The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall-2) is a UV multi-object spectrograph designed to detect emission from the circumgalactic and circumquasar medium at low redshifts (0.3 < z < 1.0). The FIREBall-2 spectrograph uses a suborbital balloon vehicle to access a stratospheric transmission window centered around 205 nm and is fed by a 1-m primary parabolic mirror and a 2-mirror field corrector that allows an ≈11’ x 35’ field of view. The slit-mask spectrograph can access dozens of galaxy targets per field, with each target spectrum read out on a UV electron-multiplying CCD detector. Following a flight in 2018, several refurbishments and modifications were made to the instrument and telescope to prepare for additional flight opportunities. Here we present an overview of upgrades and improvements made since the previous flight and discuss the 2023 field campaign, which culminated in a flight from Fort Sumner, New Mexico in September, 2023.
Type Ia supernovae (SNe Ia) are a cornerstone of modern cosmology. Upcoming missions like the Nancy Grace Roman Telescope are pushing to high redshifts to measure cosmological parameters like the dark energy equation of state. Despite the impressive success of empirically standardizing their luminosities, the explosion mechanism of SNe Ia remains hotly debated; e.g., the mass of the white dwarf (WD) when it explodes and the state of the companion star (degenerate or non-degenerate) are all currently in question.
Early-time UV observations are sensitive to the outermost layers of the ejecta (and least affected by the explosion itself) and show the most diversity for SNe Ia. This makes the UV bandpass an excellent probe to solve these open questions about the nature of these cosmological distance indicators. To achieve this science, we present UVIa, a CubeSat that will be reactive and have simultaneous optical, Near-UV (NUV), and Far-UV (FUV) coverage, takes advantage of state-of-the-art UV coatings, UV-enhanced silicon detectors with whitelight rejection filter, and autonomous observing scheduling, updated regularly based on newly discovered SNe Ia from modern transient surveys.
Our current understanding of cosmology is largely shaped by Type Ia supernovae (SNe Ia), the detonations of carbon-oxygen white dwarves (WDs). SNe Ia are powerful standard candles due to their uniform peak luminosities which decay predictably. SNe Ia progenitor system architecture is highly debated, as none have been observed pre- and post-detonation. Within the first few days after detonation, critical progenitor signatures are preserved in the ultraviolet (UV) bandpass. We present the optical design of UVIa, a proposed 12U CubeSat capable of simultaneous measurements in the far-UV, near-UV, and u-band. Double-offset Cassegrain telescopes were designed to image onto CMOS detectors. We discuss the benefits and challenges associated with double-offset telescopes. UVIa additionally serves as a technology demonstration platform for several cutting-edge UV technologies. The optical design of UVIa enables early-time observations of SNe Ia and serves as a pathfinder for future UV transient telescopes.
The balloon-borne UV telescope Faint Intergalactic Red-shifted Emission Balloon (FIREBall-2) was launched from Fort Sumner, NM on September 25, 2023, for its second attempted flight. The flight was unexpectedly terminated at 10 hours due to a mechanical issue, and no science data was obtained; however, this short flight provided an excellent opportunity to test the in-flight communications system. Testing the communication system pre-flight was challenging, and an accurate simulation of signal reception and communication errors expected during flight was not possible. From launch to landing, only a single packet was dropped. Had the flight continued for the expected duration, the success up to early termination gives confidence that the communications systems would have continued to meet our expectations. While this test was highly successful, some areas for improvement were identified and will be addressed before FIREBall-2’s next flight.
We present the integration of a new calibration system into the Faint Intergalactic-medium Redshifted Emission Balloon-2 (FIREBall-2), which added in-flight calibration capability for the recent September 2023 flight. This system is composed of a calibration source box containing zinc and deuterium lamp sources, focusing optics, electronics, 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 non-sequential modeling for the near-UV (191 to 221 nm) for spectrograph slit mask position calibration, electron multiplying charged-coupled device (EMCCD) gain amplification verification, and wavelength calibration. Then, we present the pre-flight performance testing results of the calibration system and their implications for in-flight measurements. FIREBall-2 flew in 2023, but did not collect calibration data due to early termination of the flight.
The Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SIS- TINE) sounding rocket payload is an f /30 imaging spectrograph designed to measure the far ultraviolet (1000 - 1275 and 1300 - 1565 Å) output of exoplanet host stars. The instrument is composed of an f /14 Cassegrain telescope with a 500 mm diameter primary mirror feeding a 2.1x magnifying spectrograph. Light is dispersed by a blazed, holographically ruled grating, reflected off a powered fold mirror, and recorded on a large format microchannel plate (MCP) detector. The instrument incorporates enhanced LiF (eLiF) protected aluminum on the primary, secondary, and fold mirrors. The secondary mirror also has a protective AlF3 capping layer, applied using atomic layer deposition (ALD). The detector is composed of two windowless 113 x 42 mm segments with cross delay line anodes and CsI photocathodes. The detector utilizes ALD processed borosilicate plates, and additionally serves as a flight test for detectors on future astrophysics missions. The instrument reaches a peak effective area of 99.9 cm2 at 1145 Å. The assembly of SISTINE-2 included the application of new photocathodes to the detector, showing improvements in quantum efficiency after laboratory tests. SISTINE-2 will observe the nearby F star Procyon in late 2021, making the first simultaneous observation from O VI through C IV and setting new empirical constraints on the radiation fields experienced by planets orbiting mid-F stars.
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