  Aiming to distinguish two types of progenitors of core collapse supernovae,
i.e., one with a core composed mainly of oxygen and neon (abbreviated as ONe
core) and the other with an iron core (or Fe core), we calculated the
luminosities and spectra of neutrinos emitted from these cores prior to
gravitational collapse, taking neutrino oscillation into account. We found that
the total energies emitted as $\bar{\nu}_e$ from the ONe core are $\lesssim
10^{46}\ {\rm erg}$, which is much smaller than $\sim 10^{47}\ {\rm erg}$ for
Fe cores. The average energy, on the other hand, is twice as large for the ONe
core as those for the Fe cores. The neutrinos produced by the plasmon decays in
the ONe core are more numerous than those from the electron-positron
annihilation in both cores but they have much lower average energies $\lesssim
1\ {\rm MeV}$. Although it is difficult to detect the pre-supernova neutrinos
from the ONe core even if it is located within 200$\ $pc from the earth, we
expect $ \sim 9 - 43$ and $\sim 7 - 61$ events for Fe cores at KamLAND and
Super-Kamiokande, respectively, depending on the progenitor mass and
neutrino-mass hierarchy. These numbers might be increased by an order of
magnitude if we envisage next-generation detectors such as JUNO. We will hence
be able to distinguish the two types of progenitors by the detection or
non-detection of the pre-supernova neutrinos if they are close enough
($\lesssim1\ {\rm kpc}$).
