Identification of new Galactic symbiotic stars with SALT -- II. New discoveries and characterization of the sample

TL;DR

The paper extends the census of Galactic southern symbiotic stars by selecting candidates from the SHS Hα survey and 2MASS and confirming them with SALT spectroscopy. It combines high-ionization emission diagnostics, including Raman O VI and [Fe VII], with TiO-based spectral typing and infrared properties to characterize both the cool giants and hot components, supplemented by multi-survey photometry to study variability and derive orbital and pulsational periods. The study reports 14 new bona-fide symbiotic stars and 6 strong candidates, with $P_{ m orb}$ identified for 19 bona-fide and 3 candidate systems in the range $384$--$1518$ days, and documents eight outbursts and dust-obscuration events in several objects. These results significantly expand the Galactic southern symbiotic-star census and provide a valuable dataset for probing binary interaction, mass transfer, and variability in symbiotic systems.

Abstract

We present the continuation of a systematic search for new southern Galactic symbiotic stars, selecting candidates from the SuperCOSMOS H$α$ Survey and 2MASS. Follow-up spectroscopy with the Southern African Large Telescope (SALT) was used to confirm their symbiotic nature and to characterize the cool and hot components of the full sample, including systems from earlier work. We report 14 newly confirmed bona fide symbiotic stars and identify 6 additional strong candidates. Photometric variability was examined using our data and archival light curves from multiple all-sky surveys. Most systems are variable, with the majority showing periodic modulation consistent with orbital motion or pulsations. Possible photometric orbital periods are reported for 19 confirmed and 3 candidate systems, pending spectroscopic confirmation. Eight objects exhibit signs of outburst activity. In one of the systems, multiple brightenings occur at similar orbital phases, closely resembling the evolution of FN Sgr, a symbiotic binary with a magnetic white dwarf. The peculiar variability of another symbiotic star is best explained by dust-obscuration events. These results expand the census of Galactic symbiotic stars.

Figures (21)

• Figure 1: SALT/RSS spectra of new symbiotic stars. The spectra are not dereddened, and due to limitations in absolute flux calibration due to the moving pupil design of SALT, they are normalized by the average continuum value measured in the region 6 200-6 300 Å 2014MNRAS.440.1410M. The identification of selected emission lines is shown in gray. Most of the unmarked emission lines are of Hi and Hei.
• Figure 2: SALT/RSS spectra of possible symbiotic stars.
• Figure 3: Gaia$G$-band light curve of 2MASS J14031865-5809349. The time of the issued Gaia Science Alert is marked with a red symbol. The underlying quiescent sinusoidal variability, with a period of 685 days, is shown in gray (see text for details).
• Figure 4: Comparison of the quiescent (blue) and outburst (red) spectra of 2MASS J14031865-5809349, obtained with SALT. Selected emission lines are identified in gray. Most of the remaining, unmarked emission features, particularly in the outburst spectrum, are due to Feii.
• Figure 5: AllWISE and NEOWISE W1 and W2-band light curves of 2MASS J16422739-4133105.