  We study the transverse momentum ($p_T$) spectra of neutral pions and
identified charged hadrons produced in proton--proton ($pp$), deuteron--gold
($d$--Au), and gold--gold (Au--Au) collisions at the center of mass energy
$\sqrt{s_{NN}}=200$ GeV. The study is made in the framework of a multi-source
thermal model used in the partonic level. It is assumed that the contribution
to the $p_T$-value of any hadron comes from two or three partons with an
isotropic distribution of the azimuthal angle. The contribution of each parton
to the $p_T$-value of a given hadron is assumed to obey any one of the standard
(Maxwell-Boltzmann, Fermi-Dirac, and Bose-Einstein) distributions with the
kinetic freeze-out temperature and average transverse flow velocity. The
$p_T$-spectra of the final-state hadrons can be fitted by the superposition of
two or three components. The results obtained from our Monte Carlo method are
used to fit the experimental results of the PHENIX and STAR Collaborations. The
results of present work serve as a suitable reference baseline for other
experiments and simulation studies.
