TY  - JOUR
A1  - Bozzo, Enrico
A1  - Oskinova, Lida
A1  - Feldmeier, Achim
A1  - Falanga, M.
T1  - Clumpy wind accretion in supergiant neutron star high mass X-ray binaries
JF  - BMC neuroscience
N2  - The accretion of the stellar wind material by a compact object represents the main mechanism powering the X-ray emission in classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. In this work we present the first attempt to simulate the accretion process of a fast and dense massive star wind onto a neutron star, taking into account the effects of the centrifugal and magnetic inhibition of accretion ("gating") due to the spin and magnetic field of the compact object. We made use of a radiative hydrodynamical code to model the nonstationary radiatively driven wind of an O-B supergiant star and then place a neutron star characterized by a fixed magnetic field and spin period at a certain distance from the massive companion. Our calculations follow, as a function of time (on a total timescale of several hours), the transitions of the system through all different accretion regimes that are triggered by the intrinsic variations in the density and velocity of the nonstationary wind. The X-ray luminosity released by the system is computed at each time step by taking into account the relevant physical processes occurring in the different accretion regimes. Synthetic lightcurves are derived and qualitatively compared with those observed from classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. Although a number of simplifications are assumed in these calculations, we show that taking into account the effects of the centrifugal and magnetic inhibition of accretion significantly reduces the average X-ray luminosity expected for any neutron star wind-fed binary. The present model calculations suggest that long spin periods and stronger magnetic fields are favored in order to reproduce the peculiar behavior of supergiant fast X-ray transients in the X-ray domain.
KW  - stars: neutron
KW  - X-rays: binaries
KW  - supergiants
Y1  - 2016
U6  - https://doi.org/10.1051/0004-6361/201628341
SN  - 1432-0746
VL  - 589
SP  - 369
EP  - 389
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Thomas, Timon
A1  - Feldmeier, Achim
T1  - Radiative waves in stellar winds with line scattering
JF  - Monthly notices of the Royal Astronomical Society
N2  - Photospheric radiation can drive winds from hot, massive stars by direct momentum transfer through scattering in bound-bound transitions of atmospheric ions. The line radiation force should cause a new radiative wave mode. The dispersion relation from perturbations of the line force was analysed so far either in Sobolev approximation or for pure line absorption. The former does not include the line-driven instability, and the latter cannot account for upstream propagating, radiative waves. We consider a non-Sobolev line force that includes scattering in a simplified way, accounting however for the important line-drag effect. We derive a new dispersion relation for radiative waves, and analyse wave propagation using Fourier methods, and by numerical solution of an integro-differential equation. The existence of an upstream propagating, dispersive radiative wave mode is demonstrated.
KW  - hydrodynamics
KW  - radiative transfer
KW  - waves
KW  - stars: winds
KW  - outflows
Y1  - 2016
U6  - https://doi.org/10.1093/mnras/stw1008
SN  - 0035-8711
SN  - 1365-2966
VL  - 460
SP  - 1923
EP  - 1933
PB  - Oxford Univ. Press
CY  - Oxford
ER  -