Symbiotic stars and other Halpha emission line stars towards the
  Galactic Bulge
  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 Halpha 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'-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 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 a distance of ~6.2+-1.4 kpc and M_K=-8.06+-0.12 mag. If H1-45
belongs to the Galactic Bulge, then it would be the first bona-fide luminous
Galactic Bulge carbon star. 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. (abridged)
