A low-resolution high-throughput spectrograph for the New Robotic Telescope

Abstract

The New Robotic Telescope (NRT) will be a 4-metre-class fully robotic telescope to be sited on La Palma. NRT will primarily be used in time-domain astrophysics, and, as such, there is a requirement for rapid response and high-efficiency observing and instrumentation. We have therefore developed a spectrograph concept for NRT with no moving parts. The primary design feature is a beamsplitter, where a small fraction of light will be reflected towards a dedicated acquisition detector. The rest of the light will pass through the system for spectroscopy with a second detector. We present initial calculations of the fraction of light required to be diverted from the science beam to minimize overall time spent per target. We also present the results of initial laboratory testing of a plane glass plate and a single-sided anti-reflection coated plate as beamsplitters. As expected these exhibit significant ghost images, and more sophisticated beamsplitter designs will be explored in the next phase of the project.