Solar and Stellar Astrophysics
Asteroseismic Detection of a Massive Unseen Companion to the $\delta$ Scuti Star TIC 160582982
Chenglong Lv, J. Pascual-Granado, Ali Esamdin et al. (+4 more)
We present TIC 160582982, an eccentric $\delta$ Scuti binary with a dynamically massive unseen companion. Six coherent high-frequency pressure modes used as pulsation clocks yield a phase-modulation orbit with $P_{\rm orb}=89.29\pm0.19$ d, $e=0.539^{+0.040}_{-0.037}$, and $a_1\sin i/c=145.6^{+3.7}_{-3.4}$ s, corresponding to $K_1=42.2^{+2.2}_{-1.8}$ km s$^{-1}$ and $f(M)=0.416^{+0.032}_{-0.028}\,M_\odot$. An independent frequency-modulation analysis of the two strongest modes gives a consistent orbital solution. Rotating MIST isochrones constrained by the atmospheric parameters and spectral energy distribution (SED) give $M_1=1.93\pm0.19\,M_\odot$ and $R_1=2.65\pm0.23\,R_\odot$. The mass function implies a formal edge-on minimum companion mass of approximately $1.80\,M_\odot$. Assuming a luminous main-sequence companion and including the non-eclipsing geometry gives $M_2=2.19^{+1.24}_{-0.34}\,M_\odot$ and $i=61.5^{+16.6}_{-19.6}$ deg. However, no clear evidence for the presence of a luminous counterpart is found, either photometrically or spectroscopically. This suggests the presence of a massive compact object, such as a
neutron star or even a stellar-mass black hole, as the massive unseen binary companion. Future phase-resolved high-resolution spectroscopy will be crucial for obtaining an independent orbital constraint and clarifying the nature of the companion.
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All authors Chenglong Lv, J. Pascual-Granado, Ali Esamdin, Angela Gardini, Haozhi Wang, Jianwei Yao, Shuguo Ma
Solar and Stellar Astrophysics · Cross-listed from physics.gen-ph
Einstein and the Solar Eclipses - Why Albert Einstein joined the Astronomische Gesellschaft in Potsdam 1921
Günther Rüdiger
In 1911 Einstein suggested that
photons which pass close to the Sun are deflected by its effective mass which would apparently shift the positions of
stars by up to one arcsecond, something that should be observable by astronomers during solar eclipses. Einstein`s ideas including the later doubling of the value due to relativistic space
curvature met with enthusiastic responses from astronomers. The history of these efforts, their motivations and interactions with Einstein is presented here, beginning with the expedition that failed due to WWI of the young Erwin Freundlich in 1914 and ending with the unsuccessful Potsdam campaign to Öland (Sweden) in 1954. A newly found conference photograph from the first post-war meeting of the Astronomische Gesellschaft in 1921 shows Albert Einstein as a new member of the AG on the Telegraphenberg in Potsdam.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Initial conditions for inflation
Gerasimos Kouniatalis
We propose a single-field mechanism that dynamically prepares the initial conditions required for exponential plateau inflation. The inflaton is decomposed into a coarse-grained mode and a high-occupancy, approximately Gaussian band of relativistic nonzero modes. Gaussian–Hartree averaging of the potential produces an exact variance-dependent minimum, which places the coarse-grained field high on the plateau when the excitation variance is large. Under a translation-invariant microcanonical measure, the available phase-space volume is exponentially concentrated near this minimum, while an order-one homogeneous kinetic-energy fraction is exponentially atypical. During expansion, the preparation modes
redshift as radiation, $\sigma^2\propto a^{-2}$ and $\rho_\chi\propto a^{-4}$. Although the induced minimum rapidly moves toward the
vacuum, the force acting on the coarse-grained mode is bounded by an exponentially small factor, yielding analytic upper limits on its velocity, displacement, and kinetic fraction. We derive a sufficient condition for the subsequent number of slow-roll e-folds and exhibit a
benchmark with more than 60 e-folds. The mechanism also motivates correlated finite-onset signatures: large-scale power suppression with decaying oscillations and a variance-convolution bispectrum.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Hadron resonance gas with density-dependent interactions for neutron stars and heavy-ion collisions
Volodymyr Vovchenko, Volodymyr Kuznietsov and Tripp Moss
We present a density-dependent generalization of the van der Waals
hadron resonance gas model (DD-HRG) for describing both the hot hadronic matter created in heavy-ion collisions and the cold, dense matter inside
neutron stars. Non-resonant interactions are incorporated through a generalized excluded-volume prescription with a density-dependent available-volume fraction, supplemented by an arbitrary density-dependent mean field. With isospin-dependent interaction parameters constrained by empirical properties of nuclear matter, the resulting equation of state extends the causality range to include
neutron-
star interiors and supports two-solar-mass
stars. It also improves the description of
lattice QCD thermodynamics and conserved-charge susceptibilities at vanishing baryochemical potential, with
lattice data favoring reduced repulsion among strange baryons. This DD-HRG framework is available within the latest version of the open-source Thermal-FIST package.
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High Energy Astrophysical Phenomena
A Possible X-ray and Gamma-ray Quasi-Periodic Oscillation in GRB 241030A
Noel Klingler, Cecilia Chirenti, M. Coleman Miller et al. (+2 more)
Quasiperiodic oscillations (QPOs) in gamma-ray intensity have been reported from a few gamma-ray bursts. These QPOs could be related to fundamental frequencies in the sources, which would lead to new insights about these systems. Here we report on our analysis of GRB~241030A, a several-minute-long burst with $\sim 10$ gamma-ray
flares that have approximate periodicities at f ~ 0.04 Hz and f ~ 0.08 Hz. This quasi-periodicity is seen in X-rays with the Swift X-Ray
Telescope (XRT) as well as in gamma-rays with the Swift Burst Alert
Telescope (BAT) and the Fermi Gamma-ray Burst Monitor (GBM). Compared with a power spectral model that has only red noise, the Bayes factor in favor of a Lorentzian-shaped QPO is more than $10^{200}$, even when the red noise is described by segments with up to four different slopes. However, the interpretation of this power spectral feature as a QPO rather than as a fluctuation in red noise is complicated by the low frequency of the feature as well as the extremely large number of counts, which amplifies differences from smooth power spectral distributions. After discussing the properties of the apparent QPO, we discuss a few processes that could plausibly modulate the flux at this frequency. Among the mechanisms considered, we find the most plausible explanation to be a GRB jet passing through regularly spaced shells of circumburst material, possibly produced by binary interactions near periastron in an eccentric progenitor system.
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All authors Noel Klingler, Cecilia Chirenti, M. Coleman Miller, Amy Lien, Simone Dichiara
Solar and Stellar Astrophysics
Unresolved triple systems in the aged open cluster Trumpler 19: Discovery, confirmation, and implications
D. Minniti, R. K. Saito, V. D. Ivanov et al. (+31 more)
It is difficult to identify unresolved triple and higher-order systems beyond the solar vicinity.
Star clusters yield controlled environments with known physical parameters, providing a way to explore homogeneous stellar samples. Combining modern optical and near-IR surveys, our main goal is to explore the region of the color-magnitude diagrams located above the sequence of equal-mass binaries, which is inhabited by unresolved triple and quadruple systems. Specifically, here we aim to discover and characterize the presence of multiple systems in the aged open
star cluster Trumpler 19. We selected cluster members using Gaia astrometry and photometry from the VVVX and DECAPS2 surveys. We made optical and near-IR color-magnitude diagrams to select
stars located >0.75 mag above the cluster main sequence, including suitable unresolved triple and quadruple systems. We confirm previous results that there is a sizable sequence of unresolved binaries in Trumpler 19. We also report the discovery of a sequence of unresolved multiple systems in this cluster, and confirm some of these multiple systems via radial velocities measured by the ESO KMOS VVVX-GalCen spectroscopic survey. The fraction of multiple
stars in this cluster is comparable to that of the solar neighborhood, with the caveat that the local sample probes deeper down the main sequence. The fraction of unresolved triples and quadruples is also three times higher than that of the open cluster M 67, which is of a similar age and chemical composition. The discovery of unresolved triple systems in Trumpler 19 leads to our main conclusion that these systems were able to survive within the cluster for nearly 4 Gyr. In addition, this cluster contains more multiple systems than M 67, which has a similar total present mass. Further investigations are needed to unveil if this is a primordial feature or the result of dynamical
evolution.
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All authors D. Minniti, R. K. Saito, V. D. Ivanov, C. O. Obasi, M. Gómez, P. W. Lucas, J. G. Fernández-Trincado, J. Alonso-García, E. R. Garro, J. Corral-Santana, A. Luna, Z. Guo, R. Kurtev, J. Borissova, V. Fermiano, J. Osses, C. Morris, B. Dias, C. Cáceres, S. Saroon, J. B. Pullen, P. Rodriguez, M. Lad, S. Federle, I. Petralia, D. Bhadrakumar, P. Esteves, M. G. Navarro, T. Palma, L. Baravalle, D. Galdeano, M. V. Alonso, J. L. Nilo Castellon, A. N. Chené
Astrophysics of Galaxies
Tracing the Hidden Molecular Gas in the Small Magellanic Cloud with SOFIA and APEX
K. Rodriguez-Ambler, R. Herrera-Camus, M. Rúbio et al. (+6 more)
In low-
metallicity environments, reduced dust abundance weakens molecular cloud shielding against far-ultraviolet radiation, enhancing CO photodissociation and producing extended CO-faint or CO-dark molecular gas. The [CII] 158 $\mu$m line is a key tracer of these CO-faint phases. We characterize the multiphase origin of [CII] emission and quantify the CO-faint molecular gas fraction across several regions of the Small Magellanic Cloud (SMC), the nearest low-
metallicity ($\sim 0.2 Z_\odot$)
galaxy. We combine high spectral resolution SOFIA/GREAT and upGREAT [CII], APEX CO(2-1), and ASKAP+Parkes H I 21 cm data to decompose [CII] into its atomic and molecular contributions. On average, $(78\pm 1)\%$ of [CII] intensity originates from molecular gas and $(18\pm 1)\%$ from atomic gas. The [CII]-traced H$_2$ accounts for $(77\pm4)\%$ of the total molecular gas column density, indicating that the SMC molecular reservoir is dominated by CO-faint gas. We derive a H$_2$-to-CO conversion factor $X_{CO}\approx 8.9\times10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$ on 4 pc scales in CO-emitting regions, 4.5 times the canonical Galactic value. We find no significant correlation between the CO-dark fraction and either total column density or $\Sigma_{SFR}$, suggesting that the CO-faint fraction is primarily governed by dust and gas shielding rather than current
star formation activity. Our results demonstrate that [CII] is the dominant tracer of molecular gas in the SMC and confirm the prevalence of an extended, stable CO-faint molecular phase in low-
metallicity environments.
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All authors K. Rodriguez-Ambler, R. Herrera-Camus, M. Rúbio, A. D. Bolatto, D. Riquelme-Vásquez, K. Jameson, C. Muñoz-López, E. J. Tarantino, J. Stutzki
Astrophysics of Galaxies
Reigniting the FUSE I: Star Formation in Massive Elliptical Galaxies
Michael Reefe, Michael McDonald, Eric Miller et al. (+1 more)
In this inaugural paper of our "Reigniting the FUSE" series, we present the data collection & reduction, methodology, and preliminary results for a comprehensive and homogeneous reanalysis of all 30 massive elliptical
galaxies that have archival far-ultraviolet (FUV) spectra with the Far Ultraviolet Spectroscopic Explorer (FUSE). We perform SED fitting to these spectra, with aperture-matched photometry from GALEX, SDSS, DES/DECaLS, 2MASS, and WISE, and construct a catalogue of high quality constraints on their stellar masses,
star formation histories, stellar and gas-phase
metallicities, and dust opacities. As a part of this analysis, we have also compiled a comprehensive modern set of stellar template libraries, with high resolution in the FUV, and broad coverage from $90\,\mathring{\rm A}$ - $1000\,{\rm \mu m}$ at lower resolution, which is made available through modified versions of FSPS and Python FSPS. We find strong evidence to suggest that the youngest
stars in these systems do not form out of recycled gas from the old stellar populations, but instead are fueled either by gas cooling out of the hot circumgalactic/intracluster medium, or cool gas stripped from nearby or merging dwarf systems. Future papers in this series will reexamine the O VI $\lambda\lambda$1032,1038 $\mathring{\rm A}$ emission in the context of the cooling flow problem.
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All authors Michael Reefe, Michael McDonald, Eric Miller, Thomas Brown
Cosmology and Nongalactic Astrophysics
Do DESI-DR2 BAO data imply a coupling of dark matter and dark energy?
Weiqiang Yang, Sibo Zhang, Dinorah Barbosa et al. (+3 more)
We revisit an interacting dark matter (DM) – dark energy (DE) model characterized by the interaction function $Q = \Gamma \rho_x$, where $\Gamma$ is a constant coupling parameter and $\rho_x$ is the energy density of DE. This type of interaction is independent of the Hubble rate or other external parameters, but depends only on the fundamental properties of DE, such as its equation of state (EoS), $w_x$. We pay special
attention to $w_x$ and study three distinct interacting scenarios distinguished by the nature of $w_x$, i.e. $w_x =-1$ (when DE corresponds to the
vacuum energy), $w_{x} < -1$ (when DE has a phantom behavior), and $w_x > -1$ (quintessential DE). We constrain all of them using the most recent cosmological
datasets, including CMB from Planck 2018, BAO from DESI DR2, and three compilations of SNIa (PantheonPlus, Union3, and DES-Dovekie). Our analyses reveal that evidence of interaction is supported in scenarios with $w_x =-1$ and $w_x < -1$ when all three
datasets are combined, but from the
Bayesian evidence analysis, $\Lambda$CDM remains favored over these interacting scenarios. Regarding the $S_8$ parameter, when $w_x > -1$, this interacting scenario leads to mildly lower estimates across all
datasets.
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All authors Weiqiang Yang, Sibo Zhang, Dinorah Barbosa, Marco Antonio Alvarez, Supriya Pan, Leila Graef
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Effective Field Theory of Gravity in Relativistic Media
Beka Modrekiladze
We develop an effective field theory of
gravity in relativistic media. Integrating out the medium leaves
vacuum gravity with updated Feynman rules: a graviton propagator dressed by the stress-energy two-point function of the environment, medium-induced bulk graviton vertices from higher correlators, and generalized worldline couplings encoded in matched Wilson coefficients. The diagram
topologies are unchanged from
vacuum, so different media (perfect fluids, collisionless matter, coherent scalar fields such as wave dark matter) are not different theories but different correlators inserted into the same diagrams. We derive the in-medium rules for a relativistic fluid and obtain the full 1PN Einstein-Infeld-Hoffmann potential, the 1PN Stokes drag, the gravitational self-energy and a generalized Christodoulou
memory whose new tensor structure records the orientation of the medium's anisotropy, turning the permanent strain into an $\textit{astrophysical weathervane}$. The same rules activate phenomena forbidden in
vacuum: the sound pole converts the
symmetry-protected, non-running black-hole Love number into a resonant, running one, and graviton splitting $h\to hh$ is open into the longitudinal branch of the dressed propagator, and gives the transverse graviton a width, $\Gamma=G_N\omega^3(1-c_s^2)^2/120c_s^3$, a $\textit{gravitational opacity}$ set by the sound speed. The same vertex makes a graviton suffer dynamical friction. We assess observational prospects, from dephasing and tidal resonances within reach of the Einstein
Telescope and LISA to proof-of-principle
memory and opacity signatures.
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Solar and Stellar Astrophysics
Calibration of the Next Generation Palomar Spectrograph as a Stellar Speedometer
Pranav Nagarajan and Kareem El-Badry
We calibrate the Next Generation Palomar Spectrograph (NGPS) for precision stellar radial-velocity (RV) measurements using repeated observations of 24 Gaia-ESO RV standards spanning $G=11$-$18$. Because NGPS is mounted at the Hale
telescope's Cassegrain focus, changes in instrumental flexure produce wavelength-solution shifts of tens of km s$^{-1}$, with substantial time and wavelength dependence. We develop a pipeline that measures these shifts directly from each science exposure, using telluric absorption features in the R and I channels and the [O I] 5577 Å sky-emission line in the G channel. This approach eliminates the need for frequent on-sky arc calibrations. The resulting wavelength-dependent flexure corrections reduce the median absolute discrepancy relative to Gaia-ESO RVs from tens of km s$^{-1}$ to 1.6 km s$^{-1}$. Telluric absorption provides substantially more reliable flexure calibration than sky emission lines, which do not track point-source illumination of the slit. The I channel, which contains both many telluric lines and strong photospheric lines across a range of spectral types, generally yields the most stable RVs. The achieved precision remains above the
photon-noise limit, indicating that NGPS RV performance is currently limited by calibration and modeling systematics. These results demonstrate that NGPS is well-suited for accurate and precise stellar RV measurements across a wide range of astrophysical studies.
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High Energy Astrophysical Phenomena
Rapid radio variability in the $z\sim7$ blazar VLASS J0410$-$0139: Indication of a hidden population of weak radio jets at Cosmic Dawn
Silvia Belladitta, Eduardo Bañados, Anniek J. Gloudemans et al. (+7 more)
Doppler boosting allows blazars to be detected out to high-$z$, making them promising probes of the intergalactic medium through the 21 cm forest. We report 0.144$-$11 GHz observations of the most distant known blazar, VLASS J041009.05$-$013919.88 at z$\sim$7, obtained with the upgraded Giant Metrewave
Radio Telescope (uGMRT), the LOw Frequency ARray (LOFAR) and the Very Large Array (VLA). The first uGMRT epoch (300$-$820 MHz, April 2023) revealed an inverted
radio spectrum which, combined with earlier (2021$-$2022) VLA data (1.5$-$11 GHz), unveiled a double-peaked spectrum potentially indicative of multi-epoch jet activity. A second uGMRT campaign (August 2023), simultaneous with new VLA observations (1.5$-$11 GHz), instead revealed a flat low-frequency and a peaked high-frequency spectrum, ruling out this interpretation. While limited by the two uGMRT epochs, variability analysis favors intrinsic jet processes, indicating a highly relativistic, closely aligned jet ($\theta<3$ deg, $\delta>19.3$, $\Gamma>9.7$). The equipartition
magnetic field ($> 1$ mG) exceeds the equivalent
Cosmic Microwave Background field at $z\sim7$ (0.2 mG), indicating synchrotron losses dominate. The inferred Doppler boosting ($\delta>19.3$) implies that J0410$-$0139 is intrinsically
radio-weak. As a blazar, it traces a much larger parent population of
radio quasars at $z\sim7$, detectable only with deep ($\leq \mu$Jy) next-generation
radio observations. LOFAR 144 MHz observations (April and July 2024) yielded $\sim$2 mJy, well below the $\sim$8 mJy predicted from uGMRT epochs, confirming strong variability at rest-frame $\sim$1 GHz. Low-frequency monitoring will be crucial for identifying high
radio intensity states suitable for future 21 cm forest studies.
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All authors Silvia Belladitta, Eduardo Bañados, Anniek J. Gloudemans, Timothy W. Shimwell, Emmanuel Momjian, Huib Intema, Chiara Mazzucchelli, Christian Fendt, Bhargav Vaidya, Fabian Walter
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Macroscopic dark matter constraints for extended mass functions
Zachary S. C. Picker, Andrew Buchanan, Melissa Diamond et al. (+1 more)
We compile and recompute a subset of the landscape of constraints for macroscopic dark matter (macros), explicitly including the dependence on the fraction of dark matter in macros $f_{\rm dm}$. This allows us to map these constraints to scenarios with extended mass functions for the macros, which is a generic outcome for many of the assembly processes relevant to macro formation. We compute a number of examples of constraints for extended mass functions, finding that in many cases, wider mass functions can be severely constrained by just the interactions of the tails of the distributions. Finally, we present the code and data required for computing these limits and generating these plots in a publicly accessible repository.
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All authors Zachary S. C. Picker, Andrew Buchanan, Melissa Diamond, Joseph Bramante
Astrophysics of Galaxies
LOFAR radio properties of quasars hosting Extremely High Velocity Outflows
Amy L. Rankine and Paola Rodríguez Hidalgo
Quasar winds are a potential contributor to the
radio emission observed in the so-called '
radio-quiet'
quasars. Extremely High Velocity Outflows (EHVOs), with bulk velocities >0.1c, represent some of the most energetic of these winds. In this work, we investigate the
radio properties of
quasars hosting EHVOs in order to assess whether such high-velocity winds contribute to the observed
radio emission. We cross-match the catalogue of EHVOs from the Sloan Digital Sky Survey with the high-sensitivity Low-Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) Data Release 3. We find that EHVO
quasars exhibit a significantly higher
radio-detection fraction of 38 per cent compared to an underlying parent
quasar population at 24 per cent. By constructing control samples using nearest-neighbour matching, we show that matching the C IV emission line blueshift alone is sufficient to reproduce the elevated
radio-detection fraction in a global sense; however, differences still remain in the
radio-detection fraction as a function of C IV emission blueshift between the EHVO distribution and any matched sample, suggesting that some additional mechanism is at play. Furthermore, composite spectra reveal no significant differences in the ultraviolet absorption profiles between
radio-detected and
radio-undetected EHVOs, although we identify a mild positive correlation between maximum outflow velocity and
radio luminosity. Our results suggest that EHVOs likely represent a subset of the
quasars which host fast winds that are observed along particular lines-of-sight, and that
radio emission associated with such winds remains a plausible mechanism.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
High-sensitivity Ultralight Dark Matter detector: Parametrically Amplified Casimir Devices
Muping Chen, Hideo Iizuka, Kyohei Mukaida et al. (+2 more)
We propose the use of sphere-and-plate Casimir force measurement setups to detect ultralight vector dark matter. We demonstrate that sub-picometer signals can be parametrically amplified to be detectable. We present a novel improvement that allows the continuous tuning of the natural frequency of the system, opening new research opportunities at the submicron scale. We show that the improved setup can determine the dark matter mass with high accuracy, significantly expand the detectable mass range, and achieve the best sensitivity to date in the $8\times10^{-14}\sim1\times10^{-12}{\rm~ eV}$ mass range.
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All authors Muping Chen, Hideo Iizuka, Kyohei Mukaida, Kazunori Nakayama, Burkhant Suerfu
Solar and Stellar Astrophysics
Deep H$\alpha$ Imaging Survey of IC 348 with the Hubble Space Telescope: I. Accretion Properties of Stellar and Substellar Objects
Lillian Yushu Jiang, Brendan P. Bowler, Yifan Zhou et al. (+5 more)
Accretion governs the growth of young
stars and the early
evolution of their circumstellar disks, yet population-level measurements of
accretion are often hampered by heterogeneous diagnostics and by samples preferentially selected toward disk-bearing or accreting objects. This can impact the mass
accretion rate-stellar mass ($\dot{M}$-$M_\star$) relation, particularly at substellar masses. We present a uniform analysis of
accretion in the $\sim$2 Myr-old
star-forming cluster IC 348 based on deep Hubble Space
Telescope F656N imaging. Using H$\alpha$ excess as a single, homogeneous
accretion tracer, we derive
accretion rates and robust upper limits for 200 cluster members spanning the stellar to substellar mass regime ($3\ M_\odot$ to $4\ M_{\rm Jup}$).
Accretion is detected in $37\pm3\%$ of the sample, with fractions of $34\pm4\%$ among stellar members and $46\pm6\%$ among substellar objects. For accretors alone, the inferred $\dot{M}$-$M_\star$ relation is consistent with those measured in similarly aged regions such as Lupus. In contrast, including weak accretors and non-detections increases the scatter and flattens the slope while lowering the intercept, demonstrating the strong influence of the low-
accretion tail on population-level
accretion relations. For free-floating planetary-mass objects in IC 348, extrapolating the accretors-only fit overpredicts $\dot{M}$ by approximately an order of magnitude compared to the fit that includes upper limits, which instead implies mass
accretion rates of $<10^{-12}$ $M_{\odot}\ \mathrm{yr}^{-1}$. These results show that sample selection, specifically whether the sample is restricted to disk-bearing or accreting targets, or instead is drawn from a complete membership census, is a dominant factor shaping population-level
accretion relations across a wide dynamic range in stellar mass.
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All authors Lillian Yushu Jiang, Brendan P. Bowler, Yifan Zhou, Adam L. Kraus, Sean M. Andrews, Lynne A. Hillenbrand, Michael J. Ireland, Zhaohuan Zhu
Earth and Planetary Astrophysics
Rotational broadening of exoplanet spectra in arbitrarily oriented systems: Application to reflected light
Sophia R. Vaughan and Laura Kreidberg
Exoplanet reflection spectra contain a wealth of information, which we are now beginning to access. At a high spectral resolution, the rotation of both the
star and the
planet affects the shape of the reflected spectral lines. This effect must be accounted for in high-resolution analyses and could be used to measure the orbital
alignment of systems. In this work, we derive the rotational broadening kernels for arbitrarily aligned systems, both for the stellar spectrum viewed by the
planet and for the reflected component of the
planet's spectrum. We then determine the relation between the parameters of the kernels and the standard orbital parameters of an
exoplanet system. Finally, we show examples of these kernels, compare them with previous models, and investigate the limitations imposed by our assumptions. We find that the difference in the rotational broadening of a non-aligned system relative to the broadening expected from a prograde aligned orbit can be of the order of 50 km s$^{-1}$. We also highlight how the equations and kernels presented in this work could be modified for other uses, such as thermal emission spectra.
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Astrophysics of Galaxies
Halo mass, star formation, and morphology in galaxies: A morphology-dependent connection between halo environment and star formation activity
G. Mountrichas, F. Shankar, F. J. Carrera et al. (+1 more)
Understanding the mechanisms responsible for quenching
star formation in
galaxies requires disentangling the roles of internal structure and large-scale environment. We investigate how
galaxy morphology and specific
star formation rate (sSFR) relate to the typical masses of host dark-matter
halos (DMHs), and whether the
halo–
star formation connection depends on morphology. We analyse non-active
galaxies in the VIPERS and Stripe 82 fields at $0.5 \leq z \leq 1.2$, combining DESI-based Sérsic classifications with stellar masses and SFRs from spectral energy distribution fitting.
Galaxies are separated into disc- and bulge-dominated systems and divided into
quantile-based sSFR bins designed to minimise stellar-mass differences between morphologies. Each bin is characterised by its median $\Delta{\rm MS}=\log {\rm SFR}-\log {\rm SFR}_{\rm MS}$, and characteristic DMH masses are inferred from projected
galaxy cross-correlations. The
halo-mass relation with
star formation activity depends strongly on morphology: disc-dominated
galaxies show little variation in
halo mass across the probed $\Delta{\rm MS}$ range, whereas bulge-dominated
galaxies occupy lower-mass
halos at high $\Delta{\rm MS}$ and higher, mutually consistent
halo masses toward lower $\Delta{\rm MS}$. These trends are unlikely to be driven mainly by stellar-mass differences. Typical
halo mass alone therefore does not map cleanly onto quiescence; instead, the connection between
halo environment and
star formation activity is stronger in bulge-dominated than in disc-dominated
galaxies.
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All authors G. Mountrichas, F. Shankar, F. J. Carrera, A. Georgakakis
Solar and Stellar Astrophysics
Unresolved Binary Systems in the Rubin Era I: An Autoencoder Framework for Binary Identification Applied to 47 Tucanae
Tobias Géron, Alexander Laroche, Joshua S. Speagle et al. (+1 more)
Binary systems are extremely common and influence many areas of astrophysics, such as stellar
evolution and cluster dynamics. In this work, we introduce flexAE, a framework that combines a classical autoencoder architecture with a dedicated classifier component. It is designed to distinguish between single
stars and binary systems based on their broadband spectral energy distributions, using all available photometry simultaneously while accounting for observational uncertainties. We demonstrate the capability of flexAE by using it to identify unresolved main sequence binaries in the outskirts of the 47 Tucanae globular cluster (NGC 104) with photometric data from the Vera C. Rubin Observatory. We train the model on a simulated sample of single
star and binary systems created with stellar atmosphere models. The model accurately reconstructs the photometric input features and achieves a classification accuracy of 0.85 on the simulated test set. We then apply the trained model to a sample of 1,424 cluster members found in Rubin DP1 with reliable $gri$ photometry, of which 32 are identified by the model as unresolved main sequence binaries. This corresponds to an observed binary fraction of $2.2^{+0.5}_{-0.3}$%. We estimate that the intrinsic main sequence binary fraction lies between $3.7^{+0.8}_{-0.5}$% and $7.5^{+1.5}_{-1.1}$%. The binary fraction stays constant between 18-36 arcmin (5.7-11.4 half-light radii) from the cluster center. We highlight that flexAE can be easily adapted for other use cases. This makes flexAE well-suited for large-scale binary classification in upcoming wide-field surveys, such as Rubin LSST. The code is publicly available at https://github.com/tobiasgeron/flexAE.
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All authors Tobias Géron, Alexander Laroche, Joshua S. Speagle, Maria R. Drout
Astrophysics of Galaxies
A direct measurement of the tilting rate of the Milky Way disc
Guillaume F. Thomas, Benoit Famaey, Alicia Rivero et al. (+2 more)
The Milky Way disc is typically described, at lowest order, as a flattened rotating stellar component with a fixed
spin axis. However, interactions and mergers with smaller
galaxies are expected to have an impact on the disc properties. Such interactions can leave long-lasting signatures within galactic discs, including warps and corrugation waves that have already been detected in the Milky Way, but also a slow reorientation of the disc known as tilting, which has never been directly measured up to now. Here, using the vertical proper motions of 110 million
stars from the Gaia DR3 catalogue, we present the first-ever direct measurement of the tilting rate of our
Galaxy's disc. The detected signal of 14 +/- 2 deg/Gyr around the Sun-Galactic Centre axis is statistically significant and is consistent with typical values found in cosmological simulations. By comparing our measurements with high-resolution tailored simulations, we infer that the observed tilting rate is likely the long-term consequence of a major
accretion event that occurred around 8-10 billion years ago. The signal is consistent with the merger of a massive satellite
galaxy on a retrograde orbit with a ratio of about 1:4, probably associated with the Gaia-Enceladus/Sausage event. These results provide independent evidence for a key episode in the Milky Way's formation history and introduce a new way to reconstruct the assembly histories of disc
galaxies from their present-day motions.
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All authors Guillaume F. Thomas, Benoit Famaey, Alicia Rivero, Giuseppina Battaglia, Rodrigo Ibata
Cosmology and Nongalactic Astrophysics
How Cluster Pressure Profiles Scale: Mass, Redshift, and Intrinsic Scatter
S. Andreon and F. Castagna
[shortened] The thermal pressure profile of the intracluster medium is critical for cluster cosmology and understanding
galaxy-cluster astrophysics. We determine the population-averaged pressure profile of Sunyaev-Zel'dovich (SZ) selected clusters, characterize its intrinsic scatter, and measure its scaling with mass and
redshift. We select 60 clusters from the South Pole
Telescope (SPT) SZ catalog with $0.08<z<0.6$, requiring high signal-to-noise and 5 element resolution on Planck-SPT Compton-$y$ maps. We model spherical three-dimensional pressure profiles from the Compton-$y$ maps using a hierarchical
Bayesian framework with restricted cubic splines. We adopt an updated weak-
lensing-calibrated Compton-$Y$–mass scaling relation, effectively removing hydrostatic mass bias from the inferred masses. Our model accounts for cluster-to-cluster profile variations, line-of-sight foreground and background contributions, and outliers from intrinsically distinct clusters or projection effects. The code is publicly available. We derive the population-averaged pressure profile and find minimal intrinsic scatter at intermediate radii ($0.4 \le r/r_{500} \le 0.7$). Our pressure profile is approximately 40% lower than previous estimates at all radii, due to the unbiased mass scaling. We find suggestive, though not conclusive, evidence that the adopted mass dependence may require revision by removing the additional $M^{0.12}$ scaling introduced by Arnaud et al. 2010. We constrain departures from self-similar
evolution in the mean profile to less than 0.1–0.2 dex and
evolution of the intrinsic scatter to less than 8% per $\Delta z=0.1$.
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Astrophysics of Galaxies
Discovery of Very Minor Merger-Induced Star-forming Clumps at $z=3.33$ with JWST
Alexander de la Vega and Bahram Mobasher
High-
redshift galaxies often contain ”clumps:” compact, $\sim$kpc-scale regions of intense
star formation. These substructures make up significant fractions of the masses and
star-formation rates of their host
galaxies and are expected to affect the morphologies of their hosts, such as by building up bulges. Studying clumps can therefore inform theoretical models of
galaxy evolution. Two main mechanisms have been proposed for their formation: gas fragmentation from disk instabilities and compression of gas during gravitational interactions with other
galaxies. In the latter, only mergers with mass ratios greater than 1:10 have been considered. Here, we report James Webb Space
Telescope spectroscopy and imaging of JADES 1034862, a
galaxy at $z_{\textrm{spec}} = 3.33$, which hosts a clump that formed during an interaction with a companion with a stellar mass that is $\approx28$ times lower than the host. From fits to the spectral energy distributions of the clump and the companion, it is found that both of their
star-formation histories rose sharply in the most recent 100-300 Myr, during which the clump formed $\sim10^{7.2} \ M_{\odot}$ in
stars and currently makes up $\approx10\%$ of the total
star-formation rate of its host. Given the higher frequency of mergers with low mass ratios ($<1:10$) to those with higher ratios, we infer that a substantial fraction of high-
redshift clumps could have formed through weak gravitational interactions.
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Instrumentation and Methods for Astrophysics
Fast Lensing And Sub-minute High-accuracy photometry (FLASH) with JWST: Pipeline and Primordial Black Hole Microlensing Constraints from M31
David Rubin and Istvan Szapudi
Minute- and sub-minute microlensing provides a direct probe of compact dark matter at asteroid-mass scales, where primordial black holes with MPBH <~ 10^-10 Msol would produce short-duration, finite-source-suppressed amplifications of
stars in extragalactic fields. To enable these measurements, we present FLASH: Fast
Lensing And Sub-minute High-accuracy photometry with JWST, a pipeline designed to recover such events from JWST/NIRCam imaging by preserving detector-ramp time information and performing high-precision crowded-field photometry. FLASH begins from Level 1 NIRCam data products, applies microlensing-oriented detector calibration (including improved treatment of non-linearity and position-dependent detector calibration), and extracts forced multi-band light curves in crowded fields. We apply the pipeline to two public JWST/NIRCam
datasets targeting the disk of M31 with 21.5 s cadence: GO-4735 and GO-2609. Although these observations are suboptimal as a microlensing survey, they provide a stringent test of JWST time-domain performance in a high-surface-brightness, crowded stellar field. Using these data with our own microlensing simulations, we derive the first JWST-based microlensing constraints toward M31, finding fPBH <~ 100 for MPBH~ 10^-9 Msol. Our results demonstrate that JWST is a competitive platform for high-cadence microlensing and that a dedicated, continuous NIRCam monitoring program could substantially improve constraints on compact dark matter below the current ground-based frontier.
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Solar and Stellar Astrophysics
The youngest white dwarf companion to a millisecond pulsar: Insights from NGC 362D
Greta Ettorre, Emanuele Dalessandro, Mario Cadelano et al. (+7 more)
We report on the identification of the optical counterpart to the recently discovered millisecond
pulsar (MSP) NGC362D in the Galactic globular cluster NGC362 based on deep, multi-band, and multi-epoch Hubble Space
Telescope observations. Our analysis robustly shows that this object is a very low-mass ($\sim0.18 M_{\odot}$) He white dwarf (WD) still in the pre-cooling phase. Interestingly, a detailed comparison with updated binary
evolution models indicates that this object completed the mass-transfer phase only recently ($\sim0.6$ Gyr ago), thus strongly suggesting that COM-NGC362D is the youngest WD companion to a MSP identified to date. Remarkably, in this respect, the photometric properties of NGC362D show, for the first time in this class of objects, significant wavelength-dependent variations that are consistent with the presence of residual circumstellar material. This system therefore provides a valuable test case to directly probe the immediate aftermath of the MSP recycling process and to constrain the early evolutionary stages of proto-WD companions and their
radio and optical properties. Our results suggest that residual material can produce
radio and optical signatures that mimic those of systems with non-degenerate companions, potentially leading to the misclassification of young MSPs.
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All authors Greta Ettorre, Emanuele Dalessandro, Mario Cadelano, Alessandro Ridolfi, Cristina Pallanca, Paulo C. C. Freire, Vivek Venkatraman Krishnan, Maurizio Salaris, Franca D'Antona, Rouhin Nag
Cosmology and Nongalactic Astrophysics
Analytic bispectrum covariance for galaxy survey cosmology
Utkarsh Giri, Henry S. Grasshorn Gebhardt and Olivier Dore
The bispectrum of
galaxy distribution remains an underutilized statistic in cosmological data analysis. This can be attributed to mathematical and computational challenges associated with a proper modeling of the signal and its covariance. While recent theoretical advances have made it possible to analytically model the bispectrum signal and covariance using perturbation theory, a fully non-Gaussian analytical treatment of the covariance for a realistic survey with window remains elusive. The full bispectrum covariance of observed
galaxies is a non-Gaussian six-point function with each of its legs convolved with a complex window function. Although it has so far proven intractable, the problem is well-posed. In this article, we present the derivation, implementation, and validation of a numerical routine for the analytic calculation of the bispectrum covariance for a spherical window, carried out by a large
language model (LLM). The derivation uncovered terms that vanish in the windowless case but that dominate the covariance for triangles with survey scale modes. As a development
benchmark for the implementation, we used the sample covariance of the
halo bispectrum measured from 6000 fiducial Quijote
halo catalogs in real space. Over several iterations of refinement, the LLM converged on a regime-specific numerical scheme for the covariance
matrix calculation, mixing exact and approximate approaches, resulting in a highly optimized, tractable and accurate covariance across scales and shapes, using only tree-level models for the input polyspectra. Closing the loop still required human expertise, which illustrates what human-AI collaboration in research may look like in the near term.
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Solar and Stellar Astrophysics
Evidence for Enhanced Helium Enrichment from Asteroseismology
Miqaela K. Weller, Marc H. Pinsonneault, Jennifer A. Johnson et al. (+1 more)
The helium abundance of a
star has a dramatic effect on luminosity, internal structure, and evolutionary timescales, yet direct helium measurements are unavailable for most
stars. In this work, we infer stellar helium abundances by comparing observed and predicted luminosities for a sample of subgiants with asteroseismic masses from the APOKASC sample and spectroscopic parameters from recent survey compilations. Stellar luminosities are predicted using grids of theoretical stellar
evolution models and offsets are attributed to helium differences from the assumed model value. From this analysis, we see clear evidence of helium enrichment correlated with
metallicity, $\Delta Y/\Delta Z = 1.959 \pm 0.061$, with the dominant error source being systematic differences in stellar fundamental parameters. Our inferred enrichment slope exceeds the value implied by a solar-calibrated helium enrichment relation, suggesting that commonly adopted assumptions regarding helium enrichment may underestimate stellar helium abundances at high
metallicity. We further show that adopting the revised enrichment law can alter predicted main-sequence lifetimes by up to $\sim$ 1 Gyr and, in some cases, modify stellar structure through changes in convective core development. These results demonstrate that uncertainties in helium enrichment propagate directly into stellar age determinations and highlight the importance of empirical helium constraints for stellar
evolution models.
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All authors Miqaela K. Weller, Marc H. Pinsonneault, Jennifer A. Johnson, Charles Shunyu Yao
Instrumentation and Methods for Astrophysics
The information content of optical intensity interferometry
Neal Dalal, Biwei Dai and Matthew K. Browning
Optical intensity interferometry (II) can in principle resolve structure on angular scales $\theta\sim \lambda/B$, but it measures only the squared visibility $|{\cal V}|^2$, discarding
Fourier phase. We quantify what information can actually be recovered from phase-less $|{\cal V}|^2$ measurements as a function of the aggregate signal-to-noise ratio and array configuration, using score-based
diffusion models as non-parametric image priors. We construct an image reconstruction pipeline, and validate it by reconstructing a variety of images, including GRMHD simulations of black hole
accretion disks and actual SDO/HMI continuum images of the Sun, from phase-less
Fourier amplitudes. Using simulated data, we map the reconstruction fidelity of Sun-like stellar surfaces as a function of noise level, number of $(u,v)$ samples, and maximum baseline $B_{\rm max}$, for surface maps spanning a range of activity levels. We find that fidelity depends on the data only through the total signal to noise ratio (SNR) of the surface features of interest, provided that the $(u,v)$ plane is sampled sufficiently densely. These results show that the SNR levels achieved by next-generation intensity interferometers observing realistic sources are sufficient to image highly complicated stellar surfaces.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
A compact time-frequency representation for gravitational-wave data analysis
Noah Pearson, Mesut Çal{\i}şkan, Sophie Bini et al. (+1 more)
Time-frequency (wavelet) domain analyses are seeing greater use for gravitational-wave data analysis due to the advantages they have in handling non-stationary noise. A popular choice is the Wilson-Daubechies-Meyer (WDM) wavelet transform, which uses a window function that is very compact in frequency, but more spread out in time. In this work, we consider an alternative window function that is built from a sum of phase-shifted Gaussians. This "Gaussian" window is more symmetric in time-frequency, and consequently more compact. We examine the properties of this window function and the implications it has for gravitational-wave analyses. We calculate the window's time-frequency variance product analytically and verify it numerically. For the symmetric case, where the window has the same form in time and frequency, the construction comes within $\sim2.4\%$ of saturating the Heisenberg-Gabor uncertainty limit. We
conjecture that this Gaussian window achieves the minimum time-frequency area of any WD wavelet window.
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All authors Noah Pearson, Mesut Çal{\i}şkan, Sophie Bini, Neil J. Cornish
Astrophysics of Galaxies
Baryon-Accelerated Core Collapse in SIDM Halos and its Imprint on Galactic Disks
Zeineb Mezghanni, Elliot Y. Davies, Adriana Dropulic et al. (+3 more)
The gravitational coupling between dark matter (DM)
halos and the baryonic structures they host is one of the most powerful windows into the particle nature of DM. Self-interacting dark matter (SIDM) presents a minimal, well-motivated extension to the dark sector with dramatic consequences for the structure of
galaxies and their
halos. However, the impact of baryons on SIDM
halo evolution and the resulting galactic structure has been underexplored in Milky Way (MW)-size
galaxies. In this paper, we demonstrate that the inclusion of a baryonic component in a MW-size
galaxy causes accelerated core collapse to begin within the MW's lifetime for a cross section as low as $\sigma/m = 1 \, \rm{cm}^2/\rm{g}$. We present a suite of $N$-body simulations of cold dark matter and SIDM MW-size
galaxies with and without a baryonic component for cross sections $\sigma/m =[1.0, 2.5, 5.0]$ cm$^2$/g. We find numerically, and semi-analytically, that the presence of a stellar disk and bulge shortens the predicted core collapse timescales from the DM only simulations by a factor of $\sim 40$. Further, as the core collapse begins within the lifetime of the
galaxy, the subsequent density increase strengthens the mid-plane restoring force exerted on stellar disk orbits, leading the disk to
flare. This work quantifies both directions of the baryon–SIDM coupling: baryons accelerate core collapse in MW-sized
halos, and the resulting
halo evolution reshapes the disk through thinning and flaring. Both processes open new observational windows into DM.
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All authors Zeineb Mezghanni, Elliot Y. Davies, Adriana Dropulic, Gonzalo Herrera, Abdelaziz Hussein, Lina Necib
Earth and Planetary Astrophysics
POSTELLAR: Posterior Stellar Spectrum Sampling - An Alternative to Approximate Stellar Spectra for Exoplanetary Analysis
Dhvani Doshi, Nicolas B. Cowan, Yashar Hezaveh et al. (+2 more)
We present a novel approach to perform posterior sampling of the underlying stellar spectrum in high-resolution spectroscopic observations. Our method, postellar, coherently combines information from empirical observations and physics-based models, enabling more accurate spectral recovery while providing uncertainties that can be propagated into downstream analyses. This is accomplished by treating the intrinsic stellar spectrum as a latent variable and performing posterior sampling under a Gaussian likelihood with an informative prior constructed using a score-based
diffusion model trained on PHOENIX stellar models. We validate the framework on synthetic SPIRou radial velocity (RV) observations generated from the empirical spectra of Barnard's
Star and Proxima Centauri. Spectra inferred with postellar more accurately recover the ground truth than standard empirical templates. For medium signal-to-noise observations, postellar improves RV accuracy by up to a factor of three, while RVs derived from empirical templates tend to be biased. This method performs particularly well in low signal-to-noise and low-cadence regimes. The postellar framework is broadly applicable to other high-resolution spectroscopy science cases including stellar abundance analyses and
exoplanet atmospheric characterization.
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All authors Dhvani Doshi, Nicolas B. Cowan, Yashar Hezaveh, Gabriel Missael Barco, Étienne Artigau