SU Lyn -- a transient symbiotic star

TL;DR

SU Lyn is a binary system that exhibits transient symbiotic behavior, showing brief periods of interaction detectable in X-ray and optical observations, and may evolve into a persistent symbiotic star.

Contribution

This study provides the first detailed optical spectroscopic monitoring of SU Lyn, revealing its transient symbiotic nature and potential evolutionary path.

Findings

SU Lyn showed strong emission line variability and P Cygni profiles.

The system was interacting only during the last twelve years of monitoring.

SU Lyn may evolve into a classical, persistent symbiotic system.

Abstract

SU Lyn is a binary system composed of a white dwarf and a red giant star. Although it is known to be bright and variable at X-ray wavelengths, the optical counterpart of the source appeared as a single red giant without prominent emission lines. Because of the lack of optical features typical for interacting systems, the system was classified as a hidden symbiotic star. We present the results of optical monitoring of the system. While SU Lyn did not show substantial photometric variability, the spectroscopic observations revealed a complex behavior. The system showed strong emission line variability, including P Cygni profiles, changing line emission environments, and variable reddening. Both X-ray and optical observations indicate that the components of SU Lyn were interacting only for a short time during the last twelve years of monitoring. For the first time we showed that SU Lyn resembled a classical symbiotic star when it was X-ray bright, and remained hidden afterwards. We also discuss the current evolutionary status of the red giant, as well as possible future evolution of the system. We suggest that SU Lyn could be a progenitor of a classical, persistent symbiotic system.