  Chromospheric model calculations of the Halpha line for selected red giant
branch (RGB) and asymptotic giant branch (AGB) stars in the globular clusters
M13, M15, and M92 are constructed to derive mass loss rates. The model spectra
are compared to the observations obtained with the Hectochelle on the MMT
telescope. These stars show strong Halpha emissions and blue-shifted Halpha
cores signaling that mass outflow is present in all stars. Outflow velocities
of 3-19 km/s, larger than indicated by Halpha profiles, are needed in the upper
chromosphere to achieve good agreement between the model spectra and the
observations. The resulting mass loss rates range from 0.6*10^{-9} to 5*10^{-9}
Msun/yr, which are about an order of magnitude lower than predicted from
"Reimers' law" or inferred from the infrared excess of similar stars. The mass
loss rate increases slightly with luminosity and with decreasing effective
temperature. Stars in the more metal-rich M13 have higher mass loss rates by a
factor of ~2 than in the metal-poor clusters M15 and M92. A fit to the mass
loss rates is given by: M [Msun/yr] = 0.092 * L^{0.16} * Teff^{-2.02} *
A^{0.37} where A=10^[Fe/H]. Multiple observations of stars revealed one object
in M15, K757, in which the mass outflow increased by a factor of 6 between two
observations separated by 18 months. Other stars showed changes in mass loss
rate by a factor of 1.5 or less.
