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i review the evolution of low-mass stars with outer convective zones over timescales of millions-to-billions of years, from the pre-main sequence to solar-age, ~4.6 gyr (bahcall et al. 1995; amelin et al. 2010), and beyond. i discuss the evolution of high-energy coronal and chromospheric emission, the links with stella... | the long-term evolution of stellar activity |
the fact that stellar rotation and chromospheric emission are correlated with age was explicitly noted by wilson (1963) and reinforced by kraft (1967). wilson knew that ca ii emission was correlated with surface magnetic field in the sun. skumanich (1972) suggested a simple functional for the age-activity relation, and... | rotation-activity-age relations for solar-type and cooler stars |
using the data obtained from kepler satellite, we have analyzed an f-type ultra-fast rotator kic 6791060. we derive a rotational period of 0.34365+/-0.00004 d. multiple periodicity with a period separation of ~0.00016 d was detected, which appears to be a result of the relative velocity between the multiple spot-groups... | four years of starspot evolution on an active f-type ultra-fast rotator kic 6791060 |
the extent of the chemically mixed regions associated with convective cores remains uncertain due to our poor understanding of the interface between convective and radiative zones (e.g. overshooting). this generates large uncertainties on stellar ages. so far, several studies have shown that convective cores must exten... | calibrating core overshooting in low-mass stars with kepler data |
this paper presents the results of a set of radiative hydrodynamic simulations of convection in the near-surface regions of a rapidly rotating star. the simulations use microphysics consistent with stellar models, and include the effects of realistic convection and radiative transfer. we find that the overall effect of... | simulating the outer layers of rapidly rotating stars |
the habitability of a planet can be severely affected by the activity of its host star. several young solar-type and fully convective stars observed by the kepler mission produce superflares that are up to 1000 times more energetic than those of the sun. these superflares can increase the level of uv irradiation receiv... | superflares uv impact on the habitability of exoplanetsa |
the accretion-diffusion picture is the model par excellence for describing the presence of planetary debris polluting the atmospheres of relatively cool white dwarfs. inferences on the process based on diffusion timescale arguments make the implicit assumption that the concentration gradient of a given metal at the bas... | metal accretion onto white dwarfs. ii. a better approach based on time-dependent calculations in static models |
mean field models of rotating convection zones reproduce the solar differential rotation remarkably well. we discuss the effects of reynold stress and baroclinity on the meridional flow and the implications for stellar dynamo models. as it turns out the reynolds stress is required to reproduce both the internal rotatio... | meridional flow, differential rotation, and the solar dynamo |
convection remains one of the largest sources of theoretical uncertainty in our understanding of stellar physics. for example, bergeron (1995) show that basic parameters such as flux, line profiles, energy distribution, color indices, and equivalent widths are extremely sensitive to the assumed convective parameterizat... | nonlinear analysis of pulsating white dwarf lightcurves |
we examine the excitation of unstable magnetosonic waves in the radiative envelopes of intermediate- and high-mass stars with a magnetic field of ∼kg strength. wind clumping close to the star and microturbulence can often be accounted for when including small-scale, subphotospheric density or velocity perturbations. co... | subphotospheric fluctuations in magnetized radiative envelopes: contribution from unstable magnetosonic waves |
the measure of surface differential rotation via the motion of spots and/or magnetic features on the stellar surface is a critical part of understanding the stellar dynamo. here we present several epochs of (zeeman) doppler imaging of the young late-f star hr1817 from 2001 until 2011. these results show that hr1817 exh... | stellar differential rotation of f-stars using di and zdi: the case of hr1817 |
due to the space-borne missions corot and kepler, noteworthy breakthroughs have been made in our understanding of stellar evolution, and in particular about the angular momentum redistribution in stellar interiors. indeed, the high-precision seismic data provide with the measurement of the mean core rotation rate for t... | implications of the generation of internal gravity waves by penetrative convection for the internal rotation evolution of low-mass stars |
white dwarfs are compact objects with masses comparable to our sun, but a radius similar to our earth. they are the final evolutionary stage for about 95% of all stars in the galaxy, i.e., for all stars that have a final mass less than the chandrasekhar mass (about 1.4 times the solar mass), the upper mass limit for wh... | numerical simulation of da white dwarf surface convection |
atmospheric tides can have a strong impact on the rotational dynamics of planets. they are of most importance for terrestrial planets located in the habitable zone of their host star, where their competition with solid tides is likely to drive the body towards non-synchronized rotation states of equilibrium, as observe... | atmospheric tides and their consequences on the rotational dynamics of terrestrial planets |
linear damping rates of radial oscillation modes in selected kepler stars are estimated with the help of a nonadiabatic stability analysis. the convective fluxes are obtained from a nonlocal, time-dependent convection model. the mixing-length parameter is calibrated to the surface-convection-zone depth of a stellar mod... | calibrating damping rates with legacy |
the advent of helioseismology has determined in detail the average rotation rate of the sun as a function of radius and latitude. these data immediately reveal two striking boundary layers of shear in the solar convection zone (cz): a tachocline at the base, where the differential rotation of the cz transitions to soli... | exploring the influence of density contrast on solar near-surface shear |
in stellar interiors, the turbulent thermal convection transports matters and energy, and dominates the structure and evolution of stars. the convective overshoot, which results from the non-local convective transport from the convection zone to the radiative zone, is one of the most uncertain and difficult factors in ... | convective overshoot in stellar interior |
the mass of the convection zone in models of pulsating white dwarfs is a sensitive function of the instantaneous surface temperature; this mass can vary by up to a factor of 10 between the minimum and maximum temperature variations. due to this sensitivity, the outer turning point for finite-amplitude g-mode pulsations... | an amplitude limitation mechanism for pulsating white dwarfs |
here, we present a set of time-dependent 3d rmhd simulations of a m-dwarf star representative of ad leo, which extend from the upper convection zone into the chromosphere. the 3d model atmospheres are characterized by a very dynamic and intermittent structure on small spatial and temporal scales and a wealth of physica... | synthetic activity indicators for m-type dwarf stars |
we identified a new strongly metal polluted white dwarf, and report the determination of hydrogen and traces of o, na, mg, si, ca, ti, cr, and fe in a helium-dominated atmosphere. the four most common rock-forming elements, i.e. o, mg, si, and fe embody almost entirely the 1024 g of metals that are mixed in the convect... | is the oxygen-rich white dwarf sdss j1242+5226 accreting water-abundant debris? |
unique observational data from the kepler mission open new perspectives for detail investigation of dynamical and internal properties of numerous stars. however, the new observational results require better understand links between the stellar turbulent convection and oscillations. we perform 3d numerical radiative hyd... | properties of turbulent dynamics and oscillations of main-sequence stars deduced from numerical simulations |
turbulent, density stratified convection is ubiquitous in stars and planets. numerical simulation has become an indispensable tool for understanding it. a primary contribution of this dissertation work is the creation of the compressible high-order unstructured spectral-difference (chorus) code for simulating the conve... | chorus code for solar and planetary convection |
late-type stars with thick convective zones and rapid rotations exhibit magnetic activity phenomena, such as starspots, plages, and flares. however, in many such kinds of eclipsing binaries, the details of the active phenomena are not well understood. in order to improve our understanding of stellar magnetic activities... | lightcurve studies and magnetic activities of several eclipsing binaries |
the inverse problem in a spherical shell to find the two-dimensional spatial distributions of the α-effect and differential rotation in a mean-field dynamo model has been solved. the derived distributions lead to the generation of a magnetic field concentrated inside the convection zone. the magnetic field is shown to ... | invisible dynamo in mean-field models |
a quite remarkable aspect of non-interacting o-stars with detected surface magnetic fields is that they all are very slow rotators. this paper uses this unique property to first demonstrate that the projected rotational speeds of massive, hot stars, as derived using current standard spectroscopic techniques, can be sev... | constraining general massive-star physics by exploring the unique properties of magnetic o-stars: rotation, macroturbulence & sub-surface convection |
we study the field amplification processes in non-rotating stellar cores in axisymmetric simulations with two-moment neutrino transport. flux-freezing in the radial infall compresses the magnetic field and contributes most to the amplification. furthermore, convection in the proto-neutron star (pns) and convection and ... | magnetic field amplification in non-rotating stellar core collapse |
we explore the question of whether the interior state of massive red supergiant supernova progenitors can be probed with asteroseismology. we have computed a suite of ten models with zams masses from 15 to 25 \msun in intervals of 1 \msun, including the effects of rotation, with the stellar evolutionary code {\it mesa}... | asteroseismology of red supergiants |
the unusual light curve of the star kic 8462852, also known as tabbys star or boyajians star, has puzzled us since its discovery last year. a new study now explores whether the stars missing flux is due to internal blockage rather than something outside of the star.mysterious dipsmost explanations for the flux dips of ... | another possibility for boyajian's star |
the ``solar problem'' was revealed when a change in measured solar abundances produced disagreement between solar model predictions and helioseismic measurements. the discrepancy could be resolved if the opacity of materials at conditions near the convection zone base (czb) is higher than predicted by models. oxygen an... | oxygen opacity experiments to advance our understanding of stellar interiors |
the launch of the first bright target explorer (brite) satellites in early 2013 marked the beginning of a generation of nanosatellites (wet mass <10 kg) fully dedicated to astrophysics. the mission is now a constellation of five nanosatellites located on low-earth, sun-synchronous terminator orbits. each brite nanos... | the diverse nature of massive star photometric variability uncovered by the brite nanosatellites |
thermal convection in a periodic, horizontally extended layer of aspect ratio γ = 60 that is driven by a constant heat flux is analysed by means of high-resolution spectral element simulations of three-dimensional turbulent rayleigh-bénard convection. in this case, a process of gradual aggregation results - independent... | controlling supergranule aggregation in convection by weak rotation |
scientific goals and objectives: the primary scientific goal of the proposed study is to understand and characterize the internal structure and turbulent dynamics of the outer convection zones, photospheres, and chromospheres of moderate-mass main-sequence stars using advanced 3d radiative mhd models that are built fro... | realistic radiative 3d mhd modeling of outer convection zones and atmospheres of moderate-mass stars |
to interpret the high-quality data produced from recent space-missions it is necessary to develop theoretical and computational modeling of convection under realistic stellar conditions. we use the multi-dimensional, time implicit, fully compressible, hydrodynamic, implicit large eddy simulation code music, to study th... | penetration beneath the convection zone of solar-like stars of different age |
a decrease in the ice-period on lakes against the background of climate warming improves its oxygen regime in the cold half of the year by reducing the winter anoxia. a decrease in the thickness of the snow-ice cover can contribute to an increase in under-ice irradiation, which can provoke an earlier onset of spring un... | dissolved oxygen variability in a small ice-covered lake during the spring under-ice convection |
gas giant planets are differentially rotating magnetic objects that have strong and complex interactions with their environment. in our solar system, they interact with their numerous moons while exoplanets with very short orbital periods (hot jupiters), interact with their host star. the dissipation of waves excited b... | hydrodynamical modelling of tidal dissipation in gas giant planets at the time of space missions |
opacity calculations for hot dense plasma are challenging due to environment effects on the atoms. in fact, modeled iron opacities are notably different from measurements performed at matter conditions similar to the boundary between the solar radiation and convection zones. the calculated iron opacities have narrower ... | systematic measurements of opacity dependence on temperature, density, and atomic number at stellar interior conditions |
the structure of zeolite ssz‑43 was determined by 3d electron diffraction, synchrotron x‑ray powder diffraction, and high‑resolution transmission electron microscopy. the ssz‑43 framework forms one‑dimensional, sinusoidal 12‑ring channels from 5461 butterfly units commonly found in other zeolites, but with unique 6.5×6... | structure elucidation and computationally guided synthesis of ssz‑43: a one‑dimensional 12‑ring zeolite with unique sinusoidal channels |
we propose to observe a sample of late a to early f stars with xmm-newtonto systematically investigate coronal properties at the onset of stellarmagnetic activity in x-rays. these stars feature a thin or localizedouter convection zone and have been only poorly explored by modern x-rayinstruments. we focus on nearby, pr... | the onset of magnetic activity in x-rays - from late a to early f stars |
non-lte modeling is essential for interpreting the spectra of o stars and their decendents, and much progress has been made. the major uncertainty associated with analyzing photospheric spectra of o stars arises from issues related to microturbulence and macroturbulence. many supergiants, for example, have microturbule... | spectra of hot stars |
in close exoplanetary systems, tidal interactions are known to shape the orbital architecture of the system, modify star and planet spins, and have an impact on the internal structure of the bodies through tidal heating. most stars around which planets have been discovered are low-mass stars and thus feature a magnetis... | nonlinear tidal interactions in the convective envelopes of low-mass stars and giant gaseous planets |
the runaway greenhouse effect [1-4] is a very interesting process for terrestrial planets, studied in particular to determine the inner limit of the habitable zone (hz). this is also important to understand a possible evolution of terrestrial planets from temperate earth-like planets to magma-ocean planets. this runway... | first exploration of the entire runaway greenhouse transition with a 3d global climate model |
the z astrophysical plasma properties (zapp) collaboration is staging z experiments that simultaneously investigate multiple topics in radiative properties of hot dense matter. the four astrophysics questions presently guiding this research are: 1) why can’t we predict the location of the convection zone base in the su... | measuring the radiative properties of astrophysical matter using the z x-ray source |
testing oxygen opacity calculations is important for understanding the sun and white dwarf stars. near the solar convection zone base, te ~ 180 ev, ne ~ 9e22 electrons/cc, and oxygen is mostly h-like or fully-stripped. highly-ionized oxygen produces a relatively simple opacity spectrum, but its calculation relies on un... | oxygen opacity experiments for stellar interiors |
condensation reactions in silanol nests create strain in the structure of zeolite ssz-55. a sufficiently high defect concentration allows the formation of 3-rings due to cooperative relaxation of the framework. deboronation treatment of zeolite b-ssz-55 can generate vacancy defects consisting of four silanol groups (si... | cooperativity of silanol defect chemistry in zeolites |
most stars host convection zones in which heat is transported directly by fluid motion. parameterizations like mixing length theory adequately describe convective flows in the bulk of these regions, but the behavior of convective boundaries is not well understood. here we present 3d numerical simulations which exhibit ... | convective penetration exists and we found it |
our current state-of-the-art computer simulations allow us to build 3d dynamical and radiation models of f-type stars from physical first principles. using the stellar interior's structure from the mesa stellar evolution code as initial conditions, we generate models of main-sequence stars with the mass from 1.4 msun t... | 3d realistic modeling of main-sequence stars with shallow outer convection zone |
main-sequence stars with masses less than 30% that of the sun are fully convective and are the most abundant stars in the galaxy. the question of how fully convective stars generate their magnetic field is of intrinsic interest and also bears upon the habitability of their orbiting planets. these stars currently provid... | flare statistics and high resolution spectroscopy of a volume complete sample of mid-to-late m dwarfs within 15 parsecs |
the rotation-activity relation of m dwarfs is of high astrophysicalinterest due to (i) the predicted dynamo transition at the fullyconvective boundary (spt ~ m3), (ii) differences in angular momentum losswith respect to solar-type stars, and (iii) the small radii of theirplanets habitable zones where they are strongly ... | spin-down, dynamos, and habitability: xmm and k2 exploration of nearby m dwarfs |
for open cluster ages between about 100 myr and 500 myr, plots of rotational period vs. color (or equivalently, stellar mass) are almost bimodal, with distinct groups fast and slow rotators at all masses between roughly 0.5 and 1.3 m_sun. one cannot explain these diagrams without invoking some process with a lifetime o... | is there a relation between stellar wind braking and the spatial structure of surface magnetic fields? |
late-type stars with thick convective zones and rapid rotations exhibit magnetic activity phenomena, such as starspots, plages, and flares. however, in many such kinds of eclipsing binaries, the details of the active phenomena are not well understood. in order to improve our understanding of stellar magnetic activities... | magnetic activities of several eclipsing binaries |
the sun's deep-seated convective flows must ultimately sustain not just the efficient emf from which solar magnetism derives, but also the large-scale shearing and circulatory flows thought to imbue that magnetism with its remarkable spatiotemporal ordering. exploration of the dynamo process ultimately requires knowled... | numerical modeling of a laboratory star |
the gradual aggregation of turbulent plumes and circulation rolls to a large-scale cell which eventually fills the whole periodic, horizontally extended layer of aspect ratio γ = 60 is reported in high-resolution spectral element simulations of three-dimensional turbulent rayleigh-bénard convection. it is shown that th... | large-scale cell formation in turbulent rayleigh-bénard convection |
the accretion of heavy material from debris disk on the surface of hydrogen-rich white dwarfs induces a double-diffusivity instability known as the fingering (thermohaline) convection. it leads to an efficient extra mixing which brings the accreted material deeper in the star than by considering only mixing in the surf... | the role of fingering convection in accreting hydrogen-rich white dwarfs: the case of gd 133 and g 29-38 |
i will present an overview of the current developments to determine flows in the solar interior and recent results from helioseismology. i will lay special focus on the inference of the deep structure of the meridional flow, which is one of the most challenging problems in helioseismology. in recent times, promising ap... | measuring flows in the solar interior: current developments, results, and outstanding problems |
model predictions for iron opacity are notably different from measurements performed at matter conditions similar to the boundary between the solar radiation and convection zones. the calculated iron opacities have narrower spectral lines, weaker quasi-continuum at short wavelength, and deeper opacity windows than the ... | systematic measurements of opacity dependence on temperature, density, and atomic number at stellar interior conditions |
the structures of stellar interiors are known to transition from partially convective for stars like the sun to fully convective around mid-m dwarfs. in the past, identifying the location of the transition has relied on estimated masses or spectral types rather than empirical measurements. however, the discovery of a `... | studying activities of m dwarfs close to the gap in the lower main sequence |
in this paper, we discuss about the correlation between microturbulence and the fluctuations of central depth of s ii line profile of iota herculis a b3 iv star, based on 144 spectra from the elodie archive data (may 17 to 21, 1995) and 47 spectra from the archive data of ritter observatory (february 6, 1994 to october... | on correlation of microturbulence and the line depth of s ii line profile in iota herculis |
we have spectroscopically identified 61 very cool (below 9000 k) and old (1-7 gyr) dz white dwarfs from the sloan digital sky survey (sdss). these stars have evaded prior detection as the extremely broad ca h/k lines in the blue part of their spectra dramatically alter their colours, mixing them into the colour-space o... | evolved planetary systems around very cool and old white dwarfs |
the amplification of magnetic fields inside the star, a process known as stellar dynamo, is driven by convection of the plasma within, and forces introduced by stellar (differential) rotation. the exact mechanisms behind the stellar dynamo are, however, poorly understood. one way to discriminate between different dynam... | mapping flare locations with time series observations of stellar ensembles |
how does energy propagate from the core to the surface of the sun, where it emerges to warm the earth? nearly a century ago eddington recognized that the attenuation of radiation by stellar matter controls the internal structure of stars like the sun. opacities for high energy density (hed) matter are challenging to ca... | measuring the opacity of stellar interior matter in terrestrial laboratories |
younger and fully convective stars are much more active than our sun, producing many superflares. here we estimate the impact of the superflares uv radiation on living organisms on the surface of orbiting planets in the habitable zone of the star. for this we study two active stars, kepler-96 (solar type) and trappist-... | the biological impact of superflares on planets in the habitable zone |
it is known that lithium is destroyed in the inner layers of a star via proton capture ( 7li(p, α)α) at temperatures near to 2.5 ∗ 106 k. due to the fact that li burning happens when the element is transported to the innermost and hotter regions through convective motions of the star, li abundance studies offers an exc... | lithium depletion and the star age connection |
current state-of-the-art computer simulations allow us to build 3d dynamical and radiative models of stars from physical first principles with a high degree of realism. the radiative 3d dynamical stellar models obtained with the stellarbox code take into account the effects of turbulence, stellar abundances, a realisti... | effects of rotation on internal structure and dynamics of main-sequence stars |
we model the observed precision differential abundance (pda) pattern of three g-type dwarfs: hip 29432, hip 77052, and hip 101905. pdas are from bedell et al. (2018, apj, 865, 68, 2018, bd18). we also model the wide pair hip 34407 and hip 34426, where galactic chemical evolution (gce) corrections are assumed unnecessar... | modeling the abundance patterns resulting from addition of earthlike material |
we re-analsed all kepler photometric data of the fast rotating b-type pulsator kic 11971405; we extracted pulsation frequencies, and found five period spacing patterns, i.e. sequences of frequencies quasi-equally spaced in period. our modelling shows that four sequences could be associated with prograde sectoral modes ... | kic 11971405 - the spb star with the four asymptotic sequences of g modes |
flares are the most extreme evidence of the magnetic activities of the sun and the stars. observations of the flares are essential to provide valuable constraints to the existing dynamo theory. we present the analysis of thirteen x-ray flares on a 6.44-day period active rs canum venaticorum-type tidally locked binary u... | nicer and swift observations of x-ray superflares on active rs cvn-type binary ux ari |
the tide raised by the companion in the red giant branch (rgb) star leads to an exchange of angular momentum between the orbit and the stellar spin, causing the orbit to contract. two mechanisms are often invoked to explain tidal friction in binary systems. the ``dynamical tide" is the resonant excitation of internal g... | orbital decay in binaries containing post-main-sequence stars |
internal gravity waves (igws) that propagate in stellar interiors have become essential in stellar physics. these waves are well known for transporting angular momentum (am), energy and chemical elements in stably stratified media, i.e. radiative zones of stars. for instance, they could explain the solid rotation of th... | exploring waves properties with multi-dimensional fully compressible hydrodynamical simulations: from solar type stars to intermediate-mass stars |
over the past two decades, observations and numerical simulations revealed the ubiquitous presence of small-scale vortical motions in the quiet solar atmosphere. similar swirling flows can be expected to occur in other stellar atmospheres than solar. we investigate the presence and properties of small-scale vortices in... | small-scale vortices in stellar atmospheres |
magnetic reconnection lies at the heart of much stellar phenomena in the cool half of the h-r diagram, and x-ray studies of stellar coronae have revealed the intricate interplay of plasma and magnetic fields, ultimately produced as the result of a dynamo process. the breakthrough of chandra and xmm-newtons high resolut... | coronal spectroscopy for dynamo studies |
model predictions for iron opacity are notably different from measurements performed at conditions similar to the boundary between the solar radiation and convection zone. new measurements at the sandia z facility with chromium, iron, and nickel are providing a systematic study of how opacity changes with temperature, ... | systematic measurements of opacity dependence on temperature, density, and atomic number at stellar interior conditions |
clouds are important for the climates of earth and other planets. using atmospheric general circulation models (gcms), previous studies have shown that on tidally locked planets and slowly rotating planets, convective clouds form over the permanent or slowly moving substellar region. these clouds are effective to refle... | global high-resolution simulations of clouds on tidally locked planets |
natural disasters have profound effects on community security and economic damage of china's hubei province. in june 1st, 2015, a cruise ship, easter star, capsized on yangtze river in hubei province with 442 died. what reason gives rise to such strong convection causing ship sunk? based on the wind disasters of hubei ... | is enso related to 2015 easter star capsized on the yangtze river of china? |
we compare predicted enrichments of s-process nucleosynthesis products during the asymptotic giant branch (agb) from independent theoretical models, focusing on stars with initial masses of 2.0 and 3.0 m⊙ and near-solar and half-solar metallicities: z = 0.005-0.015. the motivation for this study, in part, is to compare... | comparison of the predicted s-process enrichments from different agb evolutionary models |
motivated by the dynamics in the deep interior of the sun and solar-type stars, we study overshooting convection in a spherical shell that consists of a convection zone overlying a stably stratified region. we focus on the effect of density stratification and rotation on the overshooting dynamics. this is accomplished ... | overshooting in anelastic convection: effect of density stratification and rotation |
although seismic inference has proven to be valuable on many occasions when determining stellar parameters of solar-like pulsators, estimating these very parameters can be subject to biases and thus remain uncertain. a particularly important example is the helium-mass degene- racy, where the uncertainties on the intern... | inférence des propriétés physiques de régions d'ionisation stellaires au moyen de glitchs sismiques |
most red giant models do not reproduce the position of the observed luminosity bump, a diagnostic of the maximum extension of the convective envelope during the first-dredge up. global seismic parameters, the large frequency separation and frequency of maximum oscillation, show that overshoot below the convective envel... | red giant seismology: seismic signatures of convective overshoot |
starspots are windows into a star’s internal dynamo mechanism. however, the manner by which the dynamo-generated magnetic field traverses the stellar interior to emerge at the surface is not especially well understood. establishing the details of magnetic flux emergence plays a key role in deciphering stellar dynamos a... | simulations of magnetic flux emergence in cool, low-mass stars: toward linking dynamo action with starspots |
low-mass stars spin-down over time due to angular momentum loss from magnetized stellar winds. this spin-down is interrupted by an epoch of stalling where stars halt their spin-down for 0.1-2 gyr. duration of the stalling epoch is mass-dependent, with higher mass stars spending less time stalled than the lowest mass st... | rotational stalling ends when main-sequence core temperatures are at a minimum |
the presence of (unresolved) small-scale mixed polarity regions in the quiet sun photosphere plays an important role in determining the basal magnetic flux. observationally, the magnitude of the vertical component of this field is estimated to be ~50-100 g on the sun. this field is important for determining the energy ... | effects of inclusion of small-scale dynamo in near-surface structure of f-stars |
thermal convection, constrained by rapid rotation and/or large-scale magnetic fields, is observed almost everywhere in the universe: stars, galaxies, and planetary interiors. however, little is known about the essential behaviors of turbulent convection in liquid metals and even less is known about the essential dynami... | container-scale hydrodynamic and magnetohydrodynamic modes in liquid metal rotating convection experiments with and without an imposed magnetic field |
dramatic deficiencies of li in the mid-f dwarf stars of the hyades cluster were discovered by boesgaard and tripicco in 1986. using high-resolution, high signal-to-noise spectra from the keck 10-m telescope, boesgaard and king discovered the corresponding, but smaller, deficiencies in be in the same narrow temperature ... | boron abundances across the "li-be dip" in the hyades cluster |
the rosseland-mean opacity (rmo) is an important quantity in determining radiation transport through stars. the solar-convection-zone boundary predicted by the standard solar model disagrees with helioseismology measurements by many sigma; a 14% increase in the rmo would resolve this discrepancy. experiments at sandia ... | influence of projection operator on oxygen line shapes and its effect on rosseland-mean opacity in stellar interiors |
improving our understanding of stellar interior mixing physics is important in many areas of astrophysics since astronomers rely on stellar modeling to produce reliable estimates for stellar ages. the complex process of convective fluid parcels moving past convection zone boundaries into radiative zones in stars is cur... | red giant seismology: seismic signatures of convective overshoot |
we study the convective flow in a rapidly rotating spherical shell that models planet cores or stellar convective zones. flows in these astrophysical objects are often in a strongly rotationally constrained regime (low ekman number) which is out of reach of current analytical, numerical, and experimental studies. rotat... | equatorially localized convection in a rapidly rotating shallow spherical shell |
the rotation-activity relation of m dwarfs is of high astrophysicalinterest due to (i) the predicted dynamo transition at the fullyconvective boundary (spt ~ m3), (ii) differences in angular momentum losswith respect to solar-type stars, and (iii) the small separation of theirplanets' habitable zones where they are str... | spin-down, dynamos, and habitability: the xmm-k2 exploration of nearby m dwarfs |
we investigate the interaction between a molecule and a pore mouth—a critical step in adsorption processes—by characterizing the conformation of a macrocyclic calix[4]arene‑tiiv complex, which is grafted on the external surface of a zeotype (*‑svy). x‑ray absorption and 13c{1h} cpmas nmr spectroscopies independently de... | characterization of a molecule partially confined at the pore mouth of a zeotype |
recent interferometric data have been able to constrain the brightness distribution at the surface of nearby stars, in particular the gravity darkening that makes fast rotating stars brighter at their poles than at their equator. however, good models of gravity darkening are missing when the stars own a convective enve... | gravity darkening in late-type stars |
it has been recently claimed that the sun's activity is abnormally low relative to analogous stars observed by nasa's kepler space telescope (reinhold et al. 2020). stars were identified that have temperatures, luminosities, and rotation periods that are similar to the modern sun. using the range of photometric variabi... | the sun's magnetic activity is normal for its age |
in close exoplanetary systems, tidal interactions are known to shape orbital architectures, to modify star and planet spins, and to have an impact on the internal structures of the bodies through tidal heating. most stars around which planets have been discovered are low-mass stars and thus feature a convective envelop... | nonlinear tidal interactions in the convective envelopes of low-mass stars and giant gaseous planets |
much of our knowledge of the universe stems from our understanding of the sun. however, ongoing disagreement between solar models and helioseismic measurements of the interior structure of the sun raises concerns about the accuracy of stellar models. one hypothesis that could resolve this discrepancy is if the opacitie... | oxygen opacity experiments for stellar interiors at z |
plato has been selected for esa's m3 launch opportunity with launch foreseen end 2024. plato will follow the very successful space missions corot and kepler, as well as esa's first small mission cheops and nasa's mission tess. plato will carry out high-precision, long-term photometric and astroseismic monitoring of up ... | the plato 2.0 mission |
iron is the dominant heavy element that determines radiation transport in stellar interiors. in particular, a few iron ions, constitute the abundance and opacity of iron at the solar radiative-convection zone boundary at the base of the convection zone (bcz) where the temperature is 2 . 11 ×106 k and the electron densi... | the iron project & the opacity project: iron ions at the solar radiative-convection boundary - fe xvii, fe xviii, fe xix |
in the solar context, important insight into the flux emergence process has been obtained by assuming the magnetism giving rise to sunspots consists partly of idealized flux tubes. global-scale dynamo models are only now beginning to capture some aspects of flux emergence. in certain regimes, these simulations self-con... | exploring the flux tube paradigm in solar-like convection zones |
barnard's star is among the most studied stars given its proximity to the sun. it is often considered the radial velocity (rv) standard for fully convective stars due to its rv stability and equatorial declination. recently, an m sin i = 3.3m⊕ super-earth planet candidate with a 233 day orbital period was announced by ... | stellar activity manifesting at a one year alias explains barnard b as a false positive |
the so-called "solar problem" was revealed when a change in measured solar abundances produced disagreement between solar model predictions and helioseismic measurements. the discrepancy could be resolved if the opacity of materials at conditions near the convection zone base (czb) were higher than predicted by models.... | oxygen opacity of stellar interiors in the laboratory |
we present the tess discovery of the lhs 1678 (toi-696) exoplanet system, comprised of two sub-earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright m2 dwarf at 19.89 pc. the two tess-detected planets are of radius 0.7 earth radii and 0.9 earth radii in 0.86-day and 3.69-day orbits, resp... | the lhs 1678 system: a peculiar m dwarf at 20 pc with two small planets and an astrometric companion |
the problem of asynchronous rotation of massive stars in close binary systems is investigated in this paper. a massive star with twice the sun's mass, a convective core, and an external radiative transfer zone (envelope) is examined. the model takes into account the influence of the companion on the star. it is assumed... | asynchronous rotation of a massive star in close binary systems |
the onset of eruptive flare energy release requires both a buildup of stored energy and a trigger for the release of that energy. this talk will review key models of how this storage and release occurs in solar eruptions, in particular for breakout eruptions and for torus instability eruptions. in both cases, the erupt... | theory and models of flare/cme onset via flux emergence and/or shear flows |
we present multidimensional modeling of convection and oscillations in main-sequence stars somewhat more massive than the sun, using three separate approaches: 1) applying the spherical 3d mhd ash (anelastic spherical harmonics) code to simulate the core convection and radiative zone. our goal is to determine whether c... | 2d and 3d models of convective turbulence and oscillations in intermediate-mass main-sequence stars |
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