2.1m

Supporting Capabilities for

Large Telescopes

Todd Boroson


NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under cooperative agreement with the National Science Foundation


[ Panel Members ] [ Science Programs ] [ Table 1 ] [ Table 2 ] [ Table 3 ]


A community workshop was held in Tucson on September 26-28, 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 a) the ability to study in detail objects fainter than the limiting magnitudes of most existing wide-area surveys and b) the requirement to come to the telescope with accurate astrometry and photometry for both unknowns and reference stars. 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. Eight discipline-based panels were created (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), each with two co-chairs to lead the panel discussions. The entire group heard presentations on the capabilities and observing constraints of a number of large telescopes (Keck, Hobby-Eberly Telescope, MMT, Magellan, LBT, and Gemini). The charge to the panels was 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 co-chairs and the workshop organizers met the final day to merge the panel results, attempt to quantify the common needs, and identify capabilities to which general access does not exist.

Table 1 gives for each program a summary of the observations on the large (6.5-10 meter) telescope, including the type of instrument needed and the estimated number of nights.

All of the panels identified large-scale surveys as essential in order 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 fields of view that range from 10-20 arcminutes in the IR to one degree in the optical. The survey parameters are given in Table 2, including the area to be surveyed, the filter bands (or spectral resolution) required, and the limiting magnitude for each filter.

In order to understand the practicality of undertaking these surveys using various existing or planned facilities, the number of nights to carry out each survey has been estimated for a uniform set of assumptions. Four cases were considered: a "new" 2.5 meter telescope that produces 0.5 arcsecond FWHM images and has 3% emissivity in the thermal IR, an "old" 2.5 meter telescope that produces 1.0 arcsecond FWHM images and has 10% emissivity in the thermal IR, and two telescopes of 4 meter aperture with the same sets of imaging/emissivity performance. In all cases an 8K X 8K optical imager and a 1K X 1K IR imager were assumed. Table 3 shows the predicted number of nights to carry out the imaging surveys under these conditions. It can be seen that:

The facilities and infrastructure that were identified as prerequisites to carry out these surveys include:

Detectors 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.

Software/protocols/pipelines 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. Uniform procedures for ingesting data into (and delivering data out of) archives will permit the entire community to make better use of this information.

Community sociology 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.

Other desired capabilities Although lower in priority than the survey requirements, several additional capabilities were identified as desirable. There was some 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.

Three general aspects of the results are worth noting. First, 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 and 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 and in a more quantitative way. Second, we must acknowledge the limitations of the process of the workshop. Many disciplines, wavelength ranges, and types of observation were not well represented. We did not do a good job of including radio and x-ray observatories and the connection to ongoing or planned space observatories is not as strong as it could be. Third, we did succeed in identifying 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 we must engage the community in starting now to assemble the tools and the infrastructure to carry them out.

The scientific programs proposed by the panels are appended to this summary.


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