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

TL;DR

This study characterizes the orbital and stellar parameters of the symbiotic binary St 2-22, analyzes its jet evolution during outbursts, and provides insights into its nature and behavior over 16 years of observations.

Contribution

It presents the first detailed orbital and stellar parameters of St 2-22 and documents jet evolution following its 2019 outburst, expanding understanding of jet-producing symbiotic systems.

Findings

Orbital period of 918 days with significant eccentricity.

Mass ratio of approximately 3.5 between red giant and white dwarf.

Jet velocities reaching up to 1800 km/s during outbursts.

Abstract

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. 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. Photometric monitoring for over 16 yrs and high-quality spectroscopic data enabled us to shed new light on its nature. The high-resolution SALT spectra and $V I_C$ 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. We present the orbital and stellar parameters of the system components. The orbital period is $P_{orb} = 918 \pm6^d$. The double-line spectroscopic orbits indicate the mass ratio $q = M_{g} M_{h}^{-1} = 3.50 \pm0.53$, and the components masses $M_{g} \sin^3{i} \sim 2.35$ M$_{sun}$ and $M_{h} \sin^3{i} \sim 0.67$ M$_{sun}$. The orbit shows significant eccentricity, $e = 0.16 \pm0.07$. The orbital inclination is close to 70 degrees. During outbursts, accelerating and decelerating jets are observed with changes in their radial velocity component in a range from $\sim 1500$ 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.