The WIYN One Degree Imager in 2018: An Extended 30-Detector Focal Plane

TL;DR

The paper details the upgrade of the WIYN One Degree Imager, expanding its detector array to enhance sky coverage, improving performance, calibration, and filter mechanisms, and sharing operational insights after three years of use.

Contribution

It presents the design, implementation, and operational experience of a significantly expanded and upgraded wide-field imager at the WIYN telescope.

Findings

Expanded focal plane to 30 detectors, increasing field of view to 40' x 48'

Improved charge transfer efficiency and calibration methods

Enhanced filter mechanisms with new filters and reliable drive systems

Abstract

We report on the upgraded One Degree Imager (ODI) at the WIYN 3.5 meter telescope at the Kitt Peak Observatory after the focal plane was expanded by an additional seventeen detectors in spring 2015. The now thirty Orthogonal Transfer Array CCD detectors provide a total field of view of 40' x 48' on the sky. The newly added detectors underwent a design revision to mitigate reduced charge transfer efficiency under low light conditions. We discuss the performance of the focal plane and challenges in the photometric calibration of the wide field of view, helped by the addition of telescope baffles. In a parallel project, we upgraded the instrument's three filter arm mechanisms, where a degrading worm-gear mechanism was replaced by a chain drive that is operating faster and with high reliability. Three more filters, a u' band and two narrow band filters were added to the instrument's complement, with two additional narrow band filters currently in procurement (including an H-alpha filter). We review the lessons learned during nearly three years of operating the instrument in the observatory environment and discuss infrastructure upgrades that were driven by ODI's needs.