Solar and Stellar Astrophysics · Cross-listed from gr-qc
Nonlinear Perturbations of Relativistic Stars
K. J. Kwon, Abhishek Hegade K. R., Tejaswi Venumadhav et al. (+2 more)
We extend the general relativistic Lagrangian perturbation formalism of Friedman and Schutz [Astrophys. J. 200, 204 (1975)] beyond linear order, retaining full time dependence of the perturbations. We provide general formulae to relate the Lagrangian and Eulerian perturbations to any general perturbative order. As a proof of principle, we apply the framework to tidally perturbed relativistic
stars in Regge-Wheeler gauge and reduce the second-order field and conservation equations to master equations with a nonlinear source. Projecting the source onto the
star's eigenmodes, we obtain a nonlinear equation of motion for the mode amplitudes and the coupling coefficients, which describe the interactions among the eigenmodes and with the external tidal field. Approximating the tidal field and the coupling coefficients, we compute the static quadratic Love number from the quadrupolar fundamental mode alone and find that it reproduces the direct metric-matching value to a reasonable accuracy of $4\%$, up to a further correction arising from the
Hamiltonian and momentum constraints of the second-order tidal field.
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All authors K. J. Kwon, Abhishek Hegade K. R., Tejaswi Venumadhav, Hang Yu, Nicolás Yunes
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Peering into the Midplane of the DM Tau Disk using N2H+ and DCO+
Amina Diop, Kevin Flaherty, Chunhua Qi et al. (+7 more)
Planets form in the midplanes of protoplanetary disks, thus investigating the properties of the midplane region can shed light on the physical and chemical processes governing the
evolution of planetary systems. In this work, we study the conditions near the midplane of the disk around DM Tau using 0."3 (~43 au) ALMA observations of N2H+ (J = 3 - 2) and DCO+ (J = 4 - 3). The radial profiles reveal that DCO+ is centrally peaked, with a depression near 120 au, while N2H+ exhibits a central depression and a peak near 100 au. In addition, both molecules display extended emission out to 400 au. Using parametric models to interpret our observations, we note that a fiducial model based on CO-derived parameters captures the features within 200 au, but fails to reproduce the outer disk emission. We explore various mechanisms that could account for this extended emission and conclude that it is best reproduced by an increased external UV penetration and
cosmic ray/X-ray ionization rate, possibly enhanced by radial drift. These processes affect the precursors of N2H+ and DCO+ : increased UV leads to the photodesorption of CO and N2, while ionization enhances H3+ abundance. Besides, the observed N2H+ and DCO+ features are broadly consistent with previous CO snowline constraints, but can also be shaped by processes such as ionization, CO depletion, and multiple chemical pathways. Thus, using these molecular ions as robust CO snowline tracers requires additional constraints from complementary molecular tracers and detailed chemical modeling.
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All authors Amina Diop, Kevin Flaherty, Chunhua Qi, Ilse Cleeves, A. Meredith Hughes, Agnes Kospal, Sean Andrews, David J. Wilner, Jacob B. Simon, Deryl E. Long
Solar and Stellar Astrophysics
Differential Luminosity Response of Balmer-Line Profiles in Galactic B/A Luminous Stars
N. L. Vaidman, S. A. Khokhlov, Sh. T. Nurmakhametova et al. (+3 more)
We investigate the differential luminosity response of the optical Balmer series from H8 to H-alpha in Galactic B5-A5 luminous
stars using homogeneous measurements of central depth, FWHM, and equivalent width at a resolving power of approximately 12,000. Direct line-to-line comparisons show a systematic change in the central-depth response toward the lower-order transitions. For the primary 72-
star luminosity sample, the fitted luminosity coefficients show an overall positive trend with upper-level
quantum number, with a point-estimate gradient of dq/dn = 0.0419. A joint Monte Carlo analysis with 10,000 realisations gives a median dq/dn = 0.0387 and a 95 percent interval from 0.0253 to 0.0532, with no non-positive gradients obtained. The higher-order H8-H-delta coefficients form a statistically unresolved plateau, followed by a well-supported increase in response magnitude from H-delta toward H-alpha. The result is robust to the adopted effective-temperature scale. The FWHM coefficients show no comparable Balmer-order progression, and the directly fitted profile-shape response is consistent with zero from H8 through H-beta. For H-alpha, the full logarithmic sample is not formally significant, whereas removal of the three remaining strongly filled-core profiles yields a significantly negative shape response. The observed behaviour is qualitatively compatible with the systematic variation of pressure broadening across the Balmer series, while the enhanced H-alpha response may additionally reflect non-LTE and wind-related effects.
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All authors N. L. Vaidman, S. A. Khokhlov, Sh. T. Nurmakhametova, N. A. Litvinov, A. T. Agishev, D. A. Alimbetova
Solar and Stellar Astrophysics
Anchoring the Chromospheric Activity$-$Rotation Relation: A Study of the Pleiades and Group X
A. Núñez, M. A. Agüeros, J. L. Curtis et al. (+1 more)
We present a study of the rotation and the chromospheric H$\alpha$ activity of low-mass
stars in the $\approx$120 Myr-old Pleiades and the $\approx$400 Myr-old Group X open clusters. We combine published and new rotation periods ($P_\mathrm{rot}$) from TESS and ZTF, and use LAMOST, SDSS, and MDM spectra to measure H$\alpha$ equivalent widths (EWs). While overall the Group X distributions of $P_\mathrm{rot}$ and EWs are as expected, detailed comparisons to the Pleiades and to the 700-Myr-old
benchmark Praesepe produce some surprises. For F through mid K
stars, the Group X color$-$period sequence lies between those of the Pleiades and of Praesepe, as expected. But the $P_\mathrm{rot}$ for its late K and early M dwarfs and the Praesepe slow-rotator sequence overlap, indicating that the 700 Myr-old
stars have not spun down significantly despite being nearly twice as old as their Group X counterparts. In the Rossby number$-L_\mathrm{H\alpha}/L_\mathrm{bol}$ plane, rapid rotators in Group X are saturated, as is seen in older clusters, whereas the rapid rotators in the Pleiades show a weak but measurable dependence of $L_\mathrm{H\alpha}/L_\mathrm{bol}$ on rotation. This implies that the chromospheric activity$-$rotation relation attains its mature form between 120 and 400 Myr. Dividing the sample by color reveals that K, M0, and M1 dwarfs are no longer saturated by $\approx$120 Myr, M2 and M3 dwarfs become unsaturated between $\approx$400 and $\approx$700 Myr, and later M dwarfs remain largely saturated through field ages even as their saturated $L_\mathrm{H\alpha}/L_\mathrm{bol}$ levels decline, indicating that chromospheric
evolution is not determined by rotation period alone.
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All authors A. Núñez, M. A. Agüeros, J. L. Curtis, C. A. Ospinal Achicanoy
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
Dynamical formation of dormant black holes: Predictions for Gaia DR4
Daniel Marín Pina, Michela Mapelli, Giuliano Iorio et al. (+1 more)
Dormant black holes (dormant BHs, i.e., X-ray quiet binaries comprising a BH and a companion
star) are probes of the effect of cluster dynamics and binary stellar
evolution on compact-object binaries. A dozen dormant BH binaries are known, a number that will increase substantially with the upcoming Gaia Data Release 4 (DR4). Their origin is uncertain, and dynamical formation is proposed as one possible channel. Here, we study the formation of dormant BHs in low-mass
star clusters, accounting for the interplay of binary stellar
evolution and cluster dynamics. We present new simulations with the $N$-body code PeTar, interfaced with the population synthesis code SEVN for single and binary
star evolution. Our grid spans a range of cluster masses ($300-4800\,$M$_\odot$),
metallicities ($1.4\times10^{-2}$, $1.4\times10^{-4}$), and natal kick models (with and without fallback). We find that almost all dormant BH binaries escape the parent cluster within $\sim1\,$Gyr ($\sim10\,$Myr) when assuming weak (strong) natal kicks. Most ($73\%$) dormant BHs form via the exchange of a BH (or its progenitor
star) into a stellar binary, or of a
star into a binary with a BH. Dormant BHs in low-mass clusters have a wide orbital period distribution (from a few hours to $10^8\,$d), with an upper limit set by natal kicks, a bimodal eccentricity distribution (a first peak at zero eccentricity for circularised systems and a second at high eccentricity), and stellar masses that follow the (evolved) initial mass function. Large BH masses are a smoking gun of dynamical formation, via exchanges and stellar collisions. We expect Gaia DR4 to contain $\sim1-64$ high-
metallicity and $\sim0.4-48$ low-
metallicity dormant BHs, with a period distribution peaking at $\sim10^3\,$d, $\gtrsim90\%$ of them with eccentricity $e>0.1$, and $\sim20\%$ with large BH masses ($m_{\rm BH} \gtrsim 30\,$M$_\odot$).
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All authors Daniel Marín Pina, Michela Mapelli, Giuliano Iorio, Cecilia Sgalletta
Solar and Stellar Astrophysics
Star spots mimic the proposed abundance signatures of planet formation
Andrew R. Casey, Megan Bedell, Adam Wheeler et al. (+2 more)
Trends with stellar elemental abundances and condensation temperature have been proposed as a possible tracer of rocky
planet formation. Here we present an alternative explanation, where we show that stellar activity (
star spots) can also cause apparent abundance changes in refractory elements preferentially over volatile elements. This effect arises naturally from atomic physics: refractory (rocky; high-$T_c$) elements preferentially have low first-ionization potentials, with strong transitions that are most sensitive to the cooler, magnetically-perturbed spot conditions, making any spot-induced change in line strength correlated with $T_c$. We re-examine literature on Sun-like
stars in the Solar neighborhood and find that the $\log{R'_{HK}}$ stellar activity indicator is correlated with the so-called $T_c$ slope: the gradient of chemical abundances with respect to condensation temperature. Using 1D LTE Korg.jl simulations of the Sun with spots of varying size and contrast, we show that a wide range of spot configurations can manifest as abundance patterns that mimic a signal of abundance trends with condensation temperature. Finally, we conduct a line-by-line differential analysis of an ambient Solar spectrum relative to a Solar sunspot umbra to represent an extreme case, where we find that elements with high condensation temperature can show a factor of three (0.5 dex) increase. We discuss implications that stellar activity poses for precision spectroscopy, and provide some direction on how this effect might be mitigated.
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All authors Andrew R. Casey, Megan Bedell, Adam Wheeler, Julianne Dalcanton, Lily Zhao
Solar and Stellar Astrophysics
The EBLM project - XX. Absolute dynamical masses of five low-mass eclipsing binaries, and an evaluation of mass estimation methods
Adam T. Stevenson, Yasmin T. Davis, Daniel Sebastian et al. (+8 more)
Eclipsing binaries consisting of a solar-type primary and an M dwarf secondary are key laboratories to study objects at the bottom of the main sequence. Fundamental parameters of such
stars have a direct impact upon exoplanetary studies, as searches for temperate Earth-sized
planets focus on M dwarf hosts. Eclipsing binaries are essential to measure these parameters. However for stellar masses $<$ 0.35 M$_\odot$ , few double-lined eclipsing systems are known. Thus, stellar
evolution models and empirical relations have had to rely on single-lined eclipsing binaries, for instance those from the EBLM project (Eclipsing Binary - Low Mass). Using high resolution spectroscopy to extract the weak signal of the secondary (flux ratio $<$ 1 per cent in the optical), we transform five more systems from single to double-lined, deriving absolute masses for both
stars. We then compare methods typically employed to estimate stellar masses for field
stars or single-lined binaries with the absolute dynamical masses we obtain, to assess their accuracy. Our results for SB1 and SB2 analyses are mostly consistent within 1-$\sigma$, though we identify a small systematic overestimation of SB1 masses derived from a combination of radial velocities and eclipse photometry. We show that the bias originates from primary radius overestimation during isochronal analysis, wherein the secondary light reduces photometric magnitudes and impacts the recovered radii by modifying the spectral energy distribution. With proper calibration, we can ensure the accuracy of using the full EBLM SB1 sample to constrain mass-radius-luminosity relationships for the smallest, yet most abundant,
stars in the
Galaxy
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All authors Adam T. Stevenson, Yasmin T. Davis, Daniel Sebastian, Amaury H. M. J. Triaud, Pierre F. L. Maxted, Alix V. Freckelton, Thomas A. Baycroft, Neda Heidari, David V. Martin, Nicola J. Miller, Alexandre Santerne
Solar and Stellar Astrophysics
The EBLM Project - XIX. The absence of radius inflation in a homogeneous analysis of 66 Northern low-mass eclipsing binaries
Yasmin T. Davis, Amaury H.M.J. Triaud, David V. Martin et al. (+30 more)
Precise and accurate measurements of host
stars are crucial in the search for Earth-like
exoplanets, and M-dwarfs are favourable targets in this quest. Low-mass eclipsing binaries offer unique opportunities to empirically determine stellar masses and radii for low-mass
stars where stellar models may be systematically biased. We present results from the EBLM-North sample, the largest homogeneous study of low-mass eclipsing binaries with secondary characterisation yet, combining high-resolution and high-precision radial velocities from SOPHIE and TESS photometry. We measure a median precision for stellar companions of 4.2% in radius and 8.6% in mass within a sub-sample of 50 high-quality binaries, all with orbital periods $P_{\rm bin} > 5\,\rm days$. We compare our data to the Baraffe and MIST isochrones, and find our sample is statistically consistent with those models, producing reduced chi-squared values, $\chi^2_\nu\sim 1$. Our measured radius inflation is $0.3\pm 1.6$% indicating no statistically significant trend. We likewise detect no significant trend with
metallicity, despite having the precision to identify such a relationship. As such, our observations do not appear to follow the general
metallicity trend predicted in MIST. A $\chi_\nu^2 \sim 1$ indicates the scatter in our results is commensurate with our uncertainties alone. These results constrain the scope for unmodelled effects on the mass-radius relation that would produce radius deviations greater than 4.2%. However, our secondary effective temperatures do not reproduce this high level of agreement with the models, and we do not recover the predicted trends with
metallicity.
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All authors Yasmin T. Davis, Amaury H.M.J. Triaud, David V. Martin, Alix V. Freckelton, Jenni R. French, Adam T. Stevenson, Annelies Mortier, Karen Collins, Pierre F. L. Maxted, Daniel Sebastian, Aleyna Adamson, Thomas A. Baycroft, Isabelle Boisse, Gavin A. L. Coleman, Georgina Dransfield, Yilen Gómez Maqueo Chew, Leslie Hebb, Neda Heidari, Vedad Kunovac, James McCormac, Nikki J. Miller, Richard Nelson, Martin Nielsen, Alexandre Santerne, Madison G. Scott, Owen Scutt, Alexis M. S. Smith, Matthew R. Standing, Amalie Stokholm, Matthew I. Swayne, Mathilde Timmermans, Peter J. Wheatley, Emma Willett
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
Fast Radio Bursts from Monster Shocks and Flares of Inspiraling Binary Neutron Stars: A Kinetic Model for Double Pulsar
Jan Benáček, Benoît Cerutti, Martin Pohl et al. (+2 more)
The coalescence of binary
neutron star systems offers unprecedented possibilities for multimessenger observations, including the detection of gravitational waves, gamma-ray bursts, kilonovae, and potentially fast
radio bursts. For a detailed investigation of the latter, one requires a kinetic
plasma model to describe the interacting magnetospheres of the
stars. We present a three-dimensional particle-in-
cell kinetic simulation of the combined magnetosphere of a binary
neutron star in which the two
stars physically orbit one another so that the orbital motion itself twists the
magnetic loops. We find that the stellar
magnetic-field intensity ratio controls the emergence of
flares, while the stellar
spins set the direction and modulation of the
flare. We identify four spatially and dynamically distinct regions of strong electromagnetic energy release: (i) an expanding fast magnetosonic wave that steepens into a monster shock, (ii) a
plasma flare being pushed by (iii) an expanding fireball and containing (iv) a reconnecting current sheet. The fast magnetosonic wave is a promising source of coherent
radio emission. It is released when orbital motion cuts a closed
plasma loop. The electric and
magnetic wave amplitudes are similar and reach that of the background
magnetic field. Our kinetic treatment yields particle spectra and
plasma structures that can be used to assess coherent emission in kinetic-scale simulations. In conclusion, the stellar orbital motion constitutes a driving channel distinct from models with
spin-driven magnetospheric twisting.
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All authors Jan Benáček, Benoît Cerutti, Martin Pohl, Tim Dietrich, Anna Neuweiler
Solar and Stellar Astrophysics
MATISSE unveils a dusty disc in the interior of EP Aquarii. First evidence of a misaligned hierarchical triple system with a central AGB star?
J. Alonso-Hernández, C. Paladini, C. Sánchez Contreras et al. (+26 more)
Aims. We have mapped the dust and molecular gas emission distributions in the vicinity (a few stellar radii) of the asymptotic giant branch (AGB)
star EP\,Aquarii, with a previously reported stellar companion at $\sim$50\,au, to search for binary-induced asymmetries. Methods. We present an analysis of new high-angular-resolution ($\gtrsim$4\,mas) images obtained with MATISSE (in the wavelength range $\sim$3–8\,\mum) as well as archival high-angular-resolution ($\gtrsim$20\,mas) ALMA $\rm^{12}$CO\,(c$J$=2-1) line and continuum emission observations ($\sim$230\,GHz), to study the circumstellar morphology and kinematics of the molecular gas on these spatial scales. Results. The MATISSE images display a bright central source and two slightly extended emission features ("blobs") located on opposite sides of the AGB
star (at radial distances of $\sim$4–10\,au). These structures are consistent with previous mid-infrared interferometric observations, suggesting stability over decades. The central source is elongated along the direction defined by the blobs, in both the MATISSE and ALMA continuum images. The ALMA $\rm^{12}$CO\,($J$=2-1) maps display an asymmetric inner wind with a velocity gradient. Conclusions. The observations are consistent with an edge-on dusty equatorial overdensity (disc-like), hinting the presence of a close ($\lesssim$4\,au) companion. The inferred
symmetry axis is almost perpendicular to the CO velocity gradient and the orbital plane proposed for the distant ($\sim$50\,au) companion. EP\,Aqr may represent the first misaligned hierarchical triple system with a central AGB
star.
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All authors J. Alonso-Hernández, C. Paladini, C. Sánchez Contreras, J. Drevon, J. P. Fonfría, L. Planquart, T. Khouri, L. Siess, A. Jorissen, B. Aringer, F. Baron, E. De Beck, S. Höfner, J. Hron, F. Lykou, F. Millour, M. Montargès, N. Nardetto, K. Ohnaka, H. Olofsson, V. Răstău, J. Sanchez-Bermudez, L. Velilla-Prieto, W. Vlemmings, M. Wittkowski, G. Weigelt, W. C. Danchi, F. Kerschbaum, B. Lopez
Solar and Stellar Astrophysics
Dynamical and thermal evolution of localized reconnecting current sheets under varying guide-fields in the solar corona
Saksham Pande, Abhishekh Kumar Srivastava, Fabio Bacchini et al. (+9 more)
Although
magnetic reconnection in coronal current sheets (CSs) is a fundamental energy release mechanism in the solar corona, the role of guide-fields in governing its formation and self-consistent
evolution is not fully understood. Through 2.5D resistive magnetohydrodynamic (MHD) simulations, we investigate how guide-fields affect the formation and
evolution of a localized reconnecting coronal CS. Strong guide-fields prevent oppositely directed field lines from approaching sufficiently to form a CS, delaying and suppressing its subsequent
evolution. The reconnection rate exhibits a rising phase resembling a power-law, with exponent $\delta_1$ decreasing with rising guide-fields, indicating slower temporal growth of the reconnection rate. The aspect ratio of the CS follows a similar power-law trend with the exponent $\alpha_1$ decreasing with rising guide-fields. A subsequent slower growth phase of the reconnection rate shows a power-law exponent $\delta_2$ that increases with rising guide-fields, as does the corresponding aspect-ratio exponent $\alpha_2$. As the CS evolves, the latter phase is achieved due to a sharp decremental transition of the guide-field within the CS after a time when the increasing inflows are inefficiently resisted by the guide-field itself. In the reconnection regime during prior phases, the power-law exponents of the maximum temperature and the outflow velocities also decrease with rising guide-fields demonstrating that stronger guide-fields suppress the growth of these indicators also. This study suggests that a self-consistently formed CS displays phases of efficient and inefficient quenching of the reconnection mechanism, promoted by non-zero guide-fields. We also quantify this behavior for indicators of the reconnection process and discuss their applicability to observations of apparent CSs and probing background coronal conditions.
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All authors Saksham Pande, Abhishekh Kumar Srivastava, Fabio Bacchini, Sripan Mondal, Akash Bairagi, Balveer Singh, Kartika Sangal, Sudheer K. Mishra, Xinping Zhou, Ding Yuan, R. -Y. Kwon, B. N. Dwivedi
Solar and Stellar Astrophysics
Simulating Ionospheric Distortions in Mock SKA-Low Solar Radio Observations
Rohit Sharma and Mitin
The Square Kilometre Array Observatory (SKAO) will provide unprecedented angular resolution for low-frequency solar
radio imaging, enabling access to fine-scale coronal structures. However, the improved spatial resolution of SKA-Low also increases the sensitivity of solar images to ionospheric propagation effects. We investigate the impact of ionospheric fluctuations on simulated SKA-Low solar observations at 50, 100, 150, and 200 MHz using the Karabo simulator and turbulent, moving ionospheric phase screens. We quantify the resulting image distortions using spatial power spectral density (PSD) analysis and compare the SKA response with corresponding MWA simulations. The results show that ionospheric distortions are strongly scale- and frequency-dependent, with the maximum fractional PSD distortion decreasing with observing frequencies. SKA resolves ionospheric fluctuations over spatial scales that are largely smoothed by the MWA instrumental response, with significant distortions occurring on scales comparable to solar active-region structures. These results demonstrate that ionospheric propagation effects should be considered when interpreting high-resolution SKA-low solar
radio images, particularly at the lower end of the frequency band.
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Solar and Stellar Astrophysics
Revisiting the Role of Global Magnetic Variables in Coronal Heating of Solar Active RegionsDavid H. Brooks
David H. Brooks, Harry P. Warren and Johnathan R. Stauffer
Reconnection-based models of coronal heating predict that
magnetic complexity—non-potential configurations, currents, shear—should enhance coronal emission independently of total
magnetic flux. Previous work, however, found no evidence that complexity contributes independently to coronal heating (Fisher et al. 1998). We revisit this question using SDO/HMI vector magnetograms and SDO/AIA EUV imaging. HMI Space-weather Active Region Patches (SHARPs) provide 16
magnetic parameters characterizing field strength, gradients, currents, helicity, and non-potentiality. We measure spatially-integrated transition region and coronal emission using AIA 304A, 193A, 94A, and isolated Fe XVIII emission for 137 active regions, sampling
plasma at ~0.09MK, ~1.4MK, and ~7.1MK. Partial correlation analysis isolates the contribution of each complexity parameter after controlling for total unsigned vertical
magnetic flux. Unsigned flux (Phi_M) explains 72–82% of variance in emission, following power laws (I ~ Phi_M^alpha, where alpha=0.61-1.19) consistent with prior soft X-ray results. Partial correlations reveal weak positive contributions (r = 0.2-0.3) to transition region (304A) emission from some vertical current and field parameters, but little evidence that other active-region-averaged measures of
magnetic complexity enhance coronal emission. The exception is total photospheric
magnetic free energy density (rho_tot), which shows a positive partial correlation (r = 0.49, p < 0.001) with Fe XVIII emission, but negative, or non-existent, partial correlations with other AIA filters. These results suggest quasi-steady coronal heating scales with
magnetic flux, while rho_tot may contribute to high temperature coronal heating. At lower temperatures, regions with more stored energy than expected for their flux produce less EUV emission than expected.
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Solar and Stellar Astrophysics
A breath of fresh air: Oxygen enhancement from silicate sublimation during early protostellar evolution
F.J. Ballieux, M.K. McClure, Ł. Tychoniec et al. (+5 more)
Recently, an analog to the t = 0 moment of our Solar System's meteoritic record was identified for the first time around the Class I protostar HOPS-315. Crystalline silicates were found to recondense from SiO gas that cools as it advects upward from a hot thermostat region in the inner midplane. This t=0 moment may be associated with the formation of the first planetesimals in this disk. We explore whether HOPS-68, a Class I protostar with similar properties and system geometries, is engaged in such refractory recondensation as well. A detection of cooler gas-phase SiO in absorption above a hot disk midplane would allow us to achieve this goal, thanks to a previous detection of crystalline silicates. HOPS-68 was observed with the JWST MIRI and NIRSpec, showing multiple bands of molecular absorption. We use local thermal
equilibrium slab models to measure the temperature, column density, velocity, and radial location of these bands. The molecular absorption bands of gaseous SiO, H2O, CO2, and 13CO trace a warm molecular inversion layer (300-500 K) at mid-altitudes above the hot disk midplane from 0.3-16 AU, which is consistently blue-shifted with respect to the system velocity by 33-53 km/s. Atacama Large Millimeter/submillimeter Array (ALMA) observations of HOPS-68 kinematically resolve an SiO-rich jet and wind. We confirm that HOPS-68, like HOPS-315, is undergoing an epoch analogous to the t=0 moment in the Solar System's
planet formation timeline. The detected warm molecular layer traces the base of a disk wind, which carries sublimated material from the thermostat region near 2 AU up into the outer disk. As for HOPS-315, the molecular layer in the inner few AU of HOPS-68 is enhanced in bulk oxygen as a result of this sublimation. Since HOPS-68 is less evolved than HOPS-315, this may indicate a prolonged epoch in protostellar
evolution in which such oxygen enhancement occurs.
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All authors F.J. Ballieux, M.K. McClure, Ł. Tychoniec, L. Francis, A. Egliene, E.A. Bergin, M.R. Van 't Hoff, E.F. Van Dishoeck
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Tracing the Influence of Distant companions on Exoplanetary Systems (TIDES) I. Highly Eccentric and Misaligned Binary Companions to Hot Jupiters
Marvin Morgan, Jerry W. Xuan, Brendan P. Bowler et al. (+9 more)
The origin of hot Jupiters remains an open question. A significant fraction reside in binary or multiple
star systems, suggesting that stellar companions may play an important role in shaping their present-day architectures. However, the orbits of the vast majority of these stellar companions remain poorly constrained, leaving their role in hot Jupiter
evolution an open question. We present the Tracing the Influence of Distant companions on Exoplanetary Systems (TIDES) survey, a campaign to map the orbits of stellar companions in systems hosting hot Jupiters to assess the extent to which binaries play a role in hot Jupiter formation and migration. Here, we introduce our survey design and new orbital fits for the first six systems in our sample—$\tau$ Boo, WASP-2, WASP-11, WASP-76, HAT-P-14, and HAT-P-16—by combining previous observations of the stellar companions together with new Keck/NIRC2 imaging and Keck/KPIC relative radial velocities. Among these six systems, the four with the most precisely constrained orbits exhibit high eccentricities ($e \geq 0.8$), and three of these systems also display significant
planet–binary misalignments ($\Delta i \geq 20^\circ$). This suggests the orbital properties of stellar companions to hot Jupiter host
stars are qualitatively different than field binaries and binaries hosting inner transiting small
planets. These orbital architectures are consistent with stellar companions shaping the
evolution of hot Jupiters, either through high-eccentricity migration or by participating in an earlier episode of dynamical
evolution that ultimately led to hot Jupiter formation. Continued orbital monitoring of the full sample will reveal whether outer stellar companions play a causal role in the
evolution of hot Jupiters.
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All authors Marvin Morgan, Jerry W. Xuan, Brendan P. Bowler, Kyle Franson, Michael C. Liu, Konstantin Batygin, Heather A. Knutson, Björn Benneke, Julianne Cronin, Luke Finnerty, Chih-Chun Hsu, Aniket Sanghi
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
IC 1297: The Most Distant Known X-ray Planetary Nebula and One of the Most Luminous
H. Yuan, Q. A. Parker and M. A. Guerrero
We present the first targeted Einstein Probe (EP) X-ray observations of any planetary nebula (PN). Using the onboard Follow-up X-ray
Telescope (FXT), we detect X-ray emission within the central region of IC 1297. The spectral analysis yields a
plasma temperature of $kT = 0.086^{+0.054}_{-0.058}$ keV ($T\sim1.0 \times 10^{6}$ K), characteristic of shocked wind bubbles in PNe, whereas there is no evidence that its Wolf-Rayet central
star emits X-rays. The absorption-corrected X-ray luminosity in the 0.3–2.0 keV energy band is $L_{\mathrm{X}} = 2.8 \times 10^{32}$ erg s$^{-1}$, also consistent with a hot bubble. At an adopted distance of $\sim3.8$ kpc, IC 1297 is the most distant X-ray emitting PN found to date, opening up a new observational window on hot-bubble formation and
evolution. It is also among the most luminous known X-ray-emitting PNe. Our results demonstrate the capability of the EP FXT for detecting and characterizing faint, extended X-ray sources in the soft X-ray band for distant PNe, extending the known spectral properties of detectable X-ray emitting PNe. We also compiled the X-ray properties of all 41 known Galactic XPNe, finding a clear correlation between distance and X-ray luminosity that reflects an observational bias toward detecting the brightest sources at large distances. The compilation also shows a separation in X-ray luminosity between hot bubbles powered by H-rich and [WR]-type central
stars, with the latter reaching luminosities up to an order of magnitude higher. The ten most luminous XPNe all host [WR]/PG 1159 central
stars.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Dynamically Coupled Three-dimensional Cloud-Chemistry in Rapidly Rotating Irradiated Atmospheres: an Application to the Compact White Dwarf-Brown Dwarf system ZTFJ0038+2030
Yanhong Lai, Xianyu Tan, Daphne Broski-Laing et al. (+7 more)
Clouds and disequilibrium chemistry shape the observable properties of substellar and planetary atmospheres, and JWST time-resolved spectroscopy now enables direct tests of their three-dimensional structures. We present an update to the 3D atmospheric framework ADAM, coupling the dynamical core to a miniature kinetic chemistry scheme (mini-chem) and a saturation-relaxation tracer cloud module. Using this framework, we investigate the atmosphere of the brown dwarf orbiting the white dwarf ZTFJ0038+2030 in a 10-hour orbit. The brown dwarf receives stellar irradiation comparable to its internal heat flux, placing the atmosphere in a regime where the circulation is characterized by a standing Matsuno–Gill wave response and equatorial superrotation. Rapid rotation confines these structures closer to the equator, producing more symmetric broadband light curves with smaller hotspot offsets than canonical hot Jupiters, in agreement with recent JWST observations of this system. Although most species are globally homogenized, rapid rotation limits global-scale horizontal mixing and allows circulation-driven vertical transport to maintain strong CO and CO$_2$ inhomogeneities in the photosphere. These chemical inhomogeneities produce asymmetric phase curves in the CO and CO$_2$ absorption bands, which could qualitatively explain the observed CO$_2$ light-curve asymmetry. When clouds are included, Na$_2$S clouds dominate the photosphere and weaken the large-scale circulation, lowering photospheric CO and CO$_2$ abundances, while MgSiO$_3$ and Fe clouds rain out at deeper levels. Because the dominant Na$_2$S clouds reside mostly above the quench region, cloud-driven convection has limited impact on the quenched abundances, which are instead regulated mainly by large-scale circulation.
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All authors Yanhong Lai, Xianyu Tan, Daphne Broski-Laing, Yifan Zhou, Sarah L. Casewell, Jenni R. French, Elspeth K. H. Lee, Joshua D. Lothringer, Vivien Parmentier, Shang-Min Tsai
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
Observational evidence of black hole event horizon from ultra-compact X-ray binaries
Qian-Qi Ma, Wei-Min Gu, Shan-Shan Weng et al. (+1 more)
The event horizon is the most crucial feature that distinguishes black hole (BH) from all other objects in the universe. However, since no radiation can escape from the event horizon, its direct observational evidence remains lacking. Although both are compact objects, the event horizon leads to differences in the radiative behavior between black hole and
neutron star (NS) X-ray binaries. Historically efforts to probe the existence of event horizons revealed that the BH X-ray binaries are fainter than NSs with similar orbital periods in their quiescent states. Here, we use a special class of X-ray binaries namely the ultra-compact X-ray binaries (UCXBs), to reveal the existence of the event horizon near stellar-mass black holes. In short-period UCXBs, gravitational radiation dominates the orbital angular momentum loss, allowing us to accurately determine their
accretion rates. Based on five UCXBs with orbital periods shorter than 40 min, located in globular clusters, and identified accretors (NS or BH), we obtained their
accretion rates. Combining their
accretion rates and X-ray luminosities, we calculated the X-ray radiative efficiencies of NS and BH. The radiative efficiency of BH is about two to three orders of magnitude lower than that of NS systems, indicating the
accretion energy is swallowed by the BH, thereby indirectly probe the presence of the event horizon.
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All authors Qian-Qi Ma, Wei-Min Gu, Shan-Shan Weng, Mouyuan Sun
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
Non-equilibrium chemistry and radiation hydrodynamics in metal-poor and metal-rich interstellar gas
Shyam H. Menon, Piyush Sharda, Blakesley Burkhart et al. (+1 more)
We present a flexible implementation of non-
equilibrium chemical networks with the $\texttt{KROME}$ framework, coupled to a nonlocal variable Eddington tensor-closed radiation transport scheme ($\texttt{VETTAM}$). Our fiducial network is designed to explicitly capture the formation pathways of important molecular species such as CO, OH, and $\rm H_2O$, intermediaries like $\rm H_3^+$, and the destruction of these species through
photon and
cosmic-ray dissociation. We validate our scheme through
benchmark tests, and demonstrate its success in 1D and 3D problems covering a broad range of
metallicities ($0 \leq Z \lesssim \rm Z_{\odot}$) and densities ($n \lesssim 10^{17} \, \rm cm^{-3}$). We confirm earlier works that suggest that OH and $\rm H_2O$ are the key molecular species in dense gas ($n \gtrsim 10^{5} \, \rm cm^{-3}$) for $Z\lesssim 0.01 \rm Z_{\odot}$, dominate the cooling at these densities, and demonstrate that our scheme can reproduce their abundances with similar accuracy as dedicated static photo-dissociation region (PDR) codes. We also find that the dominant fine-structure coolant in dense ($n \gtrsim 10^3 \, \, \rm cm^{-3}$) PDRs transitions from CI to CII to OI at increasingly lower $Z$. Finally, we find that in turbulent media, rapid mixing at PDR interfaces renders the chemical species out of
equilibrium, and show that this could potentially alleviate the long-standing problem of (static) PDR models producing excess CI in the diffuse ISM over UV absorption-line measurements. We conclude by presenting and comparing with alternative implementations of reduced but faster chemical networks in our scheme, discussing the problem-dependent performance-accuracy tradeoffs and future prospects.
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All authors Shyam H. Menon, Piyush Sharda, Blakesley Burkhart, Tommaso Grassi