Solar structure and evolution Christensen-Dalsgaard, Jørgen
Living reviews in solar physics,
12/2021, Letnik:
18, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The 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.
Asteroseismology of 1.0-2.0 M sub(middot in circle) red giants by the Kepler satellite has enabled the first definitive measurements of interior rotation in both first ascent red giant branch (RGB) ...stars and those on the helium burning clump. The inferred rotation rates are 10-30 days for the approximately 0.2 M sub(middot in circle) He degenerate cores on the RGB and 30-100 days for the He burning core in a clump star. Using the Modules for Experiments in Stellar Evolution code, we calculate state-of-the-art stellar evolution models of low mass rotating stars from the zero-age main sequence to the cooling white dwarf (WD) stage. We include transport of angular momentum due to rotationally induced instabilities and circulations, as well as magnetic fields in radiative zones (generated by the Tayler-Spruit dynamo). We find that all models fail to predict core rotation as slow as observed on the RGB and during core He burning, implying that an unmodeled angular momentum transport process must be operating on the early RGB of low mass stars. Later evolution of the star from the He burning clump to the cooling WD phase appears to be at nearly constant core angular momentum. We also incorporate the adiabatic pulsation code, ADIPLS, to explicitly highlight this shortfall when applied to a specific Kepler asteroseismic target, KIC8366239.
Searching for dark energy with the Sun Saltas, Ippocratis D.; Christensen-Dalsgaard, Jørgen
Astronomy and astrophysics (Berlin),
11/2022, Letnik:
667
Journal Article
Recenzirano
Odprti dostop
General extensions of general relativity (GR) based on bona fide degrees of freedom predict a fifth force which operates within massive objects, opening up an exciting opportunity to perform ...precision tests of gravity at stellar scales. Here, focussing on general scalar-tensor theories for dark energy, we utilise the Sun as our laboratory and search for imprints of the fifth-force effect on the solar equilibrium structure. With analytic results and numerical simulations, we explain how the different solar regions offer powerful ways to test gravity. Accounting for the delicate interplay between the fifth force and solar microphysics such as opacity, diffusion, equation of state, and metallicity, we demonstrate that the fifth force still leaves a sharp signature on the solar sound speed, in a region where simple estimates of input physics uncertainties become negligible. For general scalar-field extensions of GR, known as (U-)DHOST, based solely on the observational helioseismic errors, our analysis at the equilibrium level allows us to place an approximate constraint on the fifth-force coupling strength of −10
−3
≲ ≲ 5 × 10
−4
at 2
σ
. This result improves previous stellar constraints by ∼3 orders of magnitude, and should be confirmed and improved by future helioseismic inversions in modified gravity, combined with an elaborate accounting of theoretical uncertainties. Our analysis can be applied to a wide set of theories beyond GR, and also paves the way for helioseismic analyses in this context. In this regard, we discuss how the solar radiative and convective zone can be employed as promising laboratories to test generic theories of gravity.
We investigate the variation of the gravitational constant G over the history of the universe by modeling the effects on the evolution and asteroseismology of the low-mass star KIC 7970740, which is ...one of the oldest (∼11 Gyr) and best-observed solar-like oscillators in the Galaxy. From these data we find G ˙ G = ( 1.2 2.6 ) × 10 − 12 yr − 1 , that is, no evidence for any variation in G. We also find a Bayesian asteroseismic estimate of the age of the universe as well as astrophysical S-factors for five nuclear reactions obtained through a 12-dimensional stellar evolution Markov Chain Monte Carlo simulation.
Asteroseismology Aerts, C; Christensen-Dalsgaard, J; Kurtz, D. W
2010, 20091127, 2007-02-15
eBook
Odprti dostop
The recent research domain of asteroseismology studies the internal structure of stars, which is not directly observable, through the interpretation of the frequency spectra of stellar oscillations. ...The basic principles of asteroseismology are very similar to those developed by earth seismologists. Stellar interiors can be probed from oscillations because different oscillation modes penetrate to different depths inside the star. Asteroseismology is the only available method to derive the internal structure of the stars with high precision.This book the first on asteroseismology offers a practical guide for graduate students and scientists working in stellar astrophysics. It provides a general introduction to asteroseismology and comprehensive coverage of all its aspects: fundamental theory, observations and observational techniques, methodology of data analysis and seismic interpretations of various classes of multi-periodic pulsating stars.
On the red-giant luminosity bump Christensen-Dalsgaard, Jørgen
Monthly notices of the Royal Astronomical Society,
10/2015, Letnik:
453, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The increase in luminosity as a star evolves on the red-giant branch is interrupted briefly when the hydrogen-burning shell reaches the vicinity of the composition discontinuity left behind from the ...first convective dredge-up. The non-monotonic variation of luminosity causes an accumulation of stars, known as the ‘bump’, in the distribution of stars in the colour–magnitude diagrams of stellar clusters, which has substantial diagnostic potential. Here, I present numerical results on this behaviour and discuss the physical reason for the luminosity variation, with the goal of strengthening the understanding of origin of the phenomenon and hence of its diagnostic potential.
Development of the Aarhus adiabatic pulsation code started around 1978. Although the main features have been stable for more than a decade, development of the code is continuing, concerning numerical ...properties and output. The code has been provided as a generally available package and has seen substantial use at a number of installations. Further development of the package, including bringing the documentation closer to being up to date, is planned as part of the HELAS Coordination Action.
Towards solar measurements of nuclear reaction rates Bellinger, Earl Patrick; Christensen-Dalsgaard, Jørgen
Monthly notices of the Royal Astronomical Society,
11/2022, Letnik:
517, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Nuclear reaction rates are a fundamental yet uncertain ingredient in stellar evolution models. The astrophysical S-factor pertaining to the initial reaction in the proton–proton (pp) chain ...is uncertain at the 1 per cent level, which contributes a systematic but generally unpropagated error of similar order in the theoretical ages of stars. In this work, we study the prospect of improving the measurement of this and other reaction rates in the pp chain and CNO cycle using helioseismology and solar neutrinos. We show that when other aspects of the solar model are improved, then it shall be possible using current solar data to improve the precision of this measurement by nearly an order of magnitude and hence the corresponding uncertainty on the ages of low-mass stars by a similar amount.
In this brief communication we provide the rationale for and the outcome of the International Astronomical Union (IAU) resolution vote at the XXIXth General Assembly in Honolulu, Hawaii, in 2015, on ...recommended nominal conversion constants for selected solar and planetary properties. The problem addressed by the resolution is a lack of established conversion constants between solar and planetary values and SI units: a missing standard has caused a proliferation of solar values (e.g., solar radius, solar irradiance, solar luminosity, solar effective temperature, and solar mass parameter) in the literature, with cited solar values typically based on best estimates at the time of paper writing. As precision of observations increases, a set of consistent values becomes increasingly important. To address this, an IAU Working Group on Nominal Units for Stellar and Planetary Astronomy formed in 2011, uniting experts from the solar, stellar, planetary, exoplanetary, and fundamental astronomy, as well as from general standards fields to converge on optimal values for nominal conversion constants. The effort resulted in the IAU 2015 Resolution B3, passed at the IAU General Assembly by a large majority. The resolution recommends the use of nominal solar and planetary values, which are by definition exact and are expressed in SI units. These nominal values should be understood as conversion factors only, not as the true solar/planetary properties or current best estimates. Authors and journal editors are urged to join in using the standard values set forth by this resolution in future work and publications to help minimize further confusion.
We perform a calibration of the mixing length of convection in stellar structure models against realistic 3D radiation-coupled hydrodynamics simulations of convection in stellar surface layers, ...determining the adiabat deep in convective stellar envelopes. The mixing-length parameter α is calibrated by matching averages of the 3D simulations to 1D stellar envelope models, ensuring identical atomic physics in the two cases. This is done for a previously published grid of solar-metallicity convection simulations, covering from 4200 to 6900 K on the main sequence, and from 4300 to 5000 K for giants with log g = 2.2. Our calibration results in an α varying from 1.6 for the warmest dwarf, which is just cool enough to admit a convective envelope, and up to 2.05 for the coolest dwarfs in our grid. In between these is a triangular plateau of α ∼ 1.76. The Sun is located on this plateau and has seen little change during its evolution so far. When stars ascend the giant branch, they largely do so along tracks of constant α, with α decreasing with increasing mass.
PDF
