Cosmology and Nongalactic Astrophysics
Cross-Bispectrum Constraints from HI Intensity Mapping and Galaxy Surveys
Warren Naidoo, Moumita Aich and Kavilan Moodley
Future neutral hydrogen (HI) intensity mapping (IM) and optical surveys probe large-scale structure over unprecedented volumes, offering powerful constraints on cosmological models. We study the cross-correlation between the HI IM field and the
galaxy density and
cosmic shear fields from optical surveys. By formulating the HI-HI-
galaxy and HI-HI-shear cross-bispectra, we recover sensitivity to long-wavelength radial modes otherwise removed by foreground subtraction in HI maps, evaluating their detectability for HIRAX and Rubin-LSST. Combining the probes breaks degeneracies in
redshift-dependent quantities, including the $f$-$\sigma_8$ degeneracy. Our constraints range from $0.74\%$ to $9.8\%$ on $f$ and $0.073\%$ to $3.5\%$ on $\sigma_8$ across the six
redshift bins that we consider. Our constraints on the first- and second-order HI bias parameters range from $0.42\%$ to $5.6\%$ on $b_{\rm HI}^{(1)}$ and from $2.0\%$ to $29\%$ on $b_{\rm HI}^{(2)}$, while the
galaxy bias constraints range from $2.6\%$ to $11\%$ on $b_{\rm gal}.$ The HI-HI-
galaxy density cross-bispectrum measurement allows us to constrain a linear scale-dependent model for the
stochastic cross-correlation coefficient between HI and
stars, $r_{{\rm HI \,HI\,}\delta_g} = r_0 + r_1 k,$ with a break scale of $0.14\,\mbox{Mpc}^{-1}.$ We obtain $r_0$ constraints that range from $3.8\%$ to $13.5\%$ and $r_1$ constraints that range from $7.5\%$ to $19.9\%$. For cosmology, adding cross-bispectra enhances Lambda CDM constraints, notably via the HI-HI-shear cross-bispectrum. For the $w_0\, w_a$CDM model, the power-spectrum-only constraints on $w_0$ and $w_a,$ including Planck priors, improve from $(\sigma_{w_0},\sigma_{w_a})=(0.036,0.15)$ and $(0.032,0.12)$ to $(\sigma_{w_0},\sigma_{w_a})=(0.014,0.057)$ and $(0.015,0.059)$ when adding the HI-HI-
galaxy and HI-HI-shear cross-bispectra, respectively.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Cosmology in sixth-order higher-derivative theories of gravity
Carlos Aguilar, Manuel Asorey, Diego Muñoz et al. (+1 more)
We analyze the cosmological implications of theories of
gravity with quadratic
curvature invariants $R^2$ and $C^{\mu\nu\rho\sigma}C_{\mu\nu\rho\sigma}$, and six-derivative operators $R\Box R$ and $C^{\mu\nu\rho\sigma}\Box C_{\mu\nu\rho\sigma}$. We first analyze homogeneous and isotropic cosmological solutions, showing that the theory admits expanding, recollapsing and non-singular bouncing solutions. We clarify in the Einstein-frame formulation the mechanism that circumvents the Hawking–Penrose singularity
theorems, and identify the role played by the additional higher-derivative degrees of freedom in that mechanism. We show that the complete set of linear equations governing tensor perturbations on standard backgrounds admit analytically stable solutions. The analysis reveals that the stability properties are determined by the pole structure of the propagator and by specific relations among the higher-derivative couplings, while the singularity-free backgrounds are found to be unstable against tensor perturbations. For scalar cosmological perturbations, the higher-derivative theories presents super-horizon scalar instabilities in de Sitter spacetimes for both quadratic and sixth-order
gravity. To extract inflationary observables, we adopt an EFT approach to the sixth-order theory, treating these terms as perturbative corrections around the Starobinsky background. Within this framework, we compute the modification of the primordial scalar and tensor power spectra, obtaining predictions for the scalar spectral index and tensor-to-scalar ratio. We find that sixth-order operators produce controlled deviations from the Starobinsky model while preserving the EFT expansion, thereby providing a consistent phenomenological framework to probe ultraviolet gravitational corrections through cosmological observables.
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All authors Carlos Aguilar, Manuel Asorey, Diego Muñoz, Miguel Pardina
Astrophysics of Galaxies
SALVAGE II: no systematic molecular gas depletion in the central 2 kpc of AGN hosts
Scott Wilkinson, Chiara Circosta, Toby Brown et al. (+5 more)
In cosmological simulations, active galactic
nuclei (AGN) feedback is found to be necessary for the shutdown of
galaxy-wide
star-formation by heating and/or removing molecular gas. However, at low-
redshift, there is little evidence of systematic large-scale gas depletion. Some recent observations have found molecular gas depletion in AGN hosts, but limited to the central regions of
galaxies. In this work, we use the SDSS-ALMA Legacy-Value Archival Gas Exploration (SALVAGE)
dataset, which provides molecular gas and stellar mass measurements from the inner (r < 0.5-2 kpc) and outer region of the
galaxy. Using AGN diagnostics from optical emission lines, mid-IR colour, and X-ray luminosity, we identify 70 AGN at z < 0.07 and inspect their central molecular gas reservoirs with a suite of metrics compared to non-AGN controls. In agreement with global studies of low-z AGN hosts, we find that, compared to matched non-AGN, the central regions of AGN have equal molecular gas fractions and enhanced molecular gas surface densities. For the first time, we explore the central gas reservoirs of AGN identified with different selection criteria and find two optical AGN classes that show a tentative 1.5$\sigma$ and 1.8$\sigma$ signal of central molecular gas depletion. However, the AGN with central gas depletion do not occupy any specific region of the parameter space, such as AGN luminosity, that can provide a physical explanation for the depletion. If AGN are responsible for large-scale gas removal, the lack of systematic gas depletion in SALVAGE AGN sets an upper limit on the physical scale of the gas removal while the AGN remains observable.
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All authors Scott Wilkinson, Chiara Circosta, Toby Brown, Sara L. Ellison, Shoshannah Byrne-Mamahit, Almudena Alonso-Herrero, Santiago Garcia-Burillo, Federico Esposito
Astrophysics of Galaxies
Calcium Triplet Absorption is Common around Little Red Dots
Jenny E. Greene, Hanpu Liu, Raphael E. Hviding et al. (+29 more)
We present new evidence for an optically thick atmosphere surrounding Little Red Dots (LRDs) in the form of Ca absorption at rest-frame 8500A, the calcium triplet (CaT). Building on the detection of CaT absorption in one local LRD analog (the "Egg", Lin et. al. 2025), we investigate the region around rest-frame 8500A for an archival sample of 17 LRDs ($2 < z < 5$) with JWST/NIRSpec grating data. We detect CaT absorption in three individual sources, and find that on average there is an absorption equivalent width (EW) EW$_{\rm CaT} \approx -5$ A. Among the three detections, two are approaching the deepest absorption seen in integrated light from
stars. Given that the continuum around CaT is probably dominated by the central engine, we argue that the absorbers are likely to be associated with the LRD. Such absorption has not historically been associated with any components of an AGN central engine, but a cool, optically thick photosphere as proposed for LRDs would naturally produce such absorption. The EW$_{\rm CaT}$ that we observe can be matched by hydrostatic atmosphere models at relatively low
metallicity ([M/H]$<-1$) combined with an effective temperature $T_{\rm eff} > 4500$ K. Alternatively, the distribution can be matched at a low photospheric gas density $\rho_{\rm ph}<10^{-11}{\rm~g~cm^{-3}}$ that requires a non-hydrostatic gas structure on dynamical grounds. In the future, metal absorption lines should be a powerful complementary probe of the gas conditions, and possibly the enclosed mass, of LRDs.
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All authors Jenny E. Greene, Hanpu Liu, Raphael E. Hviding, Rohan P. Naidu, David J. Setton, Bingjie Wang, Ivo Labbe, Vasily Kokorev, Xiaojing Lin, Hollis B. Akins, Anna de Graaff, Joel Leja, Jorryt Matthee, Alberto Torralba, Karl Glazebrook, Rachel Bezanson, Leindert A. Boogaard, Gabriel Brammer, Caitlin M. Casey, John Chisholm, Xiaohui Fan, Lukas Furtak, Seiji Fujimoto, Yan-Fei Jiang, Yilun Ma, Themiya Nanayakkara, Erica J. Nelson, Richard Pan, Eliot Quataert, Anthony J. Taylor, Christina Williams, Adi Zitrin
Instrumentation and Methods for Astrophysics
Convolutional Neural Network for Extraction of $n = 1$ Photon Ring of Black Holes
Courtney Duong, Frank Myhre and Joseph R. Farah
Very-long-baseline interferometry (VLBI) may enable direct imaging of fine, event-horizon scale black hole structures such as the
photon ring. In particular, the $n=1$
photon subring encodes information about black hole
spin in its radial profile and azimuthal brightness modulation, making it a key proxy for spacetime properties. However, the $n=1$ subring overlaps with emission from the $n=0$ subring in observations, requiring isolation of the $n=1$ subring for measurements. We present a convolutional neural network (CNN) capable of extracting the $n=1$ subring from composite images containing $n=0$ and $n=1$ subrings. We simulate $111,000$ $m$-ring images with eht-imaging to train and validate the CNN. The CNN accurately recovers the radial and angular brightness profiles of the $n=1$ subring with a mean normalized cross correlation (NXcorr) of $\sim0.99$. The CNN provides a detection capability by predicting no false positives when input images lack a $n=1$ subring. We perform feature extraction with ringfit to show that the CNN-predicted $n=1$ subring accurately recovers the ground truth radial profiles and azimuthal brightness modulation, demonstrating the CNN's capability to extract
spin-sensitive features. We further test the CNN on black hole images generated by KerrBAM and general relativistic magnetohydrodynamic (GRMHD) simulations, finding that it recovers the overall $n=1$ subring radial profiles while exhibiting discrepancies in the recovered intensity profiles. These results demonstrate the potential of deep learning methods to isolate the $n=1$ subring from overlapping emission, providing a framework for analyzing future high resolution black hole images from proposed VLBI missions such as the Black Hole Explorer (BHEX).
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Solar and Stellar Astrophysics
Asteroseismology and interferometry of the F7V spectroscopic binary $\chi$ Draconis A in the TESS CVZ
Jonatan Rudrasingam, Mikkel N. Lund, Frank Grundahl et al. (+26 more)
We present a detailed analysis of the asteroseismic main-sequence
benchmark star $\chi$ Dra A in the TESS northern CVZ. We aim to derive stellar mass and radius from asteroseismic modelling of individual mode frequencies and test the asteroseismic mass and radius against an independent dynamical mass and interferometric radius measurement. We determined the dynamical mass of $\chi$ Dra using 618 radial velocity measurements obtained with the SONG
telescope at Tenerife, and 53 relative astrometric measurements. With the PAVO beam combiner at CHARA, we obtained the interferometric radius of $\chi$ Dra A. We determined asteroseismic parameters from 16 sectors of 20-sec cadence TESS photometry. We determined $T_{\rm eff}=6277\pm30$ K, $\rm [Fe/H] =-0.51\pm0.03$ dex, and $[\alpha/\rm Fe]=0.08\pm0.03$ dex from the spectroscopic analysis. For the dynamical fit we obtained a mass of $M_{\rm A}=1.028 \pm 0.004$ $\rm M_{\odot}$ for $\chi$ Dra A, and $M_{\rm B}=0.735 \pm 0.003$ $\rm M_{\odot}$ for $\chi$ Dra B. Combining the derived interferometric angular diameter with dynamical parallax yields an interferometric radius of $R_{\rm A} = 1.159^{+0.029}_{-0.028}$ $\rm R_{\odot}$. In the TESS power spectrum, we identified 38 individual oscillating modes. Using these modes, we modelled the
star with nine independent pipelines to test the resulting model mass and radius against our independently calculated mass and radius. All models yielded masses slightly lower than the dynamical mass. Using asteroseismic scaling relations, we found that scaling masses from corrected scaling relations best reproduce the dynamical mass. The combination of spectroscopy, interferometry, and asteroseismology has yielded precise results for the main component of the $\chi$ Dra system, making it one of the best-characterised main-sequence solar-like oscillators.
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All authors Jonatan Rudrasingam, Mikkel N. Lund, Frank Grundahl, Arnab Chowhan, Timothy R. Bedding, Poul E. Nissen, Aldo Serenelli, Joel M. J. Ong, Jeppe S. Thomsen, Yaguang Li, Eva Panetier, Sarbani Basu, Owen J. Scutt, Travis S. Metcalfe, Savita Mathur, Mark Lykke Winther, George T. Hookway, Benjamin J. S. Pope, Amalie Stokholm, Desmond H. Grossmann, Jens R. Larsen, Jørgen Christensen-Dalsgaard, Daniel Huber, Mads S. Fredslund, Timothy R. White, Paul G. Beck, Pere L. Pallé, Rafael A. García, Hans Kjeldsen
High Energy Astrophysical Phenomena
Multi-scale variability in the optical afterglow of GRB 251013C from high-cadence LAST observations
R. Konno, E. O. Ofek, S. Garrappa et al. (+8 more)
Context. Optical afterglows of gamma-ray bursts (GRBs) are often described by smooth power-law decays, but deviations such as
flares and rebrightenings provide important constraints on the underlying emission processes. Aims. We investigate the temporal variability of the optical afterglow of GRB 251013C using high-cadence observations, and assess the origin of the observed variability. Methods. We analyze continuous optical observations obtained with the Large Array Survey
Telescope (LAST), complemented by publicly available X-ray data from Swift-XRT. The optical light curve is modeled using a power-law decay with superposed variability components, and contemporaneous optical and X-ray measurements are used to constrain the broadband spectrum. Results. The optical light curve shows pronounced variability on multiple timescales, including broad rebrightening episodes with $\Delta t \sim t$ and superposed faster fluctuations with $\Delta t/t < 1$. The main rebrightening exhibits a structured rise with a clear steepening prior to the peak. The fast variability comprises asymmetric fast-rise, slow-decay features whose durations increase with peak time. The optical flux lies on the extrapolation of the X-ray spectrum, and the spectrum hardens by the same amount whether measured within the X-ray band or from optical to X-ray. Conclusions. We favor a refreshed external-shock interpretation for the main rebrightening. The broadband spectrum and post-peak decay are consistent with slow-cooling synchrotron emission in a wind-like medium. The spectral hardening requires a newly dominant, harder electron population, while the faster optical variability indicates structure within the refreshed ejecta or shocked region.
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All authors R. Konno, E. O. Ofek, S. Garrappa, O. Teboul, E. Waxman, S. Ben-Ami, D. Kovaleva, A. Krassilchtchikov, D. Polishook, E. Segre, E. A. Zimmerman
Earth and Planetary Astrophysics
A Very Fast Symplectic Integrator for Planetary Systems: WHFast512 in x86 Assembly
Rishit Dagli and Hanno Rein
Long-term integrations of planetary systems are used in a variety of astrophysical applications, for example to determine a system's stability. In this paper, we describe significant speed and accuracy improvements to the WHFast512 integrator. By completely rewriting WHFast512 in x86 assembly, we gain fine-grained control over CPU instructions and are able to keep the entire simulation state in CPU registers, only writing to
memory when an output is required. We also reduce the number of branches in the code, improve the Kepler solver's speed and accuracy with a convergence check, switch the
Hamiltonian splitting to Jacobi coordinates, implement symplectic correctors, and add support for ejection and collision detection. As a
benchmark we run simulations of the Solar System with all eight
planets and general relativistic corrections for 5 Gyr. With our improvements, we can integrate this system in 9 hours, more than 8x faster than the standard version of WHFast. This makes WHFast512 by far the fastest N-body integrator for this kind of simulation. We run extensive tests to verify the integrator's accuracy, with a particular focus on removing any long-term bias, and show that the accuracy is now five orders of magnitude better for typical setups compared to the earlier version of WHFast512. The new WHFast512 integrator is freely available in the REBOUND integrator package.
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Solar and Stellar Astrophysics
TIC 366240660 - A Dynamically Active Triple With a Very Short Outer Period of 30.5 Days
S.A. Rappaport, T. Borkovits, G. Torres et al. (+17 more)
Methods: We analyze TESS photometric data, radial velocity measurements, and eclipse timing variation curves for the triple
star system, TIC 366240660, with a photodynamical code to infer the properties of all three
stars and orbital motions. Results: With an outer orbital period of only 30.5 d, this is the second most compact triple reported in the literature. We have determined the masses and $T_{\rm eff}$ values of the three
stars with an accuracy of about 1% and the radii to about 2%. The inclination angles of the two planes, and the mutual inclination angle are found with an accuracy of better than 1/3$^\circ$. The system is determined to be quite flat (to within 1/2$^\circ$), but with an outer eccentricity of $e_{\rm out} \simeq 0.33$. We find that the properties of the secondary
star of the inner binary are completely inconsistent with the
evolution of a single
star in isolation, and it must have transferred most of its envelope to the current primary
star in the inner binary during a prior episode of mass transfer. The eclipse timing variation (ETV) curve derived from the TESS photometric data shows that, in addition to a typical dynamical delay curve at the period of the outer orbit, there is also a much larger amplitude anomalous sinusoidal-like delay with a period of 840 d. This latter feature in the ETV curve is not yet describable in simple analytic terms, but it appears certain that it can be explained by the near integer ($\simeq$13:1) ratio of the outer to the inner orbital periods. Conclusions: We have extensively explored the exotic and anomalous ETVs of this highly compact triple system and found that they can exceed hours for the inner binary eclipses, and several days for the outer orbital eclipses. We provide a preliminary explanation for how these are related to the 13:1 mean motion resonance of the outer to inner orbits.
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All authors S.A. Rappaport, T. Borkovits, G. Torres, H.-L. Chen, P. Zasche, D. Vokrouhlický, B. Deme, M. Mašek, H. Kučáková, R. Uhlař, M. Wolf, Z. Garai, T. Pribulla, I.B. Bíró, I. Csányi, Z. Dencs, D. Latham, T. Mitnyan, V.B. Kostov, B.P. Powell
Instrumentation and Methods for Astrophysics
Emerging Technologies for Astrophysics Missions: Workshop Summary Report
Brendan P Crill, Nicholas Siegler, Dan Sirbu et al. (+3 more)
NASA's Astrophysics Division convened the Emerging Technologies for Astrophysics Missions (ETAM) Workshop in March 2025 at the Ames Research Center in Silicon Valley, California. The workshop's goal was to identify emerging technologies that could critically impact or enable future space missions-including concepts previously considered unachievable. Four key technology areas were examined: Astrophotonics, Artificial Intelligence and Machine Learning, Advanced Materials, and
Quantum Sensors. Approximately 60 participants from academia, industry, government laboratories, and NASA centers attended. The workshop fostered an inspiring and collaborative atmosphere that encouraged interaction among experts both within and across disciplines. The workshop's three-day novel format featured landscape presentations outlining the state of each field, followed by breakout sessions where participants, grouped in their own disciplines, identified high-impact technologies for astrophysics missions. Cross-pollination sessions then brought together experts from multiple technology domains to foster interdisciplinary insights. The event successfully identified several high-priority emerging technologies (summarized in subsequent sections of this report). In addition to the field-specific insights, the workshop also produced five key cross-cutting suggestions for the NASA Astrophysics Division to consider.
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All authors Brendan P Crill, Nicholas Siegler, Dan Sirbu, Luc Peterson, Sanaz Vahidinia, Ryan Watkins
Cosmology and Nongalactic Astrophysics
Basis function expansions of the two-point correlation function and reconstruction of the cosmological distance scale
Fatima Abd Alrahman, Farnik Nikakhtar, Marcello Musso et al. (+2 more)
The shape of the correlation function of
galaxy pairs can be used as a cosmological distance indicator. Most
estimators of this shape require that one bin the pair counts, and considerable effort is expended in finding the optimal bin size. Cosmological constraints are then derived, in a separate step, by fitting to the binned pair counts. By projecting the pair counts on a suitable basis set, it is possible to estimate the pair correlation function without binning. Recent work suggests that, in the context of estimating the cosmological distance scale from
galaxy clustering data,
polynomials and half-integer generalized Laguerre functions are particularly useful bases. We show how to use these bases to measure the correlation function and estimate the reconstructed distance scale in a single step. Our analysis includes the effects of shot-noise and
cosmic variance, and highlights the benefits of projecting pair counts onto orthogonal basis functions.
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All authors Fatima Abd Alrahman, Farnik Nikakhtar, Marcello Musso, Aseem Paranjape, Ravi K. Sheth
Solar and Stellar Astrophysics
Using Machine Learning to Model Stellar Collisions in our Galactic Center
Tristan C. Sand, Sanaea C. Rose, Elena González Prieto et al. (+9 more)
Direct collisions in the inner pc of the Galactic center can alter the orbits and properties of
stars. The outcome of a collision depends on a number of parameters, including the masses and ages of the
stars, the impact parameter, and the initial relative velocity. We utilize the newly developed $\verb|collAIder|$, a machine learning tool developed to predict the outcomes of stellar collisions, to bridge 3D hydrodynamic simulations of stellar collisions with a dynamical model of the Galactic center. Our results show a substantial population of stripped
stars, $\sim$$10\%$ of the initial stellar population, produced by mass loss during high-speed collisions. Stellar mergers are less frequent, with about $5\%$ of the
stars experiencing a collision-induced merger. We also find that high-speed, nearly head-on collisions can completely disrupt the
stars. These destructive collisions are usually preceded by 10 or more collisions, which gradually reduce the mass of the
star before it is ultimately destroyed. We estimate that mass loss during stellar collisions injects roughly $(2.5-8)\times 10^5$ M$_\odot$ of gas into the surrounding environment. Most of this gas is injected into the inner $0.1$ pc and about $90\%$ is retained within the cluster and may be accreted onto the supermassive black hole.
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All authors Tristan C. Sand, Sanaea C. Rose, Elena González Prieto, James C. Lombardi, Jr., Charles F. A. Gibson, Fulya K{\i}roğlu, Kyle Kremer, Christopher E. O'Connor, Enrico Ramirez-Ruiz, Frederic A. Rasio, Tjitske Starkenburg
Astrophysics of Galaxies
A radial basis of massless potential-density pairs
E.V. Polyachenko and I.G. Shukhman
In the
matrix method for linear perturbations of spherical stellar systems, the perturbed potential and density are expanded over a set of potential-density pairs. For radial perturbations, mass conservation makes the coefficient of $1/r$ in the perturbed potential vanish, so that the potential decays faster than $1/r$. Starting from the $\ell=0$ Hernquist–Ostriker family, we construct in closed form a set of potential-density pairs whose potentials decay as $r^{-p}$ with a prescribed $p\ge2$, the tail containing all subsequent integer powers. For $p=2$ each pair is individually massless, and the potential of the $n$-th pair is expressed through a single Jacobi
polynomial. We derive the combination weights, the leading tail coefficients and the Gram
matrix analytically; the Gram
matrix is banded with half-width $p-1$ (tridiagonal at $p=2$). The $n$-th potential element has exactly $n-1$ nodes, spread from $r\sim n^{-2}$ to $r\sim n^{2}$, so that the set resolves both the centre and the far periphery. As a test, the expansion of the dilation-mode potential of the isochrone model converges exponentially and carries no parasitic mass at any truncation, in contrast to the standard set.
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Astrophysics of Galaxies
First Trigonometric Parallax Measurements with the KVN and VERA Array (KaVA)
Nobuyuki Sakai, Daisuke Sakai, Noriyuki Kawaguchi et al. (+26 more)
To demonstrate the astrometric capability of the combined Korean VLBI (Very Long Baseline Interferometry) Network (KVN) and VLBI Exploration of
Radio Astrometry (VERA) Array (KaVA), we conducted six-epoch VLBI observations of 22-GHz H$_{2}$O masers associated with the
star-forming region W3(OH). Two atmospheric calibration methods, (1) GPS and (2) JMA (Japan Meteorological Agency) mesoscale analysis data, and two phase-reference sources were independently applied to the astrometric analysis. Trigonometric parallaxes of W3(OH) were successfully measured with all calibration strategies, including the first successful parallax measurement using JMA calibration. The combined-fit parallax is 0.497$\pm$0.024 mas, corresponding to a distance of 2.01$^{+0.10}_{-0.09}$ kpc. This value is consistent with the previous Very Long Baseline Array (VLBA) result of 0.489$\pm$0.017 mas. KaVA achieved a 55$\%$ higher signal-to-noise ratio in phase-referenced maps than VERA, in good agreement with theoretical expectations. These results suggest that KaVA will enable trigonometric parallax measurements of 22-GHz H$_2$O masers that are difficult to observe with VERA alone because of low flux densities and/or limited $uv$ coverage. A flux variation from 510\,$\pm$\,50 to 3900\,$\pm$\,400 Jy was detected in W3(OH) over a one-year observing campaign and is attributed to two nearby maser features separated by only $\sim$64 AU at 2.01 kpc. The brightest feature showed a decrease in linewidth with increasing peak flux density, consistent with unsaturated maser amplification, whereas no similar trend was found for the other feature, suggesting different responses to the same amplification conditions, possibly owing to differences in saturation state and internal velocity structure.
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All authors Nobuyuki Sakai, Daisuke Sakai, Noriyuki Kawaguchi, Shuangjing Xu, Bo Zhang, Taehyun Jung, Chungsik Oh, Jeong-Sook Kim, Soon-Wook Kim, Hiroshi Imai, Yuanwei Wu, Maria Rioja, Niu Liu, Zehao Lin, Ibnu Nurul Huda, Shuaibo Bian, Leonid Petrov, Jingdong Zhang, Takaaki Jike, Yoshiaki Tamura, Jeong Ae Lee, Hao Ding, Koichiro Sugiyama, Kazuhiro Hada, Kiyoaki Wajima, Kazuya Hachisuka, Mareki Honma, Kee-Tae Kim, Se-Jin Oh
Earth and Planetary Astrophysics
Inside the Eirenesphere: The Interplay of Porosity, Heat Flux and Mineralogy in Exoplanetary Aquable and Habitable Layers
Santiago A. Orjuela and Jorge I. Zuluaga
The classical circumstellar habitable zone restricts the search for life to planetary surfaces where stellar irradiation sustains
liquid water, overlooking vast subsurface environments. Here, we present a geophysical model integrating internal radial structure, mineralogy, radiogenic heat, and pressure-dependent porosity to quantify the three-dimensional habitable volume-the eirenesphere-of rocky
exoplanets. We distinguish between aquability (thermodynamic water stability) and habitability, which requires temperatures and pressures within extremophile biological limits, plus sufficient porosity for fluid circulation. To compare planetary capacities, we introduce the Eirenesphere Volumetric Index (EVI), measuring average subsurface biosphere volume. Applying this framework, we find that Earth's current state (EVI$\approx 0.06$ terrestrial oceans) represents only a moderate regime. Instead, mature super-Earths with high geothermal activity provide the most extensive environments for deep biospheres. Crustal mineralogy exerts a first-order control: thermally insulating felsic crusts sustain significantly larger eirenespheres than primary mafic lithologies. Tracking secular cooling reveals internal habitability is an evolutionary property; young
planets host confined biospheres due to steep thermal gradients, whereas mature worlds maximize habitable volumes over billions of years. Finally, we demonstrate that around solar-like
stars, subsurface habitability persists out to $5-7$ au, effectively decoupling life's potential from surface radiative balance. Extrapolating to the Milky Way reveals a staggering galactic capacity for subsurface life, on the order of billions of terrestrial oceans. Ultimately, this framework shifts the astrobiological paradigm from a surface-dependent phenomenon to an intrinsic planetary property, offering a metric to prioritize targets.
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High Energy Astrophysical Phenomena
A Magnetic Unification of Merging Supermassive Black Hole Binaries
Mark J. Avara, David O'Neill and Zoltán Haiman
The detection of an electromagnetic (EM) transient from a supermassive black hole binary (SMBHB) merging within a gaseous environment will constitute a multi-messenger milestone. Numerical simulations of these systems have mostly been performed in 2D with a constant viscosity parameter representing turbulent and
magnetic stresses. These simulations predict a steep drop in
accretion rate and X-ray luminosity at merger, followed by a slow recovery. However, 3D-GRMHD and 3D-MHD simulations have shown only a modest reduction in
accretion rate and a fast post-merger recovery. We present a new 2D pseudo-Newtonian framework with physically motivated prescriptions for
stochastic viscosity, relativistic apsidal precession, and large-scale
magnetic fields. When suitably calibrated, this 2D framework accurately captures key 3D-GRMHD behavior, demonstrating that it can be used to explore binary
accretion without the high computational cost of 3D-GRMHD simulations. We find that the merger signatures are most sensitive to the strength of the
magnetic field, with a drop in the
accretion rate at merger progressively less pronounced for stronger fields. Post-merger
evolution is determined by both magnetization and relativistic precession of orbiting gas, yielding rapid recovery of
accretion. For low-magnetization disks, recovery is driven by self-intersection shocks, and the dip at merger is followed by a distinct second dimming. Large-scale
magnetic fields of increasing magnitude lead to magnetically arrested disk (MAD) behavior which disturbs the merging system progressively earlier before merger, and longer after. Our results unify the EM signatures of the merger of embedded coplanar SMBHBs, and provide novel observational constraints on their intrinsic magnetization.
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Astrophysics of Galaxies
Giant Low-Surface Brightness Galaxies in the Global Picture of Galaxy Formation and Evolution
Fedor M. Kolganov, Igor V. Chilingarian, Anna S. Saburova et al. (+5 more)
Giant low-surface brightness
galaxies (gLSBGs) challenge standard merger-driven
galaxy assembly models due to their large, dynamically cold disks, with radii often larger than 100~kpc and dynamical masses exceeding ${\sim}10^{12}$~\Ms. We identify $60$ gLSBGs, including a volume-complete subsample of $35$
galaxies out to $z=0.1$ in the 120~sq.deg. area. Using new and archival photometric and spectroscopic data, we homogeneously analyze their structural properties and derive central velocity dispersions. We update the gLSBG volume density estimate in the local Universe to $(3.6 \pm 0.6) \cdot 10^{-5}~\text{Mpc}^{-3}$. This number corresponds to about 1 in 4000
galaxies in the $g$-band luminosity range $0.14-1.37 \cdot 10^{11}~L_{\odot}$ out to $z=0.1$, which is consistent with EAGLE cosmological simulations but 3.8 times lower than the corresponding value in TNG100. Central surface brightness and scalelength of the gLSB disks scale with the luminosity of the central component, becoming fainter and flatter as the central component grows more luminous, suggesting rapid disk formation rather than the inside-out growth typical of high surface brightness late-type
galaxies. Many gLSBGs also show extended UV counterparts in GALEX, strengthening their connection to XUV-disk
galaxies. Finally, comparison with superluminous spirals shows that even complete gas-to-
star conversion cannot transform a typical gLSBG into a superspiral, owing to their lower total baryonic mass.
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All authors Fedor M. Kolganov, Igor V. Chilingarian, Anna S. Saburova, Damir Gasymov, Evgenii V. Rubtsov, Vladislav I. Klochkov, Kirill A. Grishin, Mariia Demianenko
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Reconnection of Gravitational Fields
Luca Comisso and Felipe A. Asenjo
In a tetrad formulation of general relativity, an ideal Ohm-type condition for the gravitational field implies the conservation of gravitational fluxes and the preservation of the connectivity of gravitational field sheets. We investigate the consequences of departures from ideal gravitational
evolution by developing a theory of gravitational reconnection, defined as a change in the connectivity of gravitational field sheets arising from the breakdown of the ideal frozen-in
evolution of the gravitational field. We derive quantitative measures of the gravitational reconnection rate, show that gravitational reconnection alters the energy-momentum exchange between the gravitational and matter sectors, and determine how it modifies the
evolution of gravitational helicity. Our results provide a quantitative framework for describing changes in gravitational connectivity and their consequences in dynamical spacetimes.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Frozen-In Gravitational Fields
Felipe A. Asenjo, Maricarmen A. Winkler and Luca Comisso
Spacetime can undergo complex nonlinear
evolution, as governed by the Einstein field equations, and a central challenge is to understand the
geometric structures that arise, persist, and interact throughout its
evolution. Using a formulation of Einstein equations that parallels nonlinear electrodynamics of continuous media, we show that general relativity admits gravitational field connections—two-surfaces and associated field lines whose connectivity is maintained by the spacetime dynamics. This gravitational frozen-in behavior is enabled by an ideal Ohm-type condition for the gravitational field. We further show that the same framework naturally leads to a conserved “gravitational
magnetic” flux. A conserved gravitational helicity also emerges, with a clear topological interpretation in terms of gravitational field-line structures. These results identify well-defined topological constraints on admissible spacetime
evolution and provide an organizing principle underlying the nonlinear dynamics of spacetime.
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Cosmology and Nongalactic Astrophysics · Cross-listed from physics.hist-ph
Before WIMPs: Neutrinos and the origins of particle dark matter
Jaco de Swart
After four decades of null-results, the experimental quest to discover a dark matter particle ardently continues. While confidence in the leading candidate, the Weakly Interacting Massive Particle (WIMP), is waning, its explanatory success still shapes current experimental approaches and theoretical expectations - from underground detecting efforts in Europe, China, and the U.S. to modern theories of
cosmic structure. This paper traces the origins of this particle-based paradigm to a critical predecessor: the
neutrino-dominated universe. Proposed in the early 1970s as a solution to extra-galactic anomalies,
neutrinos became the leading explanation of 'missing matter' following experimental hints of
neutrino mass in 1980. Although short-lived, the model's coherent picture of
cosmic evolution and structure formation set strong conceptual and methodological standards - providing critical impetus to the field of particle cosmology. Examining this history invites renewed reflection on how such past aims and expectations continue to guide dark matter inquiry today.
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Solar and Stellar Astrophysics
The oldest low-$\alpha$ thin disc stars
Riano E. Giribaldi, Laura Magrini, Marco Palla et al. (+1 more)
The formation pathway of the $\alpha$-poor Milky Way thin disc remains under debate. The latest observational data indicates the presence of comparable numbers of old
stars in both the low- and high-$\alpha$ disc components, suggesting either coeval or overlapping formation epochs. Using GALAH DR4, we provide evidence that the $\alpha$-poor
stars coexist with $\alpha$-rich
stars up to $\sim$12.5 Gyr. Stellar ages of 0.5 Gyr precision were re-derived for nearly $30\,000$ subgiant
stars using accurate effective temperatures ($T_{\rm{eff}}$) from the infrared flux method (IRFM) together with distances based on Gaia parallaxes. About 22% of the sample constitutes a population peaking at 9.2 Gyr, with evidence for an extended old-age tail reaching 12.5 Gyr. Among
stars older than 10 and 11 Gyr, between 20 and 30% have relative low [$\alpha$/Fe] and solar-like
metallicities ($-0.5 \leq \mathrm{[Fe/H]} \leq +0.5$ dex). These
stars exhibit kinematics consistent with those of near solar-age $\alpha$-poor
stars in the thin disc. These
stars can be evolved Sun-like
stars, i.e. old solar analogues, whose $T_{\rm{eff}}$ and
gravity modified with the time. Comparison with a well-tested Galactic disc chemical
evolution model supports the presence of a significant fraction of old, $\alpha$-poor disc
stars, confirming the plausibility of our selection criteria. We provide a catalogue with the selected sample to facilitate spectroscopic follow-ups at high resolution.
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All authors Riano E. Giribaldi, Laura Magrini, Marco Palla, Carlos Viscasillas Vázquez
Earth and Planetary Astrophysics
Probing Exoplanetary Rings with Asterodensity Profiling: A PhotoRing Analysis of Kepler-51
Jorge I. Zuluaga, Sebastian Numpaque, David M. Kipping et al. (+1 more)
The Kepler-51 system hosts transiting super-puff
planets whose extremely low bulk densities challenge structural models, possibly because unresolved rings inflate their inferred radii. We test this hypothesis by combining asterodensity profiling with TTV-aware transit fits of Kepler long-cadence photometry. For Kepler-51b we measure a density ratio $\Psi\equiv\rho_{\star,\mathrm{obs}}/\rho_{\star,\mathrm{true}} = 1.18\pm0.06$, a $2.9\sigma$ offset from $\Psi=1$; for Kepler-51d we find $\Psi=1.04\pm0.08$ ($0.6\sigma$), consistent with no anomaly. Unmodelled eccentricity is disfavoured for
planet b by TTV-derived dynamical constraints ($p=0.007$) but remains viable for
planet d ($p=0.33$). The offset of Kepler-51b is also compatible with the PhotoRing (PR) effect of unmodeled rings. Using a
geometric ringed-transit forward model and
Bayesian retrieval, we identify ring configurations that reproduce the transit observables and the measured density ratios. The preferred solutions are consistent with compact, moderately inclined rings that raise the true bulk densities by factors of $2-5$. Conversely, the absence of a large PR offset excludes extended, optically thick, high-obliquity rings at $99\%$ credibility for b and $70\%$ for d from archival photometry alone. These objects may thus be "puff ringed
planets" although recent JWST observations of Kepler-51d show no direct signature of an opaque ring. While the required impact parameters and stellar densities show tension with independent constraints -attributable to Kepler's 30-minute cadence- this study presents the first complete application of the PR effect, offered as a methodological demonstration and exclusion experiment rather than as evidence that rings are present. All code is publicly available to support applications to other systems.
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All authors Jorge I. Zuluaga, Sebastian Numpaque, David M. Kipping, Jaime A. Alvarado-Montes
High Energy Astrophysical Phenomena
Early NIR echo and the time variable mass loss history of Type IIn SN 2024kgi
Naveen Dukiya, Kuntal Misra, Andrea Pastorello et al. (+30 more)
We present a comprehensive analysis of the long-term photometric and spectroscopic monitoring campaign of the Type IIn
Supernova (SN) 2024kgi. The SN reaches at peak an $r$-band absolute magnitude of $-19.81 \pm 0.06$ mag and a bolometric luminosity of $\sim 2 \times 10^{43}$ erg s$^{-1}$. We observe a break in the lightcurve at day $\sim 312$, after which the luminosity decline changes from $t^{-1.0}$ to $t^{-4.5}$, likely due to the shock sweeping the dense CSM. We introduce a semi-analytical lightcurve modeling approach for CSM-interaction in transients that accounts for variable
diffusion time. We hence estimate a CSM mass of $2.34^{+11.8}_{-1.6} M_{\odot}$ and with a density profile $\rho_{csm} \propto r^{-2.74}$, indicating progressively increasing mass loss toward the SN explosion. The ejecta signatures emerge as broad H, He, and Ca II triplet lines, at day $\sim 80$, much earlier than expected from a spherically symmetric CSM, suggesting asymmetry in the CSM. After the lightcurve break, the H lines exhibit a wavelength-dependent deficit in the red-wing flux, indicating new dust formation in the ejecta and/or in the post-shock gas. We observe an NIR excess from day $\sim 40$ onwards. We attribute the early NIR excess before the lightcurve break solely to the NIR echo from pre-existing dust, as there are no other indications for new dust formation. The late-time NIR excess likely has contributions from both the preexisting and newly formed dust. The steady increase in mass loss, slow CSM velocity, and asymmetric CSM favor a binary interaction-induced mass loss.
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All authors Naveen Dukiya, Kuntal Misra, Andrea Pastorello, Andrea Reguitti, Anjasha Gangopadhyay, Aravind P. Ravi, Brian Hsu, Noah Franz, David J. Sand, Nathan Smith, Jennifer E. Andrews, Moira Andrews, K. Azalee Bostroem, Collin Christy, Monalisa Dubey, Joseph R. Farah, Archana Gupta, Estefania Padilla Gonzalez, Emily Hoang, D. Andrew Howell, Curtis McCully, Darshana Mehta, Megan Newsome, Jeniveve Pearson, Nicolas Meza Retamal, Jeonghee Rho, Manisha Shrestha, Bhagya Subrayan, Giacomo Terreran, Lina Tomasella, Stefano Valenti, Giorgio Valerin, Kathryn Wynn
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Cosmological stasis and the coupled dark sector of the Dark Dimension
Alexander Stewart
We study cosmological stasis in coupled dark matter and dark energy models in which a scalar field drives the dark energy and sets the dark matter mass, with the Dark Dimension as the motivating realization. Treating dark matter, dark energy, baryons, and radiation as an autonomous dynamical system, we show that exact stasis requires exponential slopes along the trajectory, and that running slopes give exact stasis or a drifting quasi-stasis depending on whether the running is integrable. The constant abundance solutions are the stationary solutions of coupled quintessence, which we read as stasis epochs with computable lifetimes and exits. Anchoring the cosmology to the measured abundances at matter-radiation equality and today, we show that the stasis region for this model cannot accelerate for any initial conditions, and that the total equation of state is never phantom although the effective dark energy of a $\Lambda$CDM fit can appear so. For the Dark Dimension, capture into stasis in the future is excluded for
geometric sources of the potential once dark fifth-force bounds are imposed, and dark matter production from the Standard Model brane supports a further stasis which the standard scenario does not reach. The stasis solutions provide analytic exclusions of the parameter space which do not depend on initial conditions.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Gravitational wave signatures of subsolar neutron star formation in collapsar disks
Vishal Baibhav, Valerio De Luca, Loris Del Grosso et al. (+3 more)
Standard models for stellar core collapse predict the birth of
neutron stars with masses exceeding a solar mass. In the collapsar model, a rapidly rotating massive
star collapses to a black hole surrounded by a dense,
neutrino-cooled
accretion disk, whose outer regions may in some cases fragment into
neutron-rich clumps that collapse to form subsolar-mass
neutron stars. These disk-formed objects can then merge either with one another or, following possibly hierarchical
evolution, with the central black hole. In this work, we characterize the gravitational-wave signatures of these binaries, focusing on distinctive features of the collapsar environment: Doppler and other phase modulations from orbital motion about the central black hole, gas-driven migration in the disk, and tidal interactions during inspiral. We show that the combination of anomalously low component masses with these environmental imprints produces unique waveform signatures that can distinguish the collapsar channel from other subsolar merger scenarios. Current and next-generation detectors have good prospects for identifying the intrinsic properties of such objects and, if subsolar mergers are discovered, for testing and constraining the collapsar formation pathway.
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All authors Vishal Baibhav, Valerio De Luca, Loris Del Grosso, Emanuele Berti, Brian D. Metzger, Lam Hui
Astrophysics of Galaxies
Gone with the wind? Potential gas inflow in the broad-line region of a QSO at $z=0.287$ traced by time-varying Balmer absorption
Xihan Ji, Dominic J. Walton, Francesco D'Eugenio et al. (+6 more)
We report spectroscopic observations of a remarkable QSO, J115724.80-000455.56 at $z=0.287$ from the Dark Energy Spectroscopic Instrument (DESI) survey. This QSO exhibits variability in its hydrogen Balmer absorption over a time interval of 10 months in the observed frame between 2021 and 2022. The observed Balmer absorption can be decomposed into two components with distinct kinematics: a non-varying, "stationary" component and a varying, "dynamic" component. Both absorbers have gas column densities of $N_{\rm H}\sim 10^{22}~{\rm cm^{-2}}$ and likely have densities of $n_{\rm H}\gtrsim 10^{8}~{\rm cm^{-3}}$. We inferred small effective physical sizes of $\lesssim 10^{-3}$ pc for the absorbers, which, together with the time variability, suggests that the absorption occurs in the broad-line region (BLR). The reshifted centroid velocities of both absorbers imply an inflow, where the inferred mass inflow rate is comparable to the single-epoch mass
accretion rate of this QSO. The 2022 epoch of this QSO further reveals a 10% change in the column density over 2 months, indicating the gas inflow might be continuous. We also obtained new X-ray observations using the $\it Einstein~Probe$, which reveals an X-ray-to-bolometric luminosity ratio significantly below the general AGN population. The X-ray weakness is consistent with strong gas obscuration with $N_{\rm H}= 4.0^{+ 1.6}_{- 1.5}\times10^{23}~{\rm cm^{-2}}$. The substantially higher gas obscuration seen in the X-rays compared to the optical possibly indicates a warm absorber inside the BLR or merger-driven enhancement of the galactic scale obscuration consistent with optical imaging. This QSO might thus represent an active feeding phase after a recent gas-rich merger.
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All authors Xihan Ji, Dominic J. Walton, Francesco D'Eugenio, Ignas Juodžbalis, Vasily Belokurov, Andrew C. Fabian, Roberto Maiolino, Jiamu Huang, Douglas N.C. Lin
Astrophysics of Galaxies
The KAGG survey: KCWI Analysis of Gas around Galaxies at z~3-5
Grecco A. Oyarzún, Marc Rafelski, J. Xavier Prochaska et al. (+5 more)
We present the KCWI Analysis of Gas around
Galaxies (KAGG) survey of Ly$\alpha$ emission around Damped Ly$\alpha$ Absorbers (DLAs) at z~3-5 with the Keck
Cosmic Web Imager (KCWI) integral-field spectrograph. The KAGG survey is characterized by the sample of 36 DLAs spanning a wide
metallicity range, the wide search area for associated Ly$\alpha$ emission (impact parameter b$~\lesssim 120~$kpc), and the high emission sensitivity, reaching Ly$\alpha$ luminosities $\lesssim10^{42}$ erg s$^{-1}$. We identify 7 DLA Ly$\alpha$ emitters that are likely DLA
galaxy candidates due to the good match between the Ly$\alpha$ emission and DLA
redshifts. Based on a composite sample of 11 DLA Ly$\alpha$ emitters from KAGG and MAGG (MUSE Analysis of Gas around
Galaxies), we find that the impact parameters of DLA Ly$\alpha$ emitters decrease with DLA
metallicity, from b$~>50~$kpc at [M/H]~-2 to b$~<50~$kpc at [M/H]~-1. Including Ly$\alpha$ emitters at larger velocity offsets and at larger impact parameters from the DLAs, we construct samples of 35 "Group" Ly$\alpha$ emitters and 17 "Large-scale" Ly$\alpha$ emitters. We find that their impact parameters and incidence rates also depend on DLA
metallicity. Based on simulations of our survey and comparisons with models of
galaxy formation, we conclude that higher DLA
metallicities are associated with higher
halo masses. The low Ly$\alpha$ emission detection rate at low impact parameters suggests that most DLA
galaxies either have low stellar masses (M$~\lesssim10^{8}M_{\odot}$) or have their Ly$\alpha$ emission suppressed due to HI resonant scattering and/or dust absorption.
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All authors Grecco A. Oyarzún, Marc Rafelski, J. Xavier Prochaska, Nissim Kanekar, Marcel Neeleman, Marie Wisz, Michele Fumagalli, Regina A. Jorgenson
Astrophysics of Galaxies
Dark matter haloes from dwarf to massive galaxies: no systematic inner-density tension with {\Lambda}CDM hydrodynamical simulations
Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós et al. (+1 more)
Two of the most prominent small-scale challenges to the cold dark matter (CDM) paradigm are the cusp-core and diversity-of-rotation-curves problems. The former concerns the shallow inner DM density profiles inferred for many
galaxies compared with the cusps predicted by collisionless CDM, while the latter concerns the wider range of inner DM densities and rotation curve shapes inferred observationally than hydrodynamical simulations traditionally reproduce. Robust observational constraints on DM core sizes and
halo densities are therefore essential for testing both the nature of DM and the impact of
galaxy formation processes. We analyse the inner DM distribution of a curated sample of 48 gas-rich
galaxies and 8 Milky Way gas-poor satellites, spanning 6 orders of magnitude in $M_\ast$. We find substantial scatter in DM core sizes and degrees of coreness, with both cuspy and cored
haloes occurring over a broad $M_\ast$ range. The cores are energetically consistent with stellar feedback, requiring modest
supernova energy coupling efficiencies of order $0.1-1\%$. Comparisons with the NIHAO, FIRE-2, and EDGE simulations reveal broad agreement in the inner DM densities and logarithmic slopes of observed and simulated
galaxies. The main residual differences concern the steep slopes of some massive simulated
galaxies and differences in SHMRs. Using a rotation-curve diversity diagnostic from previous work, we find that extreme discrepancies with simulations are absent from our curated sample and largely attributable to uncertain kinematics or baryonic mass distributions. Within the scope of our analysis, we find no evidence of a systematic inner-density tension between our
galaxy sample and current $\Lambda$CDM hydrodynamical simulations. Together with the modest energetic requirements for core formation, this substantially alleviates the cusp-core and diversity-of-rotation-curves problems.
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All authors Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós, Claudia Muni
Solar and Stellar Astrophysics
The white dwarf binary pathways survey - XI. The Gaia-GALEX UV Excess Sample for systems within 350 pc
James A. Garbutt, S. G. Parsons, N. Gentile Fusillo et al. (+9 more)
White dwarfs (WDs) with F, G or K type binary companions are the last common ancestor to a zoo of exotic phenomena. Finding a clean sample of such systems is difficult, as WDs in such binaries are usually outshone at optical wavelengths by their non-degenerate companion. It is useful to have a sample of such binaries - they can be studied to investigate binary
evolution, as they may have undergone a previous phase of mass transfer. Using Gaia data release 3 and GALEX, we compile a sample of 2597 candidate WD + FGK systems within 350 pc. These were identified via their ultraviolet excesses relative to MESA Isochrones and Stellar Tracks (MIST) model predictions consistent with the Gaia parameters of their non-degenerate companions. We estimate the mass, surface
gravity and effective temperature of the WDs by fitting the excess ultraviolet flux to models, or through interpolation where only one ultraviolet band was available. We also estimate the age of the system where possible, by comparing against any wide WD companions in higher-order stellar systems, or by checking if the system is a member of a cluster. On comparing against Simbad, we estimate the level of contamination within our sample to be between 10-35 per cent. This is a valuable sample for investigating WD + FGK binaries, particularly those containing hotter WDs (Teff,WD >~ 25 kK), and systems with post-main sequence companions.
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All authors James A. Garbutt, S. G. Parsons, N. Gentile Fusillo, B. T. Gänsicke, M. S. Hernandez, F. Lagos-Vilches, R. Raddi, A. Rebassa-Mansergas, J. J. Ren, M. R. Schreiber, O. Toloza, M. Zorotovic
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Jinn-Ouk Gong, TaeHun Kim, Junghwan Lee et al. (+1 more)
We establish a direct
quantum Clausius relation for conformal fields inside the apparent horizon of a quasi-de Sitter spacetime. We compute the net heat flow across the horizon from the renormalized stress-energy tensor, and independently determine the time
evolution of the renormalized von Neumann
entropy using the replica method. At leading order in the Hubble-flow expansion, the two calculations agree exactly, without using the gravitational equations of motion. Beyond leading order, we find a scheme-independent
entropy balance that includes the corresponding Wald
entropy. Our results provide a
quantum field theoretic realization of dynamical horizon thermodynamics beyond exact de Sitter
equilibrium.
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All authors Jinn-Ouk Gong, TaeHun Kim, Junghwan Lee, Chang Sub Shin