THE PRE-CATACLYSMIC BINARY EUVE-2013+4001

New optical spectroscopy shows a 0.(d)706 orbital period for EUVE 2013 +400 and confirms its membership in a class of close binary systems em erging from common-envelope evolution. This binary, like the prototype Feige 24, consists of an extreme ultraviolet (EUV) emitting hot white dwarf and a late-type dwarf. Bergeron et al.'s [ApJ, 432, 305 (1994)] optical spectroscopy and ultraviolet spectrophotometry indicate that the white dwarf is hot (T(eff)approximate to 50 000 K) and therefore v ery young (t(age)less than or equal to 5X10(6) yr), and extreme ultrav iolet photometry places EUVE 2013+400 along a neutral hydrogen column density in the interstellar medium of n(H) approximate to 10(19) cm(-2 ). The white dwarf is a DAO type and we obtained two independent estim ates of the helium abundance from EUV photometric measurements [log(y) approximate to-3.2] and from the He II lambda 4686 line profile [log(y )approximate to-2.8]. The data possibly indicate a level of heterogene ity expected in the context of on-going chemical separation in the pho tospheric layers. The Balmer lines show narrow emission that varies wi th binary phase with the equivalent widths of the emission trailing th e radial velocities by 1/4 cycle: this phasing shows that most of the emission arises on the EUV-illuminated face of the red dwarf. A spectr ophotometric decomposition shows that the secondary's spectral type is near M3 and that it contributes about 15%-25% of the total Light near 6500 Angstrom; the resulting H alpha emission is twice as strong as i n Feige 24, with an equivalent width of 37-61 Angstrom with respect to the red dwarf continuum. EUVE 2013+400 is an important addition to th e class of close binary stars discovered in EUV all-sky surveys.