Faint Intergalactic Redshifted Emission Balloon Research Articles

End-to-end ground calibration and in-flight performance of the FIREBall-2 instrument

The payload of the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2), the second generation of the FIREBall instrument (PI: C. Martin, Caltech), has been calibrated and launched from the NASA Columbia Scientific Balloon Facility in Fort Sumner, New Mexico. FIREBall-2 was launched for the first time on the September 22, 2018, and the payload performed the very first multi-object acquisition from space using a multi-object spectrograph. Our performance-oriented paper presents the calibration and last ground adjustments of FIREBall-2, the in-flight performance assessed based on the flight data, and the predicted instrument’s ultimate sensitivity. This analysis predicts that future flights of FIREBall-2 should be able to detect the HI Lyα resonance line in galaxies at z ∼ 0.67, but will find it challenging to spatially resolve the circumgalactic medium.

Delta-doped electron-multiplying CCDs for FIREBall-2

We present the status of on-going detector development efforts for our joint NASA/CNES balloon-borne UV multi-object spectrograph, the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2; FB-2). FB-2 demonstrates a new UV detector technology, the delta-doped Electron Multiplying CCD (EMCCD), in a low risk suborbital environment, to prove the performance of EMCCDs for future space missions and Technology Readiness Level (TRL) advancement. EMCCDs can be used in photon counting (PC) mode to achieve extremely low readout noise ($<$1 electron). Our testing has focused on reducing clock-induced-charge (CIC) through wave shaping and well depth optimization with a \nuvu V2 CCCP Controller, measuring CIC at 0.001 e$^{-}$/pixel/frame. This optimization also includes methods for reducing dark current, via cooling, and substrate voltage levels. We discuss the challenges of removing cosmic rays, which are also amplified by these detectors, as well as a data reduction pipeline designed for our noise measurement objectives. FB-2 flew in 2018, providing the first time an EMCCD was used for UV observations in the stratosphere. FB-2 is currently being built up to fly again in 2020, and improvements are being made to the EMCCD to continue optimizing its performance for better noise control.

Active optics in astronomy – modeling of deformable substrates: freeform surfaces for FIREBall and MESSIER

Abstract Active optics techniques on large telescopes and astronomical instrumentations provide high imaging quality. For ground-based astronomy, the co-addition of adaptive optics again increases angular resolution up to providing diffraction-limited imaging at least in the infrared. Active and adaptive optics marked milestone progress in the detection of exoplanets, super-massive black holes, and large-scale structure of galaxies. This paper is dedicated to highly deformable active optics that can generate non-axisymmetric aspheric surfaces – or freeform surfaces – by use of a minimum number of actuators: a single uniform load acts over the surface of a vase-form substrate whilst under reaction to its elliptical perimeter ring. Two such instruments are presented: (1) the Faint Intergalactic Redshifted Emission Balloon (FIREBall) telescope and multi object spectrograph (MOS) where the freeform reflective diffraction grating is generated by replication of a deformable master grating, and (2) the MESSIER wide-field low-central-obstruction three-mirror-anastigmat (TMA) telescope proposal where the freeform mirror is generated by stress figuring and elastic relaxation. Freeform surfaces were obtained by plane super-polishing. Preliminary analysis required use of the optics theory of 3rd-order aberrations and elasticity theory of thin elliptical plates. Final cross-optimizations were carried out with Zemax raytracing code and Nastran FEA elasticity code in order to determine geometry of the deformable substrates.