The symbiotic binary St 2-22: Orbital and stellar parameters and jet evolution following its 2019 outburst

Abstract

Context. St 2-22 is a relatively poorly studied S-type symbiotic system that belongs to a small group of jet-producing systems as a result of disc accretion onto a white dwarf fed by its red giant companion. Aims. The goal of this paper is to analyse the nature and derive the basic parameters of St 2-22, and to follow the jet evolution. Methods. Photometric monitoring for over 16 yr and high-quality spectroscopic data enabled us to shed new light on its nature. The high-resolution SALT spectra and V Ic photometry obtained during and between the last two outbursts have been used to search for periodic changes, to derive spectroscopic orbits of both system components, and to study the outburst and jet evolution. Results. We present the orbital and stellar parameters of the system components. The orbital period is Porb = 918 ± 6d. The double-line spectroscopic orbits indicate the mass ratio q = Mg Mh−1 = 3.50 ± 0.53, and the components masses Mgsin3i ∼ 2.35 M⊙ and Mhsin3i ∼ 0.67 M⊙. The orbit shows significant eccentricity, e = 0.16 ± 0.07. The orbital inclination is close to 70°. During outbursts, accelerating and decelerating jets are observed with changes in their radial velocity component in a range from ∼1500 up to nearly 1800 km s−1. St 2-22 turned out to be a classical symbiotic system very similar to the precursor of the group – Z And.