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

TL;DR

This paper investigates how radiative levitation influences the calculation of accretion rates in white dwarf atmospheres, emphasizing the importance of including radiative support in abundance and accretion modeling.

Contribution

It introduces time-dependent diffusion calculations that incorporate radiative levitation effects for more accurate accretion rate estimations in white dwarfs.

Findings

Radiative levitation supports certain elements, affecting abundance measurements.

Equilibrium between radiative and gravitational accelerations determines element support.

Radiative effects must be considered for precise accretion rate calculations.

Abstract

Elements heavier than hydrogen or helium that are present in the atmospheres of white dwarfs with effective temperatures lower than 25,000 K, are believed to be the result of accretion. By measuring the abundances of these elements and by assuming a steady-state accretion, we can derive the composition of the accreted matter and infer its source. The presence of radiative levitation, however, may affect the determination of the accretion rate. We present time-dependent diffusion calculations that take into account radiative levitation and accretion. The calculations are performed on C, N, O, Ne, Na, Mg, Al, Si, S, Ar, and Ca in hydrogen-rich white dwarf models with effective temperatures lower than 25,000 K and a gravity of log g = 8.0. We show that in the presence of accretion, the abundance of an element supported by the radiative levitation is given by the equilibrium between the radiative and gravitational accelerations, unless the abundance predicted by the steady-state accretion is much greater than the abundance supported by the radiative acceleration.