446494 research outputs found
Sort by
Cepheid Metallicity in the Leavitt Law (C–MetaLL) survey
No full textContext. Classical Cepheids are fundamental primary distance indicators and crucial tracers of the young stellar population in the Milky Way and nearby galaxies. While most chemical abundance studies of Cepheids have been carried out in the optical domain, near-infrared (NIR) spectroscopy offers unique advantages in terms of reduced extinction and access to new elemental tracers.
Aims. Our goal is to validate NIR abundance determinations against well-established optical results and to explore the diagnostic power of previously unexplored NIR lines. NIR spectroscopy is far less hampered by interstellar extinction than optical observations, which allows us to probe Cepheids at larger distances and in highly obscured regions of the Galaxy. Moreover, the H and K bands provide access to diagnostic lines of elements (e.g., P, K, and Yb) that are not available in the optical domain.
Methods. We acquired high-resolution (R ≈ 45 000) spectra of 21 Galactic and 2 Large Magellanic Cloud (LMC) classical Cepheids with the high-resolution Immersion Grating Infrared Spectrometer (IGRINS) in the H and K bands. Effective temperatures were derived from a photometric approach and line-depth ratios, and the gravities and microturbulent velocities were estimated using empirical calibrations and statistical constraints. The abundances of 16 elements were determined through a full spectral synthesis in local thermodynamic equilibrium. We performed an extensive error analysis and compared our results with previous optical studies of the same stars.
Results. Our NIR abundances and the optical literature values agree very well (Δ[Fe/H] ≤ 0.02 dex and σ ≈ 0.07 dex), which confirms the reliability of IGRINS-based measurements. The derived abundance gradients in the Galactic disk are fully consistent with previous optical determinations, with slopes of −0.06, −0.05, and −0.05 dex kpc−1 for Fe, Mg, and Si, respectively. We provide homogeneous determinations of P, K, and Yb abundances from NIR lines for classical Cepheids for the first time, and we report trends that are consistent with Galactic chemical evolution models. Moreover, the two LMC Cepheids included in our sample that were previously analyzed in the optical provide a direct benchmark that confirms the accuracy of NIR abundance determinations in extragalactic metal-poor environments.
Conclusions. Our study demonstrates that high-resolution NIR spectroscopy of Cepheids yields robust abundances that are fully compatible with optical results and provides access to additional elements of nucleosynthetic interest. These results pave the way for future large-scale NIR surveys of Cepheids with facilities such as MOONS, ELT, and JWST, which are crucial for tracing the chemical evolution of the Milky Way and nearby galaxies in heavily obscured regions
A single frequency approach to nonequilibrium modeling of the chromosphere
No full textContext. The solar chromosphere is a region where radiation plays a critical role in energy transfer and interacts strongly with the plasma. In this layer, strong spectral lines, such as the Lyman lines, contribute significantly to radiative energy exchange. Due to the long ionization/relaxation timescale, departures from local thermodynamic equilibrium (LTE) become significant in the chromosphere. Accurately modeling this layer therefore requires one to solve the non-LTE radiative transfer for the Lyman transitions.
Aims We present an updated version of the MURaM code to enable more accurate simulations of chromospheric hydrogen level populations and temperature evolution.
Methods. In the previous extension, a non-LTE equation of state, collisional transitions of hydrogen, and radiative transitions of non-Lyman lines were already implemented in the code. Building on this, we have now incorporated radiative transfer for the Lyman lines to compute radiative rate coefficients and the associated radiative losses. These were used to solve the population and temperature evolution equations, rendering the system self-consistent. To reduce computational cost, a single-frequency approximation was applied to each line in the numerical solution of the radiative transfer problem.
Results. The extended model shows good agreement with reference solutions from the Lightweaver framework, accurately capturing the radiative processes associated with Lyman lines in the chromosphere. The extension brings the simulated hydrogen level populations in the deep chromosphere closer to detailed radiative balance, while those in the upper chromosphere remain significantly out of balance, consistent with the expected conditions in the real solar atmosphere. Convergence tests show that the module can accurately capture the evolution of temperature and hydrogen level populations with simulation time steps constrained by the Courant–Friedrichs–Lewy (CFL) condition.
Conclusions. The extension enables the MURaM code to accurately capture chromospheric dynamics. Its robust performance under large simulation time steps renders it particularly well suited for high-resolution, three-dimensional simulations
Energetic particles accelerated via turbulent magnetic reconnection in protoplanetary discs – I. Ionisation rates
No full textContext. Ionisation controls the chemistry, thermal balance, and magnetic coupling in protoplanetary discs. However, standard ionisation vectors such as stellar UV, X-rays, Galactic cosmic rays might not be efficient enough, as UV/X-rays are attenuated rapidly with depth, while Galactic cosmic rays are modulated. Turbulence-induced magnetic reconnection in disc atmospheric layers offers a physically motivated, in situ source of energetic particles (EPs) that has never been considered.
Aims. We quantify the ionisation and heating produced by EPs accelerated by turbulent reconnection, identify where they dominate over X-rays and Galactic cosmic rays, and determine energetic thresholds for their relevance. We provide scalable diagnostics tied to the local energy budget.
Methods. We adopt a Fermi-like acceleration model with parameters linked to a turbulent reconnection geometry trigger by the magneto-rotational instability, yielding a steady-state energy distribution of the EP forming a power-law of index p = 2.5. We propagate electrons and protons through the disc and compute primary and secondary ionisation and associated heating on a fiducial T Tauri disc model background. The non-thermal normalisation is set by the fraction of local viscous accretion energy dissipation channelled to EPs, parametrised by κ.
Results. For κ ≳ 0.4%, EPs ionisation overpass standard sources such as X-rays and Galactic cosmic rays in the disc atmosphere and intermediate/deep layers out to radii of a few tens of astronomical units. Even at κ ~ 0.025%, EPs contribute at the few-percent level, thus are chemically and dynamically relevant. The EP-induced heating complements UV/X-ray heating in the atmosphere and persists deeper. These results identify EPs accelerated by turbulence-induced magnetic reconnection as a rather robust, disc-internal ionisation channel that should be included in thermo-chemical and dynamical models of protoplanetary discs
Magnetic activity on the young Sun: A case study of EK Draconis
No full textContext. Young solar analog stars provide key insights into the early stages of stellar evolution, particularly in terms of magnetic activity and rotation. Their rapid rotation, high flaring rate, and enhanced surface activity make them ideal laboratories for testing stellar models or even the solar dynamo.
Aims. Using long-term photometric data, we investigated the cyclic behavior of EK Dra over the past century. We analyzed its short-term activity based on 13 sectors of the Transiting Exoplanet Survey Satellite (TESS). Applying Doppler imaging on high-resolution spectral data, we investigated the short- and long-term spot evolution and surface differential rotation.
Methods. We used a short-term Fourier-transform on 120-year-long archival photometric data in order to search for activity cycles. The short-term space photometry data were fit with an analytic three-spot model, and we hand-selected flares from it to analyze their phase and frequency distribution. Spectral synthesis was used to determine the astrophysical parameters of EK Dra. Using the iMa
Resolving interchange reconnection dynamics in a fan-spine-like topology observed by Solar Orbiter
No full textInterchange reconnection is thought to play a significant role in the production of solar jets and the solar wind. The dynamics of interchange reconnection in the low corona might be more complex than recognized before in higher temporal and spatial resolutions, however. Using unprecedentedly high-resolution observations from the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter, we analyzed the dynamics of interchange reconnection in a small-scale fan-spine-like topology. The interchange reconnection that continuously occurs around the multinull points of the fan-spine-like system exhibits a quasi-periodicity of ∼200 s that nearly covers the entire evolution of this system. Continuous evolution and a reversal of multiple current sheets are observed over time near the null point. These results reveal that the dynamics of interchange reconnection is likely modulated by emerging magnetic structures, such as mini-filaments and emerging arcades. Moreover, a curtain-like feature with a width of 1.7 Mm is also observed near the interchange reconnection region and persistently generates outflows. This is similar to the separatrix curtain reported in the pseudostreamer structure. This study not only demonstrates the complex and variable reconnection dynamics of interchange reconnection within a small-scale fan-spine topology, but also provides insights into the self-similarity of magnetic field configurations across multiple temporal and spatial scales
Self-lensing binaries as probes of supernova physics
No full textSelf-lensing (SL) in binary systems has the potential to provide a unique observational window into the Galactic population of compact objects. Using the startrac
Early Detection of Age-Related Spatial Processing Decline: A Cross-Sectional Analysis of Four Auditory Measures
No full textAuditory spatial discrimination measures, including interaural time difference (ITD), interaural level difference (ILD), minimum audible angle (MAA) and bisection accuracy (BA), are key components of spatial auditory processing and contribute to accurate sound localization. Age-related declines in these abilities can negatively impact spatial awareness and daily communication. The study investigated the sensitivity of four spatial hearing measures— ITD, ILD, MAA and BA to age-related changes in auditory spatial discrimination. An experimental cross-sectional study design was adopted, with purposive sampling of 44 clinically normal-hearing participants (22 young and 22 middle-aged adults). Spatialized white noise bursts were generated by convolving signals with non-individualized head-related transfer functions using the 3D Tune-In Toolkit, a software environment for simulating 3D audio over headphones. ITD and ILD tasks involved detecting time and intensity differences between ears. MAA assessed the smallest discriminable angle. BA measured the ability to bisect auditory space into two hemifields. MANOVA revealed significant main effect of age across all measures (p < 0.001), with middle-aged adults showing significantly poorer spatial discrimination. Receiver Operating Characteristic analyses identified MAA as the most sensitive measure. Fisher's Discriminant analysis further validated the discriminatory power of MAA for group categorization. These findings suggest that auditory spatial discrimination abilities may begin to show subtle changes at mid-adulthood. The MAA shows to be a promising marker out of the four measures for detecting early spatial processing deficits
Peak-picking method for identifying natural frequencies and damping ratios from free vibration measurements
No full textThis paper introduces a method for identifying natural frequencies and damping ratios from a free vibration response induced by an impact, without requiring measurement of the excitation force. The approach combines the conceptual simplicity of peak-picking with the robustness of a multi-component time-domain model of the signal. Modal components are identified iteratively, based on spectral peaks selected by the user. The method is deliberately supervised, yet designed to remain accessible to non-expert users. A graphical interface provides intuitive control over the identification process and immediate feedback on the quality of the reconstructed signal, both in the time and frequency domains. The method is illustrated through experimental applications, demonstrating that natural frequencies and damping ratios can be extracted from simple, non-invasive measurements of the sound radiated by structures following an impact excitation. The robustness of the method to measurement noise and modal overlap is evaluated, and the identified parameters are shown to be consistent with those obtained from conventional FRF-based modal identification
Optimisation of the spatial configuration of microphones for robust virtual sensing in a diffuse sound field
No full textVirtual sensing methods are utilised in active noise control systems where the error sensors cannot be placed at the locations where control is physically required. Their performance critically depends on the spatial configuration of the physical monitoring microphones used to estimate the pressures at the virtual error sensor locations. This paper investigates the use of a genetic algorithm to calculate optimal microphone placements for estimation within a stationary diffuse sound field. A multi-objective optimisation framework is formulated, simultaneously minimising the estimation error and the condition number of the monitoring microphone power spectral density matrix, thereby addressing both estimation accuracy and robustness to uncertainties. Optimisations are carried out for a single frequency and for three representative frequencies spanning three octaves. The resulting Pareto fronts reveal the inherent tradeoff between performance and numerical stability. The Technique for Order of Preference by Similarity to Ideal Solution is applied to select a single optimal solution from each Pareto set. These solutions achieve a balanced compromise, offering a small reduction in estimation performance while reducing the condition number by up to an order of magnitude compared with configurations that solely minimise the error. The minimum error and optimal solutions are evaluated over a broad frequency range, where the optimal designs are shown to significantly reduce the conditioning for a modest increase in estimation errors. The study highlights characteristic spatial patterns that promote optimal performance, and demonstrates the effectiveness of a genetic algorithm-based multi-objective optimisation for designing robust microphone configurations for virtual sensing applications
Enhanced detection limits in the SHINE F150 survey through the regime switching model
No full textContext. In high-contrast imaging, a novel detection algorithm for angular differential imaging (ADI) sequences has recently been introduced: the regime switching model (RSM). This advanced statistical tool enhances the distinction between planetary signals and bright speckles by simultaneously combining multiple ADI-based post-processing techniques.
Aims. In this study, we apply the RSM algorithm to analyze the F150 sample from the SHINE high-contrast imaging survey carried out with VLT/SPHERE, aiming to enhance detection limits and identify new exoplanet candidates. Additionally, we investigate how environmental conditions influence post-processed noise distributions and detection thresholds.
Methods. We generated detection maps and contrast curves for 213 observations in the F150 SHINE sample using the RSM algorithm. A clustering approach based on environmental parameters was used to group observations with similar noise characteristics. We propose two methods for defining radial detection thresholds in the RSM maps: fitting a lognormal distribution to the post-processed noise and maximizing the F1 score. We also assessed the performance of various combinations of post-processing techniques within the RSM framework to identify optimal configurations.
Results. This study demonstrates the utility of clustering based on observational parameters, effectively distinguishing features such as wind-driven halos and low-wind effects. Detection thresholds vary significantly across clusters, differing by up to a factor of ten, highlighting the importance of considering observational environments. Lognormal thresholds provide conservative, noise-aware limits, while F1 score-based thresholds offer observation-specific results, with both showing compatibility overall. RSM improves detection limits by an average factor of two at 1" and five at inner working angles compared to standard principal component analysis processing. This study reports more than 30 newly detected signals, including one promising candidate awaiting second-epoch confirmation