Letter to the Editor

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

¹ INAF Osservatorio Astronomico di Padova, 36012 Asiago, VI, Italy
e-mail: ulisse.munari@inaf.it
² INAF Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
³ Joint Institute for VLBI ERIC, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁴ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
⁵ Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899, USA
⁶ Dept. of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
⁷ Department of Astronomy University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa

Received: 27 August 2022
Accepted: 21 September 2022

Abstract

The recurrent nova and symbiotic binary RS Oph erupted again in August 2021 for its eighth known outburst. 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⁻¹, and i = 54° 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.