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1687 Publications visible to you, out of a total of 1687
Protostellar spin-up and fast rotator formation through binary star formation

Abstract (Expand)

Context. Many fast-rotating stars (rotation periods of < 2 days) are found to be unresolved binaries with separations of tens of AU. This correlation between fast rotators and binarity leads to the …ween fast rotators and binarity leads to the question of whether the formation of binary stars inherently produces fast rotators. Aims. Our goal is to understand the spin evolution of protostars and whether the formation of companions plays a role in spinning up stars. Methods. We used magneto-hydrodynamic simulations to study the formation of multiple star systems from turbulent and non-turbulent protostellar cores. We tracked the angular momentum accreted by individual star and inner disc systems by using a sink (star) particle technique. We ran a resolution study to extrapolate protostellar properties. Results. We find in all simulations that the primary star can experience a spin-up event correlated with the formation of companions, namely fragmentation into binaries or higher-order systems. The primary star can spin up by up to 84% of its pre-fragmentation angular momentum and by up to 18% of its pre-fragmentation mass-specific angular momentum. The mechanism for the spin-up is gravitational disc instabilities in the circumstellar disc around the primary star, which leads to the accretion of material with high specific angular momentum. The simulations that experience the strongest disc instabilities fragment to form companions. Simulations with weaker spin-up events experience disc instabilities triggered by a companion flyby, and the disc instability in these cases typically does not produce further fragments (i.e. they remain binary systems). Conclusions. The primary star in multiple star systems can end up with a higher spin than single stars. This is because gravitational instabilities in the circumstellar disc around the primary star can trigger a spin-up event. In the strongest spin-up events, the instability is likely to cause disc fragmentation and the formation of companions. This spin-up mechanism, coupled with shorter disc lifetimes due to truncated circumstellar discs (and thus short spin-down times), may help produce fast rotators.

Authors: Rajika L. Kuruwita, Christoph Federrath, Marina Kounkel

Date Published: 1st Oct 2024

Publication Type: Journal

Orbital architectures of planet-hosting binaries – III. Testing mutual inclinations of stellar and planetary orbits in triple-star systems

Abstract (Expand)

ABSTRACT Transiting planets in multiple-star systems, especially high-order multiples, make up a small fraction of the known planet population but provide unique opportunities to study the environments … to study the environments in which planets would have formed. Planet-hosting binaries have been shown to have an abundance of systems in which the stellar orbit aligns with the orbit of the transiting planet, which could give insights into the planet formation process in such systems. We investigate here if this trend of alignment extends to planet-hosting triple-star systems. We present long-term astrometric monitoring of a novel sample of triple-star systems that host Kepler transiting planets. We measured orbit arcs in 21 systems, including 12 newly identified triples, from a homogeneous analysis of our Keck adaptive optics data and, for some systems, Gaia astrometry. We examine the orbital alignment within the nine most compact systems ($\lesssim 500$ au), testing if either (or both) of the stellar orbits align with the edge-on orbits of their transiting planets. Our statistical sample of triple systems shows a tendency toward alignment, especially when assessing the alignment probability using stellar orbital inclinations computed from full orbital fits, but is formally consistent with isotropic orbits. Two-population tests where half of the stellar orbits are described by a planet-hosting-binary-like moderately aligned distribution give the best match when the other half (non-planet-hosting) has a Kozai-like misaligned distribution. Overall, our results suggest that our sample of triple-star planet-hosting systems are not fully coplanar systems and have at most one plane of alignment.

Authors: Elise L Evans, Trent J Dupuy, Kendall Sullivan, Adam L Kraus, Daniel Huber, Michael J Ireland, Megan Ansdell, Rajika L Kuruwita, Raquel A Martinez, Mackenna L Wood

Date Published: 1st Oct 2024

Publication Type: Journal

Breaking Strong Alkynyl-Phenyl Bonds: Poly(para-phenylene ethynylene)s under Mechanical Stress

Abstract

Not specified

Authors: Maximilian Elter, Matthias Brosz, Daniel Sucerquia, Andrei Kuzhelev, Denis C. Kiesewetter, Markus Kurth, Andreas Dreuw, Thomas F. Prisner, Jan Freudenberg, Uwe H. F. Bunz, Frauke Gräter

Date Published: 27th Sep 2024

Publication Type: Journal

KI-Morph – User-friendly large-scale image analysis & AI on bwHPC systems

Abstract (Expand)

Artificial Intelligence (AI) has become indispensable for analyzing large-scale datasets, particularly in the realm of 3D image volumes. However, effectively harnessing AI for such tasks often requires … advanced algorithms and high-performance computing (HPC) resources, presenting significant challenges for non-technical users. To overcome these barriers, we present KI-Morph, a novel software platform for large-scale image analysis seamlessly integrated with the bwHPC infrastructure. It offers a user-friendly interface, enabling sophisticated AI-driven analysis without requiring technical expertise in either AI or HPC. KI-Morph prioritizes data privacy and sovereignty, ensuring that users retain full control over their data. Additionally, the components developed for the platform support researchers also with science outreach by enabling the creation of interactive online visualizations, for example using the 2D, 3D and augmented reality viewers.

Authors: Vincent Heuveline, Alexander Zeilmann

Date Published: 26th Sep 2024

Publication Type: InProceedings

Multivariate post‐processing of probabilistic sub‐seasonal weather regime forecasts

Abstract

Not specified

Authors: Fabian Mockert, Christian M. Grams, Sebastian Lerch, Marisol Osman, Julian Quinting

Date Published: 19th Sep 2024

Publication Type: Journal

Physics-based vs. data-driven 24-hour probabilistic forecasts of precipitation for northern tropical Africa

Abstract

Not specified

Authors: Eva–Maria Walz, Peter Knippertz, Andreas H. Fink, Gregor Köhler, Tilmann Gneiting

Date Published: 1st Sep 2024

Publication Type: Journal

Testing a non-local 1-equation turbulent convection model: A solar model

Abstract (Expand)

Context: Turbulent convection models treat stellar convection more physically than standard mixing-length theory by including non-local effects. We recently successfully applied the Kuhfuss version to … convective cores in main sequence stars. Its usefulness for convective envelopes remains to be tested. Aims: The solar convective envelope constitutes a viable test bed for investigating the usefulness of the 1-equation Kuhfuss turbulent convection model. Methods: We used the one-dimensional stellar evolution code GARSTEC to calculate a standard solar model with the 1-equation Kuhfuss turbulent convection model, and compared it to helioseismic measurements and a solar model using standard mixing-length theory. Additionally, we investigated the influence of the additional free parameters of the convection model on the solar structure. Results: The 1-equation Kuhfuss model reproduces the sound-speed profile and the lower boundary of the convective region less well than the mixing-length model, because the inherent non-local effects overestimate the amount of convective penetration below the Schwarzschild boundary. We trace this back to the coupling of the temperature gradient to the convective flux in the 1-equation version of the Kuhfuss theory. Conclusions: The temperature stratification of the solar convective envelope is not well modelled by the 1-equation Kuhfuss turbulent convection model, and the more complex 3-equation version is needed to improve the modelling of convection in the envelopes of 1D stellar evolution models.

Authors: T. A. M. Braun, F. Ahlborn, A. Weiss

Date Published: 1st Sep 2024

Publication Type: Journal

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