Solar and Stellar Astrophysics
Sunrise III/SUSI reveals extended and spectrally structured Ca II K emission above the solar limb
Ivan Milić, Christopher M. J. Osborne, Francisco A. Iglesias et al. (+32 more)
The Sunrise III/SUSI instrument performed a sit-and-stare observation of the off-limb emission in the Ca II K line core, with a combination of excellent temporal and spectral resolution. The emission reaches up to 6 Mm above the solar limb, indicating the existence of off-limb structures akin to spicules. In this letter, we describe the spatio-spectral properties of the observed emission, focusing on the spectral line shape resolved in detail by Sunrise III/SUSI, and compare the observation with simple modeling that relies on a numerical simulation of the solar chromosphere. We find that the simulation contains enough cool and dense material at Mm heights to produce off-limb emission, but that the spectral width of these features is slightly lower than observed, necessitating more detailed modeling.
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All authors Ivan Milić, Christopher M. J. Osborne, Francisco A. Iglesias, Juan Sebastián Castellanos Durán, Damien F. Przybylski, Lakshmi Pradeep Chitta, Sanghita Chandra, Andreas Lagg, Sami K. Solanki, Tino L. Riethmüller, Achim Gandorfer, Alex Feller, Johannes Hoelken, H. N. Smitha, Jose Carlos del Toro Iniesta, Yukio Katsukawa, Pietro Bernasconi, Thomas Berkefeld, Alberto Álvarez-Herrero, Masahito Kubo, Valentín Martínez Pillet, David Orozco Suárez, Bianca Grauf, Michael Carpenter, Alexander Bell, Hanna Strecker, Azaymi L. Siu-Tapia, Pablo Santamarina Guerrero, Julian Blanco Rodríguez, Yusuke Kawabata, Takuma Matsumoto, Ryohtaroh T. Ishikawa, Edvarda Harnes, Takayoshi Oba, Dušan Vukadinović
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
A triple-induced merger in T Ori C, solves the proplyd lifetime problem and the curiously young shell of M42
Maite Wilhelm, Alessandro Alberto Trani and Simon Portegies Zwart
There has long been a tension between the stellar ages in the Orion Nebula Cluster and the rapid external photoevaporation of its protoplanetary discs. Recently, the shell of the Orion Nebula has similarly been found to be dynamically younger than the
stars. We propose a new scenario to resolve both age problems. In our scenario the ONC's most massive
star, $\theta^1$~Ori~C1, formed from the merger between two binary
stars induced by vZLK oscillations due to the present-day binary companion $\theta^1$~Ori~C2. This merger, happening between the last episode of
star formation and today, resulted in an increased luminosity, leading to stronger external photoevaporation and accelerated expansion of the shell. {We use Monte Carlo simulations to explore both whether a sudden brightening of $\theta^1$~Ori~C1 could reconcile the stellar ages and shell expansion, and whether triple progenitors to $\theta^1$~Ori~C\, could result in stellar mergers on the relevant timescale. A sudden brightening of $\theta^1$~Ori~C1 a few hundred thousand years ago can reproduce today's shell while maintaining a system age close to the stellar age. However, the required increase in stellar wind luminosity is greater than a simple merger can explain. At lower luminosity, the mixing of a relatively greater amount of cool photoevaporative wind material into the hot bubble could result in the required increase, and we identify a lower limit on the required strength of this effect. Additionally, we find that progenitor triples merge readily, on timescales even shorter than the scenario would require. These mergers could be deferred by increased pre-main sequence tidal effects, rotation, and perturbing encounters with other cluster members. Our proposed scenario with a merger driven by von Zeipel-Lidov-Kozai
evolution solves two problems; the Orion Nebula's proplyd problem and the shell lifetime problems.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
HESS J1507-622: A Plausible Young Galactic Kilonova Remnant
Prantik Sarmah, Xilu Wang, Myles Carley et al. (+3 more)
HESS J1507$-$622 is an unusual TeV gamma-ray source in the H.E.S.S. Galactic Plane Survey, distinguished by its off-plane location ($b \simeq -3.5^{\circ}$) and compact angular extent ($\sim 0.3^{\circ}$). Its location and morphology challenge conventional
pulsar wind nebula and
supernova remnant interpretations, and the absence of a detected shell or associated
pulsar leaves its origin unresolved. Here, we propose that HESS J1507$-$622 is a young Galactic kilonova remnant with gamma-ray emission of leptonic origin. In this scenario, the source's off-plane location is naturally explained by the natal kick imparted to the progenitor binary
neutron star system. We demonstrate that a leptonic kilonova remnant model can successfully reproduce the observed GeV-TeV flux via inverse-Compton scattering from shock-accelerated electrons, while the corresponding synchrotron emission remains below current X-ray and
radio upper limits. Based on the source's energetics and angular size, we infer a distance of 3.8-14.3 kpc and an age of 0.2-3.0 kyr. Importantly, our analysis favors a kilonova remnant younger than 1 kyr. The lack of a historical naked-eye record can be explained by the transient's rapid fading, far-southern declination, and potential line-of-sight extinction. We further assess the detectability of unique multi-wavelength signatures that could confirm this hypothesis. We find promising prospects for detecting the unique MeV gamma rays from the decay of $r$-process radioisotopes using future observatories, alongside complementary low-energy signatures from thermal dust emission and a possible optical light echo. These distinct signals offer definitive tests of the kilonova remnant interpretation and motivate targeted observations with current and future facilities.
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All authors Prantik Sarmah, Xilu Wang, Myles Carley, Shu-Xu Yi, Ming-Yu Ge, Rebecca Surman
Solar and Stellar Astrophysics
Surveying for Close Binaries among Lithium-rich Giants
Jesús Torres, Sebastián Vilaza-Dallago, Julio Chanamé et al. (+1 more)
One of the possible scenarios usually considered to explain the existence of low-mass red giants with anomalously high lithium (Li) abundances requires the interaction with a close binary companion. If dominant, this enrichment channel predicts a significantly enhanced binary fraction among Li-rich giants relative to Li-normal ones. We aim to constrain the binary interaction hypothesis by using multi-epoch radial velocities (RVs) to measure the close binary fraction of a statistically robust sample of Li-rich giants. We are surveying both red clump (RC) and first ascent red giant (RGB) targets, which allows us to examine potential differences in the binary fraction as a function of evolutionary stage. We are monitoring 70 targets (40 RC and 30 RGB, all Li-rich) using ESPRESSO at the VLT, 57 of which (32 RC + 25 RGB) already have 4 or more visits over a $\sim$7 month baseline; the analysis in this paper is based on the latter. For the targets with RV variation larger than that expected for intrinsic jitter, we use a Monte Carlo analysis to estimate the probability that the observed RV variation is due to a stellar ($P_{SB}$) or sub-stellar ($P_{SS}$) companion. Discounting the 38 targets consistent with stellar jitter, we are left with 11 RC and 8 RGB
stars (34% and 32% of the respective sub-samples) with RV variability consistent with the presence of a close companion with an orbital period shorter than 3000 days. Of these 19, 3 can be confirmed as stellar-mass companions. The distributions of $P_{SB}$ and $P_{SS}$ are statistically indistinguishable between the RC and RGB samples. We thus find no evidence so far in our current data for a binary fraction for Li-rich giants (in either evolutionary stage) larger than that expected for a Li-normal population. Extending the RV baseline to probe longer orbital periods will be important to keep exploring the plausibility of this scenario.
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All authors Jesús Torres, Sebastián Vilaza-Dallago, Julio Chanamé, Rafael Brahm
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Constraining exoplanet population parameters with Kepler and simulation-based inference
Chloé Padois, Friedrich Anders and Daniel del Ser
In the context of the rapidly growing field of galactic
exoplanet population studies, we present an
exoplanet simulator capable of generating synthetic populations for millions of
stars in a few seconds (Padois et al., 2025). Our framework combines observed
exoplanet detections with the latest planetary formation models, incorporating dependencies between host
star properties and
planet occurrence rates, orbital period distributions, and other key demographic features. However, many model parameters remain uncertain and model-dependent. To constrain some of the most critical ones, we couple our simulator with simulation-based inference (SBI): we define a set of 44 free parameters describing the population of different
planet types (occurrence rates, mass-period distribution, mass-radius relation, etc.), run millions of simulations sampling from broad prior distributions, simulate their detectability by Kepler, and train a machine-learning
algorithm to learn the relationships between input parameters and the resulting "observed" synthetic populations. The best-fit parameters are then inferred by comparing model outputs to real observations, for which we adopt the Kepler confirmed
planet catalogue as our reference
dataset, since it provides the largest homogeneous sample from a single facility. We present preliminary results for the
planet occurrence rate as a function of stellar mass and
metallicity, across different
planet types, along with constraints on several key simulation parameters such as the orbital period distribution and the inclination dispersion within planetary systems. These refined parameters enable us to refine our yield predictions for upcoming
exoplanet detection missions, including PLATO, Roman, and HAYDN.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
Joint Mass-Radius and Magnetic-Geometry Inference of PSR J0740+6620
Chun Huang, Tuomo Salmi and Alexander Y. Chen
X-ray pulse-profile modeling can measure
neutron-
star radii, but its physical interpretation remains limited by the largely phenomenological description of the surface hotspots. Here we connect the X-ray hotspots directly to the
pulsar magnetospheric structure and jointly infer the mass, radius, and
magnetic geometry of the massive millisecond
pulsar PSR J0740+6620 from NICER and XMM-Newton observations. Using a GPU-accelerated implementation, we compare two low-dimensional
magnetic configurations that can produce non-antipodal emission: a centered axisymmetric dipole–quadrupole and a shifted dipole. The shifted-dipole model is decisively favored under the adopted priors, with $\Delta\ln Z=5.65$ (Bayes factor $\sim285$), and yields $M=2.059^{+0.068}_{-0.069}\,M_{\odot}$ and $R=13.28^{+1.47}_{-1.07}\,\mathrm{km}$, broadly consistent with previous phenomenological analyses, while requiring nearly symmetric heating of the two polar caps. Both the marginalized shifted-dipole posterior and the timing-compatible representative require an effective X-ray-emitting footprint much smaller than the nominal force-free polar cap calibrated for a centered dipole. This compact footprint is not reproduced by our exploratory
photon-conversion estimates and instead points to missing physics in the mapping from magnetospheric currents to observable X-ray emission. Our results show that physically motivated hotspots can preserve the mass–radius inference while turning hotspot morphology into a probe of
pulsar magnetospheric structure and emission physics.
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Solar and Stellar Astrophysics
Detection of fine-structured radio bursts during a superflare on EQ Peg
Zhanhao Zhao, Xin Cheng, Yuankun Kou et al. (+6 more)
Superflares are frequently observed on magnetically active
stars, particularly on active M-dwarfs, thereby influencing the habitability of nearby
exoplanets. However, the causes of superflares remain unclear. Here, combining FAST and TESS, we detected a finely structured decimetric
radio burst appearing as groups of spikes during a white-light superflare (total bolometric energy $\sim 10^{33} \ \mathrm{erg}$) on the M-dwarf binary EQ Peg on September 8th, 2022. The most significant ones appeared near the peak time of the optical
flare and lasted for about $100 \ \mathrm{s}$. The
radio spikes present extremely high brightness temperatures ($\gtrsim 10^{13} \ \mathrm{K}$) and high degrees of circular polarization ($\sim 0.84 \pm 0.16$), indicating the origin of a coherent emission process, most likely the electron cyclotron maser. Based on Zeeman-Doppler Imaging measurements of EQ Peg, we further locate the sources of the
radio spikes, including their heights and latitudes, under the assumption of a large-scale dipolar
magnetic field configuration. The results provide strong evidence for finely structured decimetric
radio bursts generated by stellar
flares and shed light on the origin of superflares.
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All authors Zhanhao Zhao, Xin Cheng, Yuankun Kou, Guoyin Chen, Hao Ning, Yao Chen, Baolin Tan, Keping Qiu, Mingde Ding
Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
Effects of Alfvénicity on the Compressible Energy Cascade in Magnetohydrodynamic Solar Wind Turbulence: Evidence from Parker Solar Probe, Solar Orbiter, and WIND observations
Nahuel Andrés, Carlos A. Gonzalez and Norberto Romanelli
The compressible MHD energy cascade in the solar wind is shaped by Alfvénicity,
plasma fluctuations, and
proton temperature, yet how these factors regulate the relative weight of compressible and incompressible energy transfer across heliocentric distances remains poorly understood. We apply compressible and incompressible exact relations to a large sample of 2-hour intervals from WIND (1~au), Parker Solar Probe ($<0.25$~au), and Solar Orbiter (0.3–1~au), classifying intervals as Alfvénic ($|\sigma_c|>0.75$) or non-Alfvénic ($|\sigma_c|<0.25$) and by wind speed, and examine the Yaglom-like and purely compressible components of the compressible cascade. Velocity fluctuation amplitude is the strongest predictor of the compressible cascade rate $\langle|\varepsilon_c|\rangle$, followed by density and
magnetic field fluctuations. $\langle|\varepsilon_c|\rangle$ and $\langle|\varepsilon_i|\rangle$ are tightly correlated in all regimes, with their ratio organized by Alfvénicity and wind speed: non-Alfvénic and Alfvénic fast winds cluster along $\langle|\varepsilon_c|\rangle=\langle|\varepsilon_i|\rangle$, while Alfvénic slow wind shows a systematic excess consistent with internal energy contributions. The largest $\langle|\varepsilon_c|\rangle$ systematically occur in hotter intervals, with a two-decade increase from cool to hot events in Alfvénic slow and non-Alfvénic wind, a trend carried mainly by the purely compressible term, while the dominant Yaglom-like term controls the overall cascade magnitude. Alfvénicity and wind speed thus govern the efficiency of turbulent energy transfer across heliocentric distances, and the tight coupling between compressible and incompressible rates points to the need for compressible, multi-fluid descriptions of the solar wind dissipation budget.
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Solar and Stellar Astrophysics
Solar spicule population properties inferred from IRIS Mg II k off-limb spectra using likelihood-free Bayesian inference
Jiri Stepan, Stanislav Gunar, Akiko Tei et al. (+1 more)
Solar spicules are ubiquitous and strongly overlapping in off-limb observations, which complicates the interpretation of individual events. We aim to infer population-level properties of spicules from IRIS Mg~II~k off-limb spectra using a forward model that explicitly accounts for line-of-sight superposition and instrumental effects. We construct a
stochastic three-dimensional spicule-population model and synthesize Mg II k spectra with radiative transfer, including instrumental degradation and
photon noise. We then constrain the hyperparameters that describe the underlying spicule population with likelihood-free
Bayesian inference based on approximate
Bayesian computation and an adaptive population Monte Carlo sampler, comparing observed and simulated
datasets through principal-component summary statistics at five heights above the limb. The inferred posterior constrains effective population-level properties of the spicules that dominate the observed Mg II k variability and height dependence. These constraints provide a route to connect off-limb spectroscopy with forthcoming spectropolarimetric diagnostics of the chromosphere-corona interface.
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All authors Jiri Stepan, Stanislav Gunar, Akiko Tei, Petr Heinzel
Solar and Stellar Astrophysics
Near-infrared periodicity in the SPICY catalog. True young stellar objects versus contaminants
C. Ordenes-Huanca, A. Bayo, M. Zoccali et al. (+2 more)
Infrared (IR) large-sky surveys allow study of how localized
star formation is, enabling searches for young stellar objects (YSOs) not only at the centers of known stellar nurseries but also across the Galactic plane. However, these spatially unbiased searches suffer from contamination, most notably from dusty asymptotic giant branch (AGB)
stars characterized by long-period variability. Using time-series analysis, and taking advantage of the different variability timescales of YSOs against long-period variables (LPVs), we assess the level of contamination of one of the most spatially unbiased YSO catalogs (Spitzer/IRAC Candidate YSO, SPICY). Distinguishing between these two groups lets us draw more robust conclusions about the frequency of isolated YSOs in our
Galaxy and their implications. We cross-match the SPICY and VIRAC2 catalogs (VVV/VVVX Survey), build near-IR light curves for common sources, and compute their periods and amplitudes. Contaminants are identified as sources with periodic flux variations with periods $P\geq 80\,d$ and amplitudes $\Delta K_{\rm s}\geq0.35\,\rm{mag}$. From $58\,737$ common sources, we identify $742$ SPICY objects as LPV contaminants based on their long-period variability, and identify $307$ high-confidence periodic YSO candidates exhibiting short-period flux changes consistent with cool spots. Near- and mid-IR amplitudes are correlated only among LPVs, suggesting a common pulsation origin. In addition, the spatial distribution of the identified populations further supports our classification, with LPVs preferentially associated with the bulge and YSOs at the lowest galactic latitudes.
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All authors C. Ordenes-Huanca, A. Bayo, M. Zoccali, V. Guzmán, A. Rojas-Arriagada
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
Fast and furious – High-velocity features of Ca and Si in the spectra of Type Ia supernovae
Zsófia Bora, József Vinkó, J. Craig Wheeler et al. (+2 more)
High velocity absorption lines of Ca II and Si II (high-velocity features, HVFs) are common in the early spectra of Type Ia
supernovae (SNe Ia), but their physical origin is still poorly understood. We used 181 optical spectra of 56 SNe Ia that show HVFs in at least the Ca II NIR triplet to better understand the nature of HVFs. To model the profiles of HVFs we applied Gaussian fitting as well as spectrum synthesis modeling with the SYNOW code. We found that Gaussian fitting usually underestimates the velocity of HVFs compared to SYNOW, and derived a linear formula for correction. In accord with many previous studies, the observed properties of HVFs (velocity, strength, duration) were found to correlate with the general observables of SNe Ia (decline rate, spectral subtype). Brighter, slow-declining SNe usually exhibit stronger, higher velocity HVFs, while fainter objects typically show weak, low velocity HVFs. SNe Ia in early-type
galaxies showed weaker and slower HVFs compared to events in late-type
galaxies in our sample. Comparing these observational findings with theoretical predictions, we conclude that the overall physical picture of HVFs is quite complex, and could be explained by multiple models. A double detonation explosion model is promising as it is inherently capable of explaining the creation of high-velocity shells that may produce HVFs, but an asymmetric delayed detonation model or interaction with circumstellar material cannot be ruled out.
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All authors Zsófia Bora, József Vinkó, J. Craig Wheeler, Réka Könyves-Tóth, G.H. Marion
Solar and Stellar Astrophysics
Common Envelope Evolution: Too stochastic to be deterministic
Noam Soker
I argue for significant
stochastic behavior in the common envelope
evolution (CEE) of cool giants and main-sequence companions to the degree that it is almost impossible to know the exact CEE outcome of an individual binary system from the average properties of the
stars and their initial orbit. I start with two observational properties of post-CEE planetary nebulae: many have jet-shaped morphologies, and they show a wide variety of morphologies. The first suggests that the standard CEE model should include jets, and the second shows that the CEE has a wide variety of evolutionary routes; for example, jets can be launched before, during, and/or after the main CEE phase. I show that the properties of the disk with which the main-sequence companion enters the CEE depend sensitively and stochastically on the pulsations and convection of the giant
star. Pulsations and giant-envelope convection stochastically determine the
evolution of the
accretion disk inside the envelope. The
stochastic nature of the
accretion disk properties implies that jet power is also
stochastic. Adopting the view that jets play a major role in CEE outcomes, I conclude that the CEE outcome is
stochastic. I conclude that the CEE efficiency parameter alpha(CE) has little merit for individual systems, although it still has meaning in population synthesis and other studies of large populations.
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Solar and Stellar Astrophysics
Abundance analysis of three new extremely metal-poor stars, including one CEMP-s star
P. François, T. Suda, S. Wanajo et al. (+5 more)
We report a detailed abundance analysis of three extremely metal-poor (EMP)
stars thanks to spectra obtained with the high-dispersion spectrograph (HDS) at the Subaru
telescope. The aim is to observe a sample of EMP candidate
stars selected from the Sloan Digital Sky Survey (SDSS) and determine their detailed chemical composition. High-resolution spectra of three faint turn-off
stars using HDS on the Subaru
telescope were acquired.We used standard 1D models to compute the abundances of several elements (Li, C, Mg, Ca, Sr, and Ba). The
stars we analysed have a
metallicity [Fe/H] of between -3.02 and -3.57 dex. We also measured accurate radial velocities that, coupled with the Gaia astrometric data, allowed us to compute actions and Galactic orbits for the
stars. Our analysis confirms that the
stars are genuine EMP
stars. One of them (SDSS J074238.68 +470537.0) can be classified as a CEMP-s
star with the highest [Mg/Fe] ratio ever measured in a turn-off CEMP-s
star with [Mg/Fe] = 1.85 dex. For the
star SDSS J012630.30+073029.3 ([Fe/H]= -3.02 dex), we have a clear detection of lithium with A(Li) = 2.05. Kinematically, SDSS J214340.08-002835.5 is a thick-disc
star, while the other two belong to the
halo and are candidate members of the Gaia- Sausage-Enceladus.
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All authors P. François, T. Suda, S. Wanajo, E. Caffau, P. Bonifacio, W. Aoki, S. Yamada, M. Y. Fujimoto
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
The Occurrence Rate of Planets Around Subgiant Stars from TESS Photometric Survey
Arkaprova Dutta and Priyanka Chaturvedi
Subgiant
stars represent a critical phase in stellar
evolution, offering an opportunity to investigate how planetary systems respond to the early stages of post-main-sequence expansion. Despite their importance, systematic occurrence-rate studies of this population remain sparse compared with those of main-sequence and red-giant hosts. In this work, we present a uniform analysis of
planet occurrence around a sample of 282,904 subgiant
stars selected from the Gaia DR3 catalogue. We perform an independent reanalysis of TESS light curves for transit-signal detection and refinement, followed by multi-stage vetting including visual inspection and statistical false-positive assessment. We quantify the detection sensitivity of the survey through injection-and-recovery experiments, with 565,808 synthetic transit signals injected across the stellar sample. Over the period range of 1–10 days and the
planet-radius range for which the detection completeness is well characterised, we measure a completeness-corrected
planet occurrence rate of 0.644^{+0.048}_{-0.041}. The occurrence rate is strongly dependent on
planet radius, with the highest occurrence contributed by
planets in the 1-4 R_earth range and a secondary enhancement at 12-15 R_earth. These results provide a demographic baseline for studying the population of close-in
planets around
stars undergoing early post-main-sequence
evolution.
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Solar and Stellar Astrophysics
On the origin of carbon- and oxygen-rich hot subdwarfs: an sdB merger scenario
Bo Tang, Xinyu Ji, Songyu Hu et al. (+2 more)
Carbon- and oxygen-rich hot subdwarfs (CO-sdO
stars) represent an extremely rare subclass of helium-rich hot subdwarfs. Recent observations of PG 1654+322, PG 1528+025, and UCAC4 108 reveal unusually large surface mass fractions of carbon and oxygen, which are difficult to explain within existing formation scenarios. We explore whether mergers involving sdB
stars can provide a viable formation channel for these objects. Using the stellar
evolution code MESA, we model the post-merger
evolution of two merger channels: mergers between two sdB
stars and mergers between a helium white dwarf and an sdB
star. Carbon and oxygen synthesized during core helium burning in sdB
stars may provide a natural chemical reservoir if efficient mixing occurs during the merger. The resulting evolutionary tracks are broadly consistent with the effective temperatures, surface gravities, and luminosities observed for the three
stars, suggesting remnant masses of about 0.8-1.0 M_sun. Our calculations suggest that mergers involving sdB
stars may represent a viable formation pathway for CO-rich hot subdwarfs.
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All authors Bo Tang, Xinyu Ji, Songyu Hu, Zhongyang Liu, Xianfei Zhang
Solar and Stellar Astrophysics
On the frequency-dependent time lags of the intermediate polar V709 Cas
Zackery A. Irving, Noel Castro Segura, Diego Altamirano et al. (+9 more)
Cataclysmic variables (CVs) are binary systems in which a white dwarf (WD) primary accretes material from a late-type secondary, typically via a disc. To date, only six CVs, all of which are non-
magnetic, have been found to exhibit lags (delayed variability in one band with respect to another). In all six cases, these lags are “red” (i.e., red lags blue) with a time lag of order seconds. While there is no generally accepted mechanism for producing red lags in CVs, current theories suggest reprocessing in the disc, either on the thermal or recombination time-scales, or inside-out shocks propagating through the disc. Using $g$-, $r$-, and $i$-band data from the OPtical TIming CAMera (OPTICAM), we report the discovery of frequency-dependent red lags from V709 Cas: a
magnetic CV of the intermediate polar (IP) subclass. These red lags reach a maximum of $\sim$4–6 s on time-scales of 7.4–13.0 min, similar to previously-reported lags in non-
magnetic CVs. The detection of lags in an IP is significant as the WD's
magnetic field truncates the
accretion disc, limiting disc-based lag mechanisms to large radii; as a result, characteristic
accretion disc time-scales cannot explain the observed lags. However, recombination can occur on second time-scales, even in systems with truncated discs. For example, we show that recombination in the disc's bright spot, where overflowing material from the secondary meets the outer-edge of the disc, plausibly explains V709 Cas's optical spectrum, the prominence of optical
spin-orbit beat pulsations, and the red lags found in this work.
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All authors Zackery A. Irving, Noel Castro Segura, Diego Altamirano, Martina Veresvarska, Mariano Mendez, Federico Garcia, Domitilla de Martino, Simone Scaringi, Federico Vincentelli, Angel Castro, Federico Soto, Raul Michel
Solar and Stellar Astrophysics
LISA Double White Dwarfs in Triple Systems
Zhijun Wang, Guoliang Lü, Chunhua Zhu et al. (+5 more)
Double white dwarfs (DWDs) in the
Laser Interferometer Space
Antenna (LISA) band are major Galactic gravitational-wave sources, but many tight DWD progenitors may reside in hierarchical triples. Triple
evolution can alter both the production rate and parameter distributions of LISA DWDs. Using the Multiple
Star Evolution (MSE) code, we study how the adiabatic mass-loss model (Ge model) and the SCATTER formalism for triple common-envelope (TCE)
evolution affect triple-channel LISA DWD formation. Our main model evolves 10^5 triples with both ingredients. Three control models, each with 10^4 triples, vary the mass-transfer stability criterion to the original MSE polytropic model, remove SCATTER, or adopt low
metallicity (Z=0.001). We also evolve 10^6 isolated binaries with the same framework as a binary-channel reference. Systems that are dynamically unstable under the polytropic model can instead undergo stable Roche-lobe overflow under the Ge model. This sustained mass transfer modifies the donor envelope, reduces its binding energy, and helps the subsequent common-envelope phase form a close DWD rather than a merger. The Ge model increases the triple-channel LISA DWD yield by about 60% relative to the polytropic model, while SCATTER changes the integrated yield by only about 3%. After residence-time weighting, triples contribute about 1.3e7 LISA-band DWDs, including 1.4e4 individually resolvable systems. In the combined triple-plus-binary normalization, the binary channel contributes 3.1e6 LISA-band DWDs and 4.7e3 resolvable systems; these are the binary share of the combined population, not the binary-only Galactic estimate. The main triple model has a flatter, higher-q mass-ratio distribution than the polytropic-model triples, is dominated by He-CO and He-He binaries, and produces rare eccentric systems only when a tertiary
star remains bound.
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All authors Zhijun Wang, Guoliang Lü, Chunhua Zhu, Xizhen Lu, Sufen Guo, Helei Liu, Renyu Luo, Tian Huang
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
Testing KMTNet–PRIME Optical–Near-Infrared Source-Color Constraints in KMT-2024-BLG-0211 and KMT-2024-BLG-1522
Kansuke Nunota, Jennifer C. Yee, Takahiro Sumi et al. (+37 more)
We present analyses of two 2024 microlensing events, KMT-2024-BLG-0211 and KMT-2024-BLG-1522, jointly observed by KMTNet in the optical and
PRIME in the near-infrared. For KMT-2024-BLG-0211, the KMTNet–
PRIME $I-H$ color provides a useful constraint on the angular source radius for a short-timescale finite-source event with a giant source. The event is consistent with a low-mass stellar lens, although the weak parallax constraint leaves the lens mass and distance uncertain. For KMT-2024-BLG-1522, we compare the results obtained from $V-I$, $I-H$, $V-H$, and $J-H$ color constraints. The microlensing parameters are nearly identical among the four analyses, yielding a robust binary-lens solution with nearly equal masses. However, the inferred source properties and lens physical parameters depend on the adopted source color because the different color estimates imply different angular source radii. Comparing the $(V-I)_{\rm KMT}$ versus $(I-H)_{\rm KMT,PRIME}$ plane shows that the inferred source colors lie off empirical color–color relations but within the scatter of observed
stars. The prevalence of such deviations should be tested with a larger sample of KMTNet–
PRIME events and this specific case can be further tested with future adaptive-optics follow-up, which can directly measure the lens–source relative proper motion and lens flux.
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All authors Kansuke Nunota, Jennifer C. Yee, Takahiro Sumi, Ryusei Hamada, Ian A. Bond, Andrew Gould, Weicheng Zang, David P. Bennett, Aparna Bhattacharya, Kotaro Daimon, Yuki Hirao, Stela Ishitani Silva, Shuma Makida, Shota Miyazaki, Tutumi Nagai, Seiya Nakayama, Ryo Ogawa, Ryunosuke Oishi, Hideaki Ose, Nicholas J. Rattenbury, Yuki K. Satoh, Daisuke Suzuki, Takuto Tamaoki, Motohide Tamura, Sean K. Terry, Chihiro Ueda, Aikaterini Vandorou, Hibiki Yama, Michael D. Albrow, Sun-Ju Chung, Cheongho Han, Kyu-Ha Hwang, Youn Kil Jung, Yoon-Hyun Ryu, In-Gu Shin, Yossi Shvartzvald, Hongjing Yang, Dong-Jin Kim, Chung-Uk Lee, Byeong-Gon Park