Spectra and Line Profiles of FU Orionis Objects: Comparisons Between Boundary Layer Models and Observations

Abstract

We present solutions for the accretion disks and boundary layers in pre-main-sequence stars undergoing FU Orionis outbursts. These solutions differ from earlier disk solutions in that they include a self-consistent treatment of the boundary layer region. In a previous paper (Popham 1996), we showed that these stars should stop accreting angular momentum once they spin up to modest rotation rates. Here we show that for reasonable values of $α$, these low angular momentum accretion rate solutions fit the spectra and line profiles observed in FU Orionis objects better than solutions with high rates of angular momentum accretion. We find solutions which fit the observations of FU Orionis and V1057 Cygni. These solutions have mass accretion rates of 2 and $1 \times 10^{-4} \msyr$, stellar masses of 0.7 and $0.5 \msun$, and stellar radii of 5.75 and $5.03 \rsun$, respectively. They also have modest stellar rotation rates $8-9 \xss$, comparable to the observed rotation rates of T Tauri stars, and angular momentum accretion rates of zero. This supports our earlier suggestion that FU Orionis outbursts may regulate the rotation rates of T Tauri stars.