The 155-day X-ray cycle of the very massive Wolf-Rayet star Melnick 34 in the Large Magellanic Cloud

The Wolf–Rayet star Mk 34 was observed more than 50 times as part of the deep T-ReX Chandra ACIS-I X-ray imaging survey of the Tarantula Nebula in the Large Magellanic Cloud conducted between 2014 May and 2016 January. Its brightness showed one bright maximum and repeated faint minima which help define an X-ray recurrence time of 155.1 ± 0.1  d that is probably the orbital period of an eccentric binary system. The maximum immediately precedes the minimum in the folded X-ray light curve as confirmed by new Swift XRT observations. Notwithstanding its extreme median luminosity of 1.2 × 1035 erg s−1, which makes it over an order of magnitude brighter than comparable stars in the Milky Way, Mk 34 is almost certainly a colliding-wind binary system. Its spectrum shows phase-related changes of luminosity and absorption that are probably related to the orbital dynamics of two of the most massive stars known

Weighing Melnick 34: the most massive binary system known

Here, we confirm Melnick 34, an X-ray bright star in the 30 Dor region of the Large Magellanic Cloud, as an SB2 binary comprising WN5h + WN5h components. We present orbital solutions using 26 epochs of VLT/UVES spectra and 22 epochs of archival Gemini/GMOS spectra. Radial velocity monitoring and automated template-fitting methods both reveal a similar high-eccentricity system with a mass ratio close to unity, and an orbital period in agreement with the 155.1 ± 1 d X-ray light-curve period previously derived by Pollock et al. Our favoured solution derived an eccentricity of 0.68 ± 0.02 and mass ratio of 0.92 ± 0.07, giving minimum masses of MAsin3(i) = 65 ± 7 M⊙ and MBsin3(i) = 60 ± 7 M⊙. Spectral modelling using WN5h templates with cmfgen reveals temperatures of T ∼ 53 kK for each component and luminosities of log(LA/L⊙) = 6.43 ± 0.08 and log(LB/L⊙) = 6.37 ± 0.08, from which BONNSAI evolutionary modelling gives masses of MA = 139+21−18 M⊙ and MB = 127+17−17 M⊙ and ages of ∼0.6 Myr. Spectroscopic and dynamic masses would agree if Mk34 has an inclination of i ∼ 50°, making Mk34 the most massive binary known and an excellent candidate for investigating the properties of colliding wind binaries. Within 2–3 Myr, both components of Mk34 are expected to evolve to stellar mass black holes, which, assuming the binary system survives, would make Mk34 a potential binary black hole merger progenitor and a gravitational wave source

Reconstruction of Objects by Direct Demodulation

High resolution reconstruction of complicated objects from incomplete and noisy data can be achieved by solving modulation equations iteratively under physical constraints. This direct demodulation method is a powerful technique for dealing with inverse problem in general case. Spectral and image restorations and computerized tomography are only particular cases of general demodulation. It is possible to reconstruct an object in higher dimensional space from observations by a simple lower dimensional instrument through direct demodulation. Our simulations show that wide field and high resolution images of space hard X-rays and soft gamma rays can be obtained by a collimated non-position-sensitive detector without coded aperture masks.Comment: 11 pages, 6 figure

Chandra HETG X-ray spectra and variability of π Aqr, a γ Cas-type Be star

High-resolution X-ray spectra of π Aqr, a γ Cas-type star, obtained with the Chandra/HETG spectrometer, revealed emission lines of H-like ions of Mg, Si, S, and Fe; a strong, hard continuum; and a lack of He-like ions, indicating the presence of very hot thermal plasma. The X-ray light curve showed significant fluctuations, with coherent variability at a period of about 3400 s in one observation. The hardness ratio was relatively constant except for one observation in which the spectrum was much harder and more absorbed. We interpret the X-ray emission as arising from accretion onto the secondary, which is likely a magnetic white dwarf, an intermediate polar system

Gamma rays from colliding winds of massive stars

Colliding winds of massive binaries have long been considered as potential sites of non-thermal high-energy photon production. This is motivated by the detection of non-thermal spectra in the radio band, as well as by correlation studies of yet unidentified EGRET gamma-ray sources with source populations appearing in star formation regions. This work re-considers the basic radiative processes and its properties that lead to high energy photon production in long-period massive star systems. We show that Klein-Nishina effects as well as the anisotropic nature of the inverse Compton scattering, the dominating leptonic emission process, likely yield spectral and variability signatures in the gamma-ray domain at or above the sensitivity of current or upcoming gamma ray instruments like GLAST-LAT. In addition to all relevant radiative losses, we include propagation (such as convection in the stellar wind) as well as photon absorption effects, which a priori can not be neglected. The calculations are applied to WR140 and WR147, and predictions for their detectability in the gamma-ray regime are provided. Physically similar specimen of their kind like WR146, WR137, WR138, WR112 and WR125 may be regarded as candidate sources at GeV energies for near-future gamma-ray experiments. Finally, we discuss several aspects relevant for eventually identifying this source class as a gamma-ray emitting population. Thereby we utilize our findings on the expected radiative behavior of typical colliding wind binaries in the gamma-ray regime as well as its expected spatial distribution on the gamma-ray sky

LETGS observations of delta Orionis: A collisional ionization equilibrium model

We present results of the analysis of the X‐ray spectrum of the giant O‐star δ Orionis (O9.5II), observed in the wavelength range 5–175 Å by the X‐ray detector HRC‐S in combination with the grating LETG on‐board Chandra. We report on the Temperatures, Emission measures, variability in the stellar wind, and the distance of the X‐ray emitting plasma to the stellar surface

Rotationally modulated X-ray emission from the single O star ζ Ophiuchi

Archived measurements by the X-ray Telescope on board the ASCA satellite of the single runaway O9.5V star, ζ Ophiuchi, are analysed. The data set is unique as it covers just more than one full rotational period of the star. We report a clearly detected periodic X-ray flux variability with amplitude ~20% in the ASCA passband (0.5-10 keV). The detected period ~0d.77 possibly indicates a connection with the recurrence time (~0d.875 ± ~0d.167) of the discrete absorption components (DACs) in UV spectra of the star, thought to be due to the presence of large scale structures in the stellar wind modulated by rotation. We attribute the X-ray fluctuation with an uneven distribution of X-ray absorbing material. We also report that an analysis of similar ASCA observations of ζ Puppis failed to confirm earlier reported variability of X-rays from this star based on ROSAT observations