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Research Trends

Latest preprints in space engineering and astrophysics.

astro-ph.SR

Presence of Solar Neutral Atom Corona and Coronal Heating

Z. Q. Qu, R. Y. Zhou, H. Su, Y. Liang, L. Chang, X. M. Cheng

By analyzing slit scanning spectral data obtained during 2024 total solar eclipse, presence of neutral atom corona is revealed along with a hidden inner F-corona detected within heights below half a solar radius. The inner F-corona is found to be essentially different from the Fraunhofer corona formed by dust scattering beyond about 2.3 solar radius heights. The two new kinds of the solar corona are deduced from the intensity difference between the spectral line intensity distribution and their…

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astro-ph.SRastro-ph.GAastro-ph.HE

Thermodynamic exchange and mode stability in strongly nonadiabatic radial pulsations

Jan Zalewski

We apply the quadratic balance relation for linear nonadiabatic pulsations to radial modes of a sequence of post-AGB envelope models covering $3.52\leq\log(T_{\rm eff})\leq4.6$. The relation separates the thermodynamic exchange power $\mathcal{P}_{\rm ex}$, response power $\mathcal{P}_{\rm rsp}$, and surface contribution $ΔB$, and introduces an effective norm through $\mathcal{P}_{\rm ex}+ΔB=2γχ_{\rm eff}\mathcal{E}_{\rm kin}$, where $γ$ is the mode growth rate. For nearly adiabatic modes $χ_{\r…

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astro-ph.GAastro-ph.IMastro-ph.SR

Decoding RR Lyrae light curves with deep learning for accurate absolute magnitude estimation

Shunxuan He, Huiwen Wu, Yang Huang, Deyi Zhang, Guirong Xue, Jifeng Liu, Xiaodian Chen, Xinyu Qi et al.

RR Lyrae stars are essential standard candles for distance measurements in the Milky Way and nearby galaxies. Traditional estimates rely on the Period--Absolute Magnitude--Metallicity relation but are limited by uncertainties in metallicity determinations. We present a deep learning approach that directly predicts absolute magnitudes from RRab and RRc light curves, eliminating the need for metallicity estimates. Our model achieves validation precisions of 0.053 mag and 0.036 mag (approximately 2…

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math.OCastro-ph.IMeess.SYmath.DS

Convex Pursuit-Evasion Games for Spacecraft Proximity Operations on Circular and Elliptical Orbits

Omer Burak Iskender

Inspecting or servicing a non-cooperative spacecraft is a two-player game: the target can thrust to defeat the inspector's plan. Hamilton-Jacobi-Isaacs reachability answers such games exactly but its cost grows exponentially with state dimension, while learning-based controllers scale yet certify nothing. Convex formulations are the usual escape, typically cast as convex-concave saddle-point problems. That framing fails in the terminal-distance orbital game: with effort regularization, the payof…

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astro-ph.SR

Supersonic flows observed by THEMIS related to a coronal bright point and filament

Garima Karki, Brigitte Schmieder, Ramesh Chandra, Pooja Devi, Pascal Demoulin, Stefaan Poedts

In this paper, we report on the dynamics of the fine structure of a solar quiescent filament observed on September 28, 2023, with the Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires (THEMIS). The main aim is to understand the relationship between the supersonic downflows measured in H$α$ at the filament end and an associated coronal bright point. We use a cloud-model method to derive the supersonic velocity of the falling, elongated cool blob. Besides, we use H$α…

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gr-qcastro-ph.IMcs.LG

Parameter Estimation of Ringdown Quasinormal Modes with Autoencoder

Momoka Iida, Hayato Motohashi, Hirotaka Takahashi

Ringdown gravitational waves from binary black hole mergers can be modeled as superpositions of quasinormal modes (QNMs), whose frequencies and excitation factors encode properties of the remnant Kerr black hole. Reliable extraction of multiple QNM components is challenging because of mode overlap and noise. We develop an autoencoder-based framework for multi-component QNM analysis, in which the latent space is trained to represent the physical parameters of individual modes, enabling waveform d…

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astro-ph.HE

Exploring the dynamics of the Coma galaxy cluster by mapping its X-ray emission line profiles with XRISM

Kosei Sakai, Kazuhiro Nakazawa, Maxim Markevitch, Dominique Eckert, Yuichiro Ezoe, Yuto Ichinohe, Richard Kelley, Richard Mushotzky et al.

The intracluster medium (ICM) in merging galaxy clusters exhibits turbulence and bulk flows. Unraveling these components is crucial not only for elucidating the geometry of the cluster mergers, but also for understanding the physics of magnetic field amplification and relativistic particle acceleration. XRISM/Resolve data for two $3'\times3'$ fields in the core of the Coma cluster reveales that the ICM in the central field moves with $Δcz = -430$~km~s$^{-1}$ relative to the cluster galaxy averag…

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astro-ph.HE

Exploring the dynamics of the Coma galaxy cluster by mapping its X-ray emission line profiles with XRISM

Kosei Sakai, Kazuhiro Nakazawa, Maxim Markevitch, Dominique Eckert, Yuichiro Ezoe, Yuto Ichinohe, Richard Kelley, Richard Mushotzky et al.

The intracluster medium (ICM) in merging galaxy clusters exhibits turbulence and bulk flows. Unraveling these components is crucial not only for elucidating the geometry of the cluster mergers, but also for understanding the physics of magnetic field amplification and relativistic particle acceleration. XRISM/Resolve data for two $3'\times3'$ fields in the core of the Coma cluster reveales that the ICM in the central field moves with $Δcz = -430$~km~s$^{-1}$ relative to the cluster galaxy averag…

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astro-ph.HE

The LGRBs Redshift and Jet Opening Angle Distributions and the Hubble Constant $H_0$

Truong Le, Joseph Chromicz

Using the Swift-Perley sample, Le, Ratke, & Mehta performed a study of the rate density of LGRBs with an assumed broken power-law GRB spectrum. They obtained a GRB-burst-rate functional form that fits the preSwift~and Swift~redshift cumulative distributions at all redshifts with an assumed Hubble constant of $H_0 = 72 \, {\rm km \, s^{-1} \, Mpc^{-1}}$. Further analysis indicated that the cumulative redshift distribution is weakly sensitive to variations in the Hubble constant $H_0$, whereas the…

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gr-qcastro-ph.HEhep-th

Quantum black hole ringdown

Konstantinos Topaloglou, Elena Cuoco, Roberto Casadio

The ringdown of a black hole following a merger is a potential candidate for revealing the signatures of quantum gravity in the emerging gravitational waves. In quantum theory, black holes are expected to have a discrete area and energy spectrum, which conflicts with the classical notion of an horizon that absorbs all infalling perturbations. We propose that the quantum black hole dissipates the energy it cannot absorb by emitting ``soft'' gravitons that carry away the energy difference between…

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astro-ph.HE

The Galactic Black Hole mass distribution

L S. Rocha, N. Pires, L. M. de Sá, B. B. Martins, L. G. Barão, G. R. C. Sampaio, D. V. Rodrigues, R. M. G. Takahashi et al.

The population of extragalactic black holes has been significantly expanded and better understood since the first detection of gravitational waves. Over the past decade, approximately 290 events have been confirmed to involve at least one black hole. In contrast, the galactic black hole population has grown at a much slower pace, with only 42 systems possessing mass estimates, while the vast majority remain as candidates. In this work, we present the first update of a Bayesian analysis of the ma…

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astro-ph.SRastro-ph.EP

Reconstruction of pretelescopic and early telescopic solar activity cycles from auroral records

Kristof Petrovay, Laura G. Magyar, Hisashi Hayakawa

The historical record of low-latitude aurorae is essentially a poorly sampled record of the largest space weather events (SWEs). Its use for the identification of individual solar cycles is hindered by the low event rate and by the fact that the solar cycle profile of the occurrence of SWEs does not closely follow the variation of sunspot numbers. Based on recent studies of the solar cycle dependence of the occurrence rates of large SWEs, here we construct Monte-Carlo simulations of a large numb…

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astro-ph.IMastro-ph.COgr-qc

A compact time-domain reduced order quadrature for gravitational wave inspirals with non-stationary noise

Benjamin Zhang, Kris Pardo, Bence Bécsy

We develop the first time-domain reduced order quadrature for gravitational waves in the early inspiral period, motivated by the need for dataset compression in the presence of gaps, uneven sampling, and dense covariance matrices. A single reduced basis with 1290 elements can represent inspirals from supermassive black hole binary sources with chirp masses between $10^7-10^{10}$ $M_\odot$, but in the presence of non-stationary noise $\sim 1290^2$ reduced order quadrature weights must be stored.…

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cs.CGastro-ph.EPcs.GR

The optimal-transport cartogram: world population as a Brenier map

Philipp Bogdan

A contiguous cartogram is a map whose area is proportional to a quantity such as population. The defining condition, that the Jacobian determinant of the deformation equals the density, is one equation for two unknown functions, so every cartogram method adds a tie-breaker, usually implicitly. Optimal transport makes the tie-breaker explicit: among all density-equalising maps of the frame onto itself, take the one that moves the population least in the mean-square sense. By Brenier's theorem tha…

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cs.CGastro-ph.EPcs.GR

The optimal-transport cartogram: world population as a Brenier map

Philipp Bogdan

A contiguous cartogram is a map whose area is proportional to a quantity such as population. The defining condition, that the Jacobian determinant of the deformation equals the density, is one equation for two unknown functions, so every cartogram method adds a tie-breaker, usually implicitly. Optimal transport makes the tie-breaker explicit: among all density-equalising maps of the frame onto itself, take the one that moves the population least in the mean-square sense. By Brenier's theorem tha…

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astro-ph.GAgr-qc

The New Dark Matter Density Profile from JWST JADES Galaxies

Aritra Sanyal, Farook Rahaman

We present the first dark matter density profile derived directly from James Webb Space Telescope JADES Data Release~3 NIRSpec observations of $N = 587$ galaxies spanning the cosmic noon epoch $1.5 \leq z \leq 3.5$. From each NIRSpec G235M/G395M spectrum we extract the H$α$ emission-line velocity dispersion $σ_{\rm ha}$, stack galaxies in four redshift bins of $Δz = 0.5$, and reconstruct representative group rotation curves within the General Theory of Relativity. Fitting the four-parameter modi…

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astro-ph.GA

Recovering turbulent velocity statistics from noisy integral-field spectroscopy

J. García-Vázquez, William J. Henney, S. Jane Arthur

Turbulence plays a critical role in the evolution of H II regions, yet recovering its statistical properties from observations remains challenging, particularly when centroid velocities are affected by instrumental noise. We present a methodology for recovering the second-order velocity structure function from intermediate spectral-resolution integral-field spectroscopy and apply it to VLT MUSE observations of the Orion Nebula. The plane-of-sky velocity field is characterized by fitting a simple…

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astro-ph.SRastro-ph.EP

Investigating Variability in Long-lived Protoplanetary Disks (>10 Myr) using NEOWISE

Gregory Mathews Ben, Jessy Jose, Jesús Hernández

We present the mid-infrared variability study of 120 long-lived disk candidates (ages 10-100 Myr) and 13 confirmed "Peter Pan" disks using NEOWISE to constrain the longevity of dynamic disk processes beyond the standard 10 Myr dispersal threshold. We identified 32 sources exhibiting significant variability by combining stochastic flux metrics and the Stetson $J$ index. The majority of these variables belong to the 10-25 Myr age range, suggesting a sharp decline in disk brightness variability aft…

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astro-ph.SRastro-ph.GA

Investigating r-Process Diversity in Mildly Metal-Poor Stars Using the Th II 5989 Angstrom Line

Kurumi Furutsuka, Satoshi Honda

The origin of the heaviest elements remains a fundamental mystery, with the "actinide-boost" (Thorium overabundance) serving as a critical diagnostic of r-process nucleosynthesis conditions. While this diversity is well documented in extremely metal-poor (EMP) stars, its frequency in the mildly metal-poor (MMP) regime ($-2.0 < $ [Fe/H] $< -0.5$) is poorly constrained due to blending issues in the commonly used 4019 angstrom line. We present a systematic abundance analysis of mildly metal-poor st…

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gr-qcastro-ph.IM

Frequency shift in gravitational lensing by Kerr metric

Samaneh Sarbaz, Sohrab Rahvar

In this study, we calculate the relative frequency shift ($Δν/ ν$) caused by gravitational lensing resulting from the transverse motion of a spinning lens described by the Kerr metric \cite{Kerr:1963ud}. While the effect of transverse velocity on the frequency shift has previously been investigated using the Schwarzschild metric \cite{Rahvar_2020,10.1093/mnras/stae1938}, extending this to the Kerr metric provides a new window for measuring the transverse velocity of a lens or its spin parameter,…

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astro-ph.SR

Multi-Instrument Analysis of NOAA AR 12781: Coupling Surface Evolution of the AR with Its In-Situ Solar Wind Signatures

Dharanesh Palaniappan, Khagendra Katuwal

Understanding the relationship between photospheric magnetic flux evolution and coronal emission remains an important problem in heliophysics. We investigate the decay of NOAA Active Region 12781 from 7 to 11 November 2020 using observations from the Solar Dynamics Observatory (SDO). Coronal emission was measured from the Atmospheric Imaging Assembly (AIA) 193\~Å images, while the photospheric signed and unsigned magnetic flux was derived from Helioseismic and Magnetic Imager (HMI) observations…

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astro-ph.IM

Consistency and precision of very long baseline interferometry source coordinate time series

X. -X. Zhang, N. Liu, S. B. Lambert, K. Le Bail, H. Krásná, O. Titov, M. Karbon, T. Nilsson et al.

Coordinate time series of extragalactic radio sources from very long baseline interferometry observations are widely used to evaluate source positional stability, select stable sources for celestial reference frames, assess reference-frame axis stability, and investigate source-related astrometric variability. Their external consistency, realistic errors, and relation to processing strategies and analysis configurations remain to be investigated. We aim to compare coordinate time series solution…

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hep-phastro-ph.COastro-ph.GAgr-qchep-th

A Unified Numerical Study of Axion Stars: From the Nonrelativistic Regime to General Relativity

Parisa Arabameri, Paola Arias, Francisco Colipí-Marchant, Enrico D. Schiappacasse

Axion-star mass-radius relations are commonly computed using different orders of relativistic approximation, making it important to determine where these descriptions remain reliable. We perform a unified numerical comparison of axion-star ground-state configurations in the Newtonian Schrödinger-Poisson description, first- and second-order relativistic effective field theories, and the full Einstein-Klein-Gordon system for a real scalar field. Using the same attractive quartic self-interaction i…

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astro-ph.HE

Examining Temporal Characteristics of GCRs in the AMS-02 era

Cheng-Rui Zhu, Yu-Lu Liu, Mei-Juan Wang, Tian-Hao Li, Yi-Hua Zhu, Kai-Kai Duan

The energy spectra of Galactic cosmic rays (GCRs) serve as critical probes of their astrophysical origins and propagation mechanisms through the interstellar medium. Among the key physical processes shaping the observed spectra, solar modulation, driven by turbulent heliospheric magnetic fields and the variability of the solar wind, plays a dominant role in modifying GCR fluxes within the inner heliosphere. The recent release of time-dependent flux measurements for He, Li, Be, B, C, N, and O by…

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astro-ph.IM

A Two-Stage Physically Grounded Optical Design Framework with Application to a Multi-Channel Focal Reducer

M. R. Najera, J. Herrera, Esteban Luna, Erika Sohn

We present a two-stage optimization framework that formalizes classical optical design strategies within a reproducible computational workflow. Starting point designs are constructed from paraxial and third-order models, providing optically consistent initial configurations. These configurations are refined through a physically grounded residual merit function evaluated by exact ray tracing, followed by RMS-based image refinement. Applied to a multi-channel astronomical focal reducer, the method…

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astro-ph.IMphysics.optics

Sensing ELT petal modes with a discrete beam combiner: an end-to-end theoretical model

Kalaga V. Madhav, Abani Shankar Nayak, Lucas Labadie, Robert R. Thomson

The European Southern Observatory's Extremely Large Telescope (ELT), the 39-m telescope under construction in Chile, forms its entrance pupil from 798 hexagonal segments that the six 0.5-m-wide spider arms fragment into six "petals". The low-wind / island effect, adaptive-optics residuals, and mechanical drift imprint an independent piston on each petal. These differential-piston (petal) modes remain largely undetected by the ELT's baseline continuous-pupil wavefront sensors, a major bottleneck…

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astro-ph.HE

Observable Signatures of Supernova Shock Breakout in Confined Circumstellar Medium

Wun-Yi Chen, Ke-Jung Chen, Keiichi Maeda, Friedrich K. Röpke

Supernova shock breakout encodes rich information about stellar explosions, including the properties of the progenitor, the explosion mechanism, and the circumstellar environment. We present the first two-dimensional multigroup radiation-hydrodynamic simulations of shock breakout from Red Supergiant (RSG) progenitor stars embedded in confined circumstellar medium (CSM) produced shortly before core collapse. Our simulations reveal that radiation escaping ahead of the shock forms a radiative precu…

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astro-ph.EP

Incompatibility of iron in post-perovskite and the stability of basal magma oceans in super-Earths

Francis Dragulet, Lars Stixrude

Post-perovskite is expected to dominate much of the solid mantles of rocky exoplanets, yet iron partitioning between post-perovskite and silicate melt, which controls the compositional evolution and buoyancy of crystallizing magma oceans, is unconstrained at these pressures. We use first-principles molecular dynamics and thermodynamic integration to compute the Fe--Mg distribution coefficient $K_D$ between post-perovskite and (Mg,Fe)SiO$_3$ liquid at 150--600~GPa and 6000--10000~K. Iron is stron…

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cs.LGastro-ph.EPastro-ph.IM

Operational Range Bounding in Spectroscopy: A Safety Cage Framework for Machine Learning Models

Nikki Grens, Luís F. Simões, Kai Hou Yip, Theresa Lueftinger

Ensuring the reliability of black-box machine learning models in safety-critical space missions remains a significant challenge, particularly when ground-truth is unavailable for validation. Although machine learning models offer a powerful means to augment standard pipelines by extracting transmission spectra from complex exoplanetary light curves, their susceptibility to unmodelled instrument anomalies, stellar activity, and domain shifts introduces unquantified risks. This study evaluates a m…

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astro-ph.IMastro-ph.EPphysics.optics

Photonic Integrated Circuits for the Habitable Worlds Observatory: Science Drivers, Material Platforms, Arrayed-Waveguide Spectrographs, and a Space-Qualification Roadmap

Kalaga Madhav

NASA's Habitable Worlds Observatory (HWO) will require ultraviolet, optical, and near-infrared instruments that are simultaneously compact, mechanically and thermally stable, high-throughput, and replicable at large channel counts. Space-qualified photonic integrated circuits (PICs) and optical fibres are key platforms that can deliver these properties: they manipulate light at the diffraction limit within micron-scale single-mode waveguide circuits. An astrophotonic instrument fully guides the…

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