Pierre Chayer1 and Jean Dupuis2
1STScI, 2CSA
17th European White Dwarf Workshop
Tübingen, Germany
August 16−20, 2010
Gemini Observatory Illustration by Jon Lomberg
Effect of Radiative Levitation on
Calculations of Accretion Rates in
White Dwarfs
Two methods exist for computing accretion
rates
1) Steady state approximation
2) Time-dependent diffusion
calculations
2
Silicon and aluminum are supported
Teff = 20,000 K, log g = 8.0
Radiative acceleration as a function of depth
3
Silicon is supported in DA with Teff < 17,500 K
Log g = 8.0
Radiative acceleration as a function of depth for Si
4
Evolution of Si in a DA in presence of
accretion but without radiative levitation
Log [dM/dt]Si = 102 g/s, Teff = 20,000 K, log g = 8.0
5
Evolution of Si in a DA in presence of
accretion and radiative levitation
Log [dM/dt]si = 102 g/s, Teff = 20,000 K, log g = 8.0
6
Evolution of Si in a DA in presence of
accretion and radiative levitation
Log [dM/dt]si = 106 g/s, Teff = 20,000 K, log g = 8.0
7
The radiative levitation has an impact on the
determination of accretion rates
Teff = 20,000 K
Log g = 8.0
Silicon abundance as a function of depth
8
In summary, the abundance of elements
supported by the radiative levitation may not
be related to the accretion rate
Log g = 8.0
25,000 K
22,500 K
20,000 K
17,500 K
9