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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 19 January

Astrophysics of Galaxies · Cross-listed from cond-mat.quant-gas

Anisotropic dispersion relation of ultralight Bose gases in modified Newtonian dynamics

Ning Liu

We investigate the dispersion relation of collective modes in ultralight Bose gases under Modified Newtonian Dynamics (MOND). Starting from the coupled Gross-Pitaevskii and MOND Poisson equations, we derive an anisotropic dispersion relation that depends on the angle between the perturbation wavevector and the background gravitational field. This anisotropy arises directly from the nonlinear structure of the MOND field equation and leads to a direction-dependent Jeans instability, with critical wavelengths and masses varying with orientation. Our results provide a distinctive signature of MOND in a quantum astrophysical context and suggest that ultralight Bose gases can serve as novel probes of modified gravity.
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Instrumentation and Methods for Astrophysics · Cross-listed from eess.SY

Lessons Learned from Structural Design and Vibration Testing of 50-kg Microsatellites Deployed from the International Space Station

Yuji Sakamoto, Junichi Kurihara, Shinya Fujita et al. (+2 more)

Hokkaido University and Tohoku University have been developing and operating a constellation of 50-cm-class microsatellites for Earth observation. DIWATA-1, launched in 2016, was deployed into a circular orbit at an altitude of approximately 400 km from the International Space Station (ISS). For the subsequent satellite developed in 2021, the structural design and vibration test campaign were optimized to meet a strict one-year development schedule. This paper summarizes how the structural design of the previous satellite was reviewed and updated, and how the vibration test was successfully completed in a single trial to minimize schedule and technical risks. These lessons learned provide valuable insights, as there are only a limited number of reported cases of 50-kg-class microsatellites deployed from the ISS.
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All authors Yuji Sakamoto, Junichi Kurihara, Shinya Fujita, Yuji Sato, Toshinori Kuwahara

Solar and Stellar Astrophysics

Identification of false positive double-lined spectroscopic binaries in LAMOST-MRS data due to moonlight contamination

Zhoulin Wang, Mikhail Kovalev, Jianping Xiong et al. (+2 more)

We present a method for identifying false positive double-lined spectroscopic binary (SB2) candidates by analysing medium-resolution survey spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR10. Specifically, we focus on spectra contaminated by moonlight, which exhibit near-zero radial velocity (RV) and solar-like spectral lines from the secondary component. By applying strict constraints on the contamination parameters and fitting the contaminated spectra, we ultimately confirmed that 126 false positive binaries are single stars contaminated by moonlight. Additionally, we identify several key factors contributing to moonlight contamination: the lunar phase during observation, the G-band magnitude of the star, and the angular distance between the star and the moon. Notably, artificial satellites in low-orbital can also introduce contamination from solar-like spectral components, but they typically display significantly higher transverse velocities. In a follow-up study, we will expand our analysis to identify additional false positive SB2 systems and systematically classify them according to their contamination sources.
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All authors Zhoulin Wang, Mikhail Kovalev, Jianping Xiong, Yanjun Guo, Xuefei Chen

Solar and Stellar Astrophysics

Classical Be Stars and Classical Be Star Binaries from LAMOST DR12

Qian-Yu An, Wei-Min Gu and Zhi-Xiang Zhang

Classical Be (CBe) stars are rapidly rotating B-type stars with Balmer emission lines that originated from the decretion disks surrounding them in their spectra. Accounting for $\sim$20% of all B-type stars, most CBe stars are thought to form through mass and angular momentum transfer from their companions. It follows that in most close CBe star binaries, the companions are expected to be post-main-sequence stars rather than main-sequence (MS) stars. Hitherto, $\sim$100 CBe star binaries have been identified, the majority of which are Be/X-ray binaries. As expected, none of the others have indeed been confirmed as CBe+MS binary stars. To further study and verify the origin of CBe stars, identifying additional CBe star binaries is indispensable. In this study, we report 504 CBe stars identified using data from Data Release 12 of the Large sky Area Multi-Object fiber Spectroscopic Telescope. Among these, 141 are newly identified and 14 exhibiting radial velocity variations are identified as CBe star binaries. Besides, 60 CBe stars with high normalized unit weight error (RUWE) but not confirmed by dynamics are proposed as potential CBe star binaries. We also find that 34 CBe stars are potential cluster members. By calculating peculiar velocities, 37 runaway stars are identified with peculiar velocities ranging from $\sim$40 km s$^{-1}$ to $\sim$101 km s$^{-1}$.
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Solar and Stellar Astrophysics

Testing Red Clump Models with the Asteroseismic Binary KIC 10841730

Lea S. Schimak, Timothy R. Bedding, Courtney L. Crawford et al. (+9 more)

Binaries in which both stars are pulsating are rare but extremely valuable. We present the first study of an asteroseismic binary system consisting of a core helium-burning red clump (RC) star and a red giant branch (RGB) star. The Kepler target KIC 10841730 is a wide binary (period $2917 \pm 8$ d) that provides ideal conditions to test the accuracy of RC models. While prior studies of RC stars have revealed discrepancies in modelling the period spacings of mixed modes, other model parameters remain largely untested. We perform a detailed modelling analysis using individual mode frequencies and cover a large parameter space in mass, metallicity, He-abundance, mixing length, overshooting, and mass-loss, and we also explore different methods to correct for surface effects. We find two possible results for the red clump models. One solution requires introducing an unexpected offset of the phase shift in the red clump model, yielding an age consistent with the companion star and current masses of $1.01 \pm 0.06$ and $1.08 \pm 0.06$ M$_\odot$ for the RC and RGB star, respectively. Alternatively, we find that excluding the identification of two questionable radial modes resolves the phase-shift offset issue but results in a higher mass and thus a much younger age for the red clump star, contradicting the age obtained from its companion. We conclude that uncertainties in red clump models affect not only the g-mode period spacings but also the properties of the p modes. We show the power of asteroseismic binaries in validating and constraining stellar models and highlight the need for refining red-clump models.
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All authors Lea S. Schimak, Timothy R. Bedding, Courtney L. Crawford, Paul G. Beck, Yaguang Li, Daniel Huber, Joel Ong, Benjamin T. Montet, May Gade Pedersen, Desmond H. Grossmann, Savita Mathur, Rafael A. García

Earth and Planetary Astrophysics

The Feasibility of Potentially Hazardous Asteroids Flybys Using Multiple Venus Gravity Assists

Vladislav Zubko

This work develops low-energy spacecraft (SC) trajectories using Venus gravity assists to study asteroids during heliocentric transfer segments between planetary encounters. The study focuses on potentially hazardous asteroids (PHAs) as primary exploration targets. This paper proposes a method for calculating SC trajectories that enable asteroid flybys after a Venus gravity assist. The method involves formulating and solving an optimization problem to design trajectories incorporating flybys of selected asteroids and Venus. Trajectories are calculated using two-body dynamics by solving the Lambert problem. A preliminary search for candidate asteroids uses an algorithm to narrow the search space of the optimization problem. This algorithm uses the V-infinity globe technique to connect planetary gravity assists with resonant orbits. The resonant orbit in this case serves as an initial approximation for the SC's trajectory between two successive planetary flybys. Four flight schemes were analyzed, including multiple flybys of Venus and asteroids, with the possibility of an SC returning to Earth. The proposed solutions reduce flight time between asteroid approaches, increase gravity assist frequency, and enhance mission design flexibility. The use of Venus gravity assists and resonant orbits ensures a close encounter with at least one asteroid during the SC's trajectory between two consecutive flybys of Venus, and demonstrates the feasibility of periodic Venus gravity assists and encounters with PHAs. The developed method was applied to construct trajectories that allow an SC to approach both Venus-resonant asteroids and PHAs via multiple Venus gravity assists. An additional study was carried out to identify asteroids accessible during the Earth-Venus segment in launch windows between 2029 and 2050.
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Solar and Stellar Astrophysics

Non-adiabatic Effect on Convective Mode

Hiroyasu Ando

The systematic analysis of non-adiabatic effect on convective mode has been conducted using wave energy relation. In the adiabatic analysis, the "propagation diagram" for convective mode is proposed as a useful tool to see its behavior. In the non-adiabatic analysis, it is found that for strongly non-adiabatic case, a monotonically growing convective mode becomes oscillatory. In this phase, the radial displacement and the distribution of wave energy show only one bump, in which the distribution of entropy energy eS almost overlaps with the distribution of gravity energy eg. Entropy energy eS seems to act as potential energy of oscillatory convection. In addition to this, this change occurs not gradually, but abruptly with change of non-adiabatic indicator.
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Astrophysics of Galaxies

Discovery of Multiple Ultra-Broad-Velocity Molecular Features Associated with the W44 Molecular Cloud

Momoko Makita, Tomoharu Oka, Shiho Tsujimoto et al. (+1 more)

We report the discovery of multiple compact molecular features exhibiting extremely broad velocity widths toward the W44 molecular cloud. ALMA CO $J$=3–2 data reveal eight “Petit–Bullets” surrounding the previously known “Bullet.” Each Petit–Bullet shows a distinct V-shaped structure in position–velocity space, reminiscent of the Y-shaped morphology of the Bullet, suggesting a common origin. These features are interpreted as the result of high-velocity plunges of compact gravitational objects into dense molecular gas. The spatial and kinematic properties of the Petit–Bullets suggest that the plunging material was not a single object but rather a small cluster of compact bodies. A virial mass of $1.0\!\times\! 10^{5}\, M_\odot$ inferred from their velocity dispersion is comparable to that of typical globular clusters. Momentum analysis further implies that the main Bullet likely formed by an isolated black hole. These findings provide new evidence for dynamical interactions between halo clusters and disk molecular gas.
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All authors Momoko Makita, Tomoharu Oka, Shiho Tsujimoto, Tatsuya Kotani

Solar and Stellar Astrophysics

Optical Continuum Light Curves and Bolometric Energy Estimates of Solar White-light Flares

Yingjie Cai, Yijun Hou, Hengkai Ding et al. (+2 more)

Solar white-light flares (WLFs) are solar flares exhibiting enhanced emission in the optical continuum. They are critical for understanding energy release and transport mechanisms in solar flares and for conducting comparative studies with stellar WLFs. However, the scarcity of accurately and reliably measured optical continuum light curves for solar WLFs significantly hampers related studies. Based on the optimized solar WLF identification method, we construct a dataset of optical continuum light curves for 70 solar WLFs using 6173 Å continuum intensity images from the Solar Dynamics Observatory. Moreover, for each solar WLF event, we also provide the location of the white-light emission enhancement signals and key parameters including bolometric energies and durations derived from both the traditional fixed-temperature blackbody model and the refined variable-temperature blackbody model. This dataset will serve as a valuable resource for future statistical investigations of solar WLFs and for comparative studies between solar and stellar flares.
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All authors Yingjie Cai, Yijun Hou, Hengkai Ding, Ting Li, Jifeng Liu

High Energy Astrophysical Phenomena

Rate of Repeating Tidal Disruption Events with 5–19 years interval

Yujun Yao, Luming Sun, Tao Wu et al. (+3 more)

Statistics on tidal disruption events (TDEs) may be contaminated by repeating TDEs (rTDEs), which have been extensively discovered recently. However, the origin of rTDEs remains unclear. In addition, no statistical research on rTDEs with time intervals $>5$ years has been made yet. In this work, we searched for rTDEs with time intervals of 5–19 years using CRTS data in a sample of 16 ZTF BTS TDEs at $z<0.05$. We found 2 rTDE candidates, AT 2019azh and AT 2024pvu, with time intervals of 13.2 and 17.1 years, respectively. The peak luminosities of CRTS flares are close to those of ZTF flares. For the CRTS flare of AT 2024pvu, using GALEX UV observations near the peak, we measured a blackbody temperature of $\sim19500$ K, consistent with TDEs and higher than SNe. Moreover, we estimated the expected number of SNe in the sample to be $\lesssim0.08$, and hence the probability that both CRTS flares are SNe is only 0.3%. Therefore, the possibility that both CRTS flares are SNe can be ruled out, and it is likely that both are TDEs. Using the two rTDEs, we inferred that the TDE rate is 2–3 orders of magnitude higher than the average over 5–19 years prior to TDE detection. Considering another two rTDEs with intervals of $\sim$2 years in the sample and possible rTDEs missed by CRTS, rTDEs with intervals of $<20$ years may account for 25%–60% of the TDE sample. We prefer to explain rTDEs as repeating partial TDEs. If so, the high fraction of rTDEs suggests that the observed optical TDE rate has been overestimated. However, the possibility of independent TDEs cannot be ruled out and requires future observational tests.
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All authors Yujun Yao, Luming Sun, Tao Wu, Ning Jiang, Shiyan Zhong, Xinwen Shu

Instrumentation and Methods for Astrophysics

PyIRD: A Python-Based Data Reduction Pipeline for Subaru/IRD and REACH

Yui Kasagi, Hajime Kawahara, Ziying Gu et al. (+4 more)

PyIRD is a Python-based pipeline for reducing spectroscopic data obtained with IRD (InfraRed Doppler; Kotani et al. (2018)) and REACH (Rigorous Exoplanetary Atmosphere Characterization with High dispersion coronagraphy; Kotani et al. (2020)) on the Subaru Telescope. It is designed to process raw images into one-dimensional spectra in a semi-automatic manner. Unlike traditional methods, it does not rely on IRAF (Tody, 1986; 1993), a software used for astronomical data reduction. This approach simplifies the workflow while maintaining efficiency and accuracy. Additionally, the pipeline includes an updated method for removing readout noise patterns from raw images, enabling efficient extraction of spectra even for faint targets such as brown dwarfs. The code is open source and available at https://github.com/prvjapan/pyird .
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All authors Yui Kasagi, Hajime Kawahara, Ziying Gu, Teruyuki Hirano, Takayuki Kotani, Masayuki Kuzuhara, Kento Masuda

Solar and Stellar Astrophysics

LAMOST J113208.06-005052.3 and LAMOST J052957.56+344127.0: two new binaries with a hot white dwarf and a flaring companion star

Yanhui Chen, Chaomi Duan and Baokun Sun

Binaries contain rich physical information, and the study of binaries has always been a hot topic in stellar physics research. The stars LAMOST J1132 and LAMOST J0529 have not yet been recorded in the SIMBAD astronomical database. We have investigated their physical properties via methods such as spectral analysis, photometric analysis, and light curve analysis. Based on comprehensive analysis, we conclude that they are two newly discovered binary systems, each consisting of a hot white dwarf and a flaring companion star. Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra indicate that both stars contain hot white dwarfs. The spectral fitting yields $T_{eff}$=53728$\pm$2467\,K, log$g$=7.98$\pm$0.08 for LAMOST J1132, and $T_{eff}$=47381$\pm$494\,K, log$g$=7.84$\pm$0.05 for LAMOST J0529. The weak neutral metal lines in the LAMOST spectra and the discrepancy between the Global Astrometric Interferometer for Astrophysics (GAIA) and LAMOST spectra both indicate that these two sources are likely binary systems. The relatively high flux values for both sources in the near-infrared and mid-infrared bands support our preliminary judgment. The color index in the near-infrared bands suggests that the companion star is K or M type for LAMOST J1132 and M type for LAMOST J0529. Light curve data from the Zwicky Transient Facility (ZTF) indicate that the companion stars of both sources are stars exhibiting flare activity. The eclipse probability is very low, indicating that these two sources are non-eclipsing binary systems. The physics of binaries is fascinating, and future data from LAMOST Medium Resolution Spectra are expected to enable the detection of magnetic fields in these two hot white dwarfs.
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Sunday 18 January

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Scalar Quasi-Normal Modes in Black Hole Gravitational Lensing

Chengjiang Yin, Zihao Lin and Jian-hua He

We investigate the excitation of quasi-normal modes (QNMs) in gravitational lensing by a Schwarzschild black hole using a scalar field model. By employing a time-domain mode-sum method, we analyze the complex interplay between an incident burst signal and the black hole spacetime. We find that the incident waves can non-resonantly excite a substantial number of high-$l$ modes, with amplitudes for modes as high as l=20 remaining significant compared to the fundamental l=0 mode. We confirm through QNM template fitting that the late-time behaviors of these excited modes are indeed QNMs. After passing through the black hole, we find that the lensed waves form a highly directional and coherent Gaussian beam whose cross-sectional intensity profile is well-described by a Gaussian profile. Unlike spherical waves, this beam's amplitude does not decrease with distance from the black hole but remains nearly constant in the near-field region. Moreover, due to the superposition of numerous QNMs, oscillations largely cancel each other out. The lensed temporal waves do not exhibit typical oscillatory patterns.
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High Energy Astrophysical Phenomena

The DESI Transients Survey: Legacy Classifications and Methodology

Xander J. Hall, Antonella Palmese, Segev BenZvi et al. (+56 more)

We present the first systematic spectroscopic observations of extragalactic transients from the Dark Energy Spectroscopic Instrument (DESI), as part of the DESI Transients Survey program. With 5,000 fibers and an ${\sim} 8$ deg$^2$ field of view, we exploit DESI as a machine for the discovery and classification of transients. We present transient classifications from archival DESI data in Data Releases 1 and 2, relying on a combination of a secondary target program and serendipitous observations. We also present observations from the first 6 months of the DESI spare fiber program dedicated to transients. The program is run in coordination with a dedicated DECam time-domain survey, serving as a pathfinder for what we will be able to achieve in conjunction with the Rubin Observatory Legacy Survey of Space and Time (LSST). We classify over 250 transients, of which the majority were previously unclassified. The sample comprises thermonuclear and core-collapse supernovae and tidal disruption events (TDEs), including a TDE observed before its discovery in imaging. We demonstrate DESI's ability to classify a population of faint transients down to $r\sim 22.5$ mag during main survey operations, with negligible impacts on DESI's main observations.
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All authors Xander J. Hall, Antonella Palmese, Segev BenZvi, John Banovetz, Brendan O'Connor, Lei Hu, Erica Hammerstein, Ariel Amsellem, Jessica Nicole Aguilar, Steven Ahlen, Steven Bailey, Davide Bianchi, David Brooks, Todd Claybaugh, Andrei Cuceu, Kyle Dawson, Axel de la Macorra, John Della Costa, Arjun Dey, Peter Doel, Simone Ferraro, Andreu Font-Ribera, Jaime E. Forero-Romero, Enrique Gaztanaga, Satya Gontcho A Gontcho, Alma Xochitl Gonzalez-Morales, Or Graur, Gaston Gutierrez, Mustapha Ishak, Jorge Jimenez, Dick Joyce, Stephanie Juneau, Anthony Kremin, Ofer Lahav, Claire Lamman, Martin Landriau, Laurent Le Guillou, Alexie Leauthaud, Michael Levi, Marc Manera, Aaron Meisner, Ramon Miquel, John Moustakas, Adam Myers, Seshadri Nadathur, Will Percival, Claire Poppett, Ignasi Perez-Rafols, Francisco Prada, Graziano Rossi, Eusebio Sanchez, Edward Schlafly, David Schlegel, Michael Schubnell, David Sprayberry, Gregory Tarle, Benjamin Alan Weaver, Rongpu Zhou, Hu Zou

Earth and Planetary Astrophysics

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) V: Comparison between scattered light and thermal emission

J. Milli, J. Olofsson, M. Bonduelle et al. (+33 more)

Debris discs are analogues to our own Kuiper belt around main-sequence stars and are therefore referred to as exoKuiper belts. They have been resolved at high angular resolution at wavelengths spanning the optical to the submillimetre-millimetre regime. Short wavelengths probe the light scattered by such discs, which is dominated by micron-sized dust particles, while millimetre wavelengths probe the thermal emission of millimetre-sized particles. Determining differences in the dust distribution between millimetre- and micron-sized dust is fundamental to revealing the dynamical processes affecting the dust in debris discs. We aim to compare the scattered light from the discs of the ALMA survey to Resolve exoKuiper belt Substructures (ARKS) with the thermal emission probed by ALMA. We focus on the radial distribution of the dust. We used high-contrast scattered light observations obtained with VLT/SPHERE, GPI, and the HST to uniformly study the dust distribution in those systems and compare it to the dust distribution extracted from the ALMA observations carried out in the course of the ARKS project. We also set constraints on the presence of planets by using these high-contrast images combined with exoplanet evolutionary models. 15 of the 24 discs comprising the ARKS sample are detected in scattered light, with TYC9340-437-1 being imaged for the first time at near-infrared wavelengths. For 6 of those 15 discs, the dust surface density seen in scattered light peaks farther out compared to that observed with ALMA. These 6 discs except one are known to also host cold CO gas. Conversely, the systems without significant offsets are not known to host gas, except one. This observational study suggests that the presence of gas in debris discs may affect the small and large grains differently, pushing the small dust to greater distances where the gas is less abundant.
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All authors J. Milli, J. Olofsson, M. Bonduelle, R. Bendahan-West, J. P. Marshall, E. Choquet, A. A. Sefilian, Y. Han, B. Zawadzki, S. Mac Manamon, E. Mansell, C. del Burgo, J. M. Carpenter, A. M. Hughes, M. Booth, E. Chiang, S. Ertel, Th. M. Esposito, Th. Henning, J. Hom, M. R. Jankovic, A. V. Krivov, J. B. Lovell, P. Luppe, M. A. MacGregor, S. Marino, B. C. Matthews, L. Matrà, A. Moór, N. Pawellek, T. D. Pearce, S. Pérez, V. Squicciarin, P. Weber, D. J. Wilner, M. C. Wyatt

Earth and Planetary Astrophysics

On the accuracy of mass and size measurements of young protoplanetary disks

Eduard I. Vorobyov, Aleksandr Skliarevskii, Vardan Elbakyan et al. (+2 more)

Knowing the masses and sizes of protoplanetary disks is of fundamental importance for the contemporary theories of planet formation. However, their measurements are associated with large uncertainties. In this proof of concept study, we focus on the very early stages of disk evolution, concurrent with the formation of the protostellar seed, because it is then that the initial conditions for subsequent planet formation are likely established. Using three-dimensional hydrodynamic simulations of a protoplanetary disk followed by radiation transfer postprocessing, we constructed synthetic disk images at millimeter wavelengths. We then calculated the synthetic disk radii and masses using an algorithm that is often applied to observations of protoplanetary disks with ALMA, and compared the resulting values with the actual disk mass and size derived directly from hydrodynamic modeling. We paid specific attention to the effects of dust growth on the discrepancy between synthetic and intrinsic disk masses and radii. We find that the dust mass is likely underestimated in Band 6 by factors of 1.4-4.2 when Ossenkopf & Henning opacities and typical dust temperatures are used, but the discrepancy reduces in Band~3, where the dust mass can be even overestimated. Dust growth affects both disk mass and size estimates via the dust-size-dependent opacity, and extremely low values of dust temperature (~ several Kelvin) are required to recover the intrinsic dust mass when dust has grown to mm-sized grains and its opacity has increased. Dust mass estimates are weakly sensitive to the distance to the source, while disk radii may be seriously affected. We conclude that the accuracy of measuring the dust mass and disk radius during the formation of a protoplanetary disk also depends on the progress in dust growth. (Abridged)
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All authors Eduard I. Vorobyov, Aleksandr Skliarevskii, Vardan Elbakyan, Michael Dunham, Manuel Guedel

Solar and Stellar Astrophysics

Clouds and Chemistry Across the Brown Dwarf T-Y Sequence: Insights from JWST Atmospheric Retrievals

A. Lueber, D. Kitzmann and K. Heng

The James Webb Space Telescope (JWST) offers exceptional spectral resolution and wavelength coverage, which are essential for studying the coldest brown dwarfs, particularly Y dwarfs. These objects are at the cold end of the sub-stellar sequence and exhibit atmospheric phenomena such as cloud formation, chemical disequilibrium, and radiative-convective coupling. We examine a curated sample of 22 late-T to Y dwarfs through Bayesian atmospheric retrieval (nested sampling) and supervised machine learning (random forests). Bayesian model comparison indicates that cloud-free models are generally favored for the hottest objects in the sample (T6-T8). Conversely, later-type dwarfs exhibit varying preferences, with both gray-cloud and cloud-free models providing comparable fits. The atmospheric parameters retrieved are consistent across the applied methodologies. Evidence of vertical mixing and disequilibrium chemistry is found in several objects; notably, the Y1 dwarf WISEPAJ1541-22 favors a gray cloud model and shows elevated abundances of both CO and CO2 compared to equilibrium chemistry calculations. As anticipated, the abundances of H2O, CH4, and NH3 increase with decreasing effective temperature over the T-Y sequence.
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Earth and Planetary Astrophysics

Analytic Modeling of Tidally Locked Rocky Planet Atmospheres Across Dynamical Regimes

Christopher P. Wirth, Diana Powell and Robin Wordsworth

We present a new first-principles analytic approach to interpreting eclipses and phase curves of rocky planets. Observations with JWST have reported nondetections of atmospheres around the majority of hot rocky planets orbiting M dwarfs. However, most of these "bare rock" inferences are based on models that are ill-suited to many currently observable planets, as they were developed for use on cooler, slower-rotating bodies. In particular, these models rely on the weak temperature gradient assumption, in which rotation is neglected and temperature gradients can be simply related to wind speeds. We find that this assumption may not be valid for over 40% of terrestrials observed with JWST, including TRAPPIST-1b, GJ 367b, and TOI-2445b. Our simple new four-box model does not rely on this assumption, and instead allows the heat transport efficiency to be specified or follow scalings derived herein. This method is fast, interpretable, physically motivated, reproduces previous general circulation model results, and can be used as a starting point for more detailed modeling. We observe that the longitudinal temperature structure of tidally locked terrestrials depends strongly on the atmospheric circulation. Considering the applicable range of atmospheric dynamical regimes, we find that a given planet's nightside temperature can plausibly vary by 100s of Kelvin (from detectable to undetectable). Furthermore, a planet's dayside energy balance can display complex behavior, with degeneracies between surface pressure and dayside temperature. Illustrating an application to observations, we find that assumptions about atmospheric dynamics and longitudinal temperature structure can bias atmospheric constraints at the order-of-magnitude level.
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Solar and Stellar Astrophysics

Magnetic field detections in massive systems at different stages of interaction

S. Hubrig, M. Abdul-Masih, S.P. Jarvinen et al. (+4 more)

Despite the importance of magnetic fields in massive stars, their origin is widely debated and still not well understood. With the mounting evidence for the importance of studying magnetic fields in interacting massive binary and multiple systems, it appears necessary to investigate the presence of magnetic fields in semi-detached systems with ongoing mass transfer, and in contact systems where mass is actively being exchanged. We present an analysis of 53 high-resolution HARPSpol spectropolarimetric observations of a sample of 14 massive binary and multiple systems using the least-squares deconvolution technique. The majority of the studied systems are classified as semi-detached or contact binaries. Definite detections of the presence of a magnetic field are achieved in all studied systems apart from the rather faint system SV Cen, for which only a marginal detection was obtained. The fact that the presence of magnetic fields is detected in all but one of the studied systems strongly suggests that interaction between the system components plays a definite role in the generation of magnetic fields in massive stars. The measured mean longitudinal magnetic field strength for all targets is of the order of a few hundred Gauss to a few kiloGauss. The strongest longitudinal magnetic fields of 4 to 5kG are discovered in the massive O-type triple system MY Ser in both components of the contact binary. kiloGauss-order magnetic fields are also detected in two other systems, V1294 Sco and V606 Cen. It is possible that there is an implication of some system characteristics, such as multiplicity, the mass ratio between the components, and a large fillout factor, on the measured magnetic field strength. Our results for the magnetic field measurements in interacting binaries present the first assessment of the occurrence rate of magnetic fields in a representative sample of such systems.
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All authors S. Hubrig, M. Abdul-Masih, S.P. Jarvinen, A. Cikota, M. Schöller, I. Ilyin, A. Escorza

Astrophysics of Galaxies

Not so-dark: High resolution HI imaging of J0139+4328 and identification of an optical counterpart

Barbara Šiljeg, Elizabeth A. K. Adams, Tom A. Oosterloo et al. (+4 more)

Dark galaxies - systems rich in neutral hydrogen (HI) gas but with no stars - are a common prediction of numerous theoretical models and cosmological simulations. However, the unequivocal identification of such sources in current HI surveys has proven challenging. In this work, we present interferometric follow-up observations with the VLA of a former dark galaxy candidate J0139+4328, originally detected with the single-dish FAST telescope. The improved spatial resolution of the VLA data allow us to identify a faint optical counterpart and characterize the galaxy. Located at a distance of about 31 Mpc, J0139+4328 has a stellar mass of 3 x 10^6 M_Sun and a relatively high gas richness of M_HI/M_star = 18. Despite its high ratio, the galaxy is consistent, within the scatter, with the stellar-to-HI mass relation of HI-selected samples in the literature and with the baryonic Tully-Fisher relation (BTFR), although its kinematic measurement is subject to large uncertainties. This case highlights the potential of modern high-sensitivity HI surveys for detecting low surface brightness, gas-rich galaxies, but underscores the need for careful interpretation of low-resolution HI data, with potentially large centroid errors, and for sufficiently deep optical imaging to ensure robust identification.
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All authors Barbara Šiljeg, Elizabeth A. K. Adams, Tom A. Oosterloo, Filippo Fraternali, Kelley M. Hess, Jin-Long Xu, Ming Zhu

High Energy Astrophysical Phenomena

Nuclear astrophysics

Roland Diehl and Michael Wiescher

Reactions between atomic nuclei are measured in great detail in terrestrial laboratory experiments; transferring and extrapolating this knowledge to how the same reactions act within cosmic environments presents major challenges. Cross-disciplinary efforts are needed in view of the many nuclear reactions that govern the chemical evolution of the universe, and occur in a broad range of stellar plasma conditions that require astrophysical exploration. Since the early identification of 'processes' of nucleosynthesis, new insights have been obtained on the complexity of nuclear reaction mechanisms. We use 12C induced capture and fusion processes to illustrate the challenge of low-energy measurements and of using theoretical methods to extrapolate measurements towards energy regimes within cosmic sources. Particle beam experiments at accelerator facilities above and deep underground simulate stellar reactions, new experimental facilities and methods complement these, and this is further complemented by improved theoretical tools to calculate the quantum effects of nuclear reactions at the various cosmic conditions. Astronomical signatures of cosmic nuclear reactions are deduced from light curves characterizing cosmic explosions through gamma-ray lines and presolar grains to the detection of rare neutrino particles from our Sun to distant cosmic events. High resolution spectroscopy of stars has been expanded to objects measured in the X-ray and the gamma energy range of the electromagnetic spectrum. Astro-seismology and isotopic analysis of meteoritic inclusions provide new tools. Chemical-evolution models describe the complex dynamics during the evolution of galaxies. This article summarizes the experimental and theoretical work, and the broad range of observational tools that test the experimental data and the theoretical interpretation of nuclear processes in the cosmos.
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Earth and Planetary Astrophysics

Observational Signatures of Planetary Tidal Disruption Events Around Solar-Mass Stars

Matías Montesinos, Sergei Nayakshin, Vardan Elbakyan et al. (+4 more)

The tidal disruption of planets by their host stars represents a growing area of interest in transient astronomy, offering insights into the final stages of planetary system evolution. We model the hydrodynamic evolution and predict the multi-wavelength observational signatures of planetary TDEs around a solar-mass host, focusing on Jupiter-like and Neptune-like progenitors and examining how different eccentricities of the planet's pre-disruption orbit shape the morphology and emission of the tidal debris. We perform 2D hydrodynamic simulations using the FARGO3D code to model the formation and viscous evolution of the resulting debris disk. We employ a viscous alpha-disk prescription and include a time-dependent energy equation to compute the disk's effective temperature and subsequently derive the bolometric and multi-band photometric light curves. Our simulations show that planetary TDEs produce a diverse range of luminous transients. A Jupiter-like planet disrupted from a circular orbit at the Roche limit generates a transient peaking at $L_{bol} \approx 10^{38}$ erg s$^{-1}$ after a 12-day rise. In contrast, the same planet on an eccentric orbit (e=0.5) produces a transient of comparable peak luminosity but on a much shorter timescale, peaking in only 1 day and followed by a highly volatile light curve. We find that the effect of eccentricity is not universal, as it accelerates the event for Jupiter but delays it for Neptune. A robust "bluer-when-brighter" colour evolution is a common feature as the disk cools over its multi-year lifetime. The strong dependence of light curve morphology on the initial orbit and progenitor mass makes these events powerful diagnostics. This framework is crucial for identifying planetary TDEs in time-domain surveys.
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All authors Matías Montesinos, Sergei Nayakshin, Vardan Elbakyan, Zhen Guo, Mario Sucerquia, Amelia Bayo, Zhaohuan Zhu

Solar and Stellar Astrophysics

Evidence of energy conversion in weakly collisional plasma during an interplanetary coronal mass ejection

Omkar Dhamane, Anil Raghav, Simone Benella et al. (+14 more)

Intervals of enhanced turbulent fluctuations are typically less frequent within the magnetic cloud region of an interplanetary coronal mass ejection (ICME). We investigate two such intervals inside an ICME observed by the Wind spacecraft on 8–9 June 2000 and characterize their associated wave populations. We focus on spectral analysis and plasma instability analysis, using ion-scale normalized magnetic helicity and polarization properties with respect to the background magnetic field $B_0$. In the first interval, the ion-scale normalized magnetic helicity shows a left-handed circularly polarized signature. In the second interval, the left-handed signature persists and an additional high-frequency right-handed population appears. The propagation is approximately parallel to $B_0$. The left-handed fluctuations are compatible with Alfvén ion-cyclotron (AIC) waves, while the right-handed fluctuations are consistent with fast magnetosonic/whistler (FM/W) waves. The ICME plasma accesses resonance conditions that support multiple ion-scale wave modes. Evolving anisotropies in the plasma and the approach to marginal stability allow the coexistence of AIC-like and fast-magnetosonic/whistler-like fluctuations, with enhanced electron heating favoring the growth of the FM/W contribution and strengthening the density–magnetic-field magnitude correlation.
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All authors Omkar Dhamane, Anil Raghav, Simone Benella, Kishor Kumbhar, Raffaella D'Amicis, Oreste Pezzi, Utkarsh Sharma, Ashok Silwal, Panini Maurya, Mirko Stumpo, Kalpesh Ghag, Ajay Kumar, Mohit Shah, Mariyam Karari, Lynn B. Wilson III, Jia Huang, Daniele Telloni

High Energy Astrophysical Phenomena

A long-term multiwavelength study of the flat spectrum radio quasar OP 313

Chiara Bartolini, Elina Lindfors, Andrea Tramacere et al. (+25 more)

The Flat Spectrum Radio Quasar OP 313 is a high-redshift (z = 0.997) blazar that entered an intense gamma-ray active phase from November 2023 to March 2024, as observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. We present a multiwavelength analysis covering 15 years of data, from August 2008 to March 2024, to contextualize this period of extreme gamma-ray activity within the long-term emission of the source. We analyzed a long-term, comprehensive, multiwavelength dataset from different facilities and projects from radio to gamma-rays. We identified the 7 most intense gamma-ray flaring periods and performed a kinematic analysis of Very Long Baseline Array (VLBA) data to determine whether new jet components emerged before or during these flares. For 2 of these flaring periods, we performed the modeling of the spectral energy distribution (SED). The VLBA-BU-BLAZAR and MOJAVE datasets reveal a new jet component appearing in both visibility datasets prior to the onset of one of the strongest gamma-ray flares. By comparing the timing of the VLBA-BU-BLAZAR knots ejection with the gamma-ray flaring periods, we constrained the setup of the SED modeling. We also found that the first gamma-ray flaring period is less Compton-dominated than the others. Our results suggest that the recent activity of OP 313 is triggered by new jet components emerging from the core and interacting with a standing shock. The {\gamma}-ray emission likely arises from dusty torus photons upscattered via Inverse Compton (IC) by relativistic jet electrons. The SED modeling indicates that this component is less dominant during the first {\gamma}-ray flaring period than the later ones.
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All authors Chiara Bartolini, Elina Lindfors, Andrea Tramacere, Marcello Giroletti, Davide Cerasole, Ivan Agudo, Emmanouil Angelakis, Elisabetta Bissaldi, Fausto Casaburo, Filippo D'Ammando, Leonardo Di Venere, Vandad Fallah Ramazani, Federica Giacchino, Fracesco Giordano, Mark Gurwell, Jenni Jormanainen, Svetlana Jorstad, Garrett Keating, Pouya M. Kouch, Alexander Kraus, Anne Lahteenmaki, Serena Loporchio, Nicola Marchili, Alan Marscher, Ioannis Myserlis, Ramprasad Rao, Simona Righini, Merja Tornikoski

Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

Plasmoid formation via competing lower-hybrid drift and Kelvin-Helmholtz instabilities: A hybrid kinetic-gyrokinetic simulation study

S. Thatikonda, F. N. De Oliveira-Lopes, A. Mustonen et al. (+3 more)

We investigate the nonlinear formation of plasmoids in 2D low-beta current sheets through the interplay between the Kelvin-Helmholtz instability (KHI) and the lower-hybrid drift instability (LHDI). Using a hybrid kinetic-gyrokinetic model-based Super Simple Vlasov (ssV) code with fully kinetic ions and drift-kinetic electrons, we simulate Harris-type current sheets and velocity shear layers with strong cross-field density gradients. Our central hypothesis is that steep density gradients drive LHDI, which can grow faster than KHI and initiate an inverse cascade from kinetic to fluid scales, potentially suppressing KHI. Our simulations confirm that, in thin current sheets, LHDI develops rapidly at the sheet edges and nonlinearly merges into larger-scale magnetic islands before KHI can evolve. These LHDI-driven structures distort the velocity shear and suppress classical KH vortices. In contrast, for thicker current sheets or weaker density gradients, KHI dominates and produces the expected rolled-up vortices and associated plasmoids. These findings demonstrate that LHDI-induced turbulence can act as both a seed and a regulator of plasmoid-generating instabilities, mediating cross-scale energy transfer. This mechanism is relevant to thin boundary layers in space plasmas, such as the solar wind magnetosphere interface, and suggests that microturbulence can govern large-scale magnetic topology during collisionless reconnection.
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All authors S. Thatikonda, F. N. De Oliveira-Lopes, A. Mustonen, K.Pommois, D. Told, F. Jenko

Cosmology and Nongalactic Astrophysics · Cross-listed from nucl-th

Revisiting $^7$Be Weak and Radiative Transition Rates in Big Bang Nucleosynthesis: Implications for the Primordial Lithium Problem

Simone Taioli, Francesca Triggiani and Stefano Simonucci

The primordial 7Li abundance predicted by standard Big Bang nucleosynthesis (BBN) exceeds observations in old, metal-poor stars by a factor of 3-4. Since most primordial 7Li is produced as 7Be and subsequently converted by electron capture (EC), additional 7Be destruction channels may affect its final abundance. We investigate EC and antineutrino capture (AC), positron decay from the 7Be nuclear excited state, and proton capture (PC), including 7Be(p,gamma)8B, stimulated emission (SE), plasma screening, and a three-body Auger-like channel transferring the capture energy to a continuum electron. Weak rates are calculated from first principles using perturbation theory with explicitly evaluated hadronic and leptonic currents, while thermally averaged nuclear rates are obtained from the relevant cross sections over 10 < kT < 100 keV. The EC rate rapidly decreases as the Universe expands and cools, while AC enhances weak destruction mainly at early times. SE and screening increase the 7Be(p,gamma)8B rate by only 1-3% at kT about 87 keV. The Auger-like cross section is about 4 x 10^-3 of the radiative channel at kT = 100 keV and falls to about 10^-10 at 10 keV. Our first-principles weak rates differ substantially from previous log(ft)-based estimates, yielding a 7Be half-life of about two days under BBN conditions, nearly one order of magnitude different from phenomenological predictions. Nevertheless, EC, PC, and beta+ decay provide only percent-level corrections to the dominant 7Be(n,p)7Li channel and cannot resolve the cosmological lithium problem. These results motivate a first-principles reassessment of the full BBN nuclear network before invoking physics beyond the Standard Model.
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High Energy Astrophysical Phenomena

Modified hadronic interactions in 3-dimensional simulations

Jiří Blažek, Jan Ebr, Jakub Vícha et al. (+3 more)

We present a method to test the impact of ad-hoc modifications of some of the generic parameters of hadronic interactions – cross section, elasticity, and multiplicity – on any observable quantity using full 3-dimensional simulations of extensive air showers induced by ultra-high-energy cosmic rays. Our approach not only extends the existing 1-dimensional tools to three dimensions, but also introduces more flexible features to better respond to the needs of both theory and experiment. We first thoroughly validate the \conexD framework for the simulation of both longitudinal and lateral features of air showers, in particular for a non-standard configuration of the framework in which different energy thresholds for modifications are applied. Moreover, we show that the implementations of the ad-hoc modifications in this configuration are consistent with the previous one-dimensional simulations. Lastly, we discuss the importance of studying the interaction modifications in three dimensions and the effects of parallel modifications of multiple parameters.
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All authors Jiří Blažek, Jan Ebr, Jakub Vícha, Eva dos Santos, Tanguy Pierog, Ralf Ulrich

High Energy Astrophysical Phenomena

Probing Circumstellar Material and Shock Acceleration in Core-Collapse Supernovae with High-Energy Neutrinos

Yi-Long Duan, Tuohuniyazi Tuniyazi and Gang Guo

We study high-energy (HE) neutrino production from interactions between supernova (SN) ejecta and the surrounding circumstellar material (CSM), focusing on regular Type~II and Type~IIn SNe. Using observationally inferred CSM density distributions, we calculate the resulting neutrino fluxes and examine their dependence on key parameters, including the CSM density normalization $D_*$, outer radius $R_{\rm csm}$, proton acceleration efficiency $\epsilon_p$, and magnetic energy fraction $\epsilon_B$. Detection prospects are assessed with a binned likelihood analysis for IceCube, indicating that nearby SNe with moderately dense, confined CSM can produce detectable signals, with a typical detection horizon of $\sim 0.1$ - 1 Mpc. For a Galactic SN at $\sim 10$ kpc, high-statistics neutrino data with detailed temporal and spectral information can constrain $D_*$, $R_{\rm csm}$, and $\epsilon_p$ to within a factor of $\sim 10$ or to a precision of $\sim 20\%$, depending on the assumed values of $D_*$ and $R_{\rm csm}$. These neutrino signals thus provide a complementary probe of the CSM profile and shock acceleration, alongside traditional electromagnetic observations.
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Astrophysics of Galaxies

Updated Metallicity Diagnostics for Precision Oxygen Abundance Measurements in High-redshift Galaxies with JWST

Shihong Liu, Yu Rong, Tie Li et al. (+7 more)

Recent work has demonstrated that widely used strong-line oxygen abundance indicators, such as O3N2, $\rm R23$, and $\widehat{\rm R}$, suffer from large uncertainties when applied to high-redshift galaxies. We show that this loss of precision primarily arises because, at fixed \Oabund, galaxies span a wide dynamic range in ionization parameter and nitrogen enrichment. Here we develop updated indicators that explicitly incorporate both effects via the proxies O32 and N2O2. We define ${\rm R}_{\rm u}\equiv \rm R23+\alpha_1 O32+\alpha_2 N2O2$, $\widehat{\rm R}_{\rm u}\equiv \rm \widehat{R}+\beta_1 O32+\beta_2 N2O2$, and ${\rm O}_{\rm u}\equiv \rm O3N2+\gamma_1 O32+\gamma_2 N2O2$, and calibrate \Oabund~as low-order polynomials in each composite indicator. Applied to a JWST sample with $T_{\rm e}$-method abundances, the updated indicators substantially tighten the correlations with \Oabund, boosting adjusted coefficients of determination from $\mathbb{R}^2\lesssim 0$ (classical indicators) to $\mathbb{R}^2\gtrsim 0.5$ for the full sample and to $\sim 0.7$ at $z>2$. The residuals reveal a redshift evolution in the mapping between \Oabund, strong lines, ionization, and nitrogen enrichment, with a pivotal turning point near the cosmic noon ($z\sim 2$). Our calibrations provide a practical, physically grounded path to precise metallicity measurements in the JWST era and a firmer basis for quantifying early chemical enrichment and feedback.
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All authors Shihong Liu, Yu Rong, Tie Li, Yao Yao, Cheng Jia, Enci Wang, Hongxin Zhang, Zhicheng He, Huiyuan Wang, Xu Kong

Earth and Planetary Astrophysics

Revisiting the exoplanet radius valley with host stars from SWEET-Cat

Juma Kamulali, Vardan Adibekyan, Benard Nsamba et al. (+7 more)

The radius valley,a deficit of planets near 2 $\mathrm{R_{\oplus}}$, was observed among exoplanets of radius $\lesssim$ 5 $\mathrm{R_{\oplus}}$ with periods $<$ 100 days by NASA's $Kepler$ mission. It separates super-Earths (rocky, $\lesssim 1.9$ $\mathrm{R_{\oplus}}$) from sub-Neptunes (volatile-rich, $\gtrsim 2$ $\mathrm{R_{\oplus}}$) and may arise from formation conditions or atmospheric loss. Disentangling these mechanisms has led to numerous studies of population-level trends, although the resulting interpretations remain sensitive to sample selection and the robustness of host-star parameters. We re-examine its existence, depth, and dependence on period, flux, stellar mass, and age. Using SWEET-Cat and MAISTEP tool, we derived stellar parameters for 1,221 main-sequence stars (1,405 planets), with effective temperatures 4400–7500 K and radii 0.62–2.75 $\mathrm{R_{\odot}}$, achieving 2% precision in radius and mass. Planetary radii were recomputed from radius ratios, yielding 5% median uncertainty. The valley is partially filled near 2 $\mathrm{R_{\oplus}}$ and depends on period, flux, and stellar mass, with slopes $-0.12^{+0.02}_{-0.01}$, $0.10^{+0.02}_{-0.03}$, and $0.19^{+0.09}_{-0.07}$. Sub-Neptunes show a stronger stellar mass-dependent trend than super-Earths ($0.17^{+0.04}_{-0.04}$ vs $0.11^{+0.05}_{-0.05}$). With stellar age, the super-Earth/sub-Neptune ratio rises from $0.51^{+0.11}_{-0.08}$ ($<3$ Gyr) to $0.64^{+0.11}_{-0.11}$ ($\gtrsim3$ Gyr), and the valley becomes shallower and shifts to larger radii. A 4D fit shows consistent slopes with 2D analyses and a weaker age trend ($0.07^{+0.03}_{-0.04}$). These results suggest prolonged atmospheric loss, which is consistent with a core-powered mass loss scenario and emphasize the need for improved determinations, a goal expected to be achieved by future missions like PLATO.
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All authors Juma Kamulali, Vardan Adibekyan, Benard Nsamba, Sergio G. Sousa, Tiago. L. Campante, Achim Weiss, Bridget Kabugho, Nuno Moedas, Nuno C. Santos, Otto Trust