Night Vision for Small Telescopes

TL;DR

This paper investigates the use of off-the-shelf InGaAs NIR detectors with small telescopes for cost-effective astronomical observations, demonstrating their capability for detecting bright and faint sources, and achieving high-precision photometry.

Contribution

It presents the first comprehensive evaluation of room-temperature InGaAs cameras for astronomical use, including laboratory characterization and on-sky testing with small telescopes.

Findings

Able to detect faint sources down to J=16.4 at 10σ in one minute

Achieved milli-magnitude precision for sources brighter than J=8

Successfully measured sub-percent flux variations in an exoplanet transit

Abstract

We explore the feasibility of using current generation, off-the-shelf, indium gallium arsenide (InGaAs) near-infrared (NIR) detectors for astronomical observations. Light-weight InGaAs cameras, developed for the night vision industry and operated at or near room temperature, enable cost-effective new paths for observing the NIR sky, particularly when paired with small telescopes. We have tested an InGaAs camera in the laboratory and on the sky using 12 and 18-inch telescopes. The camera is a small-format, 320x240 pixels of 40$\mu$m pitch, Short Wave Infra-Red (SWIR) device from Sensors Unlimited. Although the device exhibits a room-temperature dark current of $5.7 \times 10^4$ $e^-s^{-1}$ per pixel, we find observations of bright sources and low-positional-resolution observations of faint sources remain feasible. We can record unsaturated images of bright ($J=3.9$) sources due to the large pixel well-depth and resulting high dynamic range. When mounted on an 18-inch telescope, the sensor is capable of achieving milli-magnitude precision for sources brighter than $J=8$. Faint sources can be sky-background-limited with modest thermoelectric cooling. We can detect faint sources ($J=16.4$ at $10\sigma$) in a one-minute exposure when mounted to an 18-inch telescope. From laboratory testing, we characterize the noise properties, sensitivity, and stability of the camera in a variety of different operational modes and at different operating temperatures. Through sky testing, we show that the (unfiltered) camera can enable precise and accurate photometry, operating like a filtered $J$-band detector, with small color corrections. In the course of our sky testing, we successfully measured sub-percent flux variations in an exoplanet transit. We have demonstrated an ability to detect transient sources in dense fields using image subtraction of existing reference catalogs.