A community workshop was held in Tucson on 26-28 September 1997 to identify and quantify required supporting capabilities for 6.5-10 meter telescopes. The motivation for this workshop was the realization that the new generation of very large telescopes would have 1) the ability to study in detail objects fainter than the limiting magnitudes of most existing wide-area surveys and 2) the requirement for accurate astrometry and photometry for both unknowns and reference stars before large telescope observations can be made. The goal of the workshop was to formulate and develop science-based arguments that would identify capabilities that are not currently available and suggest priorities or possible approaches to acquiring these capabilities.
A total of 46 astronomers representing 26 different institutions took part in the workshop. The attendees were split into eight discipline-based panels (Solar System Studies, Extrasolar planets/Low Luminosity Stars, High Resolution Studies of Stars, Star Formation/ISM, Activity in Nearby Galaxies, Stellar Populations, Galaxy Formation and Evolution, and Large Scale Structure). The entire group heard presentations on the capabilities and observing constraints of large telescopes (Keck, Hobby-Eberley Telescope, MMT, Magellan, LBT, and Gemini). The panels were charged to:
1) Develop one or more large, representative observational programs for 6.5-10 meter telescopes.
2) Analyze the support requirements for these programs including telescopes, instruments, surveys, software, and operations modes needed for sample selection, calibration, complementary or preparatory observations.
The panel chairs and the workshop organizers met during the final day to merge the panel results, attempt to quantify the common needs, and identify capabilities to which general access does not exist.
All of the panels identified large-scale surveys as essential to undertake the observing programs on very large telescopes. These surveys, different in detail but similar in overall requirements, are needed for sample selection or refinement, identification of reference stars in certain fields, and offloading the observations of the brighter objects onto smaller telescopes. Both imaging and multi-object spectroscopy were called for over survey fields of view that range up to several tens of square degrees in both the optical and IR. While a recalculation of the required nights based on a uniform set of assumptions is necessary, the preliminary numbers that came out of the workshop total to more than 2000 nights on 4-m telescopes to perform all the imaging surveys. It is important to note, however, that a substantial fraction of the surveys require only a few tens of nights.
What facilities and infrastructure are needed to carry out these surveys?
Optical arrays are just approaching sizes to make optimal use of existing telescope focal planes. Obviously, development of IR arrays leading to larger formats and buttable physical packages would increase efficiency for survey use.
Standardized, well-tested software will allow rapid and consistent reduction of data obtained for surveys. Construction of catalogs with accurate measurement of fluxes and positions will make the use of these data more efficient. Also, uniform procedures for ingesting data into (and delivering data out of) archives will permit the entire community to make better use of this information.
The workshop participants recognized that conflicting pressures exist in trying to enable a survey. Community support requires substantial community input and ready access to the output. However, there must be a scientific return for an individual or team to put in the very large effort that is required to carry the survey out. Any plan to carry out one of these surveys must find an acceptable balance to these two forces. Various telescope resources were discussed as potential tools to carry out these surveys.
While these were prioritized behind the survey requirements, several additional capabilities were identified as desirable. These included limited interest in image quality improvement via tip-tilt correction or low-order adaptive optics. The emphasis was clearly on correction over a substantial field of view and so might be considered as correction for wind-shake, tracking errors and dome and mirror seeing. Also, non-traditional operations modes were noted as important, particularly those that would support target-of-opportunity observations.
Arguments for specific supporting capabilities have always been anecdotal. We know that the Palomar Schmidt sky survey undertaken in the 1950s provided an extremely important database for the next 30 years of observations on 4-5 meter telescopes. By analogy we expect that similar but deeper surveys (such as SDSS) will be necessary to effectively use 6.5-10 meter telescopes. Now, for the first time, we have made that argument in a scientific context. However, we must acknowledge the limitations of the process of the workshop. Many disciplines, wavelength ranges, and types of observation were not well represented. The workshop did identify some specific areas that will require development and significant effort for the effective community use of very large telescopes. It is necessary to begin immediately the job of planning and carrying out these surveys. Over the long term the results of this workshop and of future workshops should provide input for national public and private policy and funding decisions. Over the short term the community must be engaged in starting to assemble the tools and the infrastructure to carry these surveys out.
Todd Boroson