effect of radiative levitation on calculations of accretion rates in white dwarfs

Effect of Radiative Levitation on Calculations of Accretion Rates in White Dwarfs

Pierre Chayer1 and Jean Dupuis2

1STScI, 2CSA

17th European White Dwarf Workshop

Tübingen, Germany

August 16−20, 2010

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Two methods exist for computing accretion rates

2

1) Steady state approximation

2) Time-dependent diffusion calculations

Silicon and aluminum are supported

3Radiative acceleration as a function of depth

Teff = 20,000 K, log g = 8.0

Silicon is supported in DA with Teff < 17,500 K

4

Radiative acceleration as a function of depth for Si

Log g = 8.0

Evolution of Si in a DA in presence of accretion but without radiative levitation

5

Log [dM/dt]Si = 102 g/s, Teff = 20,000 K, log g = 8.0

Evolution of Si in a DA in presence of accretion and radiative levitation

6

Log [dM/dt]si = 102 g/s, Teff = 20,000 K, log g = 8.0

Evolution of Si in a DA in presence of accretion and radiative levitation

7

Log [dM/dt]si = 106 g/s, Teff = 20,000 K, log g = 8.0

The radiative levitation has an impact on the determination of accretion rates

8Silicon abundance as a function of depth

Teff = 20,000 KLog g = 8.0

In summary, the abundance of elements supported by the radiative levitation may not be related to the accretion rate

9

25,000 K

20,000 K

17,500 K

22,500 K

Log g = 8.0