  We study the effects of additional cooling due to the emission of a dark
matter candidate particle, the dark photon, on the final phases of the
evolution of a $15\,M_\odot$ star and resulting modifications of the
pre-supernova neutrino signal. For a substantial portion of the dark photon
parameter space the extra cooling speeds up Si burning, which results in a
reduced number of neutrinos emitted during the last day before core collapse.
This reduction can be described by a systematic acceleration of the relevant
timescales and the results can be estimated semi-analytically in good agreement
with the numerical simulations. Outside the semi-analytic regime we find more
complicated effects. In a narrow parameter range, low-mass dark photons lead to
an increase of the number of emitted neutrinos because of additional shell
burning episodes that delay core collapse. Furthermore, relatively strong
couplings produce a thermonuclear runaway during O burning, which could result
in a complete disruption of the star but requires more detailed simulations to
determine the outcome. Our results show that pre-supernova neutrino signals are
a potential probe of the dark photon parameter space.
