Opacities in

white dwarf atmospheres

Patrick Dufourt de physique

OUTLINE

• A brief review of the main opacity sources and physical conditions encountered in various white dwarf atmospheres

• Some past successes

• Selected challenges

“The talk should cover continuum and line opacities, abundance determinations, current challenges presented by opacities and other topics as you see fit. This would be the introductory talk for one of the workshop themes (opacities).”

Wavelength

Hydrogen dominated

Helium dominated

Helium dominated + traces of carbon(dredge-up from the core)

Helium dominated + traces of metals(accreted from debris disk)

Modeling shortcomings may easily lead to 500K error on Teff wich correspond to a change of ~ 1x109 years in the age of the star

Ultracool whtie dwarfs(Gianninas et al. 2015)

(dyn

/cm

2)

Hydrogen dominated T-P structure for various effective temperatures

Escape probability for an «average» photon emitted at τR ~ e-τR

At τR = 1, about 36% of the photons can escape without interacting

1atm

Depth at witch a photon of a given frequency typicaly comes fromfor a Teff = 25,000K DA white dwarf

(dyn

/cm

2)

Hydrogen dominated T-P structure and formation depth for Teff = 25,000K

Hydrogen dominated T-density structure for various effective temperatures

liquid water

air in this room

Calculations for the Stark broadening of hydrogen lines based on the unified theory from Vidal, Cooper, and Smith. Accounts for the non ideal effects using Hummer and Mihalas formalism in a consistent way directly inside the line profile calculations to describe effects due to perturbations on the absorber from protons and electrons.

Still room for improvements: See following talks by R. Falcon and S. Gomez

Helium dominated T-P structure for various effective temperatures

(dyn

/cm

2)

liquid water

air in this room

Helium dominated T-density structure for various effective temperatures

See poster by Marc-André Schaeuble

Helium dominated white dwarf with traces of heavy elements

Metal polluted white dwarfs offer us an unique opportunity to measure the bulk interior composition of exo planetesimals/planets/asteroids

The compositions of extrasolar

planetesimals mostly resemble bulk earth.

Xu+ 2014

Helium dominated white dwarf with traces of heavy elements

Stark: for T=10,000K

(convolved with Doppler profile = Voigt)

Stark Broadening + magnetic fields?

Fit using Helium + Hydrogen grid(Kleinman et al. : 17100 K using pure Helium)

log g = 8.2

log g = 7.8

log g = 8.0

Teff = 15,000 K

log g = 8.2

log g = 7.8

log g = 8.0

log g = 8.0 + Z

Teff = 15,000 K

Also important in hotter stars: See Klaus Werner’s talk

Solution with Z agrees with FeI/FeII, MgI/MgII, photometry and HeI for Teff =14700K!!!!

See poster by Cynthia Genest-Beaulieu

Hydrogen abundance discrepancy between Ly alpha and H alpha

Star Teff log g distance (pc) log N(H)/N(He) log N(H)/N(He)(H alpha) (Ly alpha)

_________________________________________________________________________________________

WD0100-068 19800 8.07 43 -5.0 -4.4WD0840+262 17770 8.30 49 -3.98 -3.46WD0435+410 16810 8.19 52 -4.2 -3.54WD2222+683 15230 8.20 65 <-5.4 -5.1WD2129+000 14380 8.26 49 <-6.48 -5.28HS2253+8023 14400 8.4 71 -5.62 -3.94

liquid water

air in this room

Helium dominated T-density structure for various effective temperatures

In termes of number density

25,000K

15,000K

Unified theory of spectral line broadening (Allard et al. 1999) +

ab initio potential energies

Several helium-rich white dwarf stars show an asymmetry in some lines indicating that the physical conditions present in these stars are such that the impact approximation is no longer valid. They thus require a specific treatment for line broadening owing to the high helium densities that are involved.

This blue asymmetry is a consequence of low maxima in the corresponding Mg-He potential energy difference curves at shortand intermediate internuclear distances.

Ross 640: In order to have same abundances between measurements in UV vs optical, vdw constant arbitrary multiplied by 10 (!?) (Koester and Wolff 2000).

Consistent values are now obtained usingAllard’s calculations

(Blouin et al. in prep)

Profiles available only for a few transitions of Mg, Ca and Na. Potential energies needed in order to do other lines.

Pure Helium vs Helium + traces of carbon at Teff = 8000K

with C

with Cwithout C

without C

This was the solution to get Procyon B out of the « Iron Box » (Howard Bond’s talk)

Pure Helium vs Helium + traces of carbon at Teff = 6000K

with C

with Cwithout C

without C

Using density functionaltheory, Kowalski findsthat the electronic transition energy Te increases monotonically with the helium density

Blouin et al. (in preparation)See also Piotr Kowalski’s talk