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1687 Publications visible to you, out of a total of 1687
Including a luminous central remnant in radiative transfer simulations for Type Iax supernovae

Abstract

Not specified

Authors: F. P. Callan, S. A. Sim, C. E. Collins, L. J. Shingles, F. Lach, F. K. Röpke, R. Pakmor, M. Kromer, S. Srivastav

Date Published: 1st May 2024

Publication Type: Journal

On the origin of globular clusters in a hierarchical universe

Abstract (Expand)

ABSTRACT We present an end-to-end description of the formation of globular clusters (GCs) combining a treatment for their formation and dynamical evolution within galaxy haloes with a state-of-the-art …es with a state-of-the-art semi-analytic simulation of galaxy formation. Our approach allows us to obtain exquisite statistics to study the effect of the environment and assembly history of galaxies, while still allowing a very efficient exploration of the parameter space. Our reference model, including both efficient cluster disruption during galaxy mergers and dynamical friction of GCs within the galactic potential, accurately reproduces the observed correlation between the total mass in GCs and the parent halo mass. A deviation from linearity is predicted at low-halo masses, which is driven by a strong dependence on morphological type: bulge-dominated galaxies tend to host larger masses of GCs than their later-type counterparts. While the significance of the difference might be affected by resolution at the lowest halo masses considered, this is a robust prediction of our model and a natural consequence of the assumption that cluster migration into the halo is triggered by galaxy mergers. Our model requires an environmental dependence of GC radii to reproduce the observed low-mass mass distribution of GCs in our Galaxy. At GC masses $\gt 10^6\, {\rm M}_\odot$, our model predicts fewer GCs than observed, due to an overly aggressive treatment of dynamical friction. Our model reproduces well the metallicity distribution measured for Galactic GCs, even though we predict systematically younger GCs than observed. We argue that this adds further evidence for an anomalously early formation of the stars in our Galaxy.

Authors: Gabriella De Lucia, J M Diederik Kruijssen, Sebastian Trujillo-Gomez, Michaela Hirschmann, Lizhi Xie

Date Published: 1st May 2024

Publication Type: Journal

Nature versus nurture: distinguishing effects from stellar processing and chemical evolution on carbon and nitrogen in red giant stars

Abstract (Expand)

The surface [C/N] ratios of evolved giants are strongly affected by the first dredge-up (FDU) of nuclear-processed material from stellar cores. C and N also have distinct nucleosynthetic origins and … serve as diagnostics of mixing and mass-loss. We use subgiants to find strong trends in the birth [C/N] with [Fe/H], which differ between the low-α and high-α populations. We demonstrate that these birth trends have a strong impact on the surface abundances after the FDU. This effect is neglected in current stellar models, which use solar-scaled C and N. We map out the FDU as a function of evolutionary state, mass, and composition using a large and precisely measured asteroseismic data set in first-ascent red giant branch (RGB) and core He-burning, or red clump (RC), stars. We describe the domains where [C/N] is a useful mass diagnostic and find that the RC complements the RGB and extends the range of validity to higher mass. We find evidence for extra mixing on the RGB below [Fe/H] = −0.4, matching literature results, for high-α giants, but there is no clear evidence of mixing in the low-α giants. The predicted signal of mass-loss is weak and difficult to detect in our sample. We discuss implications for stellar physics and stellar population applications.

Authors: John D Roberts, Marc H Pinsonneault, Jennifer A Johnson, Joel C Zinn, David H Weinberg, Mathieu Vrard, Jamie Tayar, Dennis Stello, Benoît Mosser, James W Johnson, Kaili Cao, Keivan G Stassun, Guy S Stringfellow, Aldo Serenelli, Savita Mathur, Saskia Hekker, Rafael A García, Yvonne P Elsworth, Enrico Corsaro

Date Published: 1st May 2024

Publication Type: Journal

EcoFreq: Compute with Cheaper, Cleaner Energy via Carbon-Aware Power Scaling

Abstract (Expand)

High-performance computing (HPC) constitutes an energy-hungry endeavor, and any efficiency gains via hardware and software advances are quickly (over-)compensated by increased consumption (rebound … effect). A large proportion of electricity is still generated by burning fossil fuels (mostly coal and gas), which is the cause of climate change, and has other potentially dangerous ecological and political consequences. Moving to a 100% renewable grid requires a plethora of solutions for electricity generation, distribution, storage, and consumption. In particular, dynamic load shifting can better align electricity consumption with the variable availability of solar and wind power. We introduce EcoFreq, a tool for dynamic power scaling on CPUs and GPUs that allows to maximize the usage of renewable, low-carbon energy. We benchmark EcoFreq via 14 HPC workloads using historical electricity market data from Germany, the UK, and the US. We show that carbon-aware power scaling leads to an over-proportional reduction in both, CO 2 emissions and energy costs (e.g., 15% to 19% savings with an induced throughput decrease of only 10%). Furthermore, we observe that simple, static power capping at 70% - 80% results in considerably improved energy efficiency and we hence recommended it as default setting. EcoFreq is freely available at: https://github.com/amkozlov/eco-freq.

Authors: Oleksiy M. Kozlov, Alexandros Stamatakis

Date Published: 1st May 2024

Publication Type: Proceedings

Morphology and Mach Number Dependence of Subsonic Bondi–Hoyle Accretion

Abstract

Not specified

Authors: Logan J. Prust, Hila Glanz, Lars Bildsten, Hagai B. Perets, Friedrich K. Röpke

Date Published: 29th Apr 2024

Publication Type: Journal

Expansion of Accreting Main-sequence Stars during Rapid Mass Transfer

Abstract (Expand)

Accreting main-sequence stars expand significantly when the mass accretion timescale is much shorter than their thermal timescales. This occurs during mass transfer from an evolved giant star onto a … main-sequence companion in a binary system and is an important phase in the formation of compact binaries including X-ray binaries, cataclysmic variables, and gravitational-wave sources. In this study, we compute 1D stellar models of main-sequence accretors with different initial masses and accretion rates. The calculations are used to derive semianalytical approximations to the maximum expansion radius. We assume that mass transfer remains fully conservative as long as the inflated accretor fits within its Roche lobe, leading stars to behave like hamsters, stuffing excess material behind their expanding cheeks. We suggest a physically motivated prescription for the mass growth of such "hamstars," which can be used to determine mass-transfer efficiency in rapid binary population synthesis models. With this prescription, we estimate that progenitors of high-mass X-ray binaries and gravitational-wave sources may have experienced highly nonconservative mass transfer. In contrast, for low-mass accretors, the accretion timescale can exceed the thermal timescale by a larger factor without causing significant radial expansion.

Authors: Mike Lau, Ryosuke Hirai, Ilya Mandel, Christopher A. Tout

Date Published: 24th Apr 2024

Publication Type: Journal

Statistical methods for probabilistic forecasts of real-valued outcomes

Abstract

Not specified

Author: Eva-Maria Walz

Date Published: 19th Apr 2024

Publication Type: Doctoral Thesis

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