arXiv subjects

L. Buchele

Publications and source records attributed to L. Buchele.

3 recordsLinked to original sources

arXiv2026

Constraining the model-based uncertainties of asteroseismic magnetic field measurements in red giants

Magnetic fields inside red giants are measured using shifts to the oscillation frequencies. However, in the asymptotic framework, converting a frequency shift into a radial magnetic field strength requires knowing the global magnetic sensitivity. This parameter (also called the core structure parameter) must be inferred from stellar models, introducing a source of uncertainty. We seek to understand how the global magnetic sensitivity depends on stellar properties such as mass and metallicity, and to quantify the model-based uncertainty on magnetic field measurements. We also explore which stellar properties are key to finding a precise and accurate estimate of the global magnetic sensitivity. Using MESA models, we examine how the global magnetic sensitivity changes with mass, metallicity, and age. We then create a set of synthetic stars and test how well we recover the sensitivity parameter. We consider different grid construction approaches and the choice of which observables are used in the fitting process. We find that the global magnetic sensitivity shows a stronger dependence on mass for higher mass models and a stronger metallicity dependence for lower metallicity models. Our approach recovers the sensitivity parameter well, with an uncertainty of 10% when precise metallicity measurements are used. We apply our method to stars with existing magnetic field measurements. In most cases, the dominant source of uncertainty remains observational, although precise modeling can significantly reduce the magnetic field uncertainty for stars with exceptional data. With careful fitting, models yield accurate values for the global magnetic sensitivity. We recommend that future work obtain the global magnetic sensitivity using both asteroseismic and high-quality spectroscopic data. Under these conditions, we recommend adopting a model-based uncertainty of 10% on the sensitivity parameter.

astro-ph.SR↗

arXiv2026

The sensitivity and behaviour of the curvature in the \'echelle diagram of red-giant stars

In the convective envelopes of relatively cool stars, oscillations are excited by turbulent convection. In these so-called solar-like oscillators, radial oscillation modes appear at nearly equally spaced frequencies. This spacing is referred to as the `large frequency separation'. Deviations from equally-spaced frequencies are a result of the internal structure of a star being different from a sphere of ideal gas at constant temperature. Hence, these deviations provide information on the internal structure of the star. In this work, we investigate the second-order deviation from uniform spacing, referred to as curvature. We aim to provide homegeneous values for observed red-giant stars, understand differences between the results from observations and predictions from stellar models, and reveal the connection between curvature and stellar structure. We used Kepler data of red-giant stars and computed the curvature for several thousand stars. We compared these to the curvature derived from MESA models. We subsequently investigated the trends and differences between results from observations and models. Finally, we computed sensitivity kernels to identify the stellar region to which the curvature is most sensitive and performed a glitch analysis. We found that the curvature is sensitive to evolutionary phase and mass. The observed values and values from models show discrepancies. The glitch analysis shows that in theory this provides information on the location and strength of the HeI and HI ionisation layers. The curvature provides a probe into the near-surface structure of the star. The deviations between the curvature derived from observations and models call henceforth for improvements in the near-surface layers of stellar models.

astro-ph.SR↗

arXiv2023

Concept for a Space-based Near-Solar Neutrino Detector

The concept of putting a neutrino detector in close orbit of the sun has been unexplored until very recently. The primary scientific return is to vastly enhance our understanding of the solar interior, which is a major NASA goal. Preliminary calculations show that such a spacecraft, if properly shielded, can operate in space environments while taking data from neutrino interactions. These interactions can be distinguished from random background rates of solar electromagnetic emissions, galactic charged cosmic-rays, and gamma-rays by using a double pulsed signature. Early simulations of this project have shown this veto schema to be successful in eliminating background and identifying the neutrino interaction signal in upwards of 75% of gamma ray interactions and nearly 100% of other interactions. Hence, we propose a new instrument to explore and study our sun. Due to inverse square scaling, this instrument has the potential to outperform earth-based experiments in several domains such as making measurements not accessible from the earth's orbit.

physics.ins-det↗