Mass outflow from the symbiotic binary RS Oph during its 2021 outburst

Abstract

Context. RS Oph is a symbiotic recurrent nova containing a massive white dwarf with heavy mass loss during activity. In August 2021, it underwent its seventh optical eruption since the end of the 19th century. Aims. The goal of this work is to analyse the structure of the outflows from the outbursting object. Methods. Based on broad-band U, B, V, RC, and IC photometry and high-resolution Hα spectroscopy obtained at days 11–15 of the outburst, we derived some parameters of the system's components and outflows and their changes during our observation. Results. The effective temperature of a warm shell (pseudophotosphere) produced by the ejected material and occulting the hot component of the system was Teff = 15 000 ± 1000 K and the electron temperature of the nebula was Te = 17 000 ± 3000 K throughout the observations. The effective radius of the pseudophotosphere was Reff = 13.3 ± 2.0 R⊙ and the emission measure of the nebula EM = (9.50 ± 0.59) × 1061 cm−3 for day 11 and Reff = 10.3 ± 1.6 R⊙ and EM = (5.60 ± 0.35) × 1061 cm−3 for day 15. To provide this emission measure, the bolometric luminosity of the outbursting object must exceed its Eddington limit. The mass-loss rate of the outbursting object through its wind is much greater than through its streams. The total rate (from wind + streams) was less than (4–5) × 10–5 (d/1.6 kpc)3/2 M⊙ yr–1. The streams are not highly collimated. Their mean outflowing velocities are υb = −3680 ± 60 km s–1 for the approaching stream and υr = 3520 ± 50 km s–1 for the receding one if the orbit inclination is 50°.