Random Papershttp://randompapers.netRandom papers chosen from the astrophysics literaturehttp://www.rssboard.org/rss-specificationpython-feedgenTue, 30 Jul 2024 00:01:02 +00003D hydrodynamic simulations of massive main-sequence stars - II. Convective excitation and spectra of internal gravity waveshttp://ui.adsabs.harvard.edu/abs/2024MNRAS.531.1316TThompson, William, Herwig, Falk, Woodward, Paul R., Mao, Huaqing, Denissenkov, Pavel, Bowman, Dominic M., Blouin, Simon, Monthly Notices of the Royal Astronomical Society<br><br>Recent photometric observations of massive stars have identified a low-frequency power excess which appears as stochastic low-frequency variability in light-curve observations. We present the oscillation properties of high-resolution hydrodynamic simulations of a $25\,\,{\rm{M}_\odot }$ star performed with the PPMstar code. The model star has a convective core mass of $\approx 12\,\,{\rm{M}_\odot }$ and approximately half of the envelope simulated. From this simulation, we extract light curves from several directions, average them over each hemisphere, and process them as if they were real photometric observations. We show how core convection excites waves with a similar frequency as the convective time-scale in addition to significant power across a forest of low and high angular degree l modes. We find that the coherence of these modes is relatively low as a result of their stochastic excitation by core convection, with lifetimes of the order of 10s of days. Thanks to the still significant power at higher l and this relatively low coherence, we find that integrating over a hemisphere produces a power spectrum that still contains measurable power up to the Brunt-Väisälä frequency. These power spectra extracted from the stable envelope are qualitatively similar to observations, with the same order of magnitude yet lower characteristic frequency. This work further shows the potential of long-duration, high-resolution hydrodynamic simulations for connecting asteroseismic observations to the structure and dynamics of core convection and the convective boundary.Predicting the linear response of self-gravitating stellar spheres and discs with LinearResponse.jlhttp://ui.adsabs.harvard.edu/abs/2024MNRAS.530.4378PPetersen, Michael S., Roule, Mathieu, Fouvry, Jean-Baptiste, Pichon, Christophe, Tep, Kerwann, Monthly Notices of the Royal Astronomical Society<br><br>We present LinearResponse.jl, an efficient, versatile public library written in JULIA to compute the linear response of self-gravitating (three-dimensional spherically symmetric) stellar spheres and (two-dimensional axisymmetric razor-thin) discs. LinearResponse.jl can scan the whole complex frequency plane, probing unstable, neutral and (weakly) damped modes. Given a potential model and a distribution function, this numerical toolbox estimates the modal frequencies as well as the shapes of individual modes. The libraries are validated against a combination of previous results for the spherical isochrone model and Mestel discs, and new simulations for the spherical Plummer model. Beyond linear response theory, the realm of applications of LinearResponse.jl also extends to the kinetic theory of self-gravitating systems through a modular interface.Toward Cosmological Simulations of the Magnetized Intracluster Medium with Resolved Coulomb Collision Scalehttp://ui.adsabs.harvard.edu/abs/2024ApJ...967..125SSteinwandel, Ulrich P., Dolag, Klaus, Böss, Ludwig M., Marin-Gilabert, Tirso, The Astrophysical Journal<br><br>We present the first results of one extremely high-resolution, nonradiative magnetohydrodynamical cosmological zoom-in simulation of a massive cluster with a virial mass of M <SUB>vir</SUB> = 2.0 × 10<SUP>15</SUP> solar masses. We adopt a mass resolution of 4 × 10<SUP>5</SUP> M <SUB>⊙</SUB> with a maximum spatial resolution of around 250 pc in the central regions of the cluster. We follow the detailed amplification process in a resolved small-scale turbulent dynamo in the intracluster medium (ICM) with strong exponential growth until redshift 4, after which the field grows weakly in the adiabatic compression limit until redshift 2. The energy in the field is slightly reduced as the system approaches redshift zero in agreement with adiabatic decompression. The field structure is highly turbulent in the center and shows field reversals on a length scale of a few tens of kiloparsecs and an anticorrelation between the radial and angular field components in the central region that is ordered by small-scale turbulent dynamo action. The large-scale field on megaparsec scales is almost isotropic, indicating that the structure formation process in massive galaxy cluster formation suppresses any memory of both the initial field configuration and the amplified morphology via the turbulent dynamo. We demonstrate that extremely high-resolution simulations of the magnetized ICM are within reach that can simultaneously resolve the small-scale magnetic field structure, which is of major importance for the injection of and transport of cosmic rays in the ICM. This work is a major cornerstone for follow-up studies with an on-the-fly treatment of cosmic rays to model in detail electron-synchrotron and gamma-ray emissions.Dynamic estimation method for pulsar periods based on photon energy distribution folding and image template matchinghttp://ui.adsabs.harvard.edu/abs/2024A&A...686A.214XXie, T. H., Ma, X., Zhang, W. J., Li, J. R., Wang, S. T., Yang, Z. N., Cui, P. L., Ning, X. L., Fang, J. C., Astronomy and Astrophysics<br><br><BR /> Aims: The accuracy of the pulsar period estimation directly affects the restoration effect of the signal profile. A more accurate pulsar profile will help improve the accuracy of pulsar delay estimation and thereby improve the performance of X-ray pulsar navigation. This paper proposes a pulsar period estimation method based on photon energy distribution folding and image template matching (PETM). <BR /> Methods: This method uses the probability distribution information of photon energy for weighted epoch folding. The one-dimensional (1D) profile information was converted into two-dimensional (2D) image information through reverse space-filling curve (SFC) encoding. Then, a feature matching was performed between the target structure and the template structure. At the same time, the criterion of Pearson correlation coefficient (PCC) was used to quantitatively evaluate the matching effect to estimate the optimal period. <BR /> Results: The simulation results show that the period estimation accuracy of the PETM method is significantly improved, as compared with the traditional χ<SUP>2</SUP>-test method. This work also analyzes the folding effect based on the photon energy distribution model and conducts simulation experiments and comparisons on influencing factors, such as noise interference and data quality. At the same time, we also specifically demonstrated the effectiveness of the PETM method for the glitch phenomenon (i.e., a sudden change in period) of pulsar periods. Finally, we also used China's XPNAV-1 satellite to conduct experiments and analysis of the actual observation data of PSR B0531+21 pulsar within a fixed period of time. The results show that the period estimation accuracy of this method is 4.8190 ns, which is 50.23% higher than the traditional χ<SUP>2</SUP>-test method. The method proposed in this article has the advantages of high estimation accuracy, stable estimation performance, strong anti-interference ability, and excellent dynamic period estimation performance. Therefore, it can further improve the navigation performance of X-ray pulsars.Stellar atmospheric parameters from Gaia BP/RP spectra using uncertain neural networkshttp://ui.adsabs.harvard.edu/abs/2024MNRAS.531.2126FFallows, Connor P., Sanders, Jason L., Monthly Notices of the Royal Astronomical Society<br><br>With the plentiful information available in the Gaia BP/RP spectra, there is significant scope for applying discriminative models to extract stellar atmospheric parameters and abundances. We describe an approach to leverage an 'Uncertain Neural Network' model trained on APOGEE data to provide high-quality predictions with robust estimates for per-prediction uncertainty. We report median formal uncertainties of 0.068 dex, 69.1 K, 0.14 dex, 0.031 dex, 0.040 dex, and 0.029 dex for [Fe/H], T<SUB>eff</SUB>, log g, [C/Fe], [N/Fe], and [α/M], respectively. We validate these predictions against our APOGEE training data, LAMOST, and Gaia GSP-PHOT stellar parameters, and see a strong correlation between our predicted parameters and those derived from these surveys. We investigate the information content of the spectra by considering the 'attention' our model pays to different spectral features compared to expectations from synthetic spectra calculations. Our model's predictions are applied to the Gaia data set, and we produce a publicly available catalogue of our model's predictions.