Rapid Rotation Research Articles

Hydrogen-free Wolf-Rayet stars: Helium stars with envelope-inflation structure and rotation

Context. Observations have shown that the effective temperature of hydrogen-free Wolf-Rayet (WR) stars is considerably lower than that of the standard model, which means that the radius of the observed H-free WR stars is several times larger than that estimated by the standard model. The envelope inflation structure (EIS) caused by the radiation luminosity being close to the Eddington luminosity in the iron opacity peak region of H-free WR stars may be the key to resolving the radius problem of H-free WR stars. Aims. We study the structure and evolution of helium (He) stars with the EIS and discuss the influence of rotation on these He stars. We aim to explain the radius problem of H-free WR stars observed in the Milky Way (MW) and the Large Magellanic Cloud (LMC) through the He stars. Methods. Using the Modules for Experiments in Stellar Astrophysics code, we compute the evolution of He stars with and without MLT++ prescriptions, and discuss their effects on the EIS. We calculated the evolution of He stars using a new mass-loss rate formula and three different relative rotational velocities and compared our results with observations on Hertzsprung–Russell diagrams. Results. The EIS has different effects on the structure and evolution of He stars with different masses. Due to the luminosity well below the Eddington limit, low-mass He stars with an initial mass of less than 12 M⊙ do not produce EIS with or without the MLT++ prescription. High-mass He stars with an initial mass exceeding 12 M⊙ and without the MLT++ prescription produce the EIS. Since the EIS is Eddington factor Γ-dependent, its radius increases with the increase in metallicity and decreases with rotational velocity increase. For rotating low-mass He stars, since the rotational mixing timescale is smaller than the evolutionary timescale, rotational mixing can increase the lifetime and allow He stars to evolve into WC stars during the helium giant phase. For rotating high-mass He stars, since rotation increases the mass-loss rate, the radius of the EIS decreases as rotational velocity increases. The rotation-decay timescale of rapidly rotating He stars is very short, and the rapidly rotating He stars only appear within the first one-tenth of their lifetime, which is consistent with the observations of WR stars. Conclusions. The low-luminosity (log(L/L⊙)≤5.2) H-free WR stars in the MW and the LMC can be explained by the helium giant phase in low-mass He stars, the high XC and XO in WC stars can only evolve through low-mass He stars with a rapid rotation. High-mass He stars with the EIS can explain H-free WR stars with a luminosity exceeding 105.7 L⊙ and an effective temperature above 104.7 K in the MW. They can also explain H-free WR stars on the right-hand side of the He zero-age main sequence in the LMC. High-mass stars with the EIS evolve into WO stars at the final evolution stage, and the shorter lifetime fraction is consistent with the small number of observed WO stars.

Rotated Transtensional Basins Formed During Back‐Arc Spreading in Japan: Simultaneous Rapid Tectonic Rotation and Basin Subsidence

AbstractPrevious models of strike‐slip basins do not consider the rotation of the basin itself; however, we show that the Tanakura transtensional basin in Japan was rotated and propose that this basin rotation was related to rifting caused by back‐arc spreading. The Tanakura Basin was formed by displacement along the Tanakura Fault Zone, one of the major active transform faults during the opening of the Sea of Japan. We carried out paleomagnetic analyses and U–Pb dating of the Neogene Tanakura Basin fill rocks. We present a revised, high‐precision stratigraphic record for the Neogene Tanakura Basin fill sequence shows that vertical‐axis counter‐clockwise rotation occurred between ∼17.2 and ∼16.6 Ma. Comparison with paleomagnetic data from adjacent areas shows that rotation was restricted to the basin. In addition, the timing of basin rotation corresponds to the rifting phase of the Tanakura Basin, suggesting that rapid basin subsidence owing to rifting and rapid basin rotation owing to strike‐slip faulting occurred simultaneously. The Tanakura Basin has the characteristics of both rift and transtensional basins that have experienced rotation. This study reveals the detailed relationships between the development and rotation of the Tanakura Basin: rifting‐related subsidence accompanied by basin rotation. Rifting owing to back‐arc spreading may have been accompanied by tectonic basin rotation in Northeast Japan, leading to variations in the magnitude and age of rotation, as the rifting occurred at different times in different locations.

Heat Transport and Convective Velocities in Compositionally Driven Convection in Neutron Star and White Dwarf Interiors

We investigate heat transport associated with compositionally driven convection driven by crystallization at the ocean–crust interface in accreting neutron stars, or growth of the solid core in cooling white dwarfs. We study the effect of thermal diffusion and rapid rotation on the convective heat transport, using both mixing length theory and numerical simulations of Boussinesq convection. We determine the heat flux, composition gradient, and Péclet number, Pe (the ratio of thermal diffusion time to convective turnover time) as a function of the composition flux. We find two regimes of convection with a rapid transition between them as the composition flux increases. At small Pe, the ratio between the heat flux and composition flux is independent of Pe, because the loss of heat from convecting fluid elements due to thermal diffusion is offset by the smaller composition gradient needed to overcome the reduced thermal buoyancy. At large Pe, the temperature gradient approaches the adiabatic gradient, saturating the heat flux. We discuss the implications for cooling of neutron stars and white dwarfs. Convection in neutron stars spans both regimes. We find rapid mixing of neutron star oceans, with a convective turnover time of the order of weeks to minutes depending on rotation. Except during the early stages of core crystallization, white dwarf convection is in the thermal-diffusion-dominated fingering regime. We find convective velocities much smaller than recent estimates for crystallization-driven dynamos. The small fraction of energy carried as kinetic energy calls into question the effectiveness of crystallization-driven dynamos as an explanation for observed magnetic fields in white dwarfs.

3D Radiation-hydrodynamic Simulations Resolving Interior of Rapidly Accreting Primordial Protostar

Direct collapse of supermassive stars is a possible pathway to form supermassive black hole seeds at high redshifts. Whereas previous three-dimensional (3D) simulations demonstrate that supermassive stars form via rapid mass accretion, those resolving the stellar interior have been limited. Here, we report 3D radiation-hydrodynamic (RHD) simulations following the evolution of rapidly accreting protostars resolving the stellar interior. We use an adaptive mesh refinement code with our newly developed RHD solver employing an explicit M1 closure method. We follow the early evolution until the stellar mass reaches ∼10 M ⊙ from two different initial configurations of spherical and turbulent clouds. We demonstrate that, in both cases, a swollen protostar whose radius is 100–1000 R ⊙ appears, as predicted by the stellar evolution calculations. Its effective temperature remains a few thousand Kelvin, and the radiative feedback by ionizing photons is too weak to disturb the accretion flow up to the epoch examined in this work. In the turbulent case, the protostar rotates rapidly at more than 0.4 times the Keplerian velocity owing to the angular momentum provided by the initial turbulence. The protostar approximates an oblate spheroid, and its equatorial radius is more than twice the polar radius. Our results suggest that we need to consider the rapid stellar rotation to elucidate the realistic 3D protostellar evolution in the supermassive star formation.

Rotation Reduces Convective Mixing in Jupiter and Other Gas Giants

Recent measurements of Jupiter’s gravitational moments by the Juno spacecraft and seismology of Saturn’s rings suggest that the primordial composition gradients in the deep interior of these planets have persisted since their formation. One possible explanation is the presence of a double-diffusive staircase below the planet’s outer convection zone, which inhibits mixing across the deeper layers. However, hydrodynamic simulations have shown that these staircases are not long-lasting and can be disrupted by overshooting convection. In this Letter, we suggests that planetary rotation could be another factor for the longevity of primordial composition gradients. Using rotational mixing-length theory and 3D hydrodynamic simulations, we demonstrate that rotation significantly reduces both the convective velocity and the mixing of primordial composition gradients. In particular, for Jovian conditions at t ∼ 108 yr after formation, rotation reduces the convective velocity by a factor of 6, and in turn, the kinetic energy flux available for mixing gets reduced by a factor of 63 ∼ 200. This leads to an entrainment timescale that is more than 2 orders of magnitude longer than without rotation. We encourage future hydrodynamic models of Jupiter and other gas giants to include rapid rotation because the decrease in the mixing efficiency could explain why Jupiter and Saturn are not fully mixed.

The evolutionary properties of the blue loop under the influence of rapid rotation and low metallicity

Context. The physical mechanism leading to the formation of the blue loop in the Hertzsprung–Russell (HR) diagram is not satisfactorily explained by the evolutionary track of single stars. Rapid rotation and low metallicity drastically modify the internal structures and surface compositions of stars. Therefore, they provide a very significant pattern to investigate the evolutionary properties of the blue loop. Aims. In this paper, we mainly explore how rapid rotation and low metallicity have an important impact on the occurrence and extension of the blue loop. Methods. To this end, we implemented the rotating stellar evolution model, including the angular momentum transportation and chemical element mixing. We incorporated several initial rotational velocities and two characteristic metallicities in various models to explore the blue loop extension. Results. The blue loop can occur when the hydrogen burning shell merges with the hydrogen–helium abundance discontinuity. We find that the blue loop extension strongly depends on the amplitude and gradient of the hydrogen–helium discontinuity. The hydrogen–helium discontinuity is created by the intermediate convective region or the convective dredge-up. A steeper hydrogen gradient in association with a greater amplitude of the hydrogen abundance discontinuity may favour a hotter star. Conclusions. Both the low metallicity and rapid rotation tend to restrain the development of the outer convective envelope and thus disfavour the occurrence and extension of the blue loop. There are three main reasons for this occurrence. Firstly, the helium core and its core potential can be enlarged by rotational mixing or low metallicity. Secondly, rapid rotation reduces the convective dredge-up depth in the star with Z = 0.014 and the mass extension of the intermediate convective region in the star with Z = 0.0008. Both of these phenomena lead to a reduction of the amplitude of the hydrogen abundance gradient. Thirdly, strong rotational mixing in the model (i.e. vini = 350 km s−1) with Z = 0.0008 reduces the energy generation rate from the hydrogen burning shell. Without bending towards higher effective temperature in the HR diagram, the additional helium brought near the H-burning shell associated with the larger He core can cause the star to expand towards becoming a red giant star directly after the core hydrogen burning. Rapid rotation and low metallicity tend to produce surface enrichment of the ratio of nitrogen to carbon and reduce the 12C left in the core; this has an important influence on the stellar compactness of the supernovae progenitor.

Assessing the effect of rotational grazing adoption in Iberian silvopastoral systems with Normalized Difference Vegetation Index time series

Adaptive Multi-Paddock (AMP) is a grazing system which combines intensive, rapid grazing livestock rotation with relatively short grazing periods and long recovery time after grazing. The study assesses, under Mediterranean silvopastoral systems, changes in pasture phenology and spatial variability after adopting the AMP under contrasting land cover (Wooded Grassland vs Grassland ) with a remote sensing approach based on the time-series analysis of Normalized Difference Vegetation Index (NDVI) from remote sensing through Landsat satellite. The study revealed an overall positive effect of rotational grazing on pasture phenology and NDVI spatial variability. The AMP adoption resulted in higher estimated values of NDVI at the beginning (under grassland land cover), the end, and the peak of the growing season, while no differences were observed in parameters estimating the length of the growing season. The spatial variability of NDVI was always lower under AMP than in continuously grazed areas, except in the early stages of the growing season under grassland land cover. The results suggested that in a relatively short period (4-5 years), the AMP grazing system can represent a strategy to improve forage availability and exploitation by grazing animals under low stocking rates in extensively managed Mediterranean silvopastoral systems.

The mechanical alignment of dust (MAD)

Context. Observations of polarized light emerging from aligned dust grains are commonly exploited to probe the magnetic field orientation in astrophysical environments. However, the exact physical processes that result in a coherent large-scale grain alignment are still far from being fully constrained. Aims. In this work, we aim to investigate the impact of a gas-dust drift on a microscopic level, potentially leading to a mechanical alignment of fractal dust grains and subsequently to dust polarization. Methods. We scanned a wide range of parameters of fractal dust aggregates in order to statistically analyze the average grain alignment behavior of distinct grain ensembles. In detail, the spin-up efficiencies for individual aggregates were determined utilizing a Monte Carlo approach to simulate the collision, scattering, sticking, and evaporation processes of gas on the grain surface. Furthermore, the rotational disruption of dust grains was taken into account to estimate the upper limit of possible grain rotation. The spin-up efficiencies were analyzed within a mathematical framework of grain alignment dynamics in order to identify long-term stable grain alignment points in the parameter space. Here, we distinguish between the cases of grain alignment in the direction of the gas-dust drift and the alignment along the magnetic field lines. Finally, the net dust polarization was calculated for each collection of stable alignment points per grain ensemble. Results. We find the purely mechanical spin-up processes within the cold neutral medium to be sufficient enough to drive elongated grains to a stable alignment. The most likely mechanical grain alignment configuration is with a rotation axis parallel to the drift direction. Here, roundish grains require a supersonic drift velocity, while rod-like elongated grains can already align for subsonic conditions. We predict a possible dust polarization efficiency in the order of unity resulting from mechanical alignment. Furthermore, a supersonic drift may result in a rapid grain rotation where dust grains may become rotationally disrupted by centrifugal forces. Hence, the net contribution of such a grain ensemble to polarization drastically reduces. In the presence of a magnetic field, the drift velocity required for the most elongated grains to reach a stable alignment is roughly one order of magnitude higher compared to the purely mechanical case. We demonstrate that a considerable fraction of a grain ensemble can stably align with the magnetic field lines and report a possible dust polarization efficiency of 0.6–0.9, indicating that a gas-dust drift alone can provide the conditions required to observationally probe the magnetic field structure. We predict that magnetic field alignment is highly inefficient when the direction of the gas-dust drift and magnetic field lines are perpendicular. Conclusions. Our results strongly suggest that mechanical alignment has to be taken into consideration as an alternative driving mechanism where the canonical radiative torque alignment theory fails to account for the full spectrum of available dust polarization observations.

Jupiter’s cloud-level variability triggered by torsional oscillations in the interior

Jupiter’s weather layer exhibits long-term and quasi-periodic cycles of meteorological activity that can completely change the appearance of its belts and zones. There are cycles with intervals from 4 to 9 years, dependent on the latitude, which were detected in 5-μm radiation, which provides a window into the cloud-forming regions of the troposphere; however, the origin of these cycles has been a mystery. Here we propose that magnetic torsional oscillations arising from the dynamo region could modulate the heat transport and hence be ultimately responsible for the variability of the tropospheric banding. These axisymmetric torsional oscillations are magnetohydrodynamic waves influenced by rapid rotation, which have been detected in Earth’s core, and have been recently suggested to exist in Jupiter by the observation of magnetic secular variations by Juno. Using the magnetic field model JRM33, together with a density distribution model, we compute the expected speed of these waves. For the waves excited by variations in the zonal jet flows, their wavelength can be estimated from the width of the alternating jets, yielding waves with a half-period of 3.2–4.7 years at 14–23° N, consistent with the intervals in the cycles of variability of Jupiter’s North Equatorial Belt and North Temperate Belt identified in the visible and infrared observations. The nature of these waves, including the wave speed and the wavelength, is revealed by a data-driven technique, dynamic mode decomposition, applied to the spatiotemporal data for 5-μm emission. Our results indicate that exploration of these magnetohydrodynamic waves may provide a new window to the origins of quasi-periodic patterns in Jupiter’s tropospheric clouds and to the internal dynamics and the dynamo of Jupiter. Torsional waves extend into the deep interior of Jupiter where they can modulate the outgoing heat flux and couple with Jupiter’s weather layer to generate the observed quasi-periodic oscillations in the cloud deck. Such waves can be used to explore the interior structure of gas giants.

Hardware design and implementation of high-efficiency cube-root of complex numbers

This study presented an algorithm for fast hardware execution of complex cube root. In this algorithm, which is based on the Laurent series of ∛z function, first, the z-plane's numbers are mapped by using a rapid scaling and rotation operation to a pre-specified limited region, and then the sequences of the series are computed. The parameters of the algorithm are thoroughly analyzed and selected to achieve high precision. The algorithm has been implemented on a field programmable gate array-based platform using the Simulink HDL Coder tool and Xilinx ISE 14.7. In addition, the resource usage and speed parameters are carefully examined for the implementation of each step of the algorithm. Hardware was implemented in two 56-bit and 32-bit versions (for comparison). The 32-bit version occupies 140 slice Regs, 421 slice LUTs, and 5 DSP48s. The hardware with the capability of computing complex cube roots has appropriate specifications comparable with those of previous implementations of real cube root calculation on FPGA.

O024 Development and validation of a “lab in a box” for remote delivery of core reconstructive surgical skills

Abstract Introduction Junior doctors and aspiring surgical trainees can have limited surgical exposure and developmental teaching because of rapid rotations, inconsistent rotas, reduced theatre time, and high working pressures. The global pandemic has also initiated a paradigm shift in education, and the methods we use to deliver education. Our aims are to assess the feasibility and validity of a low cost, remote plastic surgical skills course in comparison to the same course delivered face-to-face. Methods Our bench-model simulation “Lab in a Box” design was delivered to students remotely and in person. The essential and advanced plastic surgery course included suturing, excision, tendon repair, and local flap design. We undertook a pilot course facilitated by an online platform using a two-device set up. Equipment, including synthetic tendons and skin substitutes, were distributed to each participant. Quantitative evaluation included a global rating assessment and task specific criteria using a 1-5 Likert scale. Results were compared to the face-to-face control group. Qualitative feedback was also collected. Results A total of 40 students were recruited. A total cost of less than £30 was achieved. Quantitative feedback demonstrated comparable outcomes in remote training vs face-to-face training. Students reported excellent quality of audio-visual material and equipment, clear feedback, and 100% would recommend this course. Conclusion The simulation training course developed provides high-quality, engaging, reproducible and low-cost surgical skills training that can be delivered via distance learning. This model can be used to improve surgical skills training both in the UK and globally in resource poor environments.

Discovery of a substellar companion in the TESS light curve of the δ Scuti/γ Doradus hybrid pulsator HD 31221

Context. Close-in, sub-stellar companions to δ Scuti type stars present a highly suitable testbed for examining how planetary-mass objects can influence stellar pulsations. Aims. We aim to constrain the mass of HD 31221 b, probe its atmosphere, and demonstrate how it affects the pulsational pattern of its host, HD 31221. Methods. We made use of the available data from the short-cadence Transiting Exoplanet Survey Satellite (TESS). We modeled the nine observed transits and the out-of-phase variations, including Doppler beaming, ellipsoidal variations, and the reflection effect. We also incorporated ground-based photometry from the MuSCAT2 imager installed at the 1.52 m Telescopio Carlos Sanchez in the Teide Observatory, Spain, as well as speckle interferometry from the Southern Astrophysical Research telescope. Results. We found HD 31221 b to have an orbital period of 4.66631 ± 0.00011 days, with a radius of 1.32 ± 0.14 RJ and a mass of 11.5 ± 10.3 MJ (from the ellipsoidal effect), making it consistent with either a brown dwarf or a giant planet. As HD 31221 is a rapid rotator (v sin I⋆ = 175.31 ± 1.74 km s−1), we deduced the spin-orbit misalignment to be λ = −121.6 ± 14.4° and I⋆ = 55.9 ± 11.3°. The phase curve is dominated by the reflection effect, with a geometric albedo of 1.58 ± 0.50. We also found evidence that HD 31221 is a δ Scuti/γ Doradus hybrid pulsator. There are three cases for which the 3rd, 85th, and 221st orbital harmonics almost exactly coincide with peaks in the Fourier spectrum of the star, hinting at tidally perturbed stellar oscillations. Conclusions. HD 31221 b is the third substellar object that is found to be disrupting the pulsations of its host, following HAT-P-2 and WASP-33. Additional photometric observations by CHEOPS and/or PLATO can be used to further constrain its mass and provide a more in-depth analysis of its atmosphere.

The rotation period distribution in the young open cluster NGC 6709

Open clusters serve as a useful tool for calibrating models of the relationship between mass, rotation, and age for stars with an outer convection zone due to the homogeneity of the stars within the cluster. Cluster-to-cluster comparisons are essential to determine whether the universality of spin-down relations holds. NGC 6709 is chosen as a more distant representative Pleiades-aged cluster for which no rotation periods of members have previously been obtained. This cluster is at a distance of over 1 kpc and has two red giant members. Isochrones place the age of the cluster at around 150 Myr, or approximately the same age as the Pleiades. Photometry is obtained over a multi-month observing season at the robotic observatory for STELLar Activity (STELLA). After basic processing, point-spread-function (PSF) photometry was derived using DAOPHOT II, and a suite of related software allowed us to create time series of relative magnitude changes for each star. Four time series analysis methods were then applied to these light curves to obtain rotation periods for members stars. We obtain, for the first time, rotation periods for 45 FGK cluster members of NGC 6709. We plot the Gaia DR3 colors of the member stars against their rotation periods and find a slow-rotating sequence with increasing rotation periods toward redder stars and a smaller clump of rapid rotators that have not yet joined this sequence. NGC 6709 has rotation periods very similar to those of another Pleiades-aged open cluster, NGC 2516.

How tidal waves interact with convective vortices in rapidly rotating planets and stars

Context. The dissipation of tidal inertial waves in planetary and stellar convective regions is one of the key mechanisms that drive the evolution of star–planet and planet–moon systems. This dissipation is particularly efficient for young low-mass stars and gaseous giant planets, which are rapid rotators. In this context, the interaction between tidal inertial waves and turbulent convective flows must be modelled in a realistic and robust way. In the state-of-the-art simulations, the friction applied by convection on tidal waves is commonly modeled as an effective eddy viscosity. This approach may be valid when the characteristic length scales of convective eddies are smaller than those of the tidal waves. However, it becomes highly questionable in the case where tidal waves interact with potentially stable large-scale vortices such as those observed at the poles of Jupiter and Saturn. The large-scale vortices are potentially triggered by convection in rapidly-rotating bodies in which the Coriolis acceleration forms the flow in columnar vortical structures along the direction of the rotation axis. Aims. We investigate the complex interactions between a tidal inertial wave and a columnar convective vortex. Methods. We used a quasi-geostrophic semi-analytical model of a convective columnar vortex, which is validated by numerical simulations. First, we carried out linear stability analysis using both numerical and asymptotic Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) methods. We then conducted linear numerical simulations of the interactions between a convective columnar vortex and an incoming tidal inertial wave. Results. The vortex we consider is found to be centrifugally stable in the range –Ωp ≤ Ω0 ≤ 3.62Ωp and unstable outside this range, where Ω0 is the local rotation rate of the vortex at its center and Ωp is the global planetary (stellar) rotation rate. From the linear stability analysis, we find that this vortex is prone to centrifugal instability with perturbations with azimuthal wavenumbers m = {0,1, 2}, which potentially correspond to eccentricity, obliquity, and asynchronous tides, respectively. The modes with m > 2 are found to be neutral or stable. The WKBJ analysis provides analytic expressions of the dispersion relations for neutral and unstable modes when the axial (vertical) wavenumber is sufficiently large. We verify that in the unstable regime, an incoming tidal inertial wave triggers the growth of the most unstable mode of the vortex. This would lead to turbulent dissipation. For stable convective columns, the wave-vortex interaction leads to the mixing of momentum for tidal inertial waves while it creates a low-velocity region around the vortex core and a new wave-like perturbation in the form of a progressive wave radiating in the far field. The emission of this secondary wave is the strongest when the wavelength of the incoming wave is close to the characteristic size (radius) of the vortex. Incoming tidal waves can also experience complex angular momentum exchanges locally at critical layers of stable vortices. Conclusions. The interaction between tidal inertial waves and large-scale coherent convective vortices in rapidly-rotating planets (stars) leads to turbulent dissipation in the unstable regime and complex behaviors such as mixing of momentum and radiation of new waves in the far field or wave-vortex angular momentum exchanges in the stable regime. These phenomena cannot be modeled using a simple effective eddy viscosity.

WD J004917.14−252556.81: the most massive pulsating white dwarf

ABSTRACT We present Apache Point Observatory (APO) and Gemini time-series photometry of WD J004917.14−252556.81, an ultramassive DA white dwarf with $T_{\rm eff} = 13\, 020$ K and log g = 9.34. We detect variability at two significant frequencies, making J0049−2525 the most massive pulsating white dwarf currently known with M⋆ = 1.31 M⊙ (for a CO core) or 1.26 M⊙ (for an ONe core). J0049−2525 does not display any of the signatures of binary mergers, there is no evidence of magnetism, large tangential velocity, or rapid rotation. Hence, it likely formed through single star evolution and is likely to have an ONe core. Evolutionary models indicate that its interior is ≳99 per cent crystallized. Asteroseismology offers an unprecedented opportunity to probe its interior structure. However, the relatively few pulsation modes detected limit our ability to obtain robust seismic solutions. Instead, we provide several representative solutions that could explain the observed properties of this star. Extensive follow-up time-series photometry of this unique target has the potential to discover a significant number of additional pulsation modes that would help overcome the degeneracies in the asteroseismic fits, and enable us to probe the interior of an ≈1.3 M⊙ crystallized white dwarf.

Pulsed counterclockwise rotation of the southwestern Sichuan Basin in response to the India-Asia convergence during 128-42 Ma

Deciphering the building history of the eastern Tibetan Plateau since the India-Asia convergence is crucial to understand geodynamic models of plateau formation. The Sichuan Basin adjacent to the eastern Tibetan Plateau margin potentially provides valuable records of when and how the Tibetan Plateau expanded eastward. In this study, we reconstruct ∼128–42 Ma rotation history of the southwestern Sichuan Basin using detailed paleomagnetic declination data from the Early Cretaceous to Eocene sedimentary sequence of ∼2400 m thick. A total of 78 sampling sites (774 samples) yield primary remanent magnetization confirmed by positive paleomagnetic tests. Our results show that the southwestern Sichuan Basin experienced a long-term clockwise rotation during 128–42 Ma which was interrupted by three transient and rapid counterclockwise rotation pulses. The earlier two pulses (86–82 Ma and 66–60 Ma) coincide with two India Plate acceleration episodes which are probably induced by the Marion and/or Réunion mantle plume upwelling, whereas the later pulse (53–46 Ma) temporally corresponds to the sudden slowdown of the India Plate caused by the India-Asia collision. Our findings indicate that the eastern Tibetan Plateau experienced prolonged and episodic building processes since the Late Cretaceous, long predating the traditional view of the late Miocene. The Tibetan Plateau was built synchronously from the Himalayas to its eastern margin. Lateral extrusion, block rotation, and strike-slip deformation collectively contribute to the mountain building in the eastern Tibetan Plateau region.

Thermal ringdown of a Kerr black hole: overtone excitation, Fermi-Dirac statistics and greybody factor

We find a significant destructive interference among Kerr overtones in the early ringdown induced by an extreme mass-ratio merger of a massive black hole and a compact object, and that the ringdown spectrum apparently follows the Fermi-Dirac distribution. We numerically compute the spectral amplitude of gravitational waves induced by a particle plunging into a Kerr black hole and study the excitation of multiple quasi-normal (QN) modes. We find that the start time of ringdown is before the strain peak of the signal and corresponds to the time when the particle passes the photon sphere. When the black hole has the near-extremal rotation, the Kerr QN frequencies are close to the fermionic Matsubara frequencies with the Hawking temperature and the chemical potential of the superradiant frequency. We indeed find that the absolute square of the spectral amplitude apparently follows the Fermi-Dirac distribution with the chemical potential of around the real QN frequency of the fundamental mode. Fitting the Boltzmann distribution to the data in higher frequencies, the best-fit temperature is found out to be close to the Hawking temperature, especially for rapid rotations. In the near-extremal limit, the gravitational-wave spectrum exhibits a would-be Fermi degeneracy with the Fermi surface at the superradiant frequency ω = μ H. We show that the greybody factor, i.e., the absorption cross section of a black hole, leads to the Fermi-Dirac distribution. As the greybody factor is another no-hair quantity of black holes, this opens a new possibility that we could test general relativity by observationally searching for the Boltzmann distribution in ringdown, provided that near-extremal black holes exist in the observable region. Indeed, it has been predicted that near-extremal supermassive black holes would exist at the center of some galaxies from the X-ray reflection spectroscopy. We could measure the mass and angular momentum of ringing black holes and could probe the Kerr/CFT correspondence by measuring the greybody factor imprinted on the ringdown spectrum.

Measurement of the Angular Momenta of Pre-main-sequence Stars: Early Evolution of Slow and Fast Rotators and Empirical Constraints on Spin-down Torque Mechanisms

We use TESS full-frame imaging data to investigate the angular momentum evolution of young stars in the Orion Complex. We confirm recent findings that stars with rotation periods faster than 2 days are overwhelmingly binaries, with typical separations of tens of au; such binaries quickly clear their disks, leading to a tendency for rapid rotators to be diskless. Among (nominally single) stars with rotation periods slower than 2 days, we observe the familiar gyrochronological horseshoe-shaped relationship of rotation period versus T eff, indicating that the processes that govern the universal evolution of stellar rotation on gigayear timescales are already in place within the first few megayears. Using spectroscopic , we determine the distribution of , revealing that the youngest stars are biased toward more pole-on orientations, which may be responsible for the systematics between stellar mass and age observed in star-forming regions. We are also able for the first time to make empirical, quantitative measurements of angular momenta and their time derivatives as functions of stellar mass and age, finding these relationships to be much simpler and monotonic as compared to the complex relationships involving rotation period alone; evidently, the relationship between rotation period and T eff is largely a reflection of mass-dependent stellar structure and not of angular momentum per se. Our measurements show that the stars experience spin-down torques in the range of ∼1037 erg at ∼1 Myr to ∼1035 erg at ∼10 Myr, which provide a crucial empirical touchstone for theoretical mechanisms of angular momentum loss in young stars.

Synchrotron radiation by slowly rotating fermions

We study the synchrotron radiation emitted by a charged fermion, rotating as a part of a larger system, in a constant magnetic field $B$ parallel to the axis of rotation. The rotation is classical and independent of the magnetic field. The angular velocity of rotation $\mathrm{\ensuremath{\Omega}}$ is assumed to be much smaller than the inverse magnetic length $\sqrt{qB}$, which allows us to ignore the boundary effects at $r=1/\mathrm{\ensuremath{\Omega}}$. We refer to such rotation as slow, even though in absolute value it may be an extremely rapid rotation. Using the exact solution of the Dirac equation, we derived the intensity of electromagnetic radiation, its spectrum, and its chirality. We demonstrate by explicit numerical calculation that the effect of rotation on the radiation intensity increases with the particle energy. Depending on the relative orientation of the vectors $\mathbf{\ensuremath{\Omega}}$ and $\mathbit{B}$ and the sign of the electric charge, the rotation can either strongly enhance or strongly suppress the radiation.

New Progress in the Study of Quark Mass Unlock the Secrets of Strong Force

The unification of the four forces is the ultimate goal of physics. At present, humans have not really unified the power and the strong force, and the source of the strong force remains a mystery. In 2018, Liu Yun proposed a new formula to accurately calculate the static mass of particles. Later, Liu Ziyi assumed that the particle was composed of three charges with integer 1, and believed that the particle's high rate spin produced the strong force. According to Coulomb's law and relativity, he deduced the formula for the strong force coefficient between particles and Λc(2287), and found that the strong force decreases with the increase of the distance and finally tends to a constant. By substituting the force value into Liu Yun's static mass formula, the mass spectrum obtained is in good agreement with that of J/ψ particles. After they have the same method, found that positive and negative Λb(5500) accidentally Υ particle particle mass spectra and the experimental mass spectrum highly accord with more, more surprisingly, almost coincide with triplet experimental data. These highly consistent simulations show that the strong force comes from the rapid rotation of the charges inside the particles, and strongly suggest that the so-called quarks are ordinary particles that already exist, making the catalytic development of nuclear energy possible.