  High dispersion spectroscopy of brown dwarfs and exoplanets enables exciting
science cases, e.g., mapping surface inhomogeneity and measuring spin rate.
Here, we present $L$ band observations of HR 8799 c using Keck NIRSPEC
(R=15,000) in adaptive optics (AO) mode (NIRSPAO). We search for molecular
species (H$_2$O and CH$_4$) in the atmosphere of HR 8799 c with a template
matching method, which involves cross correlation between reduced spectrum and
a template spectrum. We detect H$_2$O but not CH$_4$, which suggests
disequilibrium chemistry in the atmosphere of HR 8799 c, and this is consistent
with previous findings. We conduct planet signal injection simulations to
estimate the sensitivity of our AO-aided high dispersion spectroscopy
observations. We conclude that $10^{-4}$ contrast can be reached in $L$ band.
The sensitivity is mainly limited by the accuracy of line list used in modeling
spectra and detector noise. The latter will be alleviated by the NIRSPEC
upgrade.
