High Energy Astrophysical Phenomena
DIPLODOCUS II: Implementation of transport equations and test cases relevant to micro-scale physics of jetted astrophysical sources
Christopher N. Everett, Marc Klinger-Plaisier and Garret Cotter
DIPLODOCUS (Distribution-In-PLateaux methODOlogy for the CompUtation of transport equationS) is a framework being developed for the mesoscopic modelling of astrophysical systems via the transport of particle distribution functions through the seven dimensions of phase space, including continuous forces and discrete interactions between particles. Following Paper I, which details the mathematical background, this second paper provides an overview of the numerical implementation in the form of the code package Diplodocus$.$jl, written in Julia, including the description of a novel Monte-Carlo sampling technique for the pre-computation of anisotropic collision integrals. In addition to the discussion of numerical implementation, a selection of test cases are presented to examine the package's capabilities. These test cases focus on micro-scale physical effects: binary collisions, emissive interactions, and external forces that are relevant to the modelling of jetted astrophysical sources, such as Active
Galactic Nuclei and X-Ray Binaries.
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Solar and Stellar Astrophysics
Polarization from Rapidly Rotating Massive Stars
J. Patrick Harrington, Richard Ignace and Kenneth G. Gayley
Stellar rotation has long been recognized as important to the
evolution of
stars, by virtue of the chemical mixing it can induce and how it interacts with binary mass transfer. Binary interaction and rapid rotation are both common in massive
stars and involve processes of angular momentum distribution and transport. An important question is how this angular momentum transport leads to the creation of two important classes of rapidly rotating massive
stars, Be
stars defined by disklike emission lines, and Bn
stars defined by rotationally broadened absorption lines. A related question is what limits this rotation places on how conservative the mass transfer can be. Central to addressing these issues is knowledge of how close to rotational break-up
stars can get before they produce a disk. Here we calculate diagnostics of this rotational criticality using the continuum polarization arising from a combination of rotational
stellar distortion (i.e., oblateness) and redistribution of
stellar flux (i.e.,
gravity darkening), and compare polarizations produced in the von Zeipel approximation with the approach of Espinosa Lara & Rieutord (ELR). Both produce similar photospheric polarizations that rise significantly in the far ultraviolet (FUV) for B
stars, with a stronger signal in the von Zeipel case. For early main-sequence and subgiant
stars, it reaches a maximum of ~1% at 140 nm for
stars rotating at 98% of critical, when seen edge-on. Rotational rates above 80% critical result in polarizations of several tenths of a percent, at high inclination. These predicted stable signal strengths indicate that determinations of near-critical rotations in B
stars could be achieved with future spectropolarimetric instrumentation that can reach deep into the FUV, such as CASSTOR, the Polstar mission concept, or the POLLUX detector design.
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Earth and Planetary Astrophysics
Limits of Standard Tidal Models at Quaoar: Matching Weywot's Orbit, Missing the Spin
Zsolt Regaly, Viktoria Frohlich and Csaba Kiss
Weywot, Quaoar's small satellite, follows a nearly circular orbit at a distance of 12.9 times Quaoar's diameter and coexists with a compact ring system. Nevertheless, Quaoar's flattening of 0.16, slow 17.7hr rotation and Weywot's low mass are difficult to reconcile with conventional
tidal-
evolution theory. We assess whether standard tides can reproduce the present-day architecture of the Quaoar-Weywot system and identify the initial conditions required. Orbit-averaged integrations spanning 4.5Gyr were carried out with two formalisms: (i) a constant phase-lag (CPL) and (ii) an Andrade creep-tide (ACT) framework. With the nominal Weywot mass, both
tidal prescriptions converge on Weywot's observed orbital distance for a wide range of initial orbital distances and eccentricities; eccentricity is damped and present-day
tidal torques are negligible, rendering the orbit quasi-stationary. Quaoar's
spin, however, remains essentially unchanged from its inferred
primordial period based on its present-day flattening, and does not reproduce the observed value. A match is possible only if Weywot is 5-10x more massive than current estimates and if its initial eccentricity is finely tuned; such scenarios are inconsistent with occultation-derived masses and imply an implausibly dense satellite. Based on the best fitting viscoelastic parameters, the most plausible composition for Quaoar is found to be a partially differentiated
dwarf planet containing roughly equal masses of silicate rock and H2O-dominated warm (150-180K) ices. Standard
tidal models reproduce Weywot's semimajor axis but cannot account for Quaoar's slow 17.7hr rotation without invoking an unrealistically massive satellite or external torques, suggesting that non-
tidal processes - such as a largely
primordial spin, early satellite loss, or a retrograde secondary
giant impact - must have influenced Quaoar's rotational
evolution.
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Astrophysics of Galaxies
A Catalog of Filaments in the Central Molecular Zone
Richard G. Arendt, F. Yusef-Zadeh and I. Heywood
We present a catalog of 1.28 GHz
radio filaments observed by MeerKAT over the innermost 200 pc of the
Galaxy (roughly $\pm 1.5\deg$), which includes the central molecular zone (CMZ). The catalog is generated by repurposing software developed for the automated detection of filaments in
solar coronal loops. There are two parts to the catalog. The first part, the main catalog, provides a point-by-point listing of locations and basic observational properties along each detected filament. The second part is a summary catalog which provides a listing of mean, median, or total values of various properties for each filament. Tabulated quantities include position, length,
curvature, brightness, and spectral index. The catalogs contain a heterogeneous mix of filamentary structures, including nonthermal
radio filaments (NRFs), and parts of
supernova remnants (SNRs) and thermally emitting regions (e.g. H II regions). We discuss criteria for selecting useful subsamples of filaments from the catalogs, and some of the details encountered in examining filaments or selections of filaments from the catalogs.
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Astrophysics of Galaxies
Faint galaxies in the Zone of Avoidance revealed by JWST/NIRCam
J. L. Nilo-Castellón, M. V. Alonso, L. Baravalle et al. (+12 more)
The Zone of Avoidance (ZoA) remains one of the last frontiers in constructing a comprehensive three-dimensional map of the Universe.
Galactic extinction,
stellar crowding, and confusion noise have historically limited the detection of background
galaxies in these regions, with implications for large-scale structure and cosmological measurements. We assess the capability of the James Webb Space
Telescope (JWST) Near Infrared Camera (NIRCam) to detect extragalactic sources in a heavily contaminated region of the Milky Way. We analyzed JWST/NIRCam wide-filter images of NGC 3324 with a customized implementation of SExtractor v2.28. Sources were detected in the F444W band, cross-matched with F090W and F200W, and validated against recent DAOPHOT point spread function (PSF) photometry. A refined sample was obtained through full width at half maximum (FWHM) - signal-to-noise ratio (SNR) criteria and visual inspection. We identified 102
galaxies across the JWST/NIRCam field of view. The magnitude (F444W) distribution is bimodal, with about 10% brighter than m_F444W < 15 mag and about 60% in the range 17 < m_F444W < 19 mag. Typical sizes are FWHM ~6.5 arcsec, from compact to extended systems with isophotal areas up to ~2000 pixels (~7.9 arcsec^2). Morphologies span from compact to spiral and lenticular systems, including a compact group at the eastern edge of the field. We also report the detection of "transnebular
galaxies", visible through the most opaque regions of the molecular cloud. These results demonstrate the potential of JWST/NIRCam to probe extragalactic sources through highly obscured
Galactic regions, opening new avenues for mapping large-scale structures across the ZoA.
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All authors J. L. Nilo-Castellón, M. V. Alonso, L. Baravalle, C. Villalon, C. N. A. Willmer, C. Valotto, M. Soto, D. Minniti, M. A. Sgró, I. V. Daza-Perilla, H. Cuevas Larenas, A. Ramirez, J. Alonso-García, P. Marchant Cortés, F. Milla Castro
Astrophysics of Galaxies
Jets in Low-Mass Protostars
Somnath Dutta
Jets and
outflows are key components of low-mass
star formation, regulating
accretion and shaping the surrounding molecular clouds. These flows, traced by molecular species at (sub)millimeter wavelengths (e.g., CO, SiO, SO, H$_2$CO, and CH$_3$OH) and by atomic, ionized, and molecular lines in the infrared (e.g., H$_2$, [Fe II], [S I]), originate from protostellar
accretion disks deeply embedded within dusty envelopes. Jets play a crucial role in removing angular momentum from the disk, thereby enabling continued mass
accretion, while directly preserving a record of the protostar's
outflow history and potentially providing indirect insights into its
accretion history. Recent advances in high-resolution, high-sensitivity observations, particularly with the James Webb Space
Telescope (JWST) in the infrared and the Atacama Large Millimeter/submillimeter Array (ALMA) at (sub)millimeter wavelengths, have revolutionized studies of protostellar jets and
outflows. These instruments provide complementary views of warm, shock-excited gas and cold molecular component of the jet-
outflow system. In this review, we discuss the current status of observational studies that reveal detailed structures, kinematics, and chemical compositions of protostellar jets and
outflows. Recent analyses of mass-loss rates, velocities, rotation, molecular abundances, and
magnetic fields provide critical insights into jet launching mechanisms, disk
evolution, and the potential formation of binary systems and
planets. The synergy of JWST's infrared sensitivity and ALMA's high-resolution imaging is advancing our understanding of jets and
outflows. Future large-scale, high-resolution surveys with these facilities are expected to drive major breakthroughs in
outflow research.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Observational Constraints on Chaplygin Gas Models in Non-Minimally Coupled Power Law $f(Q)$ Gravity with Quasars
Nakul Aggarwal, Ali Pourmand, Fatimah Shojai et al. (+1 more)
In the framework of $f(Q)$
gravity, where
gravity emerges from non-metricity $Q$, we explore the cosmological implications of its non-minimal coupling to matter. Inspired by the recent success of Chaplygin gas models in explaining dark energy, we consider a background fluid composed of baryonic matter, radiation, and a family of Chaplygin gas variants namely Generalized Chaplygin Gas (GCG), Modified Chaplygin Gas (MCG), and Variable Chaplygin Gas (VCG). We constrain these models with three recent observational
datasets: Observational Hubble Data (OHD), Baryonic Acoustic Oscillation (BAO) measurements, and Quasi-
Stellar Objects (QSO) data. For the QSO
dataset, we propose an analytical expression for errors in comoving distance to circumvent the reliance on Monte Carlo simulations. Using kinematic diagnostics such as the deceleration and jerk parameters and Om diagnostic, we assess deviations of the proposed models from $\Lambda$CDM. Our joint analysis of the three
datasets reveals that the transition
redshift from a decelerated to an accelerated expansion of the universe for the GCG, MCG and VCG models is $0.620^{+0.018}_{-0.017}$, $0.537^{+0.017}_{-0.017}$ and $0.470^{+0.012}_{-0.012}$ respectively, indicating a departure from $\Lambda$CDM.
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All authors Nakul Aggarwal, Ali Pourmand, Fatimah Shojai, Harish Parthasarathy
Solar and Stellar Astrophysics
Asteroseismic calibration of the Rossby number and its connection to the stellar dynamo and fundamental properties
Alfio Bonanno, Enrico Corsaro, Travis S. Metcalfe et al. (+3 more)
The
stellar Rossby number, a dimensionless parameter quantifying the influence of Coriolis forces on convective motions, plays a pivotal role in understanding
magnetic stellar evolution. In this work, we explore the connection between the Rossby number and potential dynamo mechanisms in Sun-like
stars, as well as its dependence on fundamental
stellar properties. We present a novel, detailed asteroseismic calibration of the convective turnover time, incorporating for the first time
Gaia photometry alongside surface
gravity, effective temperature, and
stellar metallicity. Our analysis employs an expanded sample of more than 150
stars, including targets from the Kepler LEGACY and KOI surveys, as well as more evolved
stars observed by TESS and K2. This sample spans evolutionary stages from the main sequence to the early red
giant branch (RGB), enabling a comprehensive investigation of Rossby number trends across
stellar evolution.
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All authors Alfio Bonanno, Enrico Corsaro, Travis S. Metcalfe, Sylvain Breton, Orlagh L. Creevey, Christopher J. Lindsay
Cosmology and Nongalactic Astrophysics
Enhanced Localization of Dark Lensed Gravitational Wave Events Enables Host Galaxy Identification and Precise Cosmological Inference
Zhiwei Chen, Qingjuan Yu, Youjun Lu et al. (+1 more)
Lensed gravitational wave (GW) events are expected to be powerful new probes of cosmology, contingent on
redshift measurement by electromagnetic observations. Host
galaxy identification is thus crucial but challenging due to poor localization by GW signal alone. In this paper, we show that the third-generation ground-based GW detectors will detect a population of lensed events with three or more detectable images (including the central one), each arriving at distinct times and Earth locations in the space, forming an effective network that reduces the typical localization area to $\sim0.01$ deg$^2$. For at least $90\%$ (or $50\%$) of these events, the localization improves by more than a factor of $10$ (or $30$) comparing with unlensed cases. Such precise localization and multiple-image detections enable robust host-
galaxy identification and, through lens modelling, further yield sub-arcsecond position. As “dark lensed sirens", these events become powerful probes of cosmological parameters. Using simulated lensed compact-binary mergers, we show that two-year or longer observations with third-generation GW detectors can measure the Hubble constant to $\lesssim1$% precision via “dark lensed sirens" (even when relying solely on lensed
stellar-mass binary black hole events), while simultaneously constraining other cosmological parameters. This approach will provide an independent, complementary avenue for measuring cosmological parameters.
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All authors Zhiwei Chen, Qingjuan Yu, Youjun Lu, Xiao Guo
High Energy Astrophysical Phenomena
Optically thick winds of very massive stars suppress intermediate-mass black hole formation
Stefano Torniamenti, Michela Mapelli, Lumen Boco et al. (+3 more)
Intermediate-mass black holes (IMBHs) are the link between
stellar-mass and supermassive black holes. Gravitational waves have started unveiling a population of IMBHs in the $\sim 100-300 \, \mathrm{M_{\odot}}$ range. Here, we investigate the formation of IMBHs from non-rotating very massive
stars (VMSs, $>100\,{} \mathrm{M_{\odot}}$). We calculate new VMS models that account for the transition from optically thin to optically thick winds, and study how this enhanced mass loss affects IMBH formation and the black hole mass function at intermediate and high
metallicity ($Z=10^{-4}-0.02$). We show that optically thick winds suppress the formation of IMBHs from direct VMS collapse at
metallicities $Z>0.001$, one order of magnitude lower than predicted by previous models. Our models indicate that the
stellar progenitors of GW231123 must have had a
metallicity $Z<0.002$, if the primary black hole formed via direct VMS collapse.
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All authors Stefano Torniamenti, Michela Mapelli, Lumen Boco, Filippo Simonato, Giuliano Iorio, Erika Korb
Earth and Planetary Astrophysics
Catalog and Characterization of Science Orbit Configurations for an Enceladus Orbiter
Spencer Boone, Joan Pau Sanchez Cuartialles and Stéphanie Lizy-Destrez
Saturn's moon Enceladus is an exciting destination for future exploration missions due to the scientifically interesting geyser region located on its South pole. In this work, we compile the different types of science orbit configurations that have been proposed in the literature and present numerical methods to compute each of them in the Saturn-Enceladus circular restricted three-body problem (CR3BP). In addition, we explore the utility of the higher period dynamical structures found in the CR3BP. Figures of merit such as the observational properties and geometries for each family of orbits are presented. By providing a consistent analysis of potential Enceladus science orbits, this work can serve as a baseline for future mission designs.
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High Energy Astrophysical Phenomena
Lanthanide Impact on the Infra-Red Spectra of Nebular Phase Kilonovae
Quentin Pognan, Kyohei Kawaguchi, Shinya Wanajo et al. (+3 more)
Nebular phase kilonovae (KNe) have significant infra-red (IR) emission thought to be mostly forbidden emission lines from rapid
neutron capture (r-process) species in
neutron star merger ejecta. Lanthanide elements in particular have complex, open f-shell atomic structures with many IR transitions. Using non-local thermodynamic
equilibrium (NLTE) radiative transfer simulations, we explore the impact of lanthanides on the IR spectra of KNe in the nebular phase, exploring a parameter space of ejecta mass and lanthanide fraction. We find that lanthanide impact is greater at higher densities, corresponding to earlier epochs and greater ejecta masses. The wavelengths most affected are found to be $\lambda \lesssim 4~\mu$m, with the species Ce\,iii and Nd ii being the most important contributors to spectral formation. We also find significant emission from species proposed in observations, notably Te\,iii at 2.1 $\mu$m, and Se\,iii at 4.5 and 5.7 $\mu$m, while W\,iii is subdominant at 4.5 $\mu$m. The Te\,iii feature at 2.1 $\mu$m is always blended, particularly with Zr\,ii, Ce\,iii, and Nd\,ii. We do not reproduce the smooth blackbody-like continua observed in AT2023vfi. Based on our results, we argue that line opacity alone is likely insufficient to produce optically thick continua in the nebular phase, even in the case of lanthanide/actinide-rich ejecta, as our models are optically thin in the IR at these epochs. Given that lanthanide contributions are dominant below 4 $\mu$m, we suggest that NIR observations best probe these elements, while MIR spectroscopy with JWST can reliably probe non-lanthanide emission even in relatively lanthanide-rich cases.
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All authors Quentin Pognan, Kyohei Kawaguchi, Shinya Wanajo, Sho Fujibayashi, Anders Jerkstrand, Jon Grumer
Astrophysics of Galaxies
Extremely UV-bright starbursts at the end of cosmic reionization
R. Marques-Chaves, D. Schaerer, M. Dessauges-Zavadsky et al. (+22 more)
We present a study of 27 very UV-bright (-22.0<MUV<-24.4) sources at z~6 identified in SHELLQs survey. Stacking their rest-frame UV spectra reveals a prominent NV1240A P-Cygni, consistent with very young (~6Myr)
stellar populations dominated by massive
stars. They are thus powerful and efficient ionizing starbursts with an average ionizing
photon production efficiency of log(Xi_ion/Hz erg-1)=25.54. For one of these, J0217-0208 at z=6.2 (MUV=-23.4), we analyzed NIRCam and NIRSpec data. Its SED indicates a young (~5Myr), compact (reff~260pc) starburst with a
stellar mass of 10^9Msun and high sSFR (~100Gyr^-1). This translates to high
stellar mass and SFR surface densities, about 100x higher than typical
galaxies at similar
redshifts. NIRSpec further reveals strong nebular emission, for which we derive a high electron density (~10^3 cm^-3), a
metallicity 12+log(O/H)=8.20 (from the direct method), and a super-
solar N/O ratio (log(N/O)=-0.30). Furthermore, J0217-0208 shows broad components in several rest-optical lines, indicating powerful ionized
outflows, which appear heavily obscured (E(B-V)~0.6), in contrast to the nearly
dust-free
stellar continuum (E(B-V)~0.01). Combined with ALMA detections of a massive, extended, and cold
dust reservoir, these findings point to dusty, feedback-driven
outflows carrying and pushing
dust well beyond the
stellar core, boosting the observed UV luminosity. Our results suggest that UV-bright
galaxies at high
redshift represent short-lived but extreme phases of rapid
stellar mass growth, efficient ionizing
photon production, and strong feedback. The extreme properties of J0217-0208, such as supersolar N/O, steep UV slope, compact size, and very high surface densities, closely mirror those of the brightest
galaxies at z>10, suggesting a shared evolutionary pathway.[Abridged]
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All authors R. Marques-Chaves, D. Schaerer, M. Dessauges-Zavadsky, J. Álvarez-Márquez, T. Hashimoto, L. Colina, A.K. Inoue, C. Blanco-Prieto, Y. Nakazato, L. Costantin, S. Arribas, T.J.L.C. Bakx, D. Ceverino, A. Crespo Gómez, Y. Fudamoto, M. Hagimoto, A. Hamada, Y. Matsuoka, K. Mawatari, M. Onoue, W. Osone, Y.W. Ren, Y. Sugahara, Y. Terui, N. Yoshida
Solar and Stellar Astrophysics
Infrared spectral signatures of light r-process elements in kilonovae
Anders Jerkstrand, Quentin Pognan, Smaranika Banerjee et al. (+8 more)
A central question regarding
neutron star mergers is whether they are able to produce all the r-process elements, from first to third peak. The high abundances of first-peak elements (atomic number $Z \sim 31-40$) in the
solar composition means they may dominate the ejecta mass in kilonovae. We here study theoretical infrared signatures of such light elements with spectral synthesis modelling. By combining state-of-the-art NLTE physics with new radiative and collisional data for these elements, we identify several promising diagnostic lines from Ge, As, Se, Br, Kr and Zr. The models give self-consistent line luminosities and indicate specific features that probe emission volumes at early phases ($\sim$10d), the product of ion mass and electron density in late phases ($\gtrsim$75d), and in some cases direct ionic masses at intermediate phases. Emission by [Se I] 5.03 \mum\ + [Se III] 4.55 \mum\ can produce satisfactory fits to the Spitzer photometry of AT2017gfo. However, the models show consistently that with a Kr/Te and Se/Te ratio following the
solar r-process pattern, Kr + Se emission is dominant over Te for the blend at 2.1 \mum\ observed in both AT2017gfo and AT2023vfi. The somewhat better line profile fit with [Te III] may suggest that both AT2017gfo and AT2023vfi had a strongly sub-
solar production of the light r-process elements. An alternative scenario could be that Kr + Se in an asymmetric morphological distribution generates the feature. Further JWST spectral data, in particular covering the so far unobserved $>5$ \mum\ region, holds promise to determine the light r-process production of kilonovae, and in particular whether the light elements are made in a slow disk wind or in a fast proto-NS
outflow. We identify specific needs for further atomic data on recombination rates and collision strengths for $Z=31-40$ elements.
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All authors Anders Jerkstrand, Quentin Pognan, Smaranika Banerjee, Nicholas Sterling, Jon Grumer, Niamh Ferguson, Keith Butler, James Gillanders, Stephen Smartt, Kyohei Kawaguchi, Blanka Vilagos
Astrophysics of Galaxies
Association of cold gas, massive galaxies, and AGNs in a filamentary protocluster traced by triple narrow-band imaging
Kazuki Daikuhara, Tadayuki Kodama, Haruka Kusakabe et al. (+13 more)
We investigate
galaxy populations in the HS1700+64 protocluster at $z=2.30$, characterized by two prominent linear filaments traced by spatially extended Ly$\alpha$ blobs. We conducted a wide area mapping of emission line
galaxies across the protocluster using the unique combination of three matched narrow-band filters, corresponding to Ly$\alpha$, H$\alpha$, and [OIII] emission lines at $z=2.30$. We find that H$\alpha$ emitters are strongly clustered at the intersection of the filaments, suggesting a protocluster core. In contrast, Ly$\alpha$ emitters tend to avoid the dense region and the filaments, likely due to the resonant scattering of Ly$\alpha$
photons by HII gas and/or enhanced
dust attenuation in
galaxies associated with these structures. These findings support a scenario in which cold gas flows via filaments and to the core, fed by the cold-stream mode
accretion in the early phase of protocluster assembly, and promoting active
star formation there. Further evidence of the scenario comes from the
alignment of massive, evolved
galaxies in those filaments traced by distant red
galaxies, suggesting accelerated
galaxy growth in the filaments in the early Universe. This study clearly shows observationally that accelerated
galaxy formation takes place not only in the protocluster core but also in the associated surrounding filamentary structure. This underscores the critical role of large-scale filaments in efficiently accumulating the cold gas and channeling it to
galaxies therein and to the protocluster core. Such vigorous gas assembly facilitates
star formation activity and drives
galaxy growth in the early stage of cluster formation.
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All authors Kazuki Daikuhara, Tadayuki Kodama, Haruka Kusakabe, Charles C. Steidel, Ichi Tanaka, Satoshi Kikuta, Hideki Umehata, Rhythm Shimakawa, Yusei Koyama, Kentaro Motohara, Masahiro Konishi, Jose Manuel Perez Martinez, Mariko Kubo, Dawn Erb, Kosuke Takahashi, Keita Fukushima
Earth and Planetary Astrophysics
The rings of (2060) Chiron: Evidence of an evolving system
C. L. Pereira, F. Braga-Ribas, B. Sicardy et al. (+54 more)
The centaur (2060) Chiron has long been a candidate for hosting material in orbit, based on occultation and photometric and spectroscopic data. Here, we present a multichord
stellar occultation observed on 2023 September 10 UT that reveals new and complex structures surrounding Chiron. High-cadence light curves show multiple secondary events that are best explained (when compared with a multishell interpretation) with a system of three confined rings located at average radii of 273, 325, and 438 km, the outermost of which lies beyond Chiron's Roche limit. The rings appear coplanar, with a mean pole orientation of {\lambda} = 151{\deg} +/- 4{\deg} and e̱ta} = 20{\deg} +/- 6{\deg}. A broader, disklike structure extends from about 200 to 800 km, and a newly detected faint feature is observed at ~1380 km. Chiron thus appears as the fourth small
solar system body known for hosting a ring system. Comparisons with previous occultation events that have occurred since 1994 show that these features are not permanent. With these observations, we may witness for the first time the ongoing formation and
evolution of a ring system.
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All authors C. L. Pereira, F. Braga-Ribas, B. Sicardy, R. Leiva, M. Assafin, B. E. Morgado, J. L. Ortiz, P. Santos-Sanz, J. I. B. Camargo, G. Margoti, Y. Kilic, G. Benedetti-Rossi, R. Vieira-Martins, T. F. L. L. Pinheiro, R. Sfair, F. L. Rommel, A. R. Gomes-Júnior, R. C. Boufleur, R. Duffard, J. Desmars, D. Souami, N. Morales, F. Arrese, K. Barkaoui, A. Burdanov, C. A. Colazo, C. A. Domingues, H. Dutra, R. C. Gargalhone, C. Jacques, F. Jablonski, L. Liberato, R. Melia, J. C. Oliveira, M. Sardiña, J. Spagnotto, T. Speranza, A. Wilberger, M. A. Zorzan, L. S. Brito, J. P. Cavalcante, T. Q. Costa, M. Emilio, E. Garcia-Migani, M. Gillon, E. Gradovski, E. Jehin, V. Lattari, M. Malacarne, L. A. Mammana, M. Melita, W. Melo, A. J. Ortiz, P. Quitral-Manosalva, G. Ramon, I. Rodrigues, L. Vanzi
High Energy Astrophysical Phenomena · Cross-listed from hep-th
The probe limit in MHD and its implications for magnetic transport
Giorgio Frangi, Matej Bajec, Guri K. Buza et al. (+2 more)
Many phenomenological and effective field-theoretical (EFT) applications of magnetohydrodynamics (MHD) in the presence of a background
magnetic field employ a simplifying assumption whereby the electromagnetic and the energy-momentum fluctuations decouple. In studies of
magnetic transport, for example in
magnetic diffusion, the conservation of energy and momentum is then neglected. In this paper, we investigate the details and the consistency of this so-called $\textit{probe limit}$ in different parametric regimes of MHD
plasmas. In the first part of the paper, our discussion explores the hydrodynamic (higher-form) theory of MHD. In the second part, we then explicitly test the probe limit by using a microscopic
holographic (AdS/CFT) model of a strongly coupled
plasma. In the process, we develop the
holographic Schwinger-Keldysh EFT prescription for describing the bulk 2-form fields and their dual 1-form
symmetries. Moreover, we find evidence of a phase transition at low temperatures and show that
magnetic Hall transport can emerge as a consequence of background charge density that breaks the charge conjugation
symmetry of the state. Finally, we discuss the implications for
magnetic transport, with a particular view towards the dynamics of dense
nuclear matter in
neutron stars.
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All authors Giorgio Frangi, Matej Bajec, Guri K. Buza, Alexander Soloviev, Sašo Grozdanov
Solar and Stellar Astrophysics
Discovery of new magnetic {\delta} Scuti stars and impact of magnetism on pulsation excitation
K. Thomson-Paressant, C. Neiner, J. Labadie-Bartz et al. (+3 more)
Context. At this time, the list of known
magnetic {\delta} Scuti
stars is extremely limited, with only a handful of well-studied examples. Aims. We seek to expand this list, by retrieving targets from a variety of sources and demonstrating that they present simultaneously a surface
magnetic field signature and {\delta} Scuti pulsations. Methods. We obtained archival and new spectropolarimetric
datasets for a variety of known {\delta} Scuti
stars and analysed them using the Least Squares Deconvolution method to generate mean Stokes I and V profiles for each target, from which we can determine longitudinal
magnetic field measurements. Additionally, we assessed photometric data from the TESS satellite to discern frequency peaks consistent with {\delta} Scuti pulsations in known
magnetic stars, and to identify
magnetic candidates via rotational modulation. Results. We present a compiled list of all the confirmed
magnetic {\delta} Scuti
stars discovered to date, containing 13
stars. The majority of this sample lies outside the usual {\delta} Scuti instability strip in the H-R diagram, though we do not observe any specific correlations between
magnetic field strength and various
stellar parameters. This indicates that strong global
magnetic fields play a fundamental role in shaping interior structure and processes.
Magnetic fields thus must be included in realistic
stellar models in order to more accurately predict structure and
evolution. Conclusions. This work constitutes the largest database to date of strongly
magnetic {\delta} Scuti
stars, one that will continue to grow over time with subsequent studies.
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All authors K. Thomson-Paressant, C. Neiner, J. Labadie-Bartz, R.-M. Ouazzani, S. Mathis, L. Manchon
Astrophysics of Galaxies
Hidden Figures of Globular Clusters: Integrated Stellar Populations Impacted by Hot Subdwarfs
Thayse A. Pacheco, Paula R. T. Coelho, Lucimara P. Martins et al. (+8 more)
Globular clusters (GCs) are fundamental for understanding the integrated light of old
stellar populations and
galaxy assembly processes. However, the role of hot, evolved
stars, such as horizontal branch (HB), extreme HB, and blue stragglers, remains poorly constrained. These
stars are often underrepresented or entirely excluded from
stellar population models, despite their dominant contribution to the ultraviolet (UV) flux. Their presence can bias age estimates by mimicking the spectral signatures of younger populations. We examined the impact of evolved hot
stars on the models using two well-studied
Galactic GCs with high-quality Hubble Space
Telescope photometry and integrated spectra from the International Ultraviolet Explorer and the Blanco
Telescope. NGC 2808 and NGC 7089 (M 2) have extended HBs and are proxies for old
stellar populations. Integrated spectra were constructed using a color magnitude diagram-based (CMD-based) method, matching observed
stars to evolutionary phases and then to appropriate synthetic
stellar libraries, enabling the HB morphology to be taken into account. Our findings show that the inclusion of evolved hot
stars significantly improves the agreement between the model and observed spectra from the UV to the optical. The inclusion of these phases reduced the residuals in spectral comparisons. Our results reinforce that comprehensive
stellar population models incorporating evolved hot components are essential to accurately date unresolved systems and to robustly trace formation histories of extragalactic
galaxies.
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All authors Thayse A. Pacheco, Paula R. T. Coelho, Lucimara P. Martins, Ricardo P. Schiavon, Erik V. R. de Lima, Marcos P. Diaz, Domenico Nardiello, Ronaldo S. Levenhagen, Rogerio Riffel, Charles J. Bonatto, Ana L. Chies-Santos
High Energy Astrophysical Phenomena
Fe XVIII-XXIV K beta Inner-shell Absorption Lines in the X-ray Spectra of Neutron Star and Black Hole Binaries with XRISM
Masahiro Tsujimoto, Daiki Miura, Hiroya Yamaguchi et al. (+8 more)
The advent of the X-ray microcalorimeter spectrometer Resolve onboard the XRISM space
telescope opened a new era for high-resolution X-ray spectroscopy of astrophysical
plasmas. Many spectral features were newly detected, including the K alpha and K beta inner-shell transition lines of mildly ionized (F- to Li-like) Fe at 6-8 keV in the spectra of X-ray binaries and active
galactic nuclei. The widely used atomic databases contain information on the K alpha but not K beta lines of these ions. We conducted the atomic structure calculation using FAC to derive the Fe K alpha and K beta lines and verified the result against ground experiments and other calculations of the Fe K alpha lines. We then implemented the Fe K beta lines in a radiative transfer code (cloudy) and compared the synthesized and observed spectra with XRISM. A reasonably good agreement was obtained between the observation and the ab initio calculations. This exemplifies the need to expand the atomic databases to interpret astrophysical spectra.
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All authors Masahiro Tsujimoto, Daiki Miura, Hiroya Yamaguchi, Ehud Behar, Chris Done, Maria Diaz Trigo, Chamani M. Gunasekera, Peter A. M. van Hoof, Stefano Bianchi, Maryam Dehghanian, Gary J. Ferland
Solar and Stellar Astrophysics
Spatio-Temporal Evolution of the March 2022 ICME Revealed by Multi-Point Observations of Forbush Decreases
Gaku Kinoshita, Beatriz Sanchez-Cano, Yoshizumi Miyoshi et al. (+13 more)
Interplanetary coronal mass ejections (ICMEs) cause Forbush Decreases (FDs) effects, which are local decreases in background
galactic cosmic rays (GCR). Even though FDs can be observed with simple particle instruments, their amplitude and shape provide physical profiles of passing ICMEs. However, in some cases, previous statistical studies of the heliocentric distance dependence of FD changes associated with ICME propagation have found no strong correlation. We need the criteria for evaluating the relationship between ICMEs structure and FD, necessary for FDs statistical analysis. This study investigates the effect of evolutions and interactions of ICMEs on FDs profiles in the inner
Solar System, using multipoint comparisons. We focus on multipoint ICME observations by
Solar Orbiter, BepiColombo, and near-Earth spacecraft from March 10-16, 2022, when these spacecraft were ideally located for studying the radial and longitudinal evolutions of ICME and accompanying FDs. We compared GCR variations with the multiple in-situ data and ICME model, clarifying the correspondence between the
evolution of each ICME structure in radial and azimuthal directions and the depth and gradients of the FD. The radial comparison revealed decreases in FD intensities and gradients associated with the expansion of the ICME. The longitudinal difference found in FD intensity indicates longitudinal variations of the ICMEs shielding effect. These results suggest that accurate multi-point FD comparisons require determining the relationship between the observers position and the inner structure of the passing ICMEs.
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All authors Gaku Kinoshita, Beatriz Sanchez-Cano, Yoshizumi Miyoshi, Laura Rodriguez-Garcia, Emilia Kilpua, Benoit Lavraud, Mathias Rojo, Marco Pinto, Yuki Harada, Go Murakami, Yoshifumi Saito, Shoichiro Yokota, Daniel Heyner, David Fischer, Nicolas Andre, Kazuo Yoshioka
Instrumentation and Methods for Astrophysics
Experimental tests of the calibration of high precision differential astrometry for HWO
Manon Lizzana, Fabien Malbet, Alain Leger et al. (+7 more)
Many different scientific applications require sub-micro arcsecond precision astrometry, including researching rocky
exoplanets in the vicinity of the Sun and studying dark matter. The Habitable Worlds Observatory (HWO) is a promising candidate to carry an astrometric instrument because it provides a stable, space-based
telescope with a large aperture, which allows faint sources and small displacements to be observed. This paper presents the characterization of an appropriate detector for an astrometric instrument: the 46Mpx Gigapyx from Pyxalis. Moreover it explains the implementation of a testbed enabling interferometric characterization of pixel positions. Finally, the paper introduces a method for calibrating the
telescope's optical distortion. This method was implemented in simulation and tested thanks to an optical bench developed at IPAG in France.
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All authors Manon Lizzana, Fabien Malbet, Alain Leger, Fabrice Pancher, Sébastien Soler, Hugo Rousset, Thierry Lepine, Julien Michelot, Yahya Er-Rahmaouy, Youssef Bakka
Astrophysics of Galaxies
Is Milky Way gravitationally stable? A TNG50 view from cosmic noon to the present day
K. Aditya and Sandeep Kataria
We investigate the stability of Milky Way analogs (MWAs) in the TNG50 simulation against the growth of local axisymmetric instabilities, tracing their
evolution from
cosmic noon ($z=2.5$) to the present day ($z=0$). Using a two-component stability criterion that accounts for
stars, gas, and the force field of the dark matter
halo, we compute the net stability parameter ($Q_{T}$), the critical gas surface density ($\Sigma_{c}$), and the instability timescale ($\tau$) for 10 barred and 10 unbarred MWAs. We find that these
galaxies remain stable to axisymmetric instabilities at all epochs, with $Q_{T}^{\min}>2$. The stability levels increase toward higher
redshift, where enhanced gas velocity dispersion counterbalances the destabilizing effect of larger gas fractions. Further, the barred MWAs consistently show lower $Q_{T}^{\min}$ than unbarred ones. The gas density remains subcritical ($\Sigma_{g}<\Sigma_{c}$) across radii and epochs, implying that local axisymmetric instabilities are not the primary channel for
star formation. Growth timescales are short (a few Myr) in central regions but increase exponentially to several Gyr in the outer disc, naturally explaining the concentration of
star formation toward
galactic centers. We study the effect of gas dissipation and
turbulence in ISM and find that while MWAs are stable against axisymmetric instabilities $(Q_{T}>1)$, a combination of gas dissipation and
turbulence in ISM can destabilize the disc at small scales even when $Q_{T}>1$.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Importance of being nonminimally coupled: Scalar Hawking radiation from regular black holes
Marco Calzà, Massimiliano Rinaldi and Sunny Vagnozzi
In curved space-time, a scalar field $\phi$ is generically expected to couple to
curvature, via a coupling of the form $\xi\phi^2R$. Yet in the study of Hawking emission from regular black holes (RBHs), where scalar fields are often introduced as simple probes of the geometry, and the
Ricci scalar is generically non-zero, this non-minimal coupling is almost always ignored. We revisit this assumption by studying scalar Hawking emission from four representative RBHs (the Bardeen, Hayward, Simpson-Visser, and D'Ambrosio-Rovelli space-times), within two
benchmark cases: the conformal case $\xi=1/6$, and a large negative value $\xi=-10^4$ motivated by
Higgs inflation. We compute the graybody factors and emission spectra, showing that the latter can be either enhanced or suppressed, even by several orders of magnitude. A crucial role is played by the sign of the term $\xi fR$, with $f(r)=-g_{tt}$ in Schwarzschild-like coordinates, as it determines whether the non-minimal coupling suppresses or enhances the
geometric potential barrier. For the D'Ambrosio-Rovelli case with large negative $\xi$, the low-energy emission spectrum is enhanced by up to five orders of magnitude, since $\xi fR<0$ throughout the space-time, leading to a deep potential well which broadens the transmissive window. The deviations we find can be particularly relevant in the case where
primordial RBHs are dark matter candidates, given the impact of the non-minimal coupling on their evaporation history.
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Earth and Planetary Astrophysics · Cross-listed from physics.flu-dyn
Model of deep zonal flows in giant planets
Laura K. Currie and Chris A. Jones
A mechanism by which the surface zonal flows of
giant planets can be gradually attenuated with depth is explored. The zonal flow is driven by an imposed forcing in a thin layer near the surface. A meridional circulation is set up, analogous to the Ferrel-like
cells observed in Jupiter's atmosphere. Acting on a stably stratified thin surface layer, the meridional flow induces a horizontal temperature anomaly which leads to a gradual reduction of the zonal winds with depth, governed by the thermal wind equation. Our model is a Boussinesq plane layer, with
gravity acting parallel to the rotation axis. A suite of fully three-dimensional time-dependent numerical simulations has been performed to investigate the model behaviour. Below the forced stable layer, convection is occurring, typically in the form of tall thin
cells. The fluctuating components of the three-dimensional flow can be driven by either the convection or the Reynolds stresses associated with the jet shear flow. When fluctuations are mainly driven by convection in the form of tall thin columns and the forcing is relatively weak, the horizontal temperature anomaly persists much deeper into the interior than when it is driven by shear flow. The zonal jets can therefore extend deep into the interior, consistent with the Juno
gravity data.
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Astrophysics of Galaxies
A census of quiescent galaxies across $0.5 < z < 8$ with JWST/MIRI: Mass-dependent number density evolution of quiescent galaxies in the early Universe
Tiancheng Yang, Tao Wang, Ke Xu et al. (+12 more)
Recent JWST observations have revealed a large population of quiescent
galaxies (QGs) at high
redshift ($z \sim 4-8$), challenging current models of early
galaxy formation and quenching. Accurate number density estimates are crucial but remain uncertain. We present a systematic study of QGs at $0.5 < z < 8$ using a mass-complete sample from the JWST/PRIMER survey with deep NIRCam and MIRI imaging. We demonstrate that MIRI photometry is essential for refining the QG sample: it helps to mitigate contamination from dusty
star-forming
galaxies in the high-mass regime at $z \sim 3-5$ and aids in recovering lower-mass QG candidates at $z > 5$ that are often missed without including MIRI data. We find that the
evolution of the QG number density is strongly mass-dependent. The density of massive QGs ($\log (M_{\star}/M_{\odot}) > 10.6$) declines rapidly, falling from $n \approx 1.32\times10^{-5}~~\mathrm{Mpc^{-3}}$ at $z \sim 3-4$ to $n < 1 \times10^{-6}~~\mathrm{Mpc^{-3}}$ at $z \sim 6$, and becomes negligible at $z > 6$. In contrast, low-mass QGs ($9.5 < \log (M_{\star}/M_{\odot}) < 10.6$) exhibit a remarkably constant number density of $n \sim 3\times10^{-6}~\mathrm{Mpc^{-3}}$ across the
redshift range $z = 4-8$. This plateau suggests that these high-
redshift, low-mass QGs may be
galaxies undergoing temporary quenching episodes, likely subject to rejuvenation upon future gas
accretion. Comparisons with leading
galaxy formation models reveal significant tensions: most models underestimate the abundance of massive QGs at $z > 4$ and fail to reproduce the flat density
evolution observed for the low-mass population.
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All authors Tiancheng Yang, Tao Wang, Ke Xu, Hanwen Sun, Luwenjia Zhou, Lizhi Xie, Gabriella De Lucia, Claudia del P. Lagos, Kai Wang, Fabio Fontanot, Qi Guo, Yuxuan Wu, Shiying Lu, Longyue Chen, Michaela Hirschmann
Instrumentation and Methods for Astrophysics
Encapsulating Textual Contents into a MOC data Structure for Advanced Applications
Giuseppe Greco, Thomas Boch, Pierre Fernique et al. (+12 more)
Context. The Multi-Order Coverage map (MOC) is a widely adopted standard promoted by the International Virtual Observatory Alliance (IVOA) to support data sharing and interoperability within the Virtual Observatory (VO) ecosystem. This hierarchical data structure efficiently encodes and visualizes irregularly shaped regions of the sky, enabling applications such as cross-matching large astronomical catalogs. Aims. This study aims to explore potential enhancements to the MOC data structure by encapsulating textual descriptions and semantic
embeddings into sky regions. Specifically, we introduce "Textual MOCs", in which textual content is encapsulated, and "Semantic MOCs" that transform textual content into semantic
embeddings. These enhancements are designed to enable advanced operations such as similarity searches and complex queries and to integrate with generative artificial intelligence (GenAI) tools. Method. We experimented with Textual MOCs by annotating detailed descriptions directly into the MOC sky regions, enriching the maps with contextual information suitable for interactive learning tools. For Semantic MOCs, we converted the textual content into semantic
embeddings, numerical representations capturing textual meanings in multidimensional spaces, and stored them in high-dimensional vector databases optimized for efficient
retrieval. Results. The implementation of Textual MOCs enhances user engagement by providing meaningful descriptions within sky regions. Semantic MOCs enable sophisticated query capabilities, such as similarity-based searches and context-aware data
retrieval. Integration with
multimodal generative AI systems allows for more accurate and contextually relevant interactions supporting both spatial, semantic and visual operations for advancing astronomical data analysis capabilities.
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All authors Giuseppe Greco, Thomas Boch, Pierre Fernique, Manon Marchand, Mark Allen, Francois Xavier Pineau, Matthieu Baumann, Marco Molinaro, Roberto De Pietri, Marica Branchesi, Steven Schramm, Gergely Dalya, Elahe Khalouei, Barbara Patricelli, Giulia Stratta
Solar and Stellar Astrophysics
YSO Variability in the W51 Star-Forming Region
Mi-Ryang Kim, Jeong-Eun Lee, Contreras Peña Carlos et al. (+3 more)
Time-domain studies of mid-infrared and submillimeter variability have shown that at least half of protostars are variable. We present a statistical analysis of mid-infrared variability among young
stellar objects (YSOs) in the distant, massive
star-forming region W51 using NEOWISE data. From a catalog of 81 protostars, 527 disk objects, and 37,687 other sources including diskless pre-main sequence and evolved contaminants, we identified significant variability in the 3.4 um (W1) and 4.6 um (W2) bands. Because of W51's distance (~5.4 kpc) and extinction, the sample mainly includes intermediate- to high-mass YSOs (>2 Msun), unlike nearby regions dominated by low-mass
stars. This mass bias may affect the observed variability. In W2, 11.1% of protostars, 7.6% of disk objects, and 0.6% of PMS+E sources showed secular variability, while 8.6%, 2.3%, and 0.5% showed
stochastic variability; similar fractions were found in W1. The variability fraction and amplitude increase toward earlier stages. Protostars exhibit high-amplitude
stochastic changes likely driven by dynamic
accretion and extinction, whereas disk objects show more secular patterns-linear, curved, or periodic-possibly due to moderate
accretion variations or disk geometry. Color-magnitude analysis shows that protostars generally redden as they brighten, consistent with enhanced
dust emission or variable extinction, while disk objects show mixed trends: roughly balanced in W1 but more often bluer in W2, suggesting reduced extinction or hotspot modulation. These results highlight distinct mechanisms of variability across evolutionary stages and demonstrate that mid-infrared monitoring offers key insight into
accretion and disk
evolution in young
stars.
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All authors Mi-Ryang Kim, Jeong-Eun Lee, Contreras Peña Carlos, Gregory Herczeg, Doug Johnstone, Miju Kang
Astrophysics of Galaxies
Computational advances and challenges in simulations of turbulence and star formation
Christoph Federrath and Stella Offner
We review recent advances in the numerical modeling of turbulent flows and
star formation. An overview of the most widely used simulation codes and their core capabilities is provided. We then examine methods for achieving the highest-resolution magnetohydrodynamical
turbulence simulations to date, highlighting challenges related to numerical viscosity and resistivity. State-of-the-art approaches to modeling
gravity and
star formation are discussed in detail, including implementations of
star particles and feedback from jets, winds, heating, ionization, and
supernovae. We review the latest techniques for radiation hydrodynamics, including ray tracing, Monte Carlo, and moment methods, with comparisons between the flux-limited
diffusion, moment-1, and variable Eddington tensor methods. The final chapter summarizes advances in
cosmic-ray transport schemes, emphasizing their growing importance for connecting small-scale
star formation physics with
galaxy-scale
evolution.
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Solar and Stellar Astrophysics
Violent mergers can explain the inflated state of some of the fastest stars in the Galaxy
Aakash Bhat, Rüdiger Pakmor, Ken J. Shen et al. (+2 more)
A significant number of hypervelocity
stars with velocities between $1500-2500$ km/s have recently been observed. The only plausible explanation so far is that they have been produced through thermonuclear
supernovae in white
dwarf binaries. Since these
stars are thought to be surviving donors of Type Ia
supernovae, a surprising finding was that these
stars are inflated, with radii an order of magnitude more than expected for Roche-lobe filling donors. Recent attempts at explaining them have combined 3-dimensional hydrodynamical
supernova explosion simulations with 1-dimensional
stellar modelling to explain the impact of
supernova shocks on runaway white
dwarfs. However, only the hottest and most compact of those runaway
stars can so far marginally be reproduced by detailed models of runaways from
supernova explosions. In this and a companion paper, we introduce a new Arepo simulation of two massive CO white
dwarfs that explode via a violent merger. There, the primary white
dwarf ignites when the secondary is on its last orbit and plunging towards the primary. In the corresponding aftermath, the core of the secondary white
dwarf of 0.16 M$_\odot$, remains bound, moving at a velocity of $\sim2800$ km/s. We map this object into MESA, and show that this runaway
star can explain the observations of two hypervelocity
stars that were dubbed D6-1 and D6-3 based on their original discovery motivated by the D6 scenario, though the violent merger scenario presented here is somewhat distinct from the D6 scenario.
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All authors Aakash Bhat, Rüdiger Pakmor, Ken J. Shen, Evan B. Bauer, Abinaya Swaruba Rajamuthukumar