(Sn)DICE: A Calibration System Designed for Wide Field Imagers

TL;DR

The paper introduces (Sn)DICE, a calibration system for wide field imagers that improves photometric accuracy crucial for Dark Energy studies, by providing a stable, well-characterized light source for precise instrument calibration.

Contribution

It presents the design, implementation, and deployment of the (Sn)DICE calibration system tailored for wide field imagers like MegaCam and SkyMapper, addressing calibration challenges.

Findings

Successful installation of SnDICE at CFHT

Deployment of SkyDICE at SkyMapper

Enhanced calibration accuracy for wide field imagers

Abstract

Dark Energy studies with type Ia supernovae set very tight constraints on the photometric calibration of the imagers used to detect the supernovae and follow up their flux variations. Among the key challenges is the measurement of the shape and normalization of the instrumental throughput. The DICE system was developed by members of the Supernova Legacy Survey (SNLS), building upon the lessons learnt working with the MegaCam imager. It consists in a very stable light source, placed in the telescope enclosure, and generating compact, conical beams, yielding an almost flat illumination of the imager focal plane. The calibration light is generated by narrow spectrum LEDs selected to cover the entire wavelength range of the imager. It is monitored in real time using control photodiodes. A first DICE demonstrator, SnDICE has been installed at CFHT. A second generation instrument (SkyDICE) has been installed in the enclosure of the SkyMapper telescope. We present the main goals of the project. We discuss the main difficulties encountered when trying to calibrate a wide field imager, such as MegaCam (or SkyMapper) using such a calibrated light source.