  Using CHARA and VLTI near-infrared spectro-interferometry with hectometric
baseline lengths (up to 330m) and with high spectral resolution (up to 12000),
we studied the gas distribution and kinematics around two classical Be stars.
The combination of high spatial and spectral resolution achieved allows us to
constrain the gas velocity field on scales of a few stellar radii and to
obtain, for the first time in optical interferometry, a dynamical mass estimate
using the position-velocity analysis technique known from radio astronomy. For
our first target star, Beta Canis Minoris, we model the H+K-band continuum and
Br-gamma line geometry with a near-critical rotating stellar photosphere and a
geometrically thin equatorial disk. Testing different disk rotation laws, we
find that the disk is in Keplerian rotation (v(r)=r^(-0.5+/-0.1)) and derive
the disk position angle (140+/-1.7 deg), inclination (38.5+/-1 deg), and the
mass of the central star (3.5+/-0.2 M_sun). As a second target star, we
observed the prototypical Be star Zeta Tauri and spatially resolved the
Br{\gamma} emission as well as nine transitions from the hydrogen Pfund series
(Pf14-Pf22). Comparing the spatial origin of the different line transitions, we
find that the Brackett (Br-gamma), Pfund (Pf14-17), and Balmer (H-alpha) lines
originate from different stellocentric radii (R_cont < R_Pf < R_Br-gamma =
R_H-alpha), which we can reproduce with an LTE line radiative transfer
computation. Discussing different disk-formation scenarios, we conclude that
our constraints are inconsistent with wind compression models predicting a
strong outflowing velocity component, but support viscous decretion disk
models, where the Keplerian-rotating disk is replenished with material from the
near-critical rotating star.
