Refined theorems of approximation theory in the space of $p$-absolutely continuous functions

In this paper, we prove direct and inverse theorems of approximation theory in the space of $p$-absolutely continuous functions which generalize Terekhin's results in the same way as Timan's results in $L_p$ generalize the classical theorems of approximation theory. The main theorems are refined for functions with quasimonotone Fourier coefficients and, in a number of cases, the resulats are shown to be sharp.