  Symbiotic stars often exhibit broad wings around Balmer emission lines, whose
origin is still controversial. We present the high resolution spectra of the S
type symbiotic stars Z Andromedae and AG Draconis obtained with the ESPaDOnS
and the 3.6 m Canada France Hawaii Telescope to investigate the broad wings
around H$\alpha$ and H$\beta$. When H$\alpha$ and H$\beta$ lines are
overplotted in the Doppler space, it is noted that H$\alpha$ profiles are
overall broader than H$\beta$ in these two objects. Adopting a Monte Carlo
approach, we consider the formation of broad wings of H$\alpha$ and H$\beta$
through Raman scattering of far UV radiation around Ly$\beta$ and Ly$\gamma$
and Thomson scattering by free electrons. Raman scattering wings are simulated
by choosing an H I region with a neutral hydrogen column density $N_{HI}$ and a
covering factor $CF$. For Thomson wings, the ionized scattering region is
assumed to cover fully the Balmer emission nebula and is characterized by the
electron temperature $T_e$ and the electron column density $N_e$. Thomson wings
of H$\alpha$ and H$\beta$ have the same width that is proportional to
$T_e^{1/2}$. However, Raman wings of H$\alpha$ are overall three times wider
than H$\beta$ counterparts, which is attributed to different cross section for
Ly$\beta$ and Ly$\gamma$. Normalized to have the same peak values and presented
in the Doppler factor space. H$\alpha$ wings of Z And and AG Dra are observed
to be significantly wider than H$\beta$ counterpart, favoring the Raman
scattering origin of broad Balmer wings.
