  You & Cheng (1980) argued that, for relativistic electrons moving through a
dense gas, the Cerenkov effect will produce peculiar atomic and/or molecular
emission lines--Cerenkov lines. They presented a series of formulae to describe
the new line-mechanism. Elegant experimental confirmation has been obtained by
Xu. et al. in the laboratory which definitely verified the existence of
Cerenkov lines. Owing to the potential importance in high energy astrophysics,
in this paper we give a more detailed physical discussion of the emission
mechanisms and improve the previous formulae system into a form which is more
convenient for astrophysical application. Specifically, the extended formulae
in this paper can be applied to other species of atoms and/or ions rather than
hydrogen as in the previous paper, and also to X-ray astronomy. They can also
be used for the calculation of a nonuniform plane-parallel slab of the emissive
gas.
