Context: 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.
Aims: Revisions to the known WR content of NGC 300 are presented. We investigate the WR nature of candidate #41 from Schild et al. which is spatially coincident with the bright X-ray point source NGC 300 X-1.
Methods: VLT/FORS2 multi-object spectroscopy of WR candidates in NGC 300 is obtained.
Results: 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.
Conclusions: If #41 is the optical counterpart for NGC 300 X-1, we estimate a WR mass of 38 M☉ based upon ground-based photometry, from which a black hole mass of ≥10 M☉ results from the 32.8 h period of the system and WR wind velocity of 1250 km s-1. 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. Based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 278.D-5019.
Astronomy and Astrophysics
- Pub Date:
- July 2007
- galaxies: individual: NGC 300;
- stars: Wolf-Rayet;
- X-rays: binaries;
- X-rays: individuals: NGC 300 X-1;
- 5 pages, 5 figures, accepted for A&