Earth and Planetary Astrophysics
Tracing the main belt origins of S-complex near-Earth objects: From space mission targets to meteorite sources
P. N. Simon, P. Vernazza, M. Marsset et al. (+5 more)
Context. Space missions to near-Earth objects (NEOs) provide unique opportunities to study and characterise their physical and compositional properties. Interpreting these results requires knowledge of their provenance, i.e. their source family in the main asteroid belt. Aims. We aim to identify the family sources of six S-complex NEOs visited or soon to be visited by space missions, and to investigate the size-dependent orbital behaviour of the broader S-complex NEO population using the MITHNEOS
dataset. Methods. We combine near-infrared spectral fitting with ordinary chondrite (OC) analogues reddened by a space-weathering model, using reduced $\chi^2$ minimisation, and cross-validation with probabilistic dynamical maps of the main NEO source families. Results. We identify LL6-7 chondrites and the Flora family for Eros, Itokawa, Apophis, and Torifune; LL3 chondrites and the Nysa family for Toutatis; L chondrites and the Massalia family for Didymos-Dimorphos. Where in situ observations exist (Itokawa and Eros), the classifications are consistent. Applied to the broader S-complex NEO population, the spectral classification and orbital properties distributions are broadly consistent with dynamical models. Accounting for observational biases, we find that at small diameters ($\leq$100 m), the fractions of H- and L-type objects increase at the expense of LL6-7 types, with low-inclination orbits consistent with origins in the Massalia (L) and Koronis (H) families. Conclusions. Combining spectral fitting with OC analogues and dynamical probability maps robustly identifies the source families of individual NEOs. Below $D\sim$100 m, the compositional distribution of S-complex NEOs approaches that of meteorite falls, providing direct observational evidence, based on spectroscopic measurements of S-complex NEOs, of the emergence of the source regions of OC meteorites.
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All authors P. N. Simon, P. Vernazza, M. Marsset, M. Brož, R. P. Binzel, F. DeMeo, C. A. Thomas, L. Jorda
Astrophysics of Galaxies
Occam's Razor and a Three-Family Ultralight Fermionic Dark Matter Model
Fabian Hernandez-Gutierrez and Juan Barranco
Inspired by the three generations in the Standard Model, we propose that dark matter particles are simply three non-interacting ultralight
fermions. This model is tested at galactic scales with the SPARC catalog of rotational velocity curves. This is done by modeling the dark matter
halo as the self-gravitating configuration of three gravitationally coupled
fermion species. This configuration is capable of forming more complex rotational curves which gives it flexibility to describe more complex and diverse morphologies of
galaxy rotation curves. The core of the
halos will be described by degenerate
fermions and the transitions from a degenerate core to a non-degenerate
halo will be described by either a perfect-fluid-like
halo or a NFW density profile. In order to construct the priors of the three-
fermion model, first we performed a single-
fermion analysis and obtained three characteristic mass regions around 20, 40, and 65-70 eV, for both
halo types. It is found that the three-component
fermion model improves the goodness of fit for 94.9% of the
galaxies considered. To estimate if the additional parameters are favored despite the added complexity by the corresponding improvement in the fit, the information criteria of AICc and BIC were computed and we found that more than $50\%$ of the
galaxies analyzed prefer the three-component
fermion model over a single
fermion model. The three-
fermion model is particularly favored for
galaxies with larger radial extent and more complex rotation curves. The multicomponent fermionic dark sector is able to describe a large diversity of rotation curves while maintaining characteristic
fermion mass scales across the
galaxy sample.
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Instrumentation and Methods for Astrophysics
SPECULATE: A synthetic spectral library, emulator and fitting package for accretion disc winds – Infrastructure and application to CVs
Austen G. W. Wallis, Christian Knigge, James H. Matthews et al. (+6 more)
Disc winds are critical components of accreting astrophysical systems and their observations can yield a wide variety of spectral line profiles. Yet, inferring disc wind parameters remains challenging: the underlying parameter spaces are high-dimensional and degenerate, while the radiative-transfer simulations are imperfect and computationally expensive. This paper tackles bridging this gap. Here, we present 'Speculate', an open-source framework for rapidly emulating and fitting observations with synthetic
accretion disc wind spectra, generated from the Monte Carlo radiative-transfer code Sirocco. Speculate includes the release of our cataclysmic variable (CV) training data, a library of 88,680 sparsely gridded Sirocco spectra spanning the ultraviolet and optical wave bands, a suite of pre-trained emulators, and its interactive Marimo user interface. Speculate compresses spectral grids using principal component analysis and then provides three approaches to interpolate the resulting latent representation: with a regular-grid interpolation, a neural network, or a Gaussian process. All three architectures enable Speculate to generate a Sirocco spectrum between $1-40\,\mathrm{ms}$, thereby enabling efficient inference. The first two support rapid $\chi^2$ optimisation. The Gaussian process utilises a
Bayesian inference engine coupled with a covariance-aware, flexible likelihood function, adapted and accelerated from the Starfish framework. This function helps absorb correlated discrepancies between simulations and data. Tests show all architectures reproduce unseen Sirocco spectra with broadly comparable accuracy and can recover their physical parameters. Subsequently, we apply Speculate to 5 representative nova-like CV spectra, reproducing several observed line features while also exposing mismatches where the current model grid omits relevant physics.
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All authors Austen G. W. Wallis, Christian Knigge, James H. Matthews, Knox S. Long, Madeleine-Mai Ward, Stuart A. Sim, Adam B. Hill, Amin Mosallanezhad, Nicolas Scepi
Astrophysics of Galaxies
The universal thickness of mid-infrared bubbles
Michael M. Schulreich and A. Beate C. Patzer
Several hundred ring-like structures seen at $8\mu$m in the Spitzer GLIMPSE surveys share a uniform morphology: the shell thickness $\Delta R$ is a nearly constant fraction of the outer radius $R$, $\Delta R/R\sim0.3$, across a factor of 40 in size and all exciting spectral types. This invariance is unexplained. We ask what sets this thickness and whether its near-constancy is physical or a measurement artifact. We derive analytic constraints on the location, temperature, and heating of the emitting grains, and confront the predicted scaling with radius against the GLIMPSE I and II catalogs (591 objects, 91 with kinematic distances). Grains in radiative
equilibrium at the observed radii reach only 20-35 K and fall short of the required $8\mu$m emissivity by more than 20 orders of magnitude; the emission must come from stochastically heated PAHs and very small grains, and therefore from the
photon-dominated region, where the ring width is the far-ultraviolet penetration depth. This gives $\Delta R/R=A_V^{\rm PDR}/A_V^{\rm cloud}$, independent of radius; a swept-up shell instead predicts $\Delta R/R\propto(R/R_S)^{3/2}$, with $R_S$ the initial Strömgren radius. We find a pronounced angular-resolution systematic that inflates the ratio for the smallest bubbles; once this is accounted for, $\Delta R/R=0.217$, with a residual dependence on physical radius of $0.03\pm0.05$, consistent with zero. A fixed ambient density is excluded at $20\sigma$, the swept-up shell at 9-28$\sigma$. The implied columns are $N_{\rm cloud}\approx8.7\times10^{21}$ cm$^{-2}$ with only 0.112 dex of scatter. The near-universal appearance of mid-infrared bubbles follows from the ratio of two nearly invariant column densities – the dust-opacity-fixed far-ultraviolet shielding column and the Larson-like column of the parent molecular cloud – and requires no reference to stellar winds.
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Instrumentation and Methods for Astrophysics
A Classifier Framework for ALMA Bandpass Calibration Anomalies
Ci Xue, Brian S. Mason, Gazi A. Rakib et al. (+8 more)
Bandpass calibration corrects instrumental responses across observing frequencies in interferometric
radio observations, so the measured calibration solutions inherently contain spectral variation that varies with instrumental configurations and noise conditions. However, some signals contain anomalies, which if not caught can lead to poorly constructed science products. Observatory pipelines often use scalar metrics with individual, linear decision boundaries. Constructing a simple parametric model can be effective for observations with a relatively limited parameter space, but it becomes progressively less accurate as the parameter space expands. To address this challenge, we design a machine learning framework that treats anomaly identification as a supervised classification task and learns complex, non-linear decision boundaries across multiple features optimized for predictive performance. In particular, we use an XGBoost model that sits on top of several features and specialized scan statistic models to classify anomalies in amplitude solutions from ALMA bandpass calibrations. Trained on an extensive, quality-controlled ALMA
dataset, this classifier framework leverages features derived from kernel-based scan statistics to characterize deviating spectral intervals, while remaining extensible to additional feature sets. This method substantially reduces misclassifications in bandpass anomaly detection compared to the current pipeline heuristics. By improving flagging decisions and calibration quality, this classifier framework provides a scalable supplement for observatory operations and is generalizable to next-generation
radio facilities.
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All authors Ci Xue, Brian S. Mason, Gazi A. Rakib, Tristan Ashton, Jeff M. Phillips, Ignacio Toledo, Ryan A. Loomis, Ilsang Yoon, John E. Hibbard, Omkar Bait, Eric J. Murphy
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Spectator Dark Matter and the Higgs Portal
Stephen E. Henrich, Yann Mambrini and Keith A. Olive
Light scalar spectators generically acquire large
stochastic fluctuations during inflation, which can lead to a catastrophic overproduction of dark matter if the resulting primordial condensate survives until late times. We show that this inflationary
memory can be sufficiently suppressed by an extremely feeble
Higgs portal interaction with sub-freeze-in couplings ($10^{-28} \lesssim \lambda_{HS} \lesssim 10^{-9}$). The
Higgs portal induces both a radiative self-interaction for the spectator as well as a thermal mass, both of which can lead to early onset of oscillations and efficient redshifting of the condensate's energy density without thermalizing the spectator or destroying the condensate. The
Higgs portal also alters the
stochastic equilibrium distribution of the spectator fluctuations, leading to a suppression of the field variance relative to an isolated spectator. We include a detailed treatment of the possibility that inflation may not have lasted sufficiently long for the spectator to reach its
equilibrium distribution of fluctuations, finding the major constraint on such a scenario to come from isocurvature, which requires $N \gtrsim10^{10}$ e-folds. We also consider the addition of a non-minimal gravitational coupling, which extends the parameter space significantly. This model generally favors sub-GeV light dark matter ($0.1 \text{ eV} \lesssim m_S \lesssim 10 \text{ GeV}$) and in the absence of non-minimal
gravity it also favors low reheating temperatures. While this mechanism can supply the entire relic abundance with sub-freeze-in portal couplings, it also naturally provides a suppressed initial condition for standard
Higgs portal freeze-in.
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High Energy Astrophysical Phenomena
A spatially resolved view of Fast Radio Burst host metallicities with Integral-field Spectroscopy
Sunil Simha, Hsiao-Wen Chen, Wen-fai Fong et al. (+15 more)
Magnetar sources are the leading theory for Fast
Radio Burst (FRB) progenitors. If magnetars are indeed the dominant sources, we may thus expect any
metallicity preference for magnetar formation to be reflected in the FRB site in host
galaxies. Here, we leverage Integral Field Unit (IFU) spectroscopy to spatially resolve gas-phase
metallicity distribution in five FRB host
galaxies: FRB 20240210A, FRB 20240312D, FRB 20250227A, FRB 20211127I, and FRB 20250316A, at $z < 0.05$, including the FRB site, with the O3N2 index. We observed the first four sources with the newly commissioned Large Lenslet Array Magellan Spectrograph (LLAMAS) IFU on the Magellan
Telescopes and used archival Keck/KCWI data for FRB 20250316A. We find ISM
metallicity variations of at least 0.3 dex within individual hosts for the majority of the sample, with median values spanning $12 + log(O/H) \approx$ 8.5–8.7. At the burst sites, four have
metallicities of $12 + \log(O/H) \approx 8.5$–8.9, while the fifth has a
metallicity below 8.5. These findings reveal substantial
metallicity variations both among FRB host
galaxies and within the local environments of the bursts. Consequently, our study shows that longslit-based global estimates of host
galaxy metallicity do not always represent the true burst-site distributions. We therefore advocate for IFU follow-up of larger host samples to ultimately provide FRB-site-relevant observational constraints on
metallicity preferences for FRB occurrence.
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All authors Sunil Simha, Hsiao-Wen Chen, Wen-fai Fong, Sarah Hughes, Yuxin Dong, J. Xavier Prochaska, Nicolas Tejos, Tarraneh Eftekhari, Alexa C. Gordon, Stuart D. Ryder, Mawson W. Sammons, Alice P. Curtin, Victoria M. Kaspi, Adam E. Lanman, Calvin Leung, Kiyoshi W. Masui, Aaron B. Pearlman, Ryan M. Shannon
High Energy Astrophysical Phenomena
Investigating X-ray Emission from Radio-detected Broad- and Narrow-line Seyfert 1 Galaxies
Minhua Zhou, Minfeng Gu, Lei Xu et al. (+2 more)
Context: This paper presents a study of the X-ray emission for a sample of
radio-detected (RD-) broad- and narrow-line Seyfert 1
galaxies (NLS1s and BLS1s). Aims: To investigate the X-ray emission properties of early-stage
accretion activity or early jets in NLS1s. Methods: By fitting XMM-Newton X-ray spectra and combining with multi-band data from SDSS and FIRST, we conducted a statistical comparative study on the X-ray emission and multi-band correlations of NLS1s and BLS1s. Results: NLS1s and BLS1s show no significant difference in their soft X-ray blackbody temperatures, but NLS1s exhibit steeper hard X-ray
photon indices and optical-to-X-ray slopes ($\alpha_{\rm ox}$). Moreover, correlation analyses of various parameters reveal intrinsic differences in the X-ray emission between the two samples. For instance, at comparable optical luminosities, NLS1s exhibit a higher $ \alpha_{\rm ox} $ (i.e., weaker X-ray emission), marginally distinct dependencies between
radio luminosity and black hole mass in the fundamental plane, and different correlations between $\alpha_{\rm ox} $ and
radio loudness. Based on the relationship between UV luminosity and $\alpha_{\rm ox} $ in RQ-AGN, the estimated X-ray excess ($\Delta \alpha_{\rm ox} $) in both samples is positively correlated with
radio loudness. RQ-BLS1s generally display the X-ray excess, whereas RQ-NLS1s tend to show an X-ray deficiency. The Eddington ratio of RQ-NLS1s derived from X-ray luminosity is lower than that inferred from optical luminosity, further supporting their intrinsically weaker X-ray emission. Conclusions: These differences in X-ray emission between NLS1s and BLS1s may ultimately stem from the earlier evolutionary stage of NLS1s. Multivariate linear fits among
radio luminosity, X-ray luminosity, and
radio loudness for NLS1s and BLS1s support a multi-wavelength radiative connection associated with jets.
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All authors Minhua Zhou, Minfeng Gu, Lei Xu, Mai Liao, ZhengXue Chang
Astrophysics of Galaxies
Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VII. First interstellar detection of fully deuterated methanol
A. Belloche, S. Spezzano, A. Coutens et al. (+12 more)
There have been no robust identifications of fully deuterated methanol, CD3OD, in the interstellar medium (ISM) to date. Our goal is continue the search for CD3OD in
star-forming regions to determine the deuteration pattern of methanol and set constraints on the deuteration process. We used a sensitive imaging spectral survey of the protostellar system IRAS4A in the NGC1333 molecular cloud performed as part of the large program carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) called Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). The column densities of methanol and several of its less abundant isotopologs, including deuterated ones, were derived under the assumption of local thermodynamic
equilibrium (LTE). Along with the detection of several methanol isotopologs toward the binary component IRAS4A2, we report the first interstellar detection of CD3OD. The deuteration pattern of methanol in IRAS4A2 is similar to the pattern measured in other low-mass protostars, with an increase in the apparent D/H ratio from the singly to multiply deuterated isotopologs. Chemical models of prestellar and protostellar cores focused on deuteration do not reproduce this pattern quantitatively. This discrepancy is even more exacerbated by the detection of CD3OD. Our LTE modeling of the spectra yields low column density ratios of methanol to its 13C and 18O isotopologs while the 13C to 18O and 18O to 17O ratios are consistent with the isotopic ratios expected in the local ISM. We suspect that the column density of methanol is underestimated. One possible explanation is that the emission is clumpy rather than monolithic. The first detection of a fully deuterated COM highlights the power of deuterium fractionation as a diagnostic tool for investigating the formation and inheritance of organic molecules during the process of
star formation.
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All authors A. Belloche, S. Spezzano, A. Coutens, M. N. Drozdovskaya, J. K. Jørgensen, J.-E. Lee, A. L. Plunkett, D. Harsono, S. Maret, F. Cruz-Sáenz de Miera, J.-H. Jeong, P. Nazari, Y.-L. Yang, H.-S. Yun, S. Zeng
Astrophysics of Galaxies
Multiple H I 21-cm absorbers towards blazar PKS 1158+007
Abhisek Mohapatra, R. Srianand and R. Dutta
We report an interesting line of sight towards the blazar PKS 1158+007 (J1201+0028) ($z_{\rm em}$ = 1.369), revealing the rare detection of two intervening HI 21-cm absorption systems within a narrow
redshift interval ($\Delta z \sim 0.04$) using the MeerKAT
radio telescope. The stronger absorber at $z_{\rm abs}$ $=0.5653$ ($\int\tau dv = 1.31\pm0.04$ \kms) is associated with a strong MgII $\lambda2796$ system seen in the Sloan Digital Sky Survey (SDSS) and Dark Energy Spectroscopic Instrument (DESI) spectra, with rest-frame equivalent widths of $W_{2796} = 1.40\pm0.07$~Å\ and $1.21\pm0.11$~Å, respectively. In stark contrast, the second detection at $z_{\rm abs}$ $= 0.5305$ reveals a distinct HI 21-cm absorption feature ($\int\tau dv = 0.31 \pm 0.04$ \kms) with no associated metal absorption detectable in the optical spectra. This system represents a
prime example of a "metal-poor” HI 21-cm absorber. Using photometric
redshifts from Hyper Suprime-Cam (HSC) PDR3 and DESI Legacy Surveys DR10, we identify a broad
galaxy overdensity (at $z \sim0.53\pm0.06$) coincident with these absorbers, suggesting the sightline pierces a complex large-scale structure or filament, which would be interesting to confirm with follow-up observations. These results underscore the power of blind HI 21-cm surveys to uncover the "invisible” cold gas phase of the Universe that optical/UV metal-line selection may systematically miss.
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High Energy Astrophysical Phenomena
Chana: A GPU-Accelerated AMR GRRMHD Code
Tianshu Wang
This paper presents Chana, a GPU-accelerated, block-structured adaptive-mesh code for general relativistic magnetohydrodynamics, multigroup M1
neutrino transport, and dynamical spacetime
evolution using the Z4c formulation. Each physical module uses independently selected spatial discretizations and ghost-zone widths to balance accuracy and computational cost. Stiff radiation-matter interactions are treated implicitly, with Jacobians calculated analytically from the chain-rules. The code is written in C++20 and it uses MPI and Kokkos 5 for distributed-
memory and performance-portable parallelism. The code is validated through a number of GRMHD, radiation transport, and dynamic spacetime tests. For a representative core-collapse
supernova configuration with three
neutrino species and 12 energy groups per species, the code achieves approximately $1.1 \times 10^6$
cell updates per GPU second on NVIDIA A100 GPUs using four-stage RK4 integration. Weak-scaling efficiency remains above 85% up to 256 GPUs on Perlmutter.
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Cosmology and Nongalactic Astrophysics
Lensing in the Blue IV: The First Weak Gravitational Lensing Maps from the Stratosphere
Sayan Saha, Maya Amit, Jacqueline E. McCleary et al. (+42 more)
The Super-Pressure Balloon-borne Imaging
Telescope (SuperBIT) completed its science flight in April 2023, obtaining imaging data for 30
galaxy clusters. In this work, we present the first weak-
lensing convergence maps from these observations, using six clusters selected from the 30 targets. We construct background-
galaxy catalogs using SuperBIT's three-band photometry and a color-color-based method to separate foreground and background
galaxies, and use the calibrated
galaxy shapes presented in
Lensing in the Blue III to reconstruct the weak-
lensing convergence field using Kaiser-Squires inversion. We compare the convergence signal-to-noise maps for the six clusters with independent tracers, including X-ray emission and red-sequence cluster-member number-density maps. These results demonstrate the first successful weak-
lensing mass mapping with imaging from a sub-orbital astronomical observatory.
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All authors Sayan Saha, Maya Amit, Jacqueline E. McCleary, Georgios N. Vassilakis, Emaad Paracha, Giulia Cerini, Spencer W. Everett, Leila Ohashi, Eric M. Huff, Gavin Leroy, Leo W.H. Fung, Richard Massey, Steven J. Benton, William C. Jones, Thuy Vy T. Luu, Ajay S. Gill, Mohamed M. Shaaban, Philippe Voyer, Adam Field, Adam Aoua, Anthony M. Brown, Paul Clark, Matthew Craigie, Christopher J. Damaren, Tim Eifler, David Harvey, Eric Habjan, John W. Hartley, Bradley Holder, Mathilde Jauzac, David Lagattuta, Jason S.-Y. Leung, Lun Li, Johanna M. Nagy, C. Barth Netterfield, Susan F. Redmond, Jason D. Rhodes, Andrew Robertson, L. Javier Romualdez, Jürgen Schmoll, Ellen Sirks, Sut Ieng Tam, Karuna Tarafdar, André Z. Vitorelli, Alfredo Zenteno
High Energy Astrophysical Phenomena
Radial Modes of Hot Neutrino-Trapped Hybrid Stars
Peter B. Rau, Andrea Sabatucci and Armen Sedrakian
We study the fundamental radial oscillation mode of hot hadronic and hybrid
stars under conditions relevant to proto-
neutron stars and
neutron-
star merger remnants. The stellar backgrounds are constructed from finite-temperature equations of state with a covariant density functional for hadronic matter and three-flavor 2SC
quark matter at high density. We consider two isentropic configurations in both
neutrino-transparent matter and with trapped electron
neutrinos at fixed electron-lepton fraction. For trapped matter we compare a Gibbs-type construction with global electron-lepton-number conservation to a locally constrained Maxwell-type prescription; in both cases the fixed-
entropy stellar equation of state contains an extended coexistence region and no sharp interface requiring conversion rate-dependent junction conditions. We find that the fundamental radial frequency follows the corresponding purely hadronic sequence up to the onset of deconfinement and then decreases relative to it.
Neutrino trapping shifts this dynamical signature to larger stellar masses and central pressures, reflecting the delayed appearance of
quark matter. The Maxwell-type prescription moves the onset of deconfinement to still higher central pressure and produces a more rapid decrease of the mode frequency near the stability limit. We quantify the deconfinement effect through the fractional frequency shift between hybrid and hadronic
stars at equal gravitational mass. These results show that the fundamental radial mode provides a sensitive dynamical probe of the interplay among
entropy, lepton trapping, phase-transition construction, and
quark deconfinement in hot compact
stars.
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Earth and Planetary Astrophysics
Exploring the ultrahot Neptune LTT 9779 b with CRIRES+. Non-detection of helium transmission spectra and detection of H$_2$O on the dayside
S. Liu, F. Yan, L. Nortmann et al. (+15 more)
Ultrahot Neptunes reside in the most extreme irradiation regime of the hot Neptune desert and remain challenging targets for atmospheric characterization because of their low
planet-to-
star flux ratios. We present high-resolution transit and dayside thermal emission spectroscopy of the ultrahot Neptune LTT 9779 b obtained with CRIRES$^+$, to probe atmospheric escape and dayside molecular emission. No significant absorption is detected in the metastable He I $\lambda 1083$ nm triplet during transit, yielding a $3\sigma$ upper limit of 0.45% on the excess helium absorption depth and supporting previous non-detections that suggest weak ongoing atmospheric escape. For the dayside emission spectra in the $K$ band, our cross-correlation analysis reveals an $\mathrm{H_2O}$ absorption signal and a tentative $\mathrm{CO}$ feature, with the combined signal reaching a detection significance of $4.8\sigma$. Both the CRIRES$^+$ and previous JWST data favor a non-inverted temperature structure, providing no evidence of a thermal inversion on the planetary dayside. We further perform a joint atmospheric
retrieval combining the CRIRES$^+$ high-resolution spectra with JWST/NIRISS SOSS secondary-eclipse observations. The joint
retrieval yields a low $\mathrm{H_2O}$ abundance, while the $\mathrm{CO}$ abundance remains weakly constrained. The inferred planetary equatorial rotational velocity, $v_{\rm eq}=4.9^{+4.4}_{-3.0}~\mathrm{km\,s^{-1}}$, is consistent within $1\sigma$ with the synchronous rotation velocity expected for a tidally locked
planet ($\sim2.8~\mathrm{km\,s^{-1}}$). However, the large uncertainties prevent us from placing strong constraints on the
planet's rotation state. Future phase-resolved CRIRES$^+$ observations with broader orbital-phase coverage and higher signal-to-noise ratios would improve the abundance constraints and probe the atmospheric dynamics of this rare ultrahot Neptune.
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All authors S. Liu, F. Yan, L. Nortmann, B. Guo, D. Cont, F. Lesjak, D. Shulyak, A. Reiners, N. Piskunov, A. P. Hatzes, U. Seemann, A. Lavail, A. D. Rains, H. L. Ruh, L. Boldt-Christmas, M. Rengel, O. Kochukhov, T. Marquart
Astrophysics of Galaxies
Hierarchical Black Hole Mergers at High Redshift: Predictions for LISA and LGWA from SEEDZ
Daxal H. Mehta, Lewis R. Prole, John A. Regan et al. (+13 more)
We investigate the hierarchical assembly of black holes (BHs) in the early Universe using the next-generation SEEDZ cosmological zoom-in simulations. Our suite follows two independent regions (Rarepeak and Normal1) evolved with three BH feedback prescriptions: no feedback (NoFB), weak feedback (WeakFB), and standard thermal isotropic feedback (FidBH). Focusing on BH mergers at $z \geq 10$, we explore merger-driven BH growth and detectability with next-generation gravitational-wave observatories. We find that stronger AGN feedback models dramatically suppress hierarchical BH assembly compared to weaker feedback implementations. In the NoFB simulations, BHs frequently undergo repeated mergers, with some experiencing more than 50 merger events within a few hundred Myr and gaining over $10^8,\mathrm{M_{\odot}}$ through mergers alone. In contrast, BHs in the FidBH simulations rarely undergo more than three mergers. NoFB therefore represents an upper limit to BH merger-driven growth beyond what is expected in the Universe. The suppression of BH mergers in the FidBH case is not driven by differences in
galaxy assembly, BH occupation fractions, or BH seed abundances, which remain broadly similar across the simulation suites. Instead, feedback disrupts the dense gas surrounding newly formed BH seeds, suppressing their early
accretion-driven growth and preventing them from entering runaway hierarchical merger pathways. Our results demonstrate that early-Universe feedback prescriptions strongly influence hierarchical BH growth through both mergers and
accretion, producing distinct high-
redshift merger populations. Coupled with seeding choices and other BH subgrid prescriptions, this introduces multiple degeneracies that will need to be broken in advance of LISA and other next-generation GW facilities.
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All authors Daxal H. Mehta, Lewis R. Prole, John A. Regan, Rüdiger Pakmor, Sophie Koudmani, Ricarda S. Beckmann, Michael Tremmel, John H. Wise, Martin A. Bourne, Ralf S. Klessen, Simon C. O. Glover, Martin G. Haehnelt, John Brennan, Pelle Van De Bor, Debora Sijacki, Paul C. Clark
Astrophysics of Galaxies
Spectroscopic Confirmation of the Milky Way Satellites Boötes V and Leo Minor I and the LMC Satellite DELVE 2: Three Small Ultra-Faint Dwarf Galaxies
W. Cerny, M. Geha, J. D. Simon et al. (+22 more)
We present the first multi-object spectroscopy of Boötes V, Leo Minor I, and DELVE 2 – three small (20 pc $\le r_{1/2}\le$ 26 pc), ultra-faint ($-3.2\le M_V\le-2.1$) stellar systems in the outer Galactic
halo (71 kpc $\le D_\odot\le$ 102 kpc) with heretofore ambiguous classifications. Leveraging at least two epochs of Keck/DEIMOS or Magellan/IMACS observations targeting each satellite, we identify 13, 7, and 7 spectroscopic members in the three systems, respectively. We tentatively resolve a $\sigma_v=2.1^{+1.5}_{-0.9}$ km s$^{-1}$ velocity dispersion for DELVE 2 but place upper limits of $\sigma_v<2.7$ km s$^{-1}$ and $\sigma_v<7.8$ km s$^{-1}$ for Boötes V and Leo Minor I. We find that all three systems are very metal-poor, with mean iron abundances $-2.85\le\overline{\rm [Fe/H]}\le-2.15$. Both Boötes V and Leo Minor I display unambiguous
metallicity spreads ($\sigma_{\rm [Fe/H]}=0.46^{+0.18}_{-0.12}$ dex and $\sigma_{\rm [Fe/H]}=0.57^{+0.23}_{-0.18}$ dex), while DELVE 2 displays a modestly significant spread ($\sigma_{\rm [Fe/H]}=0.52^{+0.29}_{-0.25}$ dex) across three
stars. Based primarily on these
metallicity measurements, we confidently classify Boötes V and Leo Minor I as dwarf
galaxies and determine that DELVE 2 is most likely a dwarf
galaxy as well. We explore the orbit of each satellite in a joint Milky Way + LMC potential, confirming for the first time that DELVE 2 is a long-term bound satellite of the LMC. Finally, we review the empirical Milky Way satellite classification landscape and find that nearly every spectroscopically characterized satellite with azimuthally averaged half-light radius $r_{1/2}>15$ pc and surface brightness $\mu_{V,1/2}>26.5$ mag arcsec$^{-2}$ is likely a dwarf
galaxy. This result can guide initial probabilistic classifications for satellites discovered by $\textit{Rubin}$, $\textit{Roman}$, and $\textit{Euclid}$.
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All authors W. Cerny, M. Geha, J. D. Simon, T. S. Li, A. B. Pace, R. P. van der Marel, N. Kallivayalil, A. P. Ji, A. Drlica-Wagner, D. Crnojević, G. Limberg, N. E. D. Noël, A. H. Riley, D. J. Sand, G. S. Stringfellow, Y. Choi, P. S. Ferguson, C. E. Martínez-Vázquez, P. Massana, G. E. Medina, B. Mutlu-Pakdil, J. D. Sakowska, C. Y. Tan, A. K. Vivas, J. Bruce
Earth and Planetary Astrophysics
Enhancing the Interpretability of Radial Velocity Analysis Using Leave-one-out Cross-validation
Matthew C. Nixon, Ritvik Basant, Rafael Luque et al. (+2 more)
Radial velocity (RV) observations are reaching increasingly high precision, enabling the targeting of low-amplitude signals. Assessing results obtained at the limits of our capabilities requires understanding the relationship between data, models and inference. Leave-one-out cross-validation (LOO-CV) has become an increasingly popular tool for interpretable model criticism in astronomical data analysis. In this work, we demonstrate how LOO-CV can provide insight into the RV analysis of exoplanetary systems through three case studies. We first investigate the anomalously high mass of HD 119130 b inferred from CARMENES RVs, later revised significantly downward after follow-up observations with other instruments. We show that this high mass was strongly driven by two individual measurements, whose removal significantly reduces the tension between data sets. Next, we use LOO-CV as a model selection tool for the GJ 4276 system. Here, LOO-CV prefers an eccentric single-
planet model over a two-
planet model, and identifies the orbital phases at which follow-up observations would best discriminate between them. Finally, we extend LOO-CV to models with correlated noise, applying it to the GJ 357 system, whose RVs are modeled with a Gaussian process. We find no predictive support for a fourth planetary signal that is moderately favored by the
Bayesian evidence, strengthening the interpretation of a three-
planet architecture previously reported in the literature. We provide practical guidance for implementing LOO-CV in RV analysis, together with an online tutorial. Such methods will become ever more important as future RV surveys push the limits of
planet detection and characterization.
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All authors Matthew C. Nixon, Ritvik Basant, Rafael Luque, Luis Welbanks, Pierrot Lamontagne
Astrophysics of Galaxies
Molecular hydrogen formation on dust: The impact of gas-dust drift on formation efficiency
Stefan Reissl, Simon C. O. Glover, Ralf S. Klessen et al. (+2 more)
Molecular hydrogen is predominantly formed on dust-grain surfaces in the interstellar medium, where relative gas-dust motion can arise in dynamically active environments. While the dependence of H$_2$ formation on grain temperature and surface properties is well studied, the impact of gas-dust drift has received little
attention. We investigate how gas-dust drift modifies H$_2$ formation, focusing on the competition between the drift-enhanced H-atom collision rate and reduced sticking at higher impact energies. We use an event-driven kinetic Monte Carlo model that follows individual H atoms on spherical silicate and carbonaceous grains, including adsorption, surface migration, thermal desorption, and Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) reactions. Drift is described by a shifted Maxwellian velocity distribution, and we compare constant and impact-energy-dependent sticking probabilities. Drift produces increasingly anisotropic distributions of adsorbed H and H$_2$ formation across the grain surface. Assuming constant sticking, increasing drift enhances H$_2$ formation through the higher collision rate, with efficiencies up to $\epsilon=0.3-0.4$. With energy-dependent sticking, strong drift instead suppresses formation on both materials, reducing efficiencies to $\epsilon=0.01-0.03$. Carbonaceous grains remain efficient to higher dust temperatures than silicate grains. ER reactions dominate over most of the investigated parameter space and become increasingly important at strong drift as the reduced surface population suppresses LH reactions. Thus, enhanced collision rates under gas-dust drift do not necessarily increase H$_2$ formation. Models of dynamically active environments should account for both relative gas-dust velocities and their effects on sticking.
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All authors Stefan Reissl, Simon C. O. Glover, Ralf S. Klessen, Liam S. Morrissey, Mordecai-Mark Mac Low
Astrophysics of Galaxies
DIGging into HII regions: the role of ionizing photon leakage and spectral hardening in coupling HII regions and diffuse ionized gas
Dalya Baron, Kathryn Kreckel, Gwen C. Rudie et al. (+15 more)
The optical emission-line ratios of
star-forming
galaxies are broadly understood in the framework of photoionization, yet some systematic trends remain unexplained. Using 50–100 pc resolution PHANGS-MUSE observations of 19 nearby
galaxies, we investigate how escaping ionizing radiation couples HII regions to the diffuse ionized gas (DIG), analyzing thousands of HII regions and DIG sightlines. HII regions and the DIG form a continuous sequence across standard line-ratio diagnostic diagrams (e.g., BPT diagrams), where progressively fainter regions show elevated high- and low-ionization line ratios, and the DIG extends the same trends into the composite–LINER regime. Line-ratio variations with global specific
star formation rate (sSFR) suggest progressively harder ionizing radiation with increasing
star formation activity, contrary to expectations for emission increasingly dominated by older stellar populations. Line-of-sight mixing explains part of the behavior but cannot reproduce all line-ratio trends. We therefore develop a model in which ionizing
photons escape HII regions and propagate through the diffuse ISM, undergoing
geometric dilution, attenuation, and spectral hardening. The model predicts that progressively fainter HII regions are increasingly ionized by leaked radiation from neighboring luminous regions, implying radiative coupling between HII regions. Joint modeling of HII regions and the DIG reproduces the HII region luminosity distribution and DIG surface brightness for escape fractions of $\sim$0.4$-$0.6 and ionizing-
photon mean free paths of $\sim$0.5$-$1 kpc, and qualitatively reproduces the observed line-ratio sequences and their dependence on sSFR. Our results suggest that ionizing
photon leakage may provide an important non-local feedback channel linking compact
star-forming sites to large-scale
galaxy disks.
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All authors Dalya Baron, Kathryn Kreckel, Gwen C. Rudie, Karin M. Sandstrom, Alberto D. Bolatto, Guillermo A. Blanc, Oleg V. Egorov, Eva Schinnerer, Ashley T. Barnes, Enrico Congiu, Daniel A. Dale, Simon C. O. Glover, Jaeyeon Kim, Ralf S. Klessen, José Eduardo Méndez-Delgado, Justus Neumann, Ismael Pessa, Thomas G. Williams
Earth and Planetary Astrophysics
Discovery of a second-generation planet candidate accreting onto a white dwarf
Jamie T. Williams, Boris T. Gänsicke, Nicholas C. Stone et al. (+10 more)
Many white dwarfs accrete the debris of disrupted planetary bodies, detected in the form of metal-enrichment in their atmospheres, dusty or gaseous circumstellar discs, and photometric transits from debris. The composition of accreted debris has been shown to be diverse yet overall closely resembles Solar System bodies. We report the discovery of a white dwarf accreting material that is unlike any Solar System object. The atmosphere of HS 0209+0832 is strongly enriched in trans-iron elements including zinc, copper, and niobium but depleted in the canonical rock-forming elements silicon and iron. The composition of the accreted object is consistent with a candidate second-generation
planet, formed from the stellar material ejected during the giant phase. The key abundance signature which differentiates it from a first-generation
planet is the high enrichment of s-process elements. Photospheric helium and the absence of terrestrial rock-forming elements implies the white dwarf is accreting from the escaped atmosphere of a photo-evaporating giant
planet candidate. This is further supported by the detection of a sinusoidal photometric period of 4.399+/-0.026 days at an amplitude of 0.120+/-0.018 %, which we attribute to thermal emission phase variability from a planetary day-night cycle or a transiting cometary tail of an evaporating gas giant.
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All authors Jamie T. Williams, Boris T. Gänsicke, Nicholas C. Stone, Detlev Koester, Benjamin D. R. Davies, Christopher Tong, David J. Wilson, Snehalata Sahu, Andrew Swan, Thomas G. Beatty, Sergio H. Ramírez, Tim Cunningham, Knox S. Long
High Energy Astrophysical Phenomena
Power-Law Injection Spectrum from an Ensemble of Reconnecting Current Sheets
Omar French
A collisionless, low-$\beta$
plasma undergoing strong sub-Alfvénic
turbulence is expected to form a broad hierarchy of reconnecting current sheets immersed in a strong guide
magnetic field. If the reconnecting field strength of a sheet scales with its length as a power law of index $\kappa$, and the number of sheets per unit interval of sheet length decreases as a power law of index $x$, the current-sheet ensemble injects nonthermal particles with a power-law energy spectrum $\propto \gamma^{-s}$, where $s = 1 + (x-2)/(1 + \kappa)$. The spectrum is hard ($s < 2$) when the longest sheets deliver most of the injected energy, which requires $x < 3 + \kappa$. Past numerical studies have measured $2 \lesssim x \lesssim 3.3$, and the scalings of intense current sheets support $\kappa \gtrsim 0$, resulting in $1 \lesssim s \lesssim 2.3$. This injection may yield flat or mildly steep
radio spectra in optically thin sources and hard ion spectra in the coronae of active galactic
nuclei.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Magnus: neutrino oscillation probabilities for any Hermitian Hamiltonian, any number of flavors, and any matter profile
Mauricio Bustamante
Interpreting
neutrino oscillation measurements requires computing the probability that a
neutrino born with one flavor is detected with another. In
vacuum and in matter of constant density, this probability has exact formulas. Where the density varies along the path, as in the Earth, the Sun, or a
supernova, it does not. There, the usual approaches either replace the profile by constant-density steps, whose error falls only as the square of their width, or integrate the
evolution equation with a general-purpose solver, which must shorten its steps to meet a tighter tolerance. Both become slow at high accuracy, yet an analysis needs the probability at many energies, directions, and parameter values. Each new experiment or model often requires writing and validating a new solver. We present Magnus, an open-source Python code that avoids these limitations. It uses the Magnus expansion, whose error falls as a high power of its step width and whose cost is set by how fast the density varies, not by how many oscillations the path holds. Magnus accepts any density profile, any number of flavors, and any Hermitian
Hamiltonian, such as those of non-standard interactions, sterile
neutrinos, Lorentz-invariance violation, and pseudo-Dirac
neutrinos. Where a cheaper route exists, it takes it automatically. For example, where the density varies slowly, as in the Sun, it follows the instantaneous eigenstates and applies the expansion only at resonances. Besides oscillating probabilities, Magnus returns phase-averaged ones, which describe solar and astrophysical
neutrinos. A typical probability takes a few milliseconds, and batched scans are one to two orders of magnitude cheaper per point. Among the public codes we compared, Magnus is the fastest at high accuracy on a varying profile. Magnus shifts the effort of studying a new experiment or model from writing a solver to specifying its physics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Coherent versus incoherent amplification: from parametric resonance to the kinetic regime in stimulated axion decay
Clemente Smarra and Elisa Todarello
Although the spontaneous decay of
axions into two
photons is extremely slow on cosmological timescales, it can be strongly enhanced in environments with large bosonic occupation numbers. From a classical field perspective, stimulated
axion decay is described by modified Maxwell equations. For a coherent
axion background, these equations exhibit a parametric resonance characterized by a
photon growth exponent $s\propto g_{a\gamma}$. By contrast, a standard kinetic description, for instance based on Boltzmann equations, involves the squared
matrix element of the decay process and therefore would naturally predict a characteristic rate scaling as $s\propto g_{a\gamma}^2$. In this work, we show that these apparently different behaviors originate from the coherence properties of the
axion field. Starting from an
axion field with a finite momentum dispersion, we show how dephasing among its momentum modes modifies the
photon instability and derive an effective
evolution equation in which this effect is encoded in a kernel. For a continuous Maxwell-Boltzmann distribution of
axion velocities, we obtain an implicit expression for the
photon growth exponent that reproduces the two asymptotic regimes and provides an approximate description of the crossover. When amplification develops on scales shorter than the
axion coherence length, the parametric resonance scaling $s\propto g_{a\gamma}$ is recovered, whereas in the opposite limit an effectively kinetic behavior with $s\propto g_{a\gamma}^2$ emerges. Although the detailed form of the crossover depends on the
axion momentum distribution, we expect the asymptotic scaling with $g_{a\gamma}$ to be largely insensitive to the specific distribution assumed.
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High Energy Astrophysical Phenomena
Uncovering the Physical Origins of Black Holes in the Milky Way for Astronomical Surveys
Ilia Kiato, Pierson Lipschultz, Vicky Kalogera et al. (+5 more)
The observational landscape of stellar-mass black holes (BHs) in the Milky Way is expanding beyond X-ray binaries, with Gaia DR4 and Roman expected to open new windows onto BH populations. We use the binary population synthesis framework POSYDON to predict the present-day Galactic BH population and connect it to its evolutionary origins. We test the robustness of these predictions to uncertainties in binary
evolution and BH formation, including core-collapse mechanisms, natal kicks, common-envelope efficiency,
metallicity, and initial binary distributions. Across our models, we find that most Galactic BHs are isolated, with stellar mergers providing the largest contribution and binary disruptions the second largest. Among surviving binaries, detached BH-BH systems dominate. We identify a distinct, narrow feature at higher BH masses ($\simeq13\,\mathrm{M}_{\odot}$ in the fiducial model) produced by wind-driven
evolution of massive Wolf-Rayet progenitors. This feature is particularly prominent among detached BH-BH binaries and persists across variations in binary-
evolution and BH-formation physics, but depends strongly on
metallicity. At lower masses, these BH-BH systems predominantly originate from progenitors that undergo stable mass transfer before BH formation. Finally, for more direct observational applications, we embed the synthetic populations in a Galactic model, evolve their kinematics, perform first-order microlensing calculations for BH-BH lenses, and examine BH systems with luminous companions in the context of the Gaia BHs. In the latter, we uncover a robust stable-mass-transfer population largely absent in rapid population-synthesis predictions. These results provide an evolutionary framework for interpreting the emerging Galactic BH population across complementary observational channels.
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All authors Ilia Kiato, Pierson Lipschultz, Vicky Kalogera, Jeff J. Andrews, Max M. Briel, Abhishek Chattaraj, Seth Gossage, Philipp M. Srivastava
Earth and Planetary Astrophysics
Detecting multiple planets in Gaia data using Bayesian model selection
Emmanuel J. Greenfield and James E. Owen
Gaia will soon provide a census of cold giant
planets. However, an astrometric signal contains the superimposed reflex motion of all companions, so planetary signals cannot be treated individually. We therefore investigate Gaia's
planet-detection capabilities for 1-
planet and 2-
planet systems, with special
attention to systems near 2:1 mean-motion resonance. Gaia can detect 2-
planet systems, although the lower-S/N
planet requires a higher S/N threshold, especially when the outer
planet is more massive and near 2:1 commensurability. When fitting a 1-
planet model to a circular 2-
planet resonant system, the resulting fit shows biases in eccentricity (up to e = 0.8), mass (up to 100%), and inclination (up to 50 deg). The bias is maximised when the
planets' astrometric signatures are similar, since the combined orbital signal deviates most from a single Keplerian orbit. Many of these systems can be identified as having 2
planets using
Bayesian model selection. Still, in some cases the second
planet is hidden and undetectable due to its S/N, leading to these biases for the outer
planet's orbital parameters. When the outer
planet is roughly over three times as massive as the inner
planet, orbital approximations allow us to recover the astrometric resoeccentric degeneracy from the bias. When the
planets are in dynamical resonance, apsidal precession observed over a long enough baseline (e.g. DR5) can contribute to breaking the degeneracy at short orbital periods. Overall, these biases might significantly affect constraints on
planet formation, migration, and
evolution models from Gaia population-wide demographics.
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Solar and Stellar Astrophysics
Unlocking new information in stellar circular polarisation with second-order least-squares deconvolution
Oleg Kochukhov
Least-squares deconvolution (LSD) is the standard technique for measuring stellar
magnetic fields from circular polarisation spectra. It rests on the weak-field approximation and yields the longitudinal field alone. We aim to extend LSD beyond the weak-field limit and interpret departures from a linear field response in terms of the field modulus. The Stokes V absorption coefficient is expanded in odd wavelength derivatives of the intensity profile, with coefficients given by the Zeeman pattern moments. Truncation after two terms gives every line a second weight, formed from the third moment of its splitting pattern, and two mean Stokes V profiles follow from multiprofile LSD. This description was tested with polarised spectrum synthesis and applied to archival spectra of two Ap
stars and two active M dwarfs. The second mean profile is proportional to the second derivative of the first, with a coefficient measuring the mean square field modulus weighted by the longitudinal flux. This observable separates field strength from the area it covers. Simulations at realistic signal-to-noise ratios show that the second component is reliably detected from about 500 G and constrains the field modulus up to several kG. Applying this methodology to the Ap
stars, we found the modulus consistent with their known field strengths, whereas for the M dwarfs it was close to the Zeeman-broadening measurements and far above the large-scale fields from Zeeman-Doppler imaging. Second-order LSD turns the breakdown of the weak-field approximation from a source of error into a new
magnetic observable, revealing for the first time the field strength in the regions emitting circular polarisation. It applies to any
star with a detectable Stokes V signature and bridges the gap between polarimetry and Zeeman broadening, most promisingly for cool active
stars in the infrared.
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Cosmology and Nongalactic Astrophysics
And Then There WEre Baryons (ATWEB): The Baryon Budget of the Universe in Halos and the IGM over 13 Billion Years of Cosmic Time
Mohammadreza Ayromlou, G. Mark Voit, Thomas H. Reiprich et al. (+2 more)
Observations of the local Universe show that, except in the most massive
galaxy clusters, the baryon fraction within
halos falls below the
cosmic mean. This deficit can be characterized using the previously established closure radius, the halocentric distance within which the enclosed baryon fraction reaches the
cosmic value. Using the TNG, EAGLE and SIMBA simulations, we examine how, when, and on what scales the baryonic and dark matter distributions diverge. At z=0 less than 30% of
cosmic baryons reside within
galaxy-hosting
halos, compared with ~45% of the dark matter, leaving over 70% of all baryons in the IGM. Building on the closure radius, we introduce three further characteristic scales: the compensation radius, closure envelope, and compensation envelope. The compensation radius marks where the enclosed total mass recovers its
gravity-only value, and today it typically lies inside the closure radius in all three models. The closure and compensation envelopes are the largest median radii across
halo mass.
Galaxy groups provide the largest contribution per dex of
halo mass to IGM enrichment with
halo-associated baryons and redistribute baryons over the largest distances. They set the closure envelope, which reaches ~2-6.5 Mpc at z=0, depending on the model. The closure radius usually increases with
cosmic time at fixed
halo mass. Tracking individual
halos, we find open baryon cycles with substantial redistribution beyond
halo boundaries across all
halo masses, while even the progenitors of today's most massive clusters fall below the
cosmic baryon fraction. The compensation envelope grows toward low
redshift, reaching ~1.5-5.5 Mpc at z=0. Across
cosmic time, it coincides with the scale on which the matter power spectrum recovers its
gravity-only form, establishing a direct link between the spatial extent of baryon redistribution and the impact of feedback on large-scale structure.
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All authors Mohammadreza Ayromlou, G. Mark Voit, Thomas H. Reiprich, Cristiano Porciani, Dominique Eckert
Astrophysics of Galaxies
Cracking open the "dragon egg": ALMA 1.3mm observations of a compact, young high-mass core candidate at 30mas resolution
A. T. Barnes, J. D. Henshaw, Á. Sánchez-Monge et al. (+14 more)
Massive prestellar cores are a central assumption of core-
accretion models of high-mass
star formation, yet convincing observational examples remain rare. The "dragon egg" (C2c1a) core in the infrared-dark cloud G028.37+00.07 has been proposed as a promising compact high-mass core candidate. We present new ALMA Band 6 observations at $0.035''$-$0.078''$ ($\sim175$-400 au at 5 kpc), providing one of the most stringent high-resolution tests of such a candidate. The region resolves into multiple fragments, but the brightest component, C2c1a(a), remains a single compact continuum peak down to $\sim175$ au, with a deconvolved radius of $\sim87$ au and a nearest neighbouring fragment at a projected separation of $\sim2400$ au. The continuum peak reaches a brightness temperature of $\sim40$ K, exceeding the $\sim10$ K gas temperatures inferred from lower-resolution NH$_3$ observations and indicating a strong radial temperature gradient. Continuum-based mass estimates range from $\sim2$ to $\sim30$ $M_\odot$ (implying extreme densities of $n_\mathrm{H2} > 10^9$cm$^{-3}$), depending on temperature, while lower-resolution data indicate a much larger mass reservoir of $\sim110$ $M_\odot$ on $\sim10^4$ au scales. The spectrum shows no strong hot-core tracers and only weak, spatially extended H$_2$CO and CO emission; no high-velocity outflow can be unambiguously associated with C2c1a(a). We conclude that C2c1a(a) is an exceptionally compact core embedded within a massive cold reservoir, with no additional compact fragments detected within the present resolution and sensitivity limits, potentially tracing the earliest formation of a central protostellar "seed" within a still-dominant reservoir. [abridged]
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All authors A. T. Barnes, J. D. Henshaw, Á. Sánchez-Monge, P. Caselli, I. Jiménez-Serra, J. E. Pineda, K. Immer, M. De Simone, R. J. Parker, F. Fontani, E. Redaelli, S. N. Longmore, L. Böhm, Q. Zhang, C. Y. Law, G. Cosentino, J. C. Tan
Instrumentation and Methods for Astrophysics
Optimal Photon Counting with Fast, Low Noise Astronomical Imagers
Jack T. Dinsmore, Christopher Layden, Roger W. Romani et al. (+9 more)
Measuring rapid astrophysical phenomena requires many short exposures, which suffer from repeated read noise. A variety of recent technologies are achieving sub-electron read noise, which enable rapid time-domain studies of faint sources. These data can be analyzed with traditional methods, but the ability to resolve individual electrons enables a new class of more precise,
photon-counting techniques. We present a
photon-counting method for sub-electron read noise detectors which delivers optimal statistical uncertainties. We focus on Complementary Metal-Oxide-
Semiconductor (CMOS) detectors and demonstrate our method on optical data collected by CMOS instrument "proto-Lightspeed," recently commissioned at the Magellan Clay
telescope at Las Campanas Observatory. The method can be applied to non-CMOS detectors as well, such as skipper CCDs and linear-mode avalanche photodiodes. The method substantially improves analysis of faint sources, increasing signal to noise ratios by up to $\sim 130\%$, which would require 5.3$\times$ more observing time to accomplish with data alone. As an example we show detections of four normal rotation-powered
pulsars with confirmed optical pulses, achieved in under two hours of total exposure. We provide the lightspeedpy pipeline for reducing proto-Lightspeed data with both
photon counting and standard techniques.
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All authors Jack T. Dinsmore, Christopher Layden, Roger W. Romani, Vera L. Berger, Kevin B. Burdge, Geoffrey Mo, Deepto Chakrabarty, Emma T. Chickles, Gabor Furesz, Juliana García-Mejía, Dave Osip, Jack Piotrowski
Earth and Planetary Astrophysics
First Direct Identification of a Multi-Star Microlens System Hosting a Planet
Sean K. Terry, David P. Bennett, Jean-Philippe Beaulieu et al. (+11 more)
Nearly 25 years have passed since gravitational microlensing delivered its first
exoplanet discoveries. The relative proper motion between lens and source systems allows them to be resolved as they separate on the sky over many years. This enables scientists to study light coming directly from the lenses and place tight constraints on the physical properties of these planetary systems. In this paper we present an analysis of high angular resolution images of the microlensing target OGLE-2006-BLG-284 using Keck adaptive optics and HST data taken more than 15 years after the event. We clearly detect the lens system and measure its motion across the Keck and HST epochs. We measure a lens-source relative proper motion of $5.80 \pm 0.15$ mas yr$^{-1}$. A combination of the light curve parameters and the host
star(s) brightnesses in $V,\, I$, and $K$ passbands gives primary and secondary host
star masses of $M_{\rm 1} = 0.43 \pm 0.05\,M_{\odot}$ and $M_{\rm 2} = 0.12 \pm 0.02\,M_{\odot}$, and a planetary companion mass of $m_p = 165^{+40}_{-33}\,M_{\oplus}$. Although we are unable to determine if the
planet orbits one or both
stars in the system, our analysis motivates next-generation high-precision RV measurements that can distinguish these two possibilities. This is the first direct detection of flux coming from a two-
star microlensing system which hosts a
planet.
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All authors Sean K. Terry, David P. Bennett, Jean-Philippe Beaulieu, T. Dex Bhadra, Aparna Bhattacharya, Joshua W. Blackman, Ian A. Bond, Andrew A. Cole, Przemek Mróz, Kansuke Nunota, Clément Ranc, Natalia E. Rektsini, Daisuke Suzuki, Aikaterini Vandorou