  We present the time-dependent properties of a poorly known OH/IR star $-$
IRAS 18278+0931 (hereafter, IRAS 18+09) towards the Ophiuchus constellation. We
have carried out long-term optical/near-infrared (NIR) photometric and
spectroscopic observations to study the object. From optical $R$- and $I$-band
light curves, the period of IRAS 18+09 is estimated to be 575 $\pm$ 30 days and
the variability amplitudes range from $\Delta$R $\sim$ 4.0 mag to $\Delta$I
$\sim$ 3.5 mag. From the standard Period-Luminosity (PL) relations, the
distance ($D$) to the object, 4.0 $\pm$ 1.3 kpc, is estimated. Applying this
distance in the radiative transfer model, the spectral energy distribution
(SED) are constructed from multi-wavelength photometric and IRAS-LRS spectral
data which provides the luminosity, optical depth, and gas mass-loss rate (MLR)
of the object to be 9600 $\pm$ 500 $L_{\odot}$, 9.1 $\pm$ 0.6 at 0.55 $\mu$m
and 1.0$\times$10$^{-6}$ M$_\odot$ yr$^{-1}$, respectively. The current mass of
the object infers in the range 1.0 $-$ 1.5 $M_\odot$ assuming solar
metallicity. Notably, the temporal variation of atomic and molecular features
(e.g., TiO, Na I, Ca I, CO, H$_2$O) over the pulsation cycle of the OH/IR star
illustrates the sensitivity of the spectral features to the dynamical
atmosphere as observed in pulsating AGB stars.
