The GALAH Survey and Symbiotic Stars. I. Discovery and follow-up of 33 candidate accreting-only systems

Abstract

We have identified a first group of 33 new candidates for symbiotic stars (SySt) of the accretingonly variety among the 600 255 stars so far observed by the GALAH high-resolution spectroscopic survey of the Southern Hemisphere, more than doubling the number of those previously known. GALAH aims to high latitudes and this offers the possibility to sound the Galaxy for new SySt away from the usual Plane and Bulge hunting regions. In this paper we focus on SySt of the M spectral type, showing an H emission with a peak in excess of 0.5 above the adjacent continuum level, and not affected by coherent radial pulsations. These constraints will be relaxed in future studies. The 33 new candidate SySt were subjected to a vast array of follow-up confirmatory observations (X-ray/UV observations with the Swift satellite, search for optical flickering, presence of a near-UV upturn in ground-based photometric and spectroscopic data, radial velocity changes suggestive of orbital motion, variability of the emission line profiles). According to Gaia DR3 parallaxes, the new SySt are located at the tip of the Giant Branch, sharing the same distribution in M(K ) of the well established SySt. The accretion luminosities of the new SySt are in the range 1−10 L ⊙ , corresponding to mass-accretion rates of 0.1-1 10 −9 M ⊙ yr −1 for WDs of 1 M ⊙ . The M giant of one of the new SySt presents a large Lithium over-abundance.

Spectroscopic and photometric analysis of symbiotic candidates -- I. Ten candidates on classical symbiotic stars

“…For this reason, the data do not allow us to confirm the symbiotic status of V1988 Sgr. On the other hand, as Munari et al (2021) pointed out, even in the case of well-known accreting-only symbiotic stars such as SU Lyn or MWC 560, flickering is not always detectable.…”

“…They do not manifest prominent optical emission lines, but are bright in UV, show significant flickering in this spectral region and are hard X-ray sources (e.g. Luna et al 2013;Mukai et al 2016;Munari et al 2021).…”