Performance of the HgCdTe Detector for MOSFIRE, an Imager and Multi-Object Spectrometer for Keck Observatory

TL;DR

This paper evaluates the performance of a HgCdTe detector used in MOSFIRE, a near-infrared spectrometer and imager for Keck Observatory, focusing on its noise, dark current, and stability for faint object spectroscopy.

Contribution

It provides detailed performance metrics of the HgCdTe detector, including noise levels, dark current, and persistence, demonstrating its suitability for high-precision astronomical observations.

Findings

Dark current measured at <0.008 e- s-1 pixel-1

Read noise as low as 3 e- rms with 64 samples

Persistence decay time constant approximately 660 seconds

Abstract

MOSFIRE is a new multi-object near-infrared spectrometer for the Keck 1 telescope with a spectral resolving power of R 3500 for a 0.7" slit (2.9 pixels). The detector is a substrate-removed 2K x 2K HAWAII 2-RG HgCdTe array from Teledyne Imaging Sensors with a cut-off wavelength of 2.5 {\mu}m and an operational temperature of 77K. Spectroscopy of faint objects sets the requirement for low dark current and low noise. MOSFIRE is also an infrared camera with a 6.9' field of view projected onto the detector with 0.18" pixel sampling. Broad-band imaging drives the requirement for 32-channel readout and MOSFIREs fast camera optics implies the need for a very flat detector. In this paper we report the final performance of the detector selected for MOSFIRE. The array is operated using the SIDECAR ASIC chip inside the MOSFIRE dewar and v2.3 of the HxRG software. Dark current plus instrument background is measured at <0.008 e- s-1 pixel-1 on average. Multiple Correlated Double Sampling (MCDS) and Up-The-Ramp (UTR) sampling are both available. A read noise of <5e- rms is achieved with MCDS 16 and the lowest noise of 3e- rms occurs for 64 samples. Charge persistence depends on exposure level and shows a large gradient across this detector. However, the decay time constant is always \sim 660 seconds. Linearity and stability are also discussed.