Symbiotic stars are interacting binaries with the longest orbital periods and their multi-component structure makes them rich astrophysical laboratories .
The accretion of a high mass loss rate red giant wind on to a white dwarf ( WD ) makes them promising Type Ia supernovae ( SNe Ia ) progenitors .
Systematic surveys for new Galactic symbiotic stars are critical to identify new promising SNe Ia progenitors ( e.g .
RS Oph ) and to better estimate the total population size to compare against SNe Ia rates .
Central to the latter objective is building a complete census of symbiotic stars towards the Galactic Bulge .
Here we report on the results of a systematic survey of H \alpha emission line stars covering 35 deg ^ { 2 } .
It is distinguished by the combination of deep optical spectroscopy and long-term lightcurves that improve the certainty of our classifications .
A total of 20 bona-fide symbiotic stars are found ( 13 S-types , 6 D-types and 1 D ^ { \prime } -type ) , 35 % of which show the symbiotic specific Raman-scattered OVI emission bands , as well as 15 possible symbiotic stars that require further study ( 6 S-types and 9 D-types ) .
Lightcurves show a diverse range of variability including stellar pulsations ( semi-regular and Mira ) , orbital variations and slow changes due to dust .
Orbital periods are determined for 5 S-types and Mira pulsation periods for 3 D-types .
The most significant D-type found is H1-45 and its carbon Mira with a pulsation period of 408.6 days , corresponding to an estimated period-luminosity relation distance of \sim 6.2 \pm 1.4 kpc and M _ { K } = -8.06 \pm 0.12 mag .
If H1-45 belongs to the Galactic Bulge , then it would be the first bona-fide luminous carbon star to be identified in the Galactic Bulge population .
The lack of luminous carbon stars in the Bulge is a longstanding unsolved problem .
A possible explanation for H1-45 may be that the carbon enhancement was accreted from the progenitor of the WD companion .
A wide variety of unusual emission line stars were also identified .
These include central stars of PNe ( one [ WC10-11 ] Wolf-Rayet and 5 with high density cores ) , 2 novae , 2 WN6 Wolf-Rayet stars , 2 possible Be stars , a B [ e ] star with a bipolar outflow , an ultracompact HII region and a dMe flare star .
Dust obscuration events were found in two central stars of PNe , increasing the known cases to 5 , as well as one WN6 star .
There is considerable scope to uncover several more symbiotic stars towards the Bulge , many of which are currently misclassified as PNe , provided that deep spectroscopy is combined with optical and near-infrared lightcurves .