Despite the fact that the APOGEE project is focused on the
structure of the galaxy, it also offers a lot to explore for stellar
astrophysicists. In this colloquium, I will talk about two projects
which are using the dwarf M (dM) stars in APOGEE. The first project is
searching for HW Vir type (subdwarf B (sdB) + dM / brown-dwarf)
systems, which are believed to compose a high percentage of subdwarfs
despite not proven yet. The aim is to look at the IR spectra of dM
stars in order to find a trace of an sdB companion. The results would
reveal the binarity nature of sdB stars and common-envelope evolution,
and contribute to the theoretical and evolutionary studies of sdBs
through dM stars. The second project is to to define a chromospheric
activity indicator in IR region by using active and inactive dwarf M
stars' spectra and determine candidates for a 'Chromospherically
Active Cool Stars Survey'.