The VLT-FLAMES Tarantula Survey

Abstract

We present spectral classifications for 438 B-type stars observed as part of the VLT-FLAMES Tarantula Survey (VFTS) in the 30 Doradus region of the Large Magellanic Cloud. Radial velocities are provided for 307 apparently single stars, and for 99 targets with radial-velocity variations which are consistent with them being spectroscopic binaries. We investigate the spatial distribution of the radial velocities across the 30 Dor region, and use the results to identify candidate runaway stars. Excluding potential runaways and members of two older clusters in the survey region (SL 639 and Hodge 301), we determine a systemic velocity for 30 Dor of 271.6 ± 12.2 km s −1 from 273 presumed single stars. Employing a 3σ criterion we identify nine candidate runaway stars (2.9% of the single stars with radial-velocity estimates). The projected rotational velocities of the candidate runaways appear to be significantly different to those of the full B-type sample, with a strong preference for either large (≥345 km s −1 ) or small (≤65 km s −1 ) rotational velocities. Of the candidate runaways, VFTS 358 (classified B0.5: V) has the largest differential radial velocity (−106.9 ± 16.2 km s −1 ), and a preliminary atmospheric analysis finds a significantly enriched nitrogen abundance of 12 + log (N/H) 8.5. Combined with a large rotational velocity (v e sin i = 345 ± 22 km s −1 ), this is suggestive of past binary interaction for this star.

Hubble Tarantula Treasury Project. V. The Star Cluster Hodge 301: The Old Face of 30 Doradus*

“…Finally, it is intriguing that the MSTO/PMS TOn age estimate is also older than the spectroscopic age derived by Evans et al (2015). Part of the discrepancy could be attributed to the presence of blue stragglers.…”

“…In clusters of this approximate age the PMSG is populated by bright B-type giants and supergiants (of similar color to the MS dwarfs and sub-giants), in the case of Hodge 301 these two stars are confirmed cluster members with spectral types B3 Ib and B2 II-III(n)e (see Evans et al 2015). While the fact that the precursor of SN1987A was a B3 I star (Walborn et al 1989) indicates that core He burning stars can inhabit this part of the CMD/Hertzsprung Russel diagram (HRD), there is as yet no unambiguous method for distinguishing between core H and He burning blue stars (see Grebel et al 1996, Hunter et al 2008, Vink et al 2010, and McEvoy et al 2015 for discussions of how rotational velocity distributions, mass-loss considerations and binary frequency might define the width of the MS for B-stars in the LMC).…”

“…More recently, using spectroscopy and a qualitative comparison with the evolutionary models of Brott et al (2011), Evans et al (2015) found an age of 15±5 Myr.…”

The VLT-FLAMES Tarantula Survey

“…Spectral sequences in both effective temperature and luminosity class have been given in Evans et al (2015) and illustrate the high quality of the supergiant spectroscopy. Table 1 summarises aliases, binary status (Sect.…”

“…) and Evans et al (2015), respectively, because of their unusual radial velocities. Both of these stars have high nitrogen abundances, VFTS 165 having a nitrogen abundance derived from the singlet at 3995 Å of 7.83 dex and VFTS 831 of 7.94 dex.…”