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Symbiotic stars and other Halpha emission line stars towards the Galactic Bulge


, : Symbiotic stars and other Halpha emission line stars towards the Galactic Bulge.

Symbiotic stars are interacting binaries with the longest orbital periods andtheir multi-component structure makes them rich astrophysical laboratories. Theaccretion of a high mass loss rate red giant wind on to a white dwarf (WD)makes them promising Type Ia supernovae (SNe Ia) progenitors. Systematicsurveys for new Galactic symbiotic stars are critical to identify new promisingSNe Ia progenitors (e.g. RS Oph) and to better estimate the total populationsize to compare against SNe Ia rates. Central to the latter objective isbuilding a complete census of symbiotic stars towards the Galactic Bulge. Herewe report on the results of a systematic survey of Halpha emission line starscovering 35 deg^2. It is distinguished by the combination of deep opticalspectroscopy and long-term lightcurves that improve the certainty of ourclassifications. A total of 20 bona-fide symbiotic stars are found (13 S-types,6 D-types and 1 D'-type), 35% of which show the symbiotic specificRaman-scattered OVI emission bands, as well as 15 possible symbiotic stars thatrequire further study (6 S-types and 9 D-types). Lightcurves show a diverserange of variability including stellar pulsations (semi-regular and Mira),orbital variations and slow changes due to dust. Orbital periods are determinedfor 5 S-types and pulsation periods for 3 D-types. The most significant D-typefound is H1-45 and its carbon Mira with a pulsation period of 408.6 days,corresponding to a distance of ~6.2+-1.4 kpc and M_K=-8.06+-0.12 mag. If H1-45belongs to the Galactic Bulge, then it would be the first bona-fide luminousGalactic Bulge carbon star. The lack of luminous carbon stars in the Bulge is alongstanding unsolved problem. A possible explanation for H1-45 may be that thecarbon enhancement was accreted from the progenitor of the WD companion. A widevariety of unusual emission line stars were also identified. (abridged).

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