  Astrospheres and wind bubbles of massive stars are believed to be sources of
cosmic rays with energies $E\lesssim 1\,$TeV. These particles are not directly
detectable, but their impact on surrounding matter, in particular ionisation of
atomic and molecular hydrogen, can lead to observable signatures. A correlation
study of both gamma ray emission, induced by proton-proton interactions of
cosmic ray protons with kinetic energies $E_\mathrm{p}\ge 280\,$MeV with
ambient hydrogen, and ionisation induced by cosmic ray protons of kinetic
energies $E_\mathrm{p}< 280\,$MeV can be performed in order to study potential
sources of (sub)TeV cosmic rays.
