The Galah survey and symbiotic stars. II. Discovery, validation, and intensive follow-up of 44 new systems accreting at the lowest detectable levels
We report the discovery, validation, and characterization of 44 new symbiotic stars (SySts) accreting at the lowest detectable levels (Lacc =< 3 Lsun). Candidates were initially selected from the Galah survey among non-pulsating M-type red giants exhibiting Halpha excess. Between 2021 and 2025, these targets were subjected to intensive multi-wavelength campaigns, including ground-based, high-resolution Echelle spectroscopy over 544 nights, multi-epoch flickering searches down to 1 mmag, and UV/X-ray observations with the Swift satellite. Our high-resolution spectra allowed for a detailed investigation of Halpha flux and line-profile variability. Crucially, the radial velocities measured for the M-giant components yielded reliable spectroscopic orbits for 22 objects and preliminary orbits for an additional eight, corroborated by binary-induced modulations in ASAS-SN photometry. Measured accretion levels vary by factors of up to 20X, emphasizing the need for high-sensitivity, long-term monitoring. Swift X-ray data exclude neutron star companions in all targets, consistent with predominance of white-dwarf degenerates in known SySts. Combined with the 33 objects from Paper I, this sample of 77 new SySts significantly exceeds the number of previously known, accreting-only Galactic symbiotic stars, constituting the bulk of the low-accretion (LowAcc) variety discovered to date and representing >10 percent of all known SySts in the Galaxy. As SySts likely spend most of their lifetimes in LowAcc faint states, characterizing this population is essential for estimating the total Galactic SySt population and evaluating the role of SySts as Type Ia supernova progenitors or sources of UV excess in elliptical galaxies.