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Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Tuesday 11 August

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

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

Solar and Stellar Astrophysics

Observational Insights into Post-Main-Sequence Rotation and Magnetism: 20 Years of Science, from the Subgiant to the White Dwarf Phase

Emily Hatt

Rotation and magnetism are important phenomena to consider when trying to understand stars. By shaping the structure and chemical mixing in the interior of stars, they can induce significant changes in both their fundamental and observable properties. Despite this, our theoretical picture of how rotation and magnetism evolve throughout the stellar lifecycle remains incomplete. Gaps in our understanding are particularly stark for evolved stars, where slow rotation rates and weak magnetic fields make observational studies difficult. In response to this issue, the last 20 years have seen instrumentation to probe magnetism and rotation progressing in leaps and bounds. Through these new tools we have found that evolved stars rotate in ways that we cannot predict and have magnetic fields with properties that we did not expect. In the following, I will provide a brief overview of some recent observational results and their implications for our understanding of stars. I will focus on advances in asteroseismology and high-precision spectropolarimetry, as these techniques have advanced significantly over the last few decades. In keeping with the theme of Cool Stars, I'll cover stars with low to intermediate masses and their evolution from the subgiant to the white dwarf phase.
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Solar and Stellar Astrophysics

Spectroscopic Binary Detection as Agent-Callable Tools: Detecting 40,000+ Main-Sequence Binary Candidates from SDSS DR19 APOGEE Spectra

Serat M. Saad and Yuan-Sen Ting

Unresolved binaries are common in spectroscopic surveys, and their blended light biases the parameters inferred for them. Methods to detect them exist, but applying one to a new data release is limited mostly by operating know-how that is rarely written down. We package the double-lined spectroscopic binary decomposition of El-Badry et al. (2018b) for reuse on APOGEE spectra, with the executable operations as nine tool servers built on the Model Context Protocol (MCP) and the operating decisions as a Skill. Run over the 238,205 DR19 dwarfs under a fixed driver script, the classifier flags 41,466 SB2 candidates with median mass ratio q = 0.91, about fifteen times the 2,645 identified in DR13, though not at matched purity. The 8.1% control false-positive rate implies that close to 40% are single stars, so we release the sample as a candidate list. Refitting the individual visits confirms 68.5% of the multiply-visited SB2 and adds 519 single-lined velocity variables and 8,981 orbit-ready systems. We compare the eccentricities of the best-sampled binaries and find no significant difference between the close twins (q > 0.95) and matched non-twins, which excludes an eccentricity excess of the kind measured at wide separations. An ablation of two operating decisions illustrates that a fresh agent recovers a removed decision only when its absence leaves a measurable trace in the fit. We release the tools, the Skill, and the DR19 catalog with its multi-epoch supplement.
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Solar and Stellar Astrophysics

Evidence for Solar-Cycle Modulation of the Alpha-to-Proton Temperature Ratio in Solar Wind

Aakash Gupta, Yogesh, Dibyendu Chakrabarty et al. (+2 more)

The influence of collisional age $(A_c)$ on the alpha-to-proton temperature ratio $(T_\alpha/T_p)$ has been explored in the past. However, the modulation of this ratio with respect to the solar cycle has remained unexplored so far. We show solar-cycle modulation of $T_\alpha/T_p$ and $A_c$ using nearly three decades of in-situ observations from Wind spacecraft across distinct solar wind speed regimes and solar activity phases. Our results reveal that in the slow solar wind with velocity $<400$ km s$^{-1}$, where $A_c$ happens to be typically $>1$, the ratio $T_\alpha/T_p$ stays close to unity. This suggests frequent Coulomb collisions efficiently iron out temperature differences. In contrast, the fast wind with velocity $>500$ km s$^{-1}$, where $A_c$ happens to be typically $<1$, mass-proportional heating is most pronounced, with $T_\alpha/T_p$ often exceeding 4. The intermediate speed regime ($400$-$500$ km s$^{-1}$) represents a gradual transition between the slow and fast wind populations in terms of their solar-cycle dependence. This behavior reflects the changing dominance of high-speed streams from polar coronal holes during minima to denser slow wind during maxima. These results suggest that mass-proportional ion heating at 1 AU is not solely governed by local collisional physics but is significantly modulated by the solar cycle dependent variations in the solar wind sources.
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All authors Aakash Gupta, Yogesh, Dibyendu Chakrabarty, Leon Ofman, Gregory G. Howes

Solar and Stellar Astrophysics

Bernhard-1: An Eccentric Binary Periodically Obscured by its Misaligned Circumbinary Disk

Zhecheng Hu, Wei Zhu, Ping Chen et al. (+2 more)

Bernhard-1 is a proposed KH 15D-like circumbinary disk occultation (CBO) system, but its binary nature and disk geometry have not previously been confirmed. We present new optical and near-infrared spectroscopy together with multi-band photometric monitoring of the system. The radial velocities confirm that Bernhard-1 hosts a highly eccentric binary with $e = 0.80 \pm 0.09$, confirming that the periodic photometric variability arises from occultation by a misaligned circumbinary disk. Joint modeling of the spectra and phase-dependent spectral energy distributions yields pre-main-sequence components with masses of $\sim 1.1\,M_\odot$ and $\sim 0.8\,M_\odot$. Combining stellar isochrones with the measured lithium abundance yields a system age of $\sim$ 10 Myr. Together with the spatial, astrometric, and metallicity properties of Bernhard-1, this suggests that Bernhard-1 is probably a member of the open cluster Dolidze 42. By combining the RV orbit with a semi-transparent occultation-screen model, we infer a disk–binary mutual inclination of roughly $50^\circ$ or $130^\circ$, with the degeneracy arising from the unknown disk rotation direction. This geometric method can be applied to any CBO system once radial velocity monitoring yields an orbital solution. The new light curves deviate from earlier model predictions, consistent with ongoing disk precession, while the phase-dependent H$\alpha$ profiles indicate pulsed accretion near periastron. Bernhard-1 therefore joins KH 15D and Bernhard-2 as a rare spectroscopically confirmed CBO system.
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All authors Zhecheng Hu, Wei Zhu, Ping Chen, Richard Post, Weicheng Zang

Solar and Stellar Astrophysics

Exploring the long-term temporal variability in polarization through multi-epoch optical spectro-polarimetry - Part II: A sample of symbiotic and red-giant stars

Arijit Maiti, Ruchi Pandey, Sube Singh Gurjar et al. (+1 more)

Measuring polarization and its temporal variability in the continuum and across emission features provides a powerful probe of the small-scale circumstellar environments of astrophysical sources, on spatial scales otherwise inaccessible to direct imaging techniques. However, the photon-hungry nature of spectro-polarimetry has significantly limited the availability of such datasets in the literature. Here we present the results of a multi-epoch spectro-polarimetric survey of a sample of symbiotic and red giant stars. These observations were first conducted during the performance verification phase of a recently developed medium-resolution echelle spectro-polarimeter, named ProtoPol, mounted on the Physical Research Laboratory (PRL) 2.5m telescope, Mt Abu, India. Considering the scarcity of such observing samples in the literature, the targets were re-observed over a period exceeding 26 months, from March 2024 to May 2026, in order to explore the time variability of their polarimetric measurements. Our sample comprises 6 symbiotic stars and 18 red giant stars. Our observations found that, unlike the Raman-scattered $\lambda \lambda$ 6830, 7088 angstrom features, the H$\alpha$ emission in most of the symbiotics did not exhibit any notable polarization signature. However, the continuum polarization of most symbiotics and red giants in the sample showed significant variation between observation epochs. The observations presented here constitute one of the rare multi-epoch spectro-polarimetric datasets spanning more than two years and should be of considerable interest to the broader astronomical community. This paper is Part-II of a two-part series of sample studies; corresponding results for Herbig Ae/Be and classical Be stars are presented in Part-I.
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All authors Arijit Maiti, Ruchi Pandey, Sube Singh Gurjar, Mudit K. Srivastava

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

SIRIUS Project: Dynamical Evolution of Primordial Binaries during Star Cluster Formation

Naoto Harada, Michiko S. Fujii, Takayuki R. Saitoh et al. (+1 more)

Binary populations are closely linked to the star formation process; however, their primordial properties can be changed by subsequent dynamical interactions within their natal clusters. The aim of this study is to clarify how different primordial binary populations affect the evolution of multiplicity and the global structure of forming star clusters. We investigate the dynamical evolution of primordial binaries during star cluster formation using self-consistent Nbody/smoothed particle hydrodynamics simulations that follow the collapse of a molecular cloud to a star cluster. We systematically compare three star formation models: close binary (CB), wide binary (WB), and single star (SS) formation model. In CB and WB models, the multiplicity fraction decreases with time due to dynamical interactions. In particular, the fraction in the WB model drops to a level comparable to that in the SS model. The multiplicity fraction of high-mass stars is similarly high in all models, whereas only the CB model shows a relatively high fraction for low-mass stars. Due to the assumption of equal-mass binary formation, the CB and WB models exhibit an excess at q= 1 in the mass-ratio distribution, while the SS model has no clear trend. Frequent few-body interactions generate distinct stellar populations inside and outside the cluster: the multiplicity fraction within the cluster is systematically higher, while mass functions in the outside have a shallower slope. Finally, stellar density profiles in the clusters are broadly similar among all models. The primordial binary population significantly affects the final binary properties, while having only a limited impact on their host cluster structures. Our results suggest that close binaries need to form at the star formation stage to reproduce the observed multiplicity fraction of low-mass stars and the excess of equal-mass binaries.
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All authors Naoto Harada, Michiko S. Fujii, Takayuki R. Saitoh, Yutaka Hirai

Solar and Stellar Astrophysics

Exploring the long-term temporal variability in polarization through multi-epoch optical spectro-polarimetry - Part I: A sample of Herbig Ae/Be and classical Be stars

Arijit Maiti and Mudit K. Srivastava

Polarization signatures across emission line features, together with their temporal evolution, offer a powerful probe of the circumstellar environments of astrophysical sources, on spatial scales otherwise inaccessible to direct imaging techniques. However, the photon-hungry nature of spectro-polarimetry has significantly limited the availability of such datasets in the literature. This work reports a multi-epoch spectro-polarimetric monitoring campaign targeting a sample of Herbig Ae/Be and classical Be stars. The initial observations were obtained during the commissioning and performance-verification phase of ProtoPol, a recently developed medium-resolution echelle spectro-polarimeter mounted on the Physical Research Laboratory (PRL) 2.5m telescope, Mt Abu, India. Given the limited number of comparable datasets available for this class of objects, follow-up observations of the same targets were carried out repeatedly over more than 28 months (December 2023-March 2026), enabling an investigation of the temporal behavior of their polarimetric properties. Our sample comprises 11 Herbig Ae/Be stars and 10 classical Be stars. Our observations found that, while the H$\alpha$ polarization remained relatively constant for the classical Be stars, they showed significant variability for most of the Herbig stars in the sample. The observations presented here constitute one of the rare multi-epoch spectro-polarimetric datasets spanning more than two years and should be of considerable interest to the broader astronomical community. This paper is Part-I of a two-part series of sample studies; corresponding results for symbiotic and red giant stars are presented in Part-II.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Mapping the Inner Milky Way with Infrared-Derived Distances to AGB Stars

Rajorshi Bhattacharya, Subhajit Kar, Loránt O. Sjouwerman et al. (+1 more)

The structure and evolution of the Milky Way (MW) can be traced with distance estimates to the evolved stellar populations in the inner galactic region. However, direct astrometric distances remain unavailable or highly uncertain for the majority of these sources due to instrumental limitations, large angular diameters, and complex variability. In this work, we develop a supervised machine-learning model to estimate statistical distances to oxygen-rich asymptotic giant branch (AGB) stars selected from the AKARI mid-infrared survey. We build an XGBoost regression model that maps multi-band IR photometry to distance using a training set of AGB stars with previously derived SED-based distances achieving a mean absolute percentage error (MAPE) of 6% on an independent test set. Distance estimates for over 36,000 AGB sources are obtained within a 36% total error margin, greatly expanding distance coverage (0.5-20 kpc) for dust-obscured AGB populations in the Galactic plane. We find good agreement with reported distances for Galactic Mira variables and independent period-luminosity relations. Utilizing the expanded distance set, we further investigate the spatial distribution of Mira variables in the Galactic bulge and disk. Longer-period Miras preferentially trace the bulge's barred morphology compared to their shorter-period counterparts that populate the disk. We also find roughly constant, but differing, relative scale heights for the bulge and disk, with the bulge vertical dispersion about 30% larger. These findings show that IR photometry-derived statistical distances can recover large-scale Galactic structures and establish long-period Mira variables as efficient tracers of stellar populations in heavily obscured regions of the MW.
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All authors Rajorshi Bhattacharya, Subhajit Kar, Loránt O. Sjouwerman, Anupam Bhardwaj

Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

PDS 70 c and SR 12 c: Observational Constraints on Giant-Planet and Satellite Formation

Ignacio Mosqueira

PDS~70~c and SR~12~c are the only bound planetary-mass objects with secure cold submillimeter disk detections. Together, these systems constrain giant-planet growth and satellite formation. The PDS~70 planets exhibit remarkable parallels to the Jupiter–Saturn pair in our Solar System. Both PDS~70 planets accrete within one shared gap, which links their final masses, the material reaching each Hill sphere, and the properties of the circumplanetary disk. Planetary torques deplete the finite interplanetary reservoir, causing circumplanetary supply to decline as the protoplanets open a circumstellar gap. SR~12~c separates the planetary-growth and satellite-formation timescales: gas and solids survive even though its current mass-growth timescale is $(1.9\pm0.6)\times10^9$~yr. For PDS~70~c, the 855-$\mu$m flux implies $0.007$–$0.031\,\Mearth$ of dust at 26~K in the optically thin limit. A fully dust-dominated, uniform 22–26-K optically thick emitter has an equivalent coplanar radius of $0.58$–$0.66$~au, while a fiducial radial temperature profile yields an equivalent radius of approximately 0.46~au. The continuum constraints overlap the 0.5–1.5~au circularization range estimated by ballistic calculations of late-stage gap-fed inflow. We find that the PDS~70 constraints are consistent with our \SEMM{} satellite-formation model (Mosqueira & Estrada 2003a,b, submitted in 2001). Thus the observations provide strong support for a quiescent, solids-enhanced satellite-forming environment, coupled in the early stages to planetary-gap evolution.
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Monday 10 August

Solar and Stellar Astrophysics

Astro+ database. I. Description and first results

K. Rübke, A. Marco, I. Negueruela et al. (+4 more)

The vast amounts of spectroscopic data for massive stars provided by previous and existing instruments on ground-based and space-based telescopes have saturated our capability to process them by human inspection routines. Consequently, there is a pressing need for fully automatic machine-assisted tools to help handle incoming data. To this end, we present the development of a massive star spectroscopic interactive database, Astro+. We aim to provide users with a reliable, versatile, and user-friendly platform that will be significant for understanding massive stars and set an important precedent for future open-access astrophysical research. This tool allows authorized users to upload their own spectra and, by using the fully automated tool HiLineThere, a Python-based program, it can homogeneously derive basic stellar parameters, such as v_rad, v sin i, Teff and log g for massive OB-type stars, using a solar-metallicity grid of FASTWIND models, and v_rad, [Fe/H], Teff and log g for red supergiant stars, in a completely autonomous way. Here we present the first results of the tool HiLineThere on optical spectra for OB-type stars and red supergiants. We compare the output of our analysis for OB-type stars with literature values for a large sample of well-studied objects, finding differences within the expected error ranges: Teff ~ 800 K, log g ~ 0.1 dex, and v sin i ~ 10 km/s. Preliminary tests on early-B stars also show consistent results during the transition to lower temperatures. For red supergiants, we find differences within 7 km/s in v_rad and ~300 K in Teff for two test samples.
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All authors K. Rübke, A. Marco, I. Negueruela, A. Herrero, S. Simón-Díaz, H. M. Tabernero, L. R. Patrick

Solar and Stellar Astrophysics

The Carbon Giant Population Revealed by Gaia DR3

Benjamin R. Roulston and Paul J. Green

Classical carbon stars (atmospheric C/O >1) are asymptotic giant branch (AGB) stars that become carbon-rich through third dredge-up during the thermally pulsing AGB phase. However, carbon stars also occur among red giants and main-sequence stars, where the carbon is thought to originate from binary mass transfer from a former AGB companion. Using the all-sky catalog of G<16.5 mag Gaia DR3 carbon stars from Roulston et al. (2025), we investigate a uniform, high-confidence sample of carbon giants in the Milky Way, its globular clusters, and nearby Local Group galaxies. We identify 6937 carbon giants in the Large Magellanic Cloud, 2148 in the Small Magellanic Cloud, and 219 associated with the Sagittarius dwarf spheroidal, nearly quadrupling the previously known sample in the latter. We identify several candidate carbon symbiotic stars through their X-ray counterparts. The mean absolute C-AGB magnitude, $M^0_J=-6.30$ in the LMC and -6.15 in the SMC, agrees closely with the photometrically derived values of Ripoche et al. (2020), reinforcing the utility of carbon AGB stars as distance indicators. From 4276 Galactic carbon giants with $M_G<0$ and $|b|>5^\circ$, we measure a local disk space density of $n_0=11\pm0.5\times10^{-8},\mathrm{pc}^{-3}$ and a scale height of $H_z=257\pm4$ pc. Lower-luminosity carbon giants exhibit significantly larger Gaia DR3 RUWE values than C-AGB stars, providing strong evidence that most are extrinsic post-mass-transfer systems, likely evolved dwarf carbon stars. C-AGB stars are more tightly confined to the Galactic disk and are rare inside $R\lesssim7$ kpc, consistent with Galactic age and metallicity gradients, whereas the lower-luminosity carbon giants have a larger scale height and require an additional halo component.
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Solar and Stellar Astrophysics

Parametric Study of the Torus Instability Threshold

Jun Chen, Bernhard Kliem and Rui Liu

The torus instability of an arched current channel has been suggested to initiate and drive major solar and stellar eruptions. Its threshold, given by the critical decay index of the equilibrium external poloidal field (the so-called strapping field) at the position of the current channel, is insufficiently known. Here, we carry out a parametric numerical study of the threshold, employing the force-free Titov-Démoulin (TD) equilibrium of a line-tied partial toroidal current channel and flux rope. This addresses the scatter of the threshold about its canonical value, $n_\mathrm{cr}=3/2$. Values scattering in the range $n_\mathrm{cr}\approx$\,1–2 are typically found in numerical and observational studies of flux rope eruptions on the Sun. For zero external toroidal (guide, or shear) field and approximately semicircular geometry (corresponding to minimal photospheric line-tying), we find the threshold to lie in the theoretically expected range of $\approx$\,1–1.5. An external toroidal field introduces a strong stabilizing effect on the instability, raising the threshold up to $\sim$\,2.5, which can explain observational and numerical results above the canonical value. Line-tying is found to act as a stabilizer as well. We also consider the approximate threshold based on the potential field and find a very good agreement with the exact numerical value, provided the horizontal component perpendicular to the flux rope axis is used to approximate the external poloidal field.
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Solar and Stellar Astrophysics

A Pre-Main Sequence Binary Viewed Through its Circumbinary Disk: A New Phase for KH 15D

Catrina M. Hamilton, Adi B. Chacko, George A. Carson et al. (+16 more)

The binary T Tauri system, KH 15D, is poised to provide unprecedented detail of gas and ices located between $\sim$3-5 AU of its circumbinary disk over the next few years. We analyze for the first time a complete set of ground-based time series photometry of the KH 15D system for which the 2022 October - 2025 April data have never been presented. By combining the latest $I$-band data with historical measurements, we show that the era of large amplitude photometric variability has ended. We define a revised photometric period of $P$ = 48.365 $\pm$ 0.005 days, which accurately phases data over a time span of seventy-five years. We adopt magnitudes and colors for the stars that define the epochs when either star A (1995-2008) or star B (2010-2012) is the primary source of the out-of-eclipse brightness of the system. We determine for the first time the effective optical depth for the system between 2002 and 2025 assuming gray extinction. The current out-of-eclipse system color is consistent with a combination of the light from both stars, supporting the previously suggested model in which the trailing edge of the circumbinary disk is more transparent than the leading edge. We continue to see evidence for “clumps” and variable transparency along ingress and egress when the stars are probing the occulting material and suggest that observations made during these phases should permit studies of the physical and chemical nature of the planet-forming zone with the circumbinary disk.
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All authors Catrina M. Hamilton, Adi B. Chacko, George A. Carson, Aidan J. Pidgeon, C. Nicole Foley, Hillel Finder, Kyle Gimmy, Aleezah Ali, William Herbst, Dirk Froebrich, Brian A. Skiff, Bart Staels, Shawn Dvorak, Jochen Eislöffel, Teryn Huff, Gavin Frueh, Abigail Mead, Lia M. Gilmore, Robert J. Boyle

Solar and Stellar Astrophysics · Cross-listed from astro-ph.IM

The Carruthers Mission Concept and Performance

W. Craig, T. Immel, L. Waldrop et al. (+12 more)

The Carruthers Geocoronal Observatory (Carruthers), formerly GLIDE, is a NASA Heliophysics Science Mission of Opportunity implemented through the Solar Terrestrial Probes (STP) Program and launched as a rideshare in September 2025. Carruthers is the first spaceflight mission edicated to continuous global imaging of Earth's hydrogen exosphere through observations of geocoronal Lyman-$\alpha$ emission at 121.6 nm. The observatory operates at distances of 1.3-1.7 million km in a halo orbit about the Sun-Earth L1 point, enabling retrieval of the three-dimensional distribution of atomic hydrogen, the dominant constituent of the exosphere, on hourly timescales and unprecedented spatial resolution. These new data provide the key to understanding processes governing atmospheric escape, geospace coupling, and solar-wind interaction. Carruthers carries the GeoCoronal Imager (GCI), a dual-channel ultraviolet imaging instrument comprising the Narrow-Field Imager (NFI) for high-resolution observations of the inner exosphere and the Wide-Field Imager (WFI) for synoptic imaging of the extended hydrogen halo. Along with a student-provided experiment, the instrument suite is the sole payload aboard a three-axis-stabilized spacecraft designed to support nadir viewing throughout the $\sim178$ day halo orbit about L1. Observations also measure the interplanetary Lyman-$\alpha$ background, enabling separation of heliospheric and geocoronal emissions. The student-led experiment monitors solar Lyman-$\alpha$ and extreme ultraviolet emission during portions of the orbit. Science data are returned through the Deep Space Network at data rates up to 1 Mbit s$^{-1}$. The two-year baseline mission begins in March 2026, with propellant reserves capable of supporting more than ten years of orbit maintenance and maneuvers.
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All authors W. Craig, T. Immel, L. Waldrop, J. Troeltzsch, E. Taylor, J. McPhate, K. Rider, A. Butterworth, D. Cosgrove, J. Thorsness, H. Filippini, K. Lee, S. Shomo, C. McGinn, C. Peterson

Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

SMA Observations Reveal Abundant HNC Chemistry in Transition Disks

Kyle Gresko, Charles J. Law, Deryl E. Long et al. (+8 more)

The physical and chemical conditions of protoplanetary disks shape the properties of nascent planetary systems. The line ratios and relative abundances of the HCN-HNC isomer pair are well-suited for tracing these gas conditions, since isomer chemistry is linked to the underlying temperature, elemental abundances, and irradiation environment of the emitting gas. While HCN emits bright lines regularly observed in disks, the fainter HNC lines are targeted significantly less often, precluding our ability to calibrate the HNC-to-HCN ratio as a tracer of disk properties. Here, we present new Submillimeter Array observations of five transition disks around the T Tauri stars GM Aur, J1604, LkCa 15, GG Tau, and V4046 Sgr, covering the J=3-2 and J=4-3 lines of HCN and HNC. We detected at least one line of both HCN and HNC in each source and measured disk-integrated HNC-to-HCN flux and column density ratios of $\approx$0.1-0.7 and 0.1-0.4, respectively. For all sources, measured HNC fluxes exceed predictions from models of full (non-transition) disks by $\approx$3-10x, while HCN fluxes appear typical. The relative brightness of HNC vs. HCN in transition disks strongly suggests a link between the presence of a cavity and efficient HNC production. We corroborate this trend using chemical models of the DM Tau transition disk, showing HNC production and destruction are connected to the radiation environment. In our sample, disk-integrated HNC-to-HCN column density ratio shows no trend with disk gas temperature but positively correlates with disk mass due to increased HNC abundance in the larger reservoirs of cooler gas in more massive disks.
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All authors Kyle Gresko, Charles J. Law, Deryl E. Long, L. Ilsedore Cleeves, Feng Long, Yuri Aikawa, Jennifer B. Bergner, Romane Le Gal, Viviana V. Guzmán, Karin I. Öberg, David J. Wilner

Solar and Stellar Astrophysics

Filling the Gap: Calibrating Gyrochronology at 1.3 Gyr with the Benchmark Cluster NGC-752

Andrew W. Boyle and Andrew W. Mann

Empirical gyrochronology relies on co-eval stellar associations to map stellar rotation as a function of mass and age. The accuracy of its age predictions is therefore limited by the number and quality of benchmark rotation sequences. The well-characterized clusters NGC-6811 (t ~ 1 Gyr) and NGC-6819 (t ~ 2.5 Gyr) bracket an intermediate-age interval in which stellar spin-down remains poorly constrained due to lack of available rotation data. At t ~ 1.3 Gyr, NGC-752 provides a critical benchmark within this gap, but previous measurements could not define the G- and K-dwarf rotation sequence needed for calibration. Here, we combine Gaia-based NGC-752 membership lists with literature rotation periods to map NGC-752's slow-rotator sequence for the first time. We identify a well-defined sequence intermediate between those of NGC-6811 and NGC-6819. Stars near Teff ~ 4500 K rotate more slowly than their counterparts in NGC-6811, indicating that stars experiencing stalled spin-down at ~1 Gyr have resumed appreciable spin-down by the age of NGC-752. Adopting an age of 1.3 Gyr for NGC-752, we further show that existing empirical gyrochronology models overestimate the ages of many G and early-K dwarfs by 20–50% because they lack intermediate-age calibration data, although uncertainty in the absolute age of NGC-752 may account for part of this offset. NGC-752 therefore provides a necessary anchor for improving rotational age estimates. This calibration is especially timely because Gaia DR4, Roman, and PLATO are expected to yield rotation periods for tens of millions of stars, making the age coverage of benchmark sequences a principal limitation on large-scale gyrochronology.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

A Sulfur-Rich Atmosphere for the Young Jupiter Analog AF Lep b Reveals Significant Solid Accretion

Jerry W. Xuan, William O. Balmer, Yayaati Chachan et al. (+25 more)

AF Lep b is one of the closest analogs to Jupiter in terms of mass ($3-4~M_{\rm{Jup}}$) and semi-major axis ($9$ AU) amenable to spectroscopic characterization. We present JWST/NIRSpec high-contrast spectroscopy of the planet from $2.85-5.3~\mu$m at $R\sim3000$, which provide detections of CO$_2$, H$_2$S, CH$_4$, $^{12}$CO (and $^{13}$CO), and H$_2$O, as well as complementary JWST/NIRCam imaging that captures the planet's continuum flux from $4.0-4.7~\mu$m. Combining the JWST observations with spectra from VLTI/GRAVITY and VLT/SPHERE ($1.0-2.5~\mu$m), we carry out atmospheric retrievals that include the effects of clouds and disequilibrium chemistry while allowing the C, O, and S abundances to vary independently. AF Lep b exhibits metal enrichment across C, O, and S with $\rm C/H=2.9\pm0.5$, $\rm O/H=3.7\pm0.6$, and $\rm S/H=4.7\pm0.7~\times$ solar (and stellar). The planet's slightly sub-solar C/O and C/S are consistent with formation near its observed location, and disfavor formation beyond the CO snowline. The sulfur enrichment in AF Lep b implies significant accretion of disk solids during formation, and we estimate the planet contains $56\pm7~M_{\oplus}$ of solids. The C, O, and S enrichment levels of AF Lep b are similar to those of Jupiter, and other super-Jupiters like HR 8799 bcde. We also show that the degree of atmospheric metal enrichment of these imaged planets is similar to the bulk metal enrichment of transiting gas giants with masses greater than $\sim1~M_{\rm{Jup}}$, suggesting that the process and efficiency of metal accretion for gas giants may not be strongly dependent on orbital distance or planet mass.
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All authors Jerry W. Xuan, William O. Balmer, Yayaati Chachan, Jean-Baptiste Ruffio, Kazumasa Ohno, Robert J. De Rosa, Aneesh Baburaj, Eric L. Nielsen, Ruth Murray-Clay, Jonathan J. Fortney, Marshall D. Perrin, Jason J. Wang, Brendan P. Bowler, Alexander Madurowicz, Bruce A. Macintosh, Yapeng Zhang, Björn Benneke, Alexis Bidot, Geoffrey A. Blake, Kyle Franson, Carrie He, Julie Inglis, Heather A. Knutson, Dimitri Mawet, Laurent Pueyo, Emily Rickman, Aniket Sanghi, Nicole L. Wallack

Solar and Stellar Astrophysics

IPA: Morphology and Kinematics of Molecular Hydrogen Winds in Five Young Protostars across the Mass Spectrum Observed with JWST

Himanshu Tyagi, P. Manoj, Mayank Narang et al. (+29 more)

Molecular winds may play a key role in governing angular momentum transport and accretion during the early evolution of protostars. We present the morphology and kinematic properties of the H$_2$ emission in five young, envelope-dominated, protostars across a broad bolometric luminosity range, from 0.2 to $10^4~L_{\odot}$, observed with the NIRSpec/IFU and MIRI/MRS onboard JWST as part of the Investigating Protostellar Accretion (IPA) program. A rich set of pure rotational lines of H$_2$, up to $v=0-0$ S(18), and a few ro-vibrational lines are detected in the winds, revealing bipolar structures. The H$_2$ lines show a stratified/onion-like structure morphologically and kinematically, where the lines with higher $E_{\rm up}$ show a higher degree of collimation and higher velocities. Additionally, the wind velocity scales with the $L_{\rm bol}$ of the host protostellar system. In 4 out of 5 protostars, H$_2$ emission fills the outflow cavity without showing pronounced limb brightening. We also report a tentative detection of H$_2$ wind rotation in IRAS 16253, which suggests a launch radius of $\sim4$ au and the magnetic lever arm parameter of $\sim5-10$. Taken together, these properties of the H$_2$ winds can be explained by the magnetohydrodynamic disk wind models. We detect a collimated, high-velocity H$_2$ jet toward HOPS 370, which is more evolved than the extremely young source HH 211, but is accreting at a high accretion rate. This suggests that the presence of collimated molecular jets in protostars is more closely connected to accretion rate than system age.
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All authors Himanshu Tyagi, P. Manoj, Mayank Narang, S. Thomas Megeath, Robert Gutermuth, Lee Hartmann, Alessio Caratti o Garatti, Dan M. Watson, David A. Neufeld, Ewine F. Van Dishoeck, Neal J. Evans II, Vinod Chandra Pathak, Samuel A. Federman, Tyler L. Bourke, Yao-Lun Yang, Guillem Anglada, Henrik Beuther, Leslie W. Looney, Rolf Kuiper, Pamela Klaassen, Pooneh Nazari, Bihan Banerjee, Joel Green, Sujay Vijay Jadhav, Mayra Osorio, B. Shridharan, Amelia M. Stutz, Thomas Stanke, John J. Tobin, Lukasz Tychoniec, Scott Wolk, Manya Arora

Solar and Stellar Astrophysics

Nascent Embedded-protostar Survey in Taurus (NEST) II: Measuring Dust Mass, Disk Size, and Gas Mass

Noshin Yesmin, Patrick Sheehan, John Tobin et al. (+6 more)

Envelope-embedded protostellar disks represent the earliest stage of protoplanetary disk evolution, but their masses and sizes are difficult to measure because disk emission is entangled with the envelope. We analyze 26 protostellar disk systems in Taurus using ALMA Band 7 (345 GHz; ~0.3”) and VLA Ka-band (33 GHz; ~0.2”) continuum observations, together with molecular-line data to constrain disk gas masses. At 345 GHz, the median flux density, dust mass, and radius are 71 mJy, 5.5 M_Mearth, and 28 AU, with 68% ranges of 54-107 mJy, 3.9-9.4 M_Mearth, and 25-39 AU. At 33 GHz, the corresponding medians are 0.43 mJy, 39 M_Mearth, and 32 AU, with ranges of 0.41-0.80 mJy, 34-52 M_Mearth, and 29-33 AU. Taurus Class I disks are fainter and less massive than those in Orion, comparable to Perseus Class I disks but fainter than Perseus Class 0 disks, and brighter and more massive than those in Ophiuchus. Within Taurus, Class 0/I disks are brighter than Class II disks at both frequencies, although their inferred dust masses are comparable at 345 GHz and slightly higher at 33 GHz. Radiative-transfer modeling of CO isotopologue emission yields a median gas mass of 6.7 x 10^-4 M_Msun. The resulting CO-inferred gas-to-dust ratios span a broad range, with a mean of 147 +/- 75, a median of 26, and a 16th-84th percentile range of 8-147. This distribution overlaps the Taurus Class II population at the low end and ISM-like or higher values, including the AGE-PRO Ophiuchus Class 0/I population, at the high end.
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All authors Noshin Yesmin, Patrick Sheehan, John Tobin, Aislinn Coleman-Plante, Nicholas P. Ballering, Tyler L. Bourke, Josh Eisner, Hauyu Baobab Liu, Zhi-Yun Li

Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Peak 'Nebular' Emission and Early Flux Excesses in Ca-strong Supernovae

C.-G. Touchard-Paxton, K. Maguire, C. Frohmaier et al. (+27 more)

Calcium-strong supernovae (Ca-strong SNe) are a class of thermonuclear transient characterised by rapid photometric evolution (rise times of <= 16 d) and nebular-phase spectra dominated by strong [Ca II]7291,7324 emission, in comparison to the strength of [O I]6300,6364 emission. Despite their distinctive spectra and association with remote environments, their origins remain uncertain. Using new discoveries from surveys such as the Zwicky Transient Facility, supplemented by archival data, we compile a sample of 46 Ca-strong SNe - the largest sample to date. We present a comprehensive optical photometric and spectroscopic study of Ca-strong SNe, aimed at better constraining their diversity, progenitor systems, and explosion mechanisms. Of the 35 Ca-strong SNe with spectra near peak light, we find that 32 objects exhibit significant [Ca II] emission within 10 days of peak. Forbidden [Ca II] emission is typically expected to emerge after the ejecta have expanded, cooled, and reached a sufficiently low density for forbidden transitions to occur. The prevalence of these early features in Ca-strong SNe, however, remains unexplained by current explosion models of these objects. In several objects, we identify complex, multi-component line profiles that suggest a transition between two distinct velocity regimes. These transitional features, combined with the common presence of early forbidden emission, lead us to favour a scenario in which extended material surrounds the progenitor and pre-dates the SN itself. Our results suggest that the diverse spectroscopic behaviours of Ca-strong SNe are consistent with white dwarfs exploding in extended environments polluted by prior activity of the progenitor system.
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All authors C.-G. Touchard-Paxton, K. Maguire, C. Frohmaier, W.V. Jacobson-Galán, M. Pursiainen, C. Angus, J. Sollerman, A. Polin, J.H. Terwel, R. Seth, C. O'Donnell, S.J Smartt, S. Srivastav, A. Bochenek, T. de Boer, K.K. Das, C. Fremling, A.C. Gordon, M.J. Graham, M.E. Huber, C.-C. Lin, C. Liu, F.J. Masci, P. Minguez, G.S.H. Paek, J. Purdum, B. Rusholme, K. Smith, R. Smith, R. Wainscoat

Solar and Stellar Astrophysics

Infrared Spectroscopy and Photochemistry of Aromatic Nitriles in Para-Hydrogen Matrices

Sam McGrath, Vincent J. Esposito, Linshan Zeng et al. (+6 more)

Motivated by recent detections of several aromatic nitriles in Taurus Molecular Cloud-1, we report laboratory and theoretical investigations of the vibrational spectroscopy and photochemistry of singly and doubly cyano-substituted benzene in solid para-hydrogen matrices. We compare the photochemistry of cyanobenzene (benzonitrile) and three dicyanobenzene isomers initiated by excitations at 193 nm. In addition, we report the photochemistry of deuterated cyanobenzene (d$_5$-cyanobenzene), enabling us to determine the major products produced during the cyanobenzene photodissociation. The major products observed in the photolysis of all the nitriles are HCN and HNC, which are likely produced by hydrogen abstraction from para-H$_2$ by the CN radical. This indicates that the major photodissociation channel involves cleavage of the bond between the ring and the nitrile group, forming the phenyl (or cyanophenyl) radical + CN. We observe secondary photoproducts similar to those found during benzene photolysis. Our findings may aid the interpretation of recent JWST mid-infrared observations of aromatics in photodissociation regions.
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All authors Sam McGrath, Vincent J. Esposito, Linshan Zeng, Thomas H. Speak, Brendan Moore, Pavle Djuricanin, Jun Miyazaki, Takamasa Momose, Ilsa R. Cooke

Solar and Stellar Astrophysics · Cross-listed from nucl-th

A Gaussian Process framework for constraining the nuclear equation of state from microscopic calculations with correlated uncertainties

Y. G. Lee, J. Kim, T. Zhao et al. (+1 more)

We present constraints on the nuclear equation of state (EOS) from microscopic asymmetric matter calculations at zero temperature based on chiral nucleon-nucleon and three-nucleon interactions. The constraints include the saturation point, the isospin dependence of the incompressibility, and the symmetry energy, as well as the crust-core transition density of neutron-star matter. To quantify and propagate correlated uncertainties from noisy many-body calculations to derived observables, we introduce GPDiff, an efficient JAX-based Python package for multivariate Gaussian process (GP) regression with automatic differentiation. After training, GPDiff enables joint predictions of the EOS and derivatives of arbitrary order with respect to the input variables, including mixed partial derivatives. In this initial application, we analyze recent high-order many-body perturbation theory calculations of asymmetric matter up to about twice saturation density and explore nonstationary change-surface kernels, a class of input-dependent kernels, for modeling the EOS. GPDiff is broadly applicable to microscopic nuclear EOS calculations at zero and finite temperature and provides a versatile package for GP-based uncertainty quantification and inference of the nuclear EOS.
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All authors Y. G. Lee, J. Kim, T. Zhao, C. Drischler

Solar and Stellar Astrophysics

HXI-DLA2: A Physics-Constrained Deep Learning Algorithm for the ASO-S Hard X-ray Imager

Zou SiZhong, Liu Hui, Su Yang et al. (+5 more)

Solar flare hard X-ray imaging is a key diagnostic of flare energy release and electron acceleration. The Hard X-ray Imager (HXI) aboard ASO-S compresses the two-dimensional source distribution into counts measured by 91 sub-collimators, making image reconstruction an inherently underdetermined inverse problem. Conventional algorithms such as CLEAN rely on point-source priors and manual tuning, whereas recent deep-learning methods offer no guarantee that their reconstructions obey the instrument's modulation-sampling forward equation. In this work we show that the counts decompose into two nearly decoupled quantities—the counts average energy, which tracks the total source flux, and the normalized counts distribution, which encodes the source spatial structure—and we exploit this property to construct a physics-constrained network, the Hard X-ray Imager Deep Learning Algorithm 2 (HXI-DLA2). Non-negativity and exact counts-average-energy closure are enforced at the network output, while a distribution-consistency loss aligns the re-projected counts with the measurement, so that the reconstruction satisfies the forward equation by construction. Tests on simulated Gaussian sources, observed soft X-ray morphologies, and a real HXI flare event show two main improvements over existing methods: the limiting resolvable dynamic range of double sources is pushed well beyond that of conventional imaging algorithms and our previous method; and complex morphologies on which prior reconstructions degrade, such as ring-like and diffuse structures, are reliably reconstructed, with the real-event result consistent with contemporaneous SDO/AIA imaging. Embedding the instrumental forward equation as a hard constraint while learning source priors from data offers a general inversion framework for modulation imaging.
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All authors Zou SiZhong, Liu Hui, Su Yang, Hong JunChao, Bin Wang, Chen Wei, KaiFan Ji, ZhenYu Jin

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

A Chemical Inventory of the Disk around the Class 0 Protostar L1527 IRS with ALMA

Merel L.R. van 't Hoff, Łukasz Tychoniec, John J. Tobin et al. (+1 more)

Planet formation starts in disks that are still embedded within their natal envelopes. Here, we compile an extensive inventory of the chemical composition of the disk and envelope ($<$ 3500 au) around the Class 0 protostar L1527 IRS. Using all publicly available ALMA (Atacama Large Millimeter/submillimeter Array) data, we report the detection of 40 molecules, including isotopologues. Of these, 23 are different molecular species and 29 are reported here for the first time toward L1527 in ALMA observations. CH$_3$OH is the only complex organic molecule detected, while the hydrocarbon CH$_3$CCH is the largest molecule detected. Overall, only a few programs are sensitive enough to detect emission unambiguously originating from the disk based on the kinematics. Nitrogen-bearing molecules are predominantly detected on more extended scales, while hydrocarbons show a distinct tail roughly along the southeastern outflow cavity wall, probably due to a stronger UV field in the eastern outflow lobe. The L1527 IRS protostellar system is not rich in sulfur-bearing molecules, with only strong emission observed for CS and SO. Overall, the envelope appears dominated by a carbon-rich chemistry, which seems to transition into an oxygen-rich chemistry in the disk. We calculate column densities of all detected species, providing a starting point to quantify the chemical diversity among young disks and the chemical evolution of the planet-forming material.
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All authors Merel L.R. van 't Hoff, Łukasz Tychoniec, John J. Tobin, Daniel Harsono

Solar and Stellar Astrophysics

Sector-based morphological analysis of four planetary nebulae (J 320, NGC 2610, A 6672 and PRTM 1) observed with UVIT/ASTROSAT

Anisha Hazra, Ranjan Kumar, Sonika Piridi et al. (+1 more)

Four planetary nebulae (PNe), Jonckheere 320, NGC 2610, A 6672, and PRTM 1, have been imaged in the far-ultraviolet (FUV) filter F148W ($\lambda_{\mathrm {eff}} = 1481\, \mathring{A} $) using the Ultraviolet Imaging Telescope (UVIT) onboard ASTROSAT. The FUV images reveal faint extended emission structures surrounding the bright central star. A novel sector-based structural analysis technique was employed to examine the detailed FUV morphologies of PNe. In this method, sector strengths were calculated for each nebula and used to classify their structures. Our results show that Jonckheere 320 exhibits a polypolar morphology, while NGC 2610 and PRTM 1 display spherical structures. In contrast, A 6672 shows irregular or elliptical features in the FUV.
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All authors Anisha Hazra, Ranjan Kumar, Sonika Piridi, Ananta C. Pradhan

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Dust production in the harsh environment of Sgr A* - MIRI/JWST observation of the O-rich asymptotic giant branch star IRS~3

F. Peißker, M. García Marín, A. Eckart et al. (+18 more)

Studies of the interstellar medium (ISM) have frequently revealed signatures of the dust produced in the envelopes of asymptotic giant branch (AGB) stars, demonstrating a connection between the dust composition of the ISM and that of AGB stellar envelopes. Investigating this relationship in the extreme, radiation-dominated environment surrounding Sgr A*, the center of our own galaxy, reveals how such conditions might influence dust composition and the recycling of material in galactic centers. IRS 3, the brightest L band source in the Galactic center and most prominent AGB star within the inner parsec of the Milky Way, is embedded in a dusty envelope with an estimated radius of $\sim$10000 AU. We aim to conduct a comprehensive spectral analysis to more tightly constrain the dust composition and line-emitting species within the envelope of IRS 3 in the immediate vicinity of Sgr A*. In 2025, we observed the inner parsec of the Milky Way with the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) as part of the guaranteed time observations (GTO) program Mid-Infrared Characterisation of Nearby Iconic galaxy Centres (MICONIC). We used the MIRI Medium Resolution Spectrometer (MRS) to study the spectroscopic characteristics of the AGB star IRS 3, located about 0.17 parsecs in projection from Sgr A*.
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All authors F. Peißker, M. García Marín, A. Eckart, G. Wright, O. C. Jones, D. Dicken, A. Alonso Herrero, D. Rouan, D. Law, T. Böker, T. Henning, M. Baes, A. Labiano, L. Pantoni, L. Hermosa Muñoz, P.O. Lagage, P. van der Werf, G. Östlin, J. A. D. L. Blommaert, M. Güdel, P. Guillard

Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Global simulations of accretion flows onto perturbers embedded in magnetized disks -I. MRI and jet formation in ideal MHD

Raúl O. Chametla, F. J. Sánchez-Salcedo, Martin E. Pessah et al. (+1 more)

We present the highest resolution global MHD simulations to date of gas flow around a low mass a perturber with mass ratio $q\in[10^{-4},10^{-3}]$, embedded in an accretion disk around a massive central object. We find that gas flow onto the secondary self-consistently forms a turbulent, magnetized mini-accretion disk. The mini-accretion disk sustains a large-scale magnetic field generated by the dynamo effect of the MRI and the accretion flow into the perturber. Simultaneously, a bipolar, collimated, magnetized outflow is launched, extending beyond the perturber's Hill sphere. The bipolar outflows are driven by the combined action of magnetic pressure, in the innermost regions of the mini-accretion disk, and the magnetocentrifugal acceleration of gas, which may attain speeds comparable to the escape velocity from the massive central object. Our results establish an important conceptual connection in accretion disk physics across a wide range of astrophysical systems -from mini-accretion disks to circumstellar and black hole accretion disks-by demonstrating that no fine-tuning is required for small-scale disks to naturally enter an outflow-launching regime. Beyond identifying the physical mechanism responsible for launching small-scale outflows, our framework lays the groundwork for developing more sophisticated physical models of mini-accretion disks around embedded low-mass perturbers.
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All authors Raúl O. Chametla, F. J. Sánchez-Salcedo, Martin E. Pessah, Mauricio Reyes-Ruiz

Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Rapid Orbital Decay in the Ultracompact Double-degenerate Binary eRASSU J060839.5$-$704014

Rahul Sharma, Chandreyee Maitra, Frank Haberl et al. (+9 more)

We present timing and spectral analysis of the recently identified ultracompact double-degenerate (DD) white dwarf binary eRASSU J060839.5$-$704014 using observations from NICER and Einstein Probe (EP), together with archival XMM-Newton data. By phase-connecting the long-term XMM-Newton, NICER, and EP observations, we obtain a coherent quadratic timing solution, yielding an orbital period of 374.15013 (2) s and an orbital decay rate of $\dot{P}= -4.7\,(1) \times 10^{-11} \mathrm{~s~s^{-1}}$. This orbital decay exceeds that measured in the prototypical DD binaries HM Cnc and V407 Vul. Assuming that the observed orbital evolution is primarily driven by gravitational-wave (GW) angular momentum loss, the inferred chirp mass is $\sim0.43\, M_{\odot}$, placing the source among the most massive known systems of this class. The phase-averaged spectra of NICER and EP-Follow-up X-ray Telescope (FXT) are described by a soft thermal component with temperatures of ~126 and ~144 eV, respectively, confirming the supersoft nature of the source. Phase-resolved spectroscopy reveals a clear decrease in temperature across the bright phase in both instruments, indicating a structured emission region with significant temperature gradients. These results establish eRASSU J060839.5$-$704014 as one of the most rapidly evolving ultracompact DD binaries presently known, belonging to the rare class of direct-impact ultracompact binaries, and a promising verification source for future low-frequency GW studies.
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All authors Rahul Sharma, Chandreyee Maitra, Frank Haberl, Joheen Chakraborty, Susanne Friedrich, Yong-Feng Huang, Chichuan Jin, Zhaosheng Li, Georgios Vasilopoulos, Yanjun Xu, Haonan Yang, Weimin Yuan