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tokens: expected line ratios of the prominent O i lines, when collisional excitation and Ly β fluorescence (referred to as photoexcitation by accidental resonance—PAR process—in Bhatia Kastner 1995 ) are the dominant excitation mechanisms. From a comparative analysis of the theoretical estimates with the observed emission strengths of O i λλ 7774, 8446, 11287, and 13165, Mathew et al. ( 2012b ) demonstrated that Ly β fluorescence is the dominant excitation mechanism for the production of O i λλ 8446, 11287 lines in CBe stars. CBe stars share similar spectral characteristics with HAeBe stars, such as emission lines of H α , O i , Fe ii , and Ca ii triplet. It is worth exploring whether both CBe and HAeBe stars share similar excitation mechanisms for the formation of O i lines. There could be considerable difference between the O i line forming regions in both the stellar systems. CBe stars are found to have a circumstellar gaseous decretion disk wherein the O i λ 8446 line is formed at a mean radial distance of ∼8 R ⋆ , considering Keplerian motion (Mathew et al. 2012b ). However, the location of the origin of the O i λ 8446 line in HAeBe is far from clear. Most of the accretion related emission lines in HAeBe stars (e.g., H α , Pa β , Br γ ) are thought to be formed in the magnetospheric accretion columns (Muzerolle et al. 2004 ). This work is an attempt to bring more clarity to our understanding of the formation mechanisms of O i emission lines in HAeBe stars. The paper is organized as follows. In Section 2 , we present the optical and near-infrared (near-IR) spectroscopic observations carried out over a period of 3 years and describe the data reduction techniques employed. We describe the methods and the python routines used for the spectral analysis and to estimate line flux in Section 3 . The dominant excitation mechanism for the formation of O i lines in HAeBe stars is evaluated in Section 4 . The main results of the paper are summarized in Section 5 . 2. Observations and Data Reduction The optical spectroscopic observations were carried out using the Himalayan Faint Object Spectrograph Camera mounted on the 2 m Himalayan Chandra Telescope (HCT). 6 6 http://www.iiap.res.in/iao/hfosc.html The spectroscopic observations were obtained with Grism 8 in combination with 167 l slit (192 wide and 11′ long), providing an effective resolving power of ∼1050. The spectral coverage is from 5500 to 9000 Å, which included the spectral lines relevant to this study, viz., H α , O i λ 7774, and O i λ 8446. After each on-source exposure, FeNe lamp spectra were obtained for wavelength calibration. We have followed the regular procedure of reducing the spectra after bias subtraction and flat-field correction using the standard tasks in Image Reduction and Analysis Facility (IRAF). 7 7 IRAF is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement