From cwhite at NRAO.EDU Tue Feb 6 14:58:56 2001 From: cwhite at NRAO.EDU (Carolyn White) Date: Tue, 6 Feb 2001 14:58:56 -0500 (EST) Subject: [asac] [almanews] ALMA Memos 345 and 346 Released Message-ID: LALMA Memo 345 Phase Fluctuation at the ALMA Site and the Height of the Turbulent Layer Yasmin Robson, et al. January 24, 2001 Phase compensation schemes are needed for sub-mm and mm inter- ferometry if we are to obtain high resolution images with the proposed ALMA telescope. The presence of uctuating water vapour in the at- mosphere is the main culprit as it effectively distorts the phase of the signals arriving at each element of the interferometer. There are two possible methods of correcting for this phase distor- tion. The first involves fast position-switching between the astronom- ical source and a calibrator of known phase. The second uses a ra- diometer close to the antenna to measure the amount of water vapour along the line of sight. The expected phase distortion is then calcu- lated and used to correct the astronomical signal. No matter which technique is used, it is important to know the altitude at which most of the uctuating water vapour is to be found, so that we can set lim- its on the offset between the astronomical and calibration beams. If the calibration beam does not sample a similar column of water vapour as the astronomical beam, then the phase correction will be inaccurate. We describe a method for obtaining the height at which the bulk of the turbulence occurs, using two site-testing interferometers pointing in dierent directions. The time-lag between the interferometers is found by cross-correlating the phase data and then converted to a height us- ing measurements of wind speed and direction. Our results show that much of the turbulence is close to the ground, usually within the first 500 m. This gives confidence in the use of Wa- ter Vapour Radiometers (WVR) as a means of phase compensation, as there would be a high degree of overlap between the astronomical and calibration beams. View a PDF version of ALMA Memo #345 at http://www.alma.nrao.edu/memos/html-memos/alma345/memo345.pdf Download postscript version of ALMA Memo #345 from http://www.alma.nrao.edu/memos/html-memos/alma345/memo345.ps ----------------------------------------------------------------------- ALMA Memo 346 Spatial Distribution of Near-Surface Soil Resistivity in the Cerro Chascon Science Preserve Seiichi Sakamoto, and Tomohiko Sekiguchi January 27, 2001 We examined near-surface soil resistivity of twenty-one locations in the Cerro Chascon science preserve area in the Wenner method with a fixed electrode spacing of 2 m. There were systematic differences in soil resistivity near the surface (down to a few meters): The values in the Pampa La Bola area were around 1000 Ohm-m, whereas those in the Llano de Chajnantor area were much higher and > 4400 Ohm-m in most locations topographically suitable for antenna pads. Special treatment may be needed for each pad to meet the Chilean regulation for grounding. A factor $\sim$ 1.3 difference expected from the 1.8deg C temperature difference between the Llano de Chajnantor and Pampa La Bola areas is not enough to explain all of the measured difference. The trend that quebradas systematically had higher values than their adjacent arroyos supports the idea that the difference primarily reflects probable difference of water content due to local topography and drainage. View a PDF version of ALMA Memo #346 at http://www.alma.nrao.edu/memos/html-memos/alma346/memo346.pdf Download postscript version of ALMA Memo #346 from http://www.alma.nrao.edu/memos/html-memos/alma346/memo346.ps ============================================================================= ALMAnews is a broadcast service. To unsubscribe, send an e-mail message to majordomo at nrao.edu with "unsubscribe almanews" in the message body. From guillote at iram.fr Thu Feb 8 05:19:35 2001 From: guillote at iram.fr (Stephane Guilloteau) Date: Thu, 8 Feb 2001 11:19:35 +0100 Subject: [asac] Fw: [alma-sw-announce] SSR Report ready for review Message-ID: <004001c091b8$a32513e0$cafc30c1@pctcp72.iram.fr> -----Original Message----- From: Brian Glendenning To: alma-sw-announce at cv3.cv.nrao.edu Date: Wednesday, February 07, 2001 7:48 PM Subject: [alma-sw-announce] SSR Report ready for review >"ALMA Software Science Requirements and Use Cases" by Lucas et. al. is >available as a DRAFT document at: > >http://www.alma.nrao.edu/development/computing/docs/memos/index.html > >We have started the formal review process for this document - see the >enclosed call. Note that while a review panel has been selected, reviews >from everyone are solicited. All comments will receive a written response. >Please send your comments directly to Robert Lucas (lucas at iram.fr) by close >of business February 26. It is a convenience if you send your comments in >the format: > >p.6 This is a fascinating comment about page 6. > >Or even > >p.6 s2.3 This is a fascinating comment about something on page 6 section >2.3. > >Cheers, >Brian > > -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: SSR_REVIEW.TXT URL: From awootten at NRAO.EDU Mon Feb 12 11:05:02 2001 From: awootten at NRAO.EDU (Al Wootten) Date: Mon, 12 Feb 2001 11:05:02 -0500 (EST) Subject: [asac] Current ASAC Mailing list Message-ID: <200102121605.LAA08502@polaris.cv.nrao.edu> Folks Before distributing materials for the upcoming meeting, I thought I would send a list of the email addresses to which items addressed to ASAC at nrao.edu propagate. Email from any address on this list will propagate to the entire list; email from addresses not on this list or which are too large (>40000bytes) arrive in my mailbox for redistribution. Full names and addresses of all members are on the ASAC Committee web page at http://www.alma.nrao.edu/committees/ASAC Please send me any corrections. nje at astro.as.utexas.edu crutcher at astro.uiuc.edu gab at csardas.gps.caltech.edu mgurwell at cfa.harvard.edu nzs at astro.caltech.edu welch at astron.Berkeley.EDU wilson at physics.mcmaster.ca awootten at NRAO.EDU demerson at NRAO.EDU kmenten at mpifr-bonn.mpg.de roy at oso.chalmers.se mwalmsley at arcetri.astro.it jsr at mrao.cam.ac.uk benz at astro.phys.ethz.ch guillote at iram.fr pshaver at eso.org leo at das.uchile.cl masa at naoj.org fukui at a.phys.nagoya-u.ac.jp kawabe at nro.nao.ac.jp nakai at nro.nao.ac.jp ewine at strw.leidenuniv.nl cox at ias.fr rkurz at eso.org mrafal at NRAO.EDU rbrown at NRAO.EDU bachiller at oan.es yamamoto at phys.s.u-tokyo.ac.jp cwhite at nrao.edu myun at bonito.astro.umass.edu tatematsu at nro.nao.ac.jp ishiguro at nro.nao.ac.jp h.matsuo at nao.ac.jp seiichi at nro.nao.ac.jp tsuboi at mito.ipc.ibaraki.ac.jp lucas at iram.fr tetsuo.hasegawa at nao.ac.jp Clear skies, Al From awootten at NRAO.EDU Mon Feb 12 11:55:13 2001 From: awootten at NRAO.EDU (Al Wootten) Date: Mon, 12 Feb 2001 11:55:13 -0500 (EST) Subject: [asac] Minutes of January ASAC Teleconference Message-ID: <200102121655.LAA10973@polaris.cv.nrao.edu> Folks: I have had no corrections to Peter's minutes of our last meeting; please take a look at them and let me know if they look OK. http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacjan01minutes.txt The provisional agenda for the face-to-face meeting is at: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacfirenzeagenda.html Documents to support this continue to arrive, so please check this before you leave to attend the meeting for changes or additions. Clear skies, Al From cwhite at NRAO.EDU Thu Feb 15 13:03:08 2001 From: cwhite at NRAO.EDU (Carolyn White) Date: Thu, 15 Feb 2001 13:03:08 -0500 (EST) Subject: [asac] [almanews] ALMA Memo 347 Released Message-ID: ALMA Memo #347 60 to 450 GHz Transmission and Reflection Measurements of Grooved and Un-grooved HDPE Plates G. A. Ediss * and T. Globus February 2, 2001 For the ALMA production test receivers, at present being designed in the NRAO CDL, there is a need for infrared filters to reduce the thermal loading. One possibility is the use of various plastic materials which have reasonable absorption or scattering for the infrared wavelengths but which have low loss at the signal wavelengths. One such material is HDPE, for which some sort of anti-reflection coating would be required, and because materials with the required refractive index are not available, anti-reflection grooves are a possibility. To investigate the practicality of such grooves, measurements have been made of un-grooved High Density Polyethylene (HDPE), and of samples with linear or concentric rectangular grooves and linear triangular grooves. At 75-110 GHz, measurements were made with an HP8510 and between 60 and 450 GHz with a low resolution FTS. View a pdf version of ALMA Memo 347: http://www.alma.nrao.edu/memos/html-memos/alma347/memo347.pdf Download a postscript version of ALMA Memo 347: http://www.alma.nrao.edu/memos/html-memos/alma347/memo347.ps ============================================================================= ALMAnews is a broadcast service. To unsubscribe, send an e-mail message to majordomo at nrao.edu with "unsubscribe almanews" in the message body. From awootten at NRAO.EDU Thu Feb 15 17:55:48 2001 From: awootten at NRAO.EDU (Al Wootten) Date: Thu, 15 Feb 2001 17:55:48 -0500 (EST) Subject: [asac] forwarded message from C. M. Walmsley Message-ID: <200102152255.RAA21646@polaris.cv.nrao.edu> ------- start of forwarded message (RFC 934 encapsulation) ------- Received: from cv3.cv.nrao.edu (cv3.cv.nrao.edu [192.33.115.2]) by polaris.cv.nrao.edu (8.9.3/8.9.3/CV-SOL-3.0) with ESMTP id MAA10363 for ; Thu, 15 Feb 2001 12:28:13 -0500 (EST) Received: from palantir.cv.nrao.edu (palantir.cv.nrao.edu [192.33.115.254]) by cv3.cv.nrao.edu (8.9.3/8.9.3/CV-SOL-3.0) with ESMTP id MAA11801 for ; Thu, 15 Feb 2001 12:28:12 -0500 (EST) Received: from circe.arcetri.astro.it (circe.arcetri.astro.it [193.206.154.36]) by palantir.cv.nrao.edu (8.9.3/8.9.3/CV-PALANTIR-3.1) with ESMTP id MAA00483 for ; Thu, 15 Feb 2001 12:28:11 -0500 Received: (from walmsley at localhost) by circe.arcetri.astro.it (8.9.3/8.9.3) id SAA28695 for awootten at nrao.edu; Thu, 15 Feb 2001 18:26:20 +0100 (MET) Message-Id: <200102151726.SAA28695 at circe.arcetri.astro.it> Content-Type: text Content-Length: 3199 From: "C.M. Walmsley" To: awootten at NRAO.EDU Subject: ALMA SAC Face to Face Last Call Date: Thu, 15 Feb 2001 18:26:20 +0100 (MET) Feb. 15, Dear Participants in the Florence ASAC Face-to-Face, These are some last practical comments about the Florence face-to-face. We have not heard of any great problems with hotels and presume that you can all make it there and turn up at the Calza at, say, 8.50 on Friday morning. We have arranged both "coffee breaks" morning and afternoon and a "light lunch" and we have (at the last count) 39 participants. I append the list. The coffee and cakes are paid for by the Observatory but the lunch you should pay for directly to the Convitto della Calza. The cost will be 35000 L (roughly 35 DM or 17 US Dollars) although we are still discussing it and it may come down. We need however to know if any of the 39 named below will NOT be around at lunch on either Friday 23 or Saturday 24. If you will not be present, please let us know asap and if possible by next Monday. The lunch is scheduled presently for 12.30-1.45 PM on Friday and 1.00-2.15 Saturday. Also, if anyone has special requirements (such as vegetarian), please let us know and we will see what can be done. We do not plan any formal Dinner but of course, Florence and the area around your hotels is full of restaurants. They are mostly small however and on Sat. night , it is advisable to book. The tourist area of Florence with Pitti Palace, Ponte Vecchio etc is just beyond the ANNALENA and BOBOLI hotels on that little sketch which (I hope) you all got (ie along the Via Romana away from the Porta). Weather is completely unpredictable. It is beautiful just now but it changes fast. Bring a good sweater. Buon Viaggio, Malcolm - -------------------------------------------------------------- List Of Participants --------------------- Name Arriv. Dep. Baars 22 25 Bachiller 21 25 Baudry 23 26 Blake 22 25 Bronfman 21 27 (+ Daughter) Brown 21 27 Chikada 22 25 Cox 22 24 Crutcher 22 26 DeVos 23 25 Dickman Emerson 22 26? Evans 22 26 Fukui 22 25 Guilloteau 22 25 Gurwell 22 25 Hamaker Hasegawa 21 25 Ishiguro 21 25 Kawabe 22 24 Kurz 22 25 Lucas Matsuo 22 25 Menten 22 24 Momose 22 25 Nakai 22 25 Rafal 22 25 Richer 22 25 Sakamoto 22 25 Scoville 21 25 Shaver 22 25 Tatematsu 22 25 Van Dishoeck 22 25 Walmsley Wilson 19 25 Welch 22 24 Wild 22 25 Wootten 22 25 Yun 22 25 ------- end ------- From seiichi at nro.nao.ac.jp Thu Feb 15 19:19:12 2001 From: seiichi at nro.nao.ac.jp (Seiichi Sakamoto) Date: Fri, 16 Feb 2001 09:19:12 +0900 Subject: [asac] Bola-Chajnantor comparison Message-ID: Colleagues, I have updated the web pages of the ALMA-Japan Site Working Group that can be found at http://www.nro.nao.ac.jp/~lmsa/siteWG/siteWG.html . This page includes current summary of the Bola-Chajnantor site comparison http://www.nro.nao.ac.jp/~lmsa/lmsa-memo/2001-002.pdf . You may also find some reports at ALMA-J Memo page http://www.nro.nao.ac.jp/~lmsa/lmsa-memo/ . Saludos, Seiichi ========================================= Seiichi Sakamoto ----------------------------------------- ALMA Project Office (Japan) National Astronomical Observatory Mitaka, Tokyo 181-8588, Japan phone: +81-422-34-3843 fax: +81-422-34-3764 e-mail: seiichi at nro.nao.ac.jp URL: http://www.nro.nao.ac.jp/~seiichi ----------------------------------------- From awootten at NRAO.EDU Fri Feb 16 11:46:41 2001 From: awootten at NRAO.EDU (Al Wootten) Date: Fri, 16 Feb 2001 11:46:41 -0500 (EST) Subject: [asac] New materials Message-ID: <200102161646.LAA15954@polaris.cv.nrao.edu> I have placed a few small changes in the schedule at http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacfirenzeagenda.html NEW Bob Dickman will attend the ASAC meeting. Please read the following documents received for distribution this week: -NEW- ALMA Receiver Optics ReportDRAFT from James Lamb. NEW Morita's work and Yun's work on the ACA are available in draft form. New 4bit correlation modes can be incorporated into the baseline correlator. Hamaker will attend the ASAC meeting. NEW Please read documents from Johan Hamaker:

Polarimetry discussions in ASAC: Making a fresh start (6Feb '01).

Intensity measurements with feeds in p.a. 0 and 45 degrees. See you in Florence! Clear skies, Al From wilson at physics.mcmaster.ca Fri Feb 16 14:14:33 2001 From: wilson at physics.mcmaster.ca (Christine Wilson) Date: Fri, 16 Feb 2001 14:14:33 -0500 (EST) Subject: [asac] New material on the 20 micron water vapour system In-Reply-To: <200102161646.LAA15954@polaris.cv.nrao.edu> Message-ID: Hi, everyone, Here is a short writeup on the new results from the 20 micron water vapour radiometer ("IRMA"). I'm sorry it has no figures attached; I'll have figures to show at the meeting. Chris ------------------------------------------------ Recent Results with the Infrared Radiometer for Millimetre Astronomy (IRMA) (summarized by Christine Wilson from Graeme Smith's M.Sc. thesis) IRMA has been designed and constructed by David Naylor and his group at the University of Lethbridge in collaboration with the JCMT group at HIA/NRC. A prototype device was constructed in 1999 and first tested at the JCMT in December 1999. The data from that test run have been written up and analyzed in Graeme Smith's M.Sc. thesis. A preliminary analysis of those data was presented by Chris Wilson at the ASAC meeting in Leiden in March 2000. This report summarizes the results from a more complete and final analysis of the same data. Figures illustrating the results from IRMA will be shown at the February 2001 ASAC meeting in Florence. IRMA monitors emission from water vapour in the Earth's atmosphere at a wavelength of 20 microns. It is equipped with optics to produce a diverging beam which is designed to match the footprint of the JCMT at an altitude of approximately 1 km. It can observe an ambient load, a cold load (LN2), or the sky. The optical input was chopped at a rate of 200 Hz and the data were sampled at a rate of 10 Hz. The prototype device can operate in either stare or continuous scan mode. In stare mode, a single elevation and azimuth is monitored continuously, while in continuous scan mode, the device is scanned from 1 to 3 airmasses in steps of 0.18 degrees. The instrumental error was derived from the standard deviation of the signal from the LN2 load from 16 sets of continuous scan observations (each containing typically 15 individual cycles of a continuous scan plus an observation of each load). The instrumental error was 5.8 mV in 0.1 s; assuming the noise will integrate down with the square root of the integration time, the expected noise in a 1 second integration would be 1.8 mV. The continuous scan data give measurements of the instrumental voltage as a function of airmass. These curves were calibrated to give voltage as a function of mm of precipitable water vapour (mm pwv) using two observations with the 183 GHz radiometer at the JCMT that were obtained simultaneously with observations with IRMA. The 183 GHz data were used to derive the pwv at the time the data were taken. (Similar simultaneous measurements with the 350 micron taumeter at the CSO gave a similarly good but slightly lower calibration. Attempts to calibrate the data with pwv determined from radiosonde launches from Hilo were unsuccessful due to the large scatter in the radiosonde measurements.) Once the curve of IRMA voltage versus mm pwv has been obtained, it can be combined with the instrumental error to derive the sensitivity of IRMA to changes in the pwv (or changes in the optical path). The table below gives the derived IRMA sensitivity for values of 0.5 mm and 1.0 mm for the atmospheric pwv. (The optical path was derived from the pwv by multiplying by a factor of 6.5.) Atmospheric Resolution of IRMA in 1 s ALMA specs in 1 s pwv (mm) pwv (microns) path (microns) path (microns) 0.5 mm 1.8 12 15 1.0 mm 3.0 20 20 >From the table, it can be seen that the raw sensitivity of the prototype device met the ALMA specifications for measuring the optical path above a single antenna. A Phase 2 instrument was built and installed at the JCMT in the summer of 2000. This device has a more sensitive detector, an infrared filter with improved efficiency, and improved digital electronics. This device is currently operating at the JCMT where it is used to take many continuous scan measurements whenever SCUBA does a sky dip. The idea is to correlate the pwv derived from the SCUBA estimates of the optical depth at 850 and 450 microns with the IRMA measurements. The data are currently being analyzed, and the new device seems likely to be an order of magnitude more sensitive than the prototype. Naylor's group are also researching the effects of cirrus at 20 microns. So far there are no large observable effects that might be attributable to cirrus, although this will be difficult to quantify without an independent measure of cirrus. A Phase 3 device which will be completely stand-alone and will use a Stirling cooler and two point warm blackbodies is currently being built. Since IRMA represents a new application of infrared technology to radio phase correction, there are of course a number of uncertainties and questions that would need to be resolved before IRMA could be adopted as the baseline design for a water vapour radiometer for ALMA. Some of these uncertainties were listed in the September 2000 ASAC report; I have summarized some of the issues I could think of as well as an appendix at the end of this report. However, the results from the prototype IRMA device are extremely promising, and it is important to work as quickly as possible to resolve some of the remaining uncertainties. Ultimately, installation of two IRMA devices on a millimeter array will be necessary to prove the concept. Appendix: A summary of areas of concern and future work with IRMA Uncertainties (possible sources of systematics): -- IRMA beam can't match radio beam at all heights in the atmosphere; is this a problem? -- IRMA bandpass samples mixture of optically thin and thick lines -- effects of clouds -- sensitivity of IRMA to changes of pressure, temperature, distribution of water vapour (height) -- how easy will it be to align IRMA with the radio beam? where would we put IRMA? i.e. weight loading on edge of dish? Needed in the short term: -- more direct comparisons of IRMA signals with 183 GHz system -- further calibration of V vs airmass to V vs pwv (i.e. more than 2 points should be used to calibrate it) -- refinements of the original design, including conversion to a closed-cycle cooler (on-going) Not yet tested/investigated: -- direct comparison of IRMA signals with phase on an astronomical source -- stability of IRMA over 5 minutes -- stability of IRMA over changes in zenith angle of 1 degree -- is 1 s a short enough timescale to be deriving pwv over? (a more general question than just IRMA) -- could IRMA be used to correct for anomalous refraction? From awootten at NRAO.EDU Fri Feb 16 15:32:55 2001 From: awootten at NRAO.EDU (Al Wootten) Date: Fri, 16 Feb 2001 15:32:55 -0500 (EST) Subject: [asac] ASAC Map Message-ID: <200102162032.PAA24105@polaris.cv.nrao.edu> To find Malcolm's map from the hotels to the ASAC meeting site: You may view it at by clicking the blinking word MAP at: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacfirenzeagenda.html or directly at http://www.cv.nrao.edu/~awootten/mmaimcal/asac/calza.pdf Thanks, 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 guillote at iram.fr Tue Feb 20 04:34:49 2001 From: guillote at iram.fr (Stephane Guilloteau) Date: Tue, 20 Feb 2001 10:34:49 +0100 Subject: [asac] C:\ALMA\Operation\ALMA_Science_Ops10.txt Message-ID: <000901c09b20$5f1bf3a0$cafc30c1@pctcp72.iram.fr> My previous message bounced. Here is a Text only version of the MS-Word file C:\ALMA\Operation\ALMA_Science_Ops10.txt -------------------------------------------------------------------- Dear ASAC members Please find attached a draft of the document presenting the ALMA Science Operations which is being prepared for the Phase II proposal to ESO. This document is opened for discussions. In particular, we have introduced the concept of "Regional Centers" (one in Europe, one in North America, expandable to another one in Japan if the tri-partite ALMA is funded) to keep contact with the ALMA users. The interaction of the Regional Centers with the SOC have to be considered in a more thorough way than in this draft. The location of various staff needs also be considered. This draft is the results of preliminary meetings and discussions of several people at ESO, IRAM and Observatoire de Grenoble. Stephane & Peter -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: ALMA_Science_Ops10.txt URL: From awootten at NRAO.EDU Wed Feb 21 01:27:55 2001 From: awootten at NRAO.EDU (Al Wootten) Date: Wed, 21 Feb 2001 01:27:55 -0500 Subject: [asac] CBI Experience Message-ID: <3A935FEB.51B7D0D5@nrao.edu> -------------- next part -------------- NATIONAL RADIO ASTRONOMY OBSERVATORY Charlottesville, Virginia November 27, 2000 M E M O R A N D U M To: P. Vanden Bout From: R. Brown, B. Butler, S. Radford, T. Readhead, A. Wootten Subject: CBI Experience on the Chajnantor Site and its Relevance to ALMA Planning On November 6, 2000, Tony Readhead (Cal Tech), Bob Brown, Al Wootten, Simon Radford, and Bryan Butler met in Brown's office to discuss observing and operating conditions at the Chajnantor site. The Cosmic Background Imager (CBI) group has learned a lot about Chajnantor while operating the CBI this past year, it is important to us that ALMA benefit from this experience. 1. Overview of the CBI Project on Chajnantor The CBI group brought their equipment to the Chajnantor altiplano in August 1999 and began operations in November 1999. The project is funded through next austral fall; additional funding has been sought to extend this to August 2001. The CBI is a 13-element interferometer mounted on a 6 meter platform operating in ten 1 GHz frequency bands from 26 GHz to 36 GHz. It sits in a clamshell dome about a kilometer west of the ALMA site characterization containers. Mostly, the experience on the site has been that the weather can be spectacularly good most recently, a continuous run of 46 successive nights has been limited only by the receiver noise. On 1-meter baselines the CBI was thermal noise limited about 50% of the time during its first six months of operation, whereas at the same frequency and baseline length at the OVRO this occurs only a few percent of the time. This is a strong function of baseline length, thus, for example, the OVRO Millimeter Array achieves the thermal noise limit even in the summer daytime at CBI frequencies on all baselines. 1.1 CBI Experience About a dozen nights in the past year have been problematic owing to weather at Chajnantor but apparently these nights would not have been lost had the CBI been sited at Pampa la Bola. Tony emphasized that 10 percent extra observing time would be important for any astronomical facility These lost nights can be characterized as follows: clouds form in the early evening over Chajnantor, often with snow following. CBI could not open up for observation. The 'far field' for that instrument is only a few 100 m above the site, so they actually image the atmospheric clouds as well as the distant Universe. Formation of the cloud layer is seen in the relative humidity, which rises through 90 percent when the cloud layer descends to the altitude of the site. Condensation occurs on the dewar windows during these events, a further impediment to observing. Wind has not caused much time loss, nor has inaccessibility of the site. As the team heads back to San Pedro from the CBI site, they pass through Pampa la Bola, where the sky is completely clear, and there has been no precipitation. Presumably, these microclimatic events occur as moist air arrives at the top of the plateau and undergoes a phase change. Tony estimated the number of nights when it actually snowed to be around 12-15 nights of bad snow which occurred in 4 or 5 bad storms each lasting 2-3 days; but after each bad snowstorm the wind continues to redistribute the snow for a week or so, until it becomes compacted. Over the course of four months in the period from mid-December to early-June episodes of sporadic snow were common. Wind did not often pose a problem though there was a very bad wind storm in July, where there were gusts up to 100 mph, and the mean wind was above 40 mph over a 30-hour period. They were quite worried about the integrity of the CBI dome (and were glad that they had reinforced it in Pasadena). The dome suffered only minor damage, which was repaired in a couple of hours. One of the lessons learned from experience is that the predictions being made by Prof. Erasmus for the wind on Paranal were also accurate indicators of future high winds on Chajnantor. Tony thinks that the survival wind spec for the ALMA antennas should include a time period over which the antennas will survive an ongoing, gusty, wind. Tony's experience suggests that the location of the LMSA/NRO container is also windy. In fact, it may be as bad or worse than at Chajnantor because the wind appears to be funneled between Cerros Chajnantor and Toco. If wind is an issue for ALMA one should search for shielded areas of stagnant air. Other conclusions from the CBI experience of relevance to ALMA are: Ice is not a problem. Ice buildup has not been a problem, although there are occasionally ~12" icicles on the external dome structure Dust is not a problem. No effects due to blowing dust have presented problems, however, the telescope itself is shielded by the dome. 1.2 Actions Recommended from the CBI Experience The primary recommendation from the CBI experience is to understand the micro climate episodes, where clouds form over Chajnantor but not over Pampa la Bola. By correlating the CBI logs with the data from the other instruments (tippers, etc.) can we recognize these episodes? Steve Myers plans to try to identify the episodes for study from entries in the CBI logbooks. At other times, clouds or invisible water vapor cause other effects. Sometimes increased power on shorter baselines/water in virtual clouds can be seen in the CBI data and might be detectable with the ALMA equipment. Under these conditions, the CBI receivers individually detect the water vapor fluctuations, which are easily recognisable since the individual antenna total power fluctuations are strongly correlated. Such events may have occurred but gone unrecognized in ALMA tipper measurements. Every four and a half hours, the tipper stares straight up and measures the variation of total power on the sky. This should show the water containing pockets which cause (a) the excess of power on short CBI baselines and (b) power level fluctuations on individual antennas. These data will be investigated in detail. On clear nights when the CBI registers an excess of power on the shorter baselines might be nights when anomalous refraction occurs. This also correlates well with relative humidity. Tony estimated that this had occurred on only a few nights. We have estimated the magnitude of the effect by extrapolation of data from the NRAO 300 m Site Testing Interferometer measurements to 12 m baselines. However, a direct estimate at short scales would be of great use for ALMA. Examination of data from these nights might give us some insight into the structure of the pockets causing the effect. We will try to identify these events for further investigation. Other action items: Correlate CBI evidence for liquid water in invisible clouds with 225 GHz tipper stare mode fluctuations. The 183 GHz radiometers don't tip, but stare all the time. It may be possible to see something in those data. Simon will discuss this with Richard Hills next week. Snow and black ice on the tarmac are dangerous. Several accidents have occurred this year alone. The Jama road may not be cleared while drifting continues, limiting access for periods of typically ~3 days. Correlate RH meters at ALMA/EU and LMSA sites with the CBI results. Consider ice prophylactic measures on antennas--watch out for open conduits Doors on tepees should be upwind. Consider weather stations at sites planned for array centers. 2. ALMA Requirements for Site Meteorological Conditions Simon Radford reviewed a draft ALMA memo that summarizes the data taken nearly simultaneously from the NRAO and NAO tipping radiometers. The 225 GHz optical depth measured by the NRAO tipper, and the 220 GHz optical depth from these two devices at Chajnantor and Pampa la Bola respectively provides a quantitative comparison of the atmospheric transparency that favors the Chajnantor site in the sense expected from the higher elevation of the Chajnantor site (5000 m vs. 4800m). While the difference in the quartile transparency at 225/220 GHz is not large between the two sites, approximately 0.01 at the 25 percent quartile, it is possible to use the FTS measurements to infer the difference at all ALMA frequencies. The difference can then be turned into a difference in the observation time required by ALMA to reach a given sensitivity, the time always being longer at the Pampa la Bola site. The increased observation time varies from approximately 10 percent at 230 GHz to 100 percent at 809 GHz. For the CBI the difference in atmospheric transparency is not a decisive factor because the transparency at either site at 26-36 GHz is so exceptionally good. Bryan Butler reviewed a draft ALMA memo that summarizes the data taken nearly simultaneously from the NRAO and NAO site testing interferometers. These instruments view a geostationary satellite and record the effect of a varying path length delay through the atmosphere on a baseline of 300 m. Here too, the data favor the Chajnantor site in the sense that the sky is more stable over Chajnantor than over Pampa la Bola. In terms of observing efficiency, this can be interpreted either as more time during which radiometric phase correction techniques will not be required by ALMA, or it can be interpreted as a lessened requirement for those techniques on Chajnantor as opposed to on Pampa la Bola. Again, this specification for ALMA has no direct analogous requirement for the CBI owing to the lower frequency (26-36 GHz) and shorter baselines (1-5 m) exclusively employed in the latter. 2.1 Actions Recommended from the ALMA Testing Program Experience An effort should be made to bring the NRAO and NAO tipping radiometers together at the same place to verify that they give the same quantitative result for the zenith transmission; An effort should be made to characterize the site microclimate. 3. Meeting Summary The CBI and ALMA are sensitive to different atmospheric conditions and effects which may strongly affect the optimum location for each. The CBI images directly water-bearing clouds because such clouds are in the far field of the CBI; hence the CBI cannot operate in the presence of clouds. ALMA sees such water- bearing clouds only as an increase in system temperature; there is no direct image distortion. Snow is debilitating to the CBI because it blows into, and collects within, the enclosing dome. CBI observations cease during snowstorms, and it takes a few hours to clear the snow from the dome following a serious snowstorm. The ALMA antennas operate in the open air where the wind will act to remove snow from the dish (although snow will collect against the pedestal mount); ALMA observations can proceed in the presence of episodic snow. The need to remove snow from the site access ways needs to be an integral part of ALMA site development and operations. When the relative humidity exceeds 95% condensation is likely on the CBI antenna windows, and therefore the CBI dome is not opened. For ALMA, condensation on the primary mirror may prove to be a concern but not for the receivers and optics which are protected by a Gortex window that is continuously IR heated. Both the CBI and ALMA require a site with the exceptional conditions characteristic of the Chajnantor science preserve. However, owing to the different requirements that ALMA and the CBI have for conditions of wind, snow, clouds, atmospheric turbulence and atmospheric transparency, the optimum location for each on the site is best determined by the local micro-climate and the specific requirements of each instrument independent of the differently weighted needs of the other. /bmr From cwhite at NRAO.EDU Wed Feb 21 10:01:12 2001 From: cwhite at NRAO.EDU (Carolyn White) Date: Wed, 21 Feb 2001 10:01:12 -0500 (EST) Subject: [asac] [almanews] ALMA Memo No. 348 Released Message-ID: ALMA Memo #348 A Preliminary ALMA Zoom Array Design for the Chanjnantor Site John Conway February 15, 2001 I present a preliminary zoom array design for ALMA fitted into the the Chajnantor site, and compare its properties with the proposed double ring strawperson array. Both arrays have virtually the same number of pads and require almost the same number of antenna moves. To first order the two arrays are shown to have similar radial distributions of baselines, although the coverage of the zoom array is smoother and is slightly more centrally condensed. For snapshots the peak sidelobes for the two styles of array are similar. However the zoom array has 40% smaller peak sidelobes for long track observations. For both snapshots and long tracks the degree of uv cell occupancy for the two arrays is very similar. We argue that zoom arrays will have slightly smaller or equal phase noise efects than dual ring arrays of the same resolution. For the zoom array we show that North-South extended array configurations with low sidelobes exist for observing Northern hemisphere or South polar sources. The zoom array is a very flexible design, which can accommodate many different modes of operation. It can for instance be operated as set of fixed arrays like the double ring, with the important difference that the sizes and numbers of configurations are variable. Alternatively the array could be operated in a continuous reconfiguration mode with perhaps six antennas being moved per week. This mode of operation has some astronomical advantages and significant operational advantages. However the array is operated, if antenna moves are prevented by bad weather, the zoom array is aways left in a configuration with a good uv coverage without stranded 'outlier' antennas. After a certain amount of convergence the two styles of array proposed for the intermediate configurations are no longer dramatically different. However in almost all performance areas we argue that the zoom array is slightly superior. This combined with its much greater flexibility suggests that the zoom array design should be chosen for the intermediate configurations. Put another way - we find no strong argument in favour of (and several against) building particular scale lengths into the array design as is done in the dual ring design. The full html version of ALMA Memo #348 is at URL: http://www.alma.nrao.edu/memos/html-memos/alma348/memo348.html ============================================================================= ALMAnews is a broadcast service. To unsubscribe, send an e-mail message to majordomo at nrao.edu with "unsubscribe almanews" in the message body. From ewine at strw.leidenuniv.nl Tue Feb 27 03:52:35 2001 From: ewine at strw.leidenuniv.nl (Ewine van Dishoeck) Date: Tue, 27 Feb 2001 09:52:35 +0100 Subject: [asac] draft of letter to ACC; please respond Message-ID: <200102270852.JAA27492@nitrogen.strw.LeidenUniv.nl> Dear ASAC members, Below please find the draft of the ASAC letter to the ACC, as written by Jack Welch and with comments from Geoff Blake and myself included. Please send comments to me (ewine at strw.leidenuniv.nl) by WEDNESDAY FEBRUARY 28 3 pm CET at the latest. Can the designated liaisons please send their drafts for the full ASAC report to Jack Welch (welch at astro.berkeley.edu) by the end of this week? As to the next ASAC telecon: I unfortunately have a conflict on Thursday March 15 which I cannot move. The ASAC telecon will therefore be on Wednesday March 14 at 10:15 am EST. My apologies to those who cannot make it at that date. We will move back to the regular Monday telecons in April. Many thanks to everyone for their active participation in the discussions at the Florence meeting! With best regards, Ewine ******************************************************************** To: ALMA Coordinating Committee From: ALMA Science Advisory Committee February 28, 2001 Dear ACC members, In early February 2001, the ASAC learned with dismay of further financial pressures on the ALMA project which would impose a maximum budget of 663M$. In its meeting in Berkeley in September 2000, the ASAC including (informally) its new Japanese members, developed a plan for the enhanced ALMA which would include a new compact array (the ACA) which would enable new science and enhance the capability for wide field imaging, a suite of ten receivers which would enable a rich astronomical program over all of the available millimeter/submillimeter atmospherics bands, and an enhanced correlator which would significantly increase the speed and sensitivity of the system. In October, we learned of a 10% proposed cut in the budget, and we began planning how we would discuss accomodation of that reduction during our February 23,24 2001 meeting in Florence. With the further reduction, the new budget limit of 663M$ amounts to only a modest increase over the original 552M$ budget of the combined European/American Groups, despite the joining of our Japanese colleagues in the project. Further, some of this increase must go to the additional overhead of the larger organisation. Since the observing time is now divided three ways, the advantage to each of the partners of combining the LMSA/LSA/MMA projects is considerably diluted. As regards the impact on the science program from this further proposed reduction, little more than the ACA and one receiver band (band 10) beyond the baseline complement of 4 can be added. The ASAC became convinced of the importance of the ACA through the simulations presented at the Florence meeting. At the 10% cut level, a total of 8-10 receivers could be included in addition to the ACA. With the larger cut, the loss of bands 1, 4, and 8 eliminates substantial and important science. Band 1 at a wavelength of 1 cm offers unique capability for studying large scale structures forming in the denser parts of the early universe and for investigating the inner most parts of disks forming around young stars. Band 4 is rich in molecular lines which are important for astrochemistry and the study of the formation of massive stars, both locally and as signatures of distant (early) galaxy formation. Band 8 contains perhaps the most important continuum emission from newly forming low mass stars and the emission from ubiquitous atomic carbon in nearby galaxies, important for galactic structure studies. The loss of the next generation correlator implies a decrease in observing speed for some of the highest ranked scientific programs by up to a factor of two. ALMA is a unique project, the only major world telescope in the next few decades for millimeter wavelengths. This plan for a single telescope stands in sharp contrast to the situation in ground based optical and infrared astronomy, where there are many systems including the dual Gemini 8 m telescopes, the Japanese Subaru telescope, the VLT system of ESO, and, in the private sector, a number of major instruments such as the dual 10 m Keck telescopes. The ALMA project is the major new initiative in astronomy in many countries. It is an exciting new instrument, full of the promise of answering many fundamental questions in astrophysics. It deserves the fullest support. Sincerely, The ALMA Scientific Advisory Committee From wilson at physics.mcmaster.ca Wed Feb 28 18:08:52 2001 From: wilson at physics.mcmaster.ca (Christine Wilson) Date: Wed, 28 Feb 2001 18:08:52 -0500 (EST) Subject: [asac] Copy of memo sent to NRAO staff. (fwd) Message-ID: Dear ASAC member, I apologize if you've already received this, but since I'm not sure whether I received this through the ASAC or NRAO User's Committee mailing lists, I thought I would circulate it to the ASAC email list. Chris ---------- Forwarded message ---------- Date: Wed, 28 Feb 2001 16:31:20 -0500 From: Billie Rodriguez Subject: Copy of memo sent to NRAO staff. MESSAGE TO NRAO STAFF The U.S. Office of Management and Budget released today the budgetary outline of the FY 2002 requests for federal agencies and programs that President Bush will send to Congress [see http://www.gpo.gov/usbudget/index.html]. This plan includes a request for the NSF that would increase its FY 2002 funding by only 1% relative to the FY 2001 appropriation. Targeted increases for a very few NSF Divisions would consume this modest increase, and more, and would leave all other NSF activities, including Astronomy, to share a proposed FY 2002 funding level less than that realized in FY01. In addition to the unfortunate consequences for virtually all of NSF science, no new starts for NSF facilities are proposed in FY 02. Beyond the implications for Observatory operating funds, the lack of new starts is particularly regrettable for the NRAO because it appears to mean that the construction phase of ALMA will not begin in FY 2002 as had been anticipated. Clearly, the absence of new starts is not specifically focused on ALMA. Rather, it reflects the President's desire to freeze agency programs for a time while he and his staff can review the plans, organization, progress and priorities of current initiatives. However, in the specific case of ALMA this order has the consequence of interrupting a program that has its international agreement forged, its design and development phase milestones achieved, and its recommendations from the NSF oversight body all in place for FY 2002 construction. Given the high importance of the ALMA scientific program, the timing of the restriction against FY 2002 new starts for the ALMA Project is extremely unfortunate. The President's FY 2002 budget will be under review and discussion in Congress for the next several months. During this time, we intend to work with the community to inform the Federal government of the importance of ALMA and of the need for the project to move to construction expeditiously. At the same time, we will work to preserve the momentum of the project at the NRAO and internationally by securing adequate FY02 funding for a fifth year of design and development should it not be possible for construction to begin in FY 2002. Another item of note to astronomy in the FY 2002 Budget Plan is the announcement that NASA and NSF are to form a Blue Ribbon Commission to consider the pros and cons of giving NASA the responsibility for all astronomy, both ground- and space-based. The Commission is to report by September 1, 2001. Paul Vanden Bout 28 February 2001