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Environmental effects in excitation energy transfer have mostly been modeled by baths of harmonic oscillators, but to what extent such modeling provides a reliable description of actual interactions between molecular systems and environments remains an open issue. We address this issue by investigating fluctuations in the excitation energies of the light harvesting 2 complex using a realistic all-atomistic simulation of the potential energy surface. Our analyses reveal that molecular motions exhibit significant anharmonic features, even for underdamped intramolecular vibrations. In particular, we find that the anharmonicity contributes to the broadening of spectral densities and substantial overlaps between neighboring peaks, which complicates the meaning of mode frequencies constituting a bath model. Thus, we develop a strategy to construct a minimally underdamped harmonic bath that has a clear connection to all-atomistic dynamics by utilizing actual normal modes of molecules but optimizing their frequencies such that the resulting bath model can best reproduce the all-atomistic simulation results. By subtracting the underdamped contribution from the entire fluctuations, we also show that identifying a residual spectral density representing all other contributions with overdamped behavior is possible. We find that this can be fitted well with a well-established analytic form of a spectral density function or, alternatively, modeled as explicit time dependent fluctuations with muti-exponential or power law type correlation functions. We provide an assessment and the implications of these possibilities. The approach presented here can also serve as a general strategy to construct a simplified bath model that can effectively represent the underlying all-atomistic bath dynamics. [ABSTRACT FROM AUTHOR]

This article presents a method to estimate the rotational velocity of a cylindrical plasma from its two-dimensional images by an extended use of the Fourier-rectangular function transform, which was proposed to analyze the structure and dynamics of a cylindrical plasma [K. Yamasaki e t a l., J. Appl. Phys. 126 , 043304 (2019)]. The proposed method is applied to tomography images of plasmas produced in a linear cylindrical device and succeeds in obtaining the radial distribution of rotational velocity and its fluctuations, providing an interesting finding, that is, the existence of flow modulation associated with m = 1 mode fluctuations. [ABSTRACT FROM AUTHOR]

We perform the asteroseismic fitting of four DAVs using a grid of WDEC models with chemical profiles that closely mimic those of the LPCODE models and compare them with published asteroseismic fitting results using the LPCODE. These four objects are KIC 11911480, J113655.17+040952.6, KIC 4552982, and GD 1212. The similarities in the results in those controlled experiments point to a consistency in the models. Given similar input, the LPCODE and the WDEC make similar models and calculate similar periods. We further perform the asteroseismic fitting of the same four DAVs by relaxing the constraints on the chemical profiles. We explore the effects of different methods for weighing the modes when calculating the goodness of fit of the models, as well as the effect of only including a subset of the known period spectrum. Such numerical experiments can help place recent and future efforts in the pipeline fitting of numerous DAVs and DBVs using the WDEC on a firmer footing. [ABSTRACT FROM AUTHOR]

We present the Transiting Exoplanet Survey Satellite (TESS) light curve analysis of HX Velorum, located in the Southern Hemisphere, where one of the components is found for the first time to be a β$$ \beta $$ Cep (BCEP) type pulsator. The TESS observations of HX Velorum were published in a total of 6 sectors. Fourier analysis of the observations reveals that the frequencies can be divided into two categories, one of which is related to the orbital period and the other related to the β$$ \beta $$ Cep‐type pulsation. Its non‐eclipsing light curve was analyzed with the well‐known Wilson–Devinney code, and we obtained the geometric and physical parameters of the components using published radial velocity and light curve data by making some assumptions. We obtained plausible masses and radii of the primary and secondary components as M1=9.48±0.27M⊙$$ {M}_1=9.48\pm 0.27{M}_{\odot } $$, M2=5.92±0.17M⊙$$ {M}_2=5.92\pm 0.17{M}_{\odot } $$ and R1=3.93±0.04R⊙$$ {R}_1=3.93\pm 0.04{R}_{\odot } $$, R2=3.59±0.03R⊙$$ {R}_2=3.59\pm 0.03{R}_{\odot } $$, respectively. The obtained system's distance of ∼400$$ \sim 400 $$ pc is smaller than the Gaia distances found in the literature. [ABSTRACT FROM AUTHOR]

Brown dwarfs and planetary-mass companions display rotationally modulated photometric variability, especially those near the L/T transition. This variability is commonly attributed to top-of-atmosphere (TOA) inhomogeneities, with proposed models including patchy thick and thin clouds, planetary-scale jets, or chemical disequilibrium. Surface mapping techniques are powerful tools to probe their atmospheric structures and distinguish between models. One of the most successful methods for stellar surface mapping is Doppler imaging, where the existence of TOA inhomogeneities can be inferred from their varying Doppler shifts across the face of a rotating star. We applied Doppler imaging to the nearest brown dwarf binary WISE 1049AB (also known as Luhman 16AB) using time-resolved, high-resolution spectroscopic observations from Gemini IGRINS, and obtained for the first time H - and K -band simultaneous global weather map for brown dwarfs. Compared to the only previous Doppler map for a brown dwarf in 2014 featuring a predominant mid-latitude cold spot on WISE 1049B and no feature on WISE 1049A, our observations detected persistent spot-like structures on WISE 1049B in the equatorial to mid-latitude regions on two nights, and revealed new polar spots on WISE 1049A. Our results suggest stability of atmospheric features over time-scale of days and possible long-term stable or recurring structures. H - and K -band maps displayed similar structures in and out of CO bands, indicating the cold spots not solely due to chemical hotspots but must involve clouds. Upcoming 30-m extremely large telescopes will enable more sensitive Doppler imaging of dozens of brown dwarfs and even a small number of directly imaged exoplanets. [ABSTRACT FROM AUTHOR]

Magnetar vibrational modes are theorized to be associated with energetic X-ray flares. Regular searches for gravitational waves from these modes have been performed by Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) and Advanced Virgo, with no detections so far. Presently, search results are given in upper limits on the root sum square of the integrated gravitational-wave strain. However, the increased sensitivity of current detectors and the promise of future detectors invite the consideration of more astrophysically motivated methods. We present a framework for augmenting gravitational-wave searches to measure or place direct limits on magnetar astrophysical properties in various search scenarios using a set of phenomenological and analytical models. [ABSTRACT FROM AUTHOR]

Stellar theory enables us to understand the properties of stars at different stages of their evolution, and contributes to other fields of astrophysics such as galactic and exoplanet studies. Assessing the accuracy of stellar theories necessitates high precision, model-independent measurements of the properties of real stars, such as those obtainable for the components of double-lined eclipsing binaries (DLEBs), while asteroseismology offers probing power of the stellar interior if one or both components pulsate. KIC 4851217 is a DLEB containing two late A-type stars and exhibits pulsations of the |$\delta$| Scuti type. By analysing high resolution HERMES and moderate resolution ISIS spectra, jointly with Kepler and Transiting Exoplanet Survey Satellite light curves, we measured the masses, radii, and effective temperatures of the components to precisions of |$\sim$| 0.5, |$\sim$| 1.1, and |$\sim$| 1 per cent, respectively. We additionally report the discovery and characterization of a tertiary M-dwarf companion. Models of the system's spectral energy distribution agree with an age of 0.82 Gyr, with the more massive and larger secondary component near the end of the main-sequence lifetime. An examination of the pulsating component's pulsation frequencies reveals 39 pulsation multiplets that are split by the orbital frequency. For most of these, it is evident that the pulsation axes have been tilted into the orbital plane. This makes KIC 4851217 a tidally tilted pulsator (TTP). This precisely characterized |$\delta$| Scuti DLEB is an ideal candidate for advancing intermediate-mass stellar theory, contributing to our understanding of hierarchical systems as well as to the topic of TTPs. [ABSTRACT FROM AUTHOR]

δ Scuti variables are found at the intersection of the classical instability strip and the main sequence on the Hertzsprung–Russell diagram. With space-based photometry providing millions of light curves of A-F type stars, we can now probe the occurrence rate of δ Scuti pulsations in detail. Using the 30 minutes cadence light curves from NASA's Transiting Exoplanet Survey Satellite's first 26 sectors, we identify variability in 103,810 stars within 5–24 cycles per day down to a magnitude of T = 11.25. We fit the period–luminosity relation of the fundamental radial mode for δ Scuti stars in the Gaia G band, allowing us to distinguish classical pulsators from contaminants for a subset of 39,367 stars. Out of this subset, over 15,918 are found on or above the expected period–luminosity relation. We derive an empirical red edge to the classical instability strip using Gaia photometry. The center where the pulsator fraction peaks at 50%–70%, combined with the red edge, agrees well with previous work in the Kepler field. While many variable sources are found below the period–luminosity relation, over 85% of sources inside of the classical instability strip derived in this work are consistent with being δ Scuti stars. The remaining 15% of variables within the instability strip are likely hybrid or γ Doradus pulsators. Finally, we discover strong evidence for a correlation between pulsator fraction and spectral line broadening from the Radial Velocity Spectrometer on board the Gaia spacecraft, confirming that rotation has a role in driving pulsations in δ Scuti stars. [ABSTRACT FROM AUTHOR]

The North–South asymmetry in the number density and bulk velocity of stars in the Solar neighbourhood provides valuable insights into the formation and evolution of the Milky Way disc. Our objective is to investigate the wave-like disc oscillations of mono-age stellar populations in the Solar neighbourhood using data from Gaia Data Release 3. We have selected a comprehensive sample of main-sequence turn-off stars. The ages of these stars can be accurately determined using isochrone fitting methods. Our findings indicate that the North–South density and mean vertical velocity asymmetries remain consistent across all age groups. The uniformity of perturbations across all subsamples suggests that all populations are responding to the same external influence, which likely affects them irrespective of their age. Moreover, the fact that these perturbations appear consistently implies they could be either ongoing or recent. Regarding vertical velocity dispersions, we observe that older stars exhibit larger dispersions. [ABSTRACT FROM AUTHOR]

Background: From new results presented in the literature we discuss the hypothesis, presented in an our previous work, that the ultrafast periodic spectral modulations at f S = 0.607 ± 0.08 THz found in the spectra of 236 stars of the Sloan Digital Sky Survey (SDSS) were due to oscillations induced by dark matter (DM) cores in their centers that behave as oscillating boson stars. Two other frequencies were found by Borra in the redshift-corrected SDSS galactic spectra, f 1 , G = 9.71 − 0.19 + 0.20 THz and f 2 , G = 9.17 − 0.16 + 0.18 THz; the latter was then shown by Hippke to be a spurious frequency introduced by the data analysis procedure. Results: Within the experimental errors, the frequency f 1 , G is the beating of the two frequencies, the spurious one, f 2 , G and f S that was also independently detected in a real solar spectrum, but not in the Kurucz's artificial solar spectrum by Hippke, suggesting that f S could actually be a real frequency. Independent SETI observations by Isaacson et al., taken at different epochs, of four of these 236 stars could not confirm with high confidence—without completely excluding—the presence of f S in their power spectra and with the same power initially observed. Instead, the radio SETI deep-learning analysis with artificial intelligence (AI) gave an indirect confirmation of the presence of f S through the detection of a narrowband Doppler drifting of the observed radio signals in two stars, over a sample of 7 with a high S/N. These two stars belong to the set of the 236 SDSS stars. Numerical simulations confirm that this drifting can be due to frequency and phase modulation in time of the observed frequencies (1.3–1.7 GHz) with f S . Conclusions: Assuming the DM hypothesis, the upper mass limit of the axion-like DM particle is m a ≃ 2.4 × 10 3 μ eV , in agreement with the results from the gamma ray burst GRB221009A, laser interferometry experiments, suggesting new physics with additional axion-like particle fields for the muon g-2 anomaly. [ABSTRACT FROM AUTHOR]

White dwarfs offer a unique opportunity to search nearby stellar systems for signs of life, but the habitable zone around these stars is still poorly understood. Since white dwarfs are compact stars with low luminosity, any planets in their habitable zone should be tidally locked, like planets around M dwarfs. Unlike planets around M dwarfs, however, habitable white dwarf planets have to rotate very rapidly, with orbital periods ranging from hours to several days. Here we use the ExoCAM global climate model to investigate the inner edge of the habitable zone around white dwarfs. Our simulations show habitable planets with ultrashort orbital periods (P ≲ 1 day) enter a "bat rotation" regime, which differs from typical atmospheric circulation regimes around M dwarfs. Bat rotators feature mean equatorial subrotation and a displacement of the surface's hottest regions from the equator toward the midlatitudes. We qualitatively explain the onset of bat rotation using shallow water theory. The resulting circulation shifts increase the dayside cloud cover and decrease the stratospheric water vapor, expanding the white dwarf habitable zone by ∼50% compared to estimates based on 1D models. The James Webb Space Telescope should be able to quickly characterize bat rotators around nearby white dwarfs thanks to their distinct thermal phase curves. Our work underlines that tidally locked planets on ultrashort orbits may exhibit unique atmospheric dynamics, and guides future habitability studies of white dwarf systems. [ABSTRACT FROM AUTHOR]

The article presents an interview with Dave Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics. He discusses his shift from studying cosmology to focusing on exoplanets, the difficulties he faced in detecting exoplanet reflected light, and the evolution of exoplanet research. Topics discussed include their early academic connection, the technical challenges of using spectrographs, and the significant contributions of early exoplanet discoveries to the field.

We perform a large-scale hydrodynamic simulation of a massive star cluster whose stellar population mimics that of the Cygnus OB2 association. The main-sequence stars are first simulated during 1.6 Myr, until a quasi-stationary state is reached. At this time, the three Wolf–Rayet stars observed in Cygnus OB2 are added to the simulation, which continues to 2 Myr. Using a high-resolution grid in the centre of the domain, we can resolve the most massive stars individually, which allows us to probe the kinetic structures at small (parsec) scales. We find that, although the cluster excavates a spherical 'superbubble' cavity, the stellar population is too loosely distributed to blow a large-scale cluster wind termination shock, and that collective effects from wind–wind interactions are much less efficient than usually assumed. This challenges our understanding of the ultra-high energy emission observed from the region. [ABSTRACT FROM AUTHOR]

Photometric completeness affects the photometry of stars in crowded regions such as the cores of star clusters. Some analysis such as deriving the structural parameters of star clusters using radial density profile is heavily affected by photometric completeness and the classical techniques to map this completeness in a given field are very expensive computationally. In most surveys, for example, the large quantity of data makes it impracticable to estimate the completeness using the traditional method for the whole sample due to time and computational requirements. In this work, we present a new method that is significantly faster and results in similar completeness curves and maps as the traditional approach, providing a great first-step completeness estimator for a large sample of data. Using the completeness corrected data for each cluster we built radial density profiles improving significantly the inner portion of the profile; we also fitted the King model to them, determining the clusters' structural parameters based on a more realistic cluster profile. In this preliminary analysis, we derived structural parameters for nine selected clusters covering a range of core radii (5–40 arcesc) and tidal radii (40–180 arcesc) and discuss how the photometric completeness affects the determination of these parameters when we count stars to trace the radial profile of a star cluster. [ABSTRACT FROM AUTHOR]

We study a system of equations, involving a large parameter, arising from the study of stellar pulsation for which a combination of procedures is used to approximate a fun damental solution. We present a combination of singular and non-singular perturbation methods which, aided by symbolic computation, may be of multi-disciplinary interest for the analysis as well as a astrophysics application. Example software is presented in the Wolfram Language (Mathematica version 13.2). [ABSTRACT FROM AUTHOR]

We present results from a systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, using data from the Palomar Gattini IR (PGIR) survey. RCB stars are dusty, erratic variable stars presumably formed from the merger of a He-core and a CO-core white dwarf (WD). PGIR is a 30 cm J -band telescope with a 25 deg2 camera that surveys 18,000 deg2 of the northern sky (δ > −28°) at a cadence of 2 days. Using PGIR J- band lightcurves for ∼60 million stars together with mid-IR colors from WISE, we selected a sample of 530 candidate RCB stars. We obtained near-IR spectra for these candidates and identified 53 RCB stars in our sample. Accounting for our selection criteria, we find that there are a total of ≈ 350 − 100 + 150 RCB stars in the Milky Way. Assuming typical RCB lifetimes, this corresponds to an RCB formation rate of 0.8–5 × 10−3 yr−1, consistent with observational and theoretical estimates of the He-CO WD merger rate. We searched for quasi-periodic pulsations in the PGIR lightcurves of RCB stars and present pulsation periods for 16 RCB stars. We also examined high-cadenced TESS lightcurves for RCB and the chemically similar, but dustless hydrogen-deficient carbon (dLHdC) stars. We find that dLHdC stars show variations on timescales shorter than RCB stars, suggesting that they may have lower masses than RCB stars. Finally, we identified 3 new spectroscopically confirmed and 12 candidate Galactic DY Per type stars—believed to be colder cousins of RCB star—doubling the sample of Galactic DY Per type stars. [ABSTRACT FROM AUTHOR]

Hot subdwarf B (sdB) stars are stripped helium-burning stars that are often found in close binaries, where they experience strong tidal interactions. The dissipation of tidally excited gravity waves alters their rotational evolution throughout the sdB lifetime. While many sdB binaries have well-measured rotational and orbital frequencies, there have been few theoretical efforts to accurately calculate the tidal torque produced by gravity waves. In this work, we directly calculate the tidal excitation of internal gravity waves in realistic sdB stellar models and integrate the coupled spin–orbit evolution of sdB binaries. We find that for canonical sdB (M sdB = 0.47 M ⊙) binaries, the transitional orbital period below which they could reach tidal synchronization in the sdB lifetime is ∼0.2 day, with weak dependence on the companion masses. For low-mass sdBs (M sdB = 0.37 M ⊙) formed from more massive progenitor stars, the transitional orbital period becomes ∼0.15 day. These values are very similar to the tidal synchronization boundary (∼0.2 day) evident from observations. We discuss the dependence of tidal torques on stellar radii, and we make predictions for the rapidly rotating white dwarfs formed from synchronized sdB binaries. [ABSTRACT FROM AUTHOR]

Background: From new results presented in the literature we discuss the hypothesis, presented in an our previous work, that the ultrafast periodic spectral modulations at fS=0.607±0.08 THz found in the spectra of 236 stars of the Sloan Digital Sky Survey (SDSS) were due to oscillations induced by dark matter (DM) cores in their centers that behave as oscillating boson stars. Two other frequencies were found by Borra in the redshift-corrected SDSS galactic spectra, f1,G=9.71−0.19+0.20 THz and f2,G=9.17−0.16+0.18 THz; the latter was then shown by Hippke to be a spurious frequency introduced by the data analysis procedure. Results: Within the experimental errors, the frequency f1,G is the beating of the two frequencies, the spurious one, f2,G and fS that was also independently detected in a real solar spectrum, but not in the Kurucz’s artificial solar spectrum by Hippke, suggesting that fS could actually be a real frequency. Independent SETI observations by Isaacson et al., taken at different epochs, of four of these 236 stars could not confirm with high confidence—without completely excluding—the presence of fS in their power spectra and with the same power initially observed. Instead, the radio SETI deep-learning analysis with artificial intelligence (AI) gave an indirect confirmation of the presence of fS through the detection of a narrowband Doppler drifting of the observed radio signals in two stars, over a sample of 7 with a high S/N. These two stars belong to the set of the 236 SDSS stars. Numerical simulations confirm that this drifting can be due to frequency and phase modulation in time of the observed frequencies (1.3–1.7 GHz) with fS. Conclusions: Assuming the DM hypothesis, the upper mass limit of the axion-like DM particle is ma≃2.4×103μeV, in agreement with the results from the gamma ray burst GRB221009A, laser interferometry experiments, suggesting new physics with additional axion-like particle fields for the muon g-2 anomaly.

We present the comprehensive analysis of the high-amplitude |$\delta$| Sct star V2367 Cygni. First, we perform the frequency analysis for the whole available set of the Kepler and TESS photometry. Most of the frequency peaks are harmonics or combinations of the three known independent frequencies with the highest amplitudes, i.e. |$\nu _1=5.661\,06$|  d |$^{-1}$|⁠ , |$\nu _2=7.14898$|  d |$^{-1}$|⁠ , and |$\nu _3=7.77557$|  d |$^{-1}$|⁠. The total number of independent frequencies is 26 and 25 from the Kepler and TESS light curve, respectively. Then, using the |${\it UBVRI}$| time-series photometry, we unambiguously identify the dominant frequency |$\nu _1$| as the radial mode, whereas in the case of frequencies |$\nu _2$| and |$\nu _3$| the most probable mode degrees are |$\ell =0$| or |$\ell =2$|⁠. However, only the frequency |$\nu _2$| can be associated with a radial mode, and only if higher order effects of rotation are taken into account. Including the rotational mode coupling, we constructed complex seismic models of V2367 Cyg, which fit |$\nu _1$| and |$\nu _2$| as radial modes, and reproduce the amplitude of bolometric flux variations (the parameter f) for the dominant mode. The empirical values of f are derived from the |${\it UBVRI}$| amplitudes and phases. We rely on the Bayesian analysis based on Monte Carlo simulations to derive constraints on evolutionary stage, mass, rotation, overshooting from the convective core, and efficiency of convective transport in the envelope. Our seismic analysis clearly indicates that V2367 Cyg is in a post-main sequence phase of evolution. This is the first extensive seismic modelling that takes into account the effect of rotational coupling between pulsation modes. [ABSTRACT FROM AUTHOR]

With current and planned gravitational-wave (GW) observing runs, coincident multimessenger timing of resonant shattering flares (RSFs) and GWs may soon allow for neutron star (NS) asteroseismology to be used to constrain the nuclear symmetry energy, an important property of fundamental nuclear physics that influences the composition and equation of state of NSs. In this work, we examine the effects of combining multiple RSF detections on these symmetry energy constraints, and consider how realistic uncertainties in the masses of the progenitor NSs may weaken them. We show that the detection of subsequent multimessenger events has the potential to substantially improve constraints beyond those obtained from the first, and that this improvement is insensitive to the mass of the NSs that produce the RSFs and its uncertainty. This sets these asteroseismic constraints apart from bulk NS properties such as radius, for which the NS mass is highly important, meaning that any multimessenger RSF and GW events can equally improve our knowledge of fundamental physics. [ABSTRACT FROM AUTHOR]

With space missions such as Kepler, TESS, and Gaia, we have a wealth of data on pulsating white dwarfs that can be leveraged in white dwarf asteroseismology. We address the question of the proportion of white dwarfs with thin hydrogen layers versus those with thick hydrogen layers. We also provide a mass–radius relation for carbon–oxygen-core, hydrogen-atmosphere white dwarfs. Such a relationship can be used in conjunction with magnitudes and distance measurements to constrain the mass and effective temperature of the white dwarfs. We select nine hydrogen-atmosphere pulsating white dwarfs for their rich pulsation spectra. From such pulsation spectra, we can derive the asymptotic period spacing, which in turn allows us to determine the thickness of the hydrogen and helium envelope of the models, without having to perform period-by-period fitting. We find that the majority of the white dwarfs have thicker hydrogen layers and we determine an upper limit of M r = 1–10−2.2 for the location of the base of the helium layer, in accordance with stellar evolution models. We confirm a finding from earlier studies that used a mass–radius relation and Gaia data to determine the effective temperatures of white dwarfs. The Gaia data systematically point to white dwarfs of lower effective temperature than indicated by the spectroscopy. Our results also support the hypothesis that white dwarfs with thicker hydrogen layers are more common than those with thinner layers. [ABSTRACT FROM AUTHOR]

We present new simulations investigating the impact of mass transfer on the asteroseismic signals of slowly pulsating B stars. We used MESA to simulate the evolution of a binary star system and GYRE to compute the asteroseismic properties of the accretor star. We show that, compared to a single star of the same final mass, a star that has undergone accretion (of non-enriched material) has a significantly different internal structure, which is evident in both the hydrogen abundance profile and the Brunt-Väisälä frequency profile. These differences result in significant changes in the observed period spacing patterns, implying that one may use this as a diagnostic to test whether a star's core has been rejuvenated as a result of accretion. We show that it is essential to consider the full multimodal posterior distributions when fitting stellar properties of mass-gainers to avoid drawing misleading conclusions. Even with these considerations, stellar ages will be significantly underestimated when assuming single star evolution for a mass-gainer. We find that future detectors with improved uncertainties would rule out single star models with the correct mass and central hydrogen fraction. Our proof of principle analysis demonstrates the need to further investigate the impact of binary interactions on stellar asteroseismic signals for a wide range of parameters, such as the initial mass, the amount of mass transferred, and the age of the accretor star at the onset of mass transfer. [ABSTRACT FROM AUTHOR]

Context. Numerical computations of stellar oscillations for models representative of B-type stars predict fewer modes to be excited than observations reveal from modern space-based photometric data. One shortcoming of state-of-the-art evolution models of B-type stars that may cause a lack of excited modes is the absence of microscopic diffusion in most such models. Aims. We investigate whether the inclusion of microscopic diffusion in stellar models of B-type stars, notably radiative levitation experienced by isotopes, leads to extra mode driving by the opacity mechanism compared to the case of models that do not include microscopic diffusion. Methods. We consider the case of slowly to moderately rotating stars and use non-rotating equilibrium models, while we account for (uniform) rotation in the computations of the pulsation frequencies. We calculate 1D stellar structure and evolution models with and without microscopic diffusion and examine the effect of radiative levitation on mode excitation, for both low-radial order pressure and gravity modes and for high-radial order gravity modes. As is common practice in asteroseismology, rotation is included in the pulsation computations according to the mode's frequency regime. For modes having frequencies below twice the rotation frequency, that is, modes in the sub-inertial regime, we adopt the traditional approximation of rotation. For modes in the super-inertial regime with frequency above twice the rotation frequency, rotation is treated perturbatively up to first order in the rotation. We consider macroscopic envelope mixing induced by internal gravity waves to compute the modes and study its effect on the surface abundances. Results. We find systematically more modes to be excited for the stellar models including microscopic diffusion compared to those without it, in agreement with observational findings of pulsating B-type dwarfs. Furthermore, the models with microscopic diffusion predict that excited modes occur earlier on in the evolution compared to modes without it. In order to maintain realistic surface abundances during the main sequence, we include macroscopic envelope mixing by internal gravity waves. Along with microscopic diffusion, such macroscopic envelope mixing ensures both more excited modes and surface abundances consistent with spectroscopic studies of B-type stars. Conclusions. While radiative levitation has so far largely been neglected in stellar evolution computations of B-type stars for computational convenience, it impacts mode excitation predictions for stellar models of such stars. We conclude that the process of radiative levitation is able to reduce the discrepancy between predicted and observed excited pulsation modes in B-type stars. [ABSTRACT FROM AUTHOR]

Context. The photometric observations from the recent decade revolutionized our view on classical pulsators. Low-amplitude signals have been detected photometrically in addition to the dominant high-amplitude radial mode pulsations in many RR Lyrae stars and classical Cepheids. First-overtone pulsators with an additional low-amplitude signal at a period ratio of around 0.61 with the main mode, the so-called 0.61 stars, form the most populous group among these stars. The nature of this signal has been attributed to non-radial pulsations. Another mysterious group are stars in which the additional signal forms a period ratio of around 0.68. These are the 0.68 stars. The origin of the signal remains unknown. Aims. Here, we search for similar phenomena in spectroscopic observations of first-overtone classical Cepheids collected as part of the VELOCE project. Methods. We performed a frequency analysis of several parameters derived from cross-correlation functions (CCFs), including radial velocity, the full width at half maximum, the bisector inverse span, and the CCF depth (contrast). Using standard pre-whitening, we searched for additional low-amplitude signals. We identified the location of these stars in various sequences of the Petersen diagram. Results. We detect additional signals in four first-overtone classical Cepheids: BG Cru, QZ Nor, V0391 Nor, and V0411 Lac. We classified BG Cru, QZ Nor, and V0391 Nor as 0.61 stars based on their period ratios. V0411 Lac, however, exhibits a ratio of 0.68 between the two modes, and the additional signal has a longer period. This type of multi-periodicity remains unexplained. Conclusions.VELOCE CCFs yield the first spectroscopic detections of non-radial pulsation modes in classical Cepheids. This opens an asteroseismic window for pursuing a more detailed understanding of these important stars. While the 0.61 signal of BG Cru, QZ Nor, and V0391 Nor is understood to originate from non-radial modes of moderate degrees, the 0.68 signal of V0411 Lac still lacks a physical explanation. [ABSTRACT FROM AUTHOR]

Context. Ultra-hot Jupiters (UHJs) orbiting pulsating A/F stars represent an important subset of the exoplanetary demographic. They are excellent candidates for the study of exoplanetary atmospheres, and are astrophysical laboratories for the investigation of planet-to- star interactions. Aims. We analysed the TESS light curve of the WASP-167 system, consisting of an F1V star and a substellar companion on a ~2.02 day orbit. Methods. We modelled the combination of the ellipsoidal variability and the Doppler beaming to measure the mass of WASP-167b, and the reflection effect to obtain constraints on the geometric albedo, while placing a special emphasis on noise separation. We implemented a basic model to determine the dayside (TDay), nightside (TNight), and intrinsic (TInternal) temperatures of WASP-167b, and put a constraint on its Bond albedo. Results. We confirm the transit parameters of the planet seen in the literature. We find that a resonant ~2P−1 stellar signal (which may originate from planet-to-star interactions) interferes with the phase curve analysis. After careful and thought-out treatment of this signal, we find Mp = 0.34 ± 0.22 MJ. We measure a dayside temperature of 2790 ± 100 K, classifying WASP-167b as an UHJ. We find a 2σ upper limit of 0.51 on its Bond albedo, and determine the geometric albedo at 0.34 ± 0.11 (1σ uncertainty). Conclusions. With an occultation depth of 106.8 ± 27.3 ppm in the TESS passband, the UHJ WASP-167b is an excellent target for atmospheric studies, especially those at thermal wavelength ranges, where the stellar pulsations are expected to be less influential. [ABSTRACT FROM AUTHOR]

Sharp structural variations induce specific signatures on stellar pulsations that can be studied to infer localised information on the stratification of the star. This information is key to improve our understanding of the physical processes that lead to the structural variations and how to model them. Here we revisit and extend the analysis of the signature of different types of buoyancy glitches in gravity-mode and mixed-mode pulsators presented in earlier works, including glitches with step-like, Gaussian-like, and Dirac-δ-like shapes. In particular, we provide analytical expressions for the perturbations to the periods and show that these can be reliably used in place of the expressions provided for the period spacings, with the advantage that the use of the new expressions does not require modes with consecutive radial orders to be observed. Based on a comparison with two limit cases and on simulated data, we further tested the accuracy of the expression for the Gaussian-like glitch signature whose derivation in an earlier work involved a significant approximation. We find that the least reliable glitch parameter inferred from fitting that expression is the amplitude, which can be up to a factor of two larger than the true amplitude, reaching this limit when the glitch is small. We further discuss the impact on the glitch signature of considering a glitch in the inner and outer half of the g-mode cavity, emphasising the break of symmetry that takes place in the case of mixed-mode pulsators. [ABSTRACT FROM AUTHOR]

We present synthetic line observations of a simulated molecular cloud, utilizing a self-consistent treatment of the dynamics and time-dependent chemical evolution. We investigate line emission from the three most common CO isotopologues (12CO, 13CO, C18O) and six supposed tracers of dense gas (NH3, HCN, N2H+, HCO+, CS, HNC). Our simulation produces a range of line intensities consistent with that observed in real molecular clouds. The HCN-to-CO intensity ratio is relatively invariant with column density, making HCN (and chemically similar species such as CS) a poor tracer of high-density material in the cloud. The ratio of N2H+ to HCN or CO, on the other hand, is highly selective of regions with densities above |$10^{22} \, {\rm cm}^{-2}$|⁠ , and the N2H+ line is a very good tracer of the dynamics of high volume density (⁠|$\gt 10^4 \, {\rm cm}^{-3}$|⁠) material. Focusing on cores formed within the simulated cloud, we find good agreement with the line intensities of an observational sample of prestellar cores, including reproducing observed CS line intensities with an undepleted elemental abundance of sulphur. However, agreement between cores formed in the simulation, and models of isolated cores which have otherwise-comparable properties, is poor. The formation from and interaction with the large-scale environment has a significant impact on the line emission properties of the cores, making isolated models unsuitable for interpreting observational data. [ABSTRACT FROM AUTHOR]

Extremely/super low frequency (ELF/SLF) electromagnetic (EM) waves offer efficient propagation in challenging cross‐medium environments. However, conventional coil antennas, when emitting ELF/SLF EM waves, face constraints related to size, radiation efficiency, and high power consumption. To overcome these limitations, a disc‐rod structured piezoelectric rotating resonator is proposed, which can turn a NdFeB permanent magnet disc into rotation with an impressive high‐speed up to 10 000 r min−1 via wobbling motion of the rod tip, effectively generating ELF/SLF magnetic field radiation via rotational oscillation other than common linear and swinging oscillation of the magnetic dipole moments. The piezo‐turned magnetic rotation (PTMR) method leads to a two to five‐fold enhancement in magnetic field emission compared to existing piezo‐actuated acoustic resonant antennas, and a 370 times higher emitting efficiency compared to the traditional coil antenna with a comparable size. In contrast to unidirectional EM wave radiation at their solely resonant frequencies, the PTMR antenna showcases omnidirectional B‐field radiation with continuous tunability in a dual frequency band spanning from 10 to 100 Hz. Moreover, an air–seawater cross‐medium magnetic field communication is successfully demonstrated. With outstanding performance metrics, the PTMR antenna emerges as a promising solution for efficient long‐distance ELF/SLF cross‐medium communication. [ABSTRACT FROM AUTHOR]

The details of the dynamo process in the Sun are an important aspect of research in solar-terrestrial physics and astrophysics. The surface part of the dynamo can be constrained by direct observations, but the subsurface part lacks direct observational constraints. The torsional oscillations, a small periodic variation of the Sun's rotation with the solar cycle, are thought to result from the Lorentz force of the cyclic magnetic field generated by the dynamo. In this study, we aim to discriminate between three Babcock–Leighton dynamo models by comparing the zonal acceleration of the three models with the observed one. The property that the poleward and equatorward branches of the torsional oscillations originate from about ±55° latitudes with their own migration time periods serves as an effective discriminator that could constrain the configuration of the magnetic field in the convection zone. The toroidal field, comprising poleward and equatorward branches separated at about ±55° latitudes, can generate the two branches of the torsional oscillations. The alternating acceleration and deceleration bands in time are the other property of the torsional oscillations that discriminates between the dynamo models. To reproduce this property, the phase difference between the radial (B r ) and toroidal (B ϕ ) components of the magnetic field near the surface should be about π /2. [ABSTRACT FROM AUTHOR]

The regular behavior of the pulsations of high-amplitude δ Sct (HADS) stars gives a greater chance to investigate the interiors of stars. We analyzed seven HADS stars showing peak-to-peak amplitudes of more than 0.3 mag that were newly observed by TESS. We obtained that TIC 374753270, TIC 710783, and TIC 187386415 pulsate in fundamental radial mode; also, TIC 130474019 and TIC 160120432 show double radial modes. On the other hand, TIC 148357344 and TIC 278119167 demonstrate triple-mode behavior. Our analysis shows that these seven stars are close to the red edge of the (inside) instability strip in the Hertzsprung–Russell diagram. The fundamental mode of these seven targets follows the period–luminosity (PL) relation for δ Sct stars. However, TIC 278119167 deviates slightly from the fundamental PL relation. The double-mode and triple-mode HADS stars (TIC 130474019, TIC 160120432, TIC 148357344, and TIC 278119167) are in agreement with the period ratio ranges (fundamental to first and second overtones). Using the information of 176 HADS stars (Netzel and Smolec), we find a scaling relation ( [ Fe / H ] ∝ log (M 7.95 ± 0.15 L − 1.83 ± 0.11 P 0 0.79 ± 0.14 T eff 0.047 ± 0.02 )) between the metallicity ([Fe/H]) and mass (M), luminosity (L), effective temperature (T eff), and the fundamental period (P0). We estimate the metallicity of the seven newly identified HADS stars ranging from −0.62 to 0.37 dex. [ABSTRACT FROM AUTHOR]

The article explores the search for habitable exoplanets, focusing on challenges and discoveries around M-dwarf stars like TRAPPIST-1, an ultra-cool dwarf star. Topics include the difficulties of detecting atmospheres due to stellar activity, the potential habitability of planets like LHS 1140b, a rocky exoplanet with nitrogen-dominated atmospheres, and the exploration of larger, hydrogen-rich planets such as K2-18b, a sub-Neptune as potential "hycean" worlds hydrogen and ocean planets.

Mature neutron stars are expected to exhibit gravity g modes due to stratification caused by a varying matter composition. These modes are affected by nuclear reactions, leading to complex (damped) mode frequencies and the suppression of high-order g modes. This is in contrast with the common non-dissipative analysis which leads to an infinite g-mode spectrum. Focusing on the transition between the fast- and slow-reaction regimes, we examine the precise impact of nuclear reactions on the g-mode spectrum. The general framework for the analysis is presented along with sample numerical results for a matter model based on the BSk21 equation of state with a suitable parametrization for the reaction rates. [ABSTRACT FROM AUTHOR]

In this paper, we analyze weak gravitational lensing by taking the black hole solution in Einstein Cubic gravity with the Gibbons and Werner approach. We deduce the deflection angle of light in a nonplasma and plasma medium. Firstly, we derive the Gaussian optical curvature and apply the Gauss–Bonnet theorem to find the deflection angle for the black hole spherically symmetric space–time. Additionally, we examine the graphical behavior of the deflection angle caused by the black hole in the presence of the nonplasma and plasma medium. Further, we use Einstein cubic gravity black hole geometry to discuss the quasi-periodic oscillations, effective force, and emission energy. [ABSTRACT FROM AUTHOR]

The effect of metallicity on the theoretical and empirical period–luminosity relations of Cepheid variables is not well understood and remains a highly debated issue. Here, we examine empirical colour–magnitude diagrams (CMDs) of Classical and Type-II Cepheids in the Magellanic Clouds and compare those with the theoretically predicted instability strip (IS) edges. We explore the effects of incorporating turbulent flux, turbulent pressure, and radiative cooling into the convection theory on the predicted IS at various metallicities using Modules for Experiments in Stellar Astrophysics – Radial Stellar Pulsations. We find that the edges become redder with the increasing complexity of convection physics incorporated in the fiducial convection sets, and are similarly shifted to the red with increasing metallicity. The inclusion of turbulent flux and pressure improves the agreement of the red edge of the IS, while their exclusion leads to better agreement with observations of the blue edge. About 90 per cent of observed stars are found to fall within the predicted bluest and reddest edges across the considered variations of turbulent convection parameters. Furthermore, we identify and discuss discrepancies between theoretical and observed CMDs in the low-effective temperature and high-luminosity regions for stars with periods greater than ∼20 d. These findings highlight the potential for calibrating the turbulent convection parameters in stellar pulsation models or the prediction of a new class of rare, long-period, 'red Cepheids', thereby improving our understanding of Cepheids and their role in cosmological studies. [ABSTRACT FROM AUTHOR]

The crust region is a tiny fraction of neutron stars, but it has a variety of physical properties and plays an important role in astronomical observations. One of the properties characterizing the crust is elasticity. In this review, with the approach of asteroseismology, we systematically examine neutron star oscillations excited by crust elasticity, adopting the Cowling approximation. In particular, by identifying the quasi-periodic oscillations observed in magnetar flares with the torsional oscillations, we make a constraint on the nuclear saturation parameters. In addition, we also discuss how the shear and interface modes depend on the neutron star properties. Once one detects an additional signal associated with neutron star oscillations, one can obtain a more severe constraint on the saturation parameters and/or neutron star properties, which must be a qualitatively different constraint obtained from terrestrial experiments and help us to complementarily understand astrophysics and nuclear physics. [ABSTRACT FROM AUTHOR]

In the phenomenon of mixed-mode oscillations, transitions between large-amplitude and small-amplitude oscillations may lead to anomalous jitter in the probe of a tapping mode atomic force microscope (TM-AFM) during the scanning process, thereby affecting the accuracy and clarity of the topographical images of the tested sample's surface. This work delves deeply into various mixed-mode oscillations and the corresponding formation mechanisms in TM-AFM under low-frequency resonant excitation. Through a detailed analysis of bifurcation sets of the fast subsystem, we found that the system's mixed-mode oscillations encompass the typical two coexisting branches and the novel three coexisting branches of equilibrium point attractors. In the stable case, a certain transition pattern in phase trajectory can be observed involving two jumps and four jumps, switching between quiescent and spiking states. In the bi-stable case, the trajectory undergoes distinct transitions decided by whether to pass through or crossover the middle branch of attractors when bifurcation occurs. By applying basin of attraction and fast–slow analysis methods, we unfold the dynamic mechanism of mixed-mode oscillations with distinct switching patterns. Our research contributes to a better understanding of complex oscillations of TM-AFM and provides valuable insights for improving image quality and measurement precision while mitigating detrimental oscillations. [ABSTRACT FROM AUTHOR]

The dynamics of two-dimensional dust clusters in plasma environment are studied at different strengths of a transverse external magnetic field, via Langevin dynamics simulation. The collective oscillation spectra obtained from simulation are compared with the dispersion relation derived from the analytical calculation under harmonic approximation. At high magnetic field strength, in the case of a linear chain, a longitudinal optic branch emerges, whereas in the case of a 2D isotropic cluster, two clear distinct branches appear, with the high frequency branch approaching cyclotron frequency. Mean squared displacement is obtained for the 2D cluster as a probe of single particle dynamics at different values of magnetization. At a larger value of coupling parameter, the cluster exhibits a crossover from normal to superdiffusive behavior with the change in the magnetic field strength, which is a result of the competition between the cyclotron and the harmonic time period. However, at a lower value of coupling parameter, the cluster remains subdiffusive at all field strengths. The study brings out several novel features of magnetized dust clusters in complex plasma environments. [ABSTRACT FROM AUTHOR]

Among the critical factors contributing to the decline in the aerodynamic performance of near-space aircraft under low Reynolds number conditions, a significant one lies in the occurrence of laminar separation bubbles forming on the wings. Within the scope of this investigation, the primary research methodology adopted involves utilizing an unsteady numerical simulation technique rooted in a spring-smoothed dynamic grid system. This study meticulously examines the aerodynamic attributes and flow patterns exhibited by an airfoil undergoing partial oscillation, thereby elucidating the underlying mechanisms through which such oscillations lead to enhanced lift and diminished drag forces. The outcomes of this research reveal that the imposition of partial oscillation engenders a noteworthy augmentation of 4.9% in the lift coefficient of the airfoil, concurrent with a substantial diminution of 15.3% in its drag coefficient when juxtaposed against the non-deforming counterpart. The oscillation frequency exerts a profound influence on both the onset location of transition and the extent of the laminar separation bubble's development. As the oscillation frequency escalates, it follows an initial ascending trend in the lift coefficient of the airfoil, followed by a subsequent decline, whereas the drag coefficient exhibits an initial decrement prior to a rising tendency, thus indicating the existence of an optimal frequency point where the airfoil achieves its most favorable aerodynamic characteristics. It is observed that the flow control effects are optimally pronounced when the region subjected to partial oscillation is proximate to the airfoil's leading edge or situated precisely at the centroid of the laminar separation bubble. [ABSTRACT FROM AUTHOR]

It is expected that the extreme mass accretion rate onto strongly magnetized neutron stars results in the appearance of accretion columns above the stellar surface. For a distant observer, rotation of a star results in periodic variations of X-ray flux. Because the mass accretion rate fluctuates around the average value, the pulse profiles are not stable and demonstrate fluctuations as well. In the case of bright X-ray pulsars, however, pulse fluctuations are not solely attributed to variations in the mass accretion rate. They are also influenced by the variable height of the columns, which is dependent on the mass accretion rate. This study delves into the process of pulse profile formation in bright X-ray pulsars, taking into account stochastic fluctuations in the mass accretion rate, the corresponding variations in accretion column geometry, and gravitational bending. Our analysis reveals that potential eclipses of accretion columns by a neutron star during their spin period should manifest specific features in pulse profile variability. Applying a novel pulse profile analysis technique, we successfully detect these features in the bright X-ray transient V 0332+53 at luminosities |$\gtrsim 2\times 10^{38}\, {\rm erg\ \rm s^{-1}}$|⁠. This detection serves as compelling evidence for the eclipse of an accretion column by a neutron star. Detection of the eclipse places constraints on the relation between neutron star mass, radius, and accretion column height. Specifically, we can establish an upper limit on the accretion column height, which is crucial for refining theoretical models of extreme accretion. [ABSTRACT FROM AUTHOR]

Asteroseismology can precisely characterize stars, but the accuracy of seismic inference is still an open question. In this work, we use three evolved stars, including one late subgiant (EPIC 211411922) and two young red giants (EPIC 211409560 and EPIC 211416749) in the open cluster M67 to validate seismic inferences of stellar mass and age. We start by measuring oscillation mode frequencies and identifying acoustic and mixed modes in all three stars. We then fit the stars to determine their masses and ages with a detailed modelling approach. Our age estimates for all stars agree well with the literature consensus age range of M67 (3.0–5.0 Gyr). Mass estimates for EPIC 211411922 and EPIC 211409560 are sensible because they are slightly higher than the typical turn-off mass of the cluster. The inferred mass for EPIC 211416749 is underestimated by 5–10 per cent compared with the turn-off mass, but this could be caused by poor data quality. Our results indicate that the detailed modelling can determine sensible masses and ages for evolved stars near the base of the red giant branch. [ABSTRACT FROM AUTHOR]

We use 3D computer modelling to investigate the time-scales and radiative output from maser flares generated by the impact of shock waves on astronomical unit-scale clouds in interstellar and star-forming regions, and in circumstellar regions in some circumstances. Physical conditions are derived from simple models of isothermal hydrodynamic (single-fluid) and C-type (ionic and neutral fluid) shock waves, and based on the ortho-H2O 22-GHz transition. Maser saturation is comprehensively included, and we find that the most saturated maser inversions are found predominantly in the shocked material. We study the effect on the intensity, flux density, and duration of flares of the following parameters: the pre-shock level of saturation, the observer's viewpoint, and the shock speed. Our models are able to reproduce observed flare rise times of a few times 10 d, specific intensities of up to 105 times the saturation intensity and flux densities of order 100(R / d)2 Jy from a source of radius R astronomical units at a distance of d kiloparsec. We found that flares from C-type shocks are approximately five times more likely to be seen by a randomly placed observer than flares from hydrodynamically shocked clouds of similar dimensions. We computed intrinsic beaming patterns of the maser emission, finding substantial extension of the pattern parallel to the shock front in the hydrodynamic models. Beaming solid angles for hydrodynamic models can be as small as 1.3 × 10−5 sr, but are an order of magnitude larger for C-type models. [ABSTRACT FROM AUTHOR]

Oscillating neutron stars are sources of continuous gravitational waves. We study analytically the excitation of stellar oscillations by the mechanical impact on the stellar surface of 'clumps' of stochastically accreted matter. We calculate the waveform and spectrum of the gravitational wave signal emitted by the accretion-driven pulsations. Results are generated for an idealized model of a non-rotating, unmagnetized, one-component star with uniform polytropic index n poly assuming Newtonian gravity and the Cowling approximation. We find that the excited mode amplitudes grow with increasing n poly and mode order n. The gravitational wave signal forms a sequence of amplitude-modulated packets for n poly = 1, lasting ∼10−3 s after each impact. The gravitational wave strain increases with increasing n poly, but decreases with increasing n and increasing multipole order l for n poly = 1. In the observing band of current long-baseline interferometers, g modes emit higher, narrower peaks in the amplitude spectral density than f and p modes, with the highest peaks reaching ∼10−26 Hz−1/2 for modes with damping time τ nl ∼ 108 yr. The root-mean-square strain h rms, calculated by summing over modes with 2 ≤ l ≤ 4 and τ nl ≤ 108 yr, spans the range 10−33 ≤ h rms ≤ 10−32 for 1 ≤ n poly ≤ 2. [ABSTRACT FROM AUTHOR]

The flow-induced vibrations (FIVs) of two identical tandem square cylinders with mass ratio m*=3.5 at Reynolds number Re=150 are investigated through two-dimensional direct numerical simulation (DNS) and linear stability analysis over a parameter range of spacing ratio 1.5=L*=5 and reduced velocity 3=Ur =34. Three kinds of FIV responses, namely vortex-induced vibration (VIV), biased oscillation (BO) and galloping (GA), are identified. The FIVs are then further classified into the branches of initial VIV (IV), resonant VIV (RV and RV'), flutter-induced VIV (FV), desynchronized VIV (DV), VIV developing from GA (GV), transitional state between VIV and GA (TR), BO and GA based on the characteristics of the vibration responses. The transitions among different FIV branches are examined by combining the DNS with linear stability analysis, where the transition boundaries among the VIV, BO and GA branches over the concerned parameters are identified on the branch maps. The transition from IV to RV or RV' is found to be related to the unstable wake mode, while the FV, transiting from RV or RV', is induced by the unstable structural factor in the wake-structure mode. The structural instability is considered as the physical origin of GA, whereas the mode competition between unstable wake and structure leads to DV, GV and TR, and thus delays the appearance of GA. The transition fromDV to BO with biased equilibrium position, accompanied by the even-order harmonic frequencies, is essentially induced by the symmetry breaking bifurcation. [ABSTRACT FROM AUTHOR]

In this short review we present the recent progresses in modelling fast rotating stars in two dimensions. We thus give a brief description of the features of the public domain code ESTER that can compute self-consistently the structure and the large-scale flows (differential rotation and meridional circulation) of an axisymmetric stellar model of a (fast) rotating early-type main sequence star. We illustrate these modelling with the recent results obtained on Altair, a nearby extremely fast rotator. We then discuss the various way mixing takes place in the stably stratified radiative envelope of early-type stars, and especially in massive ones where the radiative winds add a new source of large-scale flows, which are shown to be strongly anisotropic and very difficult to represent in one dimension. [ABSTRACT FROM AUTHOR]

Spectropolarimetic campaigns have established that large-scale magnetic fields are present at the surfaces of approximately 10% of massive dwarf stars. However, there is a dearth of magnetic field measurements for their deep interiors. Asteroseismology of gravity-mode pulsations combined with rotating magneto-hydrodynamical calculations of the early-B main-sequence star HD 43317 constrain its magnetic field strength to be approximately 5 × 105 G just outside its convective core. This proof-of-concept study for magneto-asteroseismology opens a new window into the observational characterisation of magnetic fields inside massive stars. [ABSTRACT FROM AUTHOR]

Context. Dust particles in protoplanetary disks rotate at velocities exceeding those of the surrounding gas due to a lack of pressure support. Consequently, they experience a headwind from the gas that drives them toward the central star. Radial drift occurs on timescales much shorter than those inferred from disk observations or those required for dust to aggregate and form planets. Additionally, turbulence is often assumed to amplify the radial drift of dust in planet-forming disks when modeled through an effective viscous transport. However, the local interactions between turbulent eddies and particles are known to be significantly more intricate than in a viscous fluid. Aims. Our objective is to elucidate and characterize the dynamic effects of Keplerian turbulence on the mean radial and azimuthal velocities of dust particles. Methods. We employed 2D shearing-box incompressible simulations of the gas, which is maintained in a developed turbulent state while rotating at a sub-Keplerian speed. Dust is modeled as Lagrangian particles set at a Keplerian velocity, therefore experiencing a radial force toward the star through drag. Results. Turbulent eddies are found to reduce the radial drift, while simultaneously enhancing the azimuthal velocities of small particles. This dynamic behavior arises from the modification of dust trajectories due to turbulent eddies. [ABSTRACT FROM AUTHOR]

Exoplanets in the ultra-hot Jupiter regime provide an excellent laboratory for testing the impact of stellar irradiation on the dynamics and chemical composition of gas giant atmospheres. In this study, we observed two transits of the ultra-hot Jupiter WASP-189 b with MAROON-X/Gemini-North to probe its high-altitude atmospheric layers, using strong absorption lines. We derived posterior probability distributions for the planetary and stellar parameters by calculating the stellar spectrum behind the planet at every orbital phase during the transit. This was used to correct the Rossiter–McLaughlin imprint on the transmission spectra. Using differential transmission spectroscopy, we detect strong absorption lines of Ca+, Ba+, Na, Hα, Mg, Fe, and Fe+, providing an unprecedented and detailed view of the atmospheric chemical composition. Ca+ absorption is particularly well suited for analysis through time-resolved narrow-band spectroscopy, owing to its transition lines formed in high-altitude layers. The spectral absorption lines show no significant blueshifts that would indicate high-altitude day-to-night winds, and further analysis is needed to investigate the implications for atmospheric dynamics. These high signal-to-noise observations provide a benchmark data set for testing high-resolution retrievals and the assumptions of atmospheric models. We also simulate observations of WASP-189 b with ANDES/ELT, and show that ANDES will be highly sensitive to the individual absorption lines of a myriad of elements and molecules, including TiO and CO. [ABSTRACT FROM AUTHOR]

Context. Binary stars cannot be fully understood without assessing the interaction effects between the two components and the impact of these effects on observational diagnostics. Periastron brightening events, also known as the heartbeat phenomenon, are a clear manifestation of this type of interaction. Aims. We aim to explore the role of tidal shear energy dissipation in stars undergoing periastron brightening events. Methods. We performed a computation from first principles that uses a quasi-hydrodynamic Lagrangian scheme to simultaneously solve the orbital motion and the equations of motion of a 3D grid of volume elements covering the inner, rigidly rotating "core" of a tidally perturbed star. The equations of motion include the gravitational acceleration of both stars, the centrifugal, Coriolis, gas pressure accelerations, and viscous coupling between volume elements. The method is illustrated for a grid of model binary systems with a 10 M⊙ primary that is perturbed by a 6.97 M⊙ companion in eccentric orbits (e = 0 − 0.7). The model is then applied to the heartbeat star MACHO 80.7443.1718. Results. We find an increase by factors ∼10−6–10−3 in tidal shear energy dissipation at periastron, consistent with the majority of observed heartbeat stars. The magnitude of the periastron effect correlates with the degree of departure from synchronicity: stars rotating much faster or much slower than the synchronous rate at periastron present the strongest effect. We confirm that for eccentricities ≤0.3, pseudo-synchronization occurs for 0.8 < ω/Ωave < 1, where Ωave is the average orbital angular velocity. The minimum energy rotation rate (pseudo-synchronism) for e = 0.5 and 0.7 occurs for 1.0 < ω/Ωave < 1.15. The tidal shear energy dissipation model reproduces from first principles the ∼23% maximum brightness enhancement at periastron of MACHO 80.7443.1718. Conclusions. Our results suggest that the magnitude and shape of the heartbeat signal may serve as diagnostics for the internal stellar rotation and turbulent viscosity values. [ABSTRACT FROM AUTHOR]

In recent years, about 150 low-mass white dwarfs (WDs), typically with masses below 0.4 M⊙, have been discovered. The majority of these low-mass WDs are observed in binary systems as they cannot be formed through single-star evolution within Hubble time. In this work, we present a comprehensive analysis of the double low-mass WD eclipsing binary system J2102−4145. Our investigation encompasses an extensive observational campaign, resulting in the acquisition of approximately 28 h of high-speed photometric data across multiple nights using NTT/ULTRACAM, SOAR/Goodman, and SMARTS-1m telescopes. These observations have provided critical insights into the orbital characteristics of this system, including parameters such as inclination and orbital period. To disentangle the binary components of J2102−4145, we employed the XTGRID spectral fitting method with GMOS/Gemini-South and X-shooter data. Additionally, we used the PHOEBE package for light curve analysis on NTT/ULTRACAM high-speed time-series photometry data to constrain the binary star properties. Our analysis unveils remarkable similarities between the two components of this binary system. For the primary star, we determine Teff,1 = 13 688−72+65 K, log g1 = 7.36 ± 0.01, R1 = 0.0211 ± 0.0002 R⊙, and M1 = 0.375 ± 0.003 M⊙, while, the secondary star is characterised by Teff,2 = 12952−66+53 K, log g2 = 7.32 ± 0.01, R2 = 0.0203−0.0003+0.0002 R⊙, and M2 = 0.314 ± 0.003 M⊙. Furthermore, we found a notable discrepancy between Teff and R of the less massive WD, compared to evolutionary sequences for WDs from the literature, which has significant implications for our understanding of WD evolution. We discuss a potential formation scenario for this system which might explain this discrepancy and explore its future evolution. We predict that this system will merge in ∼800 Myr, evolving into a helium-rich hot subdwarf star and later into a hybrid He/CO WD. [ABSTRACT FROM AUTHOR]