The Chandra survey of Carina OB stars

Abstract

Abstract. We have combined 22 deep Chandra ACIS-I pointings to map over one square degree of the Carina complex. Our x-ray survey detects 69 of 70 known O-type stars and 61 of 130 known early B stars. The majority of single O stars display soft X-ray spectra and have a mean log LX /L b ol ≈ −7.5 suggesting shocks embedded in the O-star winds. Over OB stars show unusually high X-ray luminosities, high shock temperatures or time variability, not predicted for embedded wind shocks.Keywords. X-rays: stars, X-rays: binaries, stars: early-type, stars: pre-main-sequenceThe Chandra Carina Complex Project (CCCP) survey area contains over 200 known massive stars: the LBV η Car, the Wolf Rayet stars WR 22, WR 24 and WR 25, 70 known O stars, and 130 B0-B3 stars with known spectral types. We have constructed a searchable electronic database of x-ray and optical properties for the 200 Carina OB stars. We divide the massive star population in Carina into four main groups based on spectral type and luminosity class: LBV/WR stars (4), O-type binaries (15), O-type single stars (55), and B0-B3 stars (130). We note that none of the B stars are typed as spectroscopic binaries. The goal of this study is to characterize L X , L X /L bol , the x-ray temperatures kT , and the temporal variability of single and binary OB stars, to look for new candidate colliding wind systems (e.g., Stevens et al. 1992) and magnetically confined wind shock sources (e.g., ud-Doula & Owocki 2002).The Chandra CCD spectra of the 78 OB stars with more than 50 ACIS counts were fit in XSPEC using a one-or two-temperature APEC emission model, and a two-component absorption model: a fixed TBABS column density to represent cold, neutral ISM absorption (assuming A V /N H = 1.6×10 21 cm −2 per mag), and free column density to represent absorption from the overlying stellar wind. L X was calculated correcting only for the ISM column. For single O stars, log L X /L bol = −7.59 ± 0.23, with no such trend for B stars. Table 1 highlights three notable single O stars: HD 93250, O4 III(fc), MJ 496, O8.5 V, and MJ 449, O8.5 V((f)), all of which have kT > 1.7 keV, log L X /L bol > −7

The supergiant B[e] star LHA 115-S 18 – binary and/or luminous blue variable?

“…Firstly, both GG Carina and VFTS698 are spectroscopically confirmed sgB[e] binaries with apparent circumbinary discs/toroids (Gosset et al 1985;Kraus et al 2013;Dunstall et al 2012), while Kastner et al (2006Kastner et al ( , 2010 suggest such a configuration from their modelling of the mid-IR excess of sgB[e] stars. Secondly, the X-ray luminosity of S18 is well within the range observed for colliding wind systems (∼10 32 −10 35 erg s −1 ; Gagne et al 2013) and is comparable to that of the sgB[e] star Wd1-9; a massive compact interacting binary within the starburst cluster Wd1 (Clark et al 2008(Clark et al , 2013a.…”

The VLT-FLAMES Tarantula survey

“…At its peak luminosity, VFTS 399 is an order of magnitude brighter than any O+O colliding wind binary, although seven binaries with luminous blue variable or Wolf-Rayet primaries demonstrate logL x ≥ 10 35 erg s −1 (Gagné et al 2012) 8 . However in each of these systems the primaries support significantly more powerful winds than are expected for VFTS 399, suggesting that its X-ray flux is unlikely to arise via wind collisions (indeed no signature of any secondary is visible in our optical spectroscopic observations).…”