Accurate Sky Continuum Subtraction with Fibre-fed Spectrographs

TL;DR

This paper evaluates sky subtraction techniques for fibre-fed spectrographs, demonstrating that cross beam-switching achieves 0.6% accuracy, which is promising for detecting faint astronomical sources.

Contribution

It introduces and tests dual staring and cross beam-switching techniques, showing that cross beam-switching significantly improves sky subtraction accuracy.

Findings

Cross beam-switching achieves 0.6% sky subtraction accuracy.

Fibre-fed spectrographs can match slit spectrograph performance.

Results support future faint source detection with advanced spectrographs.

Abstract

Fibre-fed spectrographs now have throughputs equivalent to slit spectrographs. However, the sky subtraction accuracy that can be reached has often been pinpointed as one of the major issues associated with the use of fibres. Using technical time observations with FLAMES-GIRAFFE, two observing techniques, namely dual staring and cross beam-switching, were tested and the resulting sky subtraction accuracy reached in both cases was quantified. Results indicate that an accuracy of 0.6% on sky subtraction can be reached, provided that the cross beam-switching mode is used. This is very encouraging with regard to the detection of very faint sources with future fibre-fed spectrographs, such as VLT/MOONS or E-ELT/MOSAIC.