A Survey of the Local Group of Galaxies for Symbiotic Binary Stars. I. First detection of symbiotic stars in M33

TL;DR

This paper reports the first detection and spectroscopic analysis of 12 symbiotic binary stars in the galaxy M33, highlighting the impact of interstellar gas on candidate selection and revealing diverse stellar types linked to low metallicity.

Contribution

It provides the first systematic search and characterization of extragalactic symbiotic stars in M33, refining detection criteria and revealing stellar composition related to galaxy metallicity.

Findings

First spectroscopic detection of 12 symbiotic binaries in M33.

Presence of diverse giant star types, including carbon-rich and Zr-enhanced MS stars.

Distribution of binaries suggests a wide range of progenitor star ages.

Abstract

We present and discuss initial selection criteria and first results in M33 from a systematic search for extragalactic symbiotic stars. We show that the presence of diffuse interstellar gas emission can significantly contaminate the spectra of symbiotic star candidates. This important effect forces upon us a more stringent working definition of an extragalactic symbiotic star. We report the first detections and spectroscopic characterisation of 12 symbiotic binaries in M33. We found that four of our systems contain carbon-rich giants. In another two of them the giant seems to be a Zr-enhanced MS star, while the remaining six objects host M-type giants. The high number ratio of C to M giants in these binaries is consistent with the low metallicity of M33. The spatial and radial velocity distributions of these new symbiotic binaries are consistent with a wide range of progenitor star ages.