Peer Revenue Fully funded

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Thursday 13 August

Solar and Stellar Astrophysics

TIC 433545934: The first 2+2 type doubly eclipsing binary with extra, mutual eclipses

Tamás Borkovits, Saul A. Rappaport, Petr Zasche et al. (+5 more)

In this work we identify and photodynamically analyze TIC 433545934, the very first doubly eclipsing 2+2-type quadruple stellar system, which shows outer eclipses, too. One such outer eclipse was discovered with TESS, which triggered a special interest in this system. Most of the data for this study come from TESS observations, but we also obtained supplemental ground-based photometric measurements for this quadruple system. The eclipse timing variation curves extracted from the TESS and ground-based follow-up data, the photometric light curves, and the spectral energy distribution are combined in a complex photodynamical analysis to yield the stellar and orbital parameters of this dynamically interesting system. The periods of the two inner, eclipsing binaries were found to be $P_A=2.07$d and $P_B=1.41$d, while the outer period is $P_{AB}=224.5$d. The outer period alone makes this system the fifth most compact known 2+2-type quadruple. Moreover, what really makes TIC 433545934 unique is that TESS observed a triple-dipped extra eclipsing event when the stars of binary B eclipsed the two components of binary A. We identified similar extra eclipsing events in the archival, ground-based data of ASAS-SN and ATLAS, as well. We found, however, that these extra events occur only once during an outer revolution, that is, binary A does not eclipse the stars of binary B. This is in accord with our finding that the outer eccentricity is quite high, being $e_{AB}=0.62$. Our analysis reveals that binary A consists of two quite similar, but slightly evolved late A-type stars ($q_A=0.92$), while in the case of binary B, the primary star, whose mass is between the masses of the two stars of binary A, is quite dominant, with $q_B=0.60$. The system was found to be substantially flat, with mutual inclination angles below $\approx2\degr$.
Read the full abstract

All authors Tamás Borkovits, Saul A. Rappaport, Petr Zasche, M. Mašek, H. Kučáková, T. Mitnyan, V. B. Kostov, B. P. Powell

Solar and Stellar Astrophysics · Cross-listed from gr-qc

Temperature effects on white dwarfs in modified gravity

Sofía Vidal, Aneta Wojnar and Laur Järv

In this article we analyze the effects of a finite temperature equation of state on the equilibrium structure of white dwarfs in massive Brans-Dicke theory as well as the symmetron and dilaton screening mechanisms. We compute and present the numerically obtained mass-radius relation, effective gravitational constant as well as radial profiles of the scalar field, pressure and metric within the star. We show that assuming a non-zero temperature effectively results in a larger radius while leaving the total mass of the star essentially unchanged, and discuss the interplay between the effective gravitational constant, central density, and radius of the star.
Read the full abstract

Solar and Stellar Astrophysics

Elemental Composition Evolution during the 2024 September 30 Solar Eruption: A Comparison of Hot and Cool Plasma Components with Solar Orbiter/SPICE, Hinode/EIS, and Chandrayaan-2/XSM

Momchil Molnar, Joseph Plowman, Amir Caspi et al. (+7 more)

Solar plasma composition differs between the photosphere and corona over a range of timescales, with preferential enhancement of elements with low first ionization potential (FIP). However, the physical origin of the FIP fractionation remains incompletely understood. Furthermore, during flares, the FIP bias also exhibits rapid changes, associated with fast transport of material with different FIP biases. We present novel observations from Solar Orbiter SPICE and EUI, Hinode/EIS, and Chandrayaan-2 XSM instruments, finding rapid abundance changes in the emitting plasma, on timescales of minutes, during the eruptive M7.6-class solar flare observed on 2024 Sept 30. These instruments have wide temperature coverage and find contrasting abundance-evolution patterns between the hotter and cooler plasma components. 3D reconstruction of the active region and additional observations from the Solar Orbiter STIX X-ray telescope show how the hot and cool plasma components, emitting in different spectral regions and observed with the various instruments, sample the plasma composition evolution in distinct locations within the observed flaring plasma. The bright post-flare loop tops observed by SPICE show coronal FIP bias, while the hot plasma observed with XSM exhibits FIP-bias decreasing from coronal to photospheric during the impulsive phase. We interpret these observations as evidence of the X-ray diagnostics seeing hot coronal reconnection outflows mixing with chromospheric plasma as flare loops sequentially energize and relax, explaining why the FIP bias decreases from coronal to a hybrid; and the cool loop tops seen with SPICE show coronal abundances due to coronal material deposited near the looptops.
Read the full abstract

All authors Momchil Molnar, Joseph Plowman, Amir Caspi, Ritesh Patel, Arpit Shrivastav, Tania Varesano, Don Hassler, Ryan French, Biswajit Mondal, L. P. Chitta

Solar and Stellar Astrophysics

Photospheric Kelvin–Helmholtz Vortices as Possible Drivers of Coronal Heating: Implications of the DKIST Observations

Katariina Nykyri

The Daniel K. Inouye Solar Telescope (DKIST) has resolved Kelvin–Helmholtz (KH) vortices at photospheric magnetic-flux boundaries with a characteristic wavelength of 65 km. I estimate whether these vortices can supply the photospheric driver for cross-scale plasma heating through reconnection across different heights from photosphere to low-corona. Using the simulated MURaM shear, density contrast, and 500 km vertical extent, together with a representative photospheric density, gives a shear-energy density of $1.35\times10^{2}$ J m$^{-3}$ and $2.2\times10^{24}$ erg per characteristic vortex. Magnetic fields $1^\circ$–$7^\circ$ from the exact perpendicular orientation ($ {\bf{B}}\perp{\bf{k}}$) remain KH unstable in an idealized calculation and provide an in-plane component that can be wound or compressed into current layers. The limiting case, in which the center-of-momentum shear reservoir becomes new magnetic free energy, gives $b_{\rm cs}=184$ G, identical to the ideal marginal-stability field and equivalent to a $7.6^\circ$ effective twist. This stores at most 135 J m$^{-3}$ in the layers. Using empirical collisionless reconnection heating fractions of 0.28–0.44, the same twist mapped to weakly collisional heights gives ion heating from $\approx$20 eV at the photosphere to $\approx$1.4 keV in the low corona. For an illustrative, snapshot-based KH-active surface fraction of 0.03, quiet-Sun and coronal-hole losses require 5–8% and 14–21%, respectively, of the shear reservoir to become reconnecting magnetic free energy that reaches such heights. Active regions likely require a separate guide-field twist and helicity reservoir. The required upward transport has not been measured by DKIST, but it is directly testable.
Read the full abstract

Solar and Stellar Astrophysics

Titanium Oxide Absorption as a Proxy to Detect Long term Variation and Activity Cycle in Proxima Centauri

Fatemeh Azizi, Mohammad Taghi Mirtorabi and Rahimeh Foroughi

Stellar activity cycles on magnetically active stars can be estimated by molecular absorption bands. We have previously introduced a molecular index which compares absorptional line strength of the TiO567nm with its nearby continuum has previously been introduced. In this work we use this indicator to evaluation long-term activity variations for Proxima Centauri star, using spectroscopic data from HARPS. The results indicate periodicity with an activity period of 2873(+47.4-53.9) days, which is similar to the previous measurements from other indicators.
Read the full abstract

Wednesday 12 August

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

Gaia parallax bias via spherical harmonics: A Python tool and discussion of possible causes

Valeri V. Makarov and Ciprian T. Berghea

Parallaxes in Gaia DR3 are known to suffer from a complex set of sky-correlated and magnitude-dependent offsets or biases at the level of a few tens of $\mu$as. Estimated from a sample of one million distant quasars and AGNs from the CRF catalog, the average offset is negative, but the actual distribution of this important parameter shows significant variations on the sky. We propose a practical method to evaluate the parallax correction as a function of sky position and, optionally, of $G$ magnitude using a spherical harmonic series, and supply a tested Python tool varpi3.py available on Zenodo\footnote{ https://zenodo.org/records/21708614}. We find that only the constant $Y_{00}$ term is significantly dependent on magnitude, while the other 80 harmonic terms are either close to zero or flat with magnitude. The directions of the smallest and largest parallax offsets are $(l,b)\simeq(220\degr,+43\degr)$ and $(l,b)\simeq(45\degr,-45\degr)$, which are close to the orientation of the quasar density dipole reported in recent publications. Motivated by this curious coincidence, we review possible physical effects resulting in a negative bias of measured parallaxes, including an anisotropic universe with a positive curvature and an orbital aberration component. The proposed method of parallax correction is tested using independent asteroseismology data for four different areas on the sphere. Finally, we show that the parallax zero-point propagates into the CRF proper-motion field through the parallax–proper-motion covariance, biasing the vector spherical harmonic determination of the secular-aberration glide, and hence the Galactocentric acceleration, at the microarcsecond-per-year level.
Read the full abstract

Solar and Stellar Astrophysics

The Wave-Regulated Precursor of a Near-Parallel Interplanetary Shock Observed by Parker Solar Probe

Immanuel Christopher Jebaraj, Lucas Colomban, Oleksiy Agapitov et al. (+7 more)

Diffusive shock acceleration, at shocks from coronal mass ejections to supernova-remnant blast waves, presupposes a scattering wave field that the accelerated particles themselves maintain. This self-regulation has not been resolved in situ. We report Parker Solar Probe observations of a fast (~2800 km/s), near-parallel interplanetary shock at 0.24 AU on 2023 March 13 and separate its upstream wave field into four families, a classification not made before at a fast shock near the Sun. Right-hand and left-hand circularly polarized families over a common wavenumber band, with a field-aligned linearly polarized family, are cyclotron-resonant with the suprathermal-to-MeV protons streaming from the shock: the beam drives the field that scatters it, and the measured mean free path, half the precursor scale, leaves the beam anisotropic enough to sustain the drive. Outside this loop lies a weak, oblique, linearly polarized component, a few per cent of the wave power, resolved here for the first time at an in situ foreshock. Its in-phase density and field-magnitude fluctuations identify the compressive part as fast magnetosonic and shift the cyclotron-resonance energies of the resonant families by up to 13 % along the precursor. Acceleration at shocks inside 0.3 AU is governed upstream, in a foreshock the shock builds for itself.
Read the full abstract

All authors Immanuel Christopher Jebaraj, Lucas Colomban, Oleksiy Agapitov, Michael Gedalin, Mikhail Malkov, Athanasios Kouloumvakos, Edin Husidic, Shiladittya Mondal, Sunil Yadav, Nicolas Wijsen

Solar and Stellar Astrophysics

Large-Scale Dynamos Driven by Shear-Flow-Induced Jets

B. Tripathi, A. E. Fraser, P. W. Terry et al. (+3 more)

At every scale they occupy, magnetic fields affect various phenomena, including star formation, cosmic ray transport, charged particle acceleration, space weather, transport in planetary atmospheres, and laboratory plasmas. These fields are often generated and sustained by turbulent flows in a process called the dynamo. In 1955, E. N. Parker parameterized the effects of small-scale turbulence to propose a mean-field dynamo theory. The widely used theory reproduces observed large-scale fields but suffers from difficulty in tuning parameters as they are not justified from first principles: Studies of turbulent flows show tangled magnetic fields, which are folded and fragmented into small-scale structures due to shear-flow straining. Here, considering a shear flow that is unstable and driven, we develop analytic theory and perform three-dimensional (3D), advanced computer simulations of turbulence with up to 4096 x 4096 x 8192 grid points, showing ab initio generation of quasi-periodic, large-scale magnetic fields. The generation occurs via the mean-vorticity effect—an additional mean-field dynamo process postulated in 1990. Crucial to this dynamo is the prior generation of large-scale 3D jets, robustly produced as topologically protected and exact nonlinear solutions of the magnetohydrodynamic equations. The jet-driven dynamo applies to shear-driven laboratory and astrophysical systems. These include binary neutron star mergers, where the reported dynamo likely operates on microsecond timescales to produce in milliseconds some of the strongest magnetic fields in the Universe, providing signals for multimessenger astronomy.
Read the full abstract

All authors B. Tripathi, A. E. Fraser, P. W. Terry, E. G. Zweibel, M. J. Pueschel, R. Fan

Solar and Stellar Astrophysics

Astronomical Cardiology II: A Search For Heartbeat Stars Using APOGEE and TESS

Jowen Callahan, D. M. Rowan, C. S. Kochanek et al. (+1 more)

Stellar binaries in short-period, highly eccentric systems with significant tidal deformations near pericenter, also known as heartbeat stars, are a laboratory for studying dynamical tides and oscillations in stars. We identify 50 heartbeat stars using TESS light curves of stars identified as binaries using SDSS APOGEE. We fit their phase-folded TESS light curves with an analytic model to measure their orbital periods, eccentricities, inclinations, and arguments of periastron. We measure the mass function of targets with enough APOGEE radial velocity observations to obtain a constraint on the secondary mass. We confirm our previous results that the non-giant heartbeat stars have started to evolve off the main sequence and that the fraction of (near) main sequence binaries that are heartbeat stars rises rapidly with effective temperature.
Read the full abstract

All authors Jowen Callahan, D. M. Rowan, C. S. Kochanek, M. M. Fausnaugh

Solar and Stellar Astrophysics

Hemispheric Asymmetry of Solar Active Regions Arises from a Nested Population

Aimee A. Norton

We investigate the longitude–time distribution of NOAA active regions (ARs) during Solar Cycles 22–24 and find statistically significant North–South asymmetry in AR emergence. Using an activity-nest identification algorithm, we show that this asymmetry is concentrated in the subset of ARs that participate in nests. Nest-member ARs exhibit substantially larger hemispheric asymmetry than either the full AR population or the non-nest population, and the asymmetry is largely removed when nest-member ARs are excluded. Monte Carlo tests with randomized longitudes and temporal perturbations show that the observed nesting and asymmetry exceed random expectations, implying that $\sim$6–18% of ARs participate in a non-random, hemispherically asymmetric nesting component. This asymmetry is associated with temporally offset bursts of activity and distinct longitudinal clustering between the hemispheres, leading to reduced cross-equatorial coherence in the longitude–time distribution of solar ARs. Intervals of enhanced nesting activity and hemispheric asymmetry broadly coincide with enhanced hemispheric quasi-biennial variability and temporal evolution of the large-scale solar magnetic field, suggesting a possible connection between intermediate-timescale dynamo variability and the hemispheric organization of solar activity.
Read the full abstract

Solar and Stellar Astrophysics

Nascent Embedded-protostar Survey in Taurus (NEST) I: Protostellar Multiplicity

Aislinn C. Plante, John J. Tobin, Patrick D. Sheehan et al. (+5 more)

We present new ALMA 0.9 mm and VLA 9 mm observations in the Taurus Molecular Cloud (TMC) of 25 protostellar systems, containing 40 protostars, observed at 0.3" (~20 au) resolution. Within separations of 18-10,000 au, the ALMA/VLA-observed Taurus sample has a multiplicity fraction (MF), defined as the fraction of systems with at least one companion, of 0.50 +/- 0.07, and a companion fraction (CF), defined as the average number of companions per system, of 0.58 +/- 0.20. To build a more complete census of protostellar multiplicity in this region, we supplement the observed sample with 24 protostars (12 protostellar systems and 5 additional companions associated with systems we observed) previously identified through archival infrared or ALMA observations. Together, these 64 individual protostars (37 systems) define our Taurus+ sample, for which we measure higher values of 0.53 +/- 0.06 and 0.72 +/- 0.19 for the MF and CF, respectively. These multiplicity statistics in the TMC are notably higher than those reported in the more clustered star-forming regions of Orion and Perseus at the ~3-4 sigma level, suggesting that Taurus may preserve a larger fraction of primordial multiples. The separation distributions in our samples show populations of both close and wide multiples, but a deficit at intermediate separations of 200-300 au. This pattern may suggest two distinct formation pathways: close binaries (<200 au) arising primarily from disk fragmentation, and wide multiples (>1000 au) from core fragmentation.
Read the full abstract

All authors Aislinn C. Plante, John J. Tobin, Patrick D. Sheehan, Noshin Yesmin, Nicholas P. Ballering, Tyler L. Bourke, Josh Eisner, Zhi-Yun Li

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

Voltage-to-temperature calibration of the High Altitude THz Solar telescope acquisition system

Gedeane G.S. Kenshima, Daniel R. Sousa, Tiago Giorgetti et al. (+2 more)

The THz range has been under-explored for solar astronomy, mainly due to technological limitations. Only recently, a few new telescopes, such as the High Altitude Terahertz Solar (HATS) photometer, have been monitoring the solar activity in this range of the spectrum. This paper presents the experimental characterization and voltage-to-temperature calibration of the HATS acquisition system. HATS uses a Golay cell for capturing the incoming radiation, modulated by a 20 Hz fork chopper. The amplitude of the signal is then obtained at predetermined time intervals by applying a windowing function and an FFT to the signal. To characterize this acquisition system, a blackbody calibrator, with temperatures varying from 100 to 500 C (373.15 K to 648.15 K), was used as a THz source, and two signal recovery methodologies were compared: sinusoidal curve fitting and FFT combined with six windowing functions (rectangular, Hamming, Hann, Barlett, Blackman, and Flat Top). Our quantitative results demonstrate high linearity in the system's response over the input source's temperature range, with the Hamming window achieving the highest precision, yielding a Root Mean Square Error (RMSE) of 15.48 and a calibration temperature-to-voltage factor of 10.32 +- 0.13 mV/K. In contrast, the Bartlett window presented the highest error (RMSE 16.02). The choice of windowing function had only a minor effect on the calibration factors, which ranged from 10.32 to 10.43 mV/K, all within the experimental uncertainties. Beyond solar photometry, the signal modulation and windowing concepts established here are highly applicable to other fields requiring high-sensitivity thermal detection, such as industrial pyrometry for high-temperature manufacturing, environmental monitoring of atmospheric water vapor, and the development of medical imaging systems based on Terahertz radiation for non-invasive tissue analysis.
Read the full abstract

All authors Gedeane G.S. Kenshima, Daniel R. Sousa, Tiago Giorgetti, Paulo J. A. Simões, C. Guillermo Giménez de Castro

Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

The Ambipolar electric field in multispecies plasma atmospheres: effects of alpha particles and stochastic heating

Luca Barbieri, Pascal Démoulin and Daniel Verscharen

We investigate stationary states of a collisionless, gravitationally stratified plasma atmosphere composed of electrons, protons, and alpha particles by extending Pannekoek–Rosseland theory to multispecies and multi-temperature plasmas. Starting from Liouville's theorem, we derive the self-consistent ambipolar electric field from kinetic equilibrium and charge neutrality. For a single-temperature atmosphere, we obtain analytical expressions for the ambipolar field, show its dependence on alpha-particle abundance, and determine the relative stratification of the three species. A first-order analytical approximation to the electrostatic potential accurately reproduces the numerical solution. We then generalize the formalism to multi-temperature plasmas generated by stochastic boundary heating, representing the stationary distribution as a superposition of Maxwellian populations. Gravitational filtering produces non-exponential density profiles and increasing temperatures with altitude, while preserving the relative species stratification, with alpha particles most strongly stratified and protons least. The ambipolar electric field contains a dominant gravitational contribution, corresponding to the generalized Pannekoek–Rosseland field, and a thermoelectric contribution arising from species-dependent temperature gradients, which accounts for its non-monotonic structure. These results provide a framework for studying the combined effects of plasma composition and stochastic heating in gravitationally stratified astrophysical plasmas.
Read the full abstract

Solar and Stellar Astrophysics

Deep MUSE observations of SNR 0509-67.5 reveal a double degenerate merger progenitor

Priyam Das, Ivo R. Seitenzahl, Gilles Ferrand et al. (+5 more)

Deep MUSE observations of SNR 0509-67.5 reveal that the coronal [Fe\,xiv] $\mathrm{\lambda}$5303 emission line appears with either one or two velocity components across the entire remnant, arising from reverse-shocked ejecta moving toward and away from the observer. A supervised dense neural network classifies each spaxel and fits Gaussian profiles plus a linear function to the observed line emission. We measure a bulk Doppler velocity of $-1000\pm60~~\mathrm{km~s^{-1}}$, interpreted as the line-of-sight component of the primary white dwarf's orbital velocity in a double-degenerate merger. The red- and blue-shifted ejecta map shows a flattened edge along the north-eastern rim, consistent with the companion's shadow, indicating a binary companion was present at explosion. Modelling this feature as a cone anchored at the explosion centre and applying Bayesian inference, we recover the cone's orientation and half-opening angle. We then use the Eggleton Roche-lobe relation to infer properties of the companion. The companion was likely a ${\sim}0.6~\mathrm{M_\odot}$ white dwarf with radius ${\sim}9800$~km and orbital velocity ${\sim}1700~\mathrm{km~s^{-1}}$ at the time of explosion. Together, these results provide a complete dynamical picture of a Type Ia supernova progenitor system whose maximum-light spectrum is independently constrained by light echo observations.
Read the full abstract

All authors Priyam Das, Ivo R. Seitenzahl, Gilles Ferrand, Rudiger Pakmor, Simon J. Murphy, Ashley Ruiter, Brian P. Schmidt, Friedrich K. Roepke

Solar and Stellar Astrophysics

New constraints on the binary system HD 327083 and its gaseous and dusty environments

L. Cidale, P. Marchiano, M. Kraus et al. (+11 more)

Binary systems with circumbinary molecular and dust rings are of great interest because they provide insights into the dynamics and evolution of stellar systems and the chemistry of the surrounding material. We aim to elucidate the nature of the B[e] binary system HD 327083 and the physical properties of its circumstellar and circumbinary envelopes. We combined multi-epoch high-spectral resolution optical and near-IR observations with VLTI/MIDI observations and ASAS-3 photometry. The data were analysed to obtain the orbital parameters, study individual members of the system, and derive the properties of the atomic and molecular gas and the dusty components of the complex environment of HD 327083. We improved the orbital solution of HD 327083 and derived a period of P = 107.699 d. Most optical lines display variations in shape and intensity when folded with the orbital motion. We assigned F6 II-III and B1 spectral types respectively to the cool and hot components. A ring of molecular gas revolves around the system and varies with the orbital phase. The MIDI data show a silicate band in absorption at 9.7 micron and indicate that the dust distribution has an elliptical shape, with its inner edge varying with orbital phase between 12.5 and 44 AU. We conclude that the B[e] binary system HD 327083 comprises a B-type massive accreting star, and an F-type companion filling over 60% of its Roche lobe and evolving towards the red supergiant stage. The deformed shape of the F-type star causes a broad minimum in the light curve. The hot companion (26 000 K, log g = 3.0) is hidden by a compact disc and shows a bi-polar outflow. The entire binary system presents an O-rich environment. It is surrounded by warm CO and SiO molecular rings, which are enclosed by an elliptical dust structure. All these components were formed by the evolved donor star during its evolution towards the red supergiant phase.
Read the full abstract

All authors L. Cidale, P. Marchiano, M. Kraus, I. Andruchow, M. L. Arias, M. Cure, M. Borges Fernandes, Y. Aidelman, A. Torres, I. Araya, G. Maravelias, J. Zorec, Y. Cochetti, J. Panei

Solar and Stellar Astrophysics

Chemical fingerprints of binary mass transfer in massive stars

Harim Jin and Norbert Langer

The majority of massive stars are born in close binary systems. As stars expand when they age, mass transfer or even a merger with their companion is inevitable. However, most binary interaction products appear as single stars, such that the main evidence of their exciting past is lost. In a comprehensive grid of detailed massive binary evolution models we find systematic trends in chemical surface abundances that allow identifying the past mass gainers. We develop an analytic framework which is independent of specific evolutionary models, to constrain the amount and composition of the accreted material from their observed surface abundances. This yields tight constraints on the uncertain mass transfer physics in massive binary stars and allows us to reconstruct the past evolutionary history of the progenitor binary system. This method, which is shown to also constrain binary mergers (for example, SN 1987A), is applied to some of the best-studied OB stars so far. For {\gamma} Columbae, suggested to be an envelope-stripped star, we show that it is a mass gainer instead, whose companion star likely formed a stripped-envelope supernova. Our results highlight surface abundance measurements as a powerful tool to improve our understanding of massive binary systems evolving towards supernovae and compact object binaries.
Read the full abstract

Solar and Stellar Astrophysics

1.5D investigation of the Hanle effect in the Ca I 4227 line using partial frequency redistribution. Comparison of synthetic Stokes profiles in Bifrost and MURaM-ChE rMHD models

Devang Agnihotri, L. S. Anusha, D. Przybylski et al. (+2 more)

Modeling scattering polarization in the Ca I 4227 Å line is important for diagnosing chromospheric magnetic fields. We investigate the relative influence of formation heights and magnetic fields, through the Hanle effect, on spatially averaged synthetic Stokes profiles using realistic solar atmospheres. We employ 1D vertical columns from 3D radiative magnetohydrodynamic simulations of the solar chromosphere performed with the Bifrost and MURaM-ChE codes, and solve the 1.5D non-local thermodynamic equilibrium polarized radiative transfer equation including partial frequency redistribution and the Hanle effect. The intensity profiles from both simulations agree at line center, while MURaM-ChE exhibits enhanced wing intensity due to deeper, hotter formation regions. The polarization signals form at greater heights in MURaM-ChE than in Bifrost. In the non-magnetic case, Bifrost produces stronger line-core polarization, whereas MURaM-ChE shows enhanced wing polarization. Including the magnetic fields from the simulations results in stronger Hanle depolarization of <Q>/<I> in Bifrost. The distinct thermal and magnetic structures at the corresponding formation heights therefore produce significantly different polarization profiles. In particular, the Hanle signatures suggest that the line-core formation region in MURaM-ChE is less strongly magnetized than that in Bifrost.
Read the full abstract

All authors Devang Agnihotri, L. S. Anusha, D. Przybylski, R. H. Cameron, S. K. Solanki

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

Three new exoplanet systems from the Dispersed Matter Planet Project

J.R. Barnes, C.A. Haswell, Z.O.B. Ross et al. (+7 more)

We present a radial velocity analysis of three bright, low-activity stars identified by the Dispersed Matter Planet Project (DMPP). We use a Bayesian framework to compare purely Keplerian models with models incorporating stellar activity via a quasi-periodic Gaussian Process (GP). DMPP-7 (HD 118006) is a slightly evolved star that harbours a single 0.72 Saturn-mass giant ($m_\textrm{p}\sin i$ = 69 M$_\oplus$) with an orbital period of P = 4.93 d. A longer 21 d - 22 d period cannot be conclusively confirmed as a stellar rotation signature rather than a purely Keplerian signal. For HD 67200, which exhibits Ca ii H&K variability, a model with only a GP is strongly favoured over a purely dynamical model. The GP model shows moderate evidence for a single Keplerian with P = 2.67 d. For HD 2134, a 21 d - 32 d rotation period signal is associated with tentative FWHM variability. A model with a GP is not conclusively favoured, but all models considered show moderate evidence for an additional single Keplerian with P = 2.78 d. Despite our target selection favouring near edge-on orbital geometries, we find no evidence for transits in TESS photometry. DMPP-7 b lies at the transition between the high-radius population and the Neptunian ridge and savannah regions. Further observations are required to establish whether the coherent short-period HD 67200 and HD 2134 signals are stellar or dynamical in origin. If planetary, the signals correspond to minimum masses of $m_\textrm{p}\sin i$ = 2.07 M$_\oplus$ and $m_\textrm{p}\sin i$ = 2.86 M$_\oplus$
Read the full abstract

All authors J.R. Barnes, C.A. Haswell, Z.O.B. Ross, E. Rutherford, M.R. Standing, A.T. Stevenson, D. Staab, L. Fossati, J.S. Jenkins, D. Alves

Solar and Stellar Astrophysics

First and Comprehensive Study of V0757 Pup : $\gamma-$Doradus Pulsator in Detached Eclipsing Binary

Bakuh Danang Setyo Budi, Bryant Randolph, Rafa Nanda Akilah et al. (+3 more)

Pulsating stars in detached eclipsing binary (EA) systems are known for providing many important physical informations which constrain both stellar structure and evolution theories. To date, fewer than 50 $\gamma$ Doradus (GDOR) stars have been found in eclipsing binary systems, making them important targets to study g-mode pulsation inside the stars. We present a comprehensive physical and pulsational analysis of V0757 Pup (TIC 6939791), a detached eclipsing binary system observed by the TESS mission (Sectors 7, 34, 61, and 88) and followed up with ground-based spectroscopy from the Thai National Telescope. By combining light curve modeling with radial velocities derived from medium-resolution spectra, we determined the fundamental stellar and atmospheric parameters with high precision. The system consists of an F2V primary ($M_1=1.305\pm0.026M_\odot, R_1=1.643\pm0.020R_\odot$) and a G1V secondary ($M_2=0.934\pm0.030M_\odot, R_2=0.941\pm0.079R_\odot$). We performed a detailed frequency analysis of the residual light curves, identifying two dominant independent pulsation frequencies at $f\sim0.79$ c/d and $0.98$ c/d. These frequencies, along with the derived pulsation constant ($Q\sim0.6$ d), confirm the primary component as a $\gamma$ Doradus pulsator. An analysis of Eclipse Timing Variations (ETV) reveals non detection of third body companions with current available dataset, strengthen by the result of Gaia astrometric analysis. Evolutionary modeling indicates the system is $\sim2.2$ Gyr old, with the primary expected to fill its Roche lobe in $\sim1$ Gyr. Additionally, we calculate a distance of $d\approx350$ pc based on orbital and SED modeling, which is in excellent agreement with the Gaia DR3 parallax distance.
Read the full abstract

All authors Bakuh Danang Setyo Budi, Bryant Randolph, Rafa Nanda Akilah, Evan Irawan Akbar, Hakim Luthfi Malasan, Puji Irawati

Solar and Stellar Astrophysics

Results from the first spectropolarimetric survey of $\gamma$ Dor pulsators

J. Labadie-Bartz, R. Ouazzani, C. Neiner et al. (+8 more)

Context. Magnetic fields can have an important influence on stellar structure and evolution. In intermediate-mass (A- and F-type) stars, there are many known stars with directly measured strong, globally organized magnetic fields, as well as indications of weak and/or small-scale variable fields. However, among the intermediate-mass $\gamma$ Dor pulsators, there are no known stars with strong surface magnetic fields. Aims. The broad goal of this work is to search for evidence of strong, globally organized fields at the surface of $\gamma$ Dor pulsators. Methods. We identified objects consistent with being $\gamma$ Dor pulsators based on an analysis of space photometry from the Transiting Exoplanet Survey Satellite (TESS) mission. A spectropolarimetric survey was then conducted on a subset of 47 of these objects, with a precision sufficient to detect dipolar surface magnetic fields down to a threshold of about 10 – 100 G. Results. We detected strong magnetism in three targets. However, upon closer inspection, none of these appear to be genuine $\gamma$ Dor pulsators. We found no evidence of surface magnetism in any of the remaining 44 objects. Conclusions. We conclude that either strong, globally organized magnetic fields and $\gamma$ Dor pulsation are mutually exclusive, or that such stars are exceedingly rare. A possible explanation is that strong global fields inhibit the excitation mechanism, which prevents $\gamma$ Dor pulsations from being driven in strongly magnetic intermediate-mass stars. The dipolar surface magnetic field strength upper limits we derive for this sample ($\lesssim$ 50 – 100 G) provide valuable constraints for surface boundary conditions for asteroseismic models that include magnetism for $\gamma$ Dor stars.
Read the full abstract

All authors J. Labadie-Bartz, R. Ouazzani, C. Neiner, V. Antoci, P. Stanley, T. Natan, K. Thomson-Paressant, S. D. Chojnowski, B. Mas Sanz, O. Dürfeldt Pedros, V. Petit

Solar and Stellar Astrophysics

Statistics of Solar Filament Mass based on CHASE Sun-as-a-star Spectroscopic Observations

T. Y. Xie, Z. H. Zhao, X. Cheng et al. (+5 more)

Filaments are cool and dense plasmas suspended in the hot corona of the Sun and other stars. Accurately estimating their masses is of great significance for understanding subsequent eruptions and induced space weather effects, but it remains hindered by their intrinsic geometric uncertainties, particularly in spatially unresolved stellar observations. To test and calibrate the methods for estimating the masses of stellar filaments, we conduct a statistical Sun-as-a-star analysis of solar filaments, utilizing full-disk H$\alpha$ spectroscopic observations from the Chinese H$\alpha$ Solar Explorer (CHASE). A total of 1346 filaments, covering a period from January 2024 to October 2025, are identified via a machine-learning segmentation model. We construct their virtual sun-as-a-star spectra by spatially integrating the filament regions and then obtain their optical parameters by cloud-model fitting. Upon correcting projection effects, we establish a representative three-dimensional morphological scaling of length, apparent width, and line-of-sight depth ($L:W_{\rm app}:D_{\rm LOS} \approx 4.5:1:1.7$), with a median filament depth of about 8000 km. Interestingly, the Sun-as-a-star estimated mass shows high consistency with the resolved intrinsic mass across the full sample, with a log-space regression slope of 1.07. As the first large-sample Sun-as-a-star study of solar filaments, our results provide empirical constraints on filament geometries and masses, offering a critical reference for estimating stellar filament masses based on H$\alpha$ spectroscopy.
Read the full abstract

All authors T. Y. Xie, Z. H. Zhao, X. Cheng, Y. H. Chen, Z. Zheng, Q. Hao, C. Li, M. D. Ding

Solar and Stellar Astrophysics

Disco in the Dust: Reflected light at the bow shock around Betelgeuse's companion explains its observed luminosity

Jared A. Goldberg, Meridith Joyce, Anna J. G. O'Grady et al. (+6 more)

Recent detections of $\alpha$ Orionis B, the putative companion to Betelgeuse, have been reported using multiple instruments and techniques. These include, most recently, a $>6\sigma$ detection using VLT/SPHERE reported by Montarges+2026. The authors infer a bright companion ($\sim10^{-3}\times$ Betelgeuse's luminosity) with a mass of $2-3\,M_\odot$ and $T_\text{eff}\approx10-12{,}000$\,K, loosely consistent with the uppermost bounds of Howell+2025's recent mass estimate from speckle-imaging. However, it is in tension by a factor of two with the reported mass-exclusion limits via non-detection from a recent HST far-UV campaign (Goldberg+2025). While mass identification from isochrone-fitting (conducted in all cases) is prone to uncertainty, the restrictive HST upper limit on FUV flux precludes the hot, blue emission of a $\gtrsim2\,M_\odot$ main-sequence star. This discrepancy is reconciled by the following hypothesis: these detections observe the reflection of Betelgeuse's own luminosity scattered off the companion's bow shock and wake as it traverses the dusty circumstellar medium. To evaluate the feasibility of this scenario, we draw from custom, filter-specific stellar models computed with MESA, as well as Athena++ simulations of the companion's bow shock in idealized conditions. Importantly, the expansive bow shock from a stellar-mass object necessarily subtends a sizable portion of Betelgeuse's outgoing flux. We find that optical luminosity ratios of $\sim10^{-3}-10^{-4}$ are straightforward to resolve within reasonable assumptions about the companion mass and circumstellar dust, and disfavor a hot $3\,M_\odot$ companion. We thereby reconcile competing mass hypotheses across observational campaigns through proper attribution of the observed brightness, motivating future multi-wavelength campaigns to further characterize this enigmatic system.
Read the full abstract

All authors Jared A. Goldberg, Meridith Joyce, Anna J. G. O'Grady, Sam D. Barber, Logan J. Prust, Mitchell Dennis, László Molnár, Christian I. Johnson, Wolfgang E. Kerzendorf

Solar and Stellar Astrophysics

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

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

Observationally, blue horizontal branch (BHB) stars are defined as hot stars occupying a characteristic region between the extreme blue horizontal branch and RR Lyrae variables in the Hertzsprung-Russell diagram. Most of them are interpreted as stripped core-helium-burning stars, but the role of binary interaction in their formation remains unclear. Here, we report the discovery of a metal-rich BHB star in a 0.82628-day binary system (Feige 64) comprising a $0.35\pm0.03\,M_{\odot}$ BHB star and a likely $1.26\pm0.17\,M_{\odot}$ white dwarf (WD). The BHB star has an effective temperature of $15{,}524\pm310$ K and a luminosity of $39.7\pm4.1\,L_{\odot}$. Stellar evolution modelling indicates that it is a helium-shell-burning star produced through the common-envelope channel, retaining a hydrogen-rich envelope that is more massive than previously thought for low-mass stars. This finding provides direct evidence for binary interaction in the formation of BHB stars, offering a fresh perspective on interpreting this emerging population.
Read the full abstract

All authors Jiao Li, Changqing Luo, Hai-Liang Chen, Zhicun Liu, Bo Zhang, Shi Jia, Hongwei Ge, Tao Wu, Yuhan Yao, Pei Wang, Marat Gilfanov, You Wu, Zhenwei Li, Zhengwei Liu, Xiangcun Meng, Xue-Fei Chen, Philipp Podsiadlowski, Chao Liu, Zhan-Wen Han

Tuesday 11 August

Solar and Stellar Astrophysics

Numerous bow shocks in the outer Helix Nebula

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

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

All authors Pieter van Dokkum, Roberto Abraham, William P. Bowman, Seery Chen, Steven R. Janssens, Deborah M. Lokhorst, Imad Pasha, Carter Rhea

Solar and Stellar Astrophysics

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

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

We present interferometric measurements of angular diameters for 27 nearby solar-type stars obtained with the Precision Astronomical Visible Observations (PAVO) beam combiner at the CHARA Array. The sample spans a broad range of metallicities, includes several known exoplanet hosts, and covers evolutionary stages from the zero-age main sequence to mildly evolved subgiants. Uniform-disk and limb-darkened angular diameters were measured for each target and combined with bolometric fluxes and Gaia parallaxes to determine precise, model-independent stellar radii, effective temperatures, and luminosities. We achieve typical uncertainties of $\sim1$% in radius and $\sim1.5$% in effective temperature. Comparisons with multiple stellar evolutionary model grids yield mass and age estimates and enable assessment of grid-to-grid systematics, highlighting sensitivities to abundances, evolutionary stage, and proximity to grid boundaries. Our results provide empirical benchmarks for testing stellar evolutionary theory, refining surface brightness-color relations, and improving the characterization of exoplanet host stars.
Read the full abstract

All authors Tabetha S. Boyajian, Ashley A. Elliott, Emelly D. Tiburcio, Kaspar von Braun, Gail Schaefer, Timothy R. White, Daniel Huber, Michael Ireland, Jeremy Jones, Tyler Ellis, Eliot Hiegel

Solar and Stellar Astrophysics

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

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

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

All authors Yanwen Wang, Rohit Chhiber, Arcadi V. Usmanov, Marc Swisdak, William H. Matthaeus

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

A Diverse Distribution of Black Hole Spins from Stable Mass Transfer

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

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

All authors Linhao Ma, Jakub Klencki, Eliot Quataert, Lieke van Son

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

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

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

The Habitable Worlds Observatory (HWO) is a future NASA flagship mission concept identified by the Astro2020 Decadal Survey as the highest priority for large space missions. HWO should conduct "transformative astrophysics" and search for biosignatures in the atmospheres of approximately 25 potentially Earth-like planets. To further the early-stage development of HWO, NASA formed the Science, Technology, Architecture Review Team (START). In turn, START invited the scientific community to join working groups to explore the potential discovery space. In this paper, we present 70 science cases that resulted from this process. The cases address four scientific pillars: growth of galaxies (15 cases), evolution of the elements (13 cases), solar systems in context (32 cases), and living worlds (10 cases). Combined, they would address 27 of the 30 science questions and discovery areas identified by Astro2020. The 140 observing programs needed for the 70 investigations encompass a rich variety of spectroscopic (for 87% of science cases) and photometric (for 30%) observations extending from the UV to the NIR. Additionally, high-contrast and polarimetric capabilities would be needed for 34% and 27% of science cases, respectively. Access to UV wavelengths is critical: 83% of science cases need data at wavelengths <400 nm, and 26% extend to <100 nm. In the NIR, 26% of science cases need observations at wavelengths >=2000 nm. Pursuing the full portfolio of science would also necessitate precise astrometry for planet mass measurement, rapid response capabilities, a large instantaneous field of regard, non-sidereal tracking, saturation mitigation strategies, and high dynamic range.
Read the full abstract

All authors Courtney D. Dressing, Danica Adams, Evelyne Alecian, Gagandeep Anand, Giada Arney, Sarah Gomes Aroucha Barbosa, Martin Barstow, Joanna K. Barstow, Rachael L. Beaton, Eduardo Bendek, Svetlana Berdyugina, Julie Biedermann, Sarah Blunt, Sanchayeeta Borthakur, Kara Brugman, Joseph N. Burchett, Eric Burns, Jenna M. Cann, Ludmila Carone, Cody A. Carr, Richard Cartwright, Renyue Cen, Jean-yves Chaufray, Pin Chen, Lígia F Coelho, Kyle Cook, Nicolas B. Cowan, Patricio E. Cubillos, Alexandre David-Uraz, Tansu Daylan, Jessica E. Doppel, Leonardo dos Santos, Meredith Durbin, Rana Ezzeddine, Tara Fetherolf, Theresa Fisher, Leigh N. Fletcher, Luca Fossati, Ana I Gómez de Castro, Kaz Gary, Varoujan Gorjian, Yasuhiro Hasegawa, Qiuhan He, Natalie Hinkel, Keri Hoadley, Renyu Hu, Noam Izenberg, Estelle Janin, Mathilde Jauzac, Stephen R. Kane, Theodora Karalidi, Émilie Anne Lafléche, David J. Lagattuta, Érika Le Bourdais, Mary Anne Limbach, Jacob Lustig-Yaeger, Eric Mamajek, Kathleen Mandt, Frédéric Marin, Taro Matsuo, Stephan R. McCandliss, Michael W. McElwain, Emma Miles, Michiel Min, Leonidas A. Moustakas, Coralie Neiner, Elisabeth Newton, James W Nightingale, Stephanie Olson, Colby Ostberg, Apurva V. Oza, Fabio Pacucci, Roberta Paladini, Niki Parenteau, Lynnae C. Quick, Ramses Ramirez, Sukrit Ranjan, Isabel Rebollido, Bin B. Ren, Kurt D Retherford, Jason Rhodes, Ian U. Roederer, Sabina Sagynbayeva, Edward Schwieterman, Adam Smercina, Krista Lynne Smith, Antoine Strugarek, Megan Taylor Tillman, Vivian U, Georgios N. Vassilakis, Hannah R. Wakeford, Sara Walker, Siyi Xu, Lulu Zhang, Alejandra Aguirre-Santaella, Munazza K. Alam, Amirnezam Amiri, Ramya M Anche, Sarah E. Anderson, David R. Ardila, Karla Z. Arellano-Córdova, Natasha E. Batalha, Thomas G.Beatty, Juliette Becker, Enrica Bellocchi, Mark Booth, Médéric Boquien, Sarah E. I. Bosman, Jean-Claude Bouret, Vincent Bourrier, Matteo Brogi, Andrew M. Buchan, Blakesley Burkhart, Jennifer A. Burt, José A. Caballero, Sarah L Casewell, Frances H. Cashman, Laura Chin, Yumi Choi, Jessie Christiansen, Francesca Civano, Kyle W. Cook, Brandon Park Coy, Brendan P Crill, Leroy Cronin, Håkon Dahle, Mario Damiano, William Danchi, Satyapriya Das, Brice-Olivier Demory, Jamie Dietrich, Steven Dillmann, Chuanfei Dong, Dwaipayan Dubey, Patrick Dufour, Arika Egan, Christiana Erba, Steve Ertel, Raissa Estrela, Vincent Van Eylen, Virginie Faramaz-Gorka, Andrzej Fludra, Sophia Flury, Andrew Fox, Kevin France, David M. French, Marina Galand, Tianmu Gao, Antonio García Muñoz, Miriam Garcia, Kenneth Gayley, Megan Gialluca, Samantha Gilbert-Janizek, Leonardos Gkouvelis, Kenneth E. Goodis Gordon, Clémence Gourvès, Jonathan Grone, Jacob Haqq-Misra, Caleb K. Harada, Zachary Hartman, Samantha Hasler, Calum Hawcroft, Matthew J. Hayes, Amanda R. Hendrix, Brandon Hensley, Svea Hernandez, Erin K. S. Hicks, Benne W. Holwerda, Carly Howett, Ziyu Huang, Richard Ignace, Caitriona M Jackman, Chafi Jamal, Shingo Kameda, Tiffany Kataria, Gagandeep Kaur, Finnegan Keller, Habib Khosroshahi, Alina Kiessling, Kristina Kislyakova, Oleg Kochukhov, Anton M. Koekemoer, Brad Koplitz, Joshua Krissansen-Totton, Jiri Krticka, Alvaro Labiano, Pierre-Olivier Lagage, Steph LaMassa, Erini Lambrides, Alexandra Le Reste, Nan Liu, Joe Llama, Emma Louden, Nataliea Lowson, Isabel Márquez, Evelyn J. R. Macdonald, Meredith MacGregor, Sangeeta Malhotra, Richard Massey, Erin May, L. C. Mayorga, Michael McElwain, Sean McGee, Alexia McKenzie, Athina Meli, Bertrand Mennesson, Connor Metz, Drew M. Miles, Aquib Moin, Mark Moussa, Themiya Nanayakkara, Dibyendu Nandy, Yaël Nazé, Marc Neveu, Eric Nielsen, John Noonan, Jessica L. Noviello, John M. O'Meara, Antonija Oklopčić, Chris Packham, Enric Palle, Emaad Paracha, Lucas Patty, Vasiliki Pavlidou, Sarah Peacock, Chris Pearson, Marc Postman, Andreas Quirrenbach, Swara Ravindranath, Seth Redfield, Joe P. Renaud, Malena Rice, Jane R. Rigby, Giulia Roccetti, Keighley E. Rockcliffe, Donna Rodgers-Lee, Jael Rojas Miguel, Maissa Salama, Samir Salim, Evan Scannapieco, Claudia Scarlata, Martin Schlecker, Steve Schulze, Paul Scowen, Darryl Zachary Seligman, Zacory Shakespear, Evgenya Shkolnik, Nick Siegler, Breann Sitarski, Louie Slocombe, Gopika SM, Russell J. Smith, Jennifer Sobeck, Daphne Stam, Kendall Sullivan, Takahiro Sumi, Yudai Suzuki, Christy Till, Armen Tokadjian, Vasuda Trehan, Grant Tremblay, Noah Tuchow, Margaret Turcotte Seavey, Jake D. Turner, Sarah Tuttle, Asif ud-Doula, Anna Grace Ulses, Connor Vancil, Aline Vidotto, Geronimo Villanueva, Jessica M Weber, Dale Weigt, Maximilian von Wietersheim-Kramsta, Thomas G. Wilson, David J. Wilson, Nicholas F. Wogan, Maria Womack, Michael L. Wong, John F Wu, Mark Wyatt, John Ziemer, Tiziano Zingales, Ryan Begley, Enrico Biancalani, Dmitry Blinov, Alexandre Branco, Esra Bulbul, Guillaume Chaverot, Catherine A. Clark, Jaime S. Crouse, Filippo D'Ammando, Achrene Dyrek, Oscar A. Flores Gaitán, Searra Foote, Cecilia Garraffo, Christopher Garry, Nikolaos Georgakarakos, Arvind F. Gupta, Daniel Huber, Brianna Isola, Nikhita Kalluri, Aafaque Khan, Amir H. Khoram, Adam B. Langeveld, Lucie Leboulleux, Briley Lewis, Anna Lewkowicz, Laurent Mahy, Liton Majumdar, Luigi Mancini, Joice Mathew, Dimitri Mawet, David Mouillet, Shantanusinh Parmar, Junellie Perez, Lorenzo Pino, Alex Polanski, Francisco J. Pozuelos, Tyler Richey-Yowell, Cleber Silva, Ramdayal Singh, Arif Solmaz, Angelle Tanner, Konstantinos Tassis, Luca Tonietti, Laura D. Vega, Aiden S. Zelakiewicz

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

Abstract PDF $PLNT ×2$EVO ×1$GLXY ×1

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

Eclipses by Artificial Satellites to Measure the Angular Sizes of Stars

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

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

All authors Leo W.H. Fung, Albert Wai Kit Lau, Richard Massey, George F. Smoot

Solar and Stellar Astrophysics

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

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

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

All authors Zheng Sun, Julián D. Alvarado-Gómez, Hui Tian, Ofer Cohen, Jeremy J. Drake, Katja Poppenhäger, Yue-Hong Chen