High Energy Astrophysical Phenomena
X-ray Observations of Nova Scorpii 2023 (V1716 Sco) in Outburst
John Worley, Marina Orio, Andrej Dobrotka et al. (+5 more)
Nova Scorpii 2023 was first detected as a luminous supersoft X-ray source (SSS) 93 days after outburst and continued emitting soft X-rays for over two months, until it was too close to the Sun to observe. The nova was monitored with the Swift X-ray
Telescope (XRT) and the
Neutron Star Interior Composition Explorer (NICER) on the International Space Station, and in long exposures with the Chandra High Resolution Camera (HRC) and Low Energy Transmission Grating (LETG) on days 128, 129, and 183-185 after optical maximum. Swift detected a rapidly decaying SSS when observations resumed, constraining the constant bolometric luminosity phase to 9 months. The SSS flux was irregularly variable. A nearly three-fold increase in flux was observed between August and October 2023 in the 15 to 35 Angstrom range, from 3.5 x 10^(-11) to 9.4 x 10^(-11) erg cm^(-2) s^(-1). The SSS duration and effective temperature derived from the October LETG spectra indicate a massive white
dwarf with temperature fitting nova evolutionary tracks for a 1.2
solar mass WD; emission lines superimposed on the WD continuum are attributed to surrounding shocked ejecta. We present a timing study based on Chandra and archival NICER data. The irregular variability timescale was days, but a 77.9 second periodic modulation in the SSS flux with varying amplitude was measured in many observations. Our analysis shows that this period was stable; short drifts derived with NICER, but not in long, uninterrupted Chandra exposures, are artifacts of measuring variable amplitude modulation. We suggest the modulations are associated with the WD rotation.
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All authors John Worley, Marina Orio, Andrej Dobrotka, Jozef Magdolen, Kim Page, Ehud Behar, Jeremy Drake, Sharon Mitrani
Astrophysics of Galaxies
The dynamics of S-stars and G-sources orbiting a supermassive compact object made of fermionic dark matter
Valentina Crespi, Carlos R. Argüelles, Eduar A. Becerra-Vergara et al. (+4 more)
Surrounding Sgr A*, a cluster of young and massive
stars coexist with a population of
dust-enshrouded objects, whose astrometric data can be used to scrutinize the nature of Sgr A*. An alternative to the black hole (BH) scenario has been recently proposed in terms of a supermassive compact object composed of self-gravitating fermionic dark matter (DM). Such horizon-less configurations can reproduce the relativistic effects measured for S2 orbit, while being part of a single continuous configuration whose extended
halo reproduces the latest
GAIA-DR3 rotation curve. In this work, we statistically compare different fermionic DM configurations aimed to fit the astrometric data of S2, and five G-sources, and compare with the BH potential when appropriate. We sample the parameter spaces via Markov Chain Monte Carlo statistics and perform a quantitative comparison estimating Bayes factors for models that share the same likelihood function. We extend previous results of the S2 and G2 orbital fits for 56 keV
fermions (low core-compactness) and show the results for 300 keV
fermions (high core-compactness). For the selected S2
dataset, the former model is slightly favoured over the latter. However, more precise S2
datasets, as obtained by the
GRAVITY instrument, remain to be analysed in light of the fermionic models. For the G-objects, no conclusive preference emerges between models. For all
stellar objects tested, the BH and fermionic models predict orbital parameters that differ by less than 1%. More accurate data, particularly from
stars closer to Sgr A*, is necessary to statistically distinguish between the models considered.
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All authors Valentina Crespi, Carlos R. Argüelles, Eduar A. Becerra-Vergara, Martín F. Mestre, Florian Peissker, Jorge A. Rueda, Remo Ruffini
Instrumentation and Methods for Astrophysics
Modeling atmospheric phase corruptions in high-frequency VLBI using Gaussian processes
Uri Rolls, Dominic W. Pesce, Paul Tiede et al. (+3 more)
Using very long baseline interferometry (VLBI) observations at (sub)millimeter wavelengths, the Event Horizon
Telescope (EHT) currently achieves the finest angular resolution of any astronomical facility, necessary for imaging the horizon-scale structure around supermassive black holes. A significant calibration challenge for high-frequency VLBI stems from rapid variations in the atmospheric water vapor content above each
telescope in the array, which induce corresponding fluctuations in the phase of the correlated signal that limit the coherent integration time and thus the achievable sensitivity. In this paper, we introduce a model that describes station-based phase corruptions jointly with a parameterization for the source structure. We adopt a Gaussian Process (GP) prescription for the time
evolution of these phase corruptions, which provides sufficient flexibility to capture even highly erratic phase behavior. The use of GPs permits the application of a Kalman filtering
algorithm for numerical marginalization of these phase corruptions, which permits efficient exploration of the remaining parameter space. Our model also removes the need to specify an arbitrary “reference station” during calibration, instead establishing a global phase zeropoint by enforcing the GPs at all stations to have fixed mean and finite variance. We validate our method using a real EHT observation of the blazar 3C 279, demonstrating that our approach yields calibration solutions that are consistent with those determined by the EHT Collaboration. The model presented here can be straightforwardly extended to incorporate frequency-dependent phase behavior, such as is relevant for the frequency phase transfer calibration technique.
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All authors Uri Rolls, Dominic W. Pesce, Paul Tiede, Lindy Blackburn, Iniyan Natarajan, Sheperd S. Doeleman
Cosmology and Nongalactic Astrophysics
Hubble tension in an anisotropic Universe
Maksym Deliyergiyev, Morgan Le Delliou and Antonino Del Popolo
We explore the Hubble tension within an anisotropic cosmological framework by revisiting the Bianchi type-I model introduced in Le Delliou et al. 2020. Motivated by ongoing debates surrounding back-reaction effects and observed anomalies in the
cosmic microwave background (CMB), we investigate whether a departure from isotropy in the late Universe could reconcile the observed discrepancies in Hubble constant measurements. Using a
Bayesian inference framework, we constrain the model parameters employing multiple nested sampling
algorithms: bilby, PyMultiNest, and nessai. We perform the analysis under both uniform and Gaussian priors, allowing us to systematically assess the sensitivity of the inferred cosmological parameters to different prior assumptions. This dual-prior strategy balances agnostic parameter exploration with constraints informed by theory and observation. Our findings demonstrate the reliability of our inference pipeline across different samplers and emphasize the crucial role of prior selection in non-standard cosmological model testing. The results suggest that anisotropic models remain viable contenders in addressing current cosmological tensions: even though the present model does not show alleviation of the Hubble tension, the data points towards anisotropies. Future work may extend this methodology to more complex anisotropic scenarios and incorporate additional cosmological probes such as CMB polarization and gravitational wave standard sirens.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Global time-frequency search for stellar-mass binary black holes in LISA
Diganta Bandopadhyay, Christian E. A. Chapman-Bird and Alberto Vecchio
We present a complete pipeline for detecting and characterizing gravitational waves (GWs) produced by the inspiral of
stellar-mass binary black holes in data from the
Laser Interferometer Space
Antenna (LISA). The analysis framework relies on an efficient time-frequency implementation of an adaptive semi-coherent detection statistic, which we show to be robust against non-stationary noise and the presence of gaps of varying duration and cadence. The search is able to detect signals with coherent signal-to-noise ratios as low as $\approx 11-14$ over the full parameter space of binary black holes with
spins aligned to the orbital angular momentum and orbital eccentricity $\le 0.01$ when deployed on the 2-year-long LISA Data Challenge Yorsh. The search can be run within a day using $\approx 40$ GPUs. The techniques presented here have wider applications in GW astronomy, in particular the search for extreme-mass-ratio inspirals in LISA data.
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Astrophysics of Galaxies
The slope and scatter of the star forming main sequence at z~5 : reconciling observations with simulations
Claudia Di Cesare, Jorryt Matthee, Rohan P. Naidu et al. (+17 more)
Galaxies exhibit a tight correlation between their
star-formation rate and
stellar mass over a wide
redshift range known as the
star-forming main sequence (SFMS). With JWST, we can now investigate the SFMS at high
redshifts down to masses of $\sim10^6$ M$_{\odot}$, using sensitive
star-formation rate tracers such as H$\alpha$ emission – which allow us to probe the variability in
star formation histories. We present inferences of the SFMS based on 316 H$\alpha$-selected
galaxies at $z\sim4$-$5$ with $\log(\rm M_\star/M_\odot) = 6.4$ -$10.6$. These
galaxies were identified behind the Abell 2744
lensing cluster with NIRCam grism spectroscopy from the “All the Little Things” (ALT) survey. At face value, our data suggest a shallow slope of the SFMS (SFR $\propto \mathrm{M}_\star^\alpha$, with $\alpha=0.45$). After correcting for the H$\alpha$-flux limited nature of our survey using a
Bayesian framework, the slope steepens to $\alpha = 0.59^{+0.10}_{-0.09}$, whereas current data on their own are inconclusive on the mass dependence of the scatter. These slopes differ significantly from the slope of $\approx1$ expected from the observed
evolution of the
galaxy stellar mass function and from simulations. When fixing the slope to $\alpha=1$, we find evidence for a decreasing intrinsic scatter with
stellar mass (from $\approx 0.5$ dex at M$_\star=10^8$ M$_\odot$ to $0.4$ dex at M$_\star=10^{10}$ M$_\odot$). This tension might be explained by a (combination of) luminosity-dependent SFR(H$\alpha$) calibration, a population of (mini)-quenched low-mass
galaxies, or underestimated
dust attenuation in high-mass
galaxies. Future deep observations across facilities can quantify these processes, enabling better insights into the variability of
star formation histories.
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All authors Claudia Di Cesare, Jorryt Matthee, Rohan P. Naidu, Alberto Torralba, Gauri Kotiwale, Ivan G. Kramarenko, Jeremy Blaizot, Joakim Rosdahl, Joel Leja, Edoardo Iani, Angela Adamo, Alba Covelo-Paz, Lukas J. Furtak, Kasper E. Heintz, Sara Mascia, Benjamín Navarrete, Pascal A. Oesch, Michael Romano, Irene Shivaei, Sandro Tacchella
Solar and Stellar Astrophysics
A very young and fast rotating shell star discovered in the eclipsing binary ZTF J200347.63+394429.8
Norbert Hauck
A photometric study in combination with existing
stellar models has revealed details of this eclipsing post-mass-transfer binary. The shell
star has an equatorial/ polar radius of ~2.60/1.90 Rsun at an equatorial rotational velocity of ~430 km s-1, an effective mean temperature Teff of ~13300 K and a mass of ~3.42 Msun. This former accretor
star is surrounded by a large decretion disk of ~47 Rsun. The secondary
star is a helium white
dwarf precursor with a radius of 0.98 Rsun, a Teff of ~17100 K and a mass of 0.29 Msun. The parameters of this former donor
star indicate an age of the binary system of only ~1.8 Myr after the end of mass transfer. The results fit to a sub-
solar metallicity of Z = 0.007.
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Astrophysics of Galaxies
Modeling the Optical Colors of Galactic Cirrus Clouds in the Stripe 82 Region
Kwang-Il Seon, Jongwan Ko, Woowon Byun et al. (+2 more)
Observations have shown that the optical colors of
Galactic cirrus clouds differ significantly from those of extragalactic sources; thus, they can be used to distinguish
Galactic cirrus from extragalactic low surface brightness (LSB) features. To understand these properties, we calculate radiative transfer models in
dust clouds, where
photons are incident from the ambient interstellar medium (ISM).
Dust clouds are modeled to mimic a turbulent medium using a fractional Brownian motion
algorithm, resulting in a lognormal density distribution and a power-law power spectral density that are appropriate for the ISM. The results are compared with optical observations of cirrus clouds in the Stripe 82 region. The observed color–color ($g-r$, $r-i$, and $i-z$) diagrams of the cirrus clouds can be reproduced by scattered light if the interstellar radiation field (ISRF) of Mathis et al. (as updated by Draine) is modified, either by reducing the intensities in the $i$ and $z$ bands or by enhancing those in the $g$ and $r$ bands. Similar results can also be obtained by adjusting the scattering albedos at the corresponding wavelengths. This demonstrates that the color–color diagrams are effective not only for identifying extragalactic LSB features but also for studying the ISRF and the properties of interstellar
dust.
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All authors Kwang-Il Seon, Jongwan Ko, Woowon Byun, Jaehyun Lee, Young-Soo Jo
High Energy Astrophysical Phenomena
Constraints on Axion-Like Particles from VERITAS Observations of a Flaring Radio Galaxy in the Perseus Cluster
C. B. Adams, A. Archer, P. Bangale et al. (+62 more)
Background:
Axion-like particles (ALPs) are hypothetical particles that emerge in numerous theoretical extensions to the Standard Model. Their coupling to electromagnetic field implies that ALPs would mix with
photons in the presence of external
magnetic fields. As ALP phenomenology is governed by the mass and strength of its coupling, there is a subset of this parameter space in which this mixing would be expected to leave an imprint on the spectra of TeV gamma-ray sources. Data: In 2017, the VERITAS gamma-ray observatory recorded the second day of a dramatic
flare of the
radio galaxy NGC 1275, embedded at the center of the Perseus
galaxy cluster. This serendipitous locale provides a spatially-extended
magnetic field of strength O(10$\mu$G) through which escaping
photons traverse, making it an excellent target to study ALPs. Methods: We analyze the VERITAS data of NGC 1275's 2017
flare with the gammapy analysis package. Extensive fitting and modeling are performed to ultimately conduct a likelihood analysis used to search for any evidence of a preference for ALPs and to explore the confidence with which constraints can be set. We adopt the CLs method for this study for its conservative approach to setting limits in regimes where the search has limited sensitivity. Results: No evidence for the existence of ALPs is found, and no combination of mass and coupling strength can be excluded at or above 95% confidence level. We provide a map showing the strength of our exclusions in the mass and coupling parameter space. The strongest exclusions are found in the mass range $2 \times 10^{-7}$eV $\lesssim m_a \lesssim 4 \times 10^{-7}$eV and at the coupling strength of $g_{a\gamma} \gtrsim 3 \times 10^{-11}$ GeV$^{-1}$ up to 80% confidence level, which are consistent with previous studies. Conclusions: We find the CLs method to be a trustworthy approach, and advocate for its...
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All authors C. B. Adams, A. Archer, P. Bangale, J. T. Bartkoske, W. Benbow, Y. Chen, J. L. Christiansen, A. J. Chromey, A. Duerr, M. Errando, M. Escobar Godoy, J. Escudero Pedrosa, S. Feldman, Q. Feng, S. Filbert, L. Fortson, A. Furniss, W. Hanlon, O. Hervet, C. E. Hinrichs, J. Holder, Z. Hughes, T. B. Humensky, M. Iskakova, W. Jin, P. Kaaret, M. Kertzman, M. Kherlakian, D. Kieda, T. K. Kleiner, N. Korzoun, F. Krennrich, S. Kumar, S. Kundu, M. J. Lang, M. Lundy, P. Moriarty, R. Mukherjee, W. Ning, R. A. Ong, A. Pandey, M. Pohl, E. Pueschel, J. Quinn, P. L. Rabinowitz, K. Ragan, P. T. Reynolds, D. Ribeiro, E. Roache, C. Rulten, I. Sadeh, L. Saha, M. Santander, G. H. Sembroski, R. Shang, D. Tak, A. K. Talluri, J. V. Tucci, J. Valverde, V. V. Vassiliev, D. A. Williams, S. L. Wong, J. Woo, T. Yoshikoshi, M. Meyer
Astrophysics of Galaxies
Resolving the Nuclear Environments of Tidal Disruption Event Host Galaxies within 45 pc
Megan Newsome, Iair Arcavi, K. Decker French et al. (+5 more)
Using HST/STIS observations, we present the highest-spatial-resolution spectroscopic study to date of four
tidal disruption event (TDE) host
galaxies, with the best observed being the post-starburst (PSB) host of ASASSN-14li. The
stellar population of ASASSN-14li's host, within 44 pc of the
nucleus, reveals a younger recent starburst ($\sim$340 Myr) compared to the population at an offset radius of 88 pc that excludes the
nucleus ($\sim$550 Myr), a radial age gradient suggesting gas inflows from a minor merger. We estimate a
stellar density of $\sim5900 \pm 800 \, M_\odot / \mathrm{pc}^3$ within 30 pc of the
nucleus of ASASSN-14li's host, exceeding densities expected for
nuclear star clusters. High-ionization “coronal" emission lines, [Fe VI] $\lambda 5677$, [Fe VII] $\lambda 6087$, and [Fe X] $\lambda 6375$, are also detected within the
nuclear spectra of the hosts of ASASSN-14li and PTF09ge, importantly alongside the non-detection of [O III] at the same scale. We similarly do not detect [O III] in the
nuclear region of ASASSN-14ae's host despite its presence in the SDSS spectrum. The different ionization radiation levels detected at various radii from TDE host
nuclei may indicate echoes of earlier
accretion episodes, including, potentially, a prior TDE. We posit that a minor merger driving gas inflow to the
nucleus could drive the enhanced TDE rates in post-starburst
galaxies, inducing variation in
nuclear gas properties and
star formation history on $<$150 pc scales in TDE hosts.
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All authors Megan Newsome, Iair Arcavi, K. Decker French, Curtis McCully, Ann Zabludoff, Nicholas Stone, Sjoert van Velzen, Tinggui Wang
Cosmology and Nongalactic Astrophysics
The Lensing Counter Narrative: An Effective Description of Small-Scale Clustering in Weak Lensing Power Spectra
Joseph DeRose and Shi-Fan Chen
We present a new formalism to separate large- and small-scale contributions to
cosmic shear through
lensing counterterms (LCT) inspired by effective field theory (EFT). Marginalizing over these LCTs isolates the large-scale cosmological signal in weak
lensing power spectra while simultaneously constraining the impact of baryonic feedback or new physics (e.g.
axion dark matter) at small scales. Our formalism removes the need for hard scale cuts in standard analyses, even when theoretical predictions are limited to below a physical cutoff $\Lambda$, resulting in significant improvements in constraining power, more than $5\times$ smaller in the case of an LSST-Y10-like analysis without marginalizing over
baryons when the analysis cutoff is set to $\Lambda = 1.0h$ Mpc$^{-1}$. We conduct a proof-of-principle analysis on the publicly available DES Y3 data, finding $S_8= 0.783\pm 0.029$ and $S_8 = 0.798\pm 0.026$ for analyses with cutoffs of $\Lambda = 0.5h$ Mpc$^{-1}$ and $1.0 h$ Mpc$^{-1}$, respectively, with no detection of modifications to small-scale clustering at $k > \Lambda$ beyond the predictions of collisionless dark matter in a $\Lambda$CDM universe. We make our JAX-based pipeline, gholax, integrated with intrinsic
alignment predictions from the EFT of large-scale structure at 1-loop, publicly available.
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Astrophysics of Galaxies
Bruno M. Celiz, Julio F. Navarro and Mario G. Abadi
We use the TNG50 cosmological hydrodynamic simulation to study the accreted
stellar component and
stellar haloes of isolated
galaxies spanning a wide range of masses ($10^8<M_*/M_\odot<10^{11}$). We find that
stars formed in the main progenitor (i.e., in-situ
stars) typically dominate the inner regions as far as $\sim$10 half-light radii from the centre, implying that detecting uncontrovertible evidence for the presence of an accreted
stellar halo requires probing the far outskirts of a
galaxy.
Stars from accreted, disrupted satellites (i.e., ex-situ
stars) dominate beyond that radius (roughly $25\%$ of the virial radius, $r_{200}$), which we identify as the inner boundary of the outer
stellar halo. The fraction of accreted
stars decreases monotonically with decreasing
galaxy mass, $M_*$, from $\sim$$20\%$ on average in $\sim$$2\times 10^{12}\, M_\odot$
haloes ($M_*\sim$$10^{11}\, M_\odot$) to $2$-$3\%$ in $\sim$$2\times 10^{10}\, M_\odot$
haloes ($M_*\sim$$10^{8}\, M_\odot$). The outer
halo has a mass comparable to roughly $10\%$ of all accreted
stars. Fewer than $\sim$$30\%$ of
stars in the outer
halo are in-situ
stars, many of which originate from
star-forming satellites during the late stages of disruption, especially in low-mass systems. Accreted
stars are systematically more metal poor in less massive systems, which makes the outer
haloes of
dwarf galaxies a fertile hunting ground for extremely metal-poor
stars. At given
galaxy mass, the more massive
stellar haloes are systematically more concentrated (smaller $R_{\rm eff}$) and have steeper density profiles (larger $n$). Our results provide a blueprint for interpreting observations of the outskirts of isolated
galaxies in terms of their assembly histories.
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Earth and Planetary Astrophysics
Eccentric discs as a gateway to giant planets outward migration
Chiara E. Scardoni, Giovanni P. Rosotti, Cathie J. Clarke et al. (+2 more)
Recent studies on
planet-dominated Type II migration demonstrated the presence of a correlation between the direction of
planet migration and the parameter K describing the depth of the planetary gap. It was found that high (low) value for K correspond to outward (inward) migration. In this paper we aim at understanding the mechanism driving inward/outward migration and why it correlates with the gap depth. We performed a suite of 2D, live-
planet, long-term simulations of massive
planets migrating in discs with the hydro-code Fargo3D. We focus on a range of
planet masses (1-13 m_J) and disc aspect ratios (0.03-0.1) and analyze the
evolution of orbital elements and gap structure. We also study the torque contributions from outer Lindblad resonances to investigate their role in the migration outcome. We find that, while all
planets initially migrate inwards, those with high enough K eventually enter a phase in which the torque reverses sign and migration becomes outwards, until eventually stalling. This behavior is associated with eccentricity growth in the outer disc and changes in the gap structure. We identify the surface density ratio at the 1:2 and 1:3 outer Lindblad resonances as a key output diagnostic that correlates with the migration direction. This ratio regulates the migration for all the cases where the massive
planet remains in an almost circular orbit and the outer gap region exhibits moderate eccentricity. This characteristic sequence of inward-reversal-outwards-stalling occurs for a variety of K values and thus further work is required to identify the simulation input parameters that determine the onset of this sequence. Our results suggest that outward migration in the
planet-dominated regime is primarily governed by the relative importance of the 1:2 and 1:3 resonances and, therefore, the gap profile plays a crucial role in determining the direction of migration.
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All authors Chiara E. Scardoni, Giovanni P. Rosotti, Cathie J. Clarke, Enrico Ragusa, Richard A. Booth
High Energy Astrophysical Phenomena
A resistive MHD module in the GPU-accelerated GRMHD code GRaM-X
Sara Azizi, Swapnil Shankar, Philipp Mösta et al. (+2 more)
Relativistic macroscopic
plasma dynamics can be described by general-relativistic magnetohydrodynamics. In many high-energy astrophysical settings, such as the interior dynamics of magnetized
stars, the ideal GRMHD approximation, in which we assume infinite conductivity, provides an excellent description. However, ideal GRMHD neglects resistive effects that are essential for processes such as
magnetic reconnection, dissipation, and magnetospheric dynamics. Incorporating resistivity into astrophysical
plasma models accounts for the fact that
plasmas in such environments are not perfect conductors. We present a resistive version of the GPU-accelerated GRMHD code GRaM-X, which evolves the full resistive GRMHD equations using the Z4c formalism for Einstein's equations. We implement a second-order implicit-explicit Runge-Kutta scheme to handle stiff source terms, obtain the primitive quantities from the conserved quantities using a one-dimensional recovery method, and employ the HLLE Riemann solver in combination with TVD and WENO reconstruction schemes. We validate the module using a range of standard tests, including 1D shocktubes, current sheets, Alfvén waves, 2D cylindrical explosions, and 3D TOV
stars. The results of these tests demonstrate accurate recovery of the ideal MHD limit, correct resistive behavior, and stable
evolution in dynamical spacetimes. Leveraging the GPU-accelerated resistive version of GRaM-X enables efficient large-scale simulations, paving the way for realistic studies of binary mergers,
accretion flows, and relativistic jets within the framework of multi-messenger astrophysics.
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All authors Sara Azizi, Swapnil Shankar, Philipp Mösta, Roland Haas, Erik Schnetter
Solar and Stellar Astrophysics
Intermediate-Mass Stripped Stars in the Magellanic Clouds: Forward Modeling the Observed Population Discovered Via UV Excess
Lisa Blomberg, Kareem El-Badry, Bethany Ludwig et al. (+2 more)
Stripped
stars are hot, helium-rich
stars formed when binary interactions remove a
star's hydrogen envelope. While low-mass ($\lesssim 1 M_\odot$) and high-mass ($\gtrsim 8 M_\odot$) stripped
stars are well studied as hot subdwarfs and Wolf-Rayet
stars, their intermediate-mass counterparts ($1-8 M_\odot$) have only recently been discovered. The Stripped-
Star Ultraviolet Magellanic Cloud Survey (SUMS) identified UV-excess sources (i.e., sources lying blueward of the main sequence) in the Magellanic Clouds using Swift-UVOT photometry and selected 820 photometric stripped-
star candidates. However, the completeness and purity of this sample remain poorly understood. We forward model the population of stripped
stars in the Magellanic Clouds using a binary population synthesis model combined with spatially resolved
star formation histories and simulated UV photometry. To assess survey sensitivity, we inject simulated sources into real Swift-UVOT images and reproduce the SUMS selection process, including crowding, extinction, and photometric quality cuts. For the SMC and LMC, we respectively recover 31% and 15% of sources with intrinsic UV excess, and $11\%$ and $7\%$ of all stripped
stars. The rest are missed due to dilution by luminous companions, crowding, high extinction, and limited survey coverage. The observed population is biased toward systems with low-mass companions formed by common envelope
evolution and systems with compact object companions. We predict contamination of the observed stripped-
star candidates by main-sequence
stars with spurious UV excess due to crowding and provide guidelines for selecting higher-purity subsamples. Our population synthesis model matches the number and properties of observed stripped
star candidates with masses of $(2-5) M_\odot$ well. It underpredicts the number of lower- and higher-mass candidates, perhaps due to contamination.
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All authors Lisa Blomberg, Kareem El-Badry, Bethany Ludwig, Maria Drout, Ylva Gotberg
Astrophysics of Galaxies
Dark Matter profiles of "in silico" galaxies: deep learning inference
Martín de los Rios, Serafina Di Gioia, Fabio Iocco et al. (+1 more)
Machine learning has the potential to improve the reconstruction of the dark matter profile of
galaxies with respect to traditional methods, like rotation curves. We demonstrate on the simulation suite Illustris-TNG that a steerable equivariant convolutional neural network (CNN) is able to infer the dark matter profiles within and around individual
galaxies from photometric and interferometric data, improving on a standard CNN. Within the in silico environment of the simulations, our architecture is able to capture the dark matter distribution within
galaxies without a parametrization of the profile. We perform an interpretability analysis to understand the internal mechanisms of the trained model and the most important data features used to estimate the dark matter profiles. The equivariant CNN recovers the dark matter profile of
galaxies within the
stellar mass range $[10^{10} - 10^{12} ]$ $M_{\odot}$ with excellent precision and accuracy: the mean squared error is reduced by a factor of ~ 3 from its value under the training distribution, demonstrating that the network has learnt from the data features. While this holds within the controlled 'in silico' environment of the simulation, we argue that few additional steps are needed before this method can be reliably applied to
galaxies in the real field observations.
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All authors Martín de los Rios, Serafina Di Gioia, Fabio Iocco, Roberto Trotta
Solar and Stellar Astrophysics
A spectral library and census of near-infrared stellar large-amplitude variables from Palomar Gattini-IR
Nicholas Earley, Viraj Karambelkar, Mansi Kasliwal et al. (+9 more)
We present a near-infrared census of
stellar large-amplitude variables (LAVs) observed by the Palomar Gattini-IR (PGIR) surveyor from 2019-2021. Over the three-year time period, PGIR performed a brightness-limited survey of the Northern sky (18,000 sq. deg) to J-band AB magnitudes of $\sim 13$ within and $\sim 15$ outside the
Galactic plane. From 70 million
stars detected in PGIR reference images, we provide a spectral and photometric library of the 128 largest amplitude
stellar variables detected to median SNR > 10 for more than 50 epochs with more than 5 high-amplitude detections, peak-to-peak magnitudes $\geq$ 2, and von Neumann ratios $\leq$ 0.2. We obtained medium-resolution near-infrared spectra with TripleSpec on the 200-inch Hale
Telescope at Palomar Observatory and SpeX at NASA's Infrared
Telescope Facility. The spectral census consists of 82 evolved and
dust-obscured Asymptotic
Giant Branch
stars, 16 R Coronae Borealis
stars, 13 young-
stellar or pre-main-sequence objects, 8 symbiotic binaries, 7 erratic carbon- and oxygen-rich
giants, and 2 RV Tauri supergiants. The spectral and photometric
dataset serves as an atlas of near-infrared LAVs and a repository of evolved
stars, eruptive variables, and binary systems for future deeper infrared surveys.
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All authors Nicholas Earley, Viraj Karambelkar, Mansi Kasliwal, Kishalay De, Lynne Hillenbrand, Roberto Soria, Aswin Suresh, Michael C. B. Ashley, Matthew J. Hankins, Anna M. Moore, Jamie Soon, Tony Travouillon
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Sensitivity forecasts for gravitational-wave detectors to dark matter decaying into gravitons
Jose A. R. Cembranos and Álvaro Cendal
Dark matter may not be perfectly stable, and its decay could generate distinctive gravitational-wave signatures. In this work, we present model-independent predictions for the
stochastic gravitational-wave background arising from the decay of ultralight dark matter into gravitons. Within this framework, we forecast the sensitivity reach of current and forthcoming gravitational-wave detectors to such signals.
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Astrophysics of Galaxies
Galaxy Activity, Torus and Outflow Survey (GATOS) X: Molecular gas clumpiness under the influence of AGN
Federico Esposito, Almudena Alonso-Herrero, Santiago García-Burillo et al. (+27 more)
The distribution of molecular gas on small scales regulates
star formation and the growth of supermassive black holes in
galaxy centers, yet the role of active
galactic nuclei (AGN) feedback in shaping this distribution remains poorly constrained. We investigate how AGN influence the small-scale structure of molecular gas in
galaxy centers, by measuring the clumpiness of CO(3 - 2) emission observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in the
nuclear regions (50 - 200 pc from the AGN) of 16 nearby Seyfert
galaxies from the
Galaxy Activity,
Torus, and
Outflow Survey (GATOS). To quantify clumpiness, we apply three different methods: (1) the median of the pixel-by-pixel contrast between the original and smoothed maps; (2) the ratio of the total excess flux to the total flux, after substracting the background smoothed emission; and (3) the fraction of total flux coming from clumpy regions, interpreted as the mass fraction in clumps. We find a negative correlation between molecular gas clumpiness and AGN X-ray luminosity (L_X), suggesting that higher AGN activity is associated with smoother gas distributions. All methods reveal a turnover in this relation around L_X = 10^{42} erg/s, possibly indicating a threshold above which AGN feedback becomes efficient at dispersing dense molecular structures and suppressing future
star formation. Our findings provide new observational evidence that AGN feedback can smooth out dense gas structures in
galaxy centers.
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All authors Federico Esposito, Almudena Alonso-Herrero, Santiago García-Burillo, Ismael García-Bernete, Françoise Combes, Richard Davies, Enrique Lopez-Rodriguez, Omaira González-Martín, Cristina Ramos Almeida, Anelise Audibert, Erin K. S. Hicks, Miguel Querejeta, Claudio Ricci, Enrica Bellocchi, Peter Boorman, Andrew J. Bunker, Steph Campbell, Daniel E. Delaney, Tanio Díaz-Santos, Donaji Esparza-Arredondo, Sebastian Hönig, Álvaro Labiano Ortega, Nancy A. Levenson, Chris Packham, Miguel Pereira-Santaella, Rogemar A. Riffel, Dimitra Rigopoulou, David J. Rosario, Antonio Usero, Lulu Zhang
Earth and Planetary Astrophysics
Intruder Alert: Breaking Resonant Chains with Planetesimal Flybys
Jiaru Li, Christopher E. O'Connor and Frederic A. Rasio
The orbital architectures of compact
exoplanet systems record their complicated dynamical histories. Recent research supports the “breaking-the-chains” hypothesis, which proposes that compact systems typically form in chains of mean-motion resonances (MMRs) but subsequently break out on a $\sim 100$Myr timescale. We investigate a scenario for breaking the chains through intermittent flybys of planetesimals originating from a distant reservoir. Using $N$-body simulations and semi-analytical calculations, we characterize the disruption of MMRs through these flybys. We find a planetesimal reservoir of total mass $\gtrsim 0.04 M_{\oplus}$ is required to disrupt MMR chains, depending on the mass distribution and the typical number of flybys executed by each planetesimal. We verify that systems disrupted in this way are frequently unstable to close encounters within $\sim 100$Myr of the final flyby. This mechanism operates in systems with both a sufficiently massive reservoir and an efficient mechanism for planetesimal injection. Consequently, we predict an anti-correlation between resonant inner systems and dynamically active outer configurations.
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Astrophysics of Galaxies
The THESAN project: Lyman-alpha emitters as probes of ionized bubble sizes
Meredith Neyer, Aaron Smith, Mark Vogelsberger et al. (+4 more)
We use the THESAN radiation-hydrodynamics simulations to investigate how Lyman-$\alpha$ emitters (LAEs) trace ionized bubble sizes during the Epoch of Reionization. We generate realistic LAE catalogs by combining accurate intrinsic Ly$\alpha$ production and intergalactic transmission with an empirical model for
dust absorption and gas
outflows. By calibrating to observationally-constrained Ly$\alpha$ luminosity functions, we reproduce the rapid decline in Ly$\alpha$ visibility toward higher
redshifts while revealing mild tensions in LAE fractions near the end of reionization. Before the midpoint of reionization,
galaxies within larger line-of-sight bubbles ($\gtrsim 10$ cMpc) have higher observed Ly$\alpha$ luminosity and equivalent width (EW), demonstrating that the evolving LAE fraction provides a practical statistical tracer for bubble size. These correlations weaken as percolation progresses and the IGM becomes increasingly ionized. In LAE selected samples with $L_{\text{Ly}\alpha} > 10^{41.5}\ \text{erg s}^{-1}$, Ly$\alpha$ properties correlate with bubble size more strongly than UV magnitude, especially at $z \gtrsim 7$. This simulation-based framework maps LAE selections to bubble-size statistics, clarifies biases in more idealized models, and will supply public catalogs to interpret current and forthcoming JWST and narrow-band LAE surveys in terms of the evolving
topology of reionization.
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All authors Meredith Neyer, Aaron Smith, Mark Vogelsberger, Luz Ángela García, Rahul Kannan, Enrico Garaldi, Laura Keating
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Axion Production and Detection Using a Dual NMR-type Experiment
Jeff A. Dror, Qiushi Wei and Fengwei Yang
Axions that couple to
nuclear spins via the axial current interaction can be both produced and detected using
nuclear magnetic resonance (NMR) techniques. In this scheme,
nuclei driven by a real oscillating
magnetic field in one device act as an
axion source, which can drive NMR in a nearby
spin-polarized sample interrogated with a sensitive magnetometer. We study the prospects for detecting
axions through this method and identify two key characteristics that result in compelling detection sensitivity. First, the gradient of the generated
axion field can be substantial, set by the inverse distance from the source. Near the source, it reduces to the inverse of the source's
geometric size. Second, because the generated
axion field is produced at a known frequency, the detection medium can be tuned precisely to this frequency, enabling long interrogation times. We show that the experimental sensitivity of a pair of centimeter-scale NMR devices operating over a 15-day integration time can already surpass existing astrophysical bounds on the
axion-nucleon coupling. A similar sensitivity can be achieved with 10 centimeter-scale NMR devices with only 1 hour of integration time. These dual NMR configurations are capable of probing a wide range of
axion masses, up to values comparable to the inverse distance between the source and the sensor.
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Astrophysics of Galaxies
Woong-Bae G. Zee, S. Lyla Jung, Sanjaya Paudel et al. (+1 more)
Galactic warps are common in disk
galaxies. While often attributed to
galaxy–
galaxy tides, a non-spherical dark matter (DM)
halo has also been proposed as a driver of disk warping. We investigate links among warp morphology, satellite distribution, and large-scale structure using the Sloan Digital Sky Survey catalog of warped disks compiled by Zee et al.\ (2022). Warps are classified into 244 S and 127 U types, hosting 1,373 and 740 satellites, respectively, and are compared to an unwarped control matched in
stellar mass,
redshift, and local density. As an indirect, population-level proxy for the host
halo's shape and orientation, we analyze the stacked spatial distribution of satellites. Warped hosts show a significant anisotropy: an excess at $45^{\circ}<\phi<90^{\circ}$ (measured from the host major axis), peaking at $P(\phi)\simeq 0.003$, versus nearly isotropic controls. Satellites of S-type warps preferentially align with the nearest
cosmic filament, whereas those of U-type warps are more often perpendicular. The incidence of warps increases toward filaments ($r_{\rm fil}<4,{\rm Mpc},h^{-1}$), while the number of satellites around warped hosts remains approximately constant with filament distance, indicating a direct influence of the large-scale environment. We discuss possible links between
galactic warps and the
cosmic web, including anisotropic
tidal fields and differences in evolutionary stage.
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All authors Woong-Bae G. Zee, S. Lyla Jung, Sanjaya Paudel, Suk-Jin Yoon
Astrophysics of Galaxies
Living with Neighbors. VI. Unraveling the Dual Impact of Bars on Star Formation in Paired Galaxies Using DESI
Woong-Bae G. Zee and Suk-Jin Yoon
We present a comprehensive investigation into the influence of
stellar bars on
star formation (SF) in
galaxy pairs, using a large sample of low-
redshift galaxies ($0.02$\,$<$\,z\,$<$\,$0.08$) from the DESI Legacy Imaging Surveys DR8. Our analysis examines whether bars enhance or suppress SF during pair interactions, and how these outcomes depend on the
star-forming properties of companion
galaxies. We find that bars either catalyze or inhibit SF in their host
galaxies, depending on the companion's SF activity. In particular, barred
galaxies paired with actively
star-forming companions experience more pronounced central starbursts (with sSFR up to $\sim$\,2.5 dex higher) than unbarred counterparts, whereas those with passive companions often have suppressed SF (sometimes below isolated
galaxy levels). The notion of the dual role of bars can reconcile conventional conflicting reports of bar-driven enhancement versus quenching of SF activity. Bars, well known to regulate kpc-scale dynamics, may also link to the impact of external environments: when a
star-forming companion provides sufficient gas, bars drive central starbursts, whereas in gas-poor interactions, bars hasten gas depletion and contribute to SF suppression. This work highlights the necessity of accounting for both internal structure and companion properties to fully understand SF regulation in interacting
galaxies.
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Instrumentation and Methods for Astrophysics
Very High Precision Astrometry for Exoplanets and Dark Matter with the Habitable Worlds Observatory
Fabien Malbet, J. Amiaux, F. Ardellier-Desages et al. (+19 more)
Astrometry, one of the oldest branches of astronomy, has been revolutionized by missions like Hipparcos and especially
Gaia, which mapped billions of
stars with extraordinary precision. However, challenges such as detecting Earth-like
exoplanets in nearby habitable zones and probing the influence of dark matter in
galactic environments require sub-microarcsecond accuracy. With a 6–8 meter large-aperture
telescope operating across at visible wavelengths, the Habitable Worlds Observatory by NASA can combine astrometry and direct imaging to detect rocky
exoplanets within 10 parsecs and study their atmospheres. We consider here the scientific requirements and present a concept for a dedicated astrometric instrument on HWO. It is capable to produce diffraction-limited images of large fields, achieving a point-spread function (PSF) precision of 20 milliarcseconds. Equipped with a detector calibration system, HWO can perform high precision astrometry, and, detect and measure the orbit of Earth-mass
planets in the habitable zone of Nearby
Solar-type
stars. HWO can dramatically improve current constraints on the self- interaction cross-section of heavy dark matter particles (WIMPs) and on the masses of ultra-high dark matter particles, through the study of
stellar motions in
galactic environments. The visible channel of the instrument features a large CMOS-based focal plane with stitched pixel arrays, enabling a large field of view. The “Detector Calibration Unit” system uses interferometric
laser fringes to calibrate pixel positions. Using differential astrometry and pointed observations with a stable
telescope design enables extended integration times, enhancing sensitivity to sub-microarcsecond precision for detecting
exoplanets and studying dark matter through
stellar motion.
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All authors Fabien Malbet, J. Amiaux, F. Ardellier-Desages, E. Doumayrou, P.-A. Frugier, R. Goullioud, T. Greene, L. Labadie, P.-O. Lagage, M. Lizzana, A. Léger, T. Lépine, G. Mamon, J. Martignac, F. Pancher, T. Pichon, A. Roberge, S. Ronayette, H. Rousset, S. Soler, A. Sozzetti, T. Tourette
Cosmology and Nongalactic Astrophysics
$B$-sure I: Minkowski functionals as robustness test for tensor-to-scalar ratio detection from CMB observations
Claudio Ranucci, Alessandro Carones, Léo Vacher et al. (+2 more)
The detection of
primordial $B$-mode polarisation of the
Cosmic Microwave Background (CMB) is a major observational goal in modern Cosmology, offering a potential window into inflationary physics through the measurement of the tensor-to-scalar ratio $r$. However, the presence of
Galactic foregrounds poses significant challenges, possibly biasing the $r$ estimate. In this study we explore the viability of using Minkowski functionals (MFs) as a robustness test to validate a potential $r$ detection by identifying non-Gaussian features associated with foregrounds contamination. To do so, we simulate sky maps as observed by a LiteBIRD-like CMB experiment, with realistic instrumental and foregrounds modelling. The CMB $B$-mode signal is recovered through blind component separation
algorithms, and the obtained (biased) value of $r$ is used to generate Gaussian realisation of CMB signal. Their MFs are then compared with those computed on maps contaminated by foreground residual left by component separation, looking for a detection of non-Gaussianity. Our results demonstrate that, with the experimental configuration considered here, MFs can not be reliably adopted as a robustness test of an eventual $r$ detection, as we find that in the majority of the cases MFs are not able to raise significant warnings about the non-Gaussianity induced by the presence of foreground residuals. In the most realistic and refined scenario we adopted, the test is able to flag non-Gaussianity in $\sim 26\%$ of the simulations, meaning that there is no warning on the biased tensor-to-scalar ratio in $\sim 74\%$ of cases. These results suggest that more advanced statistics than MFs must be considered to look for non-Gaussian signatures of foregrounds, in order to be able to perform reliable null tests in future CMB missions.
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All authors Claudio Ranucci, Alessandro Carones, Léo Vacher, Nicoletta Krachmalnicoff, Carlo Baccigalupi
High Energy Astrophysical Phenomena
Reexamining Evidence of a Pair-Instability Mass Gap in the Binary Black Hole Population
Anarya Ray and Vicky Kalogera
The fourth gravitational wave transient catalog~(GWTC-4) has enabled empirical probes of the theorized pair-instability gap in the higher end of the binary black hole~(BBH) mass-spectrum. In this letter, using flexibly parametrized models, we show that at present there is no evidence of a sharp drop-off in the spectrum of black hole masses near $~40-50M_{\odot}$. We simultaneously characterize the transition in the distribution of BBH mass-ratios, effective aligned and effective precessing
spins using our flexible models. From the transitions in our inferred
spin and mass-ratio distributions, we find that the high-mass broad-
spin sub-population has a significant fraction~($52^{+18}_{-23}\%$) of systems with mass ratios in the range $0.6-1$. This suggests that alternatives to the hypothesis of 2G+1G hierarchical systems dominating BBH formation above $\sim 40-50 M_{\odot}$ are more consistent with the GWTC-4 detection sample. By comparing with the predictions of
star cluster simulations, we further show that contributions from (2G+2G) systems are not abundant enough to alleviate this discrepancy. We also demonstrate the effects of strong model assumptions on this inference, which can lead to biased astrophysical interpretation from restricted priors. We note that our results do not exclude that a high-mass gap may be identified as our sample size increases. We constrain the lower bound on the location of a possible PISN cutoff still allowed within measurement uncertainties to be $(57^{+17}_{-10}M_{\odot})$ and discuss its implications on the S factor of $^{12}\mathrm{C}(\alpha, \gamma)^{16}O$ at 300 kev.
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High Energy Astrophysical Phenomena
AT2025ulz and S250818k: zooming in with the Hubble Space Telescope
Yu-Han Yang, Eleonora Troja, Marko Ristić et al. (+19 more)
AT2025ulz is an optical/near-infrared transient discovered during follow-up of the candidate gravitational wave (GW) event S250818k. Its young age ($\lesssim$1 d), rapid decline and strong color
evolution over the first 48 hr classify it as a potential kilonova candidate. In this work, we present the results of our observing campaign, carried out with the Gran Telescopio Canarias (GTC) and the Hubble Space
Telescope (HST). Although the early time
evolution of AT2025ulz resembles some aspects of a kilonova, its rapid onset ($\sim$3 hr after the GW trigger) and luminosity (a factor of $\sim5$ brighter than AT2017gfo in $g$-band) are difficult to reproduce. Only a small subset of our kilonova models matches its multi-color light curve, and the inferred ejecta mass is uncomfortably large given the low chirp mass ($\lesssim\!0.87\!$ M$_{\odot}$) of the GW candidate. HST observations place the transient within a nearby ($z=0.08489$) spiral
galaxy with on-going
star-formation and measure a color ($F336W-F160W\!\approx\!1.4$ mag) that is too blue to match with a kilonova. Our data support the classification of AT2025ulz as a
supernova, initially undergoing a shock-cooling phase and later entering its photospheric phase, and spectroscopically identified via its broad absorption features.
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All authors Yu-Han Yang, Eleonora Troja, Marko Ristić, Muskan Yadav, Massine El Kabir, Rubén Sánchez-Ramírez, Rosa L. Becerra, Chris L. Fryer, Brendan O'Connor, Simone Dichiara, Alberto J. Castro-Tirado, Camila Angulo-Valdez, Josefa Becerra González, José A. Font, Ori Fox, Lei Hu, Youdong Hu, William H. Lee, Margarita Pereyra, Alicia M. Sintes, Alan M. Watson, K. Océlotl C. López Mendoza
Earth and Planetary Astrophysics · Cross-listed from physics.hist-ph
The simplest complexity: The story of the three-body problem
Barak Kol
This article offers a broad-brush account of the Newtonian three-body problem, from its origins with Newton to its vibrant present, emphasizing its enduring influence on theoretical physics. It unfolds through a series of self-contained episodes that illuminate the scientific fields and the paradigm shift that have grown out of this problem.
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Earth and Planetary Astrophysics
Ever Elusive Exospheres: One Probable Detection and Two Non-Detections of H{\alpha} Transits in Young Systems
Reilly P. Milburn, Andrew W. Mann, Keighley Rockcliffe et al. (+5 more)
Gaps in the
exoplanet population, such as the Neptunian Desert, point to the importance of mass-loss in sculpting the radii of close-in
exoplanets. Young
planets ($<$500Myr) offer the opportunity to detect such mass-loss while it is still strong, and to test models of the underlying physical processes. We search for evidence of an H$\alpha$ transit in high-resolution spectra of three young
planets, HD 63433b (400 Myr), DS TucAb (45 Myr), and HIP 67522b (17 Myr) using HARPS-N, Magellan-PFS, and CHIRON respectively. We validate our method by testing it on several photospheric lines less impacted by
stellar variability. We find no evidence of a transit signal for HD 63433b and DS Tuc A b (3$\sigma$ limits of 0.9% and 0.3%, respectively). For HIP 67522b, we detect significant excess absorption (3.44$\pm$0.28%) aligned with the transit time, narrow compared to the
stellar line, and blueshifted from the
stellar rest frame. In combination, these suggest the signal is from the
planet. However,
stellar variation in the H$\alpha$ line over the course of the observations is comparable in size to the transit signature and the duration is shorter than the photometric transit, so this detection requires confirmation. Our findings, and other recent results in the literature, suggest that
planets younger than 50 Myr are more favorable for the detection of atmospheric escape with H$\alpha$ observations, though older populations might still show escape in other diagnostics.
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All authors Reilly P. Milburn, Andrew W. Mann, Keighley Rockcliffe, Erin E. Flowers, Alexis Heitzmann, Benjamin T. Montet, George Zhou, Madyson G. Barber