2D analytical modeling of distortion and sky background in multi-fiber spectrographs: the case of the Norris spectrograph at Palomar Mountain

TL;DR

This paper presents a 2D analytical modeling method for correcting geometrical distortion and sky background in multi-fiber spectrographs, significantly improving sky subtraction accuracy and radial velocity precision, demonstrated on the Norris spectrograph at Palomar Mountain.

Contribution

The paper introduces a novel 2D analytical correction method for geometrical distortion and sky background in multi-fiber spectrographs, adaptable to various instruments, enhancing data reduction accuracy.

Findings

Achieves high accuracy in airglow subtraction, even in near-infrared regions.

Improves radial velocity measurement precision by a factor of 2.

Method is adaptable to different multi-object spectrograph designs.

Abstract

A method for optimal reduction of data taken with multi-fiber spectrographs is described, based on global correction of their geometrical distortion. Though it was specifically developed for reducing observations performed at Palomar Mountain using the Norris fiber spectrograph, this method can be adapted to other types of multi-object spectrographs such as the multi-slit ones. Combined with a 2D analytical interpolation of sky-background that accounts for non-uniform spectral resolution, the Norris software package achieves very high accuracy in airglow subtraction, even in the near infrared (7000-9000A) where molecular band-emissions commonly induce strong artefacts that preclude clean sky subtraction whenever standard image processing techniques are used. Correlatively, an improvement by a factor of 2 on the precision of radial velocities is achievable. Throughout the paper possible improvements to the method are suggested for those devising similar packages for other instruments.