Figure 4.
The sample of eight stars was selected on
the basis of Paschen α emission, characteristic of massive stars. Observations using the
Gemini Near-Infrared Spectrograph (GNIRS)
and Near-infrared Integral Field Spectrometer (NIFS), both on the Gemini North telescope, provide spectroscopy with a resolution of around 50 kilometers per second.
Sample stars located near the Arches cluster
are similar to the cluster population (in terms
of age, mass, and spectral characteristics),
suggesting that they were originally cluster
members. The massive field stars could have
been dynamically ejected from the cluster,
especially through three-body interactions.
Two examples show velocities that are similar
to those of nearby molecular and ionized gas
clouds, which implies a physical association
with these neighboring star-forming regions.
The researchers suggest that one of these in
particular, dubbed P35 (Figure 4), may have
January 2015
formed at this site. In contrast, other stars
show differences in motion compared with
nearby gaseous regions, which suggests that
the stars are only passing by and were not
formed originally at these locations.
In addition, the new spectroscopy confirms
main sequence masses exceeding 50 MSun
in all cases and enables additional spectral
classification; Dong et al. also report the
identification of a new O If+ star. Complete
results appear in Monthly Notices of the Royal
Astronomical Society (view here) and a preprint is available here.
Upper panels show
near-infrared
continuum and
Paschen α images
of target P35 and its
associated HII region.
The position-velocity
plot (c) around the
wavelength of Brackett
γ is extracted from
the GNIRS longslit
spectrum (whose
location is marked
with horizontal lines
in the upper panels).
Low surface brightness
features marked
with arrows in (b) are
evident in the positionvelocity plot.
Nancy A. Levenson is Deputy Director and Head
of Science at Gemini Observatory and can be
reached at: [email protected]
Rachel Mason is an Associate Astronomer at
Gemini North. She can be reached at:
[email protected]
GeminiFocus
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