Report for ALMA Calibration and Imaging June-July 2002 Progress Report Overview During June and July activities centered on definition of the ALMA Configuration, providing ASAC support for their response to requests from the ACC, and on Calibration Group activities. The extended Y+ array configuration was refined and its imaging performance simulated. Code produced by the Paris group was modified to provide the refinements for this configuration, and also for the refinements of Conway's efforts to finalize the more compact configurations. With the imminent arrival of the first prototype antenna, calibration was also emphasized and ALMA Calibration Group Leader Bryan Butler, together with the Project Scientists, worked out a method of Memo Review to provide a mechanism for fleshing out of calibration specifications. Reviewers were identified and the process began during this period. Mangum worked on a revision of his treatment of amplitude calibration. With the SSR group, Myers worked on software audit requirements for ALMA. Radford worked with the ASAC on the definition of stringency using Chajnantor data. Wootten organized these efforts, ASAC meetings, pursued outreach and public relations activities and other Project Scientist/NA duties. ALMA Software, Simulations and Scientists Myers continued to work with the Science Software Requirements group on audit requirements for aips++. Mark Holdaway also spent some time working on the VLA and BONN data for a giant L-band mosaic of the Galactic Center. This project is being imaged in AIPS++. Earlier, the image quality had been limited by the PSF sidelobes scattering flux from the bright SAG A and SAG B sources as they leaked into the outer feilds through unmodeled sidelobes in the primary beam. A complicated script images the emission from each field along with the emission from SAG A and SAG B, and then if SAG A and SAG B are outside the primary beam, subtracts the confusing SAG A and SAG B emission from the Fourier plane. The residual visibilites are then more consistent with the primary beam model (sans sidelobes), and can be mosaiced. A defect in AIPS++'s position shifting had prevented this from working earlier, but that defect has been resolved and progress has been made. Several ASAC meetings were held. Primary topics for discussion included the charges from the ACC to the ASAC through the Project Scientists, and the face-to-face meeting to be held in Socorro in September to discuss these charges and provide a response to the ACC. In summary, that meeting will include: Friday Sept 6: Visit Vertex antenna at ATF pm Sept 7-8, meeting at AOC Sept 9 fly out to next meeting or home Together with Cox and Wilson of he ASAC and van Dishoeck and Guilloteau, Wootten worked on the agenda and plans for the meeting. He arranged a telecon for 23 July on this subject, and participated in discussions with members of the subgroup for this charge. An action item was to provide sensitivities for intermediate populations of ALMA antennas and those for competing arrays, such as CARMA. These were calculated and provided to the group. At its June 5 2002 teleconf, the ASAC was requested to `summarize the scientific and technical issues associated with the long baseline array geometries currently under consideration and to advise the ACC/ad hoc ALMA Board as to possible cost, land use, and land access impacts of which it should be aware'. The Imaging and Calibration Group, led in this effort by Holdaway and Otarola, provided designs for the array and simulated images employing it to the ASAC. As a result, the ASAC recommended to the project to abandon the 14-km Ring Configuration, and to work on optimizing an Y+ configuration with similar angular resolution. The group also discussed band edges, defining a response to the 3mm rx review on performance at various spots within the band, and on the upper edge of Band 7, for which the ASAC requested an extension of from 370 GHz to 373 GHz. One question from the 3mm receiver design review was what the sensitivity should be at the band edges, particularly near the CO 1-0 line. The group thinks that since in this region the atmosphere is the limiting factor, poorer receiver performance can be tolerated up to the point where sensitivity is no longer dominated by the atmosphere. Best performance should be in the 90-95 GHz region, where we expect workhorse use for phase correction. In the extension 84-90 GHz, the ASAC opined that poorer performance could be tolerated. Wootten also pursued an ASAC request for extension of the upper edge of Band 7. John Webber checked with Eric Bryerton about reaching 373 GHz with Band 7. The LO is not a problem. It is now specified within the Front End LO group that the LO will reach the nominal band edges so that mixer designers can test performance beyond the nominal band--useful for evaluation. Thus, the actual LO frequency will go to 370 GHz for Band 7. Site and Configuration Site Characterization One of the ASAC charges from the ACC dealt with site characterization. Radford, working with an REU student, analyzed the site data in the manner requested by the ASAC and worked with the Working Group toward their response to the ACC. Mark Holdaway is also revisiting the problem of simulating imperfect atmospheric emission cancellation in beam switched and On-The-Fly total power observations. Configuration ALMA Inaging and Calibration had a discussion concentrating on image performance of the strawman Y+ array design and Mel Wright's memo on the compact configuration. Mark Holdaway has spent most of his time this summer working on the Y+ configuration. This work falls into three categories: modifications of Boone's code to improve the optimization of the Y+ configurations generating various styles of Y+ configurations for comparison and costing performing imaging simulations of some of the Y+ configuration options Mark will make a final Y+ configuration set after John Conway has provided the locations of the antenna pads for the other configurations. The Boone software has been optimized conditions appropriate to ALMA. Two sets of configurations were defined for the tight and loose mask constraints. Together with ring configurations, and VLA-style wye configurations, imaging simulations of these three hybrid configurations have been performed. The spiral-ring hybridization, tapered to yield a circular beam, performs about as well as an intermediate Y+ configuration (sometimes a bit better, sometimes a bit worse). The highly tapered ring array also has an excellent beam, but here, the extreme loss of baselines begins to take its toll and results in significantly poorer image quality. There appears to be little or no penalty in imaging quality for the Y+ configuration. Calibration Mangum worked on an update of Memo 318 in which he generalized the chopper calibration discussion and included an analysis of the semi-transparent vane and two variants of the "dual-load" calibration system. Even though he took a different approach with the current analysis, there are no significant differences between the new analysis and those presented in Memo 318. Some of this work occurred during a visit to Charlottesville for various face-to-face discussions. Mangum also spent a week at Hat Creek working with Douglas Bock and Jack Welch on some tests of their dual-load amplitude calibration system. Very good progress has been made on this device. This device now produces an incredibly stable total power difference signal which remains stable over time scales of at least several days (the duration of our tests). Wootten attended a meeting at the CDL with receiver engineers to discuss Band 6 IF choices (some addressed in Memo No. 393 by Guilloteau). We have basic agreement with Guilloteau on all points except his point no. 2: 'Receivers for band 3 to 7 should be 2SB, 4-8 GHz IF mixers. This offers the best compromise in performance and saturation level. ' Saturation should not depend upon the bandwidth of the output IF amplifiers Spectrosopically, the most important consideration is frequency access. Of two possible flavors of Band 6 design, one 2SB 4-12 GHz IF and one 2SB 4-8 GHz IF the former provides the most flexible frequency access at very little cost in sensitivity; furthermore the mixer-amplifier combination has been tested. A larger available swath of spectrum allows the astronomer to reach a larger range of spectral lines appropriate for measuring physical conditions. A broader IF provides the most seamless coverage of an object's spectrum. A redshift search benefits from integrating over a larger frequency range in a single observation. We concluded that scientific considerations favor a 2SB 4-12 GHz IF design. The Calibration and Configuration group have adopted standards for refereeing proposals relevant to their areas; reviewers were appointed for memos by Calibration Group Leader Bryan Butler. Finally, Mark Holdaway spent some time thinking about the proposed scheme of using a laser range finder at the prototype antenna's prime focus to measure the distances to a host of retroreflectors and infer information about the surface shape from these measurements. Outreach and Public Education During the summer, NRAO has provided summer research opportunities for forty-three years, and more than eight hundred students have benefitted from the program. Mangum runs the REU program in Tucson; Wootten in Charlottesville. In Tucson, Mangum took the students to the AOC, VLA and ATF in addition to lecturing on ALMA Science. In Charlottesville, Wootten escorted students to Green Bank, West Virginia, and gave several ALMA-related lectures. In addition, the hundred and fifty attendees of the Synthesis Imaging Workshop in Socorro were provided a tour of the ATF featuring the VertexRSI antenna with Mangum, Wootten and David Woody of Caltech to answer questions. Wootten gave them a lecture on ALMA: 'We're Building It For You' to foster interest in ALMA science. Feedback from the evaluation sheets suggested that the students were enthusiastic about ALMA. Wootten presented a poster at 'Scientific Frontiers in Research on Extrasolar Planets,' a symposium held at the Carnegie Institution of Washington, featuring how ALMA will contribute to this subject. About half of the 90 odd exoplanets in the databases should have a wobble detectable by ALMA. Three planets will be brighter than 1 microJy, assuming Jovian characteristics. These won't be detectable without heroic effort. Any debris worthy of the name will be detectable easily with ALMA. ALMA's role in characterizing planets around known exoplanet systems is through astrometry, through detection of residue disks and through direct imaging of protoplanets. With Mangum and Holdaway, Wootten finished a paper on the contributions ALMA will make towards understanding planetary debris disks and submitted it for publications to the proceedings of that April Symposium. Mark showed that ALMA can easily (one transit) image a nearby (12pc) debris disk of about half a lunar mass (about what the Solar System has in the Kuiper Belt/zodiacal dust) in the continuum. Wootten also completed and submitted a paper on ALMA for the SPIE symposium in August. Science IPT ALMA Papers 'The Atacama Large Millimeter Array' A. Wootten, invited paper in Proceedings of SPIE Vol. 4837 'Large Ground-Based Telescopes.' 'Debris Disks, Planetary Systems, and The Atacama Large Millimeter Array A. Wootten, J. Mangum and M. Holdaway, to appear in Debris Disks and the Formation of Planets: A Symposium in Memory of Fred Gillett Science IPT ALMA Memos 428 Compact Configuration Evaluation Melvyn Wright (Astronomy lab, UC Berkeley ) 06/02 ALMA Science Advisory Committee Meetings and list of topics discussed Telecon on 5 June 2002: Project Status, Charges from the ACC, Calibration Group Telecon on 3 July 2002: Status, Charges from the ACC, Software Report, September Agenda