Notes, 2014 August 7
Attending: Bastian, Chen, Fleishman, Gary, Hills, Hudson, Shimojo, Wedemeyer
Absent: De Pontieu, Hales, Hurford, Krucker, Yan
Below are some brief notes from today's discussion. The next telecon will be two weeks from today at 1300 UT on Thursday, Aug 21. As always, please send corrections and revisions to me or to the team.
- Long baseline campaign - update on SD fast scanning tests (Richard)
- Richard will be going to Chile for the campaign the last week of August through the first 3 weeks of September. The single dish fast scanning components of the campaign will be executed during the first week of September. Although plans have not yet been fully developed, they will be available for comment at the following ALMA twiki site that Richard distributed during today's meeting:
- Presumably the solar tests performed in September by Richard and his team (albeit at lower priority than other pressing issues) will inform our own choices regarding the solar campaign in December.
- ALMA MD mode tests 3.1
- Pavel had earlier informed me that 27 antennas were tested in MD mode in band 3; and 17 in band 6. The MD mode behaves as expected. The data were acquired on Jul 10 and Jul 22. However, the LO and BB settings were not the optimum values on these dates. The values adopted for "standard frequencies" from Hills et al were used for tests on July 28. Pavel will comment on those data soon.
- ALMA MD mode tests 3.2.1 and 3.2.2 - results so far
- A summary set of notes regarding tests under 3.2 were attached to the agenda. The results for relatively strong calibrators looked quite promising, with the closure phases and amplitudes as expected. Richard reminded us that so long as we can solve for the complex gain of each antenna in MD mode on a calibrator, there is no need to also measure the complex gain of each antenna in SM. Nevertheless, it might be interesting to observe a calibrator with all antennas in MD mode and then switch to all antennas in SM mode in order to look at the differential phases.
- We discussed the need to measure the diff'l phase introduced by the different attenuator states used between solar and calibrator scans. We will discuss the test approach offline. Some lab measurements would also be useful. We note that the attenuators in use with ALMA are the same as those used by the Jansky VLA. Bin Chen looked into the problem of the phase shifts introduced by the stepped attenuators as part of his thesis work at the VLA. He circulated some figures and data files concerning the delta-phase introduced by the VLA input/output attenuators of the LSC converter. The ALMA IF band is 4-12 GHz.
- Richard pointed out that we also need to investigate the consequences of digitizing the data in non-optimum ways. The zero-point and the number of effective bits used to sample the signal may be out of range. We need to understand how forgiving, or unforgiving, the system is in various attenuator states. It should be possible to explore this question by observing a strong calibrator source and varying the attenuator settings.
- Discussion of December observing campaign
- Perform the campaign during the course of 1 wk (Dec 9-16) or spread the days over 14-16 days?
- The consensus seemed to be that a concentrated week would be better.
- Observing will likely occur from ~900-1300 daily, leaving plenty of time each day to reduce data and to consider next steps. Masumi pointed out that it will be very important to have robust scripts in place before the campaign so that the focus can be on the observations and the data. Presumably, if tweaks to the scripts must be made, they can be made transparently.
- Which team members are able to travel to Chile?
- At present, Shimojo, White, and Bastian can go. Richard is willing to consult with us on a daily basis. Roman Brajsa has informed me that he plans to be in Chile, too. It may be possible for one or two others to participate for all or part of the campaign. Please let me know if you have a strong interest in doing so. Otherwise, I very much hope that most, if not all, of you are willing to work with the campaign data!
- Launch of the simulations group (Sven)
- Sven has developed a prototype Solar Simulations for the Atacam Large Millimeter Observatory Network (SSALMON - cute). The link is: http://folk.uio.no/svenwe/ssalmon/
- It will serve as the central resource and repository for solar simulations work relevant to ALMA. He is going to coordinate with the EU group on its contest and use. He intends to launch it soon.
- The SSALMON web resource will be announced at the ESPM-14 in Dublin in September (http://www.espm14.ie/). Masumi will present a paper on ALMA solar observing at the LWS SDO/IRIS/Hinode workshop at Portland in November (http://lws-sdo-workshops.org/). And Sven will present a paper on ALMA solar work at the ALMA science workshop in Tokyo in December (http://www.eso.org/sci/publications/announcements/sciann14009.html)