  Mirror Stars are a generic prediction of dissipative dark matter models,
including minimal atomic dark matter and twin baryons in the Mirror Twin Higgs.
Mirror Stars can capture regular matter from the interstellar medium through
extremely suppressed kinetic mixing interactions between the regular and the
dark photon. This accumulated "nugget" will draw heat from the mirror star core
and emit highly characteristic X-ray and optical signals. In this work, we
devise a general parameterization of mirror star nugget properties that is
independent of the unknown details of mirror star stellar physics, and use the
Cloudy spectral synthesis code to obtain realistic and comprehensive
predictions for the thermal emissions from optically thin mirror star nuggets.
We find that mirror star nuggets populate an extremely well-defined and narrow
region of the HR diagram that only partially overlaps with the white dwarf
population. Our detailed spectral predictions, which we make publicly
available, allow us to demonstrate that optically thin nuggets can be clearly
distinguished from white dwarf stars by their continuum spectrum shape, and
from planetary nebulae and other optically thin standard sources by their
highly exotic emission line ratios. Our work will enable realistic mirror star
telescope searches, which may reveal the detailed nature of dark matter.
