Evolution of protostars accreting mass at very high rates: Is Orion IRc2 ahuge protostar?

The recent near-infrared spectroscopy of scattered light from Orion IRc2 su ggests that the illuminating source at the K' band is either a protostar wi th a radius greater than or similar to 300 R-circle dot or a disk with an a ccretion rate approximate to 10(-2) M-circle dot yr(-1). To test the former interpretation, we present a simplified stellar model accreting mass at a very high rate, approximate to 10(-2) M-circle dot yr(-1). We find that the protostar is fully convective at almost all stages of the stellar mass M l ess than or similar to 15 M-circle dot, and thus a polytrope of index 1.5 i s a good approximation of the stellar structure. The maximum radius less th an or similar to 30 R-circle dot is attained at M similar to 7 M-circle dot . The shell deuterium burning, which would occur afterward cannot greatly b low up the protostar because the energy released by deuterium burning is sm all and also because the protostar is already shrinking rapidly. The only r emaining possibility to make a huge protostar resides in the rotation of th e surface layer almost at its breakup velocity. On the other hand, we find no difficulty in the alternative interpretation that the illuminating sourc e is the accretion disk. In this case we predict that the 2.3 mu m CO absor ption lines should be observed with a width similar to 50 km s(-1) due to t he Keplerian motion in the disk. The accretion rate as high as 10(-2) M(cir cle dot)yr(-1) is compatible with the velocity dispersion in the Orion KL m olecular cloud core. Because the luminosity of IRc2 is dominated by accreti on, the protostellar mass is overestimated if the observed luminosity is re garded as intrinsic. Because the K'-band luminosity is emitted in the disk region far from the protostellar surface, the total accretion luminosity mu st be significantly higher than the observed K'-band luminosity.