scholarly journals Overcoming the structural surface effect with a realistic treatment of turbulent convection in 1D stellar models

2019 ◽  
Vol 488 (3) ◽  
pp. 3463-3473 ◽  
Author(s):  
Andreas Christ Sølvsten Jørgensen ◽  
Achim Weiss
Keyword(s):  
Surface Effect ◽  
Stellar Structure ◽  
The Sun ◽  
Time Step ◽  
Simplifying Assumptions ◽  
Structural Surface ◽  
Stellar Models ◽  
Stellar Oscillation ◽  
Mixing Length Theory ◽  
Oscillation Frequencies

Abstract State-of-the-art 1D stellar evolution codes rely on simplifying assumptions, such as mixing length theory, in order to describe superadiabatic convection. As a result, 1D stellar structure models do not correctly recover the surface layers of the Sun and other stars with convective envelopes. We present a method that overcomes this structural drawback by employing 3D hydrodynamic simulations of stellar envelopes: at every time-step of the evolution interpolated 3D envelopes are appended to the 1D structure and are used to supply realistic boundary conditions for the stellar interior. In contrast to previous attempts, our method includes mean 3D turbulent pressure. We apply our method to model the present Sun. The structural shortcomings of standard stellar models lead to systematic errors in the stellar oscillation frequencies inferred from the model. We show that our method fully corrects for this error. Furthermore, we show that our realistic treatment of superadiabatic convection alters the predicted evolution of the Sun. Our results hence have important implications for the characterization of stars. This has ramifications for neighbouring fields, such as exoplanet research and galactic archaeology, for which accurate stellar models play a key role.

scholarly journals On the impact of the structural surface effect on global stellar properties and asteroseismic analyses

2020 ◽  
Vol 500 (4) ◽  
pp. 4277-4295
Author(s):  
Andreas Christ Sølvsten Jørgensen ◽  
Josefina Montalbán ◽  
George C Angelou ◽  
Andrea Miglio ◽  
Achim Weiss ◽  
...  
Keyword(s):  
Surface Effect ◽  
Outer Boundary ◽  
Space Mission ◽  
Stellar Structure ◽  
Time Step ◽  
Near Surface ◽  
Seismic Properties ◽  
Stellar Properties ◽  
Mixing Length Theory ◽  
The Impact

ABSTRACT In a series of papers, we have recently demonstrated that it is possible to construct stellar structure models that robustly mimic the stratification of multidimensional radiative magnetohydrodynamic simulations at every time-step of the computed evolution. The resulting models offer a more realistic depiction of the near-surface layers of stars with convective envelopes than parametrizations, such as mixing length theory, do. In this paper, we explore how this model improvement impacts on seismic and non-seismic properties of stellar models across the Hertzsprung–Russell diagram. We show that the improved description of the outer boundary layers alters the predicted global stellar properties at different evolutionary stages. In a hare and hound exercise, we show that this plays a key role for asteroseismic analyses, as it, for instance, often shifts the inferred stellar age estimates by more than 10 per cent. Improper boundary conditions may thus introduce systematic errors that exceed the required accuracy of the PLATO space mission. Moreover, we discuss different approaches for computing stellar oscillation frequencies. We demonstrate that the so-called gas Γ1 approximation performs reasonably well for all main-sequence stars. Using a Monte Carlo approach, we show that the model frequencies of our hybrid solar models are consistent with observations within the uncertainties of the global solar parameters when using the so-called reduced Γ1 approximation.

scholarly journals Coupling 1D stellar evolution with 3D-hydrodynamical simulations on-the-fly II: stellar evolution and asteroseismic applications

2019 ◽  
Vol 491 (1) ◽  
pp. 1160-1173 ◽  
Author(s):  
Jakob Rørsted Mosumgaard ◽  
Andreas Christ Sølvsten Jørgensen ◽  
Achim Weiss ◽  
Víctor Silva Aguirre ◽  
Jørgen Christensen-Dalsgaard
Keyword(s):  
Stellar Evolution ◽  
Surface Effect ◽  
Stellar Structure ◽  
Red Giants ◽  
3D Simulations ◽  
Stellar Models ◽  
Red Giant ◽  
Hydrodynamical Simulations ◽  
Indispensable Tool ◽  
Oscillation Frequencies

ABSTRACT Models of stellar structure and evolution are an indispensable tool in astrophysics, yet they are known to incorrectly reproduce the outer convective layers of stars. In the first paper of this series, we presented a novel procedure to include the mean structure of 3D hydrodynamical simulations on-the-fly in stellar models, and found it to significantly improve the outer stratification and oscillation frequencies of a standard solar model. In this work, we extend the analysis of the method; specifically how the transition point between envelope and interior affects the models. We confirm the versatility of our method by successfully repeating the entire procedure for a different grid of 3D hydrosimulations. Furthermore, the applicability of the procedure was investigated across the HR diagram and an accuracy comparable to the solar case was found. Moreover, we explored the implications on stellar evolution and find that the red-giant branch is shifted about $40\, \mathrm{K}$ to higher effective temperatures. Finally, we present for the first time an asteroseismic analysis based on stellar models fully utilizing the stratification of 3D simulations on-the-fly. These new models significantly reduce the asteroseismic surface term for the two selected stars in the Kepler field. We extend the analysis to red giants and characterize the shape of the surface effect in this regime. Lastly, we stress that the interpolation required by our method would benefit from new 3D simulations, resulting in a finer sampling of the grid.

scholarly journals Precise and accurate interpolated stellar oscillation frequencies on the main sequence

2013 ◽  
Vol 9 (S301) ◽  
pp. 379-380
Author(s):  
Warrick H. Ball ◽  
Jesper Schou ◽  
Laurent Gizon ◽  
João P. C. Marques
Keyword(s):  
Main Sequence ◽  
Quality Data ◽  
High Quality ◽  
Small Frequency ◽  
Global Mode ◽  
High Quality Data ◽  
Mode Oscillation ◽  
Stellar Models ◽  
Stellar Oscillation ◽  
Oscillation Frequencies

AbstractHigh-quality data from space-based observatories present an opportunity to fit stellar models to observations of individually-identified oscillation frequencies, not just the large and small frequency separations. But such fits require the evaluation of a large number of accurate stellar models, which remains expensive. Here, we show that global-mode oscillation frequencies interpolated in a grid of stellar models are precise and accurate, at least in the neighbourhood of a solar model.

scholarly journals Analysis of surface effect on solar-like oscillation frequencies using 3D hydrodynamical models

2019 ◽  
Vol 82 ◽  
pp. 253-258
Author(s):  
T. Sonoi ◽  
R. Samadi ◽  
K. Belkacem ◽  
H.-G. Ludwig ◽  
E. Caffau ◽  
...  
Keyword(s):  
Effective Temperature ◽  
Surface Effect ◽  
Frequency Difference ◽  
Surface Gravity ◽  
Hydrodynamical Models ◽  
Stellar Models ◽  
Oscillation Frequencies

We evaluate the frequency difference between standard stellar models and models patched with 3D hydrodynamical models across the Teff–g plane. It allows us to constrain frequency corrections for surface effect. The coefficients in the correction functionals are thus provided as functions of effective temperature and surface gravity.

scholarly journals Stellar Seismology

1990 ◽  
Vol 121 ◽  
pp. 357-370
Author(s):  
Werner Däppen
Keyword(s):  
Theoretical Models ◽  
Acoustic Oscillation ◽  
Mode Identification ◽  
Stellar Ages ◽  
Stellar Models ◽  
Stellar Oscillation ◽  
Stellar Seismology ◽  
Oscillation Frequencies ◽  
Near Future

AbstractStellar acoustic oscillation frequencies will likely be accurately observed in the near future, in analogy to the well-known solar five-minute oscillation frequencies. Of course, we will never expect the wealth of solar data, which is a result of spatial resolution. We will therefore not be able to solve the inverse problem, that is to probe physical quantities as functions of depth, and the low number of anticipated observed frequencies will make an unambiguous mode identification difficult. Despite this restriction to the forward problem, however, observed stellar oscillation frequencies will become valuable constraints for the determination of stellar parameters. One should not forget that the present knowledge of stellar ages and compositions relies on the calibration of theoretical models (matching effective temperature and luminosity). Additional observational constraints will improve these calibrations, even if the theoretical models themselves are not questioned. We hope, however, that the observation of stellar oscillation frequencies will also lead to improvements in the physics of stellar models, in analogy to the solar case. Again, of course, stellar seismologists will be less ambitious than helioseismologists, since there are more open parameters in stellar models. However, stellar observations will allow tests of models with different age and composition.

scholarly journals Mending the structural surface effect of 1D stellar structure models with non-solar metallicities based on interpolated 3D envelopes

2019 ◽  
Vol 484 (4) ◽  
pp. 5551-5567 ◽  
Author(s):  
Andreas Christ Sølvsten Jørgensen ◽  
Achim Weiss ◽  
George Angelou ◽  
Víctor Silva Aguirre
Keyword(s):  
Surface Effect ◽  
Stellar Structure ◽  
Structural Surface

scholarly journals Investigating surface correction relations for RGB stars

2020 ◽  
Vol 495 (4) ◽  
pp. 4965-4980 ◽  
Author(s):  
Andreas Christ Sølvsten Jørgensen ◽  
Josefina Montalbán ◽  
Andrea Miglio ◽  
Ben M Rendle ◽  
Guy R Davies ◽  
...  
Keyword(s):  
Surface Effect ◽  
Dynamical Evolution ◽  
Systematic Errors ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Stellar Structure ◽  
Red Giants ◽  
Red Giant ◽  
Stellar Oscillation ◽  
Surface Correction

ABSTRACT State-of-the-art stellar structure and evolution codes fail to adequately describe turbulent convection. For stars with convective envelopes such as red giants, this leads to an incomplete depiction of the surface layers. As a result, the predicted stellar oscillation frequencies are haunted by systematic errors, the so-called surface effect. Different empirically and theoretically motivated correction relations have been proposed to deal with this issue. In this paper, we compare the performance of these surface correction relations for red giant branch stars. For this purpose, we apply the different surface correction relations in asteroseismic analyses of eclipsing binaries and open clusters. In accordance with previous studies of main-sequence stars, we find that the use of different surface correction relations biases the derived global stellar properties, including stellar age, mass, and distance estimates. We, furthermore, demonstrate that the different relations lead to the same systematic errors for two different open clusters. Our results overall discourage from the use of surface correction relations that rely on reference stars to calibrate free parameters. Due to the demonstrated systematic biasing of the results, the use of appropriate surface correction relations is imperative to any asteroseismic analysis of red giants. Accurate mass, age, and distance estimates for red giants are fundamental when addressing questions that deal with the chemo-dynamical evolution of the Milky Way galaxy. In this way, our results also have implications for fields such as galactic archaeology that draw on findings from stellar physics.

scholarly journals Scale-free convection theory

2015 ◽  
Vol 11 (A29B) ◽  
pp. 747-747
Author(s):  
Stefano Pasetto ◽  
Cesare Chiosi ◽  
Mark Cropper ◽  
Eva K. Grebel
Keyword(s):  
Surrounding Medium ◽  
Stellar Structure ◽  
Time Dependent ◽  
Length Scale ◽  
The Sun ◽  
Mixing Length ◽  
Local Pressure ◽  
Scale Free ◽  
Non Local ◽  
Stellar Models

AbstractConvection is one of the fundamental mechanisms to transport energy, e.g., in planetology, oceanography, as well as in astrophysics where stellar structure is customarily described by the mixing-length theory, which makes use of the mixing-length scale parameter to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is taken to be proportional to the local pressure scale height of the star, and the proportionality factor (the mixing-length parameter) must be determined by comparing the stellar models to some calibrator, usually the Sun. No strong arguments exist to claim that the mixing-length parameter is the same in all stars and all evolutionary phases. Because of this, all stellar models in the literature are hampered by this basic uncertainty. In a recent paper (Pasetto et al. 2014) we presented the first fully analytical scale-free theory of convection that does not require the mixing-length parameter. Our self-consistent analytical formulation of convection determines all the properties of convection as a function of the physical behaviour of the convective elements themselves and the surrounding medium (be it a star, an ocean, or a primordial planet). The new theory of convection is formulated starting from a conventional solution of the Navier-Stokes/Euler equations, i.e. the Bernoulli equation for a perfect fluid, but expressed in a non-inertial reference frame co-moving with the convective elements. In our formalism, the motion of convective cells inside convective-unstable layers is fully determined by a new system of equations for convection in a non-local and time dependent formalism. We obtained an analytical, non-local, time-dependent solution for the convective energy transport that does not depend on any free parameter. The predictions of the new theory in astrophysical environment are compared with those from the standard mixing-length paradigm in stars with exceptional results for atmosphere models of the Sun and all the stars in the Hertzsprung-Russell diagram.

scholarly journals Solar structure and evolution

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Jørgen Christensen-Dalsgaard
Keyword(s):  
Solar Surface ◽  
Solar Neutrinos ◽  
Solar Interior ◽  
Stellar Structure ◽  
The Sun ◽  
Physical Processes ◽  
Solar Evolution ◽  
Internal Properties ◽  
Atmospheric Phenomena

AbstractThe Sun provides a critical benchmark for the general study of stellar structure and evolution. Also, knowledge about the internal properties of the Sun is important for the understanding of solar atmospheric phenomena, including the solar magnetic cycle. Here I provide a brief overview of the theory of stellar structure and evolution, including the physical processes and parameters that are involved. This is followed by a discussion of solar evolution, extending from the birth to the latest stages. As a background for the interpretation of observations related to the solar interior I provide a rather extensive analysis of the sensitivity of solar models to the assumptions underlying their calculation. I then discuss the detailed information about the solar interior that has become available through helioseismic investigations and the detection of solar neutrinos, with further constraints provided by the observed abundances of the lightest elements. Revisions in the determination of the solar surface abundances have led to increased discrepancies, discussed in some detail, between the observational inferences and solar models. I finally briefly address the relation of the Sun to other similar stars and the prospects for asteroseismic investigations of stellar structure and evolution.

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