arXiv subjects

Karsten Schindler

Publications and source records attributed to Karsten Schindler.

7 recordsLinked to original sources

arXiv2026

Changes in Pluto's Atmosphere Based on Stellar Occultation Data from 2017 to 2023

Pluto's tenuous atmosphere has $μ$bar-level pressure and is composed primarily of ${\text{N}}_2$, with a variable haze. Its eccentric orbit combined with high obliquity leads to significant changes in solar insolation throughout the Plutonian year. The atmosphere is supported by vapor-pressure equilibrium with the surface ices, thus surface changes are coupled with the atmospheric properties. Volatile-transport models have anticipated Pluto's atmospheric evolution: predictions range from collapse over the coming decades to an atmosphere that remains. Previous work claims that Pluto's atmospheric pressure monotonically increased from 1988 through 2016, that the atmosphere began freezing out in 2018-2019, and that there was a plateau as of 2020. Here, we report results from ten stellar occultations by Pluto between 2017 August and 2023 July. Four events were multi-chord, while six were from single sites. Our results indicate a pressure plateau between the New Horizons flyby in 2015 through roughly 2021 and suggest that the atmospheric pressure has started to drop. Between 2015-2021 and 2022, the clear-atmosphere pressure at 1275 km decreased $7\pm6\%$, and it dropped $16\pm2\%$ for pressure at 1215 km when including haze. From 2017-2023, the upper atmospheric structure is consistent, while there is a change in light-curve slope in the lower atmosphere. This change-of-slope is consistent with haze particles settling over yearly or shorter timescales. Spikes in one light curve are indicative of intermittent buoyancy waves. More data are needed to confirm a recent pressure change.

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arXiv2026

The Astronomical Telescope of the University of Stuttgart (ATUS): Development, Optimization, and Lessons Learned

ATUS, the Astronomical Telescope of the University of Stuttgart, is a fully remote-controlled 0.6 m f/8.17 Ritchey-Chrétien telescope optimized for high-cadence, high-fidelity photometry of transient sources. Observations are time-referenced with very high accuracy and precision, making it an ideal platform for time-domain astronomy and space situational awareness. Initially conceived to support instrument developments and operations of SOFIA, the Stratospheric Observatory for Infrared Astronomy, it evolved into a scientific instrument for various use cases in instrument development, astronomical research, and teaching. This paper presents an overview of its development and optimization to achieve diffraction-limited images and highly accurate pointing and tracking, even at high speeds. The findings and lessons learned are universally applicable to other telescopes that are currently at the planning stage, or where similar issues might be encountered.

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arXiv2025

Doomed Worlds II: Reassessing Suggestions of Orbital Decay for TrES-5 b

TrES-5b is one of only three ultra-hot Jupiters (UHJs) with suggestions of a possibly decreasing orbital period that have persisted through multiple independent analyses (G. Maciejewski et al. 2021; S. R. Hagey et al. 2022; E. S. Ivshina & J. N. Winn 2022; W. Wang et al. 2024; L. C. Yeh et al. 2024). While WASP-12 b's decreasing period is well-explained by tidally induced orbital decay (K. C. Patra et al. 2017), and stellar acceleration has been proposed for WASP-4 b (L. G. Bouma et al. 2020), the cause of the apparent trend for TrES-5 b has not been satisfactorily explained. This work extends the previous observations with 14 new ground-based transits from 2016-2024 and two newly-published midtimes for data from 2007 and 2009. Four TESS sectors (75, 77, 82, and 84) have also been included for the first time. With the new data, the case for a decreasing orbital period is much weaker than before. The revised rate of period change, dP/dt=-5.3 +/- 2.2 ms yr^-1, is less than half that was found in previous work and the preference for a quadratic over a linear model, as measured through Delta BIC_LQ, has been falling since 2020, with a current value of 11. Furthermore, these results are not robust to outliers; removing a single early transit midtime causes the effect to vanish (Delta BIC_LQ = -1). Additionally, no significant periodic signals in the transit timing data are identified. The current data are well explained by a linear ephemeris.

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arXiv2023

Material Around the Centaur (2060) Chiron from the 2018 November 28 UT Stellar Occultation

A stellar occultation of Gaia DR3 2646598228351156352 by the Centaur (2060) Chiron was observed from the South African Astronomical Observatory on 2018 November 28 UT. Here we present a positive detection of material surrounding Chiron from the 74-in telescope for this event. Additionally, a global atmosphere is ruled out at the tens of mircobar level for several possible atmospheric compositions. There are multiple 3-sigma drops in the 74-in light curve: three during immersion and two during emersion. Occulting material is located between 242-270 km from the center of the nucleus in the sky plane. Assuming the ring-plane orientation proposed for Chiron from the 2011 occultation, the flux drops are located at 352, 344, and 316 km (immersion), and 357, and 364 km (emersion) from the center, with normal optical depths of 0.26, 0.36, and 0.22 (immersion) and 0.26 and 0.18 (emersion), and equivalent widths between 0.7-1.3 km. This detection is similar to the previously proposed two-ring system and is located within the error bars of that ring-pole plane; however, the normal optical depths are less than half of the previous values, and three features are detected on immersion. These results suggest that the properties of the surrounding material have evolved between the 2011, 2018, and 2022 observations.

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arXiv2016

Results from a triple chord stellar occultation and far-infrared photometry of the trans-Neptunian object (229762) 2007 UK126

A stellar occultation by a trans-Neptunian object (TNO) provides an opportunity to probe its size and shape. Very few occultations by TNOs have been sampled simultaneously from multiple locations, while a robust estimation of shadow size has been possible for only two objects. We present the first observation of an occultation by the TNO 2007 UK126 on 15 November 2014, measured by three observers, one nearly on and two almost symmetrical to the shadow's centerline. This is the first multi-chord dataset obtained for a so-called detached object, a TNO subgroup with perihelion distances so large that the giant planets have likely not perturbed their orbits. We revisit Herschel/PACS far-infrared data, applying a new reduction method to improve the accuracy of the measured fluxes. Combining both datasets allows us to comprehensively characterize 2007 UK126. We use error-in-variable regression to solve the non-linear problem of propagating timing errors into uncertainties of the ellipse parameters. Based on the shadow's size and a previously reported rotation period, we expect a shape of a Maclaurin spheroid and derive a geometrically plausible size range. To refine our size estimate of 2007 UK126, we model its thermal emission using a thermophysical model code. We conduct a parametric study to predict far-infrared fluxes and compare them to the Herschel/PACS measurements. The favorable geometry of our occultation chords, combined with minimal dead-time imaging, and precise GPS time measurements, allow for an accurate estimation of the shadow size (best-fitting ellipse with axes 645.80 $\pm$ 5.68 km $\times$ 597.81 $\pm$ 12.74 km) and the visual geometric albedo (15.0 $\pm$ 1.6 %). By combining our analyses of the occultation and the far-infrared data, we can constrain the effective diameter of 2007 UK126 to 599 - 629 km. We conclude that subsolar surface temperatures are $\approx$ 50 - 55 K.

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arXiv2016

PANIC - A surface science package for the in situ characterization of a near-Earth asteroid

This paper presents the results of a mission concept study for an autonomous micro-scale surface lander also referred to as PANIC - the Pico Autonomous Near-Earth Asteroid In Situ Characterizer. The lander is based on the shape of a regular tetrahedron with an edge length of 35 cm, has a total mass of approximately 12 kg and utilizes hopping as a locomotion mechanism in microgravity. PANIC houses four scientific instruments in its proposed baseline configuration which enable the in situ characterization of an asteroid. It is carried by an interplanetary probe to its target and released to the surface after rendezvous. Detailed estimates of all critical subsystem parameters were derived to demonstrate the feasibility of this concept. The study illustrates that a small, simple landing element is a viable alternative to complex traditional lander concepts, adding a significant science return to any near-Earth asteroid (NEA) mission while meeting tight mass budget constraints.

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arXiv2016

An innovative concept for the AsteroidFinder/SSB focal plane assembly

This paper gives a summary on the system concept and design of the focal plane assembly of AsteroidFinder/SSB, a small satellite mission which is currently under development at the German Aerospace Center (DLR). An athermal design concept has been developed in accordance to the requirements of the instrument and spacecraft. Key aspects leading to this approach have been a trade-off study of the mechanical telescope interface, the definition of electrical and thermal interfaces and a material selection which minimizes thermally induced stresses. As a novelty, the structure will be manufactured from a machinable AlN-BN composite ceramic. To enable rapid design iterations and development, an integrated modeling approach has been used to conduct a thermo-mechanical analysis of the proposed concept in order to prove its feasibility. The steady-state temperature distribution for various load cases and the resulting stress and strain within the assembly have both been computed using a finite element simulation.

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