  It is shown that the hypothesis of the axion mechanism of Sun luminosity
suggesting that the solar axion particles are born in the core of the Sun and
may be efficiently converted back into $\gamma$-quanta in the magnetic field of
the solar overshoot tachocline is physically relevant. As a result, it is also
shown that the intensity variations of the $\gamma$-quanta of axion origin,
induced by the magnetic field variations in the tachocline, directly cause the
Sun luminosity %and total solar irradiance (TSI) variations and eventually
characterize the active and quiet states of the Sun.
  Within the framework of this mechanism estimations of the strength of the
axion coupling to a photon ($g_{a \gamma} = 3.6 \cdot 10^{-11} GeV^{-1}$) and
the hadronic axion particle mass ($m_a \sim 2.3 \cdot 10^{-2} eV$) have been
obtained. It is also shown that the claimed axion parameters do not contradict
any known experimental and theoretical model-independent limitations.
