arXiv subjects

Stefan Ulrich

Publications and source records attributed to Stefan Ulrich.

6 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 $\alpha$ 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.

astro-ph.EP↗

arXiv2024

The assembly, characterization, and performance of SISTINE

The Suborbital Imaging Spectrograph for Transition region Irradiance from Nearby Exoplanet host stars (SISTINE) is a rocket-borne ultraviolet (UV) imaging spectrograph designed to probe the radiation environment of nearby stars. SISTINE operates over a bandpass of 98 -- 127 and 130 -- 158 nm, capturing a broad suite of emission lines tracing the full 10$^4$ -- 10$^5$ K formation temperature range critical for reconstructing the full UV radiation field incident on planets orbiting solar-type stars. SISTINE serves as a platform for key technology developments for future ultraviolet observatories. SISTINE operates at moderate resolving power ($R\sim$1500) while providing spectral imaging over an angular extent of $\sim$6', with $\sim$2" resolution at the slit center. The instrument is composed of an f/14 Cassegrain telescope that feeds a 2.1x magnifying spectrograph, utilizing a blazed holographically ruled diffraction grating and a powered fold mirror. Spectra are captured on a large format microchannel plate (MCP) detector consisting of two 113 x 42 mm segments each read out by a cross delay-line anode. Several novel technologies are employed in SISTINE to advance their technical maturity in support of future NASA UV/optical astronomy missions. These include enhanced aluminum lithium fluoride coatings (eLiF), atomic layer deposition (ALD) protective optical coatings, and ALD processed large format MCPs. SISTINE was launched a total of three times with two of the three launches successfully observing targets Procyon A and $α$ Centauri A and B.

astro-ph.IM↗

arXiv2024

FLUID: A rocket-borne pathfinder instrument for high efficiency UV band selection imaging

The Far- and Lyman-Ultraviolet Imaging Demonstrator (FLUID) is a rocket-borne arcsecond-level ultraviolet (UV) imaging instrument covering four bands between 92 -- 193 nm. FLUID will observe nearby galaxies to find and characterize the most massive stars that are the primary drivers of the chemical and dynamical evolution of galaxies, and the co-evolution of the surrounding galactic environment. The FLUID short wave channel is designed to suppress efficiency at Lyman-$α$ (121.6 nm), while enhancing the reflectivity of shorter wavelengths. Utilizing this technology, FLUID will take the first ever images of local galaxies isolated in the Lyman ultraviolet (90 -- 120 nm). As a pathfinder instrument, FLUID will employ and increase the TRL of band-selecting UV coatings, and solar-blind UV detector technologies including microchannel plate and solid state detectors; technologies prioritized in the 2022 NASA Astrophysical Biennial Technology Report. These technologies enable high throughput and high sensitivity observations in the four co-aligned UV imaging bands that make up the FLUID instrument. We present the design of FLUID, status on the technology development, and results from initial assembly and calibration of the FLUID instrument.

astro-ph.IM↗

arXiv2023

The Colorado Ultraviolet Transit Experiment (CUTE) Mission Overview

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.

astro-ph.IM↗

arXiv2004

A Bimachine Compiler for Ranked Tagging Rules

This paper describes a novel method of compiling ranked tagging rules into a deterministic finite-state device called a bimachine. The rules are formulated in the framework of regular rewrite operations and allow unrestricted regular expressions in both left and right rule contexts. The compiler is illustrated by an application within a speech synthesis system.

cs.CL↗

arXiv2004

A Flexible Rule Compiler for Speech Synthesis

We present a flexible rule compiler developed for a text-to-speech (TTS) system. The compiler converts a set of rules into a finite-state transducer (FST). The input and output of the FST are subject to parameterization, so that the system can be applied to strings and sequences of feature-structures. The resulting transducer is guaranteed to realize a function (as opposed to a relation), and therefore can be implemented as a deterministic device (either a deterministic FST or a bimachine).

cs.CL↗