Magnetospheric accretion at the late phases of the Pre-Main-Sequence evolution. The case of RZ Psc

Abstract

It has been shown that during the outburst of accretion activity observed in UX Ori type star RZ Psc in 2013, the accretion rate increased approximately by an order of magnitude. This means that the accretion process at the late stages of the Pre-Main Sequence evolution is very unstable. Using the spectra obtained during this episode we have studied the magnetospheric emission in the H$\alpha$ line. Models of magnetospheric accretion are calculated to obtain the parameters of the magnetosphere from this observation. In present work we have taken into account the influence of the recombination delay effect during gas motion in the stellar magnetosphere. The accounting for this effect and the presence of the magnetospheric absorption in the IR CaII triplet lines and its absence in D Na I resonance lines allowed us to place a lower limit on the temperature in the magnetosphere at $\approx$ 10000 K, which significantly improved precision of our estimate of accretion rate. According to the best fit model the logarithm of accretion rate is $\log\dot{M} = -10.1\pm0.3$ ($\dot{M} \approx 7\times10^{-11}$ M$_\odot$yr$^{-1}$) and the inclination angle of RZ Psc is $43\pm 3^\circ$. It is less than the inclination, typical for the UX Ori stars (about 70$^\circ$), that explains the weak photometric variability of this star. Using the obtained accretion rate and magnetosphere radius we estimate the strength of the dipole component of the magnetic field of RZ Psc $\approx$ 0.1 kGs.