Astronomy and Astrophysics, volume 579A, 131-131 (2015/7-1)
The VLT-FLAMES Tarantula survey. XX. The nature of the X-ray bright emission-line star VFTS 399.
CLARK J.S., BARTLETT E.S., BROOS P.S., TOWNSLEY L.K., TAYLOR W.D., WALBORN N.R., BIRD A.J., SANA H., DE MINK S.E., DUFTON P.L., EVANS C.J., LANGER N., MAIZ-APELLANIZ J., SCHNEIDER F.R.N. and SOSZYNSKI I.
Abstract (from CDS):
The stellar population of the 30 Doradus star-forming region in the Large Magellanic Cloud contains a subset of apparently single, rapidly rotating O-type stars. The physical processes leading to the formation of this cohort are currently uncertain. One member of this group, the late O-type star VFTS399, is found to be unexpectedly X-ray bright for its bolometric luminosity - in this study we aim to determine its physical nature and the cause of this behaviour. To accomplish this we performed a time-resolved analysis of optical, infrared and X-ray observations. We found VFTS399 to be an aperiodic photometric variable with an apparent near-IR excess. Its optical spectrum demonstrates complex emission profiles in the lower Balmer series and select HeI lines - taken together these suggest an OeBe classification. The highly variable X-ray luminosity is too great to be produced by a single star, while the hard, non-thermal nature suggests the presence of an accreting relativistic companion. Finally, the detection of periodic modulation of the X-ray lightcurve is most naturally explained under the assumption that the accretor is a neutron star. VFTS399 appears to be the first high-mass X-ray binary identified within 30 Dor, sharing many observational characteristics with classical Be X-ray binaries. Comparison of the current properties of VFTS399 to binary-evolution models suggests a progenitor mass>25M☉ for the putative neutron star, which may host a magnetic field comparable in strength to those of magnetars. VFTS399 is now the second member of the cohort of rapidly rotating ``single'' O-type stars in 30 Dor to show evidence of binary interaction resulting in spin-up, suggesting that this may be a viable evolutionary pathway for the formation of a subset of this stellar population.
stars: emission-line, Be - binaries: general - stars: individual: VFTS399
Paragraph 5 LS I +63 325 misprint not identified. Paragraph 3.2 CXO J1745-28 not identified (incomplete format).
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