adsabs/SciX_UAT_keywords huggingface dataset:
Magnetic Inclination Evolution of Accreting Neutron Stars in Intermediate/Low-mass X-Ray Binaries

The magnetic inclination angle χ, namely the angle between the spin and magnetic axes of a neutron star, plays a vital role in its observational characteristics. However, there are few systematic investigations of its long-term evolution, especially for accreting NSs in binary systems. Applying the model of Biryukov & Abolmasov and the binary evolution code MESA, we simultaneously simulate the evolution of the accretion rate, spin period, magnetic field, and magnetic inclination angle of accreting NSs in intermediate/low X-ray binaries. We show that the evolution of χ depends not only on the initial parameters of the binary systems, but also on the mass transfer history and the efficiency of pulsar loss. Based on the calculated results we present the characteristic distribution of χ for various types of systems including ultracompact X-ray binaries, binary millisecond pulsars, and ultraluminous X-ray sources, and discuss their possible observational implications.

Keywords: binary pulsars; low-mass x-ray binary stars
Axial Flux Evolution of Small-scale Magnetic Flux Ropes from 0.06 to 10 au

Small-scale magnetic flux ropes (SMFRs) fill much of the solar wind, but their origin and evolution are debated. We apply our recently developed, improved Grad–Shafranov algorithm for the detection and reconstruction of SMFRs to data from Parker Solar Probe, Solar Orbiter, Wind, and Voyager 1 and 2 to detect events from 0.06 to 10 au. We observe that the axial flux density is the same for SMFRs of all sizes at a fixed heliocentric distance but decreases with distance owing to solar wind expansion. Additionally, using the difference in speed between SMFRs, we find that the vast majority of SMFRs will make contact with others at least once during the 100 hr transit to 1 au. Such contact would allow SMFRs to undergo magnetic reconnection, allowing for processes such as merging via the coalescence instability. Furthermore, we observe that the number of SMFRs with higher axial flux increases significantly with distance from the Sun. Axial flux is conserved under solar wind expansion, but the observation can be explained by a model in which SMFRs undergo turbulent evolution by stochastically merging to produce larger SMFRs. This is supported by the observed log-normal axial flux distribution. Lastly, we derive the global number of SMFRs above 1015 Mx near the Sun to investigate whether SMFRs begin their journey as small-scale solar ejections or are continuously generated within the outer corona and solar wind.

Keywords: solar wind; interplanetary turbulence; interplanetary physics; interplanetary magnetic fields
On the Minimum Radius of Very Massive Neutron Stars

Prospects of establishing the radii of massive neutron stars in PSR J1614 - 2230 and PSR J0740 + 6620 from Neutron Star Interior Composition ExploreR and Chandra observatories hold the potential to constrain the equation of state (EoS) of matter to densities well beyond those encountered in canonical stars of mass $\sim 1.4\,{M}_{\odot }$. In this work, we investigate the relation between the radii of very massive neutron stars up to the maximum mass, ${M}_{\max }$, supported by dense matter EoSs. Results from models with hadronic matter are contrasted with those that include a first-order hadron-to-quark phase transition. We find that a lower bound on ${M}_{\max }$ with an upper bound on the radius of massive pulsars serves to rule out quark matter that is too soft, and an upper bound on ${M}_{\max }$ with a lower bound on the radius of massive pulsars strongly disfavors a transition into quark matter that is too stiff appearing at low densities. The complementary role played by radius inferences from future gravitational-wave events of inspiraling binary neutron stars is also briefly discussed.

Keywords: neutron stars; stellar interiors
Modeling Atmospheric Lines by the Exoplanet Community (MALBEC) Version 1.0: A CUISINES Radiative Transfer Intercomparison Project

Radiative transfer (RT) models are critical in the interpretation of exoplanetary spectra, in simulating exoplanet climates, and when designing the specifications of future flagship observatories. However, most models differ in methodologies and input data, which can lead to significantly different spectra. In this paper, we present the experimental protocol of the Modeling Atmospheric Lines By the Exoplanet Community (MALBEC) project. MALBEC is an exoplanet model intercomparison project that belongs to the Climates Using Interactive Suites of Intercomparisons Nested for Exoplanet Studies framework, which aims to provide the exoplanet community with a large and diverse set of comparison and validation of models. The proposed protocol tests include a large set of initial participating RT models, a broad range of atmospheres (from hot Jupiters to temperate terrestrials), and several observation geometries, which would allow us to quantify and compare the differences between different RT models used by the exoplanetary community. Two types of tests are proposed: transit spectroscopy and direct imaging modeling, with results from the proposed tests to be published in dedicated follow-up papers. To encourage the community to join this comparison effort and as an example, we present simulation results for one specific transit case (GJ-1214 b), in which we find notable differences in how the various codes handle the discretization of the atmospheres (e.g., sub-layering), the treatment of molecular opacities (e.g., correlated-k, line-by-line) and the default spectroscopic repositories generally used by each model (e.g., HITRAN, HITEMP, ExoMol).

Keywords: radiative transfer simulations; exoplanet atmospheres
Analysis and Modeling of High-frequency Emission and Deep Seismic Sources of Sunquakes

Recent work published by Lindsey et al. find evidence for a deep and compact seismic source for the sunquake associated with the 2011 July 30 M9.3 flare, as well as seismic emission extending up to 10 mHz. We examine the sunquake independently, and a possible wave front is found in the 8 mHz band, though no wave front is easily discernible in the 10 mHz band. Additionally, we perform numerical simulations of seismic excitation modeled with the reported parameters and changes in the power spectra with increasing depth of the excitation source are examined. It is found that the peak frequency decreases for increasing depths, but a shallow minimum is indicated between z = 0 and z = -840 km. Analysis of the suspected wave front of the M9.3 sunquake finds that the power spectrum of the reported seismic emission is close to that of background oscillations, though with a peak frequency noticeably lower than the background peak. Additionally, it is found that the amplitude of the source estimated by Lindsey et al. is too low to produce the observed wave front.

Keywords: helioseismology
The Dark Planets of the WASP-47 Planetary System

Exoplanet discoveries have demonstrated a vast range of planetary system architectures. The demographic of compact planetary systems are especially interesting from the perspective of planetary formation and the evolution of orbital dynamics. Another interesting demographic is that of giant planets in eccentric orbits, since these planets have likely had a dynamical history involving planet-planet scattering events. The WASP-47 system is particularly fascinating since it combines these two demographics, having both compact planetary orbits and a giant planet on an eccentric orbit within the system the habitable zone. Here we provide an analysis of the WASP-47 system from the perspective of atmospheric detection and characterization. We discuss the system architecture and the potential for additional long-period planets. We simulate expected phase variations as a function of planet orbital phase for the system due to the combined effect of the planets. We present an analysis of precision photometry of WASP-47 from the K2 mission, phased on each of the planets. The analysis rules out the detection of phase signatures for the two inner-most planets, enabling constraints upon their albedos and atmospheric properties. Our study concludes that WASP-47b is an example of a "dark" planet with a tentative geometric albedo of 0.016 and a 1σ upper limit of 0.17. The WASP-47e data are consistent with a broad range of albedos, but also show early evidence of having a relatively low albedo. The growing number of dark, short-period giant planets provide the framework of an ideal sample for studying low albedo dependence on atmospheric composition.

Keywords: exoplanet atmospheres; exoplanet systems; exoplanet detection methods; natural satellites (extrasolar)
The Decay of Two Adjacent Sunspots Associated with Moving Magnetic Features

The relationship between the decay of sunspots and moving magnetic features (MMFs) plays an important role in understanding the evolution of active regions. We present observations of two adjacent sunspots, the gap between them, and a lot of MMFs propagating from the gap and the sunspots' outer edges in NOAA Active Region 13023. The MMFs are divided into two types based on their magnetic field inclination angle: vertical (0° < γ < 45°) and horizontal (45° ≤ γ < 90°) MMFs (V-MMFs and H-MMFs, respectively). The main results are as follows: (1) the mean magnetic flux decay rates of the two sunspots are -1.7 × 1020 and -1.4 × 1020 Mx day-1; (2) the magnetic flux generation rate of all MMFs is calculated to be -1.9 × 1021 Mx day-1, which is on average 5.6 times higher than the total magnetic flux loss rate of the sunspots; (3) the magnetic flux of V-MMFs (including a pore separated from the sunspots) is 1.4 times larger than the total lost magnetic flux of the two sunspots, and in a later stage when the pore has passed through the reference ellipse, the magnetic flux generation rate of the V-MMFs is almost the same as the magnetic flux loss rate of the sunspots; and (4) within the gap, the magnetic flux of V-MMFs is one-third of the total magnetic flux. Few V-MMFs stream out from the sunspots at the nongap region. All observations suggest that MMFs with vertical magnetic fields are closely related to the disintegration of the sunspot, and most of the MMFs from the gap may originate directly from the sunspot umbra.

Keywords: sunspots; solar magnetic fields; solar photosphere
The High-mass Protostellar Population of a Massive Infrared Dark Cloud

We conduct a census of the high-mass protostellar population of the ∼70,000 M⊙ infrared dark cloud (IRDC) G028.37+00.07, identifying 35 sources based on their 70 μm emission, as reported in the Herschel Hi-GAL catalog of Molinari et al. We perform aperture photometry to construct spectral energy distributions, which are then fit with the massive protostar models of Zhang & Tan. We find that the sources span a range of isotropic luminosities from ∼20 to 4500 L⊙. The most luminous sources are predicted to have current protostellar masses of m* ∼ 10 M⊙ forming from cores of mass Mc ∼ 40 to 400 M⊙. The least luminous sources in our sample are predicted to be protostars with masses as low as ∼0.5 M⊙ forming from cores with Mc ∼ 10 M⊙, which are the minimum values explored in the protostellar model grid. The detected protostellar population has a total estimated protostellar mass of M* ∼ 100 M⊙. Allowing for completeness corrections, which are constrained by comparison with an ALMA study in part of the cloud, we estimate a star formation efficiency per freefall time of ∼3% in the IRDC. Finally, analyzing the spatial distribution of the sources, we find relatively low degrees of central concentration of the protostars. The protostars, including the most massive ones, do not appear to be especially centrally concentrated in the protocluster as defined by the IRDC boundary.

Keywords: star formation; infrared photometry; protostars
Jet-ISM Interaction in NGC 1167/B2 0258+35, an LINER with an AGN Past

We report the results of joint Chandra/ACIS-NuSTAR deep observations of NGC 1167, the host galaxy of the young radio jet B2 0258+35. In the ACIS data, we detect X-ray emission, extended both along and orthogonal to the jet. At the end of the southeast radio jet, we find lower-energy X-ray emission that coincides with a region of CO turbulence and fast outflow motions. This suggests that the hot interstellar medium (ISM) may be compressed by the jet and molecular outflow, resulting in more efficient cooling. Hydrodynamic simulations of jet-ISM interaction tailored to NGC 1167 are in agreement with this conclusion and with the overall morphology and spectra of the X-ray emission. The faint hard nuclear source detected with Chandra and the stringent NuSTAR upper limits on the harder X-ray emission show that the active galactic nucleus (AGN) in NGC 1167 is in a very low-accretion state. However, the characteristics of the extended X-ray emission are more consonant to those of luminous Compton-thick (CT) AGNs, suggesting that we may be observing the remnants of a past high accretion rate episode, with sustained strong activity lasting ~2 × 103 yr. We conclude that NGC1167 is presently a Low-Ionization Nuclear Emission-line Region (LINER) , but was an AGN in the past, given the properties of the extended X-ray emission and their similarity with those of CT AGN extended emission.

Keywords: active galactic nuclei
Subarcsecond-resolution Imaging of M51 with the International LOFAR Telescope

We present an International LOFAR Telescope (ILT) subarcsecond-resolution image of the nearby galaxy M51 with a beam size of 0.″436 × 0.″366 and rms of 46 μJy. We compare this image with a European VLBI Network study of M51 and discuss the supernovae in this galaxy, which have not yet been probed at these low radio frequencies. We find a flux density of 0.97 mJy for SN 2011dh in the ILT image, which is about five times smaller than the flux density reported by the LOFAR Two-metre Sky Survey (LoTSS) at 6″ resolution using the same data set without the international stations. This difference makes evident the need for LOFAR international baselines to reliably obtain flux density measurements of compact objects in nearby galaxies. Our LOFAR flux density measurement of SN 2011dh directly translates into fitting the radio light curves for the supernova and constraining the mass-loss rates of the progenitor star. We do not detect two other supernovae in the same galaxy, SN 1994I and SN 2005cs, and our observations place limits on the evolution of both supernovae at radio wavelengths. We also discuss the radio emission from the center of M51, in which we detect the active galactic nucleus and other parts of the nuclear emission in the galaxy, with a possible detection of Component N. We discuss a few other sources, including the detection of a high-mass X-ray binary not detected by LoTSS but with a flux density in the ILT image that matches well with higher-frequency catalogs.

Keywords: radio continuum emission; high angular resolution; galaxies; core-collapse supernovae; active galactic nuclei
Hidden Companions to Intermediate-mass Stars. V. Discovery of a 1.6 M ⊙, 0.3 au Companion to Marfik within the 48 au Visual Binary HIP 80883 = λ Ophiuchi

λ Ophiuchi is a nearby 48 au intermediate-mass visual binary with a hierarchical, 6400 au wide companion. We report on the discovery of a close companion to the primary star (Marfik) with a K band flux ratio of 33% at a projected separation ρ = 6.1 mas ↔ 0.32 au based on a VLTI/GRAVITY observation. Isochrone fitting yields masses M Aa = 2.39M ⊙, M Ab = 1.62M ⊙ and M B = 1.82M ⊙. λ Oph therefore joins a growing number of intermediate-mass binaries with 10-60 au separation in which the primary is found to be a close binary and which suggest that many white dwarfs with a main sequence companion at such separations (such as Sirius B) ultimately descended from merger products. In fact, λ Oph is a potential progenitor for a system resembling Sirius. *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.003.

Keywords: multiple stars; a stars; optical interferometry
Connecting the Low to the High Corona: A Method to Isolate Transients in STEREO/COR1 Images

We present a method that isolates time-varying components from coronagraph and extreme ultraviolet images, allowing substreamer transients propagating within streamers to be tracked from the low to the high corona. The method uses a temporal bandpass filter with a transmission bandwidth of ~2.5-10 hr that suppresses both high- and low-frequency variations in observations made by the STEREO/SECCHI suite. We demonstrate that this method proves crucial in linking features in the low corona, where the magnetic field is highly nonradial, to their counterparts in the high corona, where the magnetic field follows a radial path, through the COR1 instrument. We also apply our method to observations by the COR2 and EUVI instruments on board SECCHI and produce height-time profiles that reveal small density enhancements, associated with helmet streamers propagating from ~1.2 R⊙ out to beyond 5 R⊙. Our processing method reveals that these features are common during the period of solar minimum in this study. The features recur on timescales of hours, originate very close to the Sun, and remain coherent out into interplanetary space. We measure the speed of the features and classify them as slow (a few to tens of kilometers per second) or fast (~100 km s-1). Both types of features serve as an observable tracer of a variable component of the slow solar wind to its source regions. Our methodology helps overcome the difficulties in tracking small-scale features through COR1. As a result, it proves successful in measuring the connectivity between the low and high corona and in measuring the velocities of small-scale features.

Keywords: solar wind; solar corona; quiet sun; astronomical techniques; coronagraphic imaging
A New Index to Describe the Relationship between Solar Extreme Ultraviolet Variation and Solar Activity

In this paper, a new solar activity index based on a novel disturbance extraction method, the spectral whitening method (SWM), is introduced to process the solar EUV data on the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. Our research suggests that the spatial information derived by SWM can well reflect the location of disturbance extraction, which is consistent with the location of the solar active region. It indicates that the disturbance extraction is effective. From AIA 094 Å to AIA 335 Å, SWM results are strongly correlated with solar radio flux F107 and the sunspot number (SSN), especially at AIA 211 Å, where the correlation coefficient reaches the maximum, while at AIA 1600 Å and AIA 1700 Å there are no detectable correlations. The proposed new solar activity index, ${J}_{P}\left(\mathrm{AIA}\right)$ , has the following characteristics: (1) the new index can reflect the main variations of F107 and SSN, indicating that the index is valid; (2) the new index has higher temporal resolution, which is more conducive to the more detailed study of solar activities on short timescales; (3) the new index reveals that the solar atmosphere still has significant variability during solar minimum characterized by low F107 and SSN; (4) the new index can be used in conjunction with the new magnetospheric and ionospheric indices, which are also derived by SWM to deepen the understanding of the causal chain of space weather and promote the improvement of forecasting capabilities.

Keywords: solar activity
Multidirectional Mass Accretion and Collimated Outflows on Scales of 100-2000 au in Early Stages of High-mass Protostars

We observed the W51 high-mass star-forming complex with the Atacama Large Millimeter/submillimeter Array's longest-baseline configurations, achieving an angular resolution of ∼20 mas, corresponding to a linear resolution of ∼100 au at DW51 = 5.4 kpc. The observed region contains three high-mass protostars in which the dust continuum emission at 1.3 mm is optically thick up to a radius ≲1000 au and has brightness temperatures ≳200 K. The high luminosity (≳104 L⊙) in the absence of free-free emission suggests the presence of massive stars (M ≳ 20 M⊙) at the earliest stages of their formation. Our continuum images reveal remarkably complex and filamentary structures arising from compact cores. Molecular emission shows no clear signs of rotation or infall on scales from 150 to 2000 au; we do not detect disks. The central sources drive young (tdyn ∼ 100 yr), fast (v ∼ 100 km s-1), powerful ( $\dot{M}\gt {10}^{-4}$ M⊙ yr-1), collimated outflows. These outflows provide indirect evidence of accretion disks on scales r ≲ 100-500 au (depending on the object). The active outflows are connected to fossil flows that have different orientations on larger spatial scales, implying that the orientations of these small disks change over time. These results together support a variant of an accretion model for high-mass star formation in which massive protostars do not form a large, stable Keplerian disk during their early stages but instead accrete material from multiple massive flows with different angular momentum vectors. This scenario therefore contrasts with the simplified classic paradigm of a stable disk+jet system, which is the standard model for low-mass star formation, and provides experimental confirmation of a multidirectional and unsteady accretion model for massive star formation.

Keywords: jets; star formation; circumstellar matter; massive stars; compact h ii region; stellar accretion disks; radio interferometry; long baseline interferometry; stellar mass loss; stellar winds; stellar accretion
Deconstructing Alien Hunting

The search for extraterrestrial (alien) life is one of the greatest scientific quests, yet it raises fundamental questions about just what we should be looking for and how. We approach alien hunting from the perspective of an experimenter engaging in binary classification with some true- and confounding-positive probabilities (TPP and CPP). We derive the Bayes factor in such a framework between two competing hypotheses, which we use to classify experiments as either impotent, imperfect, or ideal. Similarly, the experimenter can be classified as dogmatic, biased, or agnostic. We show how the unbounded explanatory and evasion capability of aliens poses fundamental problems to experiments directly seeking aliens. Instead, we advocate framing the experiments as looking for that outside of known processes, which means the hypotheses we test do not directly concern aliens per se. To connect back to aliens requires a second level of model selection, for which we derive the final odds ratio in a Bayesian framework. This reveals that it is fundamentally impossible to ever establish alien life at some threshold odds ratio, ${{ \mathcal O }}_{\mathrm{crit}}$ , unless we deem the prior probability that some as-yet-undiscovered natural process could explain the event is less than ${(1+{{ \mathcal O }}_{\mathrm{crit}})}^{-1}$ . This elucidates how alien hunters need to carefully consider the challenging problem of how probable unknown unknowns are, such as new physics or chemistry, and how it is arguably most fruitful to focus on experiments for which our domain knowledge is thought to be asymptotically complete.

Keywords: astrobiology