arXiv subjects

Patrick R. Behr

Publications and source records attributed to Patrick R. Behr.

3 recordsLinked to original sources

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 $α$ Centauri AB and captured the FUV spectrum of both stars simultaneously. Our spectra cover 980--1570 Å, 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 Å--1 mm for both $α$ Centauri A and B. We use the SEDs to estimate the total high-energy flux (X-ray--UV) incident on a hypothetical exoplanet orbiting $α$ 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.

astro-ph.EP↗

arXiv2025

HST-COS Transit Spectroscopy of KELT-20b: First Detection of Excess Far-ultraviolet Absorption From an Ultra-hot Jupiter

KELT-20 b is an ultra-hot Jupiter with an equilibrium temperature of $2260$ K orbiting a bright (V =7.6), fast-rotating ($v\sin{i}$=117 km s$^{-1}$) A2 V star. The atmosphere of KELT-20 b has been studied extensively via transmission spectroscopy at optical wavelengths, showing strong hydrogen absorption as well as metals including Na I, Ca II, Fe I, Fe II, Mg I, Si I and Cr II. The atmospheric and ionization conditions of this planet may differ from Jupiter-mass exoplanets due to the relatively weak extreme-ultraviolet radiation from its host star, as the stellar dynamo that generates chromospheric and coronal activity is thought to shut down at spectral types earlier than A4. We present the first spectroscopic observations of KELT-20 b in the far-ultraviolet using the Hubble Space Telescope Cosmic Origins Spectrograph, searching for previously undetected low-ionization and neutral atoms in the upper atmosphere. We find that the FUV transit depth increases with decreasing wavelengths, from $1.88\pm0.04$\% at 1600--1760 Å to $2.28\pm0.04$\% at 1410--1570 Å, yielding planetary radii of $0.1139\pm0.06$ $R_*$ and $0.1222\pm0.07$ $R_*$, respectively. We report tentative detections of Fe II and N I at $2.4σ$ each, and non-detections of C I, S I, Al II, and Si II. We find no evidence for molecular absorption from CO or H$_2$ and no sign of hydrodynamic escape.

astro-ph.EP↗

arXiv2023

The MUSCLES Extension for Atmospheric and Transmission Spectroscopy: UV and X-ray Host-star Observations for JWST ERS & GTO Targets

X-ray through infrared spectral energy distributions (SEDs) are essential for understanding a star's effect on exoplanet atmospheric composition and evolution. We present a catalog of panchromatic SEDs, hosted on the Barbara A. Mikulski Archive for Space Telescopes (MAST), for 11 exoplanet hosting stars which have guaranteed JWST observation time as part of the ERS or GTO programs but have no previous UV characterization. The stars in this survey range from spectral type F4-M6 (0.14-1.57 M$_\odot$), rotation periods of ~4-132 days, and ages of approximately 0.5-11.4 Gyr. The SEDs are composite spectra using data from the Chandra X-ray Observatory and XMM-Newton, the Hubble Space Telescope, BT-Settl stellar atmosphere models, and scaled spectra of proxy stars of similar spectral type and activity. From our observations, we have measured a set of UV and X-ray fluxes as indicators of stellar activity level. We compare the chromospheric and coronal activity indicators of our exoplanet-hosting stars to the broader population of field stars and find that a majority of our targets have activity levels lower than the average population of cool stars in the solar neighborhood. This suggests that using SEDs of stars selected from exoplanet surveys to compute generic exoplanet atmosphere models may underestimate the typical host star's UV flux by an order of magnitude or more, and consequently, that the observed population of exoplanetary atmospheres receive lower high-energy flux levels than the typical planet in the solar neighborhood.

astro-ph.SR↗