Astronomy and Astrophysics, volume 469, L31-34 (2007/7-1)
On the optical counterpart of NGC 300 X-1 and the global Wolf-Rayet content of NGC 300.
CROWTHER P.A., CARPANO S., HADFIELD L.J. and POLLOCK A.M.T.
Abstract (from CDS):
Surveys of Wolf-Rayet (WR) populations in nearby galaxies provide tests of evolutionary models plus type Ib/c supernova progenitors. This spectroscopic study complements the recent imaging survey of the spiral galaxy NGC 300 by Schild et al. (2003A&A...397..859S
). Revisions to the known WR content of NGC 300 are presented. We investigate the WR nature of candidate #41 from Schild et al. (2003A&A...397..859S
) which is spatially coincident with the bright X-ray point source NGC 300 X-1. VLT/FORS2 multi-object spectroscopy of WR candidates in NGC 300 is obtained. We establish an early-type WN nature of #41, i.e. similar to the optical counterpart of IC 10 X-1, which closely resembles NGC 300 X-1. We confirm 9 new WR stars, bringing the current WR census of the inner disk to 31, with N(WC)/N(WN) ∼0.9. If #41 is the optical counterpart for NGC 300 X-1, we estimate a WR mass of 38M☉
based upon ground-based photometry, from which a black hole mass of ≥10M☉
results from the 32.8 h period of the system and WR wind velocity of 1250km/s. We estimate an 95% completeness among WC stars and 70% among WN stars, such that the total WR content is ∼40, with N(WC)/N(WN)∼0.7. From the Hα-derived star formation rate of the inner galaxy, we infer N(WR)/N(O)∼0.04.
galaxies: individual: NGC 300 - stars: Wolf-Rayet - X-rays: binaries - X-rays: individuals: NGC 300 X-1
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