  The Carina Nebula harbors a large population of high-mass stars, including at
least 75 O-type and Wolf-Rayet stars, but the current census is not complete
since further high-mass stars may be hidden in or behind the dense dark clouds
that pervade the association. With the aim of identifying optically obscured O-
and early B-type stars in the Carina Nebula, we performed the first infrared
spectroscopic study of stars in the optically obscured stellar cluster Tr
16-SE, located behind a dark dust lane south of eta Car. We used the
integral-field spectrograph KMOS at the ESO VLT to obtain H- and K-band spectra
with a resolution of R sim 4000 (Delta lambda sim 5 A) for 45 out of the 47
possible OB candidate stars in Tr 16-SE, and we derived spectral types for
these stars. We find 15 stars in Tr 16-SE with spectral types between O5 and B2
(i.e., high-mass stars with M >= 8 Msun, only two of which were known before.
An additional nine stars are classified as (Ae)Be stars (i.e.,
intermediate-mass pre-main-sequence stars), and most of the remaining targets
show clear signatures of being late-type stars and are thus most likely
foreground stars or background giants unrelated to the Carina Nebula. Our
estimates of the stellar luminosities suggest that nine of the 15 O- and early
B-type stars are members of Tr 16-SE, whereas the other six seem to be
background objects. Our study increases the number of spectroscopically
identified high-mass stars (M >= 8 Msun) in Tr 16-SE from two to nine and shows
that Tr 16-SE is one of the larger clusters in the Carina Nebula. Our
identification of three new stars with spectral types between O5 and O7 and
four new stars with spectral types O9 to B1 significantly increases the number
of spectroscopically identified O-type stars in the Carina Nebula.
