Calculating the Bohr radius or velocity of an excitons

[supercali]

while doing some calculations such as calculating the Bohr radius or velocity of an excitons in semiconductors such as GaAs I didnt understand why is it allowed to use the static permittivity even though the electron and hole aren't as heavy and the spectra is measured at high frequencies such as $$\omega=10^{15}Hz$$?

 

[supercali]

anyone ?