Double-offset Cassegrain telescopes for the Ultraviolet Type Ia (UVIa) mission concept

TL;DR

UVIa is a proposed SmallSat with dual UV telescopes designed to capture early ultraviolet signatures of Type Ia supernovae, aiding in understanding their progenitors and serving as a pathfinder for future UV transient missions.

Contribution

The paper introduces a novel instrument design featuring double-offset Cassegrain telescopes with enhanced UV sensitivity and red light rejection for early supernova observations.

Findings

High UV sensitivity (21.5 mag AB) achieved

Red light rejection better than 10^-5

Simultaneous multi-band UV observations possible

Abstract

Our understanding of cosmology is shaped by Type Ia supernovae (SNe Ia), the runaway thermonuclear detonations of white dwarfs via accretion from a companion star. The nature of this companion star is highly debated, with disparate models explaining currently available SNe Ia data. Critical ultraviolet (UV) signatures of SNe Ia progenitors are only observable within the first few days post-detonation. We present the instrument design of UVIa, a proposed SmallSat to make early UV observations of SNe Ia. UVIa conducts simultaneous observations in three photometric channels: far-UV (1500 - 1800 {\AA}), near-UV (1800 - 2400 {\AA}), and Sloan $u$-band (3000 - 4200 {\AA}). UVIa employs two 80 mm double-offset Cassegrain UV telescopes and a similar 50 mm $u$-band telescope, imaging onto three Teledyne e2v CIS120-10-LN CMOS detectors. The UV detectors are delta-doped for enhanced sensitivity, with custom metal-dielectric filters providing further in-band efficiency and red light rejection. The UV optics utilize multi-layer coatings, defining the UV bandpasses and providing additional red light rejection. The instrument design achieves high UV sensitivity (21.5 mag AB) and superior red light rejection ($<$ 10$^{-5}$ throughput), allowing UVIa to make early observations of SNe Ia while serving as a pathfinder for future UV transient telescopes.