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D. W. McCarthy (UAZ), J. Ge (LLNL), J. L. Hinz, R. A. Finn, F. J. Low (UAZ), M. Cheselka (NOAO), K. Salvestrini (IRLaboratories)
The advent of large format focal plane arrays permits efficient wide-field imaging at near-infrared wavelengths. We have commissioned a new camera (PISCES) to provide circular fields of 8.5 and 3.0 arcmin diameter at the f/9 foci of the 2.3m Bok telescope and 6.5m MMT. The design uses refractive optics with spherical lenses made from conventional materials (CaF2, BaF2, IR-SiO2). The dewar window is an achromatic doublet which produces a high quality pupil image. A cold pupil stop yields low emissivity by baffling the telescope's central obscuration, primary edge, and spider vanes. Pupil-viewing optics provide precise alignment of the telescope pupil. Four additional lenses then reimage the telescope focal plane at f/3.3, leading to scales of 0.5 and 0.18 arcsec/pixel, respectively. These scales are well matched to the seeing at the two sites. The focal plane array is a 1024x1024 pixel HgCdTe (HAWAII readout) detector from Rockwell. PISCES utilizes an SDSU array controller based on fiber-optic communication with a PCI-bus computer.
Performance measurements have been conducted at the 2.3m telescope. Image quality is FWHM <2 pixels across the full array from 1-2.5\mum. Overall instrument transmission is 50-55%, including the detector quantum efficiency. Emissivity is measured to be 5-7%. On the 2.3m telescope, point source detection limits of J=17.5, H=17.0, Ks=16.5 (10-sigma/min) are achieved routinely. At the 6.5m MMT we anticipate an improvement of ~2 magnitudes. PISCES is currently being used for scientific studies of quasar environments (Finn et al., this conference), searches for brown dwarfs as common proper motion companions, and imaging of star formation regions.
PISCES and its successor (ARIES) on the 6.5m MMT are supported by the NSF through grant AST-9623788.