From soliver at nrao.edu Mon Apr 5 14:59:42 2004 From: soliver at nrao.edu (Stacy Oliver) Date: Mon, 5 Apr 2004 11:59:42 -0700 Subject: [asac][almanews] ALMA Memo 490 Released Message-ID: <005001c41b40$27619520$8bdbc5ce@moonshine> ALMA MEMO #490 Effects of Atmospheric Emission Fluctuations and Gain Fluctuations on Continuum Total Power Observations with ALMA M.A. Holdaway 2004-03-30 Atmospheric water vapor emits strongly at millimeter wavelengths. Fast temporal and spatial fluctuations in the atmospheric water vapor results in problems in removing the atmospheric emission, which is done by very quick position switching or beam switching. Most phase fluctuations seen with the 11.2 GHz site testing interferometer are due to fluctuations in water vapor, so we can use the statistics of the phase fluctuation measurements to infer how well the cancellation of variable water vapor emission will be for a given observational strategy and a given atmosphere. In fact, we have found a (non-optimal but sufficient) way to match observations at all ALMA bands (1-10) to atmospheric opacity and stability conditions such that OTF total power continuum observations are essentially always thermal noise limited and never limited by atmospheric fluctuations. In addition to the problem of atmospheric fluctuations, the total power continuum observations also must contend with gain fluctuations, which in fact will limit these observations. Gain fluctuations of 1e-4 in one second will just barely limit total power continuum observations. However, gain fluctuations of 1e-3 will result in residuals which are an order of magnitude worse than the thermal noise limit. While other considerations might drive the decision for the receiver stability specification, it should be noted that a specification of 1e-3 in one second, or worse, will cause problems for ALMA continuum observations of large objects. All simulations were performed in AIPS++, and several reusable glish tools have been written. View a pdf version of ALMA Memo #490. http://www.alma.nrao.edu/memos/html-memos/alma490/memo490.pdf -------------- next part -------------- An HTML attachment was scrubbed... URL: From awootten at nrao.edu Mon Apr 5 22:54:59 2004 From: awootten at nrao.edu (Al Wootten) Date: Mon, 05 Apr 2004 22:54:59 -0400 Subject: [asac]ASAC Telecon 1400 UT Wednesday 7 April Message-ID: <40721C03.3050608@nrao.edu> Reminder: Here's the dial-in information for the telecon. According to notes I have received, we voted to maintain local time for Central Europe and most of the US, altering UT to account for summer time variations in these locations. CALL TIME: 14:00 Universal Time or 1000 am EDT CALL DATE: 07-April-2004 (Wednesday) DURATION: 1 hr * USA Number: 877-874-1919 * Outside USA Number: +1-203-320-9891 NOTE NEW NUMBER * Passcode: 185064 * Leader: Al Wootten An agenda will circulate soon. Clear skies, Al From awootten at nrao.edu Tue Apr 6 12:59:51 2004 From: awootten at nrao.edu (Al Wootten) Date: Tue, 6 Apr 2004 12:59:51 -0400 Subject: [asac]Agenda for tomorrow's telecon Message-ID: <16498.57863.384498.421351@polaris.cv.nrao.edu> Folks, Please view: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacapr04agenda.html for an agenda. Some items pertaining to the charges are in a red font on the linked strawman agenda, q.v. 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 | | (434)-296-0329 voice Help us build The ALMA| | (434)-296-0278 FAX {> {> {> {> | +----------------------------------^-----^-----^-----^---+ From ccarilli at aoc.nrao.edu Tue Apr 6 15:58:56 2004 From: ccarilli at aoc.nrao.edu (Chris Carilli) Date: Tue, 06 Apr 2004 13:58:56 -0600 Subject: [asac]Agenda for tomorrow's telecon In-Reply-To: <16498.57863.384498.421351@polaris.cv.nrao.edu> References: <16498.57863.384498.421351@polaris.cv.nrao.edu> Message-ID: <40730C00.8080405@aoc.nrao.edu> Al, The VLA scheduling committee meeting starts at 8:30 tomorrow, so I will only be able to participate in the first 30mn of the telecon. So if you want me to report on the ANASAC/Maryland meeting, it would have to be before 8:30. thanks, cc From soliver at nrao.edu Wed Apr 14 11:19:03 2004 From: soliver at nrao.edu (Stacy Oliver) Date: Wed, 14 Apr 2004 08:19:03 -0700 Subject: [asac][almanews] ALMA Memo 491 Released Message-ID: <002501c42233$d251f700$8bdbc5ce@moonshine> ALMA MEMO #491 Does the ACA Need Phase Compensation? M.A. Holdaway 2004-04-06 We analyze the phase monitor data from Chajnantor over the period 1996 - 2001 and infer the level of phase fluctuations that would be seen on 10- 30 m, typical baseline lengths for the Atacama Compact Array (ACA). On baselines of 10-30 m, fast switching phase compensation will be useless, but water vapor radiometry (WVR) could improve the phase stability marginally. We consider the effects of phase errors on imaging and on the flux scale, and determine that (a) the ACA will require dynamic scheduling in order to meet the ALMA scientific objectives, (b) given dynamic scheduling, the ACA will likely not require any sort of active phase correction such as WVR, and (c) by permitting high frequency ACA observations during conditions with the lowest opacities and less than optimal phase stability, WVRs could increase the ACA's efficiency, especially for high frequency observations, and can probably be justified on a cost-benefit basis. There is another reason why we would want phase calibration on the ACA - the 12 7 m dishes cannot calibrate themselves to the required accuracy in a reasonable amount of time. In order to calibrate accurately, we need to correlate the 7 m dishes with the four 12 m dishes dedicated to the ACA, or even better, with the full ALMA array. If we are correlating with the four nearby 12 m dishes, we do not need phase compensation on the ACA antennas, but if we plan to correlate with the full ALMA, we absolutely need WVR and fast switching capability. View a pdf version of ALMA Memo #491. http://www.alma.nrao.edu/memos/html-memos/alma491/memo491.pdf -------------- next part -------------- An HTML attachment was scrubbed... URL: From twilson at eso.org Fri Apr 16 10:27:25 2004 From: twilson at eso.org (Thomas Wilson) Date: Fri, 16 Apr 2004 16:27:25 +0200 Subject: [asac]Item from the last ASAC meeting Message-ID: <407FED4D.4040407@eso.org> I was unable to take part in much of the ASAC mtg due to my cell phone range. I did have a request from the ASAC for information about the EU proposal for framework program 6 (FP6). I am in the midst of the discussion about ALMA regional Centers (formerly RSC, Regional Science Centers). I could talk about that at some ASAC meeting or telecon, if there is interest. Regards, Tom Wilson ALMA European Project Scientist ESO -------------- next part -------------- A non-text attachment was scrubbed... Name: fp6-summary.ppt Type: application/vnd.ms-powerpoint Size: 112640 bytes Desc: not available URL: From awootten at nrao.edu Tue Apr 27 11:48:22 2004 From: awootten at nrao.edu (Al Wootten) Date: Tue, 27 Apr 2004 11:48:22 -0400 Subject: [asac]DRSP calibration requirements Message-ID: <16526.32966.767825.177949@polaris.cv.nrao.edu> Dear ASAC: FYI. Michiel Hogerheijde notes: A short summary of the DRSP calibration requirements, with plots, can be found at http://www.strw.leidenuniv.nl/~alma/drsp_calib_prelim.html 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 | | (434)-296-0329 voice Help us build The ALMA| | (434)-296-0278 FAX {> {> {> {> | +----------------------------------^-----^-----^-----^---+