10. Calibration, Imaging and Science July 2000 Report Major accomplishments July 2000 I. Imaging - Configuration Studies, Site and Water Vapor Radiometry A. Configuration Studies To spur on the imaging simulation work as a test of the competiting strawperson configurations, Yun started some imaging simulation using UVCON in aips. Various procedures were corrected and problems solved after some discussion among Yun, Butler, Conway and other people in the configuration working group. Multi-configuration imaging is identified as a potentially important additional issue for the array design and imaging. Steven Heddle (ALMA/Eu) has made significant progress in getting the aips-based "black box simulator". A worldwide teleconference on configuration progress will occur in late August, before the ASAC meeting. Yun discussed various options for the configuration PDR with Al Wootten. Although a detailed report will be given to the ASAC at their Berkeley meeting, it appears that the PDR should not occur before later this year. The result which is emerging from the simulations is that pointing errors dominate differences due to choice of configuration style. This suggests that operational considerations may be of more weight in the final choice of configuration than was originally thought. B. Atacama Compact Array Wootten circulated a document to the ASAC summarizing thoughts of many people on the ACA. A memo from Stephane Guilloteau was also circulated giving his views on the Atacama Compact Array, ACA. The ACA was discussed in the Imaging and Calibration Group meeting held on 18 July. Some points needing clarification surfaced. Yun announced his departure for a faculty job at U. Mass. effective September; until then he leads configuration studies as well as evaluation of the parameters for the ACA. He continued with the single pointing simulation to evaluate the imaging performance of the 6m versus 8m antennas for the ACA. In particular, the impact of pointing error was examined. These simulations and other discussions within the configuration group suggest that simulated mosaic observations are truly needed and important in addressing this question. To this end, investigation of the use of aips++ for these simulations was begun. C. Site Radford conducted a trip to Chajnantor. He also received the Inmarsat M4 (ISDN) terminal and initiated comissioning paperwork. At Chajnantor Radford conducted field work with Angel Otarola (ESO) under clear weather. He restarted the multiwavelength submm tipper after software reinstallation. At 350 um, both tippers agree. The new tipper also shows interesting results at 260 and 200 um, the 'Superterahertz windows.' Radford also repaired the lightning detector PC, and performed data backup and computer maintenance for other instruments. He launched daily radiosondes and verified correct operation of backup radiotheodolite. We now are obtaining reasonable data through the Chajnantor winter on the atmospheric structure, which has been lacking. Back in Tucson, Radford updated web pages and data files for radiosonde and tipper data and began testing the new Inmarsat M4 terminal. Radford has continued some nutator design work. Butler continues analysis of this new data from the site. Wootten and Radford discussed plans for the nutator during Wootten's visit to Tucson. II. Calibration A. Interferometer/Antenna Amplitude Calibration Mangum finished and submitted ALMA memo (No. 318) on the general amplitude calibration problem. The emphasis of this paper is to determine the uncertainty of two variants of the chopper wheel calibration technique. In this memo, Mangum recommends a chopper calibration method which has the potential for allowing ALMA to reach the 1% amplitude calibration specification recommended by the ASAC. B. Pointing Calibration Mangum also worked on pointing with particular attention to the test antennas. (1) General: Continued work on a general description of the telescope pointing problem with an emphasis on requirements for ALMA. The stringent ALMA pointing specification will force us to adopt a much more detailed model for the refractive correction term to the pointing, and will require an accurate measure of the pressure, temperature, and relative humidity at each antenna. This requirement for accurate metrological information puts some stringent requirements on these measurement devices. Mangum is writing a memo on this. (2) Optical: Continued characterization of optical pointing system. Fabrication of mount and detector housing continues guided by ALMA antenna group. Loss of access to the 12 Meter Telescope will seriously hinder the development of this system. c. Other Butler brought up the concerns Napier had on beam squint in current optics designs for discussion at the 11 July ImCal meeting. The current proposal for receiver optics poses several problems in addition to this, which Butler will follow. III. Science A. ASAC Wootten arranged for the ASAC teleconference and he and Yun participated in the ASAC teleconference on the 10th. Wootten and Yun read and commented on the draft ASAC memoranda on receiver specs and SSR group report. Of particular concern was the issue of limited capability to switch between several different bands. Wild clarified the description of this spec to the our satisfaction. Wootten put together a tentative agenda for the September face to face meeting of the ASAC, and entered the minutes of the July meeting to the website, as well as arranging the August meeting, to be held 7 August. B. Imaging and Calibration Wootten held two meetings of the Imaging and Calibration group during July, at which issues dealing with configurations, the ACA, the volcanic eruption at Lascar, and other issues were discussed. He also visited Caltech, where the progress of submillimeter instrumentation at the CSO was discussed. An 850 GHz receiver providing T(DSB)sys=205K is now operational at the CSO. The progress of water vapor radiometry was also discussed, with Sargent and Carpenter. Installation of cooled 22 GHz radiometers continues at OVRO, with a goal of completing the system during the coming year. Woody will report on progress to data at the face to face ASAC meeting in Berkeley. Plans for next month Plans for the face to face ASAC meeting in Berkeley, including the agenda and reading material will be finalized by Wootten. Wootten and Butler will present a paper on ALMA capabilities for the detection of Extrasolar Planets at the IAU meeting on this subject. Wootten will also present a report on ALMA at the Observatory Reports session of Division X, as well as attend the ALMA presentation by Kawabe at a Joint Discussion on radio continuum and line observations of distant weak sources. The most pressing issue for now is the imaging test for the ALMA Complementary Array. Yun plans to concentration on this effort during August. Yun will investigate using aips++ in simulation efforts. The simulation efforts will reach a point where the basic simulation procedure is agreed upon, and results exist for parameters agreed upon at the March face to face meeting for presentation to the ASAC. During August, the calibration scheme for the array will be sorted out for presentation to the JDRG meeting and the ASAC meeting in early September. Yun will convert the web report on the double-ring/donut strawperson configurations into a more detailed write-up. Two memos are in draft form, and these should be finished and submitted to the memo series. Issues and concerns Water vapor radiometry continues to be a key element of image production with ALMA. Efforts at the VLA have been impeded by resignations of key people (who, in any event, were not supported by ALMA). At IRAM, closure of the interferometer has been a problem. The MDC effort provides the backbone of research in this important area. It appears that portions of the configuration group are investing more effort than others in the imaging simulation and configuration evaluation. If Steven Heddle's work is productive, much of the basic ground work will be accomplished shortly. At that point, incorporation of other sorts of errors into the simulations can begin.