The FU Orionis binary system RNO 1B/1C

Abstract

Observations of CS (7→6) emission reveal a ≥3M_⊙ core, 1.8×10^4 AU in size, surrounding the FU Orionis binary system RNO 1B/1C. Fractional chemical abundances, calculated from LVG and LTE codes, are mostly similar to those in the cold core TMC 1. However, values for Si0/H_2 and CH_(3)0H/H_2 are enhanced, possibly by sputtering reactions or grain-grain collisions in tile outflow associated with the young stars. Aperture syntllesis maps of tile 2.6 and 3.1 mm continuum emission at ~5" and ~9" resolution, respectively, reveal that RNO 1C is surrounded by a flattened, dusty envelope, ~5000 AU in size, with mass ≥1.1 M_⊙. High spatial resolution (~3") interferometer observations of CS (2→1) emission may trace the dense walls of ail outflow cavity comprised of two concentric arcs with dynamical ages of 4×10^3 and 1×10^4 yr. The velocity structure of lower density gas imaged in the CO (1→0) transition is consistent with the arcs being formed by two energetic FU Orionis outbursts. Each event may have imparted more than 4 M_⊙km s^(-1) to the outflow, implying outburst mass loss rates of ~10^(-4) M_⊙ yr^(-1). It appears that RNO 1C is probably the driving source for the outflow and tllat, while pre-main sequence stars are in tile FU Orionis stage, outbursts may dominate both outflow morphology and energetics.