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High resolution (lambda / Delta-lambda = 50,000) K-band spectra of massive, embedded, young stellar objects are presented. The present sample consists of four massive young stars located in nascent clusters powering Galactic giant H II regions. Emission in the 2.3 micron 2--0 vibrational--rotational bandhead of CO is observed. A range of velocity broadened profiles seen in three of the objects is consistent with the emission arising from a circumstellar disk seen at various inclination angles. Br gamma spectra of the same spectral and spatial resolution are also presented which support an accretion disk or torus model for massive stars. In the fourth object, Br emission suggesting a rotating torus is observed, but the CO profile is narrow, indicating that there may be different CO emission mechanisms in massive stars and this is consistent with earlier observations of the BN object and MWC 349. To--date, only young massive stars of late O or early B types have been identified with clear accretion disk signatures in such embedded clusters. Often such stars are found in the presence of other more massive stars which are revealed by their photospheric spectra but which exhibit no disk signatures. This suggests the timescale for dissipating their disks is much faster than the less massive OB stars or that the most massive stars do not form with accretion disks.
Methanol and water masers indicate young stellar objects. They often exhibit flares, and a fraction shows periodic activity. Several mechanisms might explain this behavior but the lack of concurrent infrared (IR) data complicates to identify the caus
We present a study of accretion in a sample of 45 young, low mass objects in a variety of star forming regions and young associations, about half of which are likely substellar. Based primarily on the presence of broad, asymmetric Halpha emission, we
The supersonic stellar and disk winds possessed by massive young stellar objects will produce shocks when they collide against the interior of a pre-existing bipolar cavity (resulting from an earlier phase of jet activity). The shock heated gas emits
Massive young stellar objects (MYSO) are surrounded by massive dusty envelopes. Our aim is to establish their density structure on scales of ~1000 AU, i.e. a factor 10 increase in angular resolution compared to similar studies performed in the (sub)m
An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived