  The oxygen absorption line imprinted in the scattered light from the
Earth-like planets has been considered the most promising metabolic biomarker
of the exo-life. We examine the feasibility of the detection of the 1.27 micron
oxygen band from habitable exoplanets, in particular, around late- type stars
observed with a future instrument on a 30 m class ground-based telescope. We
analyzed the night airglow around 1.27 micron with IRCS/echelle spectrometer on
Subaru and found that the strong telluric emission from atmospheric oxygen
molecules declines by an order of magnitude by midnight. By compiling nearby
star catalogs combined with the sky background model, we estimate the
detectability of the oxygen absorption band from an Earth twin, if it exists,
around nearby stars. We find that the most dominant source of photon noise for
the oxygen 1.27 micron band detection comes from the night airglow if the
contribution of the stellar PSF halo is suppressed enough to detect the planet.
We conclude that the future detectors for which the detection contrast is
limited by photon noise can detect the oxygen 1.27 micron absorption band of
the Earth twins for ~50 candidates of the late type star. This paper
demonstrates the importance of deploying small inner working angle efficient
coronagraph and extreme adaptive optics on extremely large telescopes, and
clearly shows that doing so will enable study of potentially habitable planets.
