arXiv subjects

Kevin France

Publications and source records attributed to Kevin France.

At least 19 recordsLinked to original sources

arXiv2026

The future of high-resolution UV spectroscopy: Science with a UV \'Echelle spectrograph on the Habitable Worlds Observatory, or a dedicated mission

High-resolution UV spectroscopy serves a diversity of science cases, from small bodies to planets, stars, and galaxies, but is currently limited to the Hubble Space Telescope and bright targets. Major advances require increasing sensitivity by at least one order of magnitude. Here we present the UV science cases for PEGASUS (Planets, Earths, Galaxies, And Stars UV Spectrograph), a UV \'Echelle high-resolution spectrograph concept, with $R = \lambda/\delta\lambda \sim 100\,000$ (full range 10 000-140 000) and covering 90--400 nm, with a foreseen extension to at least 800 nm. PEGASUS is ideally suited for the Habitable Worlds Observatory (HWO), enabling transformative science across the UV/optical wavelength ranges. PEGASUS will be unique in high sensitivity (effective area) and high spectral resolution -- an uncharted territory -- as well as robustness, thanks to the simplicity of its design. Its UV science cases include: I) Formation and evolution of planets and their habitability: properties of exoplanets and atmospheres, protoplanetary disks, Solar System bodies; II) Stellar lives and deaths at their extremes: the first stars and the origin of the elements, compact and massive stars, Supernovae; III) Gas and metals in the baryon cycle of galaxies: the interstellar, circumgalactic, and intergalactic medium and their roles in galaxy growth. These are essential for the Astro Decadal 2020 Survey, Voyage 2050, and HWO. While this paper focuses on high-impact science enabled by UV high-resolution spectroscopy, PEGASUS will extend into the optical regime and lower spectral resolution, making it a multi-purpose, widely used, workhorse spectrograph for HWO.

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arXiv2026

The SPACE Program II: No discernible spectral features in the transmission spectrum of the sub-Neptune HD 191939 b observed with HST/WFC3

The atmospheres of sub-Neptunes provide a window into their internal structure and history, shedding light on the origin of this common, but enigmatic, class of exoplanets. However, the physical and chemical processes that shape sub-Neptunes' transmission spectra, in particular cloud and haze formation, are not well understood. To identify possible correlations between transmission spectra and UV irradiation, the SPACE (Sub-neptune Planetary Atmosphere Characterization Experiment) Program observed an array of sub-Neptunes and their host stars using the Hubble Space Telescope (HST), measuring the planets' transmission spectra between $1.1\,\mu$m and $1.7\,\mu$m with the Wide Field Camera 3 (WFC3) and the stars' UV spectra with the Space Telescope Imaging Spectrograph (STIS). Here, we present the observations of HD 191939 b carried out as part of the SPACE Program, which reveal no significant spectral features in the transmission spectrum. The data deliver moderate evidence at significance levels between $2.0\,\sigma$ and $3.2\,\sigma$ against a cloud-free atmosphere with solar metallicity, rendering this scenario unlikely, but still possible. A super-solar metallicity of HD 191939 b might be consistent with the known trend of increasing atmospheric metallicity with decreasing planet mass. Both hydrocarbon haze formation and cloud condensation can be efficient at HD 191939 b's zero-albedo equilibrium temperature of $(880\pm 20)\,$K, particularly in atmospheres with super-solar metallicity, possibly additionally muting absorption features.

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arXiv2026

Optomechanical Design of the MANTIS SmallSat: An Extreme-, Far- and Near-Ultraviolet Spectrograph for Exoplanet Host Stars

The MANTIS (Monitoring Activity of Nearby sTars with uv Imaging and Spectroscopy) observatory is a compact, multi-instrument small satellite designed for simultaneous extreme- (EUV; 100 - 560 Angstrom), far- (FUV; 1150-1800 Angstrom) and near-ultraviolet/visible (NUV/VIS; 2000-6400 Angstrom) spectroscopy of low-mass stars. The EUV optical system consists of a first-of-its-kind Hettrick-Bowyer grazing incidence telescope contributed by the Italian National Institute for Astrophysics (INAF) feeding an advanced e-beam lithographic etched variable line spacing grating developed at Pennsylvania State University (PSU). The resulting low-resolution spectrum is imaged on an advanced microchannel plate detector with a potassium iodide (KI) photocathode for extremely low background noise, resulting in a limiting sensitivity for MANTIS that exceeds that of the last EUV-sensitive astrophysics point-source spectrograph, the Deep Survey/Spectrometer (DS/S) on EUVE. The FUV and NUV/Optical channels are fed by a compact rectangular telescope that focuses onto a series of point-source apertures. The diverging beam is refocused and the FUV band dispersed by a holographic grating, then folded back onto the same detector as the EUV channel by a toroidal fold mirror. The zero-order light is picked off by a flat NUV grating, with the NUV/Optical spectrum recorded on an e2v CCD 42-10 detector. The MANTIS spacecraft is a custom build that leverages the experience derived from prior University of Colorado - LASP SmallSats for avionics, power, communications, and mechanical structure. MANTIS is projected to be completed in 2027 with an anticipated 2028 launch as an ESPA-class payload on a rideshare opportunity.

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arXiv2026

ESCAPE: a small explorer mission to study the stellar drivers of exoplanet evolution

The long-term stability of exoplanetary atmospheres depends critically on the extreme-ultraviolet (EUV) photon and high-energy particle fluxes from the host star, which are poorly constrained. To address this key gap in our understanding of atmospheric retention, we present the Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission, a NASA Small Explorer concept proposed in 2026. ESCAPE employs extreme- and far-ultraviolet spectroscopy (80 - 1650 Ang) to provide the first comprehensive study of the stellar EUV history and stellar coronal mass ejection (CME) environments that control atmospheric mass-loss and determine the habitability of rocky exoplanets. This paper outlines both the primary science goals of the mission, the breadth of future general observer investigations, and a detailed design study of the mission's instrumentation. The ESCAPE instrument comprises a grazing incidence telescope that feeds multiple diffraction gratings and a photon-counting detector. We describe a demonstration of the Hettrick-Bowyer telescope, etched silicon diffraction gratings, the microchannel plate detector and housing, and gold and zirconium coatings. We present a STOP analysis that verifies ESCAPE's ability to meet its structural integrity, thermal stability, and optical performance requirements throughout the mission environment.

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arXiv2026

Ardua: Unveiling the Baryon Cycle from Stars to the Cosmic Web

The circumgalactic medium (CGM) -- the multiphase gas reservoirs surrounding galaxies -- remains the least understood component of the baryon cycle governing galaxy growth, despite its central role in the Astro2020 Decadal Survey's priorities. Existing constraints come almost exclusively from pencil-beam absorption spectroscopy, leaving the spatial structure, kinematics, and phase interactions of CGM gas fundamentally unmapped. We present Ardua, a mission concept for NASA's ASTRA Initiative that combines wide-field far-ultraviolet spectroscopy with a Line Emission Mapper (LEM)-derived X-ray microcalorimeter instrument to obtain the first comprehensive emission maps spanning the full CGM temperature range, including cool neutral gas, ionized warm-hot phase gas, and the volume-filling hot corona. By observing more than 50 nearby galaxies comprehensively in the UV and X-ray, Ardua will test competing galaxy formation models, resolve multiphase gas flows and feedback-driven outflows, and extend baryon-cycle science to the intergalactic medium and the environments of exoplanet-hosting stars. Beyond its core CGM/IGM program, Ardua's wide-field, high-sensitivity instruments are designed to serve as a flexible community resource, supporting guest-investigator science across astrophysics. No planned or approved mission is designed to deliver this combined UV/X-ray survey capability.

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arXiv2026

Predicted Capabilities of the SPRITE SmallSat for a Low-Redshift Lyman Continuum Emission Survey

Ionizing Lyman continuum (LyC; $\lambda < 912~\rm{\mathring{A}}$) radiation from low-redshift ($z \sim 0.3$) galaxies provides crucial insight into the processes that contributed to cosmic reionization. While the \textit{James Webb Space Telescope} has observed galaxies at redshifts as high as $z \sim 14$, detecting LyC beyond $z \sim 3$ is challenging due to absorption by neutral hydrogen in the intergalactic medium (IGM). Low-redshift LyC emitters (LCEs), therefore, act as proxies for their high-redshift counterparts, enabling direct measurements of LyC escape fractions with reduced IGM interference. These observations allow detailed ancillary studies of galaxy properties and the mechanisms driving ionizing photon escape, which cannot be directly observed at the Epoch of Reionization. This paper examines the capabilities of the Supernova remnants and Proxies for Re-Ionization Testbed Experiment (SPRITE) SmallSat, designed to study LyC emission from star-forming galaxies at $0.16 < z < 0.4$. SPRITE uses advanced mirror coatings and a highly sensitive far-ultraviolet imaging spectrograph, enabling it to probe LyC from galaxies that have been difficult to study with prior and existing instruments. To assess SPRITE's predicted performance in LyC studies, we select eight previously confirmed LCEs from the Low-redshift Lyman Continuum Survey as commissioning targets. Observations of these commissioning LCEs will validate SPRITE's LyC sensitivity and characterize its detection limits. This will enable the broader SPRITE low-redshift LCE survey, which will provide new constraints on the physics of LyC escape and help bridge the gap between low- and high-redshift LyC studies. SPRITE will also inform the design and scientific potential of future Lyman-UV missions, including the Habitable Worlds Observatory.

astro-ph.GA↗

arXiv2026

A Critical UV Legacy: A Hubble Roadmap for HWO Science Readiness

The Habitable Worlds Observatory (HWO) will provide the first opportunity to directly image and spectrally characterize terrestrial exoplanets in the habitable zones of nearby stars. Maximizing its scientific return requires a comprehensive understanding of the high-energy radiation environments of target stars, which shape planetary atmospheres and govern the production, destruction, and detectability of biosignatures. Ultraviolet (UV) radiation plays a particularly critical role in atmospheric chemistry. Far-ultraviolet (FUV) and near-ultraviolet (NUV) photons regulate key photochemical pathways, influence ozone stability, and drive the formation of prebiotic molecules. However, the majority of high-priority HWO target stars lack high-quality UV observations. Existing datasets are sparse, heterogeneous, or limited by calibration uncertainties, and no comparable UV observatory is expected for at least 5-10 years (with UVEX offering more limited spectral resolution, wavelength coverage, and sensitivity). The Hubble Space Telescope (HST) remains the only observatory capable of acquiring high-resolution FUV and NUV spectra for these targets over the next 10-15 years. We therefore advocate for a coordinated HST program to systematically obtain UV spectra of high-priority HWO targets, ideally in conjunction with X-ray observations. This effort is essential for enabling accurate target prioritization, constraining stellar radiation environments, and ensuring robust interpretation of future HWO observations.

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arXiv2026

KRONOS I: The $1{-}2.8\mu$m JWST Transmission Spectrum of the 23 Myr V1298 Tau c

While recent JWST observations of mature super-Earths and sub-Neptunes have frequently revealed featureless transmission spectra, their inflated progenitors offer a unique window into understanding their primordial compositions. As part of the Keys to Revealing the Origin and Nature Of sub-neptune Systems (KRONOS) JWST program, we present the NIRISS/SOSS transmission spectrum of V1298 Tau c, a $\sim$23 Myr super-Earth progenitor orbiting a young Solar analog. We detect H$_2$O in V1298 Tau c's atmosphere with a $\log_{10}$ volume mixing ratio of $-1.83^{+0.68}_{-0.77}$, but no additional molecules from these data alone. We find consistent results for the planetary atmospheric properties in both retrievals with and without informed priors on stellar heterogeneities based on the observed stellar spectrum. We infer an atmospheric metallicity [O/H] of $14.8^{+56.0}_{-12.28}\times$ the solar value. This metallicity is similar to literature measurements for other young planets, including its massive outer companion V1298~Tau~b. In contrast, this measured metallicity is systematically lower than the metallicities of mature planets of similar mass and temperature. Altogether, these results provide tentative but growing evidence that the exoplanet mass--metallicity relation evolves with planetary age.

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arXiv2026

Astronomical Advantages of a Boost Mission to Facilitate HST Science into the 2030s: Imaging the Circumgalactic Medium of Galaxies

We present the case for imaging ultraviolet line emission from highly ionized metals and HI Lya in the circumgalactic medium of galaxies, should the Hubble Space Telescope receive an orbital boost. Hubble can uniquely probe emission lines with ionization potentials between 13 and 200 electron-volts (Lya, CIV, OVI, NeVIII, etc). Spatial mapping of the diffuse material traced by these transitions is critical to constraining the physics of feedback and the energetic exchange between galaxies and their circumgalactic environments, as well as basic morphologies of the dominant mass component. Deep high-resolution mapping of these features will not be possible with any other observatory, existing or planned, until HWO is launched, which leaves HST as a critical observatory to test key science drivers for HWO. If HST receives an orbital boost, it can (a) provide the first statistical constraints on the spatial distribution of warm-hot CGM and (b) provide important avenues for science case development, as well as target/pointing selection, for HWO's upcoming spectroscopic facilities.

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arXiv2026

Extending Hubble into the 2030s to Resolve the Physics of LyC Escape

Current observations with the James Webb Space Telescope (JWST) suggest that star-forming galaxies produce enough ionizing (LyC; $\lambda < 91.2$ nm) photons to drive cosmic reionization, but the efficiency with which these photons escape their host galaxies remains uncertain. Absorption by the neutral intergalactic medium progressively suppresses direct LyC detections above redshift $z\sim3$, forcing astronomers to rely on indirect diagnostics of LyC escape calibrated at low redshift. Low-resolution ultraviolet observations of high-redshift analogs obtained with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (HST) have been critical for developing these diagnostics. These studies suggest that stellar feedback plays a central role in regulating LyC escape, although the role of galactic winds and the underlying physical mechanisms remain poorly constrained. High-resolution spectroscopy blueward of 160.0 nm (rest-frame) is required to resolve the kinematic structure of the winds and reveal the physics governing LyC escape. Such observations are currently only possible with HST and represent a major science driver for the future Habitable Worlds Observatory (HWO). Extending the lifetime of HST and prioritizing ultraviolet observations are essential for interpreting current JWST studies of the early Universe and important preparatory science for HWO.

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arXiv2026

The unique ability of the Hubble Space Telescope to characterize young exoplanet environments

The chemical and mass evolution of exoplanet atmospheres is shaped by their specific X-ray through ultraviolet (5 - 3200 Angstroms) irradiance history. X-ray and EUV (5 - 911 Angstroms) radiation largely contributes to atmospheric heating via photoionization, while far- and near-UV emission (912 - 3200 Angstroms) drives photochemistry. The (uncharacterized) variance between young star spectra in this wavelength range for the same spectral type causes significant uncertainty in interpreting present-day transmission spectra of young exoplanets, directly impacting the science return of the James Webb Space Telescope and other programs. Additionally, the lack of direct X-ray through UV characterization for stars of all ages leads to large uncertainties in the high-energy irradiance history of all planetary systems, propagating into uncertainties in their chemical and mass evolution. This influences current and future observing programs, as well as the goal of the future flagship Habitable Worlds Observatory to find and characterize habitable exoplanets. There are less than a handful of young planet hosts with well-characterized X-ray through UV environments. The Hubble Space Telescope is the only observatory capable of measuring the UV spectrum and enabling the characterization of exoplanet high-energy environments. We advocate for an observing program to measure the UV, estimate the EUV, and measure the X-ray where possible and needed of all amenable young planet hosts, addressing the Space Telescope Science Institute's call for Building a Roadmap for Hubble Science into the 2030s.

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arXiv2026

The Ultraviolet View of Star and Planet Formation: Disks, Accretion, and Outflows with the Hubble Space Telescope into the 2030s

The spatial distribution and lifetime of molecular gas in the inner regions of young circumstellar disks are key to understanding the formation of planetary systems. Gas-rich disks are observed to disperse in the first ~10 Myr, and recent observational and theoretical evidence suggests that circumstellar disks winds may dominate the removal of angular momentum from the disk, allowing it to dissipate through accretion onto the central star and through low-velocity (<~30 km/s) outflows. The Hubble Space Telescope has revolutionized our understanding of the disks, accretion, and outflow processes that drive the evolution of planet-forming disks and is poised to answer the key questions in the field in the coming decade. We describe how HST's ultraviolet capabilities can address these questions and identify key goals and high-priority observations for HST into the 2030s.

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arXiv2026

The role of the Hubble Space Telescope in advancing our understanding of atmospheric escape in exoplanets

An important evolutionary pathway for planetary atmospheres is escape to space, which has been studied on Earth and Mars for several decades and more recently in exoplanets. A particularly important regime is the hydrodynamic escape, wherein atmospheric mass escapes the planet at high rates in a collisional fluid outflow. This process is used to partly explain the early evolution of rocky planets in and out of the Solar System, as well as key aspects of exoplanet demographics. Hydrodynamic escape is not occurring in the Solar System planets, so our only option for such observations is through exoplanets. The ultraviolet (UV) capabilities of the Hubble Space Telescope (HST) are fundamental to detect hydrodynamic escape and measure the resulting mass-loss rates for a range of planetary systems and to identify targets for surveys with the Habitable Worlds Observatory. We discuss here what kinds of observations and instrument modes are necessary to continue studying atmospheric escape in exoplanets for the next decade, as well as how to advance our understanding of planetary evolution and habitability.

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arXiv2026

Near UV Stellar Activity and Brightness Fluctuations of the Alpha Centauri AB Star System from Weeks to Decades -- Inputs for Reflected Light Spectroscopy with HWO

We present the most comprehensive near-ultraviolet (NUV: 2550-3255 Angstrom) activity record to date for the Alpha Centauri AB system, combining archival IUE and HST observations spanning nearly five decades with new high-cadence CUTE measurements. We show that Alpha Centauri A exhibits predominantly quiescent NUV behavior, with the majority of observations remaining within 1 sigma of the median flux and only rare chromospheric flaring events (1 flare every 12 years), consistent with its weak chromospheric activity and 19-year stellar cycle inferred from X-ray and FUV observations. In contrast, Alpha Centauri B displays a broader variability envelope, characterized by more frequent and higher-amplitude chromospheric excursions that track its well-established 8-year magnetic activity cycle. Using Lomb-Scargle analysis on the Mg II index derived from CUTE observations, we estimate the rotational period of Alpha Centauri A to be on timescales of 15-20 days. We also confirm the coherence of the stellar activity cycle of Alpha Centauri B in the NUV with its X-ray activity cycle. These data establish a critical reference framework for interpreting reflected-light observations of terrestrial exoplanets and for assessing the detectability of ozone and other biosignature-related features at NUV wavelengths with future facilities such as the Habitable Worlds Observatory. These results indicate that HWO observations of terrestrial exoplanets in reflected light photometry and spectroscopy around magnetically inactive early G-type stars and early K-type stars may be expected to show 10-20 percent and 30-40 percent temporal flux variability, respectively, over the course of months to years from the changing stellar inputs alone.

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arXiv2026

Stellar Coronal Mass Ejections with HWO: A Science Case Concept

The primary mission of the Habitable World Observatory (HWO) will be to constrain the prevalence of life on Earth-like planets. These planets will be subject to impacts by energetic particles generated from coronal mass ejection (CME) shocks that can dramatically deplete ozone, a key biosignature gas. Other biosignatures are also likely vulnerable, though not yet studied. Here, we make a conceptual case for factoring sensitivity to stellar coronal mass ejections into the design of HWO. We drive design considerations by requiring that HWO constrain the rate of CMEs producing 10% or greater depletions of total ozone column to fewer than one per decade, the timescale over which ozone returns to pre-event levels. As CME detection methods, we consider coronal dimming, doppler shifted emission, high contrast imaging, and planetary aurora. We explore coronal dimming most thoroughly of the four, though with appropriate design considerations each of these may be possible with HWO.

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arXiv2026

Atmospheric Escape Rates from Mars - If it Orbited an Old M-Dwarf Star

Atmospheric escape is an important process that influences the evolution of planetary atmospheres. A variety of physical mechanisms can contribute to escape from an atmosphere, including thermal escape, ion escape, photochemical escape, and sputtering. Here we estimate escape rates via each of these processes for a hypothetical Mars-like exoplanet orbiting Barnard's star (an old, inactive M dwarf star). We place the planet at an orbital distance that receives the same total stellar flux as it does in our solar system. We use the measured stellar extreme ultraviolet (EUV) spectrum and assumptions on the star's magnetic field to determine both the high-energy radiation and the stellar wind environment around the planet. This information is used to model the response of the planet's thermosphere, exosphere and magnetosphere using a variety of models that have been validated against solar system observations. We find overall escape rates that are dominated by thermal processes and elevated by 2-5 orders of magnitude relative to present-day Mars, suggesting that a Mars-like planet orbiting Barnard's star would not retain a significant atmosphere for more than 10's of millions of years. Recently reported planets around Barnard's star should also not have retained significant atmospheres. By extension, Mars-like planets orbiting any M dwarf near the 'Habitable Zone' should not retain atmospheres for extended periods of time.

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arXiv2026

PyISH: Python Integral Field Spectroscopy Simulation for HWO

The Habitable Worlds Observatory (HWO) will be a large ultraviolet/optical/near-infrared space telescope operating at the Sun-Earth Lagrange point L2. HWO was highly recommended by the National Academies` 2020 decadal survey and will be the first telescope designed specifically to search for life on planets orbiting other stars. HWO will also be able to perform a host of other transformational astrophysics, including cosmology, galaxy evolution, solar system science, and beyond. The development of the telescope and instrument suite is an iterative process. Example observatory architectures, called exploratory analytic cases (EACs) by the HWO Technology Maturation Project Office (TMPO), are modeled end-to-end to explore the engineering and science trade space. Recently, an ultraviolet Integral Field Spectrograph (UV IFS) was added to HWO's instrument suite for the EACs 4 and 5. To explore the science and engineering trade space for this specific instrument, we developed a high-fidelity UV IFS simulation tool, PyISH. The UV IFS simulation tool is designed to be used by scientists to model specific science cases as seen by a UV IFS on HWO, as well as engineers to explore the trade space when developing potential instrument architectures. The modular components, deliverables, and an example of the tool simulating a specific science case proposed for HWO are described in this paper.

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arXiv2026

Investigating the High-energy Radiation Environment of Planets in Sun-like Binary Systems

Far-ultraviolet (FUV) radiation is a driving source of photochemistry in planetary atmospheres. Proper interpretation of atmospheric observations requires a full understanding of the radiation environment that a planet is exposed to. Using the Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE) rocket-borne spectrograph, we observed the Sun-like binary system $\alpha$ Centauri AB and captured the FUV spectrum of both stars simultaneously. Our spectra cover 980--1570 {\AA}, providing the broadest FUV wavelength coverage taken in a single exposure and spanning several key stellar emission features which are important photochemical drivers. Combining the SISTINE spectrum with archival observations, model spectra, and a novel stellar activity model, we have created spectral energy distributions (SEDs) spanning 5 {\AA}--1 mm for both $\alpha$ Centauri A and B. We use the SEDs to estimate the total high-energy flux (X-ray--UV) incident on a hypothetical exoplanet orbiting $\alpha$ Centauri A. Because the incident flux varies over time due to the orbit of the stellar companion and the activity level of each star, we use the VULCAN photochemical kinetics code to estimate atmospheric chemical abundances in the case of minimum and maximum flux exposure. Our results indicate that enhanced atmospheric mass loss due to stellar binarity will likely not be an issue for future exoplanet-hunting missions such as the Habitable Worlds Observatory when searching for Earth-like planets around Sun-like stars.

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