ALMA

There are a number of milestones for the completion of ALMA. The largest is the contract for antennas, since this contract is more than 30% of the total cost of the bilateral (North America and Europe) ALMA. Here, we report the news on antenna procurement.

The ESO Council resolution from the meeting of 30 September states that “the ALMA project is affordable and compatible with ESO´s strategic priorities”. It further states that the ESO Council “requests the Finance Committee to proceed to decide on the proposal to award a contract for the production of the ESO ALMA antennas”. The ESO Finance Committee met on October 5, and has approved the negotiation and conclusion of a contract with the selected vendor. The approval of the ALMA Board will be sought for the award of the contract.

Another important milestone is the Front End Integration Center. The Band 3 (3 millimeters, or 84-116 GHz) and Band 6 (1.3 mm, or 211-275 GHz) Front ends are built in North America, while Band 7 (0.9 mm, or 275-373 GHz) is built at IRAM Grenoble and Band 9 is built at SRON, Groningen, Netherlands (0.5 mm, or 602-720 GHz). The decision has been made to have two Integration Centers, one in Europe at the Rutherford-Appleton Laboratory in Oxfordshire, UK, the other in North America, at the NRAO in Charlottesville.

With this level of progress, we are now much closer to the beginning of the assembly of individual components to produce a working system.

It is expected that the ALMA array will be used by a relatively large community of astronomers that are less experienced in using radio interferometers and/or doing science at mm- and sub-millimeter wavelengths. Therefore, it is of utmost importance to take this into account in development of software products that will eventually be used by the community.

Observing preparation

The ALMA Observing Tool (OT) will be the software tool that supports astronomers in constructing a full Observing Project for the ALMA Observatory. Basically, such Observing Programs will be submitted to the Observatory in two parts. The first is a Phase I Observing Proposal that will have its emphasis on the scientific justification of the proposed observations. The second part of the project is the Phase II Observing Program that can be submitted to the ALMA Observatory if observing time has been granted by the Time Allocation Committee (TAC) on the basis of the accepted proposal.

Central in the OT is the creating of a set of Scheduling Blocks (SBs) which are required to drive observing with ALMA. The SB is the smallest (indivisible) unit in ALMA observing that can be scheduled independently. It is self contained and usually provides scientifically meaningful data. The SB contains a full description of how the science target and the calibration targets are to be observed, and sets of SBs can be combined with a description for the post processing of the data, ultimately resulting in an image.

In order to serve both less experienced and experienced astronomers, the OT will be equipped with two so called ‘Views’ to make Observing Program preparations. It is intended that the main view on the ALMA system will be the ‘Science View’. As the name indicates in this View the usercan concentrate on inputting the science requirements of their observing program: the area to be observed for each target, required sensitivity and frequencies. For most observing even experienced users should only need to use this view. The required SBs will be constructed by the system and the user will only be bothered with system parameters when this is absolutely necessary, in general detailed parameters will be determined from the science input.

However, it is recognized that for some programs, and indeed for developing new observing modes, an ALMA-experienced observer will need more. The ‘System View’ (or expert mode) will provide such a user with a complete set of parameter fields that enable a detailed specification of each scheduling block: the observing process of science and calibration targets, including data acquisition and reduction recipes. These parameters include the frequency setting of the local oscillator, the upper and lower side bands, the correlator parameters and the selection of the basebands and subband sets within each baseband.  Whichever ‘View’ is used, SBs must be created.

An interesting functionality in the System View that has been added recently is the Visual Spectral Editor. This will help somewhat experienced users to carefully position LO frequency, and the frequency characteristics of the basebands configuration within the ALMA receiver band. In the figure a part of this editor is visible. It shows the upper part of the Visual Editor display with the all ALMA Frequency bands (note that these will not all be available; see also here ), the transmission curve of the atmosphere over the full ALMA observable spectrum (note band 6 has been selected), the setting to the LO frequency and upper and lower side bands, and one baseband selection. A later version of this tool will aid less experienced observers, without subjecting them to the detailed setup.

The development of the Observing Tool is a shared effort between the UK Astronomy

Technology Centre in Edinburgh, ESO and the NAOJ, with science advice being provided from Osservatorio Astrofisico di Arcetri and the NAOJ. Development is currently focused on the Science and System View of the Phase II Observing Program definition. Work has been on-going for two years with a major and a minor release each year. User test cycles immediately follow releases of the software. Currently, it is planned to have four major user test sessions and three minor ones. The major user tests provide important and timely input feedback to the team for possible upgrades in the following releases and are performed by typically eight people. Minor test sessions are follow ups of the major releases but possibly include further tests and input for the development team toward the next major release. The next major user test will take place this November. It is planned to hold wider `beta testing’ in advance of the first release of the tool to the community.

Data reduction

All ALMA data will be reduced using the ALMA offline reduction and imaging package. This package is based on the C++ code base in AIPS++ but the code itself is undergoing some fairly major changes to optimize it for ALMA and the user interface is being redesigned. For many observations the automated calibration and imaging pipelines will produce reference images suitable for analysis.

During the past 1.5 years, ALMA has conducted external user tests every six months to ensure that the reduction software development is adequate for ALMA needs. This is an ongoing process designed to incrementally test functionality as it is developed. To date, three test cycles have been completed. The testing has focused on verifying that the underlying C++ code has adequate functionality and is robust enough for ALMA needs (e.g. make sure that users can process datasets from end-to-end using specific ALMA cases). The user interface (both the GUIs and the script language) will change significantly over the next several years and thus, current testing could not yet evaluate the robustness or user-friendliness of the interface. Essentially, if testers could do what was necessary to get a scientifically accurate image and evaluate the image quality (even if the syntax or process was a bit complicated) then the test was considered a success. User interface elements will begin to be tested in early 2006. External testers have been volunteers from the world-wide astronomical community. So far, only expert interferometrists have been asked to test the software. Later, when the new user interface is developed, also novice users may be asked to help with the testing. The tests have been successful to date - all testers have been able to fill, edit, calibrate, image, and analyze the test datasets. Based on these tests, it appears that the offline reduction and imaging package is on schedule for meeting ALMA data processing needs at the beginning of early science operations. For more details, see the AIPS++ homepage or the latest test report.

Rein Warmels and Debra Shepherd contributed to this text