A remarkable sample of new symbiotic stars towards the Galactic Bulge

TL;DR

This study systematically identified new symbiotic stars in the Galactic Bulge using combined Halpha spectroscopy and photometry, revealing nearly two dozen new systems and providing insights into their properties and the population of old novae.

Contribution

Introduces a new survey method combining spectroscopy and photometry to discover symbiotic stars and old novae in the Galactic Bulge, including the first luminous carbon star in that region.

Findings

Discovered nearly two dozen new symbiotic stars.

Identified the first luminous carbon symbiotic Mira in the Bulge.

Captured two old novae in the nebular phase.

Abstract

Symbiotic stars are the longest orbital period interacting binaries, where nova-like outbursts are generated by the accretion of a high mass loss rate red giant wind onto a white dwarf companion. Long-term photometric monitoring surveys such as OGLE and MACHO are ideal platforms to identify nova-like events in symbiotic stars, however there are only a handful of known systems within the small footprint of these surveys. We introduce a systematic Halpha emission line object survey for new symbiotic stars covering 35 deg^2 towards the Galactic Bulge that combines deep 2dF/AAOmega spectroscopy with OGLE and MACHO photometry. This powerful combination has uncovered nearly two dozen new symbiotic stars, more than a dozen probable symbiotic stars, and several other unusual Halpha emission line stars. While we don't find any nova-like activity, the lightcurves do exhibit semi-regular and Mira pulsations, orbital variations and slower changes due to dust. Here we introduce a few of the new symbiotics, including H1-45, only the fourth known carbon symbiotic Mira. This remarkable discovery may be the first luminous carbon star belonging to the Galactic Bulge, according to its period-luminosity relation distance of 6.2+-1.4 kpc, potentially shedding new light on the puzzling lack of luminous carbon stars in the Bulge. We also present two old novae captured in the nebular phase, complementing other surveys to better characterise the old nova population.