Radio interferometric imaging of RS Oph bipolar ejecta for the 2021 nova outburst

TL;DR

This study uses radio interferometry to image the bipolar ejecta of RS Oph during its 2021 nova outburst, revealing detailed ejecta structure, expansion velocities, and the influence of the orbital plane on visibility.

Contribution

First detailed radio imaging of RS Oph's 2021 outburst revealing bipolar ejecta structure and its evolution, with insights into the impact of the orbital plane on ejecta visibility.

Findings

Ejecta extended about 90 mas (~240 AU) at 5 GHz.

Lobes expanding at approximately 7550 km/s.

Ejecta structure similar to the 2006 eruption.

Abstract

The recurrent nova and symbiotic binary RS Oph erupted again in August 2021 for its eighth known outburst. As part of a multi-epoch and frequency campaign, we observed RS Oph 34 days after the outburst at 5 GHz with the European VLBI Network (EVN). The radio image is elongated over the east-west direction for a total extension of about 90 mas (or about 240 AU at the Gaia DR3 distance d=2.68 [-0.15/+0.17] kpc), and shows a bright and compact central component coincident with the Gaia astrometric position, and two lobes east and west of it, expanding perpendicular to the orbital plane. By comparing with the evolution of emission-line profiles on optical spectra, we found the leading edge of the lobes to be expanding at 7550 km/s, and i=54 deg as the orbital inclination of the binary. The 2021 radio structure is remarkably similar to that observed following the 2006 eruption. The obscuring role of the density enhancement on the orbital plane (DEOP) is discussed in connection to the time-dependent visibility of the receding lobe in the background to the DEOP, and the origin of the triple-peaked profiles is traced to the ring structure formed by the nova ejecta impacting the DEOP.