Issue |
A&A
Volume 366, Number 2, February I 2001
|
|
---|---|---|
Page(s) | 466 - 480 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20000227 | |
Published online | 15 February 2001 |
New results on the helium stars in the galactic center using BEAR spectro-imagery
1
Institut d'Astrophysique de Paris (CNRS), 98b Bd. Arago, 75014 Paris, France
2
University of California, Los Angeles, Div. of Astronomy, Dept. of Physics and Astronomy, Los Angeles, CA 90095-1562, USA
3
Gemini North Headquarter, Hilo, HI 96720, USA
Corresponding author: J. P. Maillard, maillard@iap.fr
Received:
22
June
2000
Accepted:
17
October
2000
Integral field spectroscopy of the central parsec of the Galactic Center
was obtained at 2.06 μm using BEAR, an imaging Fourier Transform
Spectrometer, at a spectral resolution of 74 km s-1. Sixteen stars were
confirmed as "helium stars" by detecting
the HeI 2.058 μm line in emission, providing a homogeneous set
of fully resolved line profiles.
These observations allow us to discard some of the
earlier detections of such stars in the central cluster and to add three new
stars. The sources detected in the BEAR data were compared
with adaptive optics images in the K band to determine whether the
emission was
due to single stars. Two sub-classes of almost equal number are
clearly identified from the width of their line profiles,
and from the brightness of their continuum.
The first class is characterized by very broad line
profiles (FWHM
1000 km s-1) and by their relative faintness. The
other, brighter in K by an average factor of ∼ 9, has a much
narrower emission component of width
200 km s-1. Most of
the emission lines show a P Cygni profile. From these results, we propose
that the latter group is formed of stars in or near the
LBV phase, and the other one of stars at the WR
stage. The division into two groups is also shown by
their spatial distribution, with the narrow-line stars in a compact central
cluster (IRS 16) and the other group distributed at the periphery
of the central cluster of hot stars.
In the same data cube, streamers of interstellar helium gas are also detected.
The helium emission traces the densest parts
of the SgrA West Mini-Spiral. Several helium stars have a radial
velocity comparable to the velocity of the interstellar gas in which they are
embedded. In the final discussion, all these findings are examined
to present a possible scenario for the formation of very massive stars in the
exceptional conditions of the vicinity of the central Black Hole.
Key words: instrumentation: spectrograph / techniques: radial velocities / infrared: stars / galaxy: center / stars: early-type / stars: wolf-rayet
© ESO, 2001
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