SU Lyn - A transient symbiotic star

Krystian Iłkiewicz, Joanna Mikołajewska, Simone Scaringi, François Teyssier, Kiril A. Stoyanov, Matteo Fratta

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5 Scopus citations


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 behaviour. 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.

Original languageEnglish
Pages (from-to)2707-2717
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Feb 2022


  • accretion, accretion discs
  • binaries: symbiotic
  • novae, cataclysmic variables
  • stars: individual: SU Lyn


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