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recent observations of the protoplanetary disks hosted by a pair of young stars suggest the presence of hot, turbulent water vapor. though many possibilities exist, researchers propose that a compact disk around a young planet could be the source of this rare spectral signature.planet formation locationsillustration of... | researchers find hot, dense water vapor in a protoplanetary disk |
we present alma band 6 dust and gas observations of the transition disk around rxj1604.3-2130 a, known to feature nearly symmetric shadows in scattered light. we study the 12co line channel maps and moment maps of the line of sight velocity and peak intensity. we fit a keplerian model of the channel-by-channel emission... | a kinematically detected planet candidate in the transition disk around rxj1604.3–2130 a |
growing a planet from a dust grain is hard work! a new study explores how vortices in protoplanetary disks can assist this process.when dust growth failstop: alma image of the protoplanetary disk of v1247 orionis, with different emission components labeled. bottom: synthetic image constructed from the best-fit model. [... | trapping dust to form planets |
jupiter-like planets with blisteringly close-in orbits are generally friendless, with no nearbyplanets transiting along with them. giant planets with orbits a little further out, on the other hand, often have at least one companion. a new study examines the cause of hot jupiters loneliness.forming close-in giantsartist... | why are hot jupiters so lonely? |
young, forming planets can generate immense spiral structures within their protoplanetary disks. a recent study has shown that observations of these spiral structures may allow astronomers to measure the mass of the planets that create them.spirals from wavessnapshots of the surface density of a protoplanetary disk in ... | planet masses from disk spirals |
in some young stellar systems with planet formation, protoplanetary disks with a dust-free central hole (transitional disks) have been discovered. in other younger systems, in addition to the central hole, disks also show a dust-free gap (pre-transitional disks) that separates an inner disk from an outer one. these hol... | geometry of internal walls and gaps in transitional and pre-transitional disks |
can protoplanetary disks form and be maintained around low-mass stars in the harsh environment of a highly active, star-forming nebula? a recent study examines the carina nebula to answer this question.crowded clustersstars are often born in clusters that contain both massive and low-mass stars. the most massive stars ... | forming planets in the hostile carina nebula |
this remarkable image (click for the full view!) is a high-resolution map of the 870 m light emitted by the protoplanetary disk surrounding the young solar analog tw hydrae. a recent study led by sean andrews (harvard-smithsonian center for astrophysics) presents these observations, obtained with the long-baseline conf... | featured image: a gap in tw hydrae |
what causes the large-scale spiral structures found in some protoplanetary disks? most models assume theyre created by newly-forming planets, but a new study suggests that planets might have nothing to do with it.perturbations from planets?in some transition disks protoplanetary disks with gaps in their inner regions w... | forming spirals from shadows |
giant planets forming in protoplanetary disks migrate relative to their host star. by repelling the gas in their vicinity, they form gaps in the disk's structure. if they are effectively locked in their gap, it follows that their migration rate is governed by the accretion of the disk itself onto the star, in a so-call... | migration of accreting giant planets |
alma continuum image overlaid as contours on the hubble stis image of fomalhaut. [macgregor et al. 2017]this stunning image of the fomalhaut star system was taken by the atacama large millimeter/submillimeter array (alma) in chile. this image maps the 1.3-mm continuum emission from the dust around the central star, rev... | featured image: a new look at fomalhaut |
the building blocks of planets in planet-forming ("protoplanetary") disks assemble early in the lifetime of a young star. the gas disks are relatively short-lived, with a half-life of several (about 3-5) million years, as chemical reactions modify the reservoir of material from the natal molecular cloud. we present 5-7... | sofia-exes and spitzer-irs studies of gases in the circumstellar environments of young stellar objects |
the interior structure of two carbonaceous chondrites: meteorite los vientos123 (top) and meteorite el mdano 463 (bottom). click to enlarge. [pinto et al. 2021]have you ever wanted to look inside an asteroid? todays image (see the full version to the right) shows the interior structure of a type of meteorite called a c... | featured image: asteroid fragments on display |
in an effort to learn more about how planets form around their host stars, a team of scientists has analyzed the population of kepler-discovered exoplanet candidates, looking for trends in where theyre found.planetary occurrencesince its launch in 2009, kepler has found thousands of candidate exoplanets around a variet... | preferred hosts for short-period exoplanets |
future observations of exoplanets will hopefully reveal detailed constraints on planetary compositions. recently, we have developed and introduced chemcomp (schneider & bitsch 2021a), which simulates the formation of planets in viscously evolving protoplanetary disks by the accretion of pebbles and gas. the chemica... | chemcomp: modeling the chemical composition of planets formed in protoplanetary disks |
understanding the formation and evolution of planetary systems is a challenging area of study, requiring high spatial resolution and special techniques to observe planets in formation in protoplanetary disks and the resulting disk/planet systems that are created. these systems provide a point of comparison to our own s... | probing planetary architectures with spice |
giant planets around young stars serve as a clue to unveiling their formation history and orbital evolution. ci tau is a 2 myr-old classical t tauri star hosting an eccentric hot jupiter, ci tau b. the standard formation scenario of a hot jupiter predicts that planets formed further out and migrated inward. a high ecce... | high-contrast imaging around a 2 myr-old ci tau with a close-in gas giant |
sub-neptune planets formed in the protoplanetary disk accreted hydrogen-helium (h,he) envelopes. planet formation models of sub-neptunes formed by pebble accretion result in small rocky cores surrounded by polluted h,he envelopes, where most of the rock (silicate) is in vapor form at the end of the formation phase. thi... | rocky sub-neptunes formed by pebble accretion: rain of rock from polluted envelopes |
recent studies suggest that the magnetic field may play an important role in the formation of giant planets during the final stage of the formation process. in this paper, we construct a circumplanetary system around a planet that is in the final formation stage to investigate the effects of the planetary magnetic fiel... | effects of the planetary field on the accretion process of a planet in the final stage of giant planet formation |
in the conventional theory of planet formation, it is assumed that protoplanetary disks are axisymmetric and have a smooth radial profile. however, recent radio observations of protoplanetary disks have revealed that many of them have complex radial structures. in this study, we perform a series of n-body simulations t... | n-body simulation of planetary formation through pebble accretion in a radially structured protoplanetary disk |
protoplanetary discs channel accretion onto their host star. how this is achieved is critical to the growth of giant planets which capture their massive gaseous atmosphere from the surrounding flow. theoretical studies find that an embedded magnetic field could power accretion by hydromagnetic turbulence or torques fro... | magnetic fields in giant planet formation and protoplanetary discs |
thanks to "dust-to-planet" simulations (dtpss), which treat the collisional evolution directly from dust to giant-planet cores in a protoplanetary disk, we showed that giant-planet cores are formed in ≲10 au in several 105 yr, because porous pebbles grow into planetesimals via collisions prior to drift in 10 au. howeve... | rapid formation of gas-giant planets via collisional coagulation from dust grains to planetary cores. ii. dependence on pebble bulk density and disk temperature |
planets form in "protoplanetary" disks around young stars. thus, establishing an accurate disk dissipation timescale is key to constraint the maximum period available for planet formation. that timescale is smaller than ~ 10 myr, based on surveys counting the relative number of stars with disks -the disk fraction- in y... | gaia edr3 comparison of disk fractions from different spatial scales around young stellar clusters |
short contributed talk abstract: how do we discriminate an exoplanet from a brown dwarf (bd)? this question has been fiercely debated considering definitions based on either their physical properties (like the mass or the ability to fuse deuterium) or their formation. bd usually are considered as failed stars, formed i... | atmospheres of massive planets and brown dwarfs as clue to distinguish between formation mechanisms |
a recent study suggests that protoplanetary disks may tend to linger longer than we thought, meaning that planets likely have at least 5 million years to form before their building materials vanish.disk dispersal deadlinesone way that protoplanetary disks are dispersed is by radiation and winds from massive stars, as s... | planets may have more time to form than previously thought |
the sun's complex dynamics is controlled by buoyancy and rotation in the convection zone. large-scale flows are dominated by vortical motions1 and appear to be weaker than expected in the solar interior2. one possibility is that waves of vorticity due to the coriolis force, known as rossby waves3 or r modes4, remove en... | global-scale equatorial rossby waves as an essential component of solar internal dynamics |
the detection of mixed oscillation modes offers a unique insight into the internal structure of core helium burning (cheb) stars. the stellar structure during cheb is very uncertain because the growth of the convective core, and/or the development of a semiconvection zone, is critically dependent on the treatment of co... | the treatment of mixing in core helium burning models - i. implications for asteroseismology |
to study properties of magnetohydrodynamic (mhd) convection and resultant dynamo activities in proto-neutron stars (pnss), we construct a "pns in a box" simulation model and solve the compressible mhd equation coupled with a nuclear equation of state (eos) and simplified leptonic transport. as a demonstration, we apply... | convection and dynamo in newly born neutron stars |
we present the first detailed 3d hydrodynamic implicit large eddy simulations of turbulent convection of carbon burning in massive stars. simulations begin with radial profiles mapped from a carbon-burning shell within a 15 m⊙ 1d stellar evolution model. we consider models with 1283, 2563, 5123, and 10243 zones. the tu... | 3d hydrodynamic simulations of carbon burning in massive stars |
observations suggest that the large-scale convective velocities obtained by solar convection simulations might be over-estimated (convective conundrum). one plausible solution to this could be the small-scale dynamo which cannot be fully resolved by global simulations. the small-scale lorentz force suppresses the conve... | consequences of high effective prandtl number on solar differential rotation and convective velocity |
convection is ubiquitous in stars and occurs under many different conditions. here we explore convection in main-sequence stars through two lenses: dimensionless parameters arising from stellar structure and parameters that emerge from the application of mixing length theory. we first define each quantity in terms fami... | an atlas of convection in main-sequence stars |
the extent of mixed regions around convective zones is one of the biggest uncertainties in stellar evolution. one-dimensional overshooting descriptions introduce a free parameter (fov) that is, in general, not well constrained from observations. especially in small central convective regions, the value is highly uncert... | calibrating core overshooting parameters with two-dimensional hydrodynamical simulations |
we present the first three-dimensional, fully compressible gas-dynamics simulations in 4π geometry of he-shell flash convection with proton-rich fuel entrainment at the upper boundary. this work is motivated by the insufficiently understood observed consequences of the h-ingestion flash in post-asymptotic giant branch ... | hydrodynamic simulations of h entrainment at the top of he-shell flash convection |
stellar evolution models calculate convective boundaries using either the schwarzschild or ledoux criterion, but confusion remains regarding which criterion to use. here we present a 3d hydrodynamical simulation of a convection zone and adjacent radiative zone, including both thermal and compositional buoyancy forces. ... | schwarzschild and ledoux are equivalent on evolutionary timescales |
we present a set of numerical simulations that model the convection zones of solar-like stars. with this suite of numerical experiments, we explore how the nature of the convective structures transitions through a series of morphological regimes as the reduced rayleigh number increases. convection first manifests as a ... | morphological classification of the convective regimes in rotating stars |
we carry out high-resolution calculations of the solar overshoot region with unprecedentedly realistic parameters, especially the small energy flux compared with ρ {c}{{s}}3, where ρ and c s are density and speed of sound. our main purpose is to investigate the behavior of the overshoot and the small-scale dynamo with ... | solar overshoot region and small-scale dynamo with realistic energy flux |
we present numerical simulations of hydrodynamic overshooting convection in local cartesian domains. we find that a substantial fraction of the lower part of the convection zone (cz) is stably stratified according to the schwarzschild criterion while the enthalpy flux is outward directed. this occurs when the heat cond... | extended subadiabatic layer in simulations of overshooting convection |
rotational scaling relationships are examined for the degree of equipartition between magnetic and kinetic energies in stellar convection zones. these scaling relationships are approached from two paradigms, with first a glance at scaling relationship built on an energy-balance argument and second a look at a force-bas... | rossby and magnetic prandtl number scaling of stellar dynamos |
we investigate small-scale dynamo action in the solar convection zone through a series of high-resolution mhd simulations in a local cartesian domain with 1 {{r}⊙ } (solar radius) of horizontal extent and a radial extent from 0.715 to 0.96 {{r}⊙ }. the dependence of the solution on resolution and diffusivity is studied... | efficient small-scale dynamo in the solar convection zone |
the cores of main sequence intermediate- and high-mass stars are convective. mixing at the radiative–convective boundary, waves excited by the convection, and magnetic fields generated by convective dynamos all influence the main sequence and post-main sequence evolution of these stars. these effects must be understood... | multidimensional simulations of core convection |
tidal dissipation in star-planet systems can occur through various mechanisms, among which is the elliptical instability. this acts on elliptically deformed equilibrium tidal flows in rotating fluid planets and stars, and excites inertial waves in convective regions if the dimensionless tidal amplitude (ϵ) is sufficien... | tidal dissipation due to the elliptical instability and turbulent viscosity in convection zones in rotating giant planets and stars |
context. late-type stars such as the sun rotate differentially due to the interaction of turbulent convection and rotation.aims: the aim of the study is to investigate the effects of the effective thermal prandtl number, which is the ratio of kinematic viscosity to thermal diffusivity, on the transition from anti-solar... | transition from anti-solar to solar-like differential rotation: dependence on prandtl number |
we present numerical simulations, using two complementary set-ups, of rotating boussinesq thermal convection in a three-dimensional cartesian geometry with misaligned gravity and rotation vectors. this model represents a small region at a non-polar latitude in the convection zone of a star or planet. we investigate the... | convection with misaligned gravity and rotation: simulations and rotating mixing length theory |
we study the dynamics associated with the extension of turbulent convective motions from a convection zone (cz) into a stable region (rz) that lies below the latter. for that purpose, we have run a series of 3d direct numerical simulations solving the navier-stokes equations under the boussinesq approximation in a sphe... | convective overshooting and penetration in a boussinesq spherical shell |
context. in the interior of stars, a convectively unstable zone typically borders a zone that is stable to convection. convective motions can penetrate the boundary between these zones, creating a layer characterized by intermittent convective mixing, and gradual erosion of the density and temperature stratification.ai... | extreme value statistics for two-dimensional convective penetration in a pre-main sequence star |
context. a realistic parametrization of convection and convective boundary mixing in conventional stellar evolution codes is still the subject of ongoing research. to improve the current situation, multidimensional hydrodynamic simulations are used to study convection in stellar interiors. such simulations are numerica... | multidimensional low-mach number time-implicit hydrodynamic simulations of convective helium shell burning in a massive star |
context. observations of cool stars reveal dark spot-like features on their surfaces. these starspots can be more extended than sunspots and cover a large area of the stellar surface. while sunspots appear only at low latitudes, starspots are also found in polar regions, in particular on rapidly rotating stars. convent... | formation of starspots in self-consistent global dynamo models: polar spots on cool stars |
the dynamical origins of the sun’s tachocline and near-surface shear layer (nssl) are still not well understood. we have attempted to self-consistently reproduce an nssl in numerical simulations of a solar-like convection zone by increasing the density contrast across rotating 3d spherical shells. we explore the hypoth... | the role of downflows in establishing solar near-surface shear |
we performed two-dimensional, fully compressible, time-implicit simulations of convection in a solar-like model with the music code. our main motivation is to explore the impact of a common tactic adopted in numerical simulations of convection that use realistic stellar conditions. this tactic is to artificially increa... | two-dimensional simulations of solar-like models with artificially enhanced luminosity. i. impact on convective penetration |
in close exoplanetary systems, tidal interactions drive orbital and spin evolution of planets and stars over long time-scales. tidally forced inertial waves (restored by the coriolis acceleration) in the convective envelopes of low-mass stars and giant gaseous planets contribute greatly to the tidal dissipation when th... | the effects of non-linearities on tidal flows in the convective envelopes of rotating stars and planets in exoplanetary systems |
in one-dimensional (1d) evolution models of gas giant planets, an outer convection zone advances into the interior as the surface cools, and multiple convective layers form beneath that convective front. to study layer formation below an outer convection zone in a similar scenario, we investigate the evolution of a sta... | layer formation in a stably stratified fluid cooled from above: towards an analog for jupiter and other gas giants |
context. the rich harvest of seismic observations over the past decade provides evidence of angular momentum redistribution in stellar interiors that is not reproduced by current evolution codes. in this context, transport by internal gravity waves can play a role and could explain discrepancies between theory and obse... | generation of internal gravity waves by penetrative convection |
the solar convection zone rotates differentially, with its equatorial region rotating more rapidly than the polar regions. this form of differential rotation, also observed in many other low-mass stars, is understood to arise when coriolis effects are stronger than those associated with buoyant driving of the convectio... | solar-like to antisolar differential rotation: a geometric interpretation |
current state-of-the-art models of the solar convection zone consist of solutions to the navier-stokes equations in rotating, 3d spherical shells. such models are highly sensitive to the choice of boundary conditions. here we present two suites of simulations differing only in their outer thermal boundary condition, wh... | revisiting the sun's strong differential rotation along radial lines |
mean-field dynamo theory has important applications in solar physics and galactic magnetism. we discuss some of the many turbulence effects relevant to the generation of large-scale magnetic fields in the solar convection zone. the mean-field description is then used to illustrate the physics of the α effect, turbulent... | turbulent processes and mean-field dynamo |
understanding the effects driven by rotation in the solar convection zone is essential for many problems related to solar activity, such as the formation of differential rotation, meridional circulation, and others. we analyse realistic 3d radiative hydrodynamics simulations of solar subsurface dynamics in the presence... | leptocline as a shallow substructure of near-surface shear layer in 3d radiative hydrodynamic simulations |
we consider the effect of a subadiabatic layer at the base of the convection zone on convection itself and the associated large-scale dynamos in spherical wedge geometry. we use a heat conduction prescription based on the kramers opacity law which allows the depth of the convection zone to dynamically adapt to changes ... | effects of a subadiabatic layer on convection and dynamos in spherical wedge simulations |
gravito-inertial waves are excited at the interface of convective and radiative regions and by the reynolds stresses in the bulk of the convection zones of rotating stars and planets. such waves have notable asteroseismic signatures in the frequency spectra of rotating stars, particularly among rapidly rotating early-t... | a model of rotating convection in stellar and planetary interiors. ii. gravito-inertial wave generation |
convection is one of the most important mixing processes in stellar interiors. hydrodynamic mass entrainment can bring fresh fuel from neighboring stable layers into a convection zone, modifying the structure and evolution of the star. because flows in stellar convection zones are highly turbulent, multidimensional hyd... | turbulent dynamo action and its effects on the mixing at the convective boundary of an idealized oxygen-burning shell |
(abridged) context: rotation is thought to influence the size of convective eddies and the efficiency of convective energy transport in the deep convection zones of stars. rotationally constrained convection has been invoked to explain the lack of large-scale power in observations of solar flows. aims: the main aims ar... | convective scale and subadiabatic layers in simulations of rotating compressible convection |
the simplistic but ubiquitous mixing length theory (mlt) formalism is used to model convective energy transport within 1d stellar evolution calculations. the formalism relies on the free parameter α mlt, which must be independently calibrated within each stellar evolution program and for any given set of physical assum... | solar calibration of the convective mixing length for use with the æsopus opacities in mesa |
context. in a previous paper, we studied the effect of latitudinal rotation on solar equatorial rossby modes in the β-plane approximation. since then, a rich spectrum of inertial modes has been observed on the sun, which is not limited to the equatorial rossby modes and includes high-latitude modes.aims: here we extend... | viscous inertial modes on a differentially rotating sphere: comparison with solar observations |
aims: we explore the effects of an outer stably stratified coronal envelope on rotating turbulent convection, differential rotation, and large-scale dynamo action in spherical wedge models of the sun.methods: we solve the compressible magnetohydrodynamic equations in a two-layer model with unstable stratification below... | influence of a coronal envelope as a free boundary to global convective dynamo simulations |
context. inertial modes have been observed on the sun at low longitudinal wavenumbers. these modes probe the dynamics and structure of the solar convective zone down to the tachocline. while linear analysis allows the complex eigenfrequencies and eigenfunctions of these modes to be computed, it gives no information abo... | interaction of solar inertial modes with turbulent convection. a 2d model for the excitation of linearly stable modes |
the formation of low-mass x-ray binaries (lmxbs) is an ongoing challenge in stellar evolution. an important subset of lmxbs is the binary systems with a neutron star (ns) accretor. in ns lmxbs with nondegenerate donors, the mass transfer (mt) is mainly driven by magnetic braking (mb). the discrepancies between the obse... | evolving lmxbs: carb magnetic braking |
a major problem in stellar modelling is the discrepancy between solar models and helioseismology data in the position of the convective zone-radiative zone boundary in the sun. this could be explained by a large uncertainty in the calculated opacity data and recent experimental data on iron using the sandia national la... | a proposal to measure iron opacity at conditions close to the solar convective zone-radiative zone boundary |
large-scale convective flows called giant cells were once thought to transport the sun’s luminosity in the solar convection zone, but recent observations have called their existence into question. in place of large-scale flows, some authors have suggested the solar luminosity may instead be transported by small droplet... | entropy rain: dilution and compression of thermals in stratified domains |
in 1969, leighton developed a quasi-1d mathematical model of the solar dynamo, building upon the phenomenological scenario of babcock published in 1961. here we present a modification and extension of leighton's model. using the axisymmetric component (longitudinal average) of the magnetic field, we consider the radial... | an update of leighton's solar dynamo model |
context. quantifying tidal interactions in close-in two-body systems is of prime interest since they have a crucial impact on the architecture and the rotational history of the bodies. various studies have shown that the dissipation of tides in either body is very sensitive to its structure and to its dynamics. further... | the complex interplay between tidal inertial waves and zonal flows in differentially rotating stellar and planetary convective regions. i. free waves |
context. star-planet tidal interactions may result in the excitation of inertial waves in the convective region of stars. in low-mass stars, their dissipation plays a prominent role in the long-term orbital evolution of short-period planets. turbulent convection can sustain differential rotation in their envelopes with... | tidal inertial waves in differentially rotating convective envelopes of low-mass stars. i. free oscillation modes |
context. a 1d description of stellar dynamics is at the basis of stellar evolution modeling. designed to investigate open problems in stellar evolution, the multidimensional stellar implicit code expands a realistic 1d profile of a star's internal structure to examine the interior dynamics of a specific star through ei... | comparison of 2d and 3d compressible convection in a pre-main sequence star |
context. there are no strong constraints placed thus far on the amplitude of internal gravity waves (igws) that are stochastically excited in the radiative interiors of solar-type stars. late f-type stars have relatively thin convective envelopes with fast convective flows and tend to be fast rotators compared to solar... | stochastic excitation of internal gravity waves in rotating late f-type stars: a 3d simulation approach |
we present evolutionary models of massive, accreting population iii stars with constant and variable accretion rates until the end of silicon burning, with final masses of 1000 - 3000 msol. in all our models, after the core-hydrogen-burning phase, the star expands towards the red side of the hertzsprung-russell diagram... | the evolution and impact of 3000 m$_\\odot$ stars in the early universe |
core overshoot is a large source of uncertainty in constructing stellar models. whether the amount of overshoot is constant or mass dependent is not completely known, even though models sometimes assume a mass-based trend. in this work we use asteroseismic data from stars observed by kepler to investigate the relations... | examining the relationship between convective core overshoot and stellar properties using asteroseismology |
we show that the recently discovered narrow gap in the gaia hertzsprung-russell diagram near mg = 10 can be explained by standard stellar evolution models and results from a dip in the luminosity function associated with mixing of 3he during merger of envelope and core convection zones that occurs for a narrow range of... | an explanation for the gap in the gaia hrd for m dwarfs |
subsurface convection zones are ubiquitous in early-type stars. driven by narrow opacity peaks, these thin convective regions transport little heat but play an important role in setting the magnetic properties and surface variability of stars. here we demonstrate that these convection zones are not present in as wide a... | a transparent window into early-type stellar variability |
inertial waves, which are predominantly driven by the coriolis force, likely play an important role in solar dynamics, and, additionally, they provide a window into the solar subsurface. the latter allows us to infer properties that are inaccessible to the traditional technique of acoustic wave helioseismology. thus, a... | a spectral solver for solar inertial waves |
the turbulent burning of nuclei is a common phenomenon in the evolution of stars. here we examine a challenging case: the merging of the neon and oxygen burning shells in a 23 m⊙ star. a previously unknown quasi-steady state is established by the interplay between mixing, turbulent transport, and nuclear burning. the r... | turbulent mixing and nuclear burning in stellar interiors |
in an attempt to understand the role of the strong radial dependence of thermal diffusivity on the properties of convection in sun-like stars, we mimic that effect in non-oberbeck-boussinesq convection in a horizontally extended rectangular domain (aspect ratio 16) by allowing the thermal diffusivity κ to increase with... | non-boussinesq low-prandtl-number convection with a temperature-dependent thermal diffusivity |
the surface abundances of the light elements lithium (li) and beryllium (be) reveal information about the physical processes taking place in stellar interiors. the investigation of the amount of these two elements in stars in open clusters shows the effect of age on those mechanisms. we have obtained spectra of both li... | lithium and beryllium in ngc 752-an open cluster twice the age of the hyades |
it has recently been recognized that the convective velocities achieved in current solar convection simulations might be overestimated. the newly revealed effects of the prevailing small-scale magnetic field within the convection zone may offer possible solutions to this problem. the small-scale magnetic fields can red... | convective velocity suppression via the enhancement of the subadiabatic layer: role of the effective prandtl number |
the goal of stellar evolution theory is to predict the structure of stars throughout their lifetimes. usually, these predictions can be assessed only indirectly, for example by comparing predicted and observed effective temperatures and luminosities. thanks now to asteroseismology, which can reveal the internal structu... | testing stellar evolution with asteroseismic inversions of a main-sequence star harboring a small convective core |
elliptical instability is an instability of elliptical streamlines, which can be excited by large-scale tidal flows in rotating fluid bodies and excites inertial waves if the dimensionless tidal amplitude (ɛ) is sufficiently large. it operates in convection zones, but its interactions with turbulent convection have not... | the interactions of the elliptical instability and convection |
the two solar-like stars α cen a and b have long served as cornerstones for stellar physics in virtue of their immediate proximity, association in a visual binary, and masses that bracket that of the sun. the recent detection of a terrestrial planet in the cool, suspected tertiary proxima cen now makes the system also ... | the chemical composition of α centauri ab revisited |
we investigate the hypothesis that ingestion of a terrestrial or super-earth planet could cause the anomalously high metal abundances seen in a turn-off star in the open cluster m67, when compared to other turn-off stars in the same cluster. we show that the mass of the convective envelope of the star is likely only 3.... | super-earth ingestion can explain the anomalously high metal abundances of m67 y2235 |
stars between 2 and 3 m ⊙ rotate rapidly on the main sequence, and their rotation rates in the core-helium burning (secondary-clump) phase can therefore be used to test models of angular momentum loss used for gyrochronology in a new regime. because both their core and surface rotation rates can be measured, these star... | testing angular momentum transport and wind loss in intermediate-mass core-helium burning stars |
we experimentally investigate the dynamics of water cooled from below at 0 ^\circ {c} and heated from above. taking advantage of the unusual property that water’s density maximum is at about 4 ^\circ {c}, this set-up allows us to simulate in the laboratory a turbulent convective layer adjacent to a stably stratified la... | experimental study of internal wave generation by convection in water |
we present an attempt to reconcile the solar tachocline glitch, a thin layer immediately beneath the convection zone in which the seismically inferred sound speed in the sun exceeds corresponding values in standard solar models, with a degree of partial material mixing which we presume to have resulted from a combinati... | on the hydrostatic stratification of the solar tachocline |
we study the formation and inward propagation of a convective layer when a stably-stratified fluid with a composition gradient is cooled from above. we perform a series of two-dimensional simulations using the bousinessq approximation with prandtl number ranging from pr=0.1 to 7, extending previous work on salty water ... | penetration of a cooling convective layer into a stably-stratified composition gradient: entrainment at low prandtl number |
combined action of helical motions of plasma (the kinetic α effect) and non-uniform (differential) rotation is a key dynamo mechanism of solar and galactic large-scale magnetic fields. dynamics of magnetic helicity of small-scale fields is a crucial mechanism in a non-linear dynamo saturation where turbulent magnetic h... | turbulent magnetic helicity fluxes in solar convective zone |
inertial wave modes in the sun are of interest owing to their potential to reveal new insight into the solar interior. these predominantly retrograde-propagating modes in the solar subsurface appear to deviate from the thin-shell rossby-haurwitz model at high azimuthal orders. we present new measurements of sectoral eq... | a linear model for inertial modes in a differentially rotating sun |
context. hot jupiters on extremely short-period orbits are expected to be unstable due to tidal dissipation and spiral toward their host stars. that is because they transfer the angular momentum of the orbital motion through tidal dissipation into the stellar interior. although the magnitude of this phenomenon is relat... | planet-star interactions with precise transit timing. iii. entering the regime of dynamical tides |
rotation and magnetism are increasingly recognized as important phenomena in stellar evolution. surface magnetic fields from a few to 20 000 g have been observed and models have suggested that magnetohydrodynamic transport of angular momentum and chemical composition could explain the peculiar composition of some stars... | rotation and magnetism in intermediate-mass stars |
we investigate stellar magnetic activity from the theoretical point of view, by using stellar evolution models to calculate theoretical convective turnover times (τc) and rossby numbers (ro) for pre-main-sequence and main-sequence stars. the problem is that the canonical place where τc is usually determined (half a mix... | rossby numbers of fully and partially convective stars |
the amplitude of solar p-mode oscillations is governed by stochastic excitation and mode damping, both of which take place in the surface convection zone. however, the time-dependent, turbulent nature of convection makes it difficult to self-consistently study excitation and damping processes through the use of traditi... | the amplitude of solar p-mode oscillations from three-dimensional convection simulations |
double-diffusive systems, such as thermosolutal convection, in which the density depends on two components that diffuse at different rates, are prone to both steady and oscillatory instabilities. such systems can evolve into layered states, in which both components, and also the density, adopt a "staircase" profile. tu... | double-diffusive magnetic layering |
context. the envelopes of stars near the eddington limit are prone to various instabilities. a high eddington factor in connection with the iron opacity peak leads to convective instability, and a corresponding envelope inflation may induce pulsational instability. here, we investigate the occurrence and consequences o... | diagnostics of the unstable envelopes of wolf-rayet stars |
context. turbulent diffusion of large-scale flows and magnetic fields plays a major role in many astrophysical systems, such as stellar convection zones and accretion discs.aims: our goal is to compute turbulent viscosity and magnetic diffusivity which are relevant for diffusing large-scale flows and magnetic fields, r... | turbulent viscosity and magnetic prandtl number from simulations of isotropically forced turbulence |
early-type stars show a bimodal distribution of magnetic field strengths, with some showing very strong fields (≳1 kg) and others very weak fields (≲10 g). recently, we proposed that this reflects the processing or lack thereof of fossil fields by subsurface convection zones. stars with weak fossil fields process these... | magnetic archaeology of early-type stellar dynamos |
recent observations of jupiter and saturn suggest that heavy elements may be diluted in the gaseous envelope, providing a compositional gradient that could stabilize ordinary convection and produce a stably stratified layer near the core of these planets. this region could consist of semiconvective layers with a stairc... | wave propagation in semiconvective regions of giant planets |
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