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We present analysis of near-infrared, high-resolution spectroscopy towardsthe Flat-spectrum YSO (Young Stellar Object) ESO H$\alpha$ 279a (1.5 solarmass) in the Serpens star forming region, at the distance of 429 pc. Using theImmersion GRating INfrared Spectrometer (IGRINS, R=45,000), we detect emissionlines originating from the accretion channel flow, jet, and inner disk.Specifically, we identify hydrogen Brackett series recombination, [Fe II], [FeIII], [Fe IV], Ca I, Na I, H2, H2O and CO overtone emission lines. By modelingfive bands of CO overtone emission lines, and the symmetric double-peaked lineprofile for Na I emission lines, we find that ESO H$\alpha$ 279a has anactively accreting Keplerian disk. From our Keplerian disk model, we find thatNa I emission lines originate between 0.04 AU and 1.00 AU, while CO overtoneemission lines are from the outer part of disk, in the range between 0.22 AUand 3.00 AU. It reveals that the neutral atomic Na gas is a good tracer of theinnermost region of the actively accreting disk. We derive a mass accretionrate of 2-10x10^{-7} M_solar/yr from the measured Br_gamma emission luminosityof 1.78(+-0.31)x10^{31} erg/s.

Inner warm disk of ESO H$\alpha$ 279A revealed by NA I and CO overtone emission lines