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Research Trends

Latest preprints in space engineering and astrophysics.

astro-ph.HE

Peculiar Behavior of Optical Polarization in Blazar 1ES 1959+650: Role of Jet Magnetic Field and Geometry

A. Singh, A. Tolamatti, K. K. Singh, A. C. Gupta, K. K. Yadav

Measurements of high degree of optical polarization from blazars provide a strong evidence for the optically thin synchrotron radiation from the relativistic leptons in the jet. This in turn characterizes the presence of a partially ordered magnetic field in the emission region. However, the topology of magnetic field and acceleration of electrons to ultrarelativistic energies within the blazar jet are poorly understood. In this work, we investigate the decade long optical light curve of the wel…

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gr-qcastro-ph.IM

Characterization of the Scattered Light Noise in KAGRA Interferometer

Shih-Hong Hsu, Hirotaka Yuzurihara, Chia-Jui Chou, Yi Yang

In a gravitational wave (GW) telescope, non-stationary noise can prevent stable interferometer operation and limit the GW analyses. Among the non-stationary noise, we focus on the scattered light noise. It fluctuates across a wide frequency band within a short time. Therefore, the scattered light noise can mimic the GW signal, increase the false alarm rate, or bias the parameter estimation results. In this work, we propose a new analysis method, named f-cluster, to characterize these features wi…

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astro-ph.SR

Origin of the Long-Period Radial Velocity Variation in the Red Supergiant HD 216946 (V424 Lac)

Byeong-Cheol Lee, Myeong-Gu Park

We present precise radial-velocity (RV) observations of the K-type red supergiant HD~216946 (V424 Lac) obtained over approximately 22 years with the Bohyunsan Optical Astronomy Observatory Echelle Spectrograph (BOES). The RV measurements reveal a significant long-period variability with a period of 1365 days. To investigate its origin, we analyzed the RV data together with line-profile variations (LPVs), chromospheric activity indicators, and published photometric variability. The LPVs exhibit p…

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astro-ph.GAastro-ph.CO

From Dark Matter to Galaxies: Halo-Free Mock Generation via Conditional Point-Cloud Diffusion

Kana Moriwaki, Ken Osato, Naoki Yoshida

We present a diffusion-based generative model for constructing realistic galaxy catalogues from dark matter density fields. The model takes a three-dimensional dark matter density field as input and generates galaxies directly as a point cloud with positions and physical properties, including star formation rate (SFR), without identifying dark matter haloes or subhaloes. We train the model on galaxy catalogues from the IllustrisTNG hydrodynamical simulation. The generated catalogues reproduce th…

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astro-ph.SR

Metric Type II Radio Emission associated with Coronal Mass Ejections of Large Angular Widths: Some New Insights

Mayank Rajput, Susanta Kumar Bisoi, Janardhan Padmanabhan

Solar Type II radio bursts are manifestations of shocks produced by explosive and eruptive solar activities, such as solar flares and coronal mass ejections (CMEs). Metric range or coronal Type II bursts are interesting because of their association with CME-driven shocks. It is therefore important to examine the correlation between the properties of Type II bursts and the associated CMEs. This, in turn, would be useful in understanding the impact of CMEs on space weather and geomagnetic activity…

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astro-ph.SR

Boundary conditions for radial pulsations in AGB envelopes

Jan Zalewski

We present a formulation of outer and inner boundary conditions for radial non-adiabatic pulsations in AGB/post-AGB envelopes in terms of local structure of pulsation equations. This approach provides a framework to construct classes of boundary condition selectors. We show that the pulsation spectrum is primarily determined by the choice of the outer boundary selector. Different choices of the two-dimensional subspace at the outer boundary lead to different types of pulsation spectra ranging fr…

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astro-ph.SRastro-ph.EP

A Search for Exoplanets around Northern Circumpolar Stars X. The origin of radial velocity variations in the evolved star HD 216595

Sang-Hee Kim, Byeong-Cheol Lee, Shenghong Gu, Jae-Rim Koo, Beomdu Lim, Myeong-Gu Park, Huan-Yu Teng, Yeon-Ho Choi et al.

Detecting planetary companions around evolved stars, particularly asymptotic giant branch (AGB) stars, is challenging due to intrinsic stellar variability such as surface convection, pulsations, and mass loss, which can produce radial velocity (RV) signals that mimic Keplerian motion. We investigate the origin of long-period, low-amplitude RV variations observed in the AGB star HD 216595 based on high-resolution spectroscopic data spanning approximately 16 years obtained with the Bohyunsan Optic…

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astro-ph.SRastro-ph.EP

2D hydrodynamical simulations of Be star decretion disc formation through boundary layer effects

Madeline Overton, Zhaohuan Zhu, Rebecca G. Martin, Jiayin Dong

Be stars are massive main-sequence stars rotating close to their breakup rate. They possess a decretion disc of material built up due to mass loss from the star, however, there is not a consensus to the mechanism responsible for the formation of the disc because of their sub-breakup spin rates. We present the first 2D hydrodynamical simulations of the formation of a Be star decretion disc from a rapidly rotating star due to boundary layer effects that reduce the rotation rate of the disc close t…

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astro-ph.EP

CAFE follow-up of TESS hot Jupiter candidates left behind: I. Five newly confirmed planets and a false positive

J. Lillo-Box, C. Cifuentes, O. Balsalobre-Ruza, B. Montesinos, D. Latham, K. A. Collins, D. Ciardi, G. Hébrard et al.

Hot Jupiters are key targets for understanding planet formation, migration, and atmospheres. Yet, most ground-based follow-up resources for the TESS mission are focused on confirming low-mass planet candidates, leaving many giant planets without mass determinations or definitive confirmation. We use the \cafe{} spectrograph at Calar Alto Observatory to monitor the radial velocity of stars hosting hot-Jupiter candidates that have received little follow-up, aiming to confirm their planetary nature…

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astro-ph.SR

One cluster, two clusters, no cluster? -- The curious case of HSC 2686 and Lynga 3

Andreas Ritter, Quentin A. Parker, Xizhe Xie, Xingyi Guo

This study was motivated by the search for Planetary Nebulae (PNe) and Open Cluster (OCs) associations. Only 5 PNe are currently in Galactic OCs among the previous $\sim4,800$ OCs known. They are valuable because as cluster members their properties can be linked to their progenitor stars, something not possible for general field PNe. Since the GAIA astrometric satellite first data release, thousands of new OC candidates have been identified. This offers fresh motivation to search them as hosts f…

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astro-ph.SR

Solar differential rotation driven by baroclinic forcing

L. S. Menicucci, G. Guerrero, M. Dikpati, R. Hester, J. Zhang, P. K. Smolarkiewicz

A combination of recent observations and numerical simulations has called into question whether Sun's interior is characterized by strong turbulent convection, a problem known as convective conundrum. In light of a possible absence of vigorous convective motions, we examine whether the Sun's differential rotation, previously assumed to be tightly coupled to Reynolds stresses, may instead be sustained by the presence of a background latitudinal entropy gradient in thermal wind balance. By perform…

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astro-ph.SR

Exploring the Small-scale Magnetic Fields in the Atmosphere of HD 49385 by Asteroseismic Analysis

Yuetong Wang, Yaguang Li, Yan Li, Guifang Lin, Tao Wu

Recent asteroseismic studies have shown convincing evidences that magnetic fields may exist in the interior of some pulsating red giants. Inspired by this breakthrough, we explored the effect of small-scale magnetic fields on the p-mode oscillations in an evolved star, HD 49385. {\bf We incorporate a modified Eddington $T$-$τ$ equation that phenomenologically mimics the effect of the magnetic fields in the atmosphere of HD 49385,} and calculate the frequencies of p-modes with $l=0$, 1, and 2. By…

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astro-ph.SR

Asteroseismic Analysis of a Red Giant KIC 9145955 by Including the Small-scale Magnetic Fields in the Atmosphere

Yuetong Wang, Guifang Lin, Yan Li, Tao Wu, Yaguang Li

Recent convincing evidence is found within asteroseismology that suggests the magnetic fields exist in three red giants. Research on small-scale magnetic fields in the Sun and HD 49385 has shown that they have a certain corrective effect on the systematic discrepancies between observed and theoretical frequencies. Here we apply a similar method applied for the Sun to a red giant, KIC 9145955, to explore the impact of small-scale magnetic fields in the photosphere on its frequencies. We find that…

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astro-ph.GA

When Galaxies Refuel: Evolution of the Perturbed Spiral Galaxy NGC1385

Xiaoyu Kang, Eva Sextl, Rolf-Peter Kudritzki, Hassen M. Yesuf, Fenghui Zhang, Ruixiang Chang, Xiejin Li, Yunkun Han et al.

The spiral galaxy NGC 1385 is characterized by a vigorous and protracted history of star formation, particularly in its central regions, leading to a current star formation rate that surpasses those of comparable systems. We analyze the evolution history of the galaxy using spatially resolved optical and submillimeter spectroscopy obtained from the PHANGS survey combined with WALLABY radio survey data. We construct radial distributions of star formation rate and the interstellar medium (ISM) neu…

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astro-ph.HEastro-ph.SR

No Surviving Companion to the Galactic SN 1181: Evidence for a Double-Degenerate Channel for Type Iax Supernovae

Kohki Uno, Daichi Tsuna, Daichi Hiramatsu, Tomoya Kinugawa, Takatoshi Ko

Type Iax supernovae (SNe Iax) are the recently-established, yet peculiar subclass of thermonuclear supernovae, whose progenitor systems and explosion mechanisms remain debated. A leading scenario is a single-degenerate channel, in which a white dwarf accreting from a He-star companion undergoes a pure deflagration, leaving both a bound remnant and surviving companion. The Galactic SN 1181, whose distinctive properties are consistent with an SN Iax involving a weak explosion and bound white dwarf…

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astro-ph.SRastro-ph.EP

The magnetic field strength of a methane dwarf measured from its radio spectral cutoff

Timothy W. H. Yiu, Harish K. Vedantham, Joseph R. Callingham, Timothy W. Shimwell

Brown dwarfs and gas-giant planets are expected to emit coherent radio emission via the electron cyclotron maser instability (ECMI) mechanism powered by non-thermal electrons in their magnetospheres. Detection of a characteristic spectral cutoff in their cyclotron emission is likely to be the only feasible route to measure their magnetic field strengths. Previous radio measurements of a subset of cold brown dwarfs (spectral type T or methane dwarfs) have not shown such a cutoff at frequencies as…

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astro-ph.GAastro-ph.IM

AGNFormer I: Reconstruction of AGN spectra using a probabilistic transformer model

Benedict L. Rouse, Franz E. Bauer, Tomasz Różański, Guillermo Cabrera-Vives, Patricia Arévalo, Cristóbal Rodrigo Donoso Oliva, Pavlos Protopapas, Gordon T. Richards et al.

We explore how an uncertainty-aware transformer-based architecture can leverage information embedded across the entire observed optical spectra of AGN, focusing on the algorithm's ability to predict unseen or masked parts of luminous AGN spectra. This provides a direct probe of the learnable correlations between AGN continua and broad lines. We introduce AGNFormer, a transformer model trained to predict the mean expected flux and variance in masked spectral regions (major broad lines to ${\pm}10…

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astro-ph.EP

Dynamically Selected Mass-Radius Relationship for Low Mass Exoplanets

Brad Hansen, Austin Mao

We study the mass-radius relationship of planets in multiplanet systems as a function of their dynamical architecture. We isolate those planets whose proximity to resonance indicates that they have not undergone significant dynamical instability since formation, and therefore have not experienced a late giant impact with another planet. We compare the properties of these planets to those whose orbital architectures suggest a high probability of having experienced a giant impact. We find that pla…

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astro-ph.IM

RNDR noise modeling in first-generation Single electron Sensitive Readout (SiSeRO) devices

Tonya L. Peshel, Abigail Y. Pan, Tanmoy Chattopadhyay, Steven W. Allen, Marshall W. Bautz, Michael Cooper, Kevan Donlon, Catherine E. Grant et al.

Flagship observatories require single-photon detectors with ultra-fast readout, sub-electron noise performance, and scalable large-format architectures. The X-ray Astronomy and Observational Cosmology group at Stanford, in collaboration with the MIT Kavli Institute and MIT Lincoln Laboratory, is developing readout technologies for next-generation detectors. Prototypes employing Single-electron Sensitive Readout (SiSeRO) amplifiers demonstrate excellent read noise and spectral performance using r…

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astro-ph.GA

AGN Feedback Models and AGN Demographics II: Comparing Predictions of Radiative and Total Feedback to Observations

Arjun Suresh, Michael R. Blanton

We evaluate the radiative-mode active galactic nucleus (AGN) feedback models of EAGLE, SIMBA, and TNG100 by comparing their predictions for the AGN-host galaxy relationship to new observational constraints. Owing to incomplete knowledge of the underlying physics, these models differ substantially, and it remains unclear whether any of them accurately reflect reality. In a previous study, based on the demographics of narrow line AGN, we constrained $F_{\mathrm{AGN}}$, the intrinsic fraction of ga…

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astro-ph.HE

Shock cooling emission from late-time mass loss in low-mass He star binaries

Samantha C. Wu, Anthony L. Piro

A subset of hydrogen-poor supernovae (SNe) exhibit signatures of interaction with nearby dense circumstellar material (CSM). These SNe may originate from interacting binary systems, in which the SN progenitor experiences intense mass loss when it overflows its Roche lobe close to core collapse. In this work, we explore the appearance of SNe from low-mass stripped star progenitors in binary systems, for a range of initial orbital periods and masses. We model the CSM based on the stripped stars' m…

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astro-ph.SRastro-ph.IMcs.LG

A Deep Learning Framework for Predicting Solar EUV Irradiance During Significant Flares

Sathvik Soman, Jason T. L. Wang, Haimin Wang, Haodi Jiang

We present FlareEUV, a multimodal deep learning framework for predicting daily extreme ultraviolet (EUV) irradiance at 6.5 nm over three consecutive days during significant solar flares, using multi-instrument observations from NASA's Solar Dynamics Observatory (SDO). We consider 33 significant flares in the period between 2011 and 2014 in Solar Cycle 24. The SDO observations include 13 co-aligned full-disk images, comprising eight AIA EUV/UV and five HMI magnetic/continuum products. FlareEUV le…

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astro-ph.IM

Characterising the response of an International LOFAR Station

Letizia Vincetti, Sai C. Susarla, Owen A. Johnson, Evan F. Keane, David J. McKenna, Tobia D. Carozzi, Gavin Ramsay, Oisin Creaner et al.

Phased-array radio interferometers with fixed antennas are a highly scalable design which can achieve a large gain. However they are complex systems and challenging to calibrate. Here we examine the response of an International LOFAR Station, the high-band antennas of the Irish LOFAR station. In modelling our measured responses, we account for projection effects, the frequency-dependence of the aperture efficiency and pulsar spectra, as well as sky and instrumental noise contributions. We perfor…

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astro-ph.GA

Systematic Effects in Gaia CRF Photometry Related to Scanning Geometry and BP/RP excess factor

Valeri V. Makarov

I report a previously undocumented, large-amplitude systematic dependence of the median Gaia $G$-band magnitude of CRF3 sources on \texttt{ra\_dec\_corr}, which reflects the preferred direction of scans, accompanied by a partially correlated trend in the BP/RP flux excess factor. Given the imminent release of Gaia DR4, the purpose of this note is alerting the community to this artifact.

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astro-ph.EP

Atmospheric retrieval evidence for water isotopologue HDO on exoplanet WASP-39b

Fabian Gruebel, Karan Molaverdikhani, Barbara Ercolano, Katy L. Chubb, Paola Caselli, Tommaso Grassi, Rosa Arenales-Lope, Dwaipayan Dubey et al.

Hydrogen-isotopologues are commonly used to trace the chemical processing and origin of hydrogen-bearing species throughout the Universe, however, their abundance remains unconstrained for extrasolar planets. Here, we report atmospheric retrieval evidence for the deuterated water molecule HDO in an exoplanet atmosphere, retrieved from James Webb Space Telescope transmission spectra of the hot Jupiter WASP-39 b, resulting in a deuterium-to-hydrogen ratio in water of $4.0^{+1.3}_{-1.1} \times 10^{…

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astro-ph.GA

Swing amplification in star-gas disks

Abhishek Hegade K. R., Chris Hamilton

Recent JWST and ALMA observations have revealed stellar bars and spirals in gas-rich galactic disks at redshifts as high as $z \simeq 4$. The simplest theoretical paradigm we have for understanding such non-axisymmetric features is the linear theory of swing amplification (SA) in the 2D shearing sheet. However, while the SA mechanism in a gaseous shearing sheet was first studied in 1965, and that in a collisionless stellar sheet in 1966, the coupled star-gas linear SA equations have never been s…

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astro-ph.GA

The Age-Thickness Relation as a Tracer of the Merger History of Disk Galaxies

Lekshmi Thulasidharan, Elena D'Onghia, Robert Benjamin, Ronald Drimmel, Eloisa Poggio

In the hierarchical framework of galaxy formation, disk galaxies are shaped by a sequence of mergers and interactions, yet reconstructing this history from observations remains challenging. We show that the merger history of a galaxy leaves measurable imprints in the vertical structure of its stellar disk. Using Milky Way analogues from the TNG50 simulations, we demonstrate that the Age-thickness relation, quantified by the dispersion of vertical stellar positions ($Δ_z$), encodes both the dynam…

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astro-ph.GAastro-ph.HE

Discovery of Optical Filaments in the North Polar Spur/eROSITA Bubble

Julian Shapiro

I report the discovery of optical filaments in H$α$, [O III], and [S II], coincident with $144\,\mathrm{MHz}$ structure, associated with the North Polar Spur (NPS) region of the eROSITA bubbles. The optical emission is identified in the Northern Sky Narrowband Survey, and contains distinct structure and potentially elevated $\text{[S II]}/\mathrm{H}α$ relative to typical high-$b$ outflows from the warm ionized medium (WIM). $Δ$-variance and power spectrum analysis of the NPS H$α$ shows a prefere…

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astro-ph.GA

Mid-Infrared Colors Vary with Galactic Environment: Contrasting Star-Forming Disks, Young Centers, and Quiescent Star-Formation Deserts

Debosmita Pathak, Karin M. Sandstrom, Adam K. Leroy, Ryan Chown, Daniel A. Dale, Hannah B. Koziol, Mansi Padave, Jessica Sutter et al.

We present $50{-}100\,$pc-resolution JWST/MIRI and NIRCam measurements of mid-infrared (mid-IR) color variations in the diffuse interstellar medium (ISM) of 71 nearby star-forming galaxies from the PHANGS-JWST survey. Mid-IR emission traces the dust column density, intensity ($U$) and hardness of the interstellar radiation field, and the physical state (charge, size) and abundance of polycyclic aromatic hydrocarbons (PAHs). Mid-IR colors that trace PAH band-ratios remain fairly constant in the d…

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astro-ph.GAgr-qc

Local morphology and asymmetry of galactic rotation curves in a kinetic gas transport framework: NGC 3198

Anton A. Lipovka, Anna A. Lipovka

We investigate whether the observed fine structure and asymmetry of non-averaged galactic rotation curves can be reconstructed directly from the observed HI distribution within the framework of a kinetic gas transport description. Using the observed HI density profiles separately for the approaching (north-eastern) side and the receding (south-western) side of the galaxy NGC~3198, we reconstruct the corresponding rotation curves based on the equation previously derived in \citet{Lipovka2022}. It…

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