Radiative Levitation of Silicon in the Atmospheres of Two Hyades DA White Dwarfs

Understand

The presence of silicon at the surface of the two Hyades DA white dwarfs WD 0421+162 and WD 0431+126 requires mechanisms that counteract the effects of the downward diffusion.

• Radiative levitation calculations indicate that the silicon abundance observed in WD 0431+126 corresponds to the abundance supported by radiative levitation.
• Detailed time-dependent diffusion calculations that take into account radiative levitation and accretion indicate that accretion with rates of dM/dt(Si) < 1.00E4 g/s could also be present without disrupting the abundance supported by radiative levitation.
• In the case of WD 0421+162, accretion with a rate of dM/dt(Si) = 1.25E5 g/s must be invoked, because its observed silicon abundance is larger than the abundance supported by radiative levitation.