High-precision astrometry has the potential to address questions in planet formation, black hole science, Galactic structure, and more. However, in order to achieve a precision of sub-milli arcseconds (mas), we need a calibration method better than the current techniques such as on-sky calibration using crowded star fields, which have a precision of ∼ 1 mas. Precision calibration unit with a regular grid of photo-lithographically manufactured pinholes combined with self-calibration techniques, on the other hand, is a new and innovative way to potentially achieve a precision of sub-mas over the entire field of view. This technique is beneficial to adaptive optic (AO) instruments for future telescopes like the Thirty Meter Telescope (TMT). In this work, we present our design for a new astrometric calibration unit to feed the NIRC2 AO instrument at the W. M. Keck Observatory. It allows calibration over a large field of view of 47'' × 47'', spatially dithering throughout the entire field, and 360 degree continuous rotation of the pinhole mask. Our proposed calibration unit will produce > 5 times better performance than the pinhole masks deployed in first generation AO systems. Similar design principles could be used worldwide and for the upcoming thirty meter class telescopes to meet their distortion calibration requirements.
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.
Understanding the noise characteristics of high quantum efficiency silicon-based ultraviolet detectors, developed by the Microdevices Lab at the Jet Propulsion Laboratory, is critical for current and proposed UV missions using these devices. In this paper, we provide an overview of our detector noise characterization test bench that uses delta-doped, photon counting, Electron-multiplying CCDs (EMCCDs) to understand the fundamental noise properties relevant to all silicon CCDs and CMOS arrays. This work attempts to identify the source of the dark current plateau that has been previously measured with photon-counting EMCCDs and is known to be prevalent in other silicon-based arrays. It is suspected that the plateau could be due to a combination of detectable photons in the tail of blackbody radiation of the ambient instrument, low-level light leaks, and a non-temperature-dependent component that varies with substrate voltage. Our innovative test setup delineates the effect of the ambient environment during dark measurements by independently controlling the temperature of the detector and surrounding environment. We present the design of the test setup and preliminary results.
FIREBall-2 is a Balloon-Borne UV telescope designed to observe faint UV emission from the circumgalactic medium around low redshift galaxies (z 0.3 - 1.0). FIREBall-2 employs a 1m telescope with a multi-object spectrograph, custom-designed slit-masks and a delta-doped EMCCD detector. FIREBall-2 achieves steady 1-2” pointing with a CNES-provided coarse guidance system complemented by a fine guidance system which provides real time, on-sky feedback with an sCMOS camera embedded within the spectrograph enclosure. The guider system provides a live video stream, computes translational and rotational offsets and sends high rate (30 Hz) gondola pointing error corrections, while also handling slit mask selection and in-flight optimization of the image focus and PSF. We review the current state of the system after testing and use during FIREBall-2’s 2018 and 2023 campaigns and discuss its performance, challenges and development of its hardware and software functions ahead of its next flight campaign.
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.
The Faint Intergalactic-medium Redshifted Emission Balloon (FB-2), a collaborative NASA/CNES suborbital balloon telescope, targets the mapping of faint UV emissions from the circumgalactic medium around low-redshift galaxies. The initial September 2018 flight encountered challenges, including a balloon breach and subsequent damage during landing, impacting the two large telescope mirrors and the critical focal corrector. Likely due to landing shock, the focal corrector experienced misalignment beyond tolerance, necessitating reevaluation and realignment. This paper outlines a comprehensive approach to realigning the focal corrector using a computer-generated hologram (CGH) and a Zygo interferometer for feedback. The CGH enables precise alignment corrections in various degrees of freedom, while interferometer feedback aids in reducing aberrations. The paper details the methodology for optical alignment, surface measurement, and performance evaluation of the focal corrector, emphasizing its successful integration into the FB-2 spectrograph in early 2023 for the September 2023 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 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 Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall-2, FB-2) is designed to discover and map faint UV emission from the circumgalactic medium around low redshift galaxies (z ~ 0.3 (C IV); z ~ 0.7 (Lyα); z ~ 1.0 (O VI)). FIREBall-2's first launch, on September 22nd 2018 out of Ft. Sumner, NM, was abruptly cut short due to a hole that developed in the balloon. FIREBall-2 was unable to observe above its minimum require altitude (25 km; nominal: 32 km) for its shortest required time (2 hours; nominal: 8+ hours). The shape of the deflated balloon, as well as a concurrent full moon close to our observed target field, revealed a severe, off-axis scattered light path directly to the UV science detector. Additional damage to FB-2 added complications to the ongoing effort to prepare FB-2 for a quick re-flight. Upon landing, several mirrors in the optical chain, including the two large telescope mirrors, were damaged, resulting in chunks of material broken off the sides and reflecting surfaces. The magnifying optical element, called the focal corrector, was discovered to be misaligned beyond tolerance after the 2018 flight, with one of its two mirrors damaged from the landing impact. We describe the steps taken thus far to mitigate the damage to the optics, as well as procedures and results from the ongoing efforts to re-align the focal corrector and spectrograph optics. We report the throughput of the spectrograph before and after the 2018 flight and plans for improving it. Finally, we describe several methods by which we address the scattered light issues seen from FIREBall-2's 2018 campaign and present the current status of FB-2 to fly during the summer campaign in Palestine, TX in 2020.
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