bluuebunny/crossref_metadata_2025_split huggingface dataset:
eROSITA detection of a cloud obscuration event in the Seyfert AGN EC 04570–5206
Authors: Markowitz Alex , Krumpe Mirko , Homan David , Gromadzki Mariusz , Schramm Malte , Boller Thomas , Krishnan Saikruba , Saha Tathagata , Wilms Joern , Gokus Andrea , Haemmerich Steven , Winkler Hartmut , Buchner Johannes , Buckley David A. H. , Brogan Roisin , Reichart Daniel E. 
Published: January 2024

Context. Recent years have seen broad observational support for the presence of a clumpy component within the circumnuclear gas around supermassive black holes (SMBHs). In the X-ray band, individual clouds can manifest themselves when they transit the line of sight to the X-ray corona, temporarily obscuring the X-ray continuum and thereby indicating the characteristics and location of these clouds.
Aims. X-ray flux monitoring with Spectrum Roentgen Gamma extended ROentgen Survey with an Imaging Telescope Array (SRG/eROSITA) has revealed that in the Seyfert 1 active galactic nucleus (AGN) EC 04570−5206, the soft X-ray flux dipped abruptly for about 10−18 months over 2020−2021, only to recover and then drop a second time by early 2022. Here, we investigate whether these flux dips and recoveries could be associated with cloud occultation events.
Methods. We complemented the eROSITA scans with multiwavelength follow-up observations, including X-ray/UV observations with Swift, XMM-Newton, and NICER, along with ground-based optical photometric and spectroscopic observations to investigate the spectral and flux variability.
Results.XMM-Newton spectra confirm that the soft X-ray flux dips were caused by partial-covering obscuration by two separate clouds. The 2020−2021 event was caused by a cloud with column density near 1 × 1022 cm−2 and a covering fraction of roughly 60%. The cloud in the 2022 event had a column density near 3 × 1023 cm−2 and a covering fraction near 80%. The optical/UV continuum flux varied minimally and the optical emission line spectra showed no variability in Balmer profiles or intensity.
Conclusions. The transiting gas clouds are neutral or lowly-ionized, while the lower limits on their radial distances are commensurate with the dust sublimation zone (cloud 1) or the optical broad line region (cloud 2). One possible explanation is a dust-free, outflowing wind with embedded X-ray clumps. These events are the first cloud obscuration events detected in a Seyfert galaxy using eROSITA’s X-ray monitoring capabilities.
Observational mapping of the mass discrepancy in eclipsing binaries: Selection of the sample and its photometric and spectroscopic properties
Authors: Tkachenko Andrew , Pavlovski Krešimir , Serebriakova Nadezhda , Bowman Dominic M. , IJspeert Luc , Gebruers Sarah , Southworth John 
Published: January 2024

Context. Eclipsing spectroscopic double-lined binaries are the prime source of precise and accurate measurements of masses and radii of stars. These measurements provide a stringent test for models of stellar evolution that are consistently reported to contain major shortcomings.
Aims. The mass discrepancy observed for eclipsing spectroscopic double-lined binaries is one of the manifestations of the shortcomings in stellar evolution models. The problem reflects the inability of the models to accurately predict the effective temperature and surface gravity or luminosity of a star for a given mass. Our ultimate goal is to provide an observational mapping of the mass discrepancy and to propose a recipe for its solution.
Methods. We initiated a spectroscopic monitoring campaign of 573 candidate eclipsing binaries classified as such based on their TESS light curves. In this work, we present a sub-sample of 83 systems for which orbital phase-resolved spectroscopy has been obtained and subsequently analysed with the methods of least-squares deconvolution and spectral disentangling. In addition, we employed TESS space-based light curves to provide photometric classification of the systems according to the type of their intrinsic variability.
Results. We confirmed 69 systems as being either spectroscopic binaries or higher-order multiple systems. We classified twelve stars as single, and we found two more objects that cannot be decisively classified as intrinsically variable single or binary stars. Moreover, 20 eclipsing binaries were found to contain at least one component that exhibits stellar oscillations. Spectroscopic orbital elements were obtained with the spectral disentangling method and reported for all systems classified as either SB1 or SB2. The sample presented in this work contains both detached and semi-detached systems and covers a range in the effective temperature and mass of the star of Teff ∊ [7000,30 000] K and M ∊ [1.5, 15] M⊙, respectively.
Conclusions. Based on a comparison of our own results with those published in the literature for well-studied systems, we conclude that there is an appreciable capability of the spectral disentangling method to deliver precise and accurate spectroscopic orbital elements from as few as six to eight orbital phase-resolved spectroscopic observations. Orbital solutions obtained this way are accurate enough to deliver age estimates with an accuracy of 10% or better for intermediate-mass F-type stars, an important resource for the calibration of stellar evolution models for future space-based missions, such as PLATO. Finally, despite the small size relative to the 573 systems that we will ultimately monitor spectroscopically, the sample presented in this work is already suitable to kick off observational mapping of the mass discrepancy in eclipsing binaries.
How well does surface magnetism represent deep Sun-like star dynamo action?
Authors: Finley A. J. , Brun A. S. , Strugarek A. , Cameron R. 
Published: January 2024

Context. For Sun-like stars, the generation of toroidal magnetic field from poloidal magnetic field is an essential piece of the dynamo mechanism powering their magnetism. Previous authors have estimated the net toroidal flux generated in each hemisphere of the Sun by exploiting its conservative nature. This only requires observations of the photospheric magnetic field and surface differential rotation.
Aims. We explore this approach using a 3D magnetohydrodynamic dynamo simulation of a cool star, for which the magnetic field and its generation are precisely known throughout the entire star.
Methods. Changes to the net toroidal flux in each hemisphere were evaluated using a closed line integral bounding the cross-sectional area of each hemisphere, following the application of Stokes theorem to the induction equation; the individual line segments correspond to the stellar surface, base, equator, and rotation axis. We evaluated the influence of the large-scale flows, the fluctuating flows, and magnetic diffusion on each of the line segments, along with their depth-dependence.
Results. In the simulation, changes to the net toroidal flux via the surface line segment typically dominate the total line integral surrounding each hemisphere, with smaller contributions from the equator and rotation axis. The surface line integral is governed primarily by the large-scale flows, and the diffusive current; the latter acting like a flux emergence term due to the use of an impenetrable upper boundary in the simulation. The bulk of the toroidal flux is generated deep inside the convection zone, with the surface observables capturing this due to the conservative nature of the net flux.
Conclusions. Surface magnetism and rotation can be used to produce an estimate of the net toroidal flux generated in each hemisphere, allowing us to constrain the reservoir of magnetic flux for the next magnetic cycle. However, this methodology cannot identify the physical origin or the location of the toroidal flux generation. In addition, not all dynamo mechanisms depend on the net toroidal field produced in each hemisphere, meaning this method may not be able to characterise every magnetic cycle.
The treasure behind the haystack: MUSE analysis of five recently discovered globular clusters
Authors: Gran F. , Kordopatis G. , Zoccali M. , Hill V. , Saviane I. , Navarrete C. , Rojas-Arriagada A. , Carballo-Bello J. , Hartke J. , Valenti E. , Contreras Ramos R. , De Leo M. , Fabbro S. 
Published: January 2024

Context. After the second data release of Gaia, the number of new globular cluster candidates has increased significantly. However, most of them need to be properly characterised, both spectroscopically and photometrically, by means of radial velocities, metallicities, and deeper photometric observations.
Aims. Our goal is to provide an independent confirmation of the cluster nature of Gran 4, a recently discovered globular cluster, with follow-up spectroscopic observations. The derived radial velocity for individual stars, coupled with proper motions, allows us to isolate cluster members from field stars, while the analysis of their spectra allows us to derive metallicities. By including in the analysis the recently confirmed clusters Gran 1, 2, 3, and 5, we aim to completely characterise recently discovered globular clusters.
Methods. Using Gaia DR3 and VVV catalogue data and MUSE at VLT observations, we selected cluster members based on their proper motions, radial velocities and their position in colour-magnitude diagrams. Furthermore, full spectral synthesis was performed on the cluster members, extracting surface parameters and metallicity from MUSE spectra. Finally, a completeness estimation was performed on the total globular cluster population of the Milky Way.
Results. We confirm the nature of Gran 4, a newly discovered globular cluster behind the Galactic bulge, with a mean radial velocity of RV = −265.28 ± 3.92 km s−1 and a mean metallicity of [Fe/H]= − 1.72 ± 0.32 dex. Additionally, independent measurements of the metallicities were derived for Gran 1, 2, 3, and 5. We also revise the observational lower mass limit for a globular cluster to survive in the bulge and disc environment. We estimate that ∼12 − 26 globular clusters have still to be discovered on the other side of the Galaxy (i.e., behind the bulge, bar and disk), up to 20 kpc.
A star under multiple influences
Authors: Kővári Zs. , Strassmeier K. G. , Kriskovics L. , Oláh K. , Borkovits T. , Radványi Á. , Granzer T. , Seli B. , Vida K. , Weber M. 
Published: January 2024

Context.Close binaries with magnetically active components are astrophysical laboratories for studying the effects of binarity on activity. Of particular interest are binary and multiple star systems that contain a solar-type active component with an internal structure similar to the Sun, allowing us to study how the dynamo of a solar-type star would work under different conditions.Aims.We have conducted a comprehensive investigation of V815 Her using photometric and spectroscopic data to understand the origin of the activity and what influences it in the short and long term.Methods.Using space photometry we performed light curve modeling in order to derive astrophysical and orbital parameters for the eclipsing binary subsystem V815 Her B. Using archival photometric data covering a century we carried out a time frequency analysis. Spectral synthesis was applied to determine the basic astrophysical parameters of the rapidly rotating primary using high-resolution STELLA spectra recorded in 2018.Results.Photometric analysis of archived data revealed multiple cycles on timescales between ∼6.5 and ∼26 yr, some of which may be harmonic. From TESS photometry we obtained an orbital solution for the V815 Her B subsystem. By placing the primary component on the Hertzsprung–Russell-diagram, we could deduce an age of ≈30 Myr, in line with the high Li-6707 abundance. The STELLA spectra covering the 200 day-long observing season enabled us to create 19 time-series Doppler images, which revealed a constantly changing spotted surface on a timescale of a few weeks. From the consecutive image pairs we built up the average cross-correlation function map to measure the surface differential rotation of the spotted star, from which we derive a weak solar-type surface shear.Conclusions.We found evidence that the V815 Her B component previously apostrophized as a “third body” is actually an eclipsing close binary subsystem of two M dwarfs with a period of 0.5 d, that is, V815 Her is a 2+2 hierarchical quadruple system. The system is apparently young, only a few times ten million years old, consistent with the spotted primary V815 Her Aa being a zero-age main-sequence star. Spot activity on the primary was found to be vivid. Fast starspot decay suggests that convective-turbulent erosion plays a more significant role in such a rapidly rotating star. The weak surface shear of V815 Her Aa due to differential rotation is presumably confined by tidal forces of the close companion V815 Her Ab. The slowly increasing photometric cycle of about 6.5 yr on average is interpreted as a spot cycle of V815 Her Aa, which is probably modulated by the eccentric wide orbit.
A two-dimensional perspective of the rotational evolution of rapidly rotating intermediate-mass stars
Authors: Mombarg J. S. G. , Rieutord M. , Espinosa Lara F. 
Published: January 2024

Context. Recently, the first successful attempt at computing stellar structure and evolution models in two dimensions was presented with models that include centrifugal deformation and self-consistently compute the velocity field.
Aims. The aim of the present study is to explore the rotational evolution of two-dimensional models of stars rotating at a significant fraction of their critical angular velocity. From the predictions of these models, we aim to improve our understanding of the formation of single Be stars.
Methods. Using the ESTER code, which solves the stellar structure of a rotating star in two dimensions with time evolution, we computed evolution tracks of stars of between 4 and 10 M⊙ for initial rotation rates ranging between 60 and 90% of the critical rotation rate. Furthermore, we compute models for both a Galactic metallicity and an SMC metallicity.
Results. A minimum initial rotation rate at the start of the main sequence is needed to spin up the star to critical rotation within its main sequence lifetime. This threshold depends on the stellar mass, and increases with increasing mass. The models do not predict any stars above 8 M⊙ to reach (near-)critical rotation during the main sequence. Furthermore, we find the minimum threshold of initial angular velocity is lower for SMC metallicity than for Galactic metallicity, which is in agreement with the increased fraction of observed Be stars in lower metallicity environments. The strong difference in the rotational evolution between different masses is not predicted by any one-dimensional stellar evolution models.
Conclusions. Our self-consistent two-dimensional stellar evolution models provide further insight into the rotational evolution of intermediate-mass stars, and our predictions are consistent with observations of velocity distributions and the fraction of Be stars amongst B-type stars. We find that stars with a mass above 8 M⊙ do not increase their fraction of critical rotation during the main sequence. As a fraction of stars above 8 M⊙ have been observed to display the Be phenomenon, other processes or formation channels must be at play, or, alternatively, critical rotation is not required for the Be phenomenon above this mass.
Exploring the dynamics of collisionless spherical stellar systems using the matrix method: Insights from the dilation mode
Authors: Polyachenko Evgeny V. , Shukhman Ilia G. 
Published: January 2024

Context. Analytical solutions to the perturbed equations that govern self-gravitating collisionless stellar systems are crucial for both code testing and theoretical insights. For spheres, a solution has been known for years that corresponds to the entire object’s shift from the origin. We recently introduced a new exact stationary solution, relevant for models with a single length parameter. This solution, referred to as the scale-invariant or dilation mode, has led to insights regarding the concept of perturbation energy within the linear theory framework.
Aims. Our aim is to use Hénon’s isochrone model as an example to verify the ability of the standard matrix method to successfully predict the existence of a dilation mode, and to explore its potential application as a test disturbance.
Methods. We used the standard matrix method for radial perturbations and applied Clutton-Brock potential-density pairs to determine the properties of the perturbations.
Results. In this particular case of stationary radial perturbations, the typical relationship between the perturbations of the distribution function and the potential fails. This discrepancy poses a challenge when attempting to use the dilation mode as a test. When using Clutton-Brock pairs with the matrix method, a mass conservation equation as an additional equation to the ordinary set of linear equations is required. With this added equation, it’s possible to obtain the needed test: identical vanishing of the determinant of this modified set of equations with an increasing number of included basis functions.
Validity of using Elsässer variables to study the interaction of compressible solar wind fluctuations with a coronal mass ejection
Authors: Sishtla Chaitanya Prasad , Pomoell Jens , Magyar Norbert , Kilpua Emilia , Good Simon 
Published: January 2024

Context. Alfvénic fluctuations, as modelled by the non-linear interactions of Alfvén waves of various scales, are seen to dominate solar wind turbulence. However, there is also a non-negligible component of non-Alfvénic fluctuations. The Elsässer formalism, which is central to the study of Alfvénic turbulence due to its ability to differentiate between parallel and anti-parallel Alfvén waves, cannot strictly separate wavemodes in the presence of compressive magnetoacoustic waves. In this study, we analyse the deviations generated in the Elsässer formalism as density fluctuations are naturally generated through the propagation of a linearly polarised Alfvén wave. The study was performed in the context of a coronal mass ejection (CME) propagating through the solar wind, which enables the creation of two solar wind regimes, pristine wind and a shocked CME sheath, where the Elsässer formalism can be evaluated.
Aims. We studied the deviations of the Elsässer formalism in separating parallel and anti-parallel components of Alfvénic solar wind perturbations generated by small-amplitude density fluctuations. Subsequently, we evaluated how the deviations cause a misinterpretation of the composition of waves through the parameters of cross helicity and reflection coefficient.
Methods. We used an ideal 2.5D magnetohydrodynamic model with an adiabatic equation of state. An Alfvén pump wave was injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components. This wave subsequently generates density fluctuations through the ponderomotive force. A CME was injected by inserting a flux-rope modelled as a magnetic island into the quasi-steady solar wind.
Results. The presence of density perturbations creates a ≈10% deviation in the Elsässer variables and reflection coefficient for the Alfvén waves as well as a deviation of ≈0.1 in the cross helicity in regions containing both parallel and anti-parallel fluctuations.
The polarization of the boundary layer around weakly magnetized neutron stars in X-ray binaries
Authors: Farinelli R. , Waghmare A. , Ducci L. , Santangelo A. 
Published: January 2024

Context. X-ray binaries hosting a compact object have been among the main targets of the Imaging X-ray Polarimetry Explorer (IXPE) since its launch, due to their high brightness in the 2–8 keV energy band. The spectropolarimetric analysis performed so far has proved to be of great importance in providing constraints on the accretion geometry of these systems. However, the data statistics is not enough to unambiguously disentangle the contribution of the single components to the net observed polarimetric signal.
Aims. In this work, we aim to present a model for computing the polarization degree and polarization angle of the boundary layer around weakly magnetized neutron stars in low-mass X-ray binaries in the soft state. The main motivation is to provide strong theoretical support to data interpretation of observations performed by IXPE or future satellites for X-ray polarimetry.
Methods. The results were obtained by modeling the boundary layer as an equatorial belt around the compact object and locally approximating it as a plane-parallel scattering atmosphere, for which the associated radiative transfer equation for polarized radiation in the Thomson limit was solved. The polarimetric quantities were then transformed from the comoving frame to the observer frame using the numerical methods formerly developed for X-ray pulsars.
Results. For typical values of the optical depth and electron temperature of the boundary layer of these systems in a soft state, the polarization degree was less then 0.5%, while the polarization angle was rotated by ≲5° with respect to the neutron star spin axis due to special and general relativistic effects for fast rotation, the amount progressively decreasing for lower spin frequencies. The derived quantities can be used to remove degeneracy when multicomponent spectropolarimetry is performed.
The Frequency and Severity of Gastrointestinal Symptoms in Rugby
Players
Authors: Chantler Sarah , Wood-Martin Ruth , Holliday Adrian , Davison Glen , Crabtree Daniel R. , Readhead Clint , Jones Ben 
Published: January 2024

AbstractThis study aimed to assess the self-reported frequency and severity of
gastrointestinal symptoms (GIS) at rest and around rugby training and match play
in male and female rugby union players. An online questionnaire was sent to
registered rugby union players (sevens or fifteens). Thirteen GIS were assessed
alongside perceptions of appetite around rugby and rest using Likert and visual
analog scales. Questions investigating a range of medical and dietary factors
were included. Three hundred and twenty-five players (male n=271, female
n=54) participated in the study. More frequent GIS (at least one GIS
experienced weekly/more often) was reported by players at rest
(n=203; 62%) compared to around rugby (n=154;
47%). The overall severity of GIS was low (mild discomfort), but a
portion of players (33%) did report symptoms of moderate severity around
rugby. Female players reported more frequent and severe symptoms compared to
male counterparts (p<0.001). Self-reported appetite was
significantly lower after matches compared to training. There were no dietary or
medical factors associated with GIS severity scores. This study describes GIS
characteristics in male and female rugby union players. Half of the players
assessed experienced some form of GIS that may affect nutrition, training, or
performance, and should thus be a consideration for practitioners supporting
this cohort.