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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 12 August

Solar and Stellar Astrophysics

A Helium-shell Burning Blue Horizontal Branch Star Produced from Common Envelope Evolution

Jiao Li, Changqing Luo, Hai-Liang Chen et al. (+16 more)

Observationally, blue horizontal branch (BHB) stars are defined as hot stars occupying a characteristic region between the extreme blue horizontal branch and RR Lyrae variables in the Hertzsprung-Russell diagram. Most of them are interpreted as stripped core-helium-burning stars, but the role of binary interaction in their formation remains unclear. Here, we report the discovery of a metal-rich BHB star in a 0.82628-day binary system (Feige 64) comprising a $0.35\pm0.03\,M_{\odot}$ BHB star and a likely $1.26\pm0.17\,M_{\odot}$ white dwarf (WD). The BHB star has an effective temperature of $15{,}524\pm310$ K and a luminosity of $39.7\pm4.1\,L_{\odot}$. Stellar evolution modelling indicates that it is a helium-shell-burning star produced through the common-envelope channel, retaining a hydrogen-rich envelope that is more massive than previously thought for low-mass stars. This finding provides direct evidence for binary interaction in the formation of BHB stars, offering a fresh perspective on interpreting this emerging population.
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All authors Jiao Li, Changqing Luo, Hai-Liang Chen, Zhicun Liu, Bo Zhang, Shi Jia, Hongwei Ge, Tao Wu, Yuhan Yao, Pei Wang, Marat Gilfanov, You Wu, Zhenwei Li, Zhengwei Liu, Xiangcun Meng, Xue-Fei Chen, Philipp Podsiadlowski, Chao Liu, Zhan-Wen Han

Tuesday 11 August

Astrophysics of Galaxies

Deuteration of Organic Molecules as a Probe of Starless Core and Filament Evolution in Barnard 10

Hanga Andras-Letanovszky, Yancy L. Shirley, Lucille J. Steffes et al. (+4 more)

The deuterium fractionation of molecules in starless cores is sensitive to their dynamical histories, which recent magnetohydrodynamical simulations have shown to be extremely varied. The deuterated isotopologues of formaldehyde (H$_2$CO) and methanol (CH$_3$OH) probe deuterium fractionation in simple organic molecules. This complete survey targets 11 low-mass starless cores in the small, quiescent Barnard 10 (B10) region of the Taurus Molecular Cloud. The cores were observed using the 12m Arizona Radio Observatory telescope with a 100% detection rate in transitions of o/pH$_2$CO, HDCO, pD$_2$CO, A/E-CH$_3$OH, and CH$_2$DOH and the dense gas tracer N$_2$H$^+$. The HDCO and pD$_2$CO column densities and deuterium fractions are not correlated with those of the grain-surface deuteration tracer CH$_2$DOH, indicating significant gas-phase formation of deuterated formaldehyde. The observed deuterium fractions do not correlate with evolutionary indicators (e.g. core central density) or physical conditions (e.g. core mass). We also find that cores within the northwestern filament have lower deuterium fractions than cores of similar densities in the other two filaments. These could indicate differential core evolution both between and within entire filaments. Comparing the deuterium fractions of the B10 sample to published sources across different evolutionary stages suggests the inheritance of D$_2$CO from starless cores, although more surveys of organic deuteration are needed to conclusively determine inheritance.
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All authors Hanga Andras-Letanovszky, Yancy L. Shirley, Lucille J. Steffes, Brian Svoboda, Hannah Gruber, Samantha Scibelli, Emma Vertachnik

Astrophysics of Galaxies · Cross-listed from gr-qc

Effects of Quantum Spin-Connection Foam in the Solar System, Galaxies, and the Universe

Igor V. Kanatchikov and Valery A. Kholodnyi

We argue that effects of the quantum spin-connection foam, which describes quantum gravity according to the precanonical quantization of General Relativity, may already be observed in the form of the small cosmological constant and a modification of Newtonian dynamics at small accelerations, manifested in the flat rotation curves of galaxies. We obtain a modification of the Newtonian potential that takes into account the existence of a fundamental small acceleration scale, $a_* = 8\pi G\hbar\varkappa$, where $\varkappa$ is a parameter with the dimensions of inverse spatial volume that appears on dimensional grounds. The connection between $\varkappa$ and the hadronic scale of the mass gap in the pure Yang-Mills sector of the Standard Model leads to an estimated value of $a_*$ compatible with the Milgromian acceleration scale in MOND. The connection between $a_*^2$ and the cosmological constant leads to a realistic value of the latter. Milgromian MOND, together with a theoretically distinct interpolating function, is derived under the assumption that classical dynamics is modified by the mean-field acceleration calculated from the simplest solution of precanonical quantum gravity in the nonrelativistic approximation. We also indicate that the effects of Newtonian dynamics modified by the spin-connection foam may be observable in the Solar System and even in laboratory experiments.
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2608.12404 · 11 Aug · 17 pages. To appear in: The Seventeenth Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Astrophysics, and Relativistic Field Theories, Pescara 7-12 July 2024, edited by G. Vereshchagin and R. Ruffini, https://doi.org/10.1142/14814, October 2026. Corrects typos in eqs (26), (29) in the published version, adds refs [64-66]

Abstract PDF $QNTM ×4$SPIN ×3$GLXY ×2$GRAV ×2 +1

Astrophysics of Galaxies

Chemistry here and there: Comparison between the CMZ of the Milky Way and NGC 253

Sergio Martín, Álvaro López-Gallifa, David San Andrés et al. (+2 more)

For decades, chemical studies in external galaxies have been limited by sensitivity, resolution, bandwidth or a combination of them. A decade of ALMA operations, made the detailed study of the molecular abundances in nearby galaxies a routine job. We can finally bridge the ISM chemistry from Galactic to extragalactic environments, through one to one comparison, albeit probing significantly different scales. The ALMA large program ALCHEMI imaged the chemistry of the starburst galaxy NGC 253 at an unprecedented combination of sensitivity and resolution, achieving a detailed spatially resolved chemical inventory. ALCHEMI probed molecular differences among regions within its CMZ, and allowed the comparison with Galactic environments ranging from hot cores, quiescent molecular clouds and comets. This comparison can be put in the context of available data towards other extragalactic environments. Globally, the comparisons presented here show an astoundingly good correlation between the chemistry in Galactic GMCs and the central molecular zone of NGC 253, ranging scales from 1 pc up to ~0.5 kpc. The wideband sensitivity upgrade of ALMA will expand similar comparisons towards a wider range of Galactic and extragalactic objects.
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All authors Sergio Martín, Álvaro López-Gallifa, David San Andrés, Victor Rivilla, ALCHEMI Collaboration

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Torsional pseudo-inflation beyond Einstein-Cartan

Fernando Izaurieta, Samuel Lepe and Cristian Quinzacara

Torsion entered early-universe cosmology twice: through the nonsingular Einstein–Cartan bounce, where the quantum spin of fermions halts the contraction, and through the proposal that the expansion following that bounce could take over the duties of cosmic inflation. We revisit the second idea in a constructive spirit. First we compute its budget: for a Weyssenhoff spin fluid with barotropic source, $w\in\left[0,1\right]$, the accelerated window that follows the bounce spans $N_e=\ln\left[4/\left(1+3w\right)\right]/3\left(1-w\right)\leq\tfrac{1}{3}\ln4\simeq0.46$ e-folds, and positive spatial curvature only shrinks it. The mechanism is sound; its torsional “fuel” dilutes as $a^{-6}$, and the engine stops two orders of magnitude short of inflationary needs. We then ask what torsion would need in order to sustain a quasi-de Sitter phase, and give a two-branch answer in Riemann–Cartan cosmology with nonminimal couplings, where torsion is fed by the couplings rather than by spin. The vectorial branch reproduces Palatini inflation, observationally alive. On the axial branch we exhibit an exact de Sitter solution sustained by a torsion condensate: constant axial torsion $f_{0}$, a linear Gauss–Bonnet coupling, and a potential fixed to $V_{0}=6f_{0}^{2}+\tfrac{5}{2}v^{2}$ by the Friedmann constraint. The solution is an attractor of the homogeneous dynamics, with eigenvalue exactly $-3H$. The phase ends when the slope $U^{\prime}$, a decreasing function of the roll speed at fixed flat potential, drifts down to the floor $5/16V_{0}$ and the condensate switches itself off; consistency of the effective theory pins the whole episode near the Planck scale, $H\gtrsim0.3$ in reduced Planck units. We studied this branch at background level; its perturbation spectrum remains open.
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Solar and Stellar Astrophysics

Numerous bow shocks in the outer Helix Nebula

Pieter van Dokkum, Roberto Abraham, William P. Bowman et al. (+5 more)

Near the end of their lives, low- and intermediate-mass stars expel metal-enriched material in winds and outflows, ultimately producing planetary nebulae (PNe). The ejected material is expected to fragment and mix into the interstellar medium (ISM), but this final assimilation step has been difficult to observe directly. Here we report evidence for this process in the form of twenty-two bow shocks in the eastern outskirts of the Helix Nebula, detected in H$\alpha$ emission with the partially completed MOTHRA telescope. Unlike the large-scale wind-ISM bow shocks commonly observed around evolved stars, the shocks are compact and associated with individual clumps of gas. Going outward from the central star, the radius of curvature $R_c$ decreases by a factor of ~100 over the radial range r=0.4-1.4 pc. This is accompanied by a morphological transition from thin, well-defined bows to fuzzy, patchy structures. We interpret these changes as progressive stripping and fragmentation of AGB-shell remnants as they interact with the ISM. The slope of the observed $R_c - r$ relation implies a loss of fragment coherence on a timescale of ~10,000 yr, providing a rare direct constraint on the time-scale for disruption and entrainment of fragmented stellar ejecta into the ISM.
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All authors Pieter van Dokkum, Roberto Abraham, William P. Bowman, Seery Chen, Steven R. Janssens, Deborah M. Lokhorst, Imad Pasha, Carter Rhea

Solar and Stellar Astrophysics

Diameters and Temperatures VII: High-angular resolution measurements of Solar-type stars with the CHARA Array

Tabetha S. Boyajian, Ashley A. Elliott, Emelly D. Tiburcio et al. (+8 more)

We present interferometric measurements of angular diameters for 27 nearby solar-type stars obtained with the Precision Astronomical Visible Observations (PAVO) beam combiner at the CHARA Array. The sample spans a broad range of metallicities, includes several known exoplanet hosts, and covers evolutionary stages from the zero-age main sequence to mildly evolved subgiants. Uniform-disk and limb-darkened angular diameters were measured for each target and combined with bolometric fluxes and Gaia parallaxes to determine precise, model-independent stellar radii, effective temperatures, and luminosities. We achieve typical uncertainties of $\sim1$% in radius and $\sim1.5$% in effective temperature. Comparisons with multiple stellar evolutionary model grids yield mass and age estimates and enable assessment of grid-to-grid systematics, highlighting sensitivities to abundances, evolutionary stage, and proximity to grid boundaries. Our results provide empirical benchmarks for testing stellar evolutionary theory, refining surface brightness-color relations, and improving the characterization of exoplanet host stars.
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All authors Tabetha S. Boyajian, Ashley A. Elliott, Emelly D. Tiburcio, Kaspar von Braun, Gail Schaefer, Timothy R. White, Daniel Huber, Michael Ireland, Jeremy Jones, Tyler Ellis, Eliot Hiegel

Solar and Stellar Astrophysics

Solar-Cycle Modulation and Photospheric Magnetic Control of Turbulence in the Young Solar Wind

Yanwen Wang, Rohit Chhiber, Arcadi V. Usmanov et al. (+2 more)

The solar wind is an outflow of solar plasma that expands from the corona to fill the heliosphere. Its turbulence provides a pathway for non-adiabatic heating and acceleration, and is therefore central to understanding the thermodynamic and magnetohydrodynamic (MHD) evolution of the young solar wind. However, the variation of its turbulence properties over the solar activity cycle and the connection of these properties to solar source regions remains incompletely understood. Here we analyze observations from 25 solar orbits of NASA's Parker Solar Probe (PSP) mission, in combination with a global MHD model, photospheric magnetograms, and extreme ultraviolet maps of the low corona, to investigate the solar-cycle dependence and the solar sources of turbulence in the very inner heliosphere. The observations reveal pronounced solar-activity variation in fluctuation amplitude, cross helicity, and related turbulence properties. By tracing PSP-connected magnetic flux tubes to their solar sources, we demonstrate that high turbulent-energy intervals are preferentially connected to coronal-hole sources with unipolar magnetic topology, whereas low turbulent-energy intervals are associated with multipolar topology and active-region environments. Our study combines in-situ measurements with numerical modeling and remote sensing observations to reveal how solar-cycle-dependent source structure determines turbulence variability and plasma heating in the young solar wind.
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All authors Yanwen Wang, Rohit Chhiber, Arcadi V. Usmanov, Marc Swisdak, William H. Matthaeus

Astrophysics of Galaxies

Magnetic fields in extreme primordial halos: turbulent collapse and implications for early quasar formation

V.B. Díaz, D.R.G. Schleicher, M.A. Latif et al. (+1 more)

It is sometimes suggested that the most massive quasars at high redshift may have formed from rare high-sigma peaks in the cosmic density field. We explore here the evolution in a massive primordial halo corresponding to one of these rare sigma peaks, employing cosmological high-resolution magneto-hydrodynamical zoom-in simulations with initial field strength of $10^{-14}-10^{-8}$ G. The dark matter halo forms at the intersection of strongly convergent flows, leading to the formation of highly supersonic turbulence already on intergalactic scales, with turbulent Mach numbers of order $10-20$ also within the halo. Turbulent magnetic field amplification has never been explored in this regime and we therefore investigate whether this gives rise to effects similar to those observed in more typical halos. While the weaker initial field is somewhat more strongly amplified as a result of the shear flows, overall the evolution in the different simulations is rather similar and the flows are dominated by supersonic turbulence. We show in particular that the turbulent Jeans mass always dominates over the thermal and magnetic Jeans masses, and only on scales of $10^{-2}-10$ pc, the magnetic Jeans mass may become comparable to the thermal one. Our simulations thus strongly suggest the evolution to be dominated by the large-scale dynamics. As established in previous work, we thus expect the formation of central massive objects of a few times $10^4$ M$_\odot$ also in the presence of magnetic fields. The situation is somewhat different from more typical atomic cooling halos, where previous results have indicated a larger relevance of the magnetic Jeans mass on intermediate scales, potentially enhancing the mass of the massive object.
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All authors V.B. Díaz, D.R.G. Schleicher, M.A. Latif, R. Banerjee

High Energy Astrophysical Phenomena

Long-duration GW Searches for Sub-solar NSs and Superkilonovae using CoCoA

Abby Tejera, Divyajyoti, Alessandra Corsi et al. (+3 more)

On 2025 August 18, the LIGO-Virgo-KAGRA collaboration reported a sub-threshold gravitational-wave (GW) candidate, S250818k, consistent with a binary neutron star (NS) merger potentially involving a sub-solar-mass compact object. Follow-up electromagnetic (EM) observations identified a Type IIb supernova, SN 2025ulz within the broad localization area of the GW signal. This potential link between a sub-solar GW event candidate and a Type IIb SN, while not confirmed given the low statistical significance of S250818k, has nonetheless sparked renewed interest in the "superkilonova" scenario, where sub-solar-mass NSs form through processes like the fragmentation of an accretion disk or core fission in a collapsing star. In this picture, the in-spiral and merger of a sub-solar NS-NS binary is followed by the merger of the NS-NS remnant with the central black hole (BH), producing chirp-like GW signals. For sub-solar NSs with masses in the (0.1-1)M_sun range and BH masses in the so-called lower mass gap range of ~(3-5) M_sun, these signals can persist in the 20 - 1024 Hz frequency band of ground-based GW detectors for (10^2-10^3)s, potentially offering an opportunity to probe the superkilonova scenario, as well as the lower mass gap between NSs and stellar-mass BHs. However, the complexity of the underlying astrophysics may yield waveforms that deviate from standard templates, limiting the use of matched filtering in real GW searches. We therefore explore the detectability of such signals using the Cross-Correlation Algorithm (CoCoA), a more robust though less sensitive cross-correlation method. We discuss general strategies for implementing CoCoA superkilonova searches via either targeted follow-up of candidate chirps identified in matched-filter searches, or EM-triggered searches of stripped-envelope core-collapse SNe.
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All authors Abby Tejera, Divyajyoti, Alessandra Corsi, Yossef Zenati, Robert Coyne, Logan Cote

Astrophysics of Galaxies

From blue to red spirals: Slow galaxy transformation via ram pressure stripping in TNG-50

V. Lora, J. I. Gonzalez-Carbajal, A. Pasquali et al. (+5 more)

Late-type galaxies lose gas through ram-pressure stripping (RPS) after falling into a massive halo. Because this mechanism primarily removes the gaseous component while leaving the stellar disk largely undisturbed, it provides a pathway for quenching star formation without immediate morphological transformation. While RPS is well established in galaxy clusters, galaxy evolution in low-mass groups is often attributed to mergers, leaving open the question of whether RPS alone can drive the transition from blue, star-forming spirals to quenched systems in these environments. We use the high-resolution cosmological simulation TNG-50 to investigate the evolution of blue spiral galaxies, after their infall into group-scale halos. We excluded systems undergoing significant mergers, thus isolating the effect of RPS. We find that RPS in low-mass groups (M$_{group}<10^{14.5}$ M$_{\odot}$) can efficiently quench star formation while preserving the stellar disk structure. The transformation is gradual, with quenching timescales $\gtrsim6$ Gyr after infall, longer than the $\sim4$ Gyr typically associated with merger-driven evolution. The resulting galaxies are predominantly red, anemic spirals rather than fully transformed S0 systems, indicating that gas removal alone is insufficient to produce complete morphological transformation. Our results show that RPS in group environments can generate long-lived quenched spirals which might represent an intermediate evolutionary pathway preceding the formation of lenticular galaxies.
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All authors V. Lora, J. I. Gonzalez-Carbajal, A. Pasquali, A. Marasco, J. Fritz, E. K. Grebel, J. P. Ortiz-Jimenez, S. Estrada-Dorado

Earth and Planetary Astrophysics

Spectral Energy Distribution Analysis for Habitable Worlds Observatory Target Stars

Stephen R. Kane, Kaspar von Braun, Tara Fetherolf et al. (+1 more)

The Habitable Worlds Observatory (HWO) will directly image and characterize planets potentially similar to Earth orbiting nearby stars. Accurate stellar properties, particularly effective temperatures ($T_\mathrm{eff}$), angular diameters ($\theta_\star$), and bolometric fluxes ($F_\mathrm{bol}$), are essential for reliable Habitable Zone (HZ) calculations, exoplanet yield predictions, and coronagraph design trade studies. We present a spectral energy distribution (SED) analysis for the 164 stars from the HWO Exoplanet Exploration Program (ExEP) list, using $\chi^2$-minimization fits of empirical spectral templates from the Pickles stellar spectral flux library to broadband photometric data. The SED fits provide direct measurements of $F_\mathrm{bol}$. We adopt spectroscopic $T_\mathrm{eff}$ values from the PASTEL catalog for 127 of the 164 stars, with the remainder drawn from the HWO ExEP catalog, and use these in combination with $F_\mathrm{bol}$ to calculate $\theta_\star$ via the Stefan-Boltzmann equation. As a consistency check, we compare the Pickles template $T_\mathrm{eff}$ with the adopted spectroscopic values and find agreement to within $\sim$3% for 65% of the sample, with a systematic tendency for the templates to yield cooler values. We identify 48 stars with discrepancies exceeding 200~K, including close binary systems where photometric contamination compromises the SED solution. We discuss the implications for HZ boundary calculations, atmospheric retrieval of directly imaged planets, and target prioritization for HWO. This SED catalog constitutes a uniform set of empirically determined $F_\mathrm{bol}$ values and associated stellar parameters for the HWO target sample.
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All authors Stephen R. Kane, Kaspar von Braun, Tara Fetherolf, Natalie R. Hinkel

Earth and Planetary Astrophysics

A Pair of Warm Saturn-mass Planets near the 2:1 Mean Motion Resonance around TOI-3850

Sean Collins, Michelle Kunimoto, Nicolas B. Cowan et al. (+24 more)

Warm Jupiters, with orbital periods of $10$–$200~\rm{days}$ and radii exceeding $8~R_{\oplus}$, are a relatively understudied class of exoplanets occupying the parameter space between hot Jupiters and more widely separated, colder Jupiter analogs. In this work, we report the detection of a multi-planet warm Jupiter system around TOI-3850 (TIC-143008050), a moderately active, near-solar metallicity G0 dwarf star observed by TESS in Sectors 15, 21, 41, 48 and 75. Initially, a single candidate planet was discovered by TESS, displaying transit timing variations (TTVs) with an amplitude of $\sim 1~\rm hr$ and a super-period of $513~\rm days$. Through a combination of transit photometry, radial velocity observations with MAROON-X, and TTV modeling, we identify two planets: TOI-3850 b $(P_b=14.484\pm0.002~\mathrm{days},~ M_b =112\pm20~M_{\oplus},~e_b = 0.018\pm0.008, R_b = 12.07\pm0.09~R_{\oplus}, ~T_{\rm{eq}}=841\pm10~\rm{K})$, a transiting warm Jupiter, and TOI-3850 c $(P_c=29.85\pm0.01~\mathrm{days},~ M_c =90\pm15~M_{\oplus},~e_c < 0.015, ~T_{\rm{eq}}=661\pm7~\rm{K})$, a non-transiting, Saturn-mass companion. The two planets lie wide of the 2:1 mean motion resonance $(P_c/P_b \approx 2.06)$, consistent with a formation history involving disk-driven migration. $N$-body integrations indicate that TOI-3850 c may begin to transit on decadal timescales, while TOI-3850 b remains a promising target for follow-up atmospheric characterization.
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All authors Sean Collins, Michelle Kunimoto, Nicolas B. Cowan, Keivan G. Stassun, Jack J. Lissauer, Ze'ev Vladimir, Teo Močnik, Ernesto Elenter, David W. Latham, Karen A. Collins, Jacob Bean, Stephanie Striegel, Khalid Barkaoui, Ritvik Basant, Tanya Das, Raquel Forés-Toribio, Akihiko Fukui, Jose A. Muñoz, Felipe Murgas, Enric Palle, Ivan A. Strakhov, Richard P. Schwarz, Avi Shporer, Gregor Srdoc, Chris Stockdale, Neil B. Thomas, Francis P. Wilkin

High Energy Astrophysical Phenomena

XRISM Spectroscopy of Variable Accretion-driven Disk Winds in NGC 4151: When, Where, and How Fast Outflows are Launched

Xin Xiang, Jon Miller, Missagh Mehdipour et al. (+12 more)

X-ray observations probe the inner accretion flow within active galactic nuclei, revealing the highest gas column densities and fastest winds. The most diverse winds yet revealed with the Resolve calorimeter spectrometer aboard XRISM are found in NGC~4151, a nearby Seyfert-1 AGN that may qualify as a “changing-look” source (CLAGN). Herein, we report on wind variability in 14 XRISM observations of NGC~4151, summing to 0.9~Ms of exposure over a period of 395 days. We examined the dependence of key wind parameters on hardness and intensity selections, and as a function of time relative to flaring and dip events. The results suggest a globally organized but locally complex wind structure. Slow “warm absorber” components (WAs; $v_{\rm{out}} \sim 100-1000~\rm{km~s^{-1}}$) are always observed and likely represent failed winds at radius of $10^4 - 10^5 GM/c^2$, within the inner wall of the torus. In contrast, “very fast” and “ultra-fast” outflows (VFOs and UFOs; $v_{\rm{out}} \sim 10^3-10^4~\rm{km~s^{-1}}$, $v_{\rm{out}} \sim 0.033-0.33~c$) are strongest 10~ks after the peak of flares, and during periods with low flux. Ten kiloseconds is among the shortest flare–wind response timescales reported in an AGN, suggesting that the winds are observed close to the launching site. The absorption measure distribution (AMD) and the large outflow momentum rates suggest that the high-velocity flows visible in the Fe~K band are magnetically driven, while locally clumpy, likely owing to radiation pressure; one or both of these mechanisms may be enhanced following a flare and most visible during low-flux windows.
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All authors Xin Xiang, Jon Miller, Missagh Mehdipour, Ehud Behar, W. Niel Brandt, Laura Brenneman, Luigi Gallo, Elias Kammoun, Peter Kosec, Liyi Gu, Doyee Byun, Richard Mushotzky, Stephane Paltani, Elisa Costantini, Abderahmen Zoghbi

Earth and Planetary Astrophysics

Formation of multiple dust rings and gaps in protoplanetary discs by a single migrating planet. A parameter study in locally isothermal discs

Sören C. Meiners, Kim M. Weiskopf, Thomas Rometsch et al. (+1 more)

ALMA observations show that large protoplanetary discs usually contain multiple concentric dust rings separated by dark gaps. A natural explanation is dust-trapping at the edges of gaps opened by newly formed planets. However, planets typically migrate inward on timescales shorter than disc lifetimes, seemingly at odds with rings at large radii. We aim to investigate the conditions under which migrating planets can form long-lived, multi-ringed structures out to $r\sim 150$ au to constrain the parameter space for the planetary origin hypothesis of rings. Using the FargoCPT hydrodynamics code, we ran two-dimensional, locally isothermal disc models with a single migrating planet, varying disc aspect ratio, viscosity ($\alpha$), and planetary mass. In all models, the planet eventually stalls in a deep gap. At $\alpha\leq 10^{-4}$, secondary spirals launched by the planet can open additional gaps at smaller radii. When planets exceed twice the local thermal mass before stalling, they enter a regime of alternating slow and type-III rapid migration, leaving partial gaps outside their orbit. The gap edges consistently feature pressure maxima that trap dust. These begin as large vortices at $\alpha\leq 10^{-4}$, but gradually smear out into rings before dissipating. The type-III remnant rings dissipate quickly at $\alpha=10^{-3}$, but persist for at least 300-500 kyr at $\alpha\leq 10^{-4}$. Both smear-out and dissipation timescales increase with lower $\alpha$. Our results show that migrating planets can reproduce observed multi-ringed structures in discs with $\alpha\lesssim 10^{-4}$ through their stall ($r\lesssim 50$ au), secondary gap-opening ($r\lesssim 20$ au), and type-III migration remnants (extending to $r\sim 150$ au for Jupiter-mass planets in sufficiently massive discs). Longer simulations will be required to compare the statistics of ring-to-vortex occurrence to observations.
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All authors Sören C. Meiners, Kim M. Weiskopf, Thomas Rometsch, Cornelis P. Dullemond

High Energy Astrophysical Phenomena

A Diverse Distribution of Black Hole Spins from Stable Mass Transfer

Linhao Ma, Jakub Klencki, Eliot Quataert et al. (+1 more)

Gravitational wave observations have found over 300 merging binary black holes, yet their origins remain uncertain. Recent work showed that many may come from isolated stellar binaries whose orbits shrink through stable mass transfer. If true, their spins may help to distinguish this channel from other formation pathways. We investigate the tidal spin up of black hole progenitor stars with detailed modeling of binaries undergoing stable mass transfer. We calculate the tidal torques by solving tidally excited oscillation modes and predict the resulting black hole spins. We find a diverse spin distribution strongly affected by the mass transfer histories of the progenitors. Binaries can form black holes with moderate spins ($0.1\lesssim\chi_\mathrm{eff}\lesssim0.3$) if they only go through case A or case B mass transfer. In the former case, they can become super-synchronized upon detachment, while in the latter case, the donor is usually only partially stripped, leaving a puffy envelope where strong tides are excited. If both case A and case AB mass transfer occur, the resulting black hole spins are almost always negligible. As the mass transfer history is jointly determined by mass ratio and initial binary period, our results predict an anti-correlation between black hole spins and mass ratio, consistent with limited evidence from data. Our results can also potentially explain the case of GW190412, a moderately-spinning binary with a high mass ratio. We discuss the limitations of our methods and additional physics (e.g., nonlinear tides, case C, and L2 mass transfer) that need to be incorporated in future work.
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All authors Linhao Ma, Jakub Klencki, Eliot Quataert, Lieke van Son

High Energy Astrophysical Phenomena

ATLAS22kjn (AT 2022fpx): A Coronal Line Emitter with an Early Light Curve Bump and Mid-Infrared Dust Echo

Athena C. Engholm, Jason T. Hinkle, Benjamin J. Shappee et al. (+14 more)

We present an analysis of ATLAS22kjn (AT 2022fpx), whose high-ionisation coronal lines (CLs) and pre-peak light curve bump provide distinctive opportunities to investigate the physical mechanisms powering tidal disruption events (TDEs). In addition to CLs, the optical spectra show common TDE features, including a strong, blue continuum and broad Balmer and He II lines. The CLs appear before UV/optical light curve peak, preceding the detection of X-rays by $\sim 300$ days and persisting after X-rays are no longer detected, suggesting the X-ray emission is obscured at both early and late times. Using the CL luminosities, we constrain the temperature evolution of the ionising source, finding a decrease of $\lesssim 10 \%$ over 500 days. In the UV/optical light curve, we observe a $9 \substack{+4 \\ -2}$ day bump that peaks $125 \substack{+5 \\ -3}$ rest-frame days before the peak of the main flare. Although we cannot definitively determine the origins of the bump, we find that its timescale and luminosity are most consistent with theoretical predictions for a precursor feature produced by a stream-stream collision or a wind-stream collision. ATLAS22kjn also shows a prominent dust echo in its mid-infrared (MIR) light curves, indicating a high dust covering fraction $f_c \simeq 0.40 \pm 0.03$, similar to the covering fractions of other CL-emitting TDEs. From the multi-wavelength observations of ATLAS22kjn, we estimate the size and relative radii of the emission regions in its nuclear environment and determine that the CL region lies between the broad line region and the MIR-emitting dust. ATLAS22kjn demonstrates the importance of multi-wavelength and early-time observations, and the utility of CLEs in characterising the otherwise unobservable EUV/ultrasoft X-ray emission of TDEs.
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All authors Athena C. Engholm, Jason T. Hinkle, Benjamin J. Shappee, Katie Auchettl, Dhvanil D. Desai, Willem B. Hoogendam, Christopher S. Kochanek, Nicholas Earl, K. Decker French, Michael A. Tucker, Chris Ashall, Aaron Do, Allison Blum, Thomas de Jaeger, Mark E. Huber, Anna Payne, Jose L. Prieto

Cosmology and Nongalactic Astrophysics

A new measurement of the FRB DM-galaxy cross correlation and a first joint analysis with the kinematic SZ effect

Samuel McCarty, Liam Connor, Kritti Sharma et al. (+8 more)

Understanding the distribution of cosmic baryons is crucial for advancing cosmology and galaxy formation. Localized Fast Radio Bursts (FRBs) are a promising new probe of the diffuse gas, but measurements thus far have been limited by small sample size. In this work, we measure the FRB dispersion measure (DM)-galaxy cross correlation with 130 localized FRBs, including new spectroscopic host redshifts from the DSA-110, and the DESI Legacy Survey Bright Galaxy Sample. We detect this signal at the highest significance to date ($6.5\sigma$) in both configuration and harmonic space. By comparing to simulations and a halo model, we demonstrate that this statistic can constrain the strength of baryonic feedback. Our measurements disfavor a no-feedback scenario in which gas traces the underlying dark matter at $\sim\,9\sigma$. In addition to small scale feedback, this represents one of the first direct measurements of the clustering of electrons on scales larger than a few Mpc. We compare our measurement to recent kinematic Sunyaev-Zeldovich effect (kSZ) studies, which show good agreement despite the differences in observational methods and sample selection. Finally, we make a first attempt at breaking the kSZ optical depth degeneracy with FRBs, jointly measuring the growth rate of large-scale structure $f\sigma_8$. With future samples, FRB two-point statistics will provide precision constraints on the distribution of cosmic baryons and complement other probes.
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All authors Samuel McCarty, Liam Connor, Kritti Sharma, Simone Ferraro, Vikram Ravi, Elisabeth Krause, Boryana Hadzhiyska, Vishnu Balakrishnan, Casey Law, Pranav Sanghavi, Kaitlyn Shin

Instrumentation and Methods for Astrophysics

Early Exploration of the Scientific Discovery Space for the Habitable Worlds Observatory

Courtney D. Dressing, Danica Adams, Evelyne Alecian et al. (+324 more)

The Habitable Worlds Observatory (HWO) is a future NASA flagship mission concept identified by the Astro2020 Decadal Survey as the highest priority for large space missions. HWO should conduct "transformative astrophysics" and search for biosignatures in the atmospheres of approximately 25 potentially Earth-like planets. To further the early-stage development of HWO, NASA formed the Science, Technology, Architecture Review Team (START). In turn, START invited the scientific community to join working groups to explore the potential discovery space. In this paper, we present 70 science cases that resulted from this process. The cases address four scientific pillars: growth of galaxies (15 cases), evolution of the elements (13 cases), solar systems in context (32 cases), and living worlds (10 cases). Combined, they would address 27 of the 30 science questions and discovery areas identified by Astro2020. The 140 observing programs needed for the 70 investigations encompass a rich variety of spectroscopic (for 87% of science cases) and photometric (for 30%) observations extending from the UV to the NIR. Additionally, high-contrast and polarimetric capabilities would be needed for 34% and 27% of science cases, respectively. Access to UV wavelengths is critical: 83% of science cases need data at wavelengths <400 nm, and 26% extend to <100 nm. In the NIR, 26% of science cases need observations at wavelengths >=2000 nm. Pursuing the full portfolio of science would also necessitate precise astrometry for planet mass measurement, rapid response capabilities, a large instantaneous field of regard, non-sidereal tracking, saturation mitigation strategies, and high dynamic range.
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All authors Courtney D. Dressing, Danica Adams, Evelyne Alecian, Gagandeep Anand, Giada Arney, Sarah Gomes Aroucha Barbosa, Martin Barstow, Joanna K. Barstow, Rachael L. Beaton, Eduardo Bendek, Svetlana Berdyugina, Julie Biedermann, Sarah Blunt, Sanchayeeta Borthakur, Kara Brugman, Joseph N. Burchett, Eric Burns, Jenna M. Cann, Ludmila Carone, Cody A. Carr, Richard Cartwright, Renyue Cen, Jean-yves Chaufray, Pin Chen, Lígia F Coelho, Kyle Cook, Nicolas B. Cowan, Patricio E. Cubillos, Alexandre David-Uraz, Tansu Daylan, Jessica E. Doppel, Leonardo dos Santos, Meredith Durbin, Rana Ezzeddine, Tara Fetherolf, Theresa Fisher, Leigh N. Fletcher, Luca Fossati, Ana I Gómez de Castro, Kaz Gary, Varoujan Gorjian, Yasuhiro Hasegawa, Qiuhan He, Natalie Hinkel, Keri Hoadley, Renyu Hu, Noam Izenberg, Estelle Janin, Mathilde Jauzac, Stephen R. Kane, Theodora Karalidi, Émilie Anne Lafléche, David J. Lagattuta, Érika Le Bourdais, Mary Anne Limbach, Jacob Lustig-Yaeger, Eric Mamajek, Kathleen Mandt, Frédéric Marin, Taro Matsuo, Stephan R. McCandliss, Michael W. McElwain, Emma Miles, Michiel Min, Leonidas A. Moustakas, Coralie Neiner, Elisabeth Newton, James W Nightingale, Stephanie Olson, Colby Ostberg, Apurva V. Oza, Fabio Pacucci, Roberta Paladini, Niki Parenteau, Lynnae C. Quick, Ramses Ramirez, Sukrit Ranjan, Isabel Rebollido, Bin B. Ren, Kurt D Retherford, Jason Rhodes, Ian U. Roederer, Sabina Sagynbayeva, Edward Schwieterman, Adam Smercina, Krista Lynne Smith, Antoine Strugarek, Megan Taylor Tillman, Vivian U, Georgios N. Vassilakis, Hannah R. Wakeford, Sara Walker, Siyi Xu, Lulu Zhang, Alejandra Aguirre-Santaella, Munazza K. Alam, Amirnezam Amiri, Ramya M Anche, Sarah E. Anderson, David R. Ardila, Karla Z. Arellano-Córdova, Natasha E. Batalha, Thomas G.Beatty, Juliette Becker, Enrica Bellocchi, Mark Booth, Médéric Boquien, Sarah E. I. Bosman, Jean-Claude Bouret, Vincent Bourrier, Matteo Brogi, Andrew M. Buchan, Blakesley Burkhart, Jennifer A. Burt, José A. Caballero, Sarah L Casewell, Frances H. Cashman, Laura Chin, Yumi Choi, Jessie Christiansen, Francesca Civano, Kyle W. Cook, Brandon Park Coy, Brendan P Crill, Leroy Cronin, Håkon Dahle, Mario Damiano, William Danchi, Satyapriya Das, Brice-Olivier Demory, Jamie Dietrich, Steven Dillmann, Chuanfei Dong, Dwaipayan Dubey, Patrick Dufour, Arika Egan, Christiana Erba, Steve Ertel, Raissa Estrela, Vincent Van Eylen, Virginie Faramaz-Gorka, Andrzej Fludra, Sophia Flury, Andrew Fox, Kevin France, David M. French, Marina Galand, Tianmu Gao, Antonio García Muñoz, Miriam Garcia, Kenneth Gayley, Megan Gialluca, Samantha Gilbert-Janizek, Leonardos Gkouvelis, Kenneth E. Goodis Gordon, Clémence Gourvès, Jonathan Grone, Jacob Haqq-Misra, Caleb K. Harada, Zachary Hartman, Samantha Hasler, Calum Hawcroft, Matthew J. Hayes, Amanda R. Hendrix, Brandon Hensley, Svea Hernandez, Erin K. S. Hicks, Benne W. Holwerda, Carly Howett, Ziyu Huang, Richard Ignace, Caitriona M Jackman, Chafi Jamal, Shingo Kameda, Tiffany Kataria, Gagandeep Kaur, Finnegan Keller, Habib Khosroshahi, Alina Kiessling, Kristina Kislyakova, Oleg Kochukhov, Anton M. Koekemoer, Brad Koplitz, Joshua Krissansen-Totton, Jiri Krticka, Alvaro Labiano, Pierre-Olivier Lagage, Steph LaMassa, Erini Lambrides, Alexandra Le Reste, Nan Liu, Joe Llama, Emma Louden, Nataliea Lowson, Isabel Márquez, Evelyn J. R. Macdonald, Meredith MacGregor, Sangeeta Malhotra, Richard Massey, Erin May, L. C. Mayorga, Michael McElwain, Sean McGee, Alexia McKenzie, Athina Meli, Bertrand Mennesson, Connor Metz, Drew M. Miles, Aquib Moin, Mark Moussa, Themiya Nanayakkara, Dibyendu Nandy, Yaël Nazé, Marc Neveu, Eric Nielsen, John Noonan, Jessica L. Noviello, John M. O'Meara, Antonija Oklopčić, Chris Packham, Enric Palle, Emaad Paracha, Lucas Patty, Vasiliki Pavlidou, Sarah Peacock, Chris Pearson, Marc Postman, Andreas Quirrenbach, Swara Ravindranath, Seth Redfield, Joe P. Renaud, Malena Rice, Jane R. Rigby, Giulia Roccetti, Keighley E. Rockcliffe, Donna Rodgers-Lee, Jael Rojas Miguel, Maissa Salama, Samir Salim, Evan Scannapieco, Claudia Scarlata, Martin Schlecker, Steve Schulze, Paul Scowen, Darryl Zachary Seligman, Zacory Shakespear, Evgenya Shkolnik, Nick Siegler, Breann Sitarski, Louie Slocombe, Gopika SM, Russell J. Smith, Jennifer Sobeck, Daphne Stam, Kendall Sullivan, Takahiro Sumi, Yudai Suzuki, Christy Till, Armen Tokadjian, Vasuda Trehan, Grant Tremblay, Noah Tuchow, Margaret Turcotte Seavey, Jake D. Turner, Sarah Tuttle, Asif ud-Doula, Anna Grace Ulses, Connor Vancil, Aline Vidotto, Geronimo Villanueva, Jessica M Weber, Dale Weigt, Maximilian von Wietersheim-Kramsta, Thomas G. Wilson, David J. Wilson, Nicholas F. Wogan, Maria Womack, Michael L. Wong, John F Wu, Mark Wyatt, John Ziemer, Tiziano Zingales, Ryan Begley, Enrico Biancalani, Dmitry Blinov, Alexandre Branco, Esra Bulbul, Guillaume Chaverot, Catherine A. Clark, Jaime S. Crouse, Filippo D'Ammando, Achrene Dyrek, Oscar A. Flores Gaitán, Searra Foote, Cecilia Garraffo, Christopher Garry, Nikolaos Georgakarakos, Arvind F. Gupta, Daniel Huber, Brianna Isola, Nikhita Kalluri, Aafaque Khan, Amir H. Khoram, Adam B. Langeveld, Lucie Leboulleux, Briley Lewis, Anna Lewkowicz, Laurent Mahy, Liton Majumdar, Luigi Mancini, Joice Mathew, Dimitri Mawet, David Mouillet, Shantanusinh Parmar, Junellie Perez, Lorenzo Pino, Alex Polanski, Francisco J. Pozuelos, Tyler Richey-Yowell, Cleber Silva, Ramdayal Singh, Arif Solmaz, Angelle Tanner, Konstantinos Tassis, Luca Tonietti, Laura D. Vega, Aiden S. Zelakiewicz

2608.11294 · 11 Aug · 215 pages, 18 figures, 16 tables. This to-be-submitted manuscript summarizes and synthesizes science cases developed by the Habitable Worlds Observatory START and science working groups. See Table 1 for a roadmap, Table 5 for a list of science cases, Figure 11 for a visualization of common observational needs, Figure 16 for connections to Astro2020, and Tables 6-15 (after conclusions) for details

Abstract PDF $PLNT ×2$EVO ×1$GLXY ×1$SOLAR ×1

Instrumentation and Methods for Astrophysics

Full-Covariance Bayesian Inference of Stochastic Gravitational Wave Backgrounds with Time-Domain Simulations for Taiji-like Missions

Qingyuan Liang, Ju Chen, Minghui Du et al. (+1 more)

For Taiji-like missions, we implement a Bayesian spectral inference framework that combines second-generation time-domain (TD) simulations of time-delay interferometry (TDI) with a frequency-domain (FD) spectral likelihood for stochastic gravitational-wave background (SGWB) analyses. The \(X,Y,Z\) Michelson streams generated with \trianglesim{} are divided into finite segments, Fourier transformed, and modeled with a segment-dependent complex \(3\times3\) covariance matrix. For each segment we evaluate the orbit-dependent response functions and noise transfer functions, allowing unequal-arm and time-evolving effects to enter through the full \(XYZ\) covariance. Controlled simulations performed with \trianglesim{} show that the calculated functions reproduce the realization-averaged spectra at the few-percent level over the retained frequency band away from TDI nulls. We then compare parameter-estimation results for static equal-arm FD, equal-arm TD, and unequal-arm TD configurations, using in each case a full \(XYZ\)-covariance likelihood matched to the corresponding detector configuration. All three yield consistent uncertainty trends and Bayesian-evidence diagnostics for astrophysical-background recovery after marginalizing over instrumental noise and an effective Galactic double-white-dwarf foreground. Finally, in a ten-parameter model containing instrumental noise, an effective Galactic double-white-dwarf foreground, a stochastic astrophysical background, and a sound-wave spectrum from a cosmological first-order phase transition, we recover its peak amplitude and frequency and find Bayesian evidence favoring its inclusion in all three matched configurations.
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All authors Qingyuan Liang, Ju Chen, Minghui Du, Huai-Ke Guo

Instrumentation and Methods for Astrophysics

Eclipses by Artificial Satellites to Measure the Angular Sizes of Stars

Leo W.H. Fung, Albert Wai Kit Lau, Richard Massey et al. (+1 more)

Direct measurements of the angular sizes of stars (other than our Sun) are inherently limited by telescopes' optical diffraction limit. The spatial diffraction limit can be overcome by using time-domain information when stars are `eclipsed' by anything moving in the foreground: artificial satellites or the Moon (known as `lunar occultation imaging'). Here we analyse the angular resolution achievable by high-speed photon counting devices, when stars are eclipsed for several microseconds by one of the thousands of satellites now in low or mid-Earth orbit. We also build a full Bayesian statistical treatment for analysing simulated observations. We show that eclipses by the moon and satellites deliver $<2$ milliarcsecond resolution for $\sim$$10^4$ stars every year, with the diameters of $\sim$$10^1 - 10^2$ stars constrained to better than $0.5$ milliarcseconds. The application of satellites requires an ultra-fast, photon-resolving detector, capable of continuous readout with inter-frame delay controlled within $\lesssim 1$ $\mu$s. Such a fast rate can easily be handled by the SPINA instrument, which has demonstrated $8$ ns inter-frame delay, and potentially by the Cherenkov Telescope Array.
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All authors Leo W.H. Fung, Albert Wai Kit Lau, Richard Massey, George F. Smoot

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

All You Need is not $\Omega_\mathrm{gw}$: Beyond the Mean of the Cross-Correlation Estimator when Searching for an Astrophysical Gravitational-Wave Background

Haowen Zhong, Francesco Iacovelli, Vuk Mandic et al. (+1 more)

Searches for the stochastic gravitational-wave background (SGWB) using ground-based detectors rely heavily on the cross-correlation estimator $\bar C_f$, whose statistical properties determine the theoretical foundation for inference frameworks built on it. Past analyses usually assume Gaussianity of $\bar C_f$, but this assumption has not been systematically tested for a background of astrophysical origin like the one produced by compact binary coalescences. In this work, we decompose $\bar C_f$ into three physically motivated components: (1) the mean intensity, (2) the geometrical shot noise, and (3) the polarization leakage, and we compute 90% credible intervals for its cumulants up to fourth order for the binary black hole, binary neutron star, and neutron star-black hole populations by propagating local merger rate uncertainties. We find that for the upcoming LIGO O5 sensitivity, $\bar C_f$ remains effectively Gaussian for all three populations, validating current Gaussian likelihood frameworks. For Cosmic Explorer (CE), however, the $\bar C_f$ produced by binary black holes becomes non-Gaussian, with skewness and excess kurtosis of $0.31^{+0.04}_{-0.03}$ and $1.3^{+0.4}_{-0.3}$, respectively, in the most sensitive band over a one-year observation period. For binary neutron star and neutron star - black hole mergers, $\bar C_f$ remains largely Gaussian even at CE. These results indicate that the Edgeworth expansion provides an adequate leading-order description of the non-Gaussianity expected in the next-generation era, while also motivating the development of more sophisticated statistical methods for a more accurate treatment.
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All authors Haowen Zhong, Francesco Iacovelli, Vuk Mandic, Emanuele Berti

Instrumentation and Methods for Astrophysics

High-temperature photovoltaics for solar-electric Oberth maneuvers: ton-class payload feasibility for interstellar-precursor missions

Nadim Maraqten, Willem van Lynden, Carlos Gómez de Olea Ballester et al. (+1 more)

In-situ exploration beyond the giant planets remains rare because timely Solar System escape demands very high specific orbital energy, which existing concepts typically achieve only with small payloads, super-heavy launchers, or nuclear-powered propulsion. Motivated by laboratory demonstrations of high-intensity, high-temperature (HIHT) solar cells operating near $400\,^{\circ}\mathrm{C}$, we assess a solar-electric Oberth maneuver that concentrates thrust near a $0.3\,\mathrm{AU}$ perihelion. Evolutionary steering optimisation indicates that an expendable Falcon Heavy could deliver ton-class payloads to $200\,\mathrm{AU}$ within 25 years if HIHT power systems reach specific powers about $10\%$ above present-day conventional levels with a Jupiter gravity assist, or about twice those levels on a direct trajectory, under the stated assumptions. The gain stems from a threefold increase in specific orbital energy for the same $\Delta v$ compared with a $1\,\mathrm{AU}$ spiral. These results suggest HIHT photovoltaics could shift from survival hardware to propulsion-enabling technology for high-energy deep-space missions.
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All authors Nadim Maraqten, Willem van Lynden, Carlos Gómez de Olea Ballester, Andreas M. Hein

Solar and Stellar Astrophysics

Intense but Harmless: Exo-Space Weather Around an M Dwarf with a Single-Hemisphere Dynamo

Zheng Sun, Julián D. Alvarado-Gómez, Hui Tian et al. (+4 more)

M dwarfs are among the most promising host stars in the search for habitable exoplanets. However, their active atmospheres drive intense magnetic activity, including energetic flares and possibly coronal mass ejections (CMEs), which may pose serious threats to planetary habitability. In this study, we perform three-dimensional magnetohydrodynamic (MHD) simulations of CMEs on a fully convective M dwarf with a rotation period of 30 days, corresponding to the moderate-rotation regime. The magnetic topology driving our simulations is adopted from an exploratory global dynamo simulation of a fully convective low-mass star exhibiting a single-hemisphere magnetic configuration, which is not yet observationally confirmed. The large-scale magnetic field is mostly restricted to a single hemisphere and characterized by high-latitude polarity inversion lines (PILs), with the implication that most CMEs should originate from high latitudes. We find that these high-latitude CMEs propagate radially and away from the equatorial plane, producing only weak and spatially limited disturbances along the equatorial orbits of exoplanets. Moreover, low-latitude CMEs experience stronger drag within the dense and slow stellar wind near the equator, which significantly reduces both their propagation speeds and their overall impact on exoplanets. The resulting dynamic pressure enhancements on equatorial exoplanets caused by these CMEs are within two orders of magnitude above the quiescent conditions, much lower than those reported in previous M-dwarf CME simulations. These results indicate that, if such magnetic topologies indeed exist on M dwarfs, they may produce a relatively benign CME environment, which could be favorable for planetary habitability at face value.
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All authors Zheng Sun, Julián D. Alvarado-Gómez, Hui Tian, Ofer Cohen, Jeremy J. Drake, Katja Poppenhäger, Yue-Hong Chen

Earth and Planetary Astrophysics

Opposition effect of comet 28P/Neujmin observed with Subaru Hyper Suprime-Cam

Takafumi Ootsubo, Hideyo Kawakita, Tadafumi Takata et al. (+8 more)

We present an observational study of the nucleus of comet 28P/Neujmin at a heliocentric distance exceeding 10 au, where coma contamination is effectively minimized. Observations were conducted in the $g$, $r$, and $y$ bands with the Hyper Suprime-Cam (HSC) on the 8.2-m Subaru Telescope. The measured colors, $g - r = 0.67\pm0.17$ and $r - y = 0.41\pm0.19$, yield a spectral index of $S' = 8.8\pm4.2\%/100$ nm, comparable to that of D-type asteroids. By incorporating new observational data at a phase angle $\alpha = 0.334^{\circ}$ with previous observations, we determined the phase function for the nucleus of 28P and confirmed an opposition surge at small phase angles. The derived opposition effect amplitude depends on the adopted phase coefficient, which is uncertain due to potential systematic effects in multi-apparition phase curves. Nevertheless, even under conservative assumptions, the opposition effect of 28P suggests a larger coherent backscattering contribution than is typical for C- and D-type asteroids. The Subaru HSC observations suggest that, although the nucleus color resembles that of D-type asteroids, the surface microstructure of comet 28P's nucleus likely differs from those of C- and D-type asteroids. Future single-apparition observations covering a wide phase angle range from near-opposition to larger angles, combined with polarimetric measurements, will be essential to definitively establish the physical mechanisms responsible for the opposition effects of cometary nuclei.
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All authors Takafumi Ootsubo, Hideyo Kawakita, Tadafumi Takata, Junko Furusawa, Hisanori Furusawa, Tsuyoshi Terai, Toshihiro Kasuga, Akira Keida, Yoshiharu Shinnaka, Fumi Yoshida, Seitaro Urakawa

Solar and Stellar Astrophysics

Gravity modes and potential evidence for Rossby Waves in late O-type supergiants

Lydia S. Cidale, Alejandra Christen, Aldana Alberici Adam et al. (+6 more)

The properties of O-type supergiant stars remain largely unexplored. By analysing their light variations, we can unravel underlying physical phenomena, such as binarity, stellar pulsations, and rotation modes. This study aims to analyse the TESS light curves of 3 O-type supergiants to identify periodic signatures and gain deeper insights into their internal dynamics and structure. Our primary goal is to search for the presence of rotational modulation and possible evidence of Rossby waves. A period search was performed and we explored phase diagrams and searched for rotational splitting. If the observed wave frequencies were consistent with the dispersion relation of global Rossby waves, we identified them as potential signatures of this mechanism. We used a graphical method to compare the observed and predicted frequencies. The analysed stars (HD 188001, HD 192639, and HD 159952) exhibit a comparable set of frequencies. We classify most of them as g-mode oscillations (either l=1 or l=2), in agreement with the evolutionary state of the objects. In all cases, we find evidence of rotational modulation. The remaining oscillation patterns may be consistent with Rossby modes, including both tesseral and sectoral configurations. The angle of inclination of the rotation axis was estimated using stellar parameters available in the literature, together with the rotational period derived in this work. We also discuss a possible connection between the observed low-frequency waves and the red-noise component commonly observed in the periodogram of photometric time series of massive supergiants. Our results provide evidence of g-mode oscillations modulated by rotation. In addition, we find that Rossby waves may be excited in rotating O-type supergiants, which suggests that these large-scale inertial oscillations could play a role in the observed low-frequency variability of such stars.
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All authors Lydia S. Cidale, Alejandra Christen, Aldana Alberici Adam, Suryani Guha, Alex Lobel, Gunther F. Avila Marin, Michaela Kraus, Alejandro H. Corsico, Julieta Sanchez Arias

Cosmology and Nongalactic Astrophysics

Fine-tuning in mixed Dark Matter models with Primordial Black Hole relics

Amirah Aljazaeri and Christian T. Byrnes

We investigate the fine-tuning of a tripartite dark matter (DM) scenario involving ultra-light primordial black holes (PBHs), whose evaporation before Big Bang Nucleosynthesis leaves Planck-mass relics and produces DM particles together with an independently produced DM component. We uniformly evaluate the parameter sensitivity required to reproduce the observed DM abundance, $\Omega_{\rm DM}$. Considering thermal WIMP freeze-out, freeze-in, and QCD axion misalignment, and assuming PBHs form via collapse of perturbations following horizon entry, we find that the fine-tuning is normally dominated by the structure of the PBH relic abundance calculation rather than by the particle DM candidate or the details of PBH evaporation. In radiation-dominated cosmologies, the DM abundance is highly sensitive to the primordial curvature power spectrum because the PBH formation fraction depends exponentially on density fluctuations. Although an early PBH-dominated era dilutes pre-existing abundances and reduces the apparent tuning of the PBH abundance, inflationary fine-tuning remains required to produce the required initial large amplitude perturbations. We further examine alternative PBH formation channels, including supercooled first-order phase transitions and collapsing domain walls, and find that they replace the inflationary fine-tuning with alternative exponential sensitivities. We conclude that a natural realization of an order unity PBH relic abundance is hard to motivate.
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Cosmology and Nongalactic Astrophysics

Fitting trends in quasar emission and absorption line redshifts

Netra K Subramanian, Prasad Subramanian and Nimisha G Kantharia

The spectrum of a quasar consists of a few emission lines whose wavelengths are shifted by similar redshifts and numerous absorption lines whose wavelengths are shifted by different redshifts. Hence each quasar is characterised by an emission line redshift and the absorption lines redshifts are all less than the emission line redshift. The distribution of observed absorption line redshifts ($z_{abs}$) with respect to emission line redshift ($z_{em}$) for a large sample of quasars shows a systematic trend as pointed out by \citet{2016arXiv160901593K}. They noticed that increase in $z_{em}$ is accompanied by a monotonic increase in the lowest detected value of $z_{abs}$ and inferred that the emission and absorption lines were all formed in the quasar. This study focuses on modeling the systematic trend in the observed $z_{em} \rightarrow z_{abs}$ distribution. We considered the redshift data of absorption lines of singly ionized magnesium (denoted by MgII) and triply ionized carbon (denoted by CIV) for a large sample of quasars. We find that the envelope of data points defining the lowest value of the MgII absorption line redshift (which we denote by $z_{MgIImodel}$) for a given $z_{em}$ satisfies $z_{MgIImodel} = (0.418 \pm 0.008) z_{em} - (0.482 \pm 0.02)$ with an $R^2$ value of 0.99. The model can be used to predict the lowest expected MgII absorption line redshift for any $z_{em}$. We find a similar model for the lowest expected redshift of triply ionized carbon lines for any $z_{em}$ which is $z_{CIVmodel} = 0.845 (\pm 0.0002) z_{em} - 0.153 (\pm 0.0006)$.
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Solar and Stellar Astrophysics

Pulsation periods reveal tension between theoretical and empirical radii for classical Cepheids in eclipsing binary systems

O. Ziółkowska, R. Smolec, R. Singh Rathour et al. (+1 more)

Context. With their precisely determined physical parameters, classical Cepheids in eclipsing binary systems are often used to constrain stellar evolution and pulsation theories. To this end, their position in the HR diagram, effective temperature and luminosity, and radius are commonly used when matching best-fitting evolutionary models. However, the pulsation period of Cepheids, the most precise observable, is rarely used in such studies. Aims. We explore how including the pulsation period as a constraint in matching evolutionary models affects the best-fitting solution. As the pulsation period follows the period-mean density relation, we examine whether it provides information consistent with that based on the stellar radius. Methods. We modeled four eclipsing binary systems with Cepheids from the LMC. We used $\chi^2$ minimization to find the best-matching evolutionary model from a grid of models computed with MESA. The evolutionary models are supplemented with pulsation periods computed with RSP, with nonlinear period corrections taken into account. Results. Depending on whether the radius or the pulsation period is used to select the best-fitting model, discrepant solutions are obtained. In solutions selected based on the pulsation period, the stellar radius is systematically too low compared with observations. Conversely, for solutions based on the radius, the pulsation period is systematically too long. The tension amounts to a few sigma for stars with precisely determined radii and part of it is traced to a nonlinear increase in radius for large-amplitude pulsators, which has not been studied in detail in the literature. Conclusions. When using Cepheids in eclipsing binary systems to constrain stellar models, we recommend using the pulsation period instead of the radius. A systematic study of nonlinear effects on stellar radius in large-amplitude pulsators is needed.
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All authors O. Ziółkowska, R. Smolec, R. Singh Rathour, V. Hocdé

Astrophysics of Galaxies

The Radcliffe Wave is not alone in the Local System

V. V. Bobylev and A. T. Bajkova

The spatial distribution of open star clusters (OSCs) younger than 30 million years old in the Local System was studied. It was shown for the first time that a significant number of OSCs belong to the recently discovered Vela Ridge gas and dust supercloud. The most intriguing property of this sample of OSCs is the presence of periodic perturbations in their vertical coordinates with a maximum amplitude of 47 pc and a wavelength of 1.1 kpc. Thus, the discovered chain of young OSCs is analogous to the Radcliffe Wave, but with a lower amplitude of vertical perturbations, a shorter wavelength, and is, on average, 2 million years older.
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