VLT/VISIR Calibration programme and stray light modeling

Leiden Repository (Leiden University), pp. 41

Abstract

Talk with accompanying poster. For decades, the standard background subtraction scheme in ground-based thermal-infrared observations has been a combination of chopping and nodding. Since the thermal background stability of the ELT during nodding is currently unclear, we investigate an alternative background subtraction scheme using only chopping. Using data from VLT/VISIR we study the structure in chop-difference frames which is dominated by a gradient. In this research we determine the origin of this gradient with the aim to understand, qualitatively and quantitatively, the link between telescope structure and chopping residuals. To achieve that, we construct a simple model which describes the most significant warm emitter in the VLT pupil seen by VISIR (the folded M3 tower) and show that this structure is responsible for the observed gradient in the chopping residuals. We corroborate our findings by implementing this model -- and reproducing the effect -- in the ray-tracing software FRED.

Authors 1

1. L. Burtscher Aachen

   Leiden University

   Affiliation as printed

   Universiteit Leiden