Development of SED Camera for Quasars in Early Universe (SQUEAN)

TL;DR

SQUEAN is a specialized camera system designed to measure the spectral energy distributions of high-redshift quasars and other transient objects, enabling detailed studies of early universe phenomena.

Contribution

The paper introduces SQUEAN, a new camera system with a customizable filter wheel and high-precision calibration, optimized for observing distant quasars and transient astrophysical objects.

Findings

Achieved limiting magnitudes of 23.3 - 25.3 AB mag at 5-sigma in 1 hour

Successfully calibrated and verified filter wheel accuracy to less than one pixel

Installed and tested medium bandwidth filters covering 600-1050 nm

Abstract

We describe the characteristics and performance of a camera system, Spectral energy distribution Camera for Quasars in Early Universe (SQUEAN). It was developed to measure SEDs of high redshift quasar candidates (z $\gtrsim$ 5) and other targets, e.g., young stellar objects, supernovae, and gamma-ray bursts, and to trace the time variability of SEDs of objects such as active galactic nuclei (AGNs). SQUEAN consists of an on-axis focal plane camera module, an auto-guiding system, and mechanical supporting structures. The science camera module is composed of a focal reducer, a customizable filter wheel, and a CCD camera on the focal plane. The filter wheel uses filter cartridges that can house filters with different shapes and sizes, enabling the filter wheel to hold twenty filters of 50 mm $\times$ 50 mm size, ten filters of 86 mm $\times$ 86 mm size, or many other combinations. The initial filter mask was applied to calibrate the filter wheel with high accuracy and we verified that the filter position is repeatable at much less than one pixel accuracy. We installed and tested 50 nm medium bandwidth filters of 600 -- 1,050 nm and other filters at the commissioning observation in 2015 February. We found that SQUEAN can reach limiting magnitudes of 23.3 - 25.3 AB mag at 5-$\sigma$ in a 1-hour total integration time. - 25.3 AB mag at 5-$\sigma$ in a 1-hour total integration time.