TRIDENT: An Infrared Differential Imaging Camera Optimized for the Detection of Methanated Substellar Companions

Abstract

We describe a near-infrared camera in use at the Canada-France-Hawaii Telescope (CFHT) and at the 1.6 m telescope of the Observatoire du mont Mégantic (OMM). The camera is based on a Hawaii-1 1024 × 1024 HgCdTe array detector. Its main feature is the acquisition of three simultaneous images at three wavelengths across the methane absorption bandhead at 1.6 μm, enabling, in theory, an accurate subtraction of the stellar point-spread function (PSF) and the detection of faint close, methanated companions. The instrument has no coronagraph and features fast data acquisition, yielding high observing efficiency on bright stars. The performance of the instrument is described, and it is illustrated by laboratory tests and CFHT observations of the nearby stars GL 526, v And, and χ And. TRIDENT can detect (6 σ) a methanated companion with Δh = 9.5 at 0″.5 separation from the star in 1 hr of observing time. Non-common-path aberrations and amplitude modulation differences between the three optical paths are likely to be the limiting factors preventing further PSF attenuation. Instrument rotation and reference-star subtraction improve the detection limit by a factor of 2 and 4, respectively. A PSF noise attenuation model is presented to estimate the non-common-path wave-front difference effect on PSF subtraction performance. © 2005. The Astronomical Society of the Pacific. All rights reserved.