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We describe test observations made with a customized 640 x 512 pixel IndiumGallium Arsenide (InGaAs) prototype astronomical camera on the 100" DuPonttelescope. This is the first test of InGaAs as a cost-effective alternative toHgCdTe for research-grade astronomical observations. The camera exhibits aninstrument background of 113 e-/sec/pixel (dark + thermal) at an operatingtemperature of -40C for the sensor, maintained by a simple thermo-electriccooler. The optical train and mechanical structure float at ambient temperaturewith no cold stop, in contrast to most IR instruments which must be cooled tomitigate thermal backgrounds. Measurements of the night sky using a reimagerwith plate scale of 0.4 arc seconds / pixel show that the sky flux in Y iscomparable to the dark current. At J the sky brightness exceeds dark current bya factor of four, and hence dominates the noise budget. The sensor read noiseof ~43e- falls below sky+dark noise for exposures of t>7 seconds in Y and 3.5seconds in J. We present test observations of several selected science targets,including high-significance detections of a lensed Type Ia supernova, a typeIIb supernova, and a z=6.3 quasar. Deeper images are obtained for two localgalaxies monitored for IR transients, and a galaxy cluster at z=0.87. Finally,we observe a partial transit of the hot JupiterHATS34b, demonstrating thephotometric stability required over several hours to detect a 1.2% transitdepth at high significance. A tiling of available larger-format sensors wouldproduce an IR survey instrument with significant cost savings relative toHgCdTe-based cameras, if one is willing to forego the K band. Such a camerawould be sensitive for a week or more to isotropic emission from r-processkilonova ejecta similar to that observed in GW170817, over the full 190 Mpchorizon of Advanced LIGO's design sensitivity for neutron star mergers.

Background-Limited Imaging in the Near-Infrared with Warm InGaAs Sensors: Applications for Time-Domain Astronomy