the amount expected from the scale height of water. This suggests that cloudiness variations from one site to another don't severly affect transparency. Furthermore, the reduced data from the interferometers suggest that phase stability is somewhat lower at the Pampa la Bola site. Simon Radford has been working on a comparison of transparency at the two sites to complement Sakamoto's work, which I showed at the ASAC meeting. Bryan Butler is working on a similar correlation between data from the two interferometers over the past year. We will review these comparisons at the next ASAC meeting, if the committee wishes. In the meantime, I hope that people interested in this question will review recently posted ALMA Memo 322. In summary, the project feels that the case remains strongest for siting the array at Chajnantor but continues monitoring activities and study of the data. Clear skies, Al - ----------------------------Letter from Richard Hills----------------------- Date: Mon, 18 Sep 2000 09:43:45 +0100 From: Richard Hills X-Mailer: Mozilla 4.7 [en-gb] (WinNT; U) X-Accept-Language: en MIME-Version: 1.0 To: asac at kochab.cv.nrao.edu, rbrown at nrao.edu, mrafal at nrao.edu, rkurz at eso.org, sguillot at eso.org Subject: Location of centre of the array Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Dear Colleagues, I was at the ALMA site last week to do some work on the 183 GHz radiometers and the 11 GHz radiometer. I took the opportunity to speak to Tony Readhead, Steve Padin, Tim Pearson, et al., about their experiences on the Chajnantor site and the comparison with Pampa la Bola. Here is my interpretation of what they told me. It turns out that Tony had just come back from a meeting in the US where he had made a presentation to the NSF people about this (he mentioned Wayne van Sitters, but I don't know who else was involved). This is obviously a hot topic at present. John Richer told me there was a good deal of discussion about it at the ASAC so I thought I should circulate this note to you. It is clear that the CBI people have had a tough time in the 13 months or so that they have been working there. Although Tony was careful to say that they are still enthusiastic about the place in general, they are obviously disappointed with the quality of the site and have been impeded by the practical difficulties of operating in such a hostile environment. On the site quality, the main issue is the small amount of time that they have been able to observe. The causes of lost time include cloud, snow and high winds. They quoted only 46% usable nights (they only try to observe at night) for their first 3 months, which was the 'Bolivian winter' period, and somewhat less than 60% overall for the last 9 months. They did however emphasize that when conditions are such that they can observe, then the sky is very good indeed (but of course they are only working at 9 mm wavelength). There is no doubt that weather conditions on the site have been considerably worse for the last year or two than during the period when the original site testing was done. There was however an additional point that the CBI people raised as an explanation for it failing to come up to what they had been led to expect: the site test equipment is solar powered and therefore shuts down if there are extended periods of cloudiness. They wonder whether this fact has been properly accounted for in analysing the statistics. They also pointed out that the data we have on cloud cover comes from measuring insolation and therefore refers only to the daytime. A comment they made very emphatically was that there is frequently a relatively local bank of cloud over the Chajnantor site at times when the Pampa la Bola site was essentially clear. I don't think that they have any statistics on this but they feel that this is a very marked effect and point out that you can actually see the cloud forming as the air is forced up over the high ground and dissipating as it flows over onto the la Bola area. I realise that this is entirely anecdotal, but it did appear to me that this was indeed happening to a greater or lesser extent on three of the six days that I spent at the site on this trip. As far as logistics are concerned, the main problem has been the frequent blockages of the road by snow. They also mentioned the difficulty of getting any components or services locally. (They were of course expecting to have problems with the altitude and my impression is that they have coped pretty well with this by adding oxygen to the buildings and being rigorous in using the personal oxygen sets when working outside.) I think the practical difficulties caused by the cold and the wind have also been a factor for them - they certainly have been for me on both my visits. The problem of snow on the roads on site is exacerbated by the fact that the roads have been made with a bulldozer, which throws up ridges on either side. The blowing snow then fills in the road up to this level. Plowing the road makes the ridges higher so the the next time the wind blows the situation is even worse. The high winds (reaching 20 m/s or greater) in the March-September period cause the snow to be re-distributed rapidly, so they are sometimes not able to use the same route on the the up and down journeys even on the same day, which adds to the hazards significantly. The main Chile-Argentina road has also been closed quite often this year due to snow. The main problem has again been wind-driven snow forming drifts in places where the road is cut down into lumps in the terrain. There were still remnants of these drifts many feet deep to be seen when I was there, although it had been several weeks since the last storm. The CBI guys reported rescuing five people whose car had got stuck in one of these places during a snow-storm. They also said that there was often a lot of very slippery black ice on the road, presumably as a result of the big day-night temperature cycle of the black tarmac. There have been several accidents as a result of this ice, including, I believe, one fatal one. Regarding the comparison between Chajnantor and Pampa la Bola, the CBI group are completely clear that for their purposes la Bola would have been a much better choice. The factors which favour Pampa la Bola are: less cloud less build-up of snow somewhat less wind easier access. The last point applies both under good conditions, when it is 10 to 15 minutes less driving time from San Pedro to la Bola than it is to Chajnantor, and much more strongly under bad conditions, when the pass between the two sites is the place that is most often blocked. (The dirt road onto Chajnantor direct from the west is no longer being used. It is now hard to get onto it from the highway, because of new crash barriers, and it also becomes impassable in snow.) Taken together these points represent a strong case for placing the centre of the ALMA array on Pampa la Bola. An additional consideration for the array, which was not relevant for the CBI, is that the terrain appears a good deal easier on la Bola than on Chajnantor. I feel that if we have to make a decision right now it would be extremely hard to justify going to Chajnantor. (I am of course saying this in the belief that the advantages of lower water vapour and phase fluctuations on Chajnantor are marginal.) If we can afford to keep the options open for one more year, then I believe the project should do the following: 1) Purchase IR cameras and install them on both sites so that we can get both day- and night-time data on cloud cover. We must figure out a way of keeping these operating during bad weather. (In principle a wind-powered generator added to the solar panels would be a good option, but I don't know whether we can purchase wind-mills that can stand up to the conditions on this site. Alternatively the cameras should have their own power system with a long battery life.) We will have to try to relate the cloud data to the opacity and phase variations to try to understand whether the somewhat better values that have been obtained for Chajnantor outweigh the deleterious effects of cloud. (Remember that millimetre-wave and even sub-millimetre observations are not ruled out by thin cloud, especially if it consists of ice particles, although calibration and phase correction are likely to be harder.) 2) try to determine from long-term weather data (plus perhaps satellite images?) whether the conditions for this past year or so have been truly exceptional or whether snowfall and cloud cover and levels approaching these can be expected fairly frequently. (Lars-Ake and Guillermo told me that meteorological data is already being looked at, but I am not clear whether these parameters can be obtained in that way.) This will indicate whether we need to revise our planning to allow for the regular occurrence of such harsh conditions. 3) if it is felt that there is still a strong case for Chajnantor, then the project should look very hard at providing high-quality access direct from the western side. The idea here would be to keep the length of the journey that is above 4000m to an absolute minimum. Again, I learnt in Santiago (from Daniel Hofstadt) that this is already being studied and that even the idea of a (cog?) railway was being discussed. This sounds very interesting to me. 4) roads on the site must be designed to minimize build-up of blown snow. Presumably this implies raising them slightly above the surrounding ground, perhaps creating ditches on either side. Unless this is already a well-understood art we should probably test the practicalities of this on the site. A few days work with a bulldozer and a roller ought to be enough to provide suitable some test pieces on the road that is presently being used every day by the CBI people. Any tarmac roads should be constructed with a coarse and if possible porous surface and a steep camber to minimise the build-up of black ice. 5) we need to think about the problem of snow build-up around the antennas, particularly in the close-packed configuration. What are the pros and cons of having the surfaces of the antenna mounting pads above ground level? IRAM's experience on Plateau de Bure is obviously highly relevant here. REH 16th Sept 2000 ------- end ------- From rbrown at NRAO.EDU Mon Sep 25 15:42:17 2000 From: rbrown at NRAO.EDU (Robert Brown) Date: Mon, 25 Sep 2000 15:42:17 -0400 Subject: [asac] Apologies Message-ID: <39CFAA99.49D07E58@nrao.edu> To the ASAC: The message copied below is one I sent to Wolfgang Wild and John Payne following the ASAC meeting of September 9/10 in Berkeley at which we were unable to establish a teleconference connection to Wolfgang and John in Europe. I would like to make it clear that the cause of our failure to connect was solely a result of my lack of proper attention to detail. -Bob ---------------------------------------------------------------------------- 11 September 2000 > Dear Wolfgang, John: > > I would like to apologize to both of you for failing to complete > properly the telephone arrangements for you to call in to the ASAC > meeting on Sunday. After speaking with John Saturday night to confirm > the arrangements, I was sure that I had everything in place for the > conference call--the time, the phone number etc--and sufficient backup > to solve problems. I then turned my attention to some other project reports that I > wanted to try and complete. On Sunday morning I > took from the hotel with me to the meeting what I thought were all my meeting materials. > Unfortunately this was all the project reporting materials I had been working > on the night before but none of the materials related to the ASAC > meeting proper. And that briefcase didn't have my cell phone in it. As > a result, when we had a problem connecting I didn't have Wolfgang's > number, John's hotel number, or my cell phone to solve the problem. I > just screwed this up by not paying sufficient attention. > > I know that you arranged your day to accommodate the teleconference and > that you did everything possible to make the connection. I appreciate > your time/efforts and I would sincerely like to apologize to you and the > ASAC for failing to carry out my responsibilities. > > -Bob > -------------- next part -------------- An HTML attachment was scrubbed... URL: