Three-Dimensional Doppler Images of the Disk-like and Stream-like States of U Coronae Borealis

Abstract

The 3D Radioastronomical Approach to Doppler tomography has been used to study the H$α$ emission sources in U Coronae Borealis. These 3D tomograms provide greater resolution than the projected 2D version and highlight the jet-like gas flows in the $V_z$ direction transverse to the orbital plane. In this paper, the 3D tomograms are compared at two distinct epochs when U CrB was in the disk-like state (1993 data) and the stream-like state (1994 data). Both states display a prominent emission source, the circumprimary bulge, which is produced when the gas stream strikes the photosphere of the mass-gainer. This source is detected within $V_z$ = $\pm$150 km s{$^{-1}$}, and demonstrates that the bulge is not confined to the orbital plane although it achieves maximum strength near $V_z$=0 km s{$^{-1}$}. Other emission sources include the stream-star and stream-disk shocks and a Localized Region (LR) where the circling disk material strikes the incoming gas stream. The LR has $V_z$ velocities of 200 to 500 km s{$^{-1}$} in the disk-like state. The disk emission is seen over a range of $V_z$ velocities, and there is evidence that the disk is inclined to the orbital plane or may have two arms. The gas stream flows along its predicted trajectory in the stream-like state, and a comparison with the disk-like state suggests that the gas stream has a higher density than the disk in both states of this binary.