  Since the discovery of chemically peculiar stars in globular clusters in the
last century, the study of multiple populations has become increasingly
important, given that chemical inhomogeneity is found in almost all globular
clusters. Despite various proposed theories attempting to explain this
phenomenon, fitting all the observational evidence in globular clusters with
one single theory remains notoriously difficult and currently unsuccessful. In
order to improve existing models and motivate new ones, we are observing
globular clusters at critical conditions, e.g., metal-rich end, metal-poor end,
and low mass end. In this paper, we present our first attempt to investigate
multiple populations in low mass globular clusters. We obtained low-resolution
spectra around 4000 A of 30 members of the globular cluster Palomar 13 using
OSIRIS/Multi-object spectrograph mounted at the Gran Telescopio Canarias. The
membership of red giant branch stars is confirmed by the latest proper motions
from Gaia DR2 and literature velocities. After comparing the measured CN and CH
spectral indices with those of the stellar models, we found a clear sign of
nitrogen variation among the red giant branch stars. Palomar 13 may be the
lowest mass globular cluster showing multiple populations.
