CVs: Short Period Systems
€CVs
with main sequence secondaries have minimum orbital period of 80 minutes
€However,
some accreting binaries are seen to have shorter periods
Þ the secondaries must be white dwarfs, or perhaps the
degenerate core of a giant which
has been stripped away
€The
optical spectra of these systems show only Helium (no Hydrogen)
GP
Com
€The
disk behaviour is different because of the different ionisation of He compared to He;
interesting
astrophysical laboratories
€Orbital periods from ~65 min to ~15 min
€Known
as the AM CVn systems
Marsh, Horne & Rosen (1991)