Draft section for ASAC report for Charge 3 ------------------------------------------ Chris Wilson, 26 August 2005 The text of Charge 3 for the October 2005 ASAC meeting is as follows: "Following from your Sept. 2004 discussions, the ASAC is invited to continue developing proposed "demonstration science" guidelines or policies. The ultimate goals include: a. providing a proposed framework (rationale, principles) that establish the value to the astronomical community of accomplishing demonstration science as you envision it during the early operations era; and b. facilitating evaluation of the concept, its proposed timeline and the planning for its implementation during a period when demand for ALMA construction and operational resources will likely be high" Background: ---------- The concept of "demonstration science" first appears in the May 2004 ASAC report, where the ASAC recommended that the ALMA project focus on exploiting its high resolution and high frequency capability to maximize its early science impact. The ASAC recommended that these projects have community involvement and recognized that multi-configuration observations would be required. The ASAC also identified two categories of science demonstration projects: public demonstration images for publicity and the general public, and science demonstration projects to demonstrate ALMA's capabilities to the general community. The September 2004 ASAC report elaborated on demonstration science by recommending that they be carried out from end-to-end by a team of community astronomers and ALMA experts. The ASAC also cautioned that it would be unwise to attempt this too soon, as it would be hard to demonstrate ALMA's superior capabilities with only a few antennas. The ASAC suggested that demonstration science should take place before the first open call for proposals and that demonstration science should be delayed until ALMA has about 16 antennas. Clarifying our terms: -------------------- The draft ALMA Commissioning and Science Verification (CSV) Plan (2004-09-03) covers the period up to but not including Early Science. It describes demonstration science as being part of the science verification process. Science verification, in general, tests the system end-to-end (from proposal submission to final science) and involves outside observers. In comparing this document to the two ASAC reports, it becomes apparent that there is some confusion on what is meant by demonstration science and what is meant by science verification and how the two are related. First, we assume that science observations during commissioning are primarily of well-known sources to test that the array is working properly and would not involve external users. Then, we suggest replacing the original term "demonstration science" as used in the ASAC reports with the following two definitions: (1) Science verification (SV) = end-to-end test of an ALMA mode done using a science project proposed by an external user; this usage is consistent with the draft CSV plan (2) ALMA Public Image (API) = large-scale project whose primary intention is to convince wider community/public of the value of ALMA These two types of observations have different requirements and pose different constraints on ALMA and so they are discussed separately below. Science Verification: -------------------- Each mode of ALMA that will be used for early science must be tested by one or more projects in an end-to-end fashion. These tests should be done by a combination of commissioning observations of well-known sources and SV observations of scientifically interesting targets. These observations could also serve to demonstrate what ALMA can do to the broader astronomical community. Some of the SV projects (particularly the high frequency ones and high resolution ones) may be sufficiently interesting to get the wider astronomical community interested in ALMA. The APEX commissioning experience suggests that it will be possible to have a big impact with observations at high frequency because the site is so much better than Mauna Kea. Ideally, science verification projects should provide novel and unique information with professional appeal and are also important to show astronomers who are not familiar with radio interferometry what ALMA can do. This "professional publicity" role for science verification adds extra importance to these observations and implies that, once started, completing a given science verification project should be a high priority The CSV plan proposes that the science verification team be responsible for the selection of a small number of proposals of scientific interest. It would be good to supplement them with a proto-TAC or an advisory group with a broad range of scientific interests. ALMA staff would need to be involved to assess feasibility and the process would need to be light and nimble. Again based on the APEX experience, we should expect a strong response to any call for science verification projects. One issue that needs to be considered is whether science verification projects will be limited to a single configuration or allowed two configurations (i.e. compact and extended). One possibility is that the call for proposals for SV project could be very specific about the type of project required (such as 3 mm spectral line mosaic of a 4x4' region with 5" resolution, or observations at any wavelength of a single pointing on a moving target). Another possibility is to chose some projects which can be built upon in the future as ALMA grows more powerful, e.g., a low-resolution mosaic of a star-forming region to which higher resolution data could be added later. The CSV document suggests that very limited reconfiguration will occur during early commissioning (that is, the commissioning before early science) and notes that scheduling the multiple array configurations required to produce pretty pictures for demonstration science is a concern. It is important that new pads are commissioned in an order that allows good imaging with ALMA as larger configurations become available. Both commissioning and science verification are activities that will not be finished until all the modes of the completed ALMA have been tested. However, although science verification observations would continue to be carried out for new modes of ALMA as construction continues, they are expected to have less impact on the community in the later construction years, when many modes and a large fraction of the total time will be available for normal observing with ALMA ALMA Public Images: ------------------- Good publicity images will be important for ALMA to show progress in construction to the public and the funding agencies. Ideally, these images would be made as early as possible. However, the fundamental difficulty is that it is difficult to make pretty images with good publicity value with only 6-8 antennas in the array. One possibility would be to defer the first public images until ALMA has more antennas and making images is easier. However, we should not underestimate the importance of producing one or more splashy images suitable for the general public, funding agencies, etc. One alternative would be to generate a pretty image of one or two sources by careful choice of science verification projects. For example, if the ALMA project was careful to always observe some unique southern source (eta Carina, the Galactic Center, or Cen A spring to mind) in small mosaic mode with the appropriate correlator setup in each of the 6 early science configurations at one of the higher frequencies (Band 7 or 9), those data should produce a pretty spectacular image. Note that this approach also implies that individual pad should be commissioned in a sensible order so that good imaging configurations are available (see previous section). If early API observations are made with relatively small numbers of antennas, it would be worth considering a second round of API observations when ALMA has 25 antennas or so. These images could illustrate the improvement in the capabilities of ALMA as it grows, and would probably not impose a significant burden on ALMA construction or operations. Specific response to the charge: ------------------------------- a. providing a proposed framework (rationale, principles) that establish the value to the astronomical community of accomplishing demonstration science as you envision it during the early operations era; and Science Verification (SV) observations, as described here, play a critical role in the successful construction of ALMA. They also serve an important role in involving the broader community in early use of ALMA. ALMA Public Image (API) observations, as described here, are aimed at the general public, funding agencies, etc. Although they do not play an important role in the actual construction of ALMA, their overall importance to ALMA should not be underestimated. It should be possible to construct one or two early API projects from careful choice of SV projects, e.g., by observing the same unique southern source in several different configurations. b. facilitating evaluation of the concept, its proposed timeline and the planning for its implementation during a period when demand for ALMA construction and operational resources will likely be high" Science Verification observations are closely tied to commissioning observations. The first SV observations could be made as soon as soon as a single mode of ALMA has been commissioned. Additional work is required on the logistics of SV observations e.g. how to get the word out to the community, the role of the TAC, the degree of focus of the call for proposals, etc. The value of early ALMA Public Image observations needs to be weighed against other demands on ALMA resources. The simplest approach would be to defer API observations until ALMA has 15 or more antennas. Alternatively, one or two API observations might be constructed by careful combination of SV observations, e.g. repeated observations of a unique southern source in several configurations and/or wavelengths. This type of API observation would not impose much additional stress on scarce ALMA resources and should be considered further.