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* 2009-11-18 14:30 UT
Note UT time unchanged. Summer time has ended in the Northern Hemisphere for everyone, we think. . * Note: C. Wilson points out line noise may be muted by pressing *6 which works thru the call center.
* Duration: 1 hr
* USA Toll Free Number: 877-874-1919
* Toll Number: +1-203-320-9891
* Passcode: 185064
* Leader: Hills, Wootten, Testi, Morita
* Attendees:

Topics

1 Old Business The enhanced Agenda from last meeting is available. Science IPT notes from last month's telecon are not available.

Two Antennas at the  at AOS TB

DV01 and PM03 have successfully engaged in interferometry from the AOS at B3, B6 and B7, see Details.

See other images and animations.

  1. New Business--Project news/updates.(Hills, Peck)
    1. R. Hills
      1. A detailed status report may be found in ALMA Monthly Reports
      2. The report of the ASAC was delivered to the Board (edm link).
      3. Antennas: A third antenna will move to the AOS on 20 November. Elements of more than 20 antennas from all vendors are at the OSF--necessary for early science (but not sufficient). Antenna DV05, conditionally accepted, has been moved to the OSF. First ACA 7m antenna has arrived from Japan. The dummy Front and Back End equipment have been installed on the first of the AEM antennas.
    2. Employment
    3. ALMA Science IPT wiki page
    4. Astronomer Outreach: ALMA News. JAO ALMA Webpages. JAONews. NRAO eNews ESO Newsletter No 16 NAOJ News. NRAO ALMA Calendar
    5. Current ALMA System Block Diagram Vers P.
    • Current IPS attached
  2. Directories

Science IPT Group Activity Reports

Please include your Group Activity Report here (How to Enter Your Report), or email it to AlWootten

Project Scientists

  1. Change Requests. A significant change request was discussed last meeting which was rejected. A revised change request has been submitted: Band 6 CRE. This is complicated but in summary it proposes that the noise temperature requirements should apply over the 5 to 10 GHz IF range requested but that a higher slope in the power output should be allowed over the range 5 to 6 GHz than 6 to 10 GHz. The spec only applies to the cold cartridge so the problem of added WCA noise is not addressed directly but that ought to be covered by the specs on the WCA so long as the IF band is defined as 5 to 10 GHz. Unfortunately front-end have given themselves an escape clause by proposing to remove the requirement that the noise temperature at all points in the IF band should be no more than 25% worse than the average across the band.

  1. Configuration change. The location of the northernmost pad has been changed following the discussions at the last meeting and the follow-up by Bojan Nikolic and Sawada-san. Further_Note (pdf)
    • Some work has been done on all 192 foundations now. Configuration files are attached as a tar file containing both the new set of configurations and the old set. Ten locations in the outer arrays were changed. These will be incorporated into the CASA simulator simdata and into Gildas. (Unfortunately a recent check has revealed that at least 2 more pads have been moved to different positions, apparently without informing us, so these lists are not yet definitive. REH is getting a final list assembled, with the heights of the pads as well as the N-S and E-W coordinates where possible. This document will then be put into the system for approval so that the positions can come under configuration control.)
  2. Development. At the current time, the high frequency limit of Band 1 is defined as 45 GHz (low end is 31.3 GHz). The original definition of the ALMA band edges is that the windows end at the point at which atmospheric transmission is less than 50%. For Band 1, the weird edges were based on a desire not to have an impossible bandwidth, to include a protected band at 31.3 GHz, and to include the atmospherically clearest part of the 7mm spectrum. I (AW?) believe that transmission 50% occurs around 53 GHz at the ALMA site. Therefore there is a range of frequencies not within the proposed ALMA Band 1 and not as well addressed by the EVLA as could be with ALMA. What science could be served by ALMA Band 1 covering the range 45-53 GHz? What compromises might be made at the low end of the band? What instrumental limitations are there, if any?

Jeff Mangum -- Calibration

  • Temporary weather stations installed on roof of AOS TB. Some adjustments, calibrations will be done on them. Readout here.

Bojan Nikolic/John Richer -- WVRs

Lars-Ake Nyman -- eSSR

  • ALMA SciOps Implementation Plan Review was held at SCO 2009 September 29-30, 2009.

Wootten -- Site Characterization

Remijan, Markwick -- Splatalogue

Science Corner:

  1. arXiv:0910.3111 [ astro-ph.GA] Title: Rotational spectra of isotopic species of methyl cyanide, CH3CN, in their ground vibrational states up to terahertz frequencies
  2. arXiv:0911.2936v1 [astro-ph.EP] Title: Exoplanet Characterization and the Search for Life

Discussion of Band 1 frequency range: transmission curves, spectral lines, and LO considerations

  • ToddHunter: I have posted the atmospheric transmission curve from 30-55 GHz using Scott Paine's model for the ALMA site. The plot actually contains two curves -- one for 25th percentile PWV (red) and one for 75th percentile PWV (black), but they are nearly indistiguishable in this frequency range. I have also marked five of the spectral lines of interest above 45 GHz, including ground state transitions of CS (48.990) and CH3OH (48.376) and major transitions of H2CO (48.284) and CCS (45.379, 51.821). With CS(1-0), one could imagine ALMA repeating the large 1993 Nobeyama map of Orion but with arcsecond resolution. Compared with the higher bands, the larger primary beam of Band 1 would be more conducive to such large scale mapping. Regarding the ground state CH3OH transition, it is detected at 0.3K in the Nobyama-45m TMC-1 survey, compared to 1.7K for the CCS line at 45 GHz. Since Robert mentioned CCS in the meeting, I also produced CDMS plots of the predicted intensity of CCS lines from 0-55 GHz at T=18.75K and T=37.5K. You can see that for the colder of the two temperatures, the intensity of the 52 GHz line begins to drop off compared to the 45 GHz line. Because CCS is a good tracer of chemical evolution in pre-protostellar gas, one would expect it to be useful to be able to observe these two lines with ALMA in concert with VLA observations of the lower-frequency lines in K-band.
  • Emerson notes: Doing a cut-and-paste from an NTIA document "RADIO ASTRONOMY SPECTRUM PLANNING OPTIONS," the precise allocated bands around 30 GHz and above are:
    • 31.3–31.8 GHz Primary Shared with Earth exploration-satellite (passive) and space research (passive) services. (FN: US74, US246)
    • 42.5–43.5 GHz Primary Shared with fixed, mobile (except aeronautical mobile), and fixed satellite services. (FN: 900)
    • 48.94–49.04 GHz Primary Shared with fixed, mobile, and fixed satellite services. (FN: 904, US264)
    • 51.4–54.25 GHz Primary Shared with Earth exploration-satellite (passive) and space research (passive) services. (FN: US246)
    • 58.2–59 GHz Primary Shared with Earth exploration-satellite (passive) and space research (passive) services. (FN: US246)
    • 64–65 GHz Primary Shared with Earth exploration-satellite (passive) and space research (passive) services. (FN: US246)
    • Caveat: it's possible that the precise numbers have changed since that NTIA document was produced, although I think they're all still valid.
  • RichardHills: Bojan and I looked at the atmospheric emission issue a little while ago. We discovered that there was a big difference between Scott Payne's AM and the Cernecharo/Pardo ATM result when you get close to the O_2 band. We checked with other models and ATM seems to be the more accurate. I think Scott warns that his model does not treat the O_2 absorption rigorously. Here are some plots ATM (pdf). I have included a crude indication of possible system temperatures. (Note that this also revealed a defect in the ATM which is that there are steps in the values, e.g. at 42GHz, as can just be seen int he plots.) My conclusion is that, unless there is a particularly important line that would be missed, there is not much point in going above say 51GHz because the noise temperature is going bad so fast. If one sticks to the 1.5 to 1 frequency range that would put the bottom end at 34GHz. The preferred continuum band would then presumably be 34 to 42GHz. The slightly higher system temperature, compared to say 31 to 39GHz, might be balanced by higher aperture efficiency, but that would need to be checked.
  • BojanNikolic: AM vs ATM difference: yes, we exchanged emails with Scott on this and the difference is because AM does not take into account the effect of mixing of the overlapping O2 lines (see e.g., Liebe, Rozenkratz papers). ATM does take this into account. I have checked both AM and ATM against absolutely calibrated sky brightness measurements around 50 GHz and it is clear that ATM is much closer to observations in this frequency range. I believe this mixing effect is only significant for the the O2 line complex, so the accuracy of AM should be just fine outside the 50-60 GHz range.
  • EricBryerton: Current plan for Band 1 LO is a low-side LO tuned from 27.3-33 GHz to downconvert the 31.3-45 GHz sky to 4-12 GHz IF. Extending the upper sky frequency to 51 GHz means that the image frequency (the lower sideband) will now be 15.3-39 GHz and overlap the sky frequency. Therefore, the mixer (Schottky mixer, following the LNA) will need to be a sideband-separating mixer (rather than simply a 31.3-45 GHz bandpass filter followed by a DSB mixer). There would still be a 31.3-51 GHz bandpass filter before this mixer, so for LO tunings above ~35 GHz, the image rejection of the receiver would be determined by the image rejection of the sideband-separating mixer, and therefore not as good as a filter (only ~15-20dB, similar to 2SB SIS bands). So, the quick answer is yes, you can extend the upper frequency to 51 GHz, but the image rejection in this extended part of the band won't be as good. We could perhaps think up a double-conversion scheme. This increases dramatically the risk of spurs (doesn't matter in interferometric mode), but would improve image rejection in the high end of the band. This would also require another fixed-frequency phase-locked LO.

Calendar

  1. Next meeting is on Dec 16th (14:30 UT). Jan 20th 2010 for the following month.

Events of Interest

(see also Al's ALMA Biweekly Calendar)

2009
 
 
 
 
 
 
Day
Date
Time
Event
location
details
 
 
Nov 16
 
ALMA AAER
Santiago
 
 
 
Nov 18
 
Sci IPT
telecon
 
 
 
Dec 16
 
Sci IPT
telecon
 
 
 
Jan 20
 
Sci IPT
telecon
 
 

Upcoming Meetings

Astrobiology Science Conference 2010 April 26-29, 2010 League City, Texas

Recent Meetings (presentations online)

Science at Q Band Sep 14-15, Manchester

Mass Assembly and Star Formation History of Galaxies Sep 21-24, Charlottesville, Virginia

To the Edge of the Universe: 30 years of IRAM Sep 28-30, Grenoble

Data Needs For ALMA. Oct 5-7 Koln Germany

-- AlWootten - 2009-11-16
  • almaconfigsOct09.tar: A tar file containing both the new set of configurations and the old set. Ten locations in the outer arrays were changed.

Topic attachments
I Attachment Action Size Date Who Comment
Atmospheric_absorption_AT_ZENITH_from_ATM.pdfpdf Atmospheric_absorption_AT_ZENITH_from_ATM.pdf manage 32 K 2009-11-18 - 12:40 RichardHills  
Further_Note_on_change_to_the_Position_of_the_Northernmost_Pad.pdfpdf Further_Note_on_change_to_the_Position_of_the_Northernmost_Pad.pdf manage 114 K 2009-11-18 - 09:24 RichardHills  
IPFschematic_2010-2011__090930.pdfpdf IPFschematic_2010-2011__090930.pdf manage 49 K 2009-11-18 - 09:28 AlWootten 30 Sep Integrated Project Schedule
almaconfigsOct09.tartar almaconfigsOct09.tar manage 120 K 2009-11-17 - 09:20 AlWootten A tar file containing both the new set of configurations and the old set. Ten locations in the outer arrays were changed.
band1.pdfpdf band1.pdf manage 234 K 2009-11-18 - 12:03 ToddHunter atmospheric transmission from ALMA site from 30 to 55 GHz with Band 1 tuning range and a few spectral lines labeled
cdmsgraph.ccs.18.75k.pngpng cdmsgraph.ccs.18.75k.png manage 3 K 2009-11-18 - 11:22 ToddHunter CDMS intensity plot of CCS lines from 0-55 GHz at T=18.75 K
cdmsgraph.ccs.37k.pngpng cdmsgraph.ccs.37k.png manage 3 K 2009-11-18 - 11:22 ToddHunter CDMS intensity plot of CCS lines from 0-55 GHz at T=37.5K
Topic revision: r17 - 2010-08-02, ToddHunter
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