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much of our knowledge of the universe stems from our understanding of the sun. however, updated measurements of abundances have revealed a disagreement between solar models and helioseismic measurements of the interior structure of the sun. one hypothesis that could resolve this discrepancy is if the opacities of matte... | oxygen opacity experiments to advance our understanding of stellar interiors |
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 = 3.3 m⊕ 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 rossby number, the ratio of inertial to coriolis forces, of convective envelopes is a deciding parameter in the magnetic braking formulation of van saders et al. (2016) and metcalfe et al. (2016). what is needed is a bulk quantity, but the rossby number is inherently a local quantity, since those forces depend on l... | effective rossby numbers of stellar convective envelopes from 3d simulations |
the mean field hydromagnetic dynamo equations describing the generation of magnetic fields on the sun use tensor coefficients that can be calculated within the framework of a complete model that resolves all scales. however, due to the limited computing power, this is practically difficult to implement, therefore, when... | flax of small-scale magnetic helicity in the solar convective zone: theory and comparison with observations |
we investigate via direct numerical simulations the spontaneous generation and reversals of mean zonal flows in a stably-stratified fluid layer lying above a turbulent convective fluid. contrary to the leading idealized theories of mean flow generation by self-interacting internal waves, the emergence of a mean flow in... | spontaneous generation and reversals of mean flows in a convectively-generated internal gravity wave field |
to interpret the high-quality data produced from recent space-missions it is necessary to study convection under realistic stellar conditions. we describe the multi-dimensional, time implicit, fully compressible, hydrodynamic, implicit large eddy simulation code music. we use music to study convection during an early s... | convective penetration in a young sun |
the x-ray emission from intermediate-mass, pre-main-sequence stars (imps) can provide useful constraints on the ages of very young (${<}5$~myr) massive star forming regions. imps have masses between 2 and 8 $m_{\odot}$ and are getting power from the gravitational contraction of the star. main-sequence late-b and a-t... | characterizing intermediate-mass, pre-main-sequence stars via x-ray emision |
understanding the turbulent dynamics of the sun and stars is a critical element for interpreting observed processes and phenomena on different scales and for predicting extreme events such as flares and superflares. high-resolution observations of the sun and high-fidelity radiative mhd numerical simulations have subst... | realistic 3d radiative modeling of turbulent structure of moderate-mass stars and sun |
gyrochronology is a precise way to estimate stellar ages for low-mass stars, as they spin down rapidly due to their deep convection zones and strong magnetic fields. however, calibrating empirical gyrochronology relations for low-mass stars is difficult. these stars are faint and hard to observe, and most age-dating me... | gyro-kinematic ages for around 30,000 kepler stars |
the rotation and magnetic evolution of stars is examined in detail. advection of angular momentum by convective plumes is a source of differential rotation, which both reduces the angular momentum loss to stellar winds and spins up the inner regions. this spin up not only affects the rotation of the stellar remnant, bu... | properties of stellar remnants: rotational and magnetic evolution of their progenitors |
the climates and atmospheric structures of worlds throughout our solar system are substantially influenced by the formation of clouds. furthermore, the radiative properties of clouds are critical to earth remaining habitable. thus, clouds are likely key in driving habitable conditions on rocky worlds in the habitable z... | one-dimensional models of partially clouded super earths |
flare activity in late m stars remains an interesting topic since there is as yet no well tested model of how these convective stars generate the magnetic field that underlie activity such as flares, and the rate and strengths of the flare can impact the evolution of the atmospheres of planets orbiting them we present ... | exploring flares around the ultracool m dwarf vb-10 with high resolution infrared spectroscopy |
in this paper, turbulent properties and correlations of helium convective shells (due to partial ionization of helium) of 30 $\, \mathrm{m}_{\odot }$ star are researched. as evolution proceeds, the turbulence in helium convective shells becomes more and more intense. choosing the stellar models of which effective tempe... | turbulent properties of helium convective shells of massive stars |
the aim of the current study is the computation of the magnetic flux tube wave energies and fluxes generated in the convection zone of procyon a. this is a subgiant of spectral type f5 iv-v showing chromospheric and coronal activities. the mechanisms responsible for the generation of different wave modes include the in... | generation of non-linear magnetic flux tube wave energies in procyon a |
the habitable zone is an orbital region around a star in which an earth-like planet can maintain liquid water on its surface given a variety of atmospheric compositions. however, the abundance of water on the earth's surface is not controlled by the atmosphere, but rather by the deep water/silicate cycle. on the earth,... | persistence of oceans on earth-like planets |
during the pms, structure and rotation rate of stars evolve significantly. we wish to assess the consequences of these drastic changes on stellar dynamo, internal magnetic field topology and activity level by mean of hpc simulations with the ash code. to answer this question, we develop 3d mhd simulations that represen... | dynamo action and magnetic activity during the pre-main sequence: influence of rotation and structural changes |
we have been studying convection, mass entrainment, and mixing processes in the convective boundary region as well as the radiative envelope for a model star of 25 solar masses using the 3-d stellar hydrodynamics code ppmstar. we will report on the portion of this work that focuses on the effects of rotation of the mod... | 3d hydrodynamic simulations of rotating, massive, main-sequence stars: a study of the interaction of core convection with rotation |
the sun is the most observed star in the universe. thanks to this privileged status, it plays a key calibrator role for stellar physics, acting as a laboratory to test fundamental physical ingredients used in theoretical computations. therefore, any refinement of the recipe of solar models will impact the ingredients f... | a new generation of evolutionary and seismic solar models |
magnetism is paramount to most, if not all, solar and stellar physics phenomena and how stars interact with planetary environments, particularly those residing in the habitable zone. solar magnetic fields are generated by dynamo processes in the convection zone and rise through the photosphere to dominate the corona an... | observing and inferring solar chromospheric and coronal magnetic fields |
the advent of helioseismology has revealed in detail the internal differential rotation profile of the sun. in particular, the presence of two boundary layers, the tachocline at the bottom of the convection zone (cz) and the near surface shear layer (nssl) at the top of the cz, has remained a mystery. these two boundar... | toward a self-consistent dynamical model of the nssl |
criteria for habitability are often discussed in terms of the habitable zone, but in addition, a sufficient amount of water is required at the surface to develop water oceans. the majority of the water inventory could remain in the mantle during magma ocean solidification, and mantle degassing during the subsequent per... | does detecting water vapor on rocky planets indicate the presence of oceans? |
using theoretical global mhd simulations, i address two striking features of the sun's internal rotation profile revealed by helioseismology. the first of these is the sun's isorotation contours, which are significantly tilted in the bulk of the convection zone. these tilts are likely a key feature of the solar dynamo ... | new insights into the theory of the sun's internal rotation rate |
we present an analysis of a very large flare from the 3.966-day period rs cvn type (k1 iv -- f8 v) eclipsing binary system sz psc. the flare triggered the swift burst alert telescope hard x-ray detector at 09:08:42 ut on 15 january 2015. we found that the flare is out of the eclipse. it lasts for $>$1.3 days, and it... | a very long and hot x-ray superflare on an rs cvn type eclipsing binary sz psc |
nearly a century ago, eddington [1] recognized that the attenuation of radiation by stellar matter controls the internal temperature profiles within stars like the sun. opacities for high energy density (hed) matter are challenging to calculate because accurate and complete descriptions of the energy level structure, e... | laboratory opacity measurements for stellar interiors |
our understanding of material opacities in stellar interiors is under scrutiny. oxygen is among the important contributors to opacity near the base of the solar convection zone. remarkably, the conditions in this region (180ev, 1e23 e/cc) are similar to some white dwarf stars. the experimental platforms at z and nif pr... | temperature and density measurements from stellar interior oxygen opacity experiments using k-shell spectroscopy |
we extend the notion of a shell model to stratified systems, and propose one that represents stratified, nonmagnetic, nonrotating convection at low mach number. motivated by profiles of background stratification that support convection in stars such as the sun, we study numerical solutions corresponding to a highly uns... | shell model for stratified convection: implications for the solar convective conundrum |
the radiative magnetohydrodynamic css code is used to simulate 3-d spherical segments of the convective regions of two red-supergiants of differing masses. much as in the recent work of y. jiang (2015), it is found that the density inversion characteristic of 1-d stellar evolution calculations can instead become monoto... | global-scale 3-d rmhd simulations of red-supergiant convective envelopes |
we study thermal convection in rotating spherical shells as prototype models for flow in the cores of terrestrial planets, gas planets or in stars. we base our analysis on a set of about 450 direct numerical simulations of the (magneto)hydrodynamic equations under the boussinesq approximation. the ekman number ranges f... | effect of shear and magnetic field on the properties of convection in rotating spherical shells |
stars on the lower main sequence have substantial, stratified convection zones that span many density scale heights. there, low mach number convection dominates the transport of heat, angular momentum and the dynamo generation of magnetic fields. many aspects of low mach number stratified convection remain unclear. her... | stratified convection in stellar interiors |
with over 4,000 exoplanet discoveries to date, we have caught a glimpse of the broad diversity of planets that span a range of masses, compositions, and orbital configurations. the next chapter in exoplanet exploration will focus on probing the atmospheres of these worlds, and we are now poised to begin large-scale atm... | characterizing distant worlds: atmospheric reconnaissance of giant planets with hubble |
asymptotic giant branch (agb) stars are thought to be among the most important sources of fluorine in our galaxy. while observations and theory agree at close-to-solar metallicity, stellar models overestimate fluorine production in comparison to heavy elements at lower metallicities. we present predictions for 19f abun... | fluorine nucleosynthesis and s-processing in agb stars driven by magnetic-buoyancy mixing |
we have gathered optical-region spectra and derived model atmosphere parameters and elemental abundances for 15 red giant stars in the open cluster ngc 7789. during normal stellar evolution after the main sequence, stars become highly convective. this circulates lithium from the outer to the inner layers, where the hig... | chemical compositions of red giant stars in the open cluster ngc 7789 |
convective overshoot is an important non-local mixing and transport process in stars, extending the influence of turbulent stellar convection beyond the unstable portions of the atmosphere. in the sun, overshoot into the tachocline at the base of the convection zone has been ascribed a major role in the storage and org... | convective overshoot at stiffly stable interfaces |
the interior convection regime of a planet -plate tectonics or stagnant lid- is thought to be important to the habitability of its surface environments (cockell et al., 2016). the plate tectonics regime ensures sustained volcanic outgassing over geological timescales, possibly preventing global glaciation, as well as a... | detectability and habitability of stagnant-lid worlds: constrains on the required sample size |
despite the prevalence of m dwarfs, the smallest and most common type of main sequence star, their sizes, compositions, and ages are not well-constrained. empirical determination of these properties is important for gaining insight into their stellar structure, magnetic field generation, and angular momentum evolution.... | the evolution of rotation and magnetism in small stars near the sun |
whether a planet has liquid water at its surface depends on at least two energy sources: solar and internal. as a star ages, it brightens and delivers more energy to a planet at a given orbital distance. the planet ages, too. it produces heat within through radiogenic decay. one mode to eliminate internal energy is thr... | entering the habitable zone: an earth-like perspective |
the main sequence gap in the m dwarf regime reported in jao et al. (2018) is a result of 3he mixing during the merger of envelope and core convection zones. models indicate that stars in a narrow mass range around 0.3 m will exhibit instability phases during which their dynamos can switch between the alpha-omega dynamo... | connecting m dwarf pulsation and surface activity for gap stars |
over 4000 exoplanets have been discovered in the past 25 years or so, most of which orbit cool stars. star-planet tidal interactions are known to drive the late evolution of the shortest-period planetary systems via tidal dissipation. such dissipation is known to vary considerably with the mass, age, rotation, and meta... | differential rotation and stellar magnetism impact star-planet tidal interactions |
gaseous giant planets (jupiter and saturn in our solar system and hot jupiters around other stars) are turbulent rotating magnetic objects that have strong and complex interactions with their environment (their moons in the case of jupiter and saturn and their host stars in the case of hot jupiters/saturns). in such sy... | tidal dissipation modelling in gaseous giant planets at the time of space missions |
a wide range of problems requires knowledge of the structure and dynamics of stellar photospheres and interiors. for instance, the characterization of stellar jitter as a source of radial velocity background noise is needed for detecting signals induced by earth-mass exoplanets. furthermore, the proper interpretation o... | advances in 3d realistic modeling of solar-type stars to study stellar jitter and photospheric and subsurface dynamics |
in white dwarfs that undergo convective coupling, the degenerate conductive core and outer convective plasma are separated by a layer of warm dense matter. this layer acts as a bottleneck for the transport of energy from the core to the convection zone, and the cooling rate and inferred age of the white dwarf are sensi... | new thermal conductivities for warm dense matter and the age of the galaxy |
exoplanet statistics suggest that the fraction of sun-like stars with planets may be as large as $100%$. the supposed detection of an earth-mass exoplanet orbiting $\alpha$ centauri b - though retracted later - has drawn great attention to finding earth-like planets in the nearest and triple star system. the discovery ... | reasoning the chemical composition and geological evolution of terrestrial planets to be found in the alpha centauri a and b system: a top-down approach |
motivated by the deep solar interior, we study the dynamics associated with the overshooting of turbulent motions from an outer convective region into an underlying stably stratified radiative zone. we systematically examine the effect of density stratification and rotation on convective overshooting via the use of 3d ... | effect of density stratification and rotation on the dynamics of overshooting convection |
we propose to use letgs to observe the x-ray spectrum of eta lep (f1 v), which would be the earliest type coronal main sequence star successfully observed with grating spectroscopy by chandra. the goal is to better understand how coronal properties change as stellar convection zones become very thin. we are particularl... | coronal properties at the edge of coronal viability |
the rotation-activity relation of m dwarfs is of high astrophysical interest due to (i) the predicted dynamo transition at the fully convective boundary (spt ~ m3), (ii) differences in angular momentum loss with respect to solar-type stars, and (iii) the small radii of their planets' habitable zones where they are stro... | spin-down, dynamos and habitability: chandra/k2 exploration of nearby m dwarfs |
convection is an important phenomena in stars. within stellar convection zones, the transport of heat, magnetic fields and other quantities is highly non-local. at the boundaries of convection zones, the stratification becomes stable and internal gravity waves dominate the dynamics. the extent to which convection overs... | convective overshoot in the interiors of solar-type stars |
early earth conditions were largely erased, but the powerful virial theorem (vt) constrains earth's post-accretion state, which largely dictates subsequent thermal and dynamical evolution. proposals of huge initial inventories of primordial heat are based on kelvin's disproven theory of starlight. rather, the vt requir... | consequences of an immense hadean-archean heat flux that results from virial theorem constraints on the earth's initial axial spin |
opportunity of the solar flares (sf's) prediction observing the solar neutrino fluxes is investigated. in three neutrino generations the evolution of the neutrino flux traveling the coupled sunspots (cs's) which are the sf source is considered. it is assumed that the neutrinos possess both the dipole magnetic moment an... | solar neutrinos as indicators of the sun's activity |
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 thought to arise when the coriolis effects are stronger than those associated with buoyancy driving of the convect... | the transition from solar-like to antisolar differential rotation: a geometric intepretation |
der zeolithkatalysator ssz‑42 besitzt einen außerordentlich hohen anteil von wasserstoff‑verbrückten brønstedsäure‑zentren (brønsted acid sites, bas) von ≈80 %, deren 1h chemische verschiebung verglichen mit unverbrückten bas (bei typischerweise 4 ppm) stärker entschirmt ist. dies kommt durch die wechselwirkung aufgrun... | brønstedsäure‑zentren in zeolith ssz‑42 werden von wasserstoffbrücken dominiert – eine einteilung ihrer vielfalt |
overshooting convection is a physical process by which turbulent convective motions generated in a convectively unstable region can propagate into a stably stratified zone that lies either on top or on bottom of the convective one. this process can lead to mixing of chemical species, thermal mixing, as well as contribu... | dynamics of overshooting convection in a rotating spherical shell |
the sizes of stellar convective cores remain uncertain because of our poor understanding of the interface between convective and radiative zones. the very high precision of the seismic data provided by the corot and kepler space missions offers a great opportunity to search for the signature of convective cores in main... | an attempt to calibrate core overshooting using the seismic properties of low-mass stars |
tidal interactions are important in driving spin and orbital evolution in various astrophysical systems such as hot jupiters, close binary stars and planetary satellites. however, the fluid dynamical mechanisms responsible for tidal dissipation in giant planets and stars remain poorly understood. one key mechanism is t... | convective turbulent viscosity acting on equilibrium tidal flows: new frequency scaling of the effective viscosity |
with over 4,000 exoplanet discoveries to date, we have caught a glimpse of the broad diversity of planets that span a range of masses, compositions, and orbital configurations. the next chapter in exoplanet exploration will focus on probing the atmospheres of these worlds, and we are now poised to begin large-scale atm... | characterizing distant worlds: atmospheric reconnaissance of giant planets with hubble |
the habitability of a planet depends on various factors, such as delivery of water during the formation, the coevolution of the interior and the atmosphere, as well as the stellar irradiation which changes in time. we have studied the habitable zone evolution of earth-like stagnant-lid exoplanets around m, k, g and f-t... | the habitability of stagnant-lid earths around dwarf stars |
the corona of the sun, and probably also of other stars, is built up by loops defined through the magnetic field. they vividly appear in solar observations in the extreme uv and x-rays. high-resolution observations show individual strands with diameters down to a few 100 km, and so far it remains open what defines thes... | coronal loops in a box: 3d models of their internal structure, dynamics and heating |
as we advance towards the observation and comparative analysis of exoplanets atmospheres, the search for life beyond our solar system will be enhanced with a new statistical dimension, enabling population-level studies of potentially habitable worlds. here we ask, what trends in surface properties can we predict to eme... | predicting quantitative biosignature patterns from populations of exoplanets |
magnetic activity and variations of solar-type stars are governed by dynamo layers below or inside the convection zone. this layer is supposed to be much shorter than the stellar radius, so large-scale magneto-rossby waves can be trapped inside. the waves may cause variations in the dynamo magnetic field and can thus c... | magneto-rossby waves and short-term periodicity in solar-type stars |
the atmospheric evolution of terrestrial planets is sculped by a range of complex astrophysical, geophysical, and geochemical processes. interpreting observations of ostensibly habitable exoplanets will require an improved understanding of how these competing influences interact on long timescales. in particular, the i... | investigating the atmospheric evolution of habitable worlds with a coupled climate-interior-redox model |
in the plate tectonic convection regime, the external lid is subdivided into discrete plates that move independently. although it is known that the system of plates is mainly dominated by slab-pull forces, it is not yet clear how, when and why plate tectonics became the dominant geodynamic process in our planet. it cou... | emergence of plate tectonic during the archean: insights from 3d numerical modelling. |
the oscillations of a slowly rotating star have long been classified into spheroidal and toroidal modes. the spheroidal modes include the well-known 5-min acoustic modes used in helioseismology. here we report observations of the suns toroidal modes, for which the restoring force is the coriolis force and whose periods... | solar inertial modes: observations and modeling |
flares are sudden emissions of energy produced in the stellar atmospheres flares produced by m main-sequence stars are more energetic and frequent compared to flares from sun-like stars. here, we focus on the effects of a flare uv emission (100-350 nm) in the atmospheric chemistry of planets in the habitable zone (hz) ... | the effect of uv radiation from flares on the oxygen chemystry in low o2 atmospheres of potentially habitable planets around m dwarfs |
how do binaries in circular orbitscome to be, especially for pairs of solar-type stars? using stellar models, a researcher has brought us closer to understanding how the loss of energy in a system eventually leads it to circularize.good things come in pairswhen you look out into the night sky, you may just see a bunch ... | tidal dissipation makes the binary go 'round |
context. the short-time (< 700 days) periodicities of both the stellar and solar activity that controls space weather are usually are discussed as manifestations of rossby modes in tachoclines. various interpretations of this phenomenon that have been proposed, in particular for the sun, can be verified by consideri... | tachocline alfvén waves manifested in stellar activity |
we model damping rates and modal frequency corrections for twelve selected kepler legacy stars. the linear stability calculations adopt the nonlocal, time-dependent convection model by gough (1977), implemented consistently in both the stellar equilibrium-structure modelling and in the nonadiabatic pulsation calculatio... | damping rates and frequency corrections of legacy stars |
it is increasingly considered that the modern episode of plate tectonics began in the neoproterozoic following a period of reduced activity known as the boring billion, when the earth may have been in a less dynamic single lid mode (sobolev & brown, 2019; stern, 2007). the neoproterozoic was also a time of dramatic... | global scale numerical models of the emergence of plate tectonics and complex life on earth |
different planets have different sizes, masses, and gravities. in this study, we investigate how gravity influences convection and clouds in the frame of radiative-convective equilibrium (rce). rce is a typical and useful method to understand the essential interactions among convection, clouds, and radiative transfer. ... | convection and clouds under different planetary gravities: radiative-convective equilibrium experiments |
we explore how thermal rossby waves propagate within the gravitationally stratified atmosphere of the sun's convective zone. under the conditions of rotationally constrained dynamics, we derive a local dispersion relation for atmospheric waves in a fully compressible stratified fluid. this dispersion relation describes... | trapping of thermal rossby waves within the sun's convection zone |
exoplanet surveys have revealed a wide diversity of planet properties in the milky way. here, we present the results from two projects modeling planet atmospheres; one considering the hydrogen/helium envelopes of sub-neptune-mass planets, and the other, the climate of earth-like planets.first, we modify the state-of-th... | from sub-neptunes to earth-like exoplanets: modeling optically thick and thin planetary atmospheres |
we simulate three-dimensional, horizontally periodic rayleigh-bénard convection, confined between free-slip horizontal plates and rotating about a distant horizontal axis. when both the temperature difference between the plates and the rotation rate are sufficiently large, a strong horizontal wind is generated that is ... | intermittency and large-scale winds in horizontally anisotropic convection |
we present a study of photometric flares on 158 low-mass (0.2msun) objects observed by the speculoos-south observatory from 1st june 2018 to 23rd march 2020. in this sample we identify 85 flaring objects, ranging in spectral type from m4 to l0. we detect 248 flares in this sample, with energies between 1029.2 and 1032.... | a study of flares in the ultra-cool regime from speculoos-south |
a planet's heat budget is a combination of the retained heat of formation, the energy released due to the gravitational segregation of a fe core and decay of the long-lived radionuclides u, th and 40k. while secular cooling and the energy of core segregation are dependent on the formation history and magma ocean evolut... | the coupled role of stellar abundances, exoplanet radiogenic heat budgets and the lifetime of temperate climates on rocky exoplanets |
simulations are undoubtedly one of the best tools to study in detail the structure and dynamics of the atmosphere of cool stars and, in particular, their convection zone and photosphere. however, realistic 3d simulations of the stellar convection require simultaneous solution of the magnetohydrodynamics (mhd) equations... | optimized opacity for photospheric convection simulations of cool stars with the mancha code |
the paper address the effects of magnetic helicity conservation in a non-linear nonaxisymmetric mean-field solar dynamo model. we study the evolution of the shallow non-axisymmetric magnetic field perturbation with the strength about 10g in the solar convection zone. the dynamo evolves from the pure axisymmetric stage ... | magnetic helicity in non-axisymmetric mean-field solar dynamo |
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 |
the sun and many stars are pulsationally stable but display acoustic oscillations none-the-less. these stars are likely stochastically excited by small-scale convective dynamics, but the detailed properties of the acoustic sources are unknown. although global acoustic modes are readily resolvable, it remains extremely ... | unboxing the black box: learning to identify acoustic wave sources on the sun from deep learning |
direct numerical simulations (dnss) of astrophysical turbulent flows with real physical parameters, resolving all the scales of motion ranging from the largest to smallest scales without resorting to any artificial viscosity, are just impossible. in this situation, modeling the effective turbulent transport provides a ... | modeling turbulent transport associated with plumes in stellar convection |
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 |
we present recent progress made in modelling stars and their turbulent magnetized dynamics in 3-d. this work is inspired by many years of discussion with jean-paul zahn. i (asb) first met him as a professor of astrophysical fluid dynamics (afd) at the paris-meudon observatory's graduate school of astrophysics in 1994-1... | turbulence, magnetism, and transport inside stars |
laboratory experiments have found iron opacity predictions are notably different from measurements performed at conditions similar to the boundary between the solar radiation and convection zone. the measurements help resolve discrepancies between helioseismology and solar models. however, it is essential to understand... | opacity data for stellar models and its uncertainties |
many outstanding questions remain concerning the ultimate fate of terrestrial planets that pass through a runaway greenhouse phase, such as venus is thought to have in its past. developing a better understanding of this process is critical, given the concerns about the long pre-main sequence super-luminous phases of sm... | a snowball in hell: the potential steam atmosphere of toi-1266c |
there are still significant uncertainties in our understand of convection and rotation in evolved low-mass stars. to address this, we have spectroscopically, photometrically, and asteroseismically characterized a set of subgiant and lower red giant stars in the tess southern continuous viewing zone, and combined them w... | tessting subgiant physics |
as stars evolve from the main-sequence (ms) to the red giant branch (rgb) they exhibit several characteristic changes. specifically, as the outer layers expand and cool, the star's rotation rate slows, the convection zone deepens and a series of shell-burning and core-burning phases begin to take place. a number of rgb... | searching for ir excesses around li-rich and rapidly rotating k giants using wise |
of the many processes occurring in the stellar interiors, mixing is one of the most important because stars will never forget its effects, for the rest of their lives. in the placid evolutionary phases of intermediate mass stars it is perhaps the most challenging one because, while we know that convection is certainly ... | convective mixing in intermediate mass stars |
stars are active magnetic objects. in this talk i will discuss how the surface activity is linked to its deep internal origin via dynamo action and flux emergence. based on 3-d mhd simulations performed with both ash and pluto codes we will show how turbulence and shear (either in convection or radiation zones) can hel... | linking stellar dynamo action to flux emergence and flares |
the onset of the runaway greenhouse of water vapor is one of the important criteria defining the inner edge of the habitable zone, and has been extensively studied in one-dimensional (1d) radiative-convective models. one limitation of 1d simulations is the assumption of the fully saturated troposphere. in the real atmo... | high relative humidity of water-rich atmospheres and its implications |
the thermal and magnetic evolution of terrestrial planets influences surface tectonics, outgassing rates, atmospheric composition, and magnetic shielding, all of which are important habitability factors. we focus here on the habitable zone around m-stars where tidal heating is likely important and tidal locking is expe... | on the thermal, magnetic, and orbital evolution of tidally heated earth-mass exoplanets |
the transit radii of many close-in extrasolar giant planets, or "hot jupiters," are systematically larger than those expected from models considering only cooling from an initial high-entropy state. though these planets receive strong irradiation, with equilibrium temperatures of 1000-2500 kelvin, the absorption of ste... | structure and evolution of internally heated hot jupiters |
when a low mass star evolves up along the red giant branch (rgb), it will develop much more extensive convection in its envelope. such envelope convection penetrates rapidly inward into the stellar interior, and finally results in a composition discontinuity when it develops into the chemical gradient region. subsequen... | effect of overshooting mixing below the base of the convective envelope on the rgb bump |
aims: this proposal focuses on obtaining accurate temperatures and abundances for white dwarfs near the blue edge of the helium instability strip. context: the observed location of the helium white dwarf instability strip in the temperature/log g plane is a strong indicator of convective efficiency in wd atmospheres, a... | the blue edge of the helium white dwarf instability strip |
the s-process nucleosynthesis in asymptotic giant branch (agb) stars depends on the modeling of convective boundaries. we present models and s-process simulations that adopt a treatment of convective boundaries based on the results of hydrodynamic simulations and on the theory of mixing due to gravity waves in the vici... | a simulation-based convective-boundary mixing model for agb star evolution and nucleosynthesis . |
these data present new pre-main sequence evolutionary tracks (including local and global convective turnover times, rossby numbers and rotation periods) for masses in the range of 0.1 to 1.5 solar masses in 0.1 solar masses steps. the tracks were generated with a modified version of d'antona & mazzitelli's code (th... | vizier online data catalog: rossby numbers of convective stars (landin+, 2023) |
turbulent motions enhance the diffusion of large-scale flows and temperature gradients. such diffusion is often parameterized by coefficients of turbulent viscosity ( $\nu _{t}$ ) and turbulent thermal diffusivity ( $\chi _{t}$ ) that are analogous to their microscopic counterparts. we compute the turbulent diffusion c... | turbulent prandtl number from isotropically forced turbulence |
plate tectonics is a fundamental component for the habitability of the earth. yet whether it is a recurrent feature of terrestrial bodies orbiting other stars or unique to the earth is unknown. the stagnant lid may rather be the most common tectonic expression on such bodies. to understand whether a stagnant-lid planet... | the habitability of a stagnant-lid earth |
in 2014 we discovered that wasp-18, a late f type star orbited every22 hours by a massive planet, is dark in x-rays. the x-ray luminosityis about two orders of magnitude below the expected value for a starof its spectral type and age (t~800 myr). we have put forward thehypothesis that the planet can annihilate the over... | no x-rays from wasp-18. really? |
we investigate the ability of internal gravity waves that are generated by penetrative convection to redistribute angular momentum in the internal radiative zone of evolved low-mass stars. to do so, we use the semianalytical excitation model recently proposed by pinçon et al. 2016. we briefly report the preliminary res... | excitation of internal gravity waves by penetrative convection. consequences on the rotation of evolved low-mass stars |
i review the role of radiative opacity in asterosismology, as well as recent progress and remaining challenges in its calculation, highlighting the modeling difficulties, such as the accounting for myriads of lines or plasma density effects. a particular attention is paid to iron, due to its role in the understanding o... | opacity calculations for stellar astrophysics |
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 convection. it leads to an efficient extra mixing which brings the accreted material deeper in the star than by considering only mixing in the surface dynamical c... | fingering convection in accreting hydrogen white dwarfs |
gravito-inertial waves can be excited at the interface of convective and radiative regions and by the reynolds stresses in the bulk of the convection zone. the magnitude of their energy flux will therefore vary with the properties of the convection. to assess how convection changes with rotation, a simplified local mon... | rotating convection and gravito-inertial wave generation in stellar interiors |
most of what we know about stars comes from their stellar spectral features. among other things, these features can tell us about the star's temperature and chemical composition. the spectral features are not delta functions and have some width that can be explained by some well known and understood broadening mechanis... | numerical simulations of microturbulence in hot stellar atmospheres |
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