Context : Young stars are born with envelopes , which in the early stages obscure the central ( proto ) star and circumstellar disk .
In the Class I stage , the disks are still young , but the envelopes are largely dispersed .
This makes the Class I sources ideal targets for studies of the early stages of disks .

Aims : We aim to determine the masses of the envelopes , disks , and central stars of young stellar objects ( YSOs ) in the Class I stage .

Methods : We observed the embedded Class I objects IRS 63 and Elias 29 in the \rho Ophiuchi star-forming region with the Submillimeter Array ( SMA ) at 1.1 mm .

Results : IRS 63 and Elias 29 are both clearly detected in the continuum , with peak fluxes of 459 and 47 mJy/beam , respectively .
The continuum emission toward Elias 29 is clearly resolved , whereas IRS 63 is consistent with a point source down to a scale of 3 \arcsec ( 400 AU ) .
The SMA data are combined with single-dish data , and both disk masses of 0.055 and \leq 0.007 M _ { \odot } and envelope masses of 0.058 and \leq 0.058 M _ { \odot } are empirically determined for IRS 63 and Elias 29 , respectively .
The disk+envelope systems are modelled with the axisymmetric radiative-transfer code RADMC , yielding disk and envelope masses that differ from the empirical results by factors of a few .
HCO ^ { + } J = 3–2 is detected toward both sources , HCN J = 3–2 is not .
The HCO ^ { + } position-velocity diagrams are indicative of Keplerian rotation and allow an estimate of the mass of the central stars .
For a fiducial inclination of 30 ^ { \circ } , we find stellar masses of 0.37 \pm 0.13 for IRS 63 and 2.5 \pm 0.6 M _ { \odot } for Elias 29 .

Conclusions : The sensitivity and spatial resolution of the SMA at 1.1 mm allow a good separation of the disks around Class I YSOs from their circumstellar envelopes and environments , and the spectral resolution makes it possible to resolve their dynamical structure and estimate the masses of the central stars .
The ratios of the envelope and disk masses M _ { env } / M _ { disk } are found to be 0.2 for IRS 63 and 6 for Elias 29 .
This is lower than the values for Class 0 sources , which have M _ { env } / M _ { disk } \geq 10 , suggesting that this ratio is a tracer of the evolutionary stage of a YSO .