The equation of state for stellar envelopes. I - an occupation probability formalism for the truncation of internal partition functions

Hummer, D. G.; Mihalas, Dimitri

doi:10.1086/166600

Cited by 643 publications

(509 citation statements)

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“…For envelopes it is assumed that r,-> ro for all absorbers contributing significantly to the opacity. Hummer and Mihalas (1988) tentatively adopy p = 10 -2 g c m -2 for the lower boundary of envelopes. That corresponds to ro a 5.5 atomic units.…”

Section: The Opal and Op Approachesmentioning

confidence: 85%

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Radiative Opacities

Seaton

1993

International Astronomical Union Colloquium

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Section: The Opal and Op Approachesmentioning

confidence: 85%

“…The simplest example of such a potential is the static screened Coulomb potential exp(-r/r£>)/7-replacing the Coulomb potential 1/r, TD being the Debye radius. The use of such potentials has, however, been criticised by Hummer and Mihalas (1988).…”

Section: The Opal and Op Approachesmentioning

confidence: 99%

Radiative Opacities

Seaton

1993

International Astronomical Union Colloquium

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“…We assume local thermodynamical equilibrium (LTE) in our calculations, so the number densities of all ionisation and excitation states of all elements have been calculated using Boltzmann and Saha equations. We take into account pressure ionisation effects on the atomic populations using the occupation probability formalism (Hummer & Mihalas 1988) as described by Hubeny et al (1994).…”

Section: Methods Of Calculationsmentioning

confidence: 99%

Importance of Compton scattering for radiation spectra of isolated neutron stars

Suleimanov

Werner

2007

Astrophys Space Sci

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Abstract. Model atmospheres of isolated neutron stars with low magnetic field are calculated with Compton scattering taking into account. Models with effective temperatures 1, 3 and 5 MK, with two values of surface gravity (log g = 13.9 and 14.3), and different chemical compositions are calculated. Radiation spectra computed with Compton scattering are softer than the computed with Thomson scattering at high energies (E> 5 keV) for hot (T eff > 1 MK) atmospheres with hydrogen-helium composition. Compton scattering is more significant to hydrogen models with low surface gravity. The emergent spectra of the hottest (T eff > 3 MK) model atmospheres can be described by diluted blackbody spectra with hardness factors ∼ 1.6 -1.9. Compton scattering is less important for models with solar abundance of heavy elements.

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“…We have used in our model the so-called occupation probability formalism (OPF) derived by Hummer and Mihalas (1988). In this formalism, the internal free energy reads :…”

Section: The Internal Free Energymentioning

confidence: 99%

“…In practice, however, one must resort to a linearization of F con f to compute the occupation probability (see Hummer and Mihalas (1988) for details). Calculations including terms beyond the density-linear term have been computed recently for helium at high-density (Aparicio and Chabrier 1994).…”

Section: The Internal Free Energymentioning

confidence: 99%

The Equation of State of Fluid Hydrogen at High Density

Chabrier

1994

International Astronomical Union Colloquium

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A b s t r a c tWe present a free energy model for fluid hydrogen at high-density and hightemperature. This model aims at describing pressure dissociation and ionization, which occur in partially ionized plasmas encountered in the interiors of giant planets and low-mass stars. The model describes an interacting mixture of H2,H,H + and e~ in chemical equilibrium. The concentrations of H 2 + and H~ ions are found to be negligible for equation of state purposes. Our model relies on the so-called chemical picture approach, based on the factorization of the partition function into translational, internal and configurational degrees of freedom. The present model is found to be unstable in the pressure-ionization regime and predicts the existence of a first-order plasma phase transition ( P P T ) which ends up at a critical point given by T c = 15300 K, P c = 0.614 Mbar, and p c = 0.35 g e m -3 . The transition occurs between a weakly ionized phase and a partially ionized (~ 50%) phase.Nous presentons un modele d'energie libre pour l'hydrogene fiuide a haute densite et haute temperature. Le but de ce modele est de decrire la dissociation et l'ionisation en pression, telles qu'elles se produisent dans les plasmas partiellement ionises rencontres a l'interieur des planetes geantes et des

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The equation of state for stellar envelopes. I - an occupation probability formalism for the truncation of internal partition functions

Cited by 643 publications

References 0 publications

Radiative Opacities

Radiative Opacities

Importance of Compton scattering for radiation spectra of isolated neutron stars

The Equation of State of Fluid Hydrogen at High Density

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