Hubble Space Telescope Imaging of the Expanding Nebular Remnant of the Recurrent Nova RS Ophiuchi (2006)

TL;DR

This study uses Hubble imaging to analyze the structure and expansion of the nebular remnant of RS Ophiuchi after its 2006 outburst, revealing a bipolar morphology influenced by circumstellar interaction.

Contribution

First detailed imaging of RS Ophiuchi's remnant showing a bipolar structure and expansion dynamics, linking morphology to circumstellar environment and nova progenitor models.

Findings

Remnant has a double ring structure with 580 AU extent.

Expansion velocity in E-W direction is approximately 3200 km/s.

Bipolar morphology suggests interaction with denser equatorial circumstellar medium.

Abstract

We report Hubble Space Telescope imaging obtained 155 days after the 2006 outburst of RS Ophiuchi. We detect extended emission in both [O III] and [Ne V] lines. In both lines, the remnant has a double ring structure. The E-W orientation and total extent of these structures (580+-50 AU at d=1.6kpc) is consistent with that expected due to expansion of emitting regions imaged earlier in the outburst at radio wavelengths. Expansion at high velocity appears to have been roughly constant in the E-W direction (v_{exp} = 3200+-300 km/s in the plane of the sky), with tentative evidence of deceleration N-S. We present a bipolar model of the remnant whose inclination is consistent with that of the central binary. The true expansion velocities of the polar components are then v = 5600+-1100 km/s. We suggest that the bipolar morphology of the remnant results from interaction of the outburst ejecta with a circumstellar medium that is significantly denser in the equatorial regions of the binary than at the poles. This is also consistent with observations of shock evolution in the X-ray and the possible presence of dust in the infrared. Furthermore, it is in line with models of the shaping of planetary nebulae with close binary central systems, and also with recent observations relating to the progenitors of Type Ia supernovae, for which recurrent novae are a proposed candidate. Our observations also reveal more extended structures to the S and E of the remnant whose possible origin is briefly discussed.