RW Aur A: SpeX Spectral Evidence for Differentiated Planetesimal Formation, Migration, and Destruction in an ∼3 Myr Old Excited CTTS System

Abstract

We present 2007–2020 SpeX VISNIR spectral monitoring of the highly variable RW Aur A CTTS. We find direct evidence for a highly excited, IR-bright, asymmetric, and time-variable system. Comparison of the spectral and temporal trends found determines five different components: (1) a stable continuum from 0.7 to 1.3 μ m, with color temperature ∼4000 K, produced by the CTTS photospheric surface; (2) variable hydrogen emission lines emitted from hot excited hydrogen in the CTTS’s protostellar atmosphere/accretion envelope; (3) hot CO gas in the CTTS’s protostellar atmosphere/accretion envelope; (4) highly variable 1.8–5.0 μ m thermal continuum emission with color temperature ranging from 1130 to 1650 K, due to a surrounding accretion disk that is spatially variable and has an inner wall at r ∼ 0.04 au and T ∼ 1650 K and outer edges at ∼1200 K; and (5) transient, bifurcated signatures of abundant Fe ii + associated S i , Si i , and Sr i in the system’s jet structures. The bifurcated signatures first appeared in 2015, but these collapsed and disappeared into a small single-peaked protostellar atmosphere feature by late 2020. The temporal evolution of RW Aur A’s spectral signatures is consistent with a dynamically excited CTTS system forming differentiated Vesta-sized planetesimals in an asymmetric accretion disk and migrating them inward to be destructively accreted. By contrast, nearby coeval binary companion RW Aur B evinces only a stable WTTS photospheric continuum from 0.7 to 1.3 μ m + cold CO gas in absorption + stable 1.8–5.0 μ m thermal disk continuum emission with color temperature ∼1650 K.