The equation of state for stellar envelopes. II - Algorithm and selected results

Mihalas, Dimitri; Däppen, Werner; Hummer, D. G.

doi:10.1086/166601

Cited by 414 publications

(299 citation statements)

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“…Since most of the ONC and NGC 2264 objects are low-mass pMS stars, rigid body rotation was assumed. We used the opacities reported by Iglesias & Rogers (1993) and Alexander & Ferguson (1994) and the equations of state from Rogers et al (1996) and Mihalas et al (1988). The tracks start from a fully convective configuration with central temperatures in the range 5.3 < log T c < 5.8, follow deuterium and lithium burning, and end at the MS configuration.…”

Section: Modelsmentioning

confidence: 99%

Stellar models simulating the disk-locking mechanism and the evolutionary history of the Orion Nebula cluster and NGC 2264

Landin

Mendes

Vaz

et al. 2016

A&A

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Context. Rotational evolution in young stars is described by pre-main sequence evolutionary tracks including non-gray boundary conditions, rotation, conservation of angular momentum, and simulations of disk-locking. Aims. By assuming that disk-locking is the regulation mechanism for the stellar angular velocity during the early stages of pre-main sequence evolution, we use our rotating models and observational data to constrain disk lifetimes (T disk ) of a representative sample of low-mass stars in two young clusters, the Orion Nebula cluster (ONC) and NGC 2264, and to better understand their rotational evolution. Methods. The period distributions of the ONC and NGC 2264 are known to be bimodal and to depend on the stellar mass. To follow the rotational evolution of these two clusters' stars, we generated sets of evolutionary tracks from a fully convective configuration with low central temperatures (before D-and Li-burning). We assumed that the evolution of fast rotators can be represented by models considering conservation of angular momentum during all stages and of moderate rotators by models considering conservation of angular velocity during the first stages of evolution. With these models we estimate a mass and an age for all stars. Results. The resulting mass distribution for the bulk of the cluster population is in the ranges of 0.2−0.4 M and 0.1−0.6 M for the ONC and NGC 2264, respectively. For the ONC, we assume that the secondary peak in the period distribution is due to high-mass objects still locked in their disks, with a locking period (P lock ) of ∼8 days. For NGC 2264 we make two hypotheses: (1) the stars in the secondary peak are still locked with P lock = 5 days, and (2) NGC 2264 is in a later stage in the rotational evolution. Hypothesis 2 implies in a disk-locking scenario with P lock = 8 days, a disk lifetime of 1 Myr and, after that, constant angular momentum evolution. We then simulated the period distribution of NGC 2264 when the mean age of the cluster was 1 Myr. Dichotomy and bimodality appear in the simulated distribution, presenting one peak at 2 days and another one at 5−7 days, indicating that the assumption of P lock = 8 days is plausible. Our hypotheses are compared with observational disk diagnoses available in the literature for the ONC and NGC 2264, such as near-infrared excess, Hα emission, and spectral energy distribution slope in the mid-infrared. Conclusions. Disk-locking models with P lock = 8 days and 0.2 Myr ≤ T disk ≤ 3 Myr are consistent with observed periods of moderate rotators of the ONC. For NGC 2264, the more promising explanation for the observed period distribution is an evolution with disk-locking (with P lock near 8 days) during the first 1 Myr, approximately, but after this, the evolution continued with constant angular momentum.

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Section: Modelsmentioning

confidence: 99%

Stellar models simulating the disk-locking mechanism and the evolutionary history of the Orion Nebula cluster and NGC 2264

Landin

Mendes

Vaz

et al. 2016

A&A

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“…Heat losses and gains due to radiation are accounted for by solving the 3D radiative transfer equation in the local thermodynamic equilibrium (LTE) approximation. The simulations employ realistic input physics: the equation of state is an updated version of the one by Mihalas et al (1988). Continuous and line opacities are taken from Gustafsson et al (1975); Kurucz (1992Kurucz ( , 1993.…”

Section: Surface Convection Simulations and Radiative Transfer Calculmentioning

confidence: 99%

Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for interpreting interferometric observations

Chiavassa¹,

Collet²,

Casagrande³

et al. 2010

A&A

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Context. Theoretical predictions from models of red giant branch stars are a valuable tool for various applications in astrophysics ranging from galactic chemical evolution to studies of exoplanetary systems. Aims. We use the radiative transfer code Optim3D and realistic 3D radiative-hydrodynamical (RHD) surface convection simulations of red giants to explore the impact of granulation on interferometric observables. We assess how 3D simulations of surface convection can be validated against observations. Methods. We computed intensity maps for the 3D simulation snapshots in two filters, the optical at 5000 ± 300 Å and the K band 2.14±0.26 μm FLUOR filter, corresponding to the wavelength-range of instruments mounted on the CHARA interferometer. From the intensity maps, we constructed images of the stellar disks and account for center-to-limb variations. We then derived interferometric visibility amplitudes and phases. We study their behavior with position angle and wavelength, and compare them with CHARA observations of the red giant star HD 214868. Results. We provide average limb darkening coefficients for different metallicities and wavelengths ranges. We explain prospects for detecting and characterizing granulation and center-to-limb variations of red giant stars with today's interferometers. Regarding interferometric observables, we find that the effect of convective-related surface structures depends on metallicity and surface gravity. We provide theoretical closure-phases that should be incorporated into the analysis of red giant planet companion closure phase signals. We estimate 3D−1D corrections to stellar radii determination: 3D models are ∼3.5% smaller to ∼1% larger in the optical than 1D, and roughly 0.5 to 1.5% smaller in the infrared. Even if these corrections are small, they are needed to properly set the zero point of effective temperature scale derived by interferometry and to strengthen the confidence of existing red giant catalogs of calibrating stars for interferometry. Finally, we show that our RHD simulations provide an excellent fit to the red giant HD 214868 even though more observations are needed at higher spatial frequencies and shorter wavelength.

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“…In recent implementations of this approach these discontinuities in the EOS are eliminated by introducing an occupation probability (reduced statistical weight), w, that a composite particle (i.e., ion, atom, molecule) finds itself in an environment where the bound electrons are highly localized around a single nucleus. The quantity 1 À w is then the probability that, as a result of interactions with nearby neighbors, the bound electrons are in delocalized quasi-continuum states (Däppen, Anderson, & Mihalas 1987;Mihalas, Däppen, & Hummer 1988;hereafter MDH88). This is an intuitive approach whose success depends on how well w is determined.…”

Section: Introductionmentioning

confidence: 99%

Updated and Expanded OPAL Equation‐of‐State Tables: Implications for Helioseismology

Rogers

Nayfonov

2002

ApJ

885

777

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We are in the process of updating and extending the OPAL equation-of-state (EOS) and opacity data to include low-mass stars. The EOS part of that effort now is complete, and the results are described herein. The new data cover main-sequence stars having mass !0.1 M . As a result of the more extreme matter conditions encountered with low-mass stars, we have added new physics. The electrons are now treated as relativistic, and we have improved our treatment of molecules. We also consider the implications of the new results for helioseismology.

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The equation of state for stellar envelopes. II - Algorithm and selected results

Cited by 414 publications

References 0 publications

Stellar models simulating the disk-locking mechanism and the evolutionary history of the Orion Nebula cluster and NGC 2264

Stellar models simulating the disk-locking mechanism and the evolutionary history of the Orion Nebula cluster and NGC 2264

Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for interpreting interferometric observations

Updated and Expanded OPAL Equation‐of‐State Tables: Implications for Helioseismology

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