bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterisation of the stellar activity of M dwarfs
Authors: Meunier N. , Mignon L. , Kretzschmar M. , Delfosse X.
Published: January 2024

Context. The chromospheric emission estimated in the core of different lines, such as Ca II H & K, Na D1 and D2, and Ha, is not always correlated between lines. In particular, the Ca II H & K and Ha emission time series are anti-correlated for a few percent of the stars, contrary to what is observed on the Sun. This puzzling result has been observed for both solar-type stars and M stars.

Aims. Our objective is to characterise these relationships in more detail using complementary criteria, and based on a large set of spectra obtained with HARPS for a large sample of M dwarfs. This should allow to evaluate whether or not additional processes are required to explain the observations.

Methods. We analysed the time average and variability of the Ca, Na, and Hα emissions for 177 M stars ranging from subspectral types M0 to M8, paying particular attention to their (anti-)correlations on both short and long timescales as well as slopes between indices. We also computed synthetic Hα time series based on different assumptions of plage properties. We compared our findings with observations in order to evaluate whether or not the main observed properties could be reproduced.

Results. The statistical properties of our sample, in terms of correlations and slopes between indices at different timescales, differ from what we previously obtained for FGK stars: there are fewer stars with a null correlation, and the correlations we find show a weaker dependence on timescale. However, there can be a large dispersion from one season to another for stars with a well identified low or negative correlation. We also specify the complex relationship between the average activity levels, with a clear indication of a change in the sign of the slope from the relation between Ca and Hα (and between Na and Ha) for the most massive M dwarfs. In addition, we observe a change in slope in the Na–Ca relation at an intermediate activity level. At this stage, we are not able to find simple plage properties that, alone, are sufficient to reproduce the observations. However, the simulations already allow us to point out that it is not straightforward to compare the temporal variability correlation and the integrated indices. Our findings also demonstrate the need for complex activity patterns to explain some of the observations.

Conclusions. We conclude that the relation between the three indices examined here exhibits a large diversity in behaviour over the sample studied. More detailed simulations with complex activity patterns are necessary to understand these observations. This will teach us about plage properties for this type of star.
Optimising spectroscopic observations of transiting exoplanets
Authors: Boldt-Christmas Linn , Lesjak Fabio , Wehrhahn Ansgar , Piskunov Nikolai , Rains Adam D. , Nortmann Lisa , Kochukhov Oleg
Published: January 2024

Context.When observing the atmospheres of transiting exoplanets using high-resolution spectroscopy, the aim is to detect well-resolved spectral features with high signal-to-noise ratios (S/Ns), as is possible today with modern spectrographs. However, obtaining such high-quality observations comes with a trade-off: a lower cadence of fewer, longer exposures across the transit collects more photons thanks to reduced overheads, enhancing the S/N of each observation, while a higher cadence of several shorter exposures minimises spectral feature smearing due to the continuously changing radial velocity of the planet.

Aims.Considering that maximising S/N and minimising smearing are both beneficial to analysis, there is a need to identify the optimal compromise between the two for a given target. In this work, we aim to establish where this compromise lies for a typical exoplanet transit observation in order to benefit future data collection and subsequent interpretation.

Methods.We modelled real transit events based on targets as they would be observed with VLT/CRIRES+ at Paranal Observatory, Chile. Creating four hypothetical scenarios, we simulated each set of transmission spectra across 100 realisations of the same transit event in order to vary the time resolution only. We removed telluric and stellar lines from these data sets using the SYSREM algorithm and analysed them through cross-correlation with model templates, measuring how successfully each time resolution and case detected the planetary signal and exploring how the results vary.

Results.We demonstrate that there is a continuous change in the significance of the cross-correlation detection based on the trade-off between high and low time resolutions, and that, averaged over a large number of realisations, the function of this significance has clear maxima. The strength and location of these maxima vary depending on, for example, planet system parameters, instrumentation, and the number of removal iterations. We discuss why observers should therefore take several factors into account using a strategy akin to the ‘exposure triangle’ employed in traditional photography where a balance must be struck by considering the full context of the observation. Our method is robust and may be employed by observers to estimate the best observational strategies for other targets.
TOI-2266 b: A keystone super-Earth at the edge of the M dwarf radius valley
Authors: Parviainen H. , Murgas F. , Esparza-Borges E. , Peláez-Torres A. , Palle E. , Luque R. , Zapatero-Osorio M. R. , Korth J. , Fukui A. , Narita N. , Collins K. A. , Béjar V. J. S. , Morello G. , Monelli M. , Garcia N. Abreu , Chen G. , Crouzet N. , de Leon J. P. , Isogai K. , Kagetani T. , Kawauchi K. , Klagyivik P. , Kodama T. , Kusakabe N. , Livingston J. H. , Meni P. , Mori M. , Nowak G. , Tamura M. , Terada Y. , Watanabe N. , Ciardi D. R. , Lund M. B. , Christiansen J. L. , Dressing C. D. , Giacalone S. , Savel A. B. , Hirsch L. , Parsons S. G. , Brown P. , Collins K. I. , Barkaoui K. , Timmermans M. , Ghachoui M. , Soubkiou A. , Benkhaldoun Z. , McDermott S. , Pritchard T. , Rowden P. , Striegel S. , Gan T. , Horne K. , Jensen E. L. N. , Schwarz R. P. , Shporer A. , Srdoc G. , Seager S. , Winn J. N. , Jenkins J. M. , Ricker G. , Vanderspek R. , Dragomir D.
Published: January 2024

We validate the Transiting Exoplanet Survey Satellite (TESS) object of interest TOI-2266.01 (TIC 8348911) as a small transiting planet (most likely a super-Earth) orbiting a faint M5 dwarf (V = 16.54) on a 2.33 d orbit. The validation is based on an approach where multicolour transit light curves are used to robustly estimate the upper limit of the transiting object's radius. Our analysis uses SPOC-pipeline TESS light curves from Sectors 24, 25, 51, and 52, simultaneous multicolour transit photometry observed with MuSCAT2, MuSCAT3' and HiPERCAM, and additional transit photometry observed with the LCOGT telescopes. TOI-2266 b is found to be a planet with a radius of 1.54 ± 0.09 R⊕, which locates it at the edge of the transition zone between rocky planets, water-rich planets, and sub-Neptunes (the so-called M dwarf radius valley). The planet is amenable to ground-based radial velocity mass measurement with red-sensitive spectrographs installed in large telescopes, such as MAROON-X and Keck Planet Finder (KPF), which makes it a valuable addition to a relatively small population of planets that can be used to probe the physics of the transition zone. Further, the planet's orbital period of 2.33 days places it inside a ‘keystone planet’ wedge in the period-radius plane where competing planet formation scenarios make conflicting predictions on how the radius valley depends on the orbital period. This makes the planet also a welcome addition to the small population of planets that can be used to test small-planet formation scenarios around M dwarfs.
Probing the interstellar medium of the quasar BRI 0952−0115
Authors: Kade K. , Knudsen K. K. , Bewketu Belete A. , Yang C. , König S. , Stanley F. , Scholtz J.
Published: January 2024

Context. The extent of the effect of active galactic nuclei (AGN) on their host galaxies at high-redshift is not apparent. The processes governing the co-eval evolution of the stellar mass and the mass of the central supermassive black hole, along with the effects of the supermassive black hole on the host galaxy, remain unclear. Studying this effect in the distant universe is a difficult process as the mechanisms of tracing AGN activity can often be inaccurately associated with intense star formation and vice versa.

Aims. Our aim is to better understand the processes governing the interstellar medium (ISM) of the quasar BRI 0952−0952 at z = 4.432, specifically with regard to the individual heating processes at work and to place the quasar in an evolutionary context.

Methods. We analyzed ALMA archival bands 3, 4, and 6 data and combined the results with high-resolution band-7 ALMA observations of the quasar. We detected [C I](2–1), [C II](2P3/2 − 2P1/2), CO(5–4), CO(7–6), CO(12–11), OH 2Π1/2(3/2 − 1/2), and H2O(211 − 202), and we report a tentative detection of OH+. We updated the lensing model and we used the radiative transfer code MOLPOP-CEP to produce line emission models which we compared with our observations.

Results. We used the [C I] line emission to estimate the total molecular gas mass in the quasar. We present results from the radiative transfer code MOLPOP-CEP constraining the properties of the CO emission and suggest different possible scenarios for heating mechanisms within the quasar. We extended our results from MOLPOP-CEP to the additional line species detected in the quasar to place stronger constraints on the ISM properties.

Conclusions. Modeling from the CO SLED suggests that there are extreme heating mechanisms operating within the quasar in the form of star formation or AGN activity; however, with the current data, it remains unclear which of the two is the preferred mechanism as both models reasonably reproduce the observed CO line fluxes. The updated lensing model suggests a velocity gradient across the [C II] line, suggestive of ongoing kinematical processes within the quasar. We find that the H2O emission in BRI 0952 is likely correlated with star-forming regions of the ISM. We used the molecular gas mass from [C I] to calculate a depletion time for the quasar. We conclude that BRI 0952−0952 is a quasar with a significant AGN contribution while also showing signs of extreme starburst activity, indicating that the quasar could be in a transitional phase between a starburst-dominated stage and an AGN-dominated stage.
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.
The first spatio-spectral Bayesian imaging of SN1006 in X-rays
Authors: Westerkamp M. , Eberle V. , Guardiani M. , Frank P. , Scheel-Platz L. , Arras P. , Knollmüller J. , Stadler J. , Enßlin T.
Published: January 2024

Supernovae (SNs) are an important source of energy in the interstellar medium. Young remnants of supernovae (SNRs) exhibit peak emission in the X-ray region, making them interesting objects for X-ray observations. In particular, the supernova remnant SN1006 is of great interest due to its historical record, proximity, and brightness. Thus, it has been studied with a number of X-ray telescopes. Improving X-ray imaging of this and other remnants is an important but challenging task, as it often requires multiple observations with different instrument responses to image the entire object. Here, we use Chandra observations to demonstrate the capabilities of Bayesian image reconstruction using information field theory (IFT). Our objective is to reconstruct denoised, deconvolved, and spatio-spectral resolved images from X-ray observations and to decompose the emission into different morphologies, namely, diffuse and point-like. Further, we aim to fuse data from different detectors and pointings into a mosaic and quantify the uncertainty of our result. By utilizing prior knowledge on the spatial and spectral correlation structure of the diffuse emission and point sources, this method allows for the effective decomposition of the signal into these two components. In order to accelerate the imaging process, we introduced a multi-step approach, in which the spatial reconstruction obtained for a single energy range is used to derive an informed starting point for the full spatio-spectral reconstruction. We applied this method to 11 Chandra observations of SN1006 from 2008 and 2012, providing a detailed, denoised, and decomposed view of the remnant. In particular, the separated view of the diffuse emission ought to provide new insights into the complex, small-scale structures in the center of the remnant and at the shock front profiles. For example, our analysis reveals sharp X-ray flux increases by up to two orders of magnitude at the shock fronts of SN1006.
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.
SPT: Spectral transformer for age and mass estimations of red giant stars
Authors: Zhang Mengmeng , Wu Fan , Bu Yude , Li Shanshan , Yi Zhenping , Liu Meng , Kong Xiaoming
Published: January 2024

The ages and masses of red giants are key to our understanding of the structure and evolution of the Milky Way. Traditional isochrone methods for these estimations are inherently limited due to overlapping isochrones in the Hertzsprung-Russell diagram, while astero-seismology, albeit more precise, requires high-precision, long-term observations. In response to these challenges, we developed a novel framework, spectral transformer (SPT), to predict the ages and masses of red giants aligned with asteroseismology from their spectra. The main component of SPT is the multi-head Hadamard self-attention mechanism, which is designed specifically for spectra and can capture complex relationships across different wavelengths. Furthermore, we introduced a Mahalanobis distance-based loss function, to address scale imbalance and interaction mode loss, and we incorporated a Monte Carlo dropout for a quantitative analysis of the prediction uncertainty. Trained and tested on 3880 red giant spectra from LAMOST, the SPT has achieved remarkable age and mass estimations, with average percentage errors of 17.64 and 6.61%, respectively. It has also provided uncertainties for each corresponding prediction. These results significantly outperform traditional machine learning algorithms, demonstrating a high level of consistency with asteroseismology methods and isochrone-fitting techniques. In the future, our work will leverage datasets from the Chinese Space Station Telescope and Large Synoptic Survey Telescope to enhance the precision of the model and broaden its applicability in the fields of astronomy and astrophysics.
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.
New theoretical study of potassium perturbed by He and a comparison to laboratory spectra
Authors: Allard N. F. , Kielkopf J. F. , Myneni K. , Blakely J. N.
Published: January 2024

The visible and near-infrared spectra of late L- and T-type dwarf stars are dominated in large part by the resonance lines of neutral Na and K. It is the collision broadening of these atomic lines by H2 and He in the stellar atmosphere that determines the continuum from below 0.5 µm to above 0.9 µm in the spectrum. Their line profiles can be detected as far as 3000 cm−1 from the line center in T dwarfs and consequently an accurate and detailed determination of the complete profile, including the extreme far wing, is required to model the contribution of these strong alkali resonance lines to brown dwarf spectra. We report on our new calculations of unified line profiles of K perturbed by He using ab initio potential data for the conditions prevailing in cool substellar brown dwarfs and hot dense planetary atmospheres with temperatures from Teff = 500 to 3000 K. For such objects with atmospheres of H2 and He, conventional laboratory absorption spectroscopy can be used to examine the line wings and test the line shape theories and molecular potentials. We find that an analytical Lorentzian profile is useful for a few cm−1 from the line center, but not in the line wings, where the radiative transfer is a consequence of the K–He radiative collisions that are sensitive to the interaction potentials. Tables of the K–He absorption coefficients of the resonance lines allow accurate model atmospheres and synthetic spectra. For this purpose, we present new opacities from comprehensive line shape theory incorporating accurate ab initio potentials. Use of these new tables for the modeling of emergent spectra will be an improvement over previous line shape approximations based on incomplete or inaccurate potentials. We also present Lorentzian impact parameters obtained in the semi-classical and quantum theory for the K 4s − 4p resonance line centered at 0.77 µm specifically for the line core regime.
Wolf 327b: A new member of the pack of ultra-short-period super-Earths around M dwarfs
Authors: Murgas F. , Pallé E. , Orell-Miquel J. , Carleo I. , Peña-Moñino L. , Pérez-Torres M. , Watkins C. N. , Jeffers S. V. , Azzaro M. , Barkaoui K. , Belinski A. A. , Caballero J. A. , Charbonneau D. , Cheryasov D. V. , Ciardi D. R. , Collins K. A. , Cortés-Contreras M. , de Leon J. , Duque-Arribas C. , Enoc G. , Esparza-Borges E. , Fukui A. , Geraldía-González S. , Gilbert E. A. , Hatzes A. P. , Hayashi Y. , Henning Th. , Herrero E. , Jenkins J. M. , Lillo-Box J. , Lodieu N. , Lund M. B. , Luque R. , Montes D. , Nagel E. , Narita N. , Parviainen H. , Polanski A. S. , Reffert S. , Schlecker M. , Schöfer P. , Schwarz R. P. , Schweitzer A. , Seager S. , Stassun K. G. , Tabernero H. M. , Terada Y. , Twicken J. D. , Vanaverbeke S. , Winn J. N. , Zambelli R. , Amado P. J. , Quirrenbach A. , Reiners A. , Ribas I.
Published: January 2024

Planets with orbital periods shorter than 1 day are rare and have formation histories that are not completely understood. Small (Rp < 2 R⊕) ultra-short-period (USP) planets are highly irradiated, probably have rocky compositions with high bulk densities, and are often found in multi-planet systems. Additionally, USP planets found around small stars are excellent candidates for characterization using present-day instrumentation. Of the current full sample of approximately 5500 confirmed exoplanets, only 130 are USP planets and around 40 have mass and radius measurements. Wolf 327 (TOI-5747) is an M dwarf (R* = 0.406 ± 0.015 R⊙, M* = 0.405 ± 0.019 M⊙, Teff = 3542 ± 70 K, and V = 13 mag) located at a distance d = 28.5 pc. NASA’s planet hunter satellite, TESS, detected transits in this star with a period of 0.573 day (13.7 h) and with a transit depth of 818 ppm. Ground-based follow-up photometry, high resolution imaging, and radial velocity (RV) measurements taken with the CARMENES spectrograph confirm the presence of this new USP planet. Wolf 327b is a super-Earth with a radius of Rp = 1.24 ± 0.06 R⊕ and a mass of Mp = 2.53 ± 0.46 M⊕, yielding a bulk density of 7.24 ± 1.66 g cm−3 and thus suggesting a rocky composition. Owing to its close proximity to its host star (a = 0.01 au), Wolf 327b has an equilibrium temperature of 996 ± 22 K. This planet has a mass and radius similar to K2-229b, a planet with an inferred Mercury-like internal composition. Planet interior models suggest that Wolf 327b has a large iron core, a small rocky mantle, and a negligible (if any) H/He atmosphere.
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.
Protonated acetylene in the z = 0.89 molecular absorber toward PKS 1830-211
Authors: Muller S. , Le Gal R. , Roueff E. , Black J. H. , Faure A. , Guélin M. , Omont A. , Gérin M. , Combes F. , Aalto S.
Published: January 2024

We report the first interstellar identification of protonated acetylene, C2H3+, a fundamental hydrocarbon, in the z = 0.89 molecular absorber toward the gravitationally lensed quasar PKS 1830–211. The molecular species is identified from clear absorption features corresponding to the 212–101 (rest frequency 494.034 GHz) and 111–000 (431.316 GHz) ground-state transitions of ortho and para forms of C2H3+, respectively, in ALMA spectra toward the southwestern image of PKS 1830-211, where numerous molecules, including other hydrocarbons, have already been detected. From the simple assumption of local thermodynamic equilibrium (LTE) with cosmic microwave background photons and an ortho-to-para ratio of three, we estimate a total C2H3+ column density of 2 × 1012 cm−2 and an abundance of 10−10 compared to H2. However, formation pumping could affect the population of metastable states, yielding a C2H3+ column density higher than the LTE value by a factor of a few. We explore possible routes to the formation of C2H3+, mainly connected to acetylene and methane, and find that the methane route is more likely in PDR environment. As one of the initial hydrocarbon building blocks, C2H3+ is thought to play an important role in astrochemistry, in particular in the formation of more complex organic molecules.
Data Envelopment Analysis for efficient traffic management
Authors: Pokushko Mariia , Pokushko Roman , Kuzmich Roman , Karaseva Margarita , Aslanidis Ilias , Weitzel Julia
Published: January 2024

The paper describes the Data Envelopment Analysis method. It demonstrates its application to study the efficiency of traffic management. The paper solves the problem of increasing the efficiency of a T-junction by increasing exit capacity and optimizing the number of exit traffic lanes. An output-oriented DEA model is applied to solve this problem. The sample uses indicators from 56 similar T-junctions with three entry traffic lanes and a different number of exit traffic lanes.
Logical analysis of data using linear approximation and heuristic algorithms for gene expression-based diagnostics
Authors: Bartosh Maria , Masich Igor
Published: January 2024

This research aims to develop a methodology that combines logical analysis of data with a white box model to predict the progression of chronic diseases. Such diseases represent a serious health problem, and accurate prediction and management are essential to improve patients’ quality of life. Current machine learning methods such as deep learning often have high accuracy, but their solutions are ‘black boxes’, making them difficult to understand. The research combines the best aspects of both methods to create more accurate and interpretable models for predicting the progression of chronic diseases. The methodology developed is expected to contribute to informative decision-making in medical practice, enrich knowledge in medical research and improve the quality of care for patients with chronic diseases.
Development of a stress-free algorithm for controlling active running platforms
Authors: Obukhov Artem , Karpushkin Sergey , Siukhin Aleksandr , Patutin Kirill , Averin Yaroslav
Published: January 2024

The problem of increasing the accuracy of predicting human actions is an urgent task for various human-machine systems. The study examines the solution to the problem of predicting human speed using neural network algorithms, computer vision technologies, and machine learning. The formalization and software implementation of a neural network speed prediction algorithm are presented. To solve the problems of determining the current speed and predicting the upcoming positions of the human body depending on the dynamics of its movement, a comparison of various machine learning models was carried out. The RandomForestRegressor algorithm showed the best position prediction accuracy. The best determination of the current speed was demonstrated by dense multilayer neural networks. The experiment revealed that when predicting a person's position at an interval of 0.6 seconds, his speed is determined with an accuracy of more than 90%. The results obtained can be used to implement neural network algorithms for controlling human-machine systems.
System for analyzing data from camera traps based on a two-stage neural network approach for operational remote monitoring
Authors: Efremov Vladislav , Leus Andrew , Gavrilov Dmitry , Mangazeev Daniil , Zuev Victor , Radysh Alexandra , Kholodnyak Ivan , Vodichev Nikita , Vahid Dastgerdi Masoud
Published: January 2024

Camera traps are a widely used tool for monitoring wildlife with minimal human intervention. Their number can amount to several hundred, and the accumulated volume can reach several terabytes. Often, photos and videos contain empty frames that are created by accidental triggering of camera trap detectors, such as by wind. The staff of nature reserves must process the images manually and sort them by animal species. In our study we propose to consider a technology for analysing data from camera traps using a two-stage neural network processing. The task of the first stage was to separate empty images from non-empty images. To do this, using a comparative analysis, we identified the most optimal detector model from the YOLO series. The task of the second stage was to classify the objects found by the detector. For this purpose, a comparative analysis of the architectures of classifiers from the ResNet series was carried out. Based on the selected algorithms, a two-stage system for processing data from camera traps was created in the form of a graphical interface with the ability to work on any operating system. The software will significantly reduce the processing time of data from camera traps and simplify environmental analysis.
Influence of the number of attribute binarization thresholds on the quality of the generated set of rules for the method of logical analysis of data
Authors: Roman Kuzmich , Katerina Ponomareva , Artur Nikiforov
Published: January 2024

For efficient operation of machine learning methods, it is necessary to set their parameters up properly. Both the computational complexity and the accuracy of the method for the problem being solved can depend on the selected parameter values. The paper discusses the method of logical analysis of data, which is used to solve classification problems and consists of a number of steps. At each step, it is necessary to set the method parameters up to suit the problem being solved. When setting parameters, one should be guided by a compromise between the accuracy of the method and the computational complexity. With comparable values for classification accuracy of several variants of the method implementation, preference will always be given to the simplest of them in terms of computational complexity. Since the method works only with binary characteristics, at the first stage it is necessary to binarize quantitative characteristics. The binarization procedure is associated with the choice of the “number of binarization thresholds” parameter. This paper proposes an experimental approach to determine the best value of the specified method parameter for the problem being solved.