***************************************************************************** Science IPT Report ================== October-November 2002 2.9 Science IPT 2.9.1 Overview During October-November, Science IPT activity again centered on the final definition of the ALMA Configuration. Late November, a Level 2 Milestone was met by delivering the document containing the positions for the inner 172 antenna pads. The final configuration was considerably altered from the design approved by the JAO on 1 October due to a new, more accurate digital elevation model. Work commenced on design of a long baseline part of the plan, compatible with this new inner portion. There was also much activity on calibration. Final testing of one of the two amplitude calibration devices being considered for ALMA, the subreflector dual load device, commenced at BIMA. A plan for initial testing of the other device, incorporating a semi-transparent vane at the IRAM 30m, was discussed at a calibration telecon. Progress was made on the calibration memo review process. The project scientists continued to develop the science IPT organization and refine the Level 3 and 4 milestones. A lively and well attended "Science Operations with ALMA" meeting for the European astronomical community was held on November 8 at ESO Garching. 2.9.2 ASAC The Science IPT arranged the agenda and minutes for the ASAC telecons on November 6 and December 4, and commented upon the ASAC report to the ACC. Following the Chile ACC meeting, the ASAC Report was distributed to the Project and made public on the ALMA web sites. The ASAC has made the following recommendation to the Project on the baseline correlator following its December 4 telecon: "The ASAC has read with interest the proposal in ALMA Memo 441 by Escoffier and Webber to enhance the performance of the baseline ALMA correlator. The proposed enhancement will increase the number of channels in the wide band mode from 256 to 8192 points in each 2 GHz of the 16 GHz available and therefore allow for better resolution. The relatively small number of spectral channels currently available in the wide bandwidth modes is a major scientific limitation of the baseline correlator that would be remedied if this enhancement could be carried out. Therefore, the ASAC encourages the ALMA project to see if this enhancement to the correlator can be implemented within the baseline ALMA project." 2.9.3 Configuration Early October, the JAO approved the plan delivered by Conway for configurations covering less than 4km in extent. New data on the terrain at Chajnantor spurred revision of the array configuration to better conform to the landforms on the site. In particular, the site characterization group received the new aerial photographs and an autocad file of the site contours from the Chilean company Aerotop. Otarola and Holdaway converted the contour information into a digital elevation model (DEM) with 5m horizontal resolution and 0.5m vertical resolution which could later be turned into a mask for pad placement in the array optimization algorithms. They also studied the details of the new DEM and determined that it was of far superior quality to the old one, but that the coordinates showed a systematic offset from the UTM frame. Communications with Aerotop indicated that the coordinates were in fact not UTM and that the coordinate offset changes slightly over the image. Large offsets (>100 m) which were coherent over 1 km scales, but which varied over the 5 km x 5 km DEM, were found between the new and old DEM, and were attributed to errors in the old DEM. As a result, adjustment of the original pad positions was required to avoid quebradas and to more accurately place the centre of the array. At the end of November, Conway delivered the engineering specifications document for the inner 172 pad positions using the new DEM. The array was re-optimized to reduce sidelobes and the required precision on the station coordinates for uv coverage/beam constraint purposes has been quantified. Reconfiguration schemes for 4 antenna moves at a time rather than 3, and accomodation of observations at extreme declination (e.g North of +35 degrees) have been investigated. Conway also developed software to evaluate the beam and shadowing effects of having different heights for pads in the compact array, since this is an important specification for the cost of construction of the compact array. They will be submitted as a second specification document in December. Holdaway continued designing the interface from the largest Conway array to the more extended Y+ configurations. As the extended Y+ configuration has only the old DEM to guide its antenna placement, pad misplacement (e.g., onto the sides of gullys or other steep terrain) of the order of 100m is expected to be common, and this must be sorted out in the site surveying process. This process must be completed by the Level 2 milestone date of June 2003, with intermediate milestones in March 2003 (see Table). Figure 1. The inner 172 pad positions are shown upon a greyscale indicating elevation, ranging from 4800 to 5100m. The two yellow stars indicate the monuments 'Master 0' and 'Master 71' respectively. The green dotted line is the existing access road to the site from the Jama highway. The red line follows the pipeline and the red crosses note the crossing points along the pipeline. [Figure to be provided by Al Wootten] Figure 2 The ALMA Compact Configuration. Contours are at 0.5m intervals. [Figure to be provided by Al Wootten] 2.9.4 Calibration Butler, as leader of the Calibration Group, together with Wootten organized and moderated two ALMA Calibration Group telecons. Reviews of memos were discussed and minutes of the meeting are available. Several memos will be revised; in particular, Mangum revised ALMA Memo 434 on "Load Calibration at Millimeter and Submillimeter Wavelengths" in light of the reviewers' comments. Final testing of the subreflector dual load device for amplitude calibration commenced at BIMA, involving Mangum, Bock and Welch. Carter and Navarro, together with Martin-Pintado and Cernicharo, have designed a device to test the alternative semitransparent vane calibration scheme at the IRAM 30-m telescope. The device will allow to check the main assumptions of this calibration scheme and to establish the typical accuracy one can achieve with a single dish telescope. A draft document describing the tests to be performed will be circulated in the Calibration Working Group before the Leiden December meeting. Bacman, together with Guilloteau, has started working on the bandpass calibration. They are considering separating the bandpass calibration into "large scale bandpass calibration" (atmosphere+antenna+receivers) and "fine scale bandpass calibration" (downconverter+digitizers+filters). This way, three steps would be needed for the calibration: a wide-band calibration with one receiver, a wide band calibration with a second receiver (so that the contribution of the common acquisition system can be eliminated by taking the difference), and a narrow (i.e., in user configuration) band calibration. The ATM atmospheric modeling package, written by Pardo, Cernicharo and Sempere, is currently being transformed and cleaned by Pardo for specific use in the ALMA project. The current version performs forward radiative transfer calculations in user-defined bands, providing atmospheric brightness temperatures, opacities and H2O phase factors (deg/mm) for phase correction. It also allows to retrieve water vapor columns from radiometric data from devices like WVR's. The package is being installed in an array simulator, written by Viallefond et al., where it is tested for many different ALMA uses. Improvements suggested after a meeting of the software ADACE group in Grenoble are being implemented. Van Dishoeck and Guilloteau planned a joint ALMA/Herschel-HIFI calibration meeting, to be held in December in Leiden. In the next quarter, there are many upcoming Level 3 Milestones on calibration, leading up to the Level 2 Milestone of September 2003 to have a complete calibration plan. This includes: phase, amplitude, bandpass, polarization, antenna location, illumination offset, pointing , focus, delay, opacity, and decorrelation correction. The first milestone is a draft of the calibration requirements document to be produced for reviews in December 2002 and finalized by February 2003 (see Table). This is a modification of Chapter 3 of the Project Book, complete with scientific examples for drivers. The Project Scientist issued a call to the ASAC during November to provide some examples for this exercise. Two milestones during the upcoming quarter lead to the June 2003 Level 2 Milestone of the review of how calibration requirements trickle down to instrumental specifications, including special calibration devices. Leading to the September 2004 Level 2 Milestone on WVR strategies (Level 2), a December 2002 Level 3 Milestone will present a draft document on technical aspects of the WVR, along with the Front End IPT. There is concern whether the Level 2 milestone of "Review of tests of calibration strategies on prototype interferometer complete" can be met by December 2004. Although most elements of the prototype interferometer will be in place at the ATF by early 2004, the prototype receivers may not arrive until mid 2005 for testing later that year. The Science IPT believes that this must be done earlier, if these calibration tests are to involve the actual ALMA receivers. Differences between the evaluation receiver interfaces and those of the prototype receiver suggest that substantial work would be required to implement the evaluation receivers for the prototype interferometer. The project should construct a plan for component verification at the prototype interferometer as soon as possible. 2.9.5. Site Characterization As described in 2.9.3, a new map of the site, much more accurate than those previously available, was delivered. Radford and Nyman, as subgroup leaders, held an organizational meeting and proposed a plan for construction phase activities. Radford spent much of November at the site upgrading, repairing and testing NRAO equipment--this included replacement of computers for the 225 GHz tipper and the Site Testing Interferometer, installation of two new surveillance cameras, reinstallation of the seismometer, restarting the lightning detector, installing updated radiosonde software and diagnosing and repairing the submillimeter tipper at Sairecabur. Radford also observed with the SAO team at Sairecabur. Similarly, Rivera and Perez spent much of this period repairing and maintaining the ESO site-testing equipment. Together with Rantakyro and Nyman, they are continuing Delgado's work on atmospheric phase correction by means of the differential analysis of PWV data and by correlating these results with the residual phase noise measured with the site testing interferometer. Holdaway and Otarola have started to investigate whether current models can predict weather and atmospheric conditions at the site at different timescales sufficiently accurate to help planning more efficient and safe site operations. Butler and Holdaway held discussions on site data analysis, particularly on water vapor scale height and on the hygrometer data. 2.9.6.Science Software Requirements Myers continued to work with the Science Software Requirements group on audit requirements for AIPS++. Mangum, Lucas and others also work with this group. See computing IPT report for more details. 2.9.7. Imaging Holdaway has added 1/f noise to the total power atmospheric simulations, which observe in both beam-switched and on-the-fly modes. He has also started to investigate the effects of different levels of receiver stability on the images. Holdaway has made a preliminary study of a fast switching decorrelation correction, in which the atmospheric phases measured on the calibrator are used to estimate not only the mean phase correction to apply to the target source visibilities, but also the degree of decorrelation to correct the amplitudes by. This work indicates that the correction works well to correct the flux scale and recover the correct peak flux, but that it increases the image noise level. More detailed studies will follow. 2.9.8. Meetings, Outreach and Public Education Most of the NA Science IPT, along with Conway from the EU Science IPT, met face-to-face in Tucson in October during the site PDR, whereas most of the EU Science IPT met in Garching in November, to refine Level 3 and 4 milestones. Several Project Scientists telecons, joint NA/EU Science IPT, NA Science IPT and EU Science IPT telecons were held. Guilloteau and Wootten attended the ALMA Front-end specifications and requirements meeting and the Back End LO design meeting in Charlottesville. Most of the EU Science IPT will meet during a three-day workshop in Leiden in December, focussing on calibration issues. Guilloteau, Wiesemeyer, Gueth, van Dishoeck and others organized the third millimeter interferometry school held at IRAM Grenoble September 30-October 5. This school was attended by 52 PhD students and postdocs from many different countries and nationalities. Lectures were provided by Guilloteau and several science IPT members (Gueth, Hills, Dutrey, Lucas, Pety, Pardo, and van Dishoeck), and included talks on ALMA. A European "Science Operations with ALMA" meeting was held on November 8 at ESO, organized by van Dishoeck and Shaver. The meeting was very well attended, with the ESO auditorium filled to capacity (~100 participants) leading to lively discussions. The aim of the meeting was to inform the European astronomical community of the status of the ALMA project and to sollicit feedback from the community on specific operational issues, in particular the planning for the European Regional Support Center. Details of the program and presentations can be found at http://www.eso.org/projects/alma. A questionaire was distributed to the participants afterwards, with responses due in early December. Van Dishoeck, Cox, Booth, Shaver and Richer continued to investigate possibilities for EU support for ALMA within the Framework 6 program, which included a visit to meet with representatives of the program at the European Commission in Brussels on October 18. Wootten visited with scientists at the Arizona Radio Observatories during his trip to Tucson in October. Van Dishoeck gave several seminars and public lectures on science with ALMA to Dutch communities, including a presentation at an astrophysics symposium at the Technical University of Delft on December 3, attended by 270 students. Table with upcoming milestones Milestone Level Scheduled completion Status Revised configurations 3 March 2003 in progress incl. Y+ after site survey Draft configuration antenna 3 March 2003 in progress motion logic Calibration requirements 2 February 2003 in progress review Draft specifications 3 March 2003 in progress calibration devices Draft calibration plan; 3 March 2003 in progress many individual components Draft WVR technical 3 December 2002 near completion aspects (with FE IPT)