The integration of a new calibration system into FIREBall-2 (Faint Intergalactic Redshifted Emission Balloon-2) allows in-flight calibration capability for the upcoming Fall 2023 flight. This system is made up of a calibration box that contains zinc and deuterium lamp sources, focusing optics, electronics, and sensors, and a fiber-fed calibration cap with an optical shutter mounted on the spectrograph tank. We discuss how the calibration cap is optimized to be evenly illuminated through nonsequential modeling for the near-UV (200-208nm). Then, we present the pre-flight performance testing results of the calibration system and their implications for in-flight measurements.
We present a comprehensive stray light analysis and mitigation strategy for the FIREBall-2 ultraviolet balloon telescope. Using nonsequential optical modeling, we identified the most problematic stray light paths, which impacted telescope performance during the 2018 flight campaign. After confirming the correspondence between the simulation results and postflight calibration measurements of stray light contributions, a system of baffles was designed to minimize stray light contamination. The baffles were fabricated and coated to maximize stray light collection ability. Once completed, the baffles will be integrated into FIREBall-2 and tested for performance preceding the upcoming flight campaign. Given our analysis results, we anticipate a substantial reduction in the effects of stray light.
This conference presentation was prepared for the Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray conference at SPIE Astronomical Telescopes and Instrumentation, 2022.
The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall-2) is a UV multi-object spectrograph exploring the CGM of galaxies at low redshifts (0.3 < z < 1.0). The science detector is a EMCCD cooled by a Sunpower cryocooler to minimize the noise contributions from dark current. To efficiently remove the heat generated by the cryocooler and other critical hardware, we built a custom water cooling circuit which uses a water/alcohol/ice mixture to regulate temperatures during flight. We report the ground and flight performances of the thermal system during the 2018 campaign and the lessons learned since then. We will discuss the model predictions of the potential impacts of several major upgrades as well as modifications to adapt to those impacts, and the ground performance of the thermal system during the rebuild of FIREBall-2, compared with the model predictions, for the next launch of FIREBall-2 in Fort Sumner in 2020.
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.
Here we discuss advances in UV technology over the last decade, with an emphasis on photon counting, low noise, high efficiency detectors in sub-orbital programs. We focus on the use of innovative UV detectors in a NASA astrophysics balloon telescope, FIREBall-2, which successfully flew in the Fall of 2018. The FIREBall-2 telescope is designed to make observations of distant galaxies to understand more about how they evolve by looking for diffuse hydrogen in the galactic halo. The payload utilizes a 1.0-meter class telescope with an ultraviolet multi-object spectrograph and is a joint collaboration between Caltech, JPL, LAM, CNES, Columbia, the University of Arizona, and NASA. The improved detector technology that was tested on FIREBall-2 can be applied to any UV mission. We discuss the results of the flight and detector performance. We will also discuss the utility of sub-orbital platforms (both balloon payloads and rockets) for testing new technologies and proof-of-concept scientific ideas.
The circumgalactic medium (CGM) plays a critical role in the evolution of galaxy discs, as it hosts important mechanisms regulating their replenishment through inflows and outflows. Besides absorption spectroscopy, mapping of the HI Lyα emission of z>2 CGM is bringing a new perspective with a complete 2- or 3-D mapping. Despite this benefit, data in emission are very scarce in the large time span from z∼2 to the present because of the difficulties inherent to vacuum UV observations. The FIREBall-2 (Faint Intergalactic Redshifted Emission Balloon) instrument has been developed to help fill this gap and is scheduled for launch in September 2018. It has been optimized to provide a bi-dimensional (x, λ) map of the extremely faint diffuse Ly-a HI emission in the CGM at z∼0.7 and has the capability to observe ~200 galaxies and a dozen QSOs in a single night flight. Given its wide field of view (FOV) of 20x40 arcmin2, its angular resolution of 6-10 arcsec and spectral resolution above 1000, FIREBall-2 will bring important insights about the gas distribution in the CGM, and the velocity/temperature fields, and has the potential to bring statistical constraints. The instrument is a balloon-borne 1m telescope coupled to a UV multi-object spectrograph (MOS) designed to image the CGM in emission via specific spectral lines (Lya, CIV, OVI) redshifted in a narrow UV band [1990 - 2130]A for the nearby universe (0.2< z <1). The optical design relies on a 1.2-meter moving siderostat that stabilizes the beam and reflects the light on a fixed paraboloid which in turn images it at the entrance of the payload. This payload is constituted of a focal corrector followed by a slit Multi-Object Spectrograph (reflective 2400 g/mm holographic aspherical grating located between two Schmidt mirrors). The objects selection is achieved with a series of pre-installed precision mask systems that also feed the fine guidance camera. The detector is a e2v electron multiplying CCD coated and delta-doped by the Jet Propulsion Laboratory. FIREBall-2 is funded by CNES and NASA and is developed in cooperation with a Franco-American consortium composed of LAM, CALTECH, Columbia University, JPL and CST-CNES. In this presentation, we describe the final ground calibration of the instrument. We explain what technical specifications ensue from the scientific goals of the mission and we will then highlight why this optical design has been chosen. The calibration of the instrument (alignment - through focus - distortion) will be presented followed by the analysis of the instrument scientific performances. We will then describe the improvement and the calibration of the ZEMAX-coupled instrument model developed at LAM, based on these final performances. This model is finally used to make an end-to-end prediction of the observations of the emission of the CGM from a large halo in a cosmological simulation.
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