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Atmospheric escape is a fundamental process that affects the structure, composition, and evolution of many planets. The signatures of escape are detectable on close-in, gaseous exoplanets orbiting bright stars, owing to the high levels of extreme-ultraviolet irradiation from their parent stars. The Colorado Ultraviolet Transit Experiment (CUTE) is a CubeSat mission designed to take advantage of the near-ultraviolet stellar brightness distribution to conduct a survey of the extended atmospheres of nearby close-in planets. The CUTE payload is a magnifying NUV (2479~--~3306 Ang) spectrograph fed by a rectangular Cassegrain telescope (206mm x 84mm); the spectrogram is recorded on a back-illuminated, UV-enhanced CCD. The science payload is integrated into a 6U Blue Canyon Technology XB1 bus. CUTE was launched into a polar, low-Earth orbit on 27 September 2021 and has been conducting this transit spectroscopy survey following an on-orbit commissioning period. This paper presents the mission motivation, development path, and demonstrates the potential for small satellites to conduct this type of science by presenting initial on-orbit science observations. The primary science mission is being conducted in 2022~--~2023, with a publicly available data archive coming on line in 2023., 12 pages, 5 figures, AJ - accepted

Stellar mergers are a brief but common phase in the evolution of binary star systems1,2. These events have many astrophysical implications; for example, they may lead to the creation of atypical stars (such as magnetic stars3, blue stragglers4 and rapid rotators5), they play an important part in our interpretation of stellar populations6 and they represent formation channels of compact-object mergers7. Although a handful of stellar mergers have been observed directly8,9, the central remnants of these events were shrouded by an opaque shell of dust and molecules10, making it impossible to observe their final state (for example, as a single merged star or a tighter, surviving binary11). Here we report observations of an unusual, ring-shaped ultraviolet (‘blue’) nebula and the star at its centre, TYC 2597-735-1. The nebula has two opposing fronts, suggesting a bipolar outflow of material from TYC 2597-735-1. The spectrum of TYC 2597-735-1 and its proximity to the Galactic plane suggest that it is an old star, yet it has abnormally low surface gravity and a detectable long-term luminosity decay, which is uncharacteristic for its evolutionary stage. TYC 2597-735-1 also exhibits Hα emission, radial-velocity variations, enhanced ultraviolet radiation and excess infrared emission—signatures of dusty circumstellar disks12, stellar activity13 and accretion14. Combined with stellar evolution models, the observations suggest that TYC 2597-735-1 merged with a lower-mass companion several thousand years ago. TYC 2597-735-1 provides a look at an unobstructed stellar merger at an evolutionary stage between its dynamic onset and the theorized final equilibrium state, enabling the direct study of the merging process. Observations and stellar evolution models of a blue ring nebula and its central star (TYC 2597-735-1) suggest that the remnant star merged with a lower-mass companion several thousand years ago.

Ultraviolet spectra of protoplanetary disks trace distributions of warm gas at radii where rocky planets form. We combine HST-COS observations of H2 and CO emission from 12 classical T Tauri stars to more extensively map inner disk surface layers, where gas temperature distributions allow radially stratified fluorescence from the two species. We calculate empirical emitting radii for each species under the assumption that the line widths are entirely set by Keplerian broadening, demonstrating that the CO fluorescence originates further from the stars (r ~ 20 AU) than the H2 (r ~ 0.8 AU). This is supported by 2-D radiative transfer models, which show that the peak and outer radii of the CO flux distributions generally extend further into the outer disk than the H2. These results also indicate that additional sources of LyA photons remain unaccounted for, requiring more complex models to fully reproduce the molecular gas emission. As a first step, we confirm that the morphologies of the UV-CO bands and LyA radiation fields are significantly correlated and discover that both trace the degree of dust disk evolution. The UV tracers appear to follow the same sequence of disk evolution as forbidden line emission from jets and winds, as the observed LyA profiles transition between dominant red wing and dominant blue wing shapes when the high-velocity optical emission disappears. Our results suggest a scenario where UV radiation fields, disk winds and jets, and molecular gas evolve in harmony with the dust disks throughout their lifetimes., Accepted for publication in The Astronomical Journal on 7/13/2021

Understanding the origin of accretion and dispersal of protoplanetary disks is fundamental for investigating planet formation. Recent numerical simulations show that launching winds are unavoidable when disks undergo magnetically driven accretion and/or are exposed to external UV radiation. Observations also hint that disk winds are common. We explore how the resulting wind mass loss rate can be used as a probe of both disk accretion and dispersal. As a proof-of-concept study, we focus on magnetocentrifugal winds, MRI (magnetorotational instability) turbulence, and external photoevapotaion. By developing a simple, yet physically motivated disk model and coupling it with simulation results available in the literature, we compute the mass loss rate as a function of external UV flux for each mechanism. We find that different mechanisms lead to different levels of mass loss rate, indicating that the origin of disk accretion and dispersal can be determined, by observing the wind mass loss rate resulting from each mechanism. This determination provides important implications for planet formation. This work thus shows that the ongoing and future observations of the wind mass loss rate for protoplanetary disks are paramount to reliably constrain how protoplanetary disks evolve with time and how planet formation takes place in the disks., Comment: 16 pages; 7 figures, 5 tables, accepted for publication in ApJL; no change in the conclusions; the additional Monte-Carlo based, parameter study was conducted, following the referee's comment

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 (CSBF) in Fort Sumner, NM. FIREBall-2 was launched for the first time on the 22nd September 2018, and the payload performed the very first multi-object acquisition from space using a multi-object slit spectrograph (MOS). This 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 Ly\alpha resonance line in galaxies at z~0.67, but will find it challenging to spatially resolve the circumgalactic medium (CGM)., Comment: PUBLISHED IN JATIS: 20 pages, 8 figures

The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall) is a mission designed to observe faint emission from the circumgalactic medium of moderate redshift (z~0.7) galaxies for the first time. FIREBall observes a component of galaxies that plays a key role in how galaxies form and evolve, likely contains a significant amount of baryons, and has only recently been observed at higher redshifts in the visible. Here we report on the 2018 flight of the FIREBall-2 Balloon telescope, which occurred on September 22nd, 2018 from Fort Sumner, New Mexico. The flight was the culmination of a complete redesign of the spectrograph from the original FIREBall fiber-fed IFU to a wide-field multi-object spectrograph. The flight was terminated early due to a hole in the balloon, and our original science objectives were not achieved. The overall sensitivity of the instrument and telescope was 90,000 LU, due primarily to increased noise from stray light. We discuss the design of the FIREBall-2 spectrograph, modifications from the original FIREBall payload, and provide an overview of the performance of all systems. We were able to successfully flight test a new pointing control system, a UV-optimized, delta-doped and coated EMCCD, and an aspheric grating. The FIREBall-2 team is rebuilding the payload for another flight attempt in the Fall of 2021, delayed from 2020 due to COVID-19., 23 Pages, 14 Figures, Accepted for Publication in ApJ

Stellar mergers are a brief but common phase in the evolution of binary star systems

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 ($, Comment: 36 pages, 9 figures

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.

In this talk, I will describe briefly the telescope, instrument, and flight of the Faint Intergalactic medium Redshifted Emission Balloon (FIREBall-2). FIREBall-2 is a UV multi-object spectrograph fed by a 1 meter parabola mirror. The instrument was designed to observe 4 pre-selected fields and uses a UV optimized delta-doped EMCCD. The telescope flew on September 22, 2018 from Fort Sumner, NM, as part of the fall CSBF balloon campaign. The telescope collected data for several night hours before being cut down. I will describe the testing, flight, and hardware performance with an emphasis on the in flight performance of the instrument, including resolution, throughput, and the overall operation of the UV optimized EMCCD. Additional talks will be presented on other aspects of the flight and data.

I will present on-going detector developments in our joint NASA/CNES balloon-borne UV multi-object spectrograph, FIREBall-2, the Faint Intergalactic Redshifted Emission Balloon. FIREBall-2 is a path finding mission to test new technology (EMCCDs) and make new constraints on the temperature and density of this gas. This instrument has been designed to detect faint emission from the circumgalactic medium (CGM) around low redshift galaxies (z ~ 0.7). One major change from FIREBall-1 has been the use of a delta-doped Electron Multiplying CCD (EMCCD). EMCCDs can be used in photon-counting (PC) mode to achieve extremely low readout noise (< 1 electron). Our testing initially focused on reducing clock-induced-charge (CIC) through wave shaping and well depth optimisation with a NuVu CCD Controller for Counting Photons (CCCP). This optimisation also includes methods for reducing dark current, via cooling, and exploring substrate voltage levels. I will present some of our dark current results from laboratory testing. We recently launched FIREBall-2 from Fort Sumner, New Mexico on September 22nd, 2018. This was the first time an EMCCD has been used for UV/optical observations in flight! I will present performance data from the flight including cosmic ray rate measurements, and some of our preliminary on-sky UV results using our data reduction.

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, Submitted to the Proceedings of SPIE, Defense + Commercial Sensing (SI19)

We present the pilot study component of the Fluorescent Lyman-Alpha Structures in High-z Environments (FLASHES) Survey; the largest integral-field spectroscopy survey to date of the circumgalactic medium at $z=2.3-3.1$. We observed 48 quasar fields between 2015 and 2018 with the Palomar Cosmic Web Imager (Matuszewski et al. 2010). Extended HI Lyman-$\mathrm{\alpha}$ emission is discovered around 42/48 of the observed quasars, ranging in projected, flux-weighted radius from 21-71 proper kiloparsecs (pkpc), with 26 nebulae exceeding $100\mathrm{~pkpc}$ in effective diameter. The circularly averaged surface brightness radial profile peaks at a maximum of $\mathrm{1\times 10^{-17}~erg~s^{-1}~cm^{-2}~arcsec^{-2}}$ ($2\times10^{-15}~\mathrm{erg~s^{-1}~cm^{-2}~arcsec^{-2}}$ adjusted for cosmological dimming) and luminosities range from $1.9\times10^{43}~\mathrm{erg~s^{-1}}$ to $-14.1\times10^{43}~\mathrm{erg~s^{-1}}$. The emission appears to have a highly eccentric morphology and a maximum covering factor of $50\%$ ($60\%$ for giant nebulae). On average, the nebular spectra are red-shifted with respect to both the systemic redshift and Ly$\alpha$ peak of the quasar spectrum. The integrated spectra of the nebulae mostly have single or double-peaked line shapes with global dispersions ranging from $167~\mathrm{km~s^{-1}}$ to $690~\mathrm{km~s^{-1}}$, though the individual (Gaussian) components of lines with complex shapes mostly appear to have dispersions $\leq 400$ $\mathrm{km~s^{-1}}$, and the flux-weighted velocity centroids of the lines vary by thousands of $ \mathrm{km~s^{-1}}$ with respect to the systemic QSO redshifts. Finally, the root-mean-square velocities of the nebulae are found to be consistent with gravitational motions expected in dark matter halos of mass $\mathrm{M_h \simeq10^{12.5} M_\odot}$. We compare these results to existing surveys at both higher and lower redshift.

We are conducting a multi-wavelength analysis of high-resolution molecular spectra that probe the evolution of gas in the inner 10 au in protoplanetary disks. A sample of 15 disks has been combined to probe a range of inner disk structures including small and large dust cavities. Half of the sample has been observed in far-ultraviolet H2 emission with a new HST-COS program (GO-14703), that we have combined to near-infrared spectra of CO emission as observed with VLT-CRIRES and IRTF-iSHELL. This synergic dataset traces the evolution and depletion of CO and H2 in inner disk cavities and shows an evolving radial stratification of the molecular gas, where CO lines are narrower than H2 lines in disks with cavities. CO rotation diagrams also show significant evolution, suggesting a change in gas excitation as CO emission recedes to larger disk radii.

The UV radiation field is a critical regulator of gas-phase chemistry in surface layers of disks around young stars. In an effort to understand the relationship between photocatalyzing UV radiation fields and gas emission observed at infrared and sub-mm wavelengths, we present an analysis of new and archival HST, Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to measure LyA and FUV continuum fluxes reaching the disk surface, which are responsible for dissociating relevant molecular species (e.g. HCN, N2). Semi-forbidden C II] 2325 and UV-fluorescent H2 emission were also measured to constrain inner disk populations of C+ and vibrationally excited H2. We find a significant positive correlation between 14 micron HCN emission and fluxes from the FUV continuum and C II] 2325, consistent with model predictions requiring N2 photodissociation and carbon ionization to trigger the main CN/HCN formation pathways. We also report significant negative correlations between sub-mm CN emission and both C II] and FUV continuum fluxes, implying that CN is also more readily dissociated in disks with stronger FUV irradiation. No clear relationships are detected between either CN or HCN and LyA or UV-H2 emission. This is attributed to the spatial stratification of the various molecular species, which span several vertical layers and radii across the inner and outer disk. We expect that future observations with JWST will build on this work by enabling more sensitive IR surveys than were possible with Spitzer., Accepted for publication in AJ

In this proceeding, we describe the scientific motivation and technical development of the Colorado Highresolution Echelle Stellar Spectrograph (CHESS), focusing on the hardware advancements and testing of components for the fourth and final launch of the payload (CHESS-4). CHESS is a far ultraviolet rocket-borne instrument designed to study the atomic-to-molecular transitions within translucent cloud regions in the interstellar medium. CHESS is an objective echelle spectrograph, which uses a mechanically-ruled echelle and a powered (f/12.4) cross-dispersing grating; it is designed to achieve a resolving power R > 100,000 over the band pass λλ 1000–1600 A. CHESS-4 utilizes a 40 mm-diameter cross-strip anode readout microchannel plate detector, fabricated by Sensor Sciences LLC, to achieve high spatial resolution with high global count rate capabilities (∼ MHz). An error in the fabrication of the cross disperser limited the achievable resolution on previous launches of the payload to R ∼ 4000. To remedy this for CHESS-4, we physically stress the echelle grating, introducing a shallow toroidal curvature to the surface of the optic. Preliminary laboratory measurements of the resulting spectrum show a factor of 4–5 improvement to the resolving power. Results from final efficiency and reflectivity measurements for the optical components of CHESS-4 are presented, along with the pre-flight laboratory spectra and calibration results. CHESS-4 launched on 17 April 2018 aboard NASA/University of Colorado Boulder sounding rocket mission 36.333 UG. We present flight results for the observation of the γ Ara sightline.

We present a study of molecular gas in the inner disk $\left(r < 20 \, \text{AU} \right)$ around RY Lupi, with spectra from HST-COS, HST-STIS, and VLT-CRIRES. We model the radial distribution of flux from hot gas in a surface layer between $r = 0.1-10$ AU, as traced by Ly$\alpha$-pumped H$_2$. The result shows H$_2$ emission originating in a ring centered at $\sim$3 AU that declines within $r < 0.1$ AU, which is consistent with the behavior of disks with dust cavities. An analysis of the H$_2$ line shapes shows that a two-component Gaussian profile $\left(\text{FWHM}_{broad, H_2} = 105 \pm 15 \, \text{km s}^{-1}; \, \text{FWHM}_{narrow, H_2} = 43 \pm 13 \, \text{km s}^{-1} \right)$ is statistically preferred to a single-component Gaussian. We interpret this as tentative evidence for gas emitting from radially separated disk regions $\left( \left \langle r_{broad, H_2} \right \rangle \sim 0.4 \pm 0.1 \, \text{AU}; \, \left \langle r_{narrow, H_2} \right \rangle \sim 3 \pm 2 \, \text{AU} \right)$. The 4.7 $\mu$m $^{12}$CO emission lines are also well fit by two-component profiles $\left( \left \langle r_{broad, CO} \right \rangle = 0.4 \pm 0.1 \, \text{AU}; \, \left \langle r_{narrow, CO} \right \rangle = 15 \pm 2 \, \text{AU} \right)$. We combine these results with 10 $\mu$m observations to form a picture of gapped structure within the mm-imaged dust cavity, providing the first such overview of the inner regions of a young disk. The HST SED of RY Lupi is available online for use in modeling efforts., Comment: Accepted for publication in ApJ

The Colorado Ultraviolet Transit Experiment (CUTE) is a near-UV (2550 - 3300 A) 6U cubesat mission designed to monitor transiting hot Jupiters to quantify their atmospheric mass loss and magnetic fields. CUTE will probe both atomic (Mg and Fe) and molecular (OH) lines for evidence of enhanced transit absorption, and to search for evidence of early ingress due to bow shocks ahead of the planet’s orbital motion. As a dedicated mission, CUTE will observe g 60 spectroscopic transits of hot Jupiters over a nominal seven month mission. This represents the equivalent of > 700 orbits of the only other instrument capable of these measurements, the Hubble Space Telescope. CUTE efficiently utilizes the available cubesat volume by means of an innovative optical design to achieve a projected effective area of ∼ 22 cm 2 , low instrumental background, and a spectral resolving power of R ∼ 3000 over the entire science bandpass. These performance characteristics enable CUTE to discern a transit depth of l1% in individual spectral absorption lines. We present the CUTE optical and mechanical design, a summary of the science motivation and expected results, and an overview of the projected fabrication, calibration and launch timeline.

NASA is currently carrying out science and technical studies to identify its next astronomy flagship mission, slated to begin development in the 2020s. It has become clear that a Large Ultraviolet/Optical/IR (LUVOIR) Surveyor mission (primary diameter 12 m, 1000 Ang - 2 micron spectroscopic bandpass) can carry out the largest number of NASA's exoplanet and astrophysics science goals over the coming decades. There are technical challenges for several aspects of the LUVOIR Surveyor concept, including component level technology readiness maturation and science instrument concepts for a broadly capable ultraviolet spectrograph. We present the scientific motivation for, and a preliminary design of, a multiplexed ultraviolet spectrograph to support both the exoplanet and astrophysics goals of the LUVOIR Surveyor mission concept, the Combined High-resolution and Imaging Spectrograph for the LUVOIR Surveyor (CHISL). CHISL includes a high-resolution (R 120,000; 1000 - 1700 Ang) point-source spectroscopy channel and a medium resolution (R > 14,000 from 1000 - 2000 Ang in a single observation and R 24,000 - 35,000 in multiple grating settings) imaging spectroscopy channel. We present the CHISL concept, a small sample of representative science cases, and the primary technological hurdles. We are actively engaged in laboratory and flight characterization efforts for CHISL-enabling technologies as components on sounding rocket payloads under development at the University of Colorado. We describe two payloads that are designed to be pathfinder instruments for the high-resolution (CHESS) and imaging spectroscopy (SISTINE) arms of CHISL. We are carrying out this instrument design, characterization, and flight-testing today to support the new start of a LUVOIR Surveyor mission in the next decade., Accepted for publication in JATIS. 19 pages, 11 figures

In this proceeding, we describe the scientific motivation and technical development of the Colorado High-resolution Echelle Stellar Spectrograph (CHESS), focusing on the hardware advancements and testing supporting the second flight of the payload (CHESS-2). CHESS is a far ultraviolet (FUV) rocket-borne instrument designed to study the atomic-to-molecular transitions within translucent cloud regions in the interstellar medium (ISM). CHESS is an objective f/12.4 echelle spectrograph with resolving power $>$ 100,000 over the band pass 1000 $-$ 1600 {\AA}. The spectrograph was designed to employ an R2 echelle grating with "low" line density. We compare the FUV performance of experimental echelle etching processes (lithographically by LightSmyth, Inc. and etching via electron-beam technology by JPL Microdevices Laboratory) with traditional, mechanically-ruled gratings (Bach Research, Inc. and Richardson Gratings). The cross-dispersing grating, developed and ruled by Horiba Jobin-Yvon, is a holographically-ruled, "low" line density, powered optic with a toroidal surface curvature. Both gratings were coated with aluminum and lithium fluoride (Al+LiF) at Goddard Space Flight Center (GSFC). Results from final efficiency and reflectivity measurements for the optical components of CHESS-2 are presented. CHESS-2 utilizes a 40mm-diameter cross-strip anode readout microchannel plate (MCP) detector fabricated by Sensor Sciences, Inc., to achieve high spatial resolution with high count rate capabilities (global rates $>$ 1 MHz). We present pre-flight laboratory spectra and calibration results. CHESS-2 launched on 21 February 2016 aboard NASA/CU sounding rocket mission 36.297 UG. We observed the intervening ISM material along the sightline to $\epsilon$ Per and present initial characterization of the column densities, temperature, and kinematics of atomic and molecular species in the observation., Comment: 19 pages, 16 figures, to be submitted to SPIE Astronomical Telescopes + Instrumentation 2016 (9905-138)

NASA's suborbital program provides an opportunity to conduct unique science experiments above Earth's atmosphere and is a pipeline for the technology and personnel essential to future space astrophysics, heliophysics, and atmospheric science missions. In this paper, we describe three astronomy payloads developed (or in development) by the Ultraviolet Rocket Group at the University of Colorado. These far-ultraviolet (100 - 160 nm) spectrographic instruments are used to study a range of scientific topics, from gas in the interstellar medium (accessing diagnostics of material spanning five orders of magnitude in temperature in a single observation) to the energetic radiation environment of nearby exoplanetary systems. The three instruments, SLICE, CHESS, and SISTINE form a progression of instrument designs and component-level technology maturation. SLICE is a pathfinder instrument for the development of new data handling, storage, and telemetry techniques. CHESS and SISTINE are testbeds for technology and instrument design enabling high-resolution (R > 100,000) point source spectroscopy and high throughput imaging spectroscopy, respectively, in support of future Explorer, Probe, and Flagship-class missions. The CHESS and SISTINE payloads support the development and flight testing of large-format photon-counting detectors and advanced optical coatings: NASA's top two technology priorities for enabling a future flagship observatory (e.g., the LUVOIR Surveyor concept) that offers factors of roughly 50 - 100 gain in ultraviolet spectroscopy capability over the Hubble Space Telescope. We present the design, component level laboratory characterization, and flight results for these instruments., 22 pages, 14 figures. Accepted for publication in the Journal of Astronomical Instrumentation

We measure H$_2$ temperatures and column densities across the Orion BN/KL explosive outflow from a set of thirteen near-IR H$_2$ rovibrational emission lines observed with the TripleSpec spectrograph on Apache Point Observatory's 3.5-meter telescope. We find that most of the region is well-characterized by a single temperature (~2000-2500 K), which may be influenced by the limited range of upper energy levels (6000-20,000 K) probed by our data set. The H$_2$ column density maps indicate that warm H$_2$ comprises 10$^{-5}$ - 10$^{-3}$ of the total H$_2$ column density near the center of the outflow. Combining column density measurements for co-spatial H$_2$ and CO at T = 2500 K, we measure a CO/H$_2$ fractional abundance of 2$\times$10$^{-3}$, and discuss possible reasons why this value is in excess of the canonical 10$^{-4}$ value, including dust attenuation, incorrect assumptions on co-spatiality of the H$_2$ and CO emission, and chemical processing in an extreme environment. We model the radiative transfer of H$_2$ in this region with UV pumping models to look for signatures of H$_2$ fluorescence from H I Ly$\alpha$ pumping. Dissociative (J-type) shocks and nebular emission from the foreground Orion H II region are considered as possible Ly$\alpha$ sources. From our radiative transfer models, we predict that signatures of Ly$\alpha$ pumping should be detectable in near-IR line ratios given a sufficiently strong source, but such a source is not present in the BN/KL outflow. The data are consistent with shocks as the H$_2$ heating source., Comment: 24 pages, 8 figures, 3 tables, accepted to ApJ

We present the results of a preliminary aging study of new enhanced broadband reflectivity lithium fluoride mirror coatings under development at the thin films laboratory at GSFC. These coatings have demonstrated greater than 80% reflectivity from the Lyman ultraviolet (~1020 A) to the optical, and have the potential to revolutionize far-ultraviolet instrument design and capabilities. This work is part of a concept study in preparation for the fight qualification of these new coatings in a working astronomical environment. We outline the goals for TRL advancement, and discuss the instrument capabilities enabled by these high reflectivity broadband coatings on potential future space missions. We also present the early design of the first space experiment to utilize these coatings, the proposed University of Colorado sounding rocket payload SISTINE, and show how these new coatings make the science goals of SISTINE attainable on a suborbital platform.

Observations of molecular hydrogen (H$_2$) fluorescence are a potentially useful tool for measuring the H$_2$ abundance in exoplanet atmospheres. This emission was previously observed in M$\;$dwarfs with planetary systems. However, low signal-to-noise prevented a conclusive determination of its origin. Possible sources include exoplanetary atmospheres, circumstellar gas disks, and the stellar surface. We use observations from the "Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanet Host Stars" (MUSCLES) Treasury Survey to study H$_2$ fluorescence in M$\;$dwarfs. We detect fluorescence in Hubble Space Telescope spectra of 8/9 planet-hosting and 5/6 non-planet-hosting M$\;$dwarfs. The detection statistics, velocity centroids, and line widths of the emission suggest a stellar origin. We calculate H$_2$-to-stellar-ion flux ratios to compare flux levels between stars. For stars with planets, we find an average ratio of 1.7$\,\pm\,$0.9 using the fluxes of the brightest H$_2$ feature and two stellar C IV lines. This is compared to 0.9$\,\pm\,$0.4 for stars without planets, showing that the planet-hosting M$\;$dwarfs do not have significant excess H$_{2}$ emission. This claim is supported by the direct FUV imaging of GJ 832, where no fluorescence is observed at the expected star-planet separation. Additionally, the 3-$\sigma$ upper limit of 4.9$\,\times\,$10$^{-17}$ erg$\;$cm$^{-2}\;$s$^{-1}$ from these observations is two orders of magnitude below the spectroscopically-observed H$_2$ flux. We constrain the location of the fluorescing H$_2$ using 1D radiative transfer models and find that it could reside in starspots or a $\sim$2500-3000$\;$K region in the lower chromosphere. The presence of this emission could complicate efforts to quantify the atmospheric abundance of H$_2$ in exoplanets orbiting M$\;$dwarfs., Comment: 20 pages, 7 figures, 7 tables; Accepted by ApJ

The Colorado High-resolution Echelle Stellar Spectrograph (CHESS) is a far ultraviolet (FUV) rocket-borne experiment designed to study the atomic-to-molecular transitions within translucent interstellar clouds. CHESS is an objective echelle spectrograph operating at f/12.4 and resolving power of 120,000 over a band pass of 100 – 160 nm. The echelle flight grating is the product of a research and development project with LightSmyth Inc. and was coated at Goddard Space Flight Center (GSFC) with Al+LiF. It has an empirically-determined groove density of 71.67 grooves/mm. At the Center for Astrophysics and Space Astronomy (CASA) at the University of Colorado (CU), we measured the efficiencies of the peak and adjacent dispersion orders throughout the 90 – 165 nm band pass to characterize the behavior of the grating for pre-flight calibrations and to assess the scattered-light behavior. The crossdispersing grating, developed and ruled by Horiba Jobin-Yvon, is a holographically-ruled, low line density (351 grooves/mm), powered optic with a toroidal surface curvature. The CHESS cross-disperser was also coated at GSFC; Cr+Al+LiF was deposited to enhance far-UV efficiency. Results from final efficiency and reflectivity measurements of both optics are presented. We utilize a cross-strip anode microchannel plate (MCP) detector built by Sensor Sciences to achieve high resolution (25 μm spatial resolution) and data collection rates (~ 106 photons/second) over a large format (40mm round, digitized to 8k x 8k) for the first time in an astronomical sounding rocket flight. The CHESS instrument was successfully launched from White Sands Missile Range on 24 May 2014. We present pre-flight sensitivity, effective area calculations, lab spectra and calibration results, and touch on first results and post-flight calibration plans.

We present the flight performance and preliminary science results from the first flight of the Sub-orbital Local Interstellar Cloud Experiment (SLICE). SLICE is a rocket-borne far-ultraviolet instrument designed to study the diffuse interstellar medium. The SLICE payload comprises a Cassegrain telescope with LiF-coated aluminum optics feeding a Rowland Circle spectrograph operating at medium resolution (R ~ 5000) over the 102 – 107 nm bandpass. We present a novel method for cleaning LiF-overcoated Al optics and the instrumental wavelength calibration, while the details of the instrument design and assembly are presented in a companion proceeding (Kane et al. 2013). We focus primarily on first results from the spring 2013 launch of SLICE in this work. SLICE was launched aboard a Terrier-Black Brant IX sounding rocket from White Sands Missile Range to observe four hot stars sampling different interstellar sightlines. The instrument acquired approximately 240 seconds of on-target time for the science spectra. We observe atomic and molecular transitions (HI, OI, CII, OVI, H2) tracing a range of temperatures, ionization states, and molecular fractions in diffuse interstellar clouds. Initial spectral synthesis results and future plans are discussed.

We present the fabrication and testing of the Sub-orbital Local Interstellar Cloud Experiment (SLICE), a rocket-borne payload for ultraviolet astrophysics in the 1020 to 1070 A bandpass. The SLICE optical system is composed of an ultraviolet-optimized telescope feeding a Rowland Circle spectrograph. The telescope is an 8-inch Classical Cassegrain operating at F/7, with Al optics overcoated with LiF for enhanced far-ultraviolet reflectivity. The holographically-ruled grating focuses light at an open-faced microchannel plate detector employing an opaque RbBr photocathode. In this proceeding, we describe the design trades and calibration issues confronted during the build-up of this payload. We place particular emphasis on the technical details of the design, modifications, construction, and alignment procedures for SLICE in order to provide a roadmap for the optimization of future ruggedized experiments for ultraviolet imaging and spectroscopy.