Recurrent novae (RNe) are cataclysmic variables with two or more nova
eruptions within a century. Classical novae (CNe) are similar systems with only
one such eruption. Many of the so-called 'CNe' are actually RNe for which only
one eruption has been discovered. Since RNe are candidate Type Ia supernova
progenitors, it is important to know whether there are enough in our galaxy to
provide the supernova rate, and therefore to know how many RNe are masquerading
as CNe. To quantify this, we collected all available information on the light
curves and spectra of a Galactic, time-limited sample of 237 CNe and the 10
known RNe, as well as exhaustive discovery efficiency records. We recognize RNe
as having (a) outburst amplitude smaller than 14.5 - 4.5 * log(t_3), (b)
orbital period >0.6 days, (c) infrared colors of J-H > 0.7 mag and H-K > 0.1
mag, (d) FWHM of H-alpha > 2000 km/s, (e) high excitation lines, such as Fe X
or He II near peak, (f) eruption light curves with a plateau, and (g) white
dwarf mass greater than 1.2 M_solar. Using these criteria, we identify V1721
Aql, DE Cir, CP Cru, KT Eri, V838 Her, V2672 Oph, V4160 Sgr, V4643 Sgr, V4739
Sgr, and V477 Sct as strong RN candidates. We evaluate the RN fraction amongst
the known CNe using three methods to get 24% +/- 4%, 12% +/- 3%, and 35% +/-
3%. With roughly a quarter of the 394 known Galactic novae actually being RNe,
there should be approximately a hundred such systems masquerading as CNe.Comment: 3 figures, 7 tables, accepted for publication in Ap
