I surveyed two years' scheduled programs for IR imaging on the KPNO 2.1-m telescope to determine the level of use of this capability, who uses it, and for what science. I suggest some implications for the future based on both science and technology.
The period surveyed is CY1995 and 1996. Effectively three IR cameras with differing capability were available at various times: IRIM, a 1-2.4 micron camera with 1.1" pixels, 4.5 arcmin FOV, and a very limited filter complement; COB, a 1-5 micron camera with 0.55" pixels, 2.3 armin FOV, and a very extensive spatial and spectral filtering capability; and DLIRIM, a modification of COB which gave 0.2" pixels. IRIM was available continuously, COB for one semester, DLIRIM for two semesters over this period. Normalized by availability, COB was most heavily used.
There were 37 scheduled proposals for 31 distinct scientific programs assigned a total of 181 nights. Since the least "popular" instrument, IRIM, was the only one available for one semester, this is a conservative estimator of demand. (COB was temporarily withdrawn for a detector upgrade.) Optical imaging and spectroscopy and IR spectroscopy are also done with this oversubscribed telescope; in this competitive environment, IR imaging science accounts for about 30% of available science time.
How big and how broad a community does this serve? Counting only listed investigators on the proposals, there are 89 PhD's and 7 graduate students, with 85 U.S. and 11 foreign affiliations. Institutionally, they come from 22 U.S. research institutions, 4 undergraduate colleges, 3 industrial R&D firms, and 9 foreign universities. Table 1 gives a listing, and notes when other IR imaging facilities were indicated to be available to the proposers. About 1/3 of the proposers or 1/2 of the proposals indicated such availability, typically small-field, high-resolution instrumentation on 4-m class telescopes totally unsuited to the proposed science. The few U.S. institutions with both strong IR instrumentation programs and small telescope access (e.g. Ohio State, Arizona, UCLA, Hawaii) are absent from Table 1. NOAO/KPNO is effectively a unique resource for widefield IR imaging for the rest of the U.S. community.
A review of the science programs indicates that, 10 years into the IR array revolution, IR imaging has taken its proper place as another observational tool to be used as appropriate. In summary, there were 21 galactic and 16 extragalactic programs. Most popular topics are star formation (7 proposals), structure and physics of nearby galaxies (7), late stages of stellar evolution (5), cosmological sources (4), statistics and flows of galaxies at moderate redshift (3). Many of these programs support or extend work with 4m and larger telescopes. Frequently near-IR imaging complements data obtained at other wavelengths, often greatly aiding the understanding of the physics. There were 18 explicit references to space experiments, including IRAS, ROSAT, ISO, HST, and UV platforms; and 13 references to large ground based facilities including the VLA, mm-wave dishes, and the Keck telescopes.
Could the science have been done on a smaller telescope, say 1-1.5m? I judged this to be feasible for only 20% of these programs. Only two proposals would be satisfied by the 2MASS database (which is targeted at different kinds of science). A similar review of IR imaging science done on the CTIO 1.5-m yields a science mix very similar to that described above, and indicates that on this smaller telescope the observations are frequently photon-hungry. The advent of numerous 8-m telescopes will increase the need for complementary IR imaging on faint targets with subarcsecond resolution.
This workshop is exploring alternatives for community access. For widefield IR imaging in the north, KPNO provides 100 nights/year PLUS instrument development time, allocated to a large number of individuals at many institutions--a management problem in itself. Judging from other presentations here, the competitive telescope size may be beyond the capability of many institutions or small consortia to acquire and support. The instrumentation is relatively complex, there are few vendors and no identifiable off-the-shelf products (unlike, say, simple CCD imagers), and the number of research groups with instrumentation expertise and appropriate telescope access is very small. Due to the way instrument projects hve been funded and carried out, even intra-institutional arrangements for access can be restrictive. These are resource availability problems which we must face.
What instrumental capability is needed to meet the science needs? Widefield IR imaging programs carried out at the national centers show a decreasing emphasis on continuum sources and exploratory imaging (broadband 1-2 microns with arcsec or larger pixels) and growing application to physical processes characterized by line emission which varies with high spatial frequency over extended regions. This demands 1% or better spectral resolution and subarcsecond pixel scale over a wide field. Sources of interest are getting fainter, typically K>15. There is increasing interest in the 3-4 micron range which will likely be further fueled by the 2MASS survey, Gemini capabilities, and long-wave space-based facilities. The historical tension between field of view and spatial resolution, due to the small size of IR arrays, is being relieved with the advent of 1-5 micron, 1024x1024 devices. A single such device, on a 2.5-m telescope with 0.5" pixels, will provide greater sensitivity at higher resolution over a larger field than ever before for "small" telescopes.
I have just exceeded the aperture limitation of this workshop! But for IR imaging science, "small" is getting bigger.
Table 1. Institutional users of widefield IR imaging at KPNO.
Institution # proposers* other IR imaging access
=< 2m >2m
CfA 18 X
NOAO 10 X X
North Carolina 3
NASA, all centers 3 X
U. Seoul, S. Korea 2
New Mexico State 2 X
U. Cardiff, Wales 2 X
Lawrence Livermore Lab 2 X X
DAO, Canada 2 X
SUNY Stony Brook 2
Florida Inst. Tech 2
Texas 2 X
Colorado 2 X
Carnegie Observatories 1 X
Kapteyn, Netherlands 1
IBM Watson Labs 1
U. Koln, Germany 1 X
U. Crete, Greece 1
Carnegie Inst. Wash. 1
IAUNAM, Mexico 1 X
Lowell Obs. 1 X
Valparaiso U. 1
U. Calgary, Canada 1
Drake U. 1
U. Bamberg, Germany 1 X
Southwest Res. Inst. 1
* # proposers is not corrected for duplication of individuals.
The CfA number derives from a team of several individuals
carrying out a long term project with repeat proposals.
The NOAO number represents five individual staff members.
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