EG Andromedae: A New Orbit and Additional Evidence for a Photoionized Wind

TL;DR

This study refines the orbital parameters of the symbiotic binary EG Andromedae, confirming a circular orbit and providing evidence for a photoionized wind driven by a hot secondary star.

Contribution

It presents the first detailed orbital solution for EG Andromedae based on 20 years of spectroscopic data, establishing a circular orbit and supporting a photoionized wind model.

Findings

Orbital period of 483.3 days with a circular orbit.

H I emission lines vary with the orbital period.

Evidence for a hot secondary star ionizing the red giant's wind.

Abstract

We analyze a roughly 20 yr set of spectroscopic observations for the symbiotic binary EG And. Radial velocities derived from echelle spectra are best-fit with a circular orbit having orbital period P = 483.3 +- 1.6 days and semi-amplitude K = 7.34 +- 0.07 km/sec. Combined with previous data, these observations rule out an elliptical orbit at the 10-sigma level. Equivalent widths of H~I Balmer emission lines and various absorption features vary in phase with the orbital period. Relative to the radius of the red giant primary, the apparent size of the H II region is consistent with a model where a hot secondary star with effective temperature of roughly 75,000 K ionizes the wind from the red giant.