Where are the missing symbiotic stars? Uncovering hidden Symbiotic Stars in public catalogues

TL;DR

This paper introduces a novel UV-IR photometric method to uncover hidden symbiotic stars, revealing new candidates and confirming some known systems, thereby addressing the discrepancy between predicted and observed populations.

Contribution

It presents a new approach using GALEX UV and IR data to identify faint or obscured symbiotic stars missed by optical surveys.

Findings

Discovered 2 new symbiotic stars through spectroscopic follow-up.

Recovered 5 known symbiotic stars from the candidate list.

Identified 35 candidates with FUV-NUV<1 indicative of symbiotic stars.

Abstract

Theoretical predictions of the population of Galactic symbiotic stars (SySts) are highly inconsistent with the current known population. Despite intense effort over the past decades, observations are still far below the predictions. The majority of known SySts so far are identified based on selection criteria established in the optical regime. The recent discovery of SU Lyn with very faint optical emission lines uncloaked a subgroup of SySts with accreting-only white dwarfs. In this particular case, the luminous red giant may overshadow the dimmed white dwarf companion. A new approach to search for this subgroup of SySts is presented, employing GALEX UV and 2MASS/AllWISE IR photometry. The FUV-NUV colour index is an indicator, direct or indirect, for the presence of hot compact companions. The cross-match of the Catalogue of Variable Stars III obtained from the All-Sky Automated Survey for SuperNovae with the GALEX, 2MASS and AllWISE catalogues result in a sample of 814 potential SySt candidates. From them, 105 sources have photometric measurements from both FUV and NUV bands and 35 exhibit FUV-NUV<1, similar to what it is expected from known SySts. Five known SySts are recovered, while two new genuine SySts are discovered in spectroscopic follow-up observations after the detection of the typical emission lines.