  We present the first spectrum of a highly veiled, strongly accreting
protostar which shows photospheric absorption features and demonstrates the
stellar nature of its central core. We find the spectrum of the luminous (L_bol
= 10 L_sun) protostellar source, YLW 15, to be stellar-like with numerous
atomic and molecular absorption features, indicative of a K5 IV/V spectral type
and a continuum veiling r_k = 3.0. Its derived stellar luminosity (3 L_sun) and
stellar radius (3.1 R_sun) are consistent with those of a 0.5 M_sun
pre-main-sequence star. However, 70% of its bolometric luminosity is due to
mass accretion, whose rate we estimate to be 1.6 E-6 M_sun / yr onto the
protostellar core. We determine that excess infrared emission produced by the
circumstellar accretion disk, the inner infalling envelope, and accretion
shocks at the surface of the stellar core of YLW 15 all contribute signifi-
cantly to its near-IR continuum veiling. Its projected rotation velocity v sin
i = 50 km / s is comparable to those of flat-spectrum protostars but
considerably higher than those of classical T Tauri stars in the rho Oph cloud.
The protostar may be magnetically coupled to its circumstellar disk at a radius
of 2 R_*. It is also plausible that this protostar can shed over half its
angular momentum and evolve into a more slowly rotating classical T Tauri star
by remaining coupled to its circumstellar disk (at increasing radius) as its
accretion rate drops by an order of magnitude during the rapid transition
between the Class I and Class II phases of evolution. The spectrum of WL 6 does
not show any photospheric absorption features, and we estimate that its
continuum veiling is r_k >= 4.6. Together with its low bolometric luminosity (2
L_sun), this dictates that its central core is very low mass, ~0.1 M_sun.
