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the mimes project demonstrated that a small fraction of massive stars (around 7%) presents large-scale, stable, generally dipolar magnetic fields at their surface. these fields that do not present any evident correlations with stellar mass or rotation are supposed to be fossil remnants of the initial phases of stellar ... | impact of rotation on the geometrical configurations of fossil magnetic fields |
convection is the predominant mechanism by which energy and angular momentum are transported in the outer portion of the sun. the resulting overturning motions are also the primary energy source for the solar magnetic field. an accurate solar dynamo model therefore requires a complete description of the convective moti... | prandtl-number effects in high-rayleigh-number spherical convection |
differential rotation is central to a great many mysteries in stars and planets. in part i, we predicted the order of magnitude and scaling of the differential rotation in both hydrodynamic and magnetohydrodynamic convection zones. our results apply to both slowly and rapidly rotating systems, and provide a general pic... | convective differential rotation in stars and planets - ii. observational and numerical tests |
the solar tachocline is a shear layer located at the base of the solar convection zone. the horizontal shear in the tachocline is likely turbulent, and it is often assumed that this turbulence would be strongly anisotropic as a result of the local stratification. what role this turbulence plays in the tachocline dynami... | the tachocline revisited |
context. measuring the sun's internal meridional flow is one of the key issues of helioseismology. using the fourier-legendre analysis is a technique for addressing this problem.aims: we validate this technique with the help of artificial helioseismic data.methods: the analysed data set was obtained by numerically simu... | verification of the helioseismic fourier-legendre analysis for meridional flow measurements |
stellar associations should be co-eval, but some associations exhibit apparently discrepant ages: m stars appear younger than fg stars. among m stars in the upper sco association (age ≈ 11 myr), magnetic effects have been shown to slow down evolution of the lowest mass stars, thereby alleviating the age discrepancy. a ... | pre-main-sequence stars in taurus: comparison of magnetic and nonmagnetic model fits to the low-mass stars |
we revisit the problem of the thermal bulge of asynchronous hot jupiters using hd 209458 b as a fiducial study. we improve upon previous works by using a double-gray atmosphere model and interior structure from mesa as the background state and then solve for the thermal bulge in response to the semidiurnal component of... | modeling the thermal bulge of a hot jupiter with the two-stream approximation |
mean-field hydrodynamics advanced to clear explanations for the origin and properties of the global meridional flow in stellar convection zones. qualitative arguments and analysis of basic equations both show that the meridional circulation is driven by non-conservative centrifugal and buoyancy forces and results from ... | meridional circulation in the sun and stars |
the accretion-diffusion picture is the model par excellence for describing the presence of planetary debris polluting the atmospheres of relatively cool white dwarfs. some important insights into the process may be derived using an approximate approach which combines static stellar models with estimates of diffusion ti... | metal accretion onto white dwarfs. i. the approximate approach based on estimates of diffusion timescales |
interne sioh‑ und sio−‑defektgruppen werden in si‑reichen zeolithen während der synthese unter dem einfluss organischer kationen ("structure‑directing agent", sda) als negative ladungszentren gebildet. diese arbeit untersucht die defektcluster und ihre lokalisierung in den porenwänden von vier zeolithen. zsm‑12, zsm‑5 ... | defektmodelle in siliciumreichen zeolithen: cluster von wasserstoffbrücken und ihre wechselwirkungen mit organischen strukturdirigenten aus 1h‑doppel‑ und tripelquanten‑nmr |
we investigate the phenomenon of a dense circumstellar (cs) shell and powerful emission of the (type iip) sn 2020tlf progenitor. our modeling of the h$α$ line and the circumstellar (cs) interaction suggests a cs shell radius of ${∼}10^{15}$ cm and a mass of ${∼}$0.2 $m_{\odot}$ lost by the supernova (sn) progenitor wit... | circumstellar shell and emission of the sn 2020tlf progenitor |
magnetic fields impede the onset of convection, thereby altering the thermal structure of a convective envelope in a low-mass star: this has an effect on the amount of lithium depletion in a magnetized star. in order to quantify this effect, we have applied a magnetoconvective model to two low-mass stars for which lith... | magnetoconvective models of red dwarfs: constraints imposed by the lithium abundance |
the dynamics of active region (ar) 12673 is qualitatively studied using observational data obtained with the helioseismic and magnetic imager of the solar dynamics observatory on 2017 august 31-september 8. this ar was remarkable for its complex structure and extraordinary flare productivity. the sunspot group in this ... | peculiarities of the dynamics of solar noaa active region 12673 |
the antares radiation hydrodynamics code is capable of simulating the solar granulation in detail unequaled by direct observation. we introduce a state-of-the-art numerical tool to the solar physics community and demonstrate its applicability to model the solar granulation. the code is based on the weighted essentially... | structure of the solar photosphere studied from the radiation hydrodynamics code antares |
we study the relation between the internal structures of 10 benchmark main-sequence f-stars and their rotational properties. stellar rotation of main-sequence f-type stars can be characterized by two distinct rotational regimes. early-type f-stars are usually rapid rotators with periods typically below 10 d, whereas la... | the partial ionization zone of heavy elements in f-stars: a study on how it correlates with rotation |
we evolve stellar models to study the rotational profiles of the pre-explosion cores of single massive stars that are progenitors of core collapse supernovae (ccsne), and find large rotational shear above the iron core that might play an important role in the jet feedback explosion mechanism by amplifying magnetic fiel... | the rotational shear in pre-collapse cores of massive stars |
in a rigidly-rotating magnetohydrodynamic (mhd) system with convective turbulence, a large-scale dynamo, categorized as the $\alpha^2$-type, can be excited when the spin rate is large enough. in this paper, the rotational dependence of the $\alpha^2$-type dynamo and the cause of it are explored by mean-field (mf) dynam... | rotational dependence of large-scale dynamo in strongly-stratified convection: what causes it? |
pulsar winds interacting with sources of external pressure are well-established as efficient and prolific tev accelerators in our galaxy. yet, enabled by observations from fermi-lat, a growing class of non-accreting pulsars in binaries has emerged and these are likely to become apparent as tev emitters in the cta era. ... | "spider" millisecond pulsar binaries as potential tev emitters |
we report the results of long-term photometric observations of the magnetic white dwarfs wd 2047+372 and wd 0009+501, aimed to search for and study regular brightness variability in these stars. the data in the v band of the johnson filter revealed signs of irregular variability in the convectively inactive white dwarf... | search for and study of photometric variability of magnetic white dwarfs wd 2047+372 and wd 0009+501 |
we present here the first stellar models on the hertzsprung-russell diagram, in which convection is treated according to the new scale-free convection theory (sfc theory) by pasetto et al. the aim is to compare the results of the new theory with those from the classical, calibrated mixing-length (ml) theory to examine ... | theory of stellar convection - ii. first stellar models |
context. solar dynamo models of babcock-leighton type typically assume the rise of magnetic flux tubes to be instantaneous. the periods of solutions with high magnetic diffusivity are too short, and their active belts do not migrate correctly. only the low-diffusivity regime with advective meridional flows is usually c... | delayed babcock-leighton dynamos in the diffusion-dominated regime |
turbulent convection is certainly one of the most important and thorny issues in stellar physics. our deficient knowledge of this crucial physical process introduces a fairly large uncertainty concerning the internal structure and evolution of stars. a striking example is overshoot at the edge of convective cores. inde... | a non-local mixing-length theory able to compute core overshooting |
context. recent interferometric data have been used to constrain the brightness distribution at the surface of nearby stars, in particular the so-called gravity darkening that makes fast rotating stars brighter at their poles than at their equator. however, good models of gravity darkening are missing for stars that po... | gravity darkening in late-type stars. i. the coriolis effect |
we present the first observation, analysis, and modeling of solar coronal twin jets, which occurred after a preceding jet. detailed analysis on the kinetics of the preceding jet reveals its blowout-jet nature, which resembles the one studied in liu et al. however, the erupting process and kinetics of the twin jets appe... | on the observation and simulation of solar coronal twin jets |
radial structure of accretion discs around compact objects is often described using analytic approximations which are derived from averaging or integrating vertical structure equations. for non-solar chemical composition, partial ionization, or for supermassive black holes, this approach is not accurate. additionally, ... | analysis of accretion disc structure and stability using open code for vertical structure |
dark photons are particles invoked in some extensions of the standard model that could account for at least part of the dark matter content of the universe. it has been proposed that the production of dark photons in stellar interiors could happen at a rate that depends on both, the dark photon mass and its coupling to... | constraining dark photon properties with asteroseismology |
context. the adiabatic exponent γ1 is studied as a thermodynamic quantity in the partially ionized plasma of the solar convection zone.aims: the aim of this study is to understand the impact of heavy elements on the γ1 profile. we calculated γ1 with the saha-s equation of state for different chemical compositions of pl... | ionization of heavy elements and the adiabatic exponent in the solar plasma |
context. the transition between convective and radiative stellar regions is still not fully understood. this currently leads to a poor modelling of the transport of energy and chemical elements in the vicinity of these regions. the sharp variations in sound speed located in these transition regions give rise to a signa... | glitches in solar-like oscillating f-type stars. theoretical signature of the base of the convective envelope on the ratios r010 |
stars with masses $\gtrsim 4 \times 10^{27}m_{\rm{moose}} \approx 1.1 m_\odot$ have core convection zones during their time on the main sequence. in these moosive stars, convection introduces many uncertainties in stellar modeling. in this letter, we build upon the boussinesq approximation to present the first-ever sim... | moosinesq convection in the cores of moosive stars |
recent detections of g-mode pulsations in subdwarf b (sdb) stars from the space missions corot and kepler have verified that nearly all of these pulsators have regular period spacings. this discovery has been extensively applied to mode identification for the observed g-mode sdb pulsators. however, the discovery of reg... | influence of the he-flash convective overshoot on mode trapping efficiency in g-mode pulsating subdwarf b stars |
the scale separation approximation, which is in the base of the solar mean-field dynamo models, can be hardly justified both by observations and theoretical applications to astrophysical dynamos. the general expression for the mean turbulent electromotive force can be written in integral form with convolution of the tu... | spatio-temporal non-localities in a solar-like mean-field dynamo |
stars interact with their planets through gravitation, radiation, and magnetic fields. i shall focus on the interactions between late-type stars with an outer convection zone and close-in planets, i.e., with an orbital semimajor axis smaller than ≈ 0.15 au. i shall review the roles of tides and magnetic fields consider... | star-planet interactions |
evolutionary tracks and pulsational analysis of models with masses of 13-18 m⊙ are presented. we address two important questions. the first one deals with one of the most unresolved problems in astrophysics, i.e. the existence of a blue loop after core helium ignition; the so-called to loop or not to loop problem. we s... | pulsations in b-type supergiants with masses m<20 m_{⊙} before and after core helium ignition |
solar dynamo models require some mechanism for magnetic field concentration near the base of the convection zone in order to generate super-kilogauss toroidal fields with sufficiently large (∼ 1024 mx) magnetic flux. we consider the downward diamagnetic pumping near the base of the convection zone as a possible concent... | diamagnetic pumping in a rotating convection zone |
we consider the magnetic collapse as a possible process of the magnetic field singularity formation in a finite time in the framework of ideal magnetohydrodynamics for incompressible fluids, which is important for various astrophysical applications (in particular, as the mechanism of formation of magnetic filaments in ... | notes on collapse in magnetic hydrodynamics |
the winds observed around asymptotic giant branch (agb) stars are generally attributed to radiation pressure on dust, which is formed in the extended dynamical atmospheres of these pulsating, strongly convective stars. current radiation-hydrodynamical models can explain many of the observed features, and they are on th... | explaining the winds of agb stars: recent progress |
magnetic flux ropes (mfrs) rising buoyantly through the sun's convection zone are thought to be subject to viscous forces preventing them from rising coherently. numerous studies have suggested that mfrs require a minimum twist in order to remain coherent during their rise. furthermore, even mfrs that get to the photos... | the rise and emergence of untwisted toroidal flux ropes on the sun |
the jao gap, a 17% decrease in stellar density at mg~ 10 identified in both gaia data release 2 and early data release 3, presents a new method to probe the interior structure of stars near the fully convective transition mass. the gap is believed to originate from convective-kissing instability wherein asymmetric prod... | updated high-temperature opacities for the dartmouth stellar evolution program and their effect on the jao gap location |
the role of the moments of helicity distribution in rotating turbulence has been studied using the notion of helical distributed chaos. results of the direct numerical simulations, laboratory experiments and geophysical observations have been used in this investigation. it is shown, in particular, that even for the cas... | helical distributed chaos in rotating turbulence and convection (with applications to geomagnetic dynamo) |
recent numerical simulations of rotating stellar convection have suggested the possible existence of retrograde (slow equator, fast poles) or so-called antisolar differential rotation states in slowly rotating stars possessing a large rossby number. we aim to understand whether such rotational states exist from the ons... | assessment of critical convection and associated rotation states in models of sun-like stars including a stable layer |
among stars in galactic globular clusters the carbon abundance tends to decrease with increasing luminosity on the upper red giant branch, particularly within the lowest metallicity clusters. while such a phenomena is not predicted by canonical models of stellar interiors and evolution, it is widely held to be the resu... | carbon abundance inhomogeneities and deep mixing rates in galactic globular clusters |
the “bump” is a prominent feature of the red giant branch (rgb) luminosity function of stellar clusters. through constructing a grid of models with different masses and metallicities to study the feature of the rgb bump luminosity we find that the luminosity increases almost monotonically with increasing mass for a giv... | asteroseismic analysis of the internal structure and evolution of red giant branch bump stars |
the phenomenon of convection is found in a wide variety of settings on different scales -- from applications in the cooling technology of laptops to heating water on a stove, and from the movement of ocean currents to describing astrophysical events with the convective zones of stars. given its importance in these dive... | a numerical investigation of rayleigh-benard convection with an obstruction |
in this paper, we calibrate the coefficients for the one-dimensional reynolds stress model (rsm) with the data generated from the three-dimensional (3d) numerical simulations of upward overshooting in turbulent compressible convection. it has been found that the calibrated convective and isotropic coefficients are almo... | upward overshooting in turbulent compressible convection. iii. calibrate parameters for one-dimensional reynolds stress model |
knowledge of electric fields in the photosphere is required to calculate the electromagnetic energy flux through the photosphere and set up boundary conditions for data-driven magnetohydrodynamic (mhd) simulations of solar eruptions. recently, the pdfi_ss method for inversions of electric fields from a sequence of vect... | validation of the pdfi_ss method for electric field inversions using a magnetic flux emergence simulation |
mixing between convective zones is quite uncertain in the envelopes of a-type stars. to study the mixing in a-type envelopes, we use a new convection model, the k-ω model, in the mesa stellar evolution code. using the k-ω model, we find that the overshooting regions of the he ii and h/he i convection zones are integrat... | convective overshooting in the envelopes of a-type stars using the k-ω model |
on the long nuclear time scale of stellar main-sequence evolution, even weak mixing processes can become relevant for redistributing chemical species in a star. we investigate a process of "differential heating", which occurs when a temperature fluctuation propagates by radiative diffusion from the boundary of a convec... | overshooting by differential heating |
low-mass m dwarf stars, t tauri stars, as well as planets such as the earth and jupiter are permeated by large-scale magnetic fields generated by the convection-driven dynamo operating in their convection zones. these magnetic fields are often characterized by a significant time variability, most prominently expressed ... | an argument in favor of magnetic polarity reversals due to heat flux variations in fully convective stars and planets |
context. rotation affects various aspects of the stellar structure and evolution. for example, it distorts the star and causes the energy flow to be dependent on the local gravity (von zeipel effect). recent advances in the semi-empirical derivation of the gravity-darkening exponents in eclipsing binaries and very fast... | gravity-darkening exponents for neutron and non-relativistic stars |
we estimate the extent of overshooting inwards from the bottom of the intershell convective zone in thermal pulses in (s)agb stars. we find that the buoyancy is so strong that any overshooting should be negligible. the temperature inversion at the bottom of the convective zone adds to the stability of the region. any m... | overshoot inwards from the bottom of the intershell convective zone in (s)agb stars |
context. in time-distance helioseismology, wave travel times are measured from the two-point cross-covariance function of solar oscillations and are used to image the solar convection zone in three dimensions. there is, however, also information in the amplitude of the cross-covariance function, for example, about seis... | the amplitude of the cross-covariance function of solar oscillations as a diagnostic tool for wave attenuation and geometrical spreading |
the climatic evolution of the earth depends strongly on the evolution of the insolation from the sun and the amount of the greenhouse gasses, especially co2 in the atmosphere. here, we investigate the evolution of the climate of hypothetical earths around stars whose masses are different from the solar mass with a lumi... | evolutionary tracks of the climate of earth-like planets around different mass stars |
we use a seismic diagnostic, based on the derivative of the phase shift of the acoustic waves reflected by the surface, to probe the outer layers of the star hd 49933. this diagnostic is particularly sensitive to partial ionization processes occurring above the base of the convective zone. the regions of partial ioniza... | the corot target hd 49933: a possible seismic signature of heavy elements ionization in the deep convective zone |
a large fraction of white dwarfs host evolved planetary systems and show evidence of accretion from planetary debris. the accretion-diffusion model is the preferred method to understand the metal pollution in these otherwise hydrogen- and helium-rich white dwarf atmospheres. in this scenario, the accreted material firs... | convective overshoot and metal accretion onto white dwarfs. |
this work discusses theoretical models of chromospheric heating for ɛ eridani by shock waves. self-consistent, nonlinear and time-dependent ab-initio numerical computations for the excitation of the atmosphere (i.e., arrays of flux tubes) are pursued based on waves generated in stellar convective zones. based on previo... | chromospheric activity in ɛ eridani: results from theoretical wave studies |
over time, tides synchronize the rotation periods of stars in a binary system to the orbital period. however, if the star exhibits differential rotation, then only a portion of it can rotate at the orbital period, so the rotation period at the surface may not match the orbital period. the difference between the rotatio... | differential rotation in convective envelopes: constraints from eclipsing binaries |
the authors of this report met on 28-30 march 2018 at the new jersey institute of technology, newark, new jersey, for a 3-day workshop that brought together a group of data providers, expert modelers, and computer and data scientists, in the solar discipline. their objective was to identify challenges in the path towar... | roadmap for reliable ensemble forecasting of the sun-earth system |
we present the first global 3d simulations of thermal convection in the oblate envelopes of rapidly rotating solar-type stars. this has been achieved by exploiting the capabilities of the new compressible high-order unstructured spectral difference (chorus) code. we consider rotation rates up to 85% of the critical (br... | convection in oblate solar-type stars |
near-surface flows measured by the ring-diagram technique of local helioseismology show structures that persist over multiple rotations. we examine these phenomena using data from the global oscillation network group (gong) and the helioseismic and magnetic imager (hmi) and show that a correlation analysis of the struc... | persistent near-surface flow structures from local helioseismology |
in this paper, we study wave transmission in a rotating fluid with multiple alternating convectively stable and unstable layers. we have discussed wave transmissions in two different circumstances: cases where the wave is propagative in each layer and cases where wave tunneling occurs. we find that efficient wave trans... | enhancement of wave transmissions in multiple radiative and convective zones |
the corot space telescope observed nearly 160 000 light curves. among the most outstanding is that of the young, active planet host star corot-2a. in addition to deep planetary transits, the light curve of corot-2a shows strong rotational variability and a superimposed beating pattern. to study the stars that produce s... | spectral characterization and differential rotation study of active corot stars |
we review recent developments in determining the evolution of magnetic massive ob stars. one of the important scientific questions is the completeness and the detection limits of contemporaneous spectropolarimetric surveys across the hr diagram. we present the characteristics of the mimes survey of o-type stars, and ho... | recent developments in determining the evolution of magnetic ob stars |
magnetic quenching of turbulent thermal diffusivity leads to instability of the large-scale field with the production of spatially isolated regions of enhanced field. this conclusion follows from a linear stability analysis in the framework of mean-field magnetohydrodynamics that allows for thermal diffusivity dependen... | large-scale magnetic field fragmentation in flux-tubes near the base of the solar convection zone |
overshooting and semiconvection are among the most noteworthy uncertainties in the evolution of massive stars. complete mixing over a certain distance beyond the convective boundary and an exponentially decaying diffusion outside the convection zone are commonly adopted for the overshoot mixing. recently, li developed ... | overshooting in the core helium-burning stage of a 30 m ⊙ star using the k-ω model |
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.... | the rotation period distribution in the young open cluster ngc 6709 |
context. the structure characteristics of the critically-rotating accretor in binaries are investigated in this paper, on the basis of the potential function including rotational and tidal distortions.aims: our aim is to investigate the structure of the accretor when the accreting star reaches the critical velocity.met... | the structure of critically-rotating accreting stars |
binary stars in which oscillations can be studied in either or both components can provide powerful constraints on our understanding of stellar physics. the bright binary 12 boötis (12 boo) is a particularly promising system because the primary is roughly 60 per cent brighter than the secondary despite being only a few... | solar-like oscillations and ellipsoidal variations in tess observations of the binary 12 boötis |
helioseismology has revealed the internal density and rotation profiles of the sun. yet, knowledge of its magnetic fields and meridional circulation is confined much closer to the surface, and latitudinal entropy gradients are below detectable limits. while numerical simulations can offer insight into the interior dyna... | a model of solar equilibrium: the hydrodynamic limit |
computations of chromospheric models and the resulting spectral line emission fluxes are presented for late-type stars exhibiting very low level of chromospheric activity, referred to as a basal flux stars or low activity stars. the computations are self-consistent, and consider the entire acoustic wave energy spectra ... | theoretical basal ca ii and mg ii fluxes for late-type stars: results from acoustic wave spectra with time-dependent ionization and multilevel radiation treatments |
the accretion-diffusion picture is the model par excellence for describing the presence of planetary debris polluting the atmospheres of relatively cool white dwarfs. in the time-dependent approach used in paper ii of this series (fontaine et al. 2014), the basic assumption is that the accreted metals are trace element... | metal accretion onto white dwarfs. iii. a still better approach based on the coupling of diffusion with evolution |
in this paper, we study the magnetic activity properties for a sample of m-type stars in kepler field by using the two light-curve-based magnetic proxies, iac and reff, which describe the periodicity and magnitude of light-curve variations, respectively. it is found that (1) stars with short rotational period might hav... | magnetic activity properties of m-type kepler stars |
hd 176465 is a binary system for which both components are solar-like pulsators and oscillation frequencies were observed by the kepler mission. in this paper, we have modeled the asteroseismic and spectroscopic data of the stars, and have determined their convection-zone helium abundances using the signatures left by ... | asteroseismic investigations of the binary system hd 176465 |
intending to solve the decade old problem of solar opacity, we report substantial photoabsorption uncertainty due to the effect of ion-ion correlations. by performing detailed opacity calculations of the solar mixture, we find that taking into account the ionic structure changes the rosseland opacity near the convectio... | the effect of ionic correlations on radiative properties in the solar interior and terrestrial experiments |
context. helioseismology and asteroseismology allow us to probe the differential rotation deep within low-mass stars. in the solar convective envelope, the rotation varies with latitude with an equator rotating faster than the pole, which results in a shear applied on the radiative zone below. however, a polar accelera... | the 2d dynamics of radiative zones of low-mass stars |
using mean-field hydrodynamic models of the solar angular momentum balance we show that the non-monotonic latitudinal dependence of the radial angular momentum fluxes caused by λ -effect can affect the number of the meridional circulation cells stacking in the radial direction in the solar convection zone. in particula... | angular momentum fluxes caused by λ -effect and meridional circulation structure of the sun |
we use a simplified model to study wave reflection and transmission at the interface of the convective region and stably stratified region (e.g., radiative zone in a star or stratification layer in a gaseous planet). the inertial wave in the convective region and gravito-inertial wave in the stably stratified region ar... | wave reflection and transmission at the interface of convective and stably stratified regions in a rotating star or planet |
the architecture of many exoplanetary systems is different from the solar system, with exoplanets being in close orbits around their host stars and having orbital periods of only a few days. we can expect interactions between the star and the exoplanet for such systems that are similar to the tidal interactions observe... | tidal effects on stellar activity |
thermal convection is one of the main mechanisms of heat transport and mixing in stars in general and also in the photospheric layers which emit the radiation that we observe with astronomical instruments. the present lecture notes first introduce the role of convection in astrophysics and explain the basic physics of ... | thermal convection in stars and in their atmosphere |
inspired by observations of sunspots embedded in active regions, it is often assumed that large-scale, strong magnetic flux emerges from the sun's deep interior in the form of arched, cylindrical structures, colloquially known as flux tubes. here, we continue to examine the different dynamics encountered when these str... | the rise of buoyant magnetic structures through convection with a background magnetic field |
large-eddy simulations (les) and implicit les (iles) are wise and affordable alternatives to the unfeasible direct numerical simulations of turbulent flows at high reynolds (re) numbers. however, for systems with few observational constraints, it is a formidable challenge to determine if these strategies adequately cap... | numerical convergence of 2d solar convection in implicit large-eddy simulations |
it is shown, using results of recent direct numerical simulations, laboratory experiments and atmospheric measurements, that buoyancy driven turbulence exhibits a broad diversity of the types of distributed chaos with its stretched exponential spectrum $\exp(-k/k_{\beta})^{\beta}$. the distributed chaos with $\beta = 1... | buoyancy driven turbulence and distributed chaos |
convection is one of the fundamental energy transport processes in physics and astrophysics, and its description is central to allstellar models. in the context of stellar astrophysics, the mixing length theory is the most successful approximation to handle theconvection zones inside the stars because of its simplicity... | on the pressure equilibrium and timescales in the scale free convection theory |
opacity is a key ingredient of stellar structure and evolution. in the present work, we recall the role of opacity in asteroseismology, focusing mainly on two kinds of astrophysical objects: beta cephei-type stars, and the sun. the detailed opacity code sco-rcg for local-thermodynamic-equilibrium plasmas is described a... | opacity calculations for stellar astrophysics |
small-scale magnetic fields are not only the fundamental element of the solar magnetism but also closely related to the structure of the solar atmosphere. the observations have shown that there is a ubiquitous tangled small-scale magnetic field with a strength of 60-130 g in the canopy-forming layer of the quiet solar ... | can small-scale magnetic fields be the major cause for the near-surface effect of the solar p-mode frequencies? |
i will present state-of-the art calculations studying tidal dissipation in mkgf stars throughout their evolution. the models incorporate turbulent viscosity acting on equilibrium tides and inertial waves in convection zones, and internal gravity waves in radiation zones, based on our latest understanding of each mechan... | tidal dissipation in stars and predictions for planetary orbital decay |
in close two-body astrophysical systems, such as binary stars or hot jupiter systems, tidal interactions often drive dynamical evolution on secular timescales. many host stars and presumably giant gaseous planets feature a convective envelope. tidal flows generated therein by the tidal potential of the companion can be... | nonlinear simulations of tides in the convective envelopes of low-mass stars and giant gaseous planets |
the sun is the most studied of stars and a laboratory of fundamental physics. however, the understanding of our star is stained by the solar modelling problem which can stem from various causes. we combine inversions of sound speed, an entropy proxy and the ledoux discriminant with the position of the base of the conve... | combining multiple structural inversions to constrain the solar modelling problem |
the high‑silica zeolite ssz‑27 was synthesized using one of the isomers of the organic structure‑directing agent that is known to produce the large‑pore zeolite ssz‑26 (con). the structure of the as‑synthesized form was solved using multi‑crystal electron diffraction data. data were collected on eighteen crystals, and ... | ssz‑27: a small‑pore zeolite with large heart‑shaped cavities determined by using multi‑crystal electron diffraction |
the observed radii of m dwarfs in eclipsing binaries exceed predicted radii by 5%. to investigate this anomaly, the structure of low-mass stars irradiated by a close companion is considered. irradiation modifies the surface boundary conditions and thereby also the adiabatic constants of their outer convection zones. th... | irradiated stars with convective envelopes |
context. radiation magnetohydrodynamics (radiation-mhd) simulations have become a standard tool for investigating the physics of solar and stellar atmospheres.aims: the aim of this paper is to present a method that allows the efficient and accurate analysis of flows in such simulations in the lagrangian frame.methods: ... | tracing the evolution of radiation-mhd simulations of solar and stellar atmospheres in the lagrangian frame |
is the sun likely to have a more opaque interior than previously thought? the solar oxygen (or abundance) problem can be solved with higher interior opacities, reconciling abundance analyses based on 3d convective atmospheres with the helioseismic structure of the solar interior. this has been known for more than a dec... | the dark side of the sun |
a novel method for bringing sample elements to hydrodynamic conditions relevant to the base of the solar convection zone is investigated. the method is designed in the framework of opacity measurements and exploits the temporal and spatial stability of hydrodynamic parameters in counter-propagating double ablation fron... | towards a novel stellar opacity measurement scheme using stability properties of double ablation front structures |
self-consistent, nonlinear and time-dependent numerical computations of the excitation of chromospheric oscillations in a thin and non-isothermal magnetic flux tube embedded in magnetic-free atmospheres of late-type stars are performed. longitudinal tube waves are considered and the wave energy spectra and fluxes gener... | theoretical prediction of chromospheric oscillations in late-type stars |
the standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. modes which are calculated to be linearly driven should increase their amplitudes exponentially with time; the fact that nearly constant amplitudes are usually observed is evidence that nonli... | limits on mode coherence due to a non-static convection zone |
all cool stars with outer convective zones have the potential to exhibit stochastically excited stellar oscillations. in this work, we explore the outer layers of stars less massive than the sun. in particular, we have computed a set of stellar models ranging from 0.4 to 0.9 m⊙ with the aim at determining the impact on... | asteroseismology of low-mass stars: the balance between partial ionization and coulomb interactions |
slowly pulsating b stars (spb) and γ dor stars pulsate in high-order gravity (g-) modes. the frequencies of g-modes are sensitive to the detailed structure and evolution history of stars having convective cores. receding convective cores in ob-type stars leave behind a chemically inhomogenous ∇μ > 0 radiative zone. ... | on the shape of core overshooting in stellar model computations, and asteroseismic tests |
the sun and other stars are known to oscillate. through the study of small perturbations to the frequencies of these oscillations the rotation of the deep interior can be inferred. however, thus far the internal rotation of other sun-like stars is unknown. the nasa kepler mission has observed a multitude of sun-like st... | differential rotation in sun-like stars from surface variability and asteroseismology |
we calculate the abundance change if two bulk earths were added to the solar convection zone, which is assumed to be 5 × 1031 gm or 0.025 m⊙. the resulting differential abundance plot resembles those found in stellar precision differential abundance studies. | elemental abundance consequence of adding two bulk earths to the solar convection zone |
red giant stars with deep convection zones and rapid rotation maintain a strong surface magnetic field which may alter their observable astrophysical parameters. the resulting lower surface temperature due to spots makes the inferred masses and ages from evolutionary tracks uncertain. eclipsing binaries having an activ... | the importance of studying active giant stars in eclipsing binaries - and the role of citizen scientists in finding them |
although playing a key role in the understanding of the supernova phenomenon, the evolution of massive stars still suffers from uncertainties in their structure, even during their ``quiet'' main sequence phase and later on during their subgiant and helium burning phases. what is the extent of the mixed central region? ... | asteroseismology of massive stars: some words of caution |
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