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

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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

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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

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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

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25,000 K

20,000 K

17,500 K

22,500 K

Log g = 8.0