The VLT-FLAMES Tarantula survey

Abstract

Context. 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. Aims. One member of this group, the late O-type star VFTS 399, 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. Methods. To accomplish this we performed a time-resolved analysis of optical, infrared and X-ray observations. Results. We found VFTS 399 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 He i 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. Conclusions. VFTS 399 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 VFTS 399 to binary-evolution models suggests a progenitor mass 25 M for the putative neutron star, which may host a magnetic field comparable in strength to those of magnetars. VFTS 399 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.

The B-type binaries characterization programme I. Orbital solutions for the 30 Doradus population

“…With the Medusa fibres assigned to the candidate binaries, we used the remaining fibres to obtain further observations of other notable VFTS targets. These included candidate O-type runaways (Walborn et al 2014), candidate B-type runaways (Evans et al 2015), the extreme rotator VFTS 102 (Dufton et al 2011), the X-ray bright VFTS 399 (Clark et al 2015), the peculiar B[e]-like supergiant VFTS 698 (Dunstall et al 2012), and several stars of interest in the context of the nitrogen abundances from Grin et al (2017).…”

Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR

“…50 M31 BH candidates in Barnard et al 2014b). 5 Not part of the RXTE sample Galactic BH sources used to create NuS-TAR diagnostic diagrams and 19 in the LMC (Clark et al 2015;Antoniou & Zezas 2016;Haberl et al 2017;Vasilopoulos et al 2018), with sensitivity limits ∼ 10 33 erg s −1 in the 0.5 − 10 keV energy band. All but two of the 21 pulsars identified in this work have L X (4 − 25 keV) ≤ 3 × 10 38 erg s −1 , with a peak at the Eddington limit for NS.…”

Star formation history and X-ray binary populations: the case of the Large Magellanic Cloud

“…For completeness we list them here, and in Table 1, but we do not include them in our analysis. Clark et al (2015) identified an X-ray bright emission-line star as part of the VLT-FLAMES Tarantula Survey that could be the first HMXB identified within 30 Dor, if indeed XMMU J053833.9-691157 and CXOU J053833.4-691158 are associated with VFTS399. Swift J0549.7-6812 (reported in ATel #5286; Krimm et al 2013a) is located at (RA, Dec.)=(05:50:06.47, -68:14:55.7) with a 90% confidence astrometric error (r 90 ) equal to 1.4 , and a 6.2-second pulse period (ATel #5309; Krimm et al 2013c).…”