446494 research outputs found
Sort by
Asteroseismic imprints of mass transfer in binary stars: Probing the interiors of donors and accretors with gravity and acoustic modes
No full textContext. The synergy between close binary stars and asteroseismology enables constraints on mass-transfer episodes and their consequences for internal structure, rotation profiles, and oscillation modes.
Aims. We investigate how mass accretion and donation in close binaries affects the internal structure and oscillation modes of main-sequence stars.
Methods. Building on the established relation between the Brunt–Väisälä (buoyancy) glitch and the Fourier spectra of g-mode period spacings, we quantitatively explain the origins of the g-mode period-spacing differences between single-star and mass-accretion or donation models of intermediate-mass stars (M = 2.0, 3.0, and 4.5 M⊙). In particular, the hydrogen mass fraction profiles X of the donor model show two chemical gradient regions, which results in a double-peaked Brunt–Väisälä profile. The presence of additional buoyancy glitches gives rise to further periodic modulations in the g-mode period spacings.
Results. Mass-accretion–induced changes in the chemical profile create sharp features in the buoyancy frequency, which modify both the amplitudes and frequencies of the g-mode period-spacing variations. This behaviour resembles that produced by multiple chemical transition zones in compact pulsators such as white dwarfs and sub-dwarf B stars. Similarly, for acoustic modes in the M = 1 M⊙ solar-like models, we attribute the differences in frequency-separation ratios between single-star and mass-donor models to the variations in the internal sound-speed gradient (acoustic glitches). We discuss future prospects of using asteroseismology to discover the mass-transfer products and constrain the mass-transfer processes in binary star evolution
Connecting solar wind turbulence to plasma parameters at L1 using multi-spacecraft coherence
No full textContext. Solar wind propagation behavior has significant implications for solar wind forecasting and measurements. Variability in coherence and plasma turbulence under different plasma conditions is important for cross-satellite comparisons. Forecasting also depends on whether upstream measurements remain valid at the magnetosphere.
Aims. We used computational methods to analyze magnetic coherence and connections to plasma parameters, utilizing multi-decade ACE and Wind measurements to capture turbulence behavior across a wide range of spatial separations and solar cycle phases.
Methods. The measurements were separated into three frequency ranges within the inertial range of solar wind turbulence: in periods of 1–2.5 min, 2.5–10 min, and 10–30 min. We assessed the coherence in each frequency band using time-lagged cross-correlations and applied a clustering algorithm to identify connections between coherence and plasma parameters (velocity, proton density, flow pressure). We performed this analysis in the radial, nonradial, and total directions.
Results. We used a k-means clustering algorithm to find that higher coherence in all cases is associated with smaller variance in plasma parameters. Taking this into consideration, we find a trivial association with the satellite separation or solar cycle phase. Small variations in dynamic pressure and velocity appear to be the best indicators of high coherence at these high-frequency inertial scales. Identifying connections between turbulence and plasma parameters could improve our understanding of the underlying physical processes. This information will also be vital for instrument calibration on future missions such as the Space Weather Follow On L1 (SWFO-L1)
LCS: A learnlet-based sparse framework for blind source separation
No full textBlind source separation (BSS) plays a pivotal role in modern astrophysics by enabling the extraction of scientifically meaningful signals from multi-frequency observations. Traditional BSS methods, such as those that rely on fixed wavelet dictionaries, enforce sparsity during component separation but can fall short when faced with the inherent complexity of real astrophysical signals. In this work, we introduce the learnlet component separator (LCS), a novel BSS framework that bridges classical sparsity-based techniques and modern deep learning. LCS utilises the learnlet transform – a structured convolutional neural network designed to serve as a learned, wavelet-like multi-scale representation. This hybrid design preserves the interpretability and sparsity-promoting properties of wavelets while gaining the adaptability and expressiveness of learned models. The LCS algorithm integrates this learned sparse representation into an iterative source separation process, enabling the effective decomposition of multi-channel observations. While conceptually inspired by sparse BSS methods, LCS introduces a learned representation layer that significantly departs from classical fixed-basis assumptions. We evaluated LCS on both synthetic and real datasets and in this paper demonstrate its superior separation performance compared to state-of-the-art methods (average gain of about 5 dB on toy model examples). Our results highlight the potential of hybrid approaches that combine signal processing priors with deep learning to address the challenges of next-generation cosmological experiments
Early identification of optical tidal disruption events
No full textContext. The detection of tidal disruption events (TDEs) is one of the key science goals of large optical time-domain surveys such as the Zwicky Transient Facility (ZTF) and the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time. Automated and reliable classification pipelines that can select promising candidates in real time are required to identify TDEs in the vast alert streams produced by these surveys, however.
Aims. We developed a module within the FIN
On the baryon budget in the X-ray-emitting circumgalactic medium of Milky Way-mass galaxies
No full textRecent observations with SRG/eROSITA reveal the average X-ray surface brightness profile of the X-ray-emitting circumgalactic medium (CGM) around Milky Way (MW)-mass galaxies, offering valuable insights into the baryon budget in these systems. However, the estimation of the baryon mass depends critically on several assumptions regarding the gas density profile, temperature, metallicity, and the underlying halo mass distribution. Here, we assess how these assumptions affect the inferred baryon mass of the X-ray-emitting CGM in MW-mass galaxies, based on the stacked eROSITA signal. We find that variations in temperature profiles and uncertainties in the halo mass introduce the dominant sources of uncertainty, resulting in X-ray-emitting baryon mass estimates that vary by nearly a factor of four (0.8–3.5 × 1011 M⊙). Assumptions about metallicity contribute an additional uncertainty of approximately 50%. We emphasize that accurate X-ray spectral constraints on gas temperature and metallicity, along with careful modeling of halo mass uncertainty, are essential for accurately estimating the baryon mass for MW-mass galaxies. Future X-ray microcalorimeter missions will be crucial for determining the hot CGM properties and closing the baryon census at the MW-mass scale
APEX survey of interstellar HCl
No full textContext. Despite being only the nineteenth most abundant element in the interstellar medium, chlorine’s reactivity and volatility give rise to a unique interstellar chemistry, favouring the formation of several chlorine-bearing hydrides. Further, the 35Cl/37Cl ratio – shaped in supernovae and evolved stars – probes nucleosynthesis across the Galaxy. Yet, studies of Cl-bearing molecules have remained limited to a few sight lines due to observational challenges.
Aims. We systematically investigated the Galactic distribution of HCl and the [H35Cl]/[H37Cl] ratio in high-mass star-forming regions. As a probe of a region’s nucleosynthesis history, this ratio may constrain predictions of Galactic chemical evolution models.
Methods. We surveyed the ground-state J = 1–0 transitions of H35Cl and H37Cl near 625 GHz towards 28 sources with the SEPIA660 receiver on the APEX 12 m sub-millimetre telescope. This survey more than doubles the number of sources with HCl detections and reveals HCl emission arising from both the background core and associated outflows. The spectra were modelled with XCLASS to derive column densities, isotopic ratios, and the kinematics of both the core and the outflow components.
Results. H35Cl was detected in all sources, H37Cl in all but two, with spectral line profiles ranging from those with only emission to complex emission–absorption mixtures. Column densities span from 2.3–22.8 × 1013 cm−2 for H35Cl and 0.6–12.5 × 1013 cm−2 for H37Cl, resulting in isotopic ratios between 1.6 and 3.5 in emission-only sources.
Conclusions. The derived [H35Cl]/[H37Cl] aligns with Galactic chemical evolution models and shows no trend with Galactocentric radius. However, local variations may reflect recent nucleosynthesis. Overall, the results suggest that most Galactic chlorine was synthesised during epochs of lower average metallicity in the Galaxy. Notably, we detect H35Cl emission arising from outflows – particularly explosive ones – hinting at its presence in a broader range of environments. The present single-dish observations cannot reveal the origin of HCl in outflows, necessitating interferometric follow-up observations
Inferring the physics of protoplanetary disc evolution from the irradiated Cygnus OB2 region
No full textContext. Determining the physical processes driving protoplanetary disc evolution is of paramount importance for understanding planet formation. Our current understanding has crystallised around two possible evolution scenarios: turbulent viscosity and magnetohydrodynamic (MHD) wind-driven. Which of these processes dominates, however, remains unclear.
Aims. Our aims are twofold. Firstly, we investigate whether a single set of model parameters can reproduce the observational constraints of non-irradiated and irradiated discs. Secondly, we propose a novel approach to break degeneracies between these two scenarios by studying the relation of stellar accretion rate and externally driven wind mass-loss rates, which evolve differently depending on the mechanism of angular momentum transport in the outer disc, and we test this approach using our models.
Methods. We simulated the evolution of synthetic populations of protoplanetary discs using 1D vertically integrated models for both viscous and MHD wind-driven disc evolution including both internal X-ray and external far ultraviolet (FUV) photoevaporation for both evolution scenarios. We investigated both weak and strong FUV field environments, where the strong FUV field is calculated based on an environment similar to the Cygnus OB2 association. We studied the time evolution of the disc fraction, disc mass–stellar accretion rate relation, the spatial variation of the disc fraction in a highly irradiated cluster, the evolution of disc radii, and the evolution of accretion rates versus wind mass-loss rates.
Results. While both evolution scenarios are capable of reproducing observational constraints, our simulations suggest that different parameters are needed for the angular momentum transport to explain disc lifetimes and the disc mass–stellar accretion rate relation in weakly and strongly irradiated regions. We find that the predicted median disc radii are much larger in low FUV environments compared to Cygnus OB2 but also decrease with time. In the viscous scenario, the median disc radius in a low FUV field environment is ∼100 au larger than for the MHD wind-driven scenario. We further demonstrate that studying stellar accretion rates and externally driven wind mass-loss rates (provided that they can be isolated from internally driven winds, i.e. MHD wind) is indeed a promising way of disentangling the two evolution scenarios.
Conclusions. The fact that a single set of parameters for angular momentum transport is not able to reproduce disc lifetimes in both low and highly irradiated regions at the same time indicates a fundamental difference in the two regions
Sun-to-Mud observations of the May and October storms of 2024: impacts on Ireland’s Space Weather
No full textNear the peak of Solar Cycle 25 in 2024, Earth was impacted by two major solar eruptive events which triggered dramatic geomagnetic storm activity. In May 2024, multiple solar eruptive events generated the largest geomagnetic storm since the early 2000s; this was followed by a similar-sized geomagnetic storm in October 2024, driven by a single solar eruptive event. Both storms occurred in the “social media era”, when the widespread use of mobile imaging devices on “smartphones” encouraged the public to go outside and witness the storms, often capturing and sharing photographs; examples local to the island of Ireland are analysed in this study. While the socio-historic impact of the storms was significant, in this manuscript, the sources and effects of the two storms are compared and contrasted. A “Sun-to-Mud” analysis is presented, from the solar origins of the events down to regional electrodynamic effects over the island of Ireland. Results indicate that while the May storm was driven by a compound CME-CME event following a quiet period, the single CME driving the October storm arrived at a magnetosphere primed by previous activity. Both storms exhibit strong solar wind – magnetosphere-ionosphere coupling, and the precursor activity in October demonstrates that the time history of magnetosphere-ionosphere priming is an important factor that influences the ultimate effect of a transient solar-driven event. Locally over the island of Ireland, observations suggest auroral electrojets poleward of local magnetometers, and both events generate remarkable geomagnetically induced currents; these observations are presented along with local auroral photographs
Global null controllability of stochastic semilinear complex Ginzburg–Landau equations
No full textIn this paper, we study the null controllability of forward and backward stochastic semilinear complex Ginzburg–Landau equations with global Lipschitz nonlinear terms. For this purpose, by deriving an improved global Carleman estimates for linear systems, we obtain the controllability results for the stochastic linear systems with a L2-valued source term. Based on it, together with a Banach fixed point argument, the desired null controllability of semilinear systems is derived
Effect of the Sustainable Food Yard (P2L) Program on Farmer Behavior Change: Evidence from Bunyu Island, North Kalimantan
No full textThe Sustainable Food Yard Program (Pekarangan Pangan Lestari/P2L) is one of the Indonesian Ministry of Agriculture's aimed at strengthening house-hold-level food security. The Sustainable Food Yard (P2L) Program is one of the Ministry of Agriculture's initiatives aimed at strengthening household-level food security. The program primarily targets Women Farmer Groups (KWT) to ensure the availability, accessibility, utilization, and stability of food resources at the micro level. This study was conducted on Bunyu Island, Bulungan Regency, North Kalimantan, with the following objectives: (1) to describe the implementation of the P2L program on Bunyu Island; (2) to analyze behavioral and social changes among KWT members; and (3) to identify factors influencing changes in farmer behavior. Data were collected through surveys and interviews, involving 30 respondents and 2 key informants. The research employed a sequential exploratory mixed methods approach, where qualitative and quantitative data were analyzed in sequence. The findings indicate notable changes in farmer behavior, particularly in terms of knowledge, attitudes, and skills. Social change was also observed across the dimensions of adaptation, goal attainment, integration, and pattern maintenance. Regression analysis revealed an R2 value of 53.8%, indicating that attitudes had a significant effect on changes in farmer behavior, whereas perceptions and the social environment did not show a direct influence