Reverse rotation of the accretion disk in RW Aur A: Observations and a physical model

Abstract

Speckle interferometry of the young binary system RW Aur was performed with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences using filters with central wavelengths of 550 nm and 800 nm and passband halfwidths of 20 nm and 100 nm, respectively. The angular separation of the binary components was 1.448 ′′ ± 0.005 and the position angle of the system was 255.9 o ± 0.3. at the observation epoch (JD 2 454 255.9). We find using published data that these values have been changing with mean rates of +0.002 ′′ /yr and +0.02 o /yr, respectively, over the past 70 years. This implies that the direction of the orbital motion of the binary system is opposite to the direction of the disk rotation in RW Aur A. We propose a physical model to explain the formation of circumstellar accretion disks rotating in the reverse direction relative to young binary stars surrounded by protoplanetary disks. Our model can explain the characteristic features of the matter flow in RW Aur A: the high accretion rate, small size of the disk around the massive component, and reverse direction of rotation.

The effect of external environment on the evolution of protostellar disks

“…The reason is that angular momentum in the external environment is usually much greater than that of the star, and the latter may change stellar rotation to match that of the infalling material. Although the efficiency of this process should depend on how much angular momentum is lost via jets and outflows and whether or not a binary or multiple stellar system forms instead of a single star, such counterrotating systems are nevertheless expected to be rare, with RW Aur A being one possible example (Woitas et al 2005;Bisikalo et al 2012).…”

“…The final stellar mass is expected to be slightly below that of the Sun. The formation of systems with disks counter-rotating to that of the star is rare, with RW Aur A one possible example showing both the disk and jet counterrotating with respect to the rotation of the host binary system (Woitas et al 2005;Bisikalo et al 2012).…”

Wobbling and Precessing Jets From Warped Disks in Binary Systems

“…Confirmed binary systems that are sources of jets are T Tau (Hirth et al 1997;Duchêne et al 2002;Johnston et al 2003) or RW Aur (Herbst et al 1996;Bisikalo et al 2012). Another source is HK Tau, a binary system younger than four million years (Jensen & Akeson 2014).…”

Bow shocks in disks of young binary systems

“…The interaction between this jet and the surrounding gas can be traced up to distances of 4.6 × 10 4 AU. The RW Aur system is unique since the direction of rotation of the circumstellar accretion disk RW Aur A is opposite respectively to the direction of the orbital motion of the system (see Bisikalo et al [19]). The accretion disk rotates clockwise viewed from the Earth [20] while the orbital angular momentum of the system is opposite [19].…”

“…The RW Aur system is unique since the direction of rotation of the circumstellar accretion disk RW Aur A is opposite respectively to the direction of the orbital motion of the system (see Bisikalo et al [19]). The accretion disk rotates clockwise viewed from the Earth [20] while the orbital angular momentum of the system is opposite [19]. The results of our three-dimensional gas-dynamical numerical simulations allow us to suggest a physical model to explain the formation of reversed accretion disks in young binary stars surrounded by protoplanetary disks.…”