Report for ALMA Calibration and Imaging April-May 2002 Progress Report Overview During April and May activities centered on the ASAC report to the ACC for its face-to-face meeting, and ALMA Week, held in Granada. Emphasis was placed on definition of the extended Y+ array, proposed in January at the Configuration CDR by Otarola. During this period a first memo was issued, detailing issues involving the configuration of such an array. The preliminary designs for configuration were moved toward finality and imaging simulations, expected during the next bimonthly period. With the imminent arrival of the first prototype antenna, calibration was also emphasized and formed the focus of a meeting during ALMA week. Issues identified during that meeting are enumerated below. ALMA Software and Simulations Mangum and Myers attended the SSR face-to-face meeting in Granada; results for this meeting will be found in the software report. Site and Configuration Site Characterization The Site Characterization group held a review at ALMA week, in conjunction with the configuration review. Angel talked to Lars-Ake Nyman (Head of the European Site Characterisation Group), about installing a weather station at a suitable and convenient place in Calama and to gather surface weather data with 1-5 minutes time-resolution. The idea behind having this weather station in Calama is to study possible correlations between weather data from Calama and Chajnantor that might help us to predict the mean atmospheric conditions at Chajnantor within 2-3 hours time-frame. Such a predictive model, if succesful, can be use as an input to any flexible scheduling scheme. Configuration Holdaway modified software from F. Boone for optimization of the Y+ array. Holdaway and Otarola published ALMA Memo No. 419, the first assessment of the so-called Y+ configuration. Otarola presented the results of his work with Holdaway on the Y+ array at ALMA Week. One objection to this array was that it might perform inferior astrometry to the ring array. Holdaway investigated this possibility. The 18 km Y+ and the 14 km Ring arrays will probably perform with similar astrometric accuracy. While the systematic phase errors are therefore not an issue for array decisions, they are still a problem worthy of study. Holdaway and Angel Otarola worked out a plan for their Y+ array work. This includes: * Modifying the current mask, using the modified Boone software to generate a better optimized Y+ configuration set, and putting this array set out as a memo so we can all play with it. * Numerical simulations to compare image quality of the Y+ and ring arrays. Calculations to quantify the sensitivity loss experienced by each array to get to some exact resolution. Calibration A calibration meeting was held during ALMA week. Bryan Butler was appointed Leader of the Calibration Group, with a message sent to IPT leads announcing this. Wootten set up an email exploder almacal@nrao.edu for discussion of calibration matters. This is an open list; anyone may sign up for it, filling in a form at http://listmgr.cv.nrao.edu/mailman/listinfo/almacal Wootten, Mangum and Radford made presentations at ALMA Week. Issues arising during the ALMA Week Calibration Meeting included: 1) Project Book: ALMA version, rather than current grandfathered version, to be produced. 2) Evaluate the dual load system on the Vertex antenna and the semi-transparent vane on the A/C/E antenna (or both on both). Both schemes are designed to contend with saturation in the front ends, a particular problem at lower frequencies. At higher frequencies, the dual load system is not well-suited to the problem and the semi-transparent vanes are not needed; controlled temperature loads will work there. Because of the interaction between front ends, antenna and the calibration system I think we need at least one receiver at the ATF ready to test when evaluation finishes on 1 Jan 2004. (I think it should be a prototype band in an RAL dewar with dual load cal system but...) Some major questions remain--for instance what are the standing wave properties of the semi-transparent vane system, and does the structure inherent in the ambient temperature semi-transparent membrance cause problems? Can we measure coupling of the dual load system well enough? Enumerating these is an action item for posing to the Calibration Group. 3) Photonic calibration should be oriented toward a tunable and/or broadband, amplitude stable device. Timescale required for amplitude of order of a few seconds. Phase noise to be stable over the same timescale. The need is for total power measurement of sideband rejection ratio, passband calibration, and possible polarization measurement, of the relative phase between the polarizations. 4) Compression. Guilloteau is deriving specs for compression (or T_saturation) using the semi-transparent vane system and reasonable assumptions; these can be passed to the front end group for discussion. 5) WVRs. There is good progress at Cambridge and Onsala on the next-generation machines, and at the SMA with using the previous generation in an interferometer. Atmospheric modelling goes hand-in-hand with this and is in progress. 6) Atmosphere. A discussion of an FTS for ALMA will go into the Project Book chapter, along with a short discussion of how ATM (the atmospheric modeling code) fits into the project. We need to consider how this and the network of sensing devices (I don't think any observatory with a telescope is so well-instrumented as Chajnantor is without one) provides feedback to the dynamic scheduler (which needs to be put back into the project). 7) Total Power. Holdaway is working on simulations of total power observations with ALMA (see below). Wootten reported on the Calibration Meeting at the DH telecon. Payne and Wootten discussed photonic calibration tests on the prototype antennas, developing a rudimentary testing plan for the ALMA prototype interferometer. Matt Carter is considering how to test the semitransparent loads on the prototype antennas with the evaluation receivers. Holdaway worked on residual atmospheric noise in beamswitched and On-The-Fly single dish measurements. This included OTF antenna trajectories, as Vertex has not really looked into the turnaround problem in much detail. The time derivative of acceleration, or "jerk", is instrumental in exciting vibrational modes. So, he calculated the maximum jerk in the fast switching antenna trajectories which Vertex has shared with us, and applied this limiting jerk to some OTF trajectories that Simon Radford made up. This is the Limited Jerk Method. Then in simulations the antennas slew with this trajectory under a moving simulated atmospheric water screen which is consistent with Radford's phase stability data and CRUNCH. Then one fits a baseline between the two OFFS, and calculates the residuals. This is all done in glish/AIPS++ and will result in a memo. Holdaway also began work on overhauling the Imaging and Calibration chapters of the project book. Outreach and Public Education Mangum, Wootten and Holdaway presented a poster at the Tucson debris disk conference. 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. There may not be much associated gas, so a kinematic signature would be difficult. The focus of the poster paper was on a system somewhat like rho (55) Cancri, as it has a warm Jupiter planet. HST fails to detect reflection of the dusty debris about this star by two orders of magnitude, debris detected by SCUBA on the JCMT only after hours of integration, debris which ALMA would detect in seconds, and debris whose pattern ALMA would image in a few hours. This would lead to the discovery of other planets, further from the star than the Jovian mass planet lying at 0.12 AU from the central star. The imaging would also resolve the inclination of the system; a check on this would be possible by measuring the stellar reflex motions with ALMA in its extended configuration. ISO and the JCMT had reported weak submillimeter signals from the dust which agreed with the simulation Lee Mundy had done of such a system. However, the JCMT result was apparently false, found at a position 30" from the star and most likely arising from a galaxy at high redshift. As the simulation need not be tied to a real system, it can be more hypothetical. Wootten attended the 'Astrophysics of Life' conference at Space Telescope Institute and presented a poster 'ALMA and the Astrophysics of Life' . This area is very NASA-centric yet there was a growing realization that ALMA would do much of which multimillion dollar spacecraft were being designed for. Mangum observed at the OVRO Millimeter Array. Science IPT ALMA Memos 427 Antenna Position Calibration Melvyn Wright (Astronomy lab, UC Berkeley ) 05/02 422 The Dual-Load Calibration device revisited S.Guilloteau (IRAM/ESO) 05/02 419 The Y+ Long-Baseline Configuration To Achieve High Resolution With ALMA Angel Ot rola (ESO) & Mark A. Holdaway (NRAO) 04/02 415 Phase Correction using Submillimeter Atmospheric Continuum Emission S.atsushita (CfA/SMA), H.Matsuo (NAOJ), M.C.Wiedner (CfA/SMA), J.R.Pardo (Consejo Superior de Investigaciones Cientificas/CalTech) 04/02 393 DSB versus SSB and Bandwidth/Sensitivity Tradeoff S. Guilloteau (IRAM) 5/02 372 An Amplitude Calibration Strategy for ALMA S. Guilloteau (IRAM) 5/02 Additionally, Mangum worked on an update of ALMA Memo 318 on amplitude calibration. Meetings Held ALMA/NA Imaging and Calibration meetings and list of topics discussed 9 April 2002 News; ASAC, Configuration Meetings, Calibration Discussion Materials, Project Book Update (v5.5 update) and ALMA week proto schedule. 16 April 2002 News; Calibration Discussion Materials, Exoplanet Research with ALMA and Project Book Update (v5.5 update) and ALMA week proto schedule. 30 April 2002 News; ALMA Week Reports and Discussion, Upcoming meetings. 17 May 2002 News; Y+ Array, Cal Group Forms, ApLife Meeting, Star Wars Review. 21 May 2002 News; Y+ Array Masks, SiteScape, Cal Group Issues. 28 May 2002 News; Y+ Array Masks, Cal Group Issues, Proto-memos 422 and 423. ALMA Science Advisory Committee Meetings and list of topics discussed Telecon on 3 April 2002: Project status, face-to-face meeting report to ACC, setting of dates for next meeting. Telecon on 2 May 2002: News, ACC meeting, ALMA Week reports, ASAC Charge ALMA Co-ordinating Committee Meetings Face-to-face meeting on 18-20 April 2002 Attended by Wootten ALMA Week Meetings Attended by Wootten, Mangum, Myers and Radford of the science group.