ISOLATED WOLF-RAYET STARS AND O SUPERGIANTS IN THE GALACTIC CENTER REGION IDENTIFIED VIA PASCHEN-alpha EXCESS (vol 725, pg 188, 2010)
ASTROPHYSICAL JOURNAL(2011)
Abstract
We report the discovery of 19 hot, evolved, massive stars near the Galactic
center region (GCR). These objects were selected for spectroscopy owing to
their detection as strong sources of Paschen-alpha emission-line excess,
following a narrowband imaging survey of the central 0.65 x 0.25 degress (l, b)
around Sgr A* with the Hubble Space Telescope. Discoveries include 5
carbon-type (WC) and 6 nitrogen-type (WN) Wolf-Rayet stars, 6 O supergiants,
and 2 B supergiants. Two of the O supergiants have X-ray counterparts, the
properties of which are broadly consistent with colliding-wind binaries and
solitary O stars. The infrared photometry of 17 stars is consistent with the
Galactic center distance, but 2 of them are located in the foreground. Several
WC stars exhibit a relatively large infrared excesses, which is possibly the
signature of thermal emission from hot dust. Most of the stars appear scattered
throughout the GCR, with no relation to the three known massive young clusters;
several others lie near the Arches and Quintuplet clusters and may have
originated within one of these systems. The results of this work bring the
total sample of Wolf-Rayet stars in the GCR to 92. All sources of strong
P-alpha excess have been identified in the area surveyed with HST, which
implies that the sample of WN stars in this region is near completion, and is
dominated by late (WNL) types. The current WC sample, although probably not
complete, is almost exclusively dominated by late (WCL) types. The observed
Wolf-Rayet subtype distribution in the GCR is a reflection of the intrinsic
rarity of early subtypes (WNE and WCE) in the inner Galaxy, an effect that is
driven by metallicity.
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