Electron conduction opacities at the transition between moderate and strong degeneracy: Uncertainties and impact on stellar models

Abstract

Electron conduction opacities are one of the main physics inputs for the calculation of low- and intermediate-mass stellar models, and a critical question is how to bridge calculations for moderate and strong degeneracy, which are necessarily performed adopting different methods. The density-temperature regime at the boundary between moderate and strong degeneracy is in fact crucial for modelling the helium cores of red giant branch stars and the hydrogen/helium envelopes of white dwarfs. Prompted by recently published new, improved calculations of electron thermal conductivities and opacities for moderate degeneracy, we study different, physically motivated prescriptions to bridge these new computations with well established results in the regime of strong degeneracy. We find that these different prescriptions have a sizable impact on the predicted He-core masses at the He-flash (up to 0.01$M_{\odot }$ for initial total masses far from the transition to non-degenerate He-cores, and up to $\sim 0.04M_{\odot }$ for masses around the transition), the tip of the red giant branch (up to $\sim$0.1~mag) and the zero age horizontal branch luminosities (up to 0.03~dex for masses far from the transition, and up to $\sim$0.2~dex around the transition), and white dwarf cooling times (up to 40-45\% at high luminosities, and up to $\sim$25\% at low luminosities). Current empirical constraints on the tip of the red giant branch and the zero age horizontal branch absolute magnitudes do not allow yet to definitely exclude any of these alternative options for the conductive opacities. Tests against observations of slowly-cooling faint WDs in old stellar populations will need to be performed to see whether they can set some more stringent constraints on how to bridge calculations of conductive opacities for moderate and strong degeneracy.

arXiv comment9 pages, 10 figures, Astronomy & Astrophysics in press

References in corpus (16)

• Theory of Low-Mass Stars and Substellar Objects
• Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Neutron stars - cooling and transport
• Red Giant Branch stars: the theoretical framework
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• The calibration of the RGB Tip as a Standard Candle: Extension to Near Infrared colors and higher metallicity
• A large stellar evolution database for population synthesis studies: VI. White dwarf cooling sequences
• Comparison of theoretical white dwarf cooling timescales
• New Conductive Opacities for White Dwarf Envelopes
• Density-functional calculations of transport properties in the non-degenerate limit and the role of electron-electron scattering
• Ion structure factors and electron transport in dense Coulomb plasmas
• Electron thermal conductivity owing to collisions between degenerate electrons
• Heat blanketing envelopes of neutron stars
• A pulsational approach to the luminosity of Horizontal Branch stellar structures
• A Model of Electron Transport in Dense Plasmas Spanning Temperature Regimes

Cited by in corpus (16)

• Current challenges in the physics of white dwarf stars
• Buoyant crystals halt the cooling of white dwarf stars
• Carbon-Oxygen Phase Separation in MESA White Dwarf Models
• White dwarfs as Physics laboratories: lights and shadows
• Thermal evolution of neutron stars in soft X-ray transients with thermodynamically consistent models of the accreted crust
• Dynamical He Flashes in Double White Dwarf Binaries
• The HST large programme on NGC 6752 -- IV. The White Dwarf Sequence
• Ne22 distillation and the cooling sequence of the old metal-rich open cluster NGC 6791
• New calibrated models for the TRGB luminosity and a thorough analysis of theoretical uncertainties
• A Crystallizing White Dwarf in a Sirius-Like Quadruple System
• Performance of the Stellar Abundances and atmospheric Parameters Pipeline adapted for M dwarfs I. Atmospheric parameters from the spectroscopic module
• Thermal Conductivity and Thermal Hall Effect in Dense Electron-Ion Plasma
• Aerosols and hydrocarbons in the atmosphere of a white dwarf planet
• Discovery of new magnetic δ Scuti stars and impact of magnetism on pulsation excitation
• The Cooling of Old White Dwarfs in 47 Tucanae
• New theoretical Period-Luminosity-Metallicity relations for RR Lyrae in the Rubin-LSST filters