2004/07/21 by E. P. J. van den Heuvel, Heuvel, E. P. J. van den
Engineering · Physics and Astronomy · #Geophysics and Sensor Technology #Pulsars and Gravitational Waves Research #Superconducting Materials and Applications #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0407451
10 pages in pdf format; to appear in proceedings Fifth Integral Science Workshop
arxiv created 2004/07/21 · arxiv updated 2009/12/01
An important recent discovery by Pfahl et al. (2002) is that there are two classes of Be X-ray binaries: one with orbits of small eccentricity (<0.25), in which the neutron stars received hardly any kick velocity at birth and a class with substantial orbital eccentricities, in which the neutron stars received a kick velocity of order 100 km/s at birth. Also many of the double neutron stars (5 out of 7) have a low orbital eccentricity (0.09 to 0.27), which indicates that their second-born neutron stars received hardly any velocity kick at birth. These second-born neutron stars tend to have low masses (1.25 to 1.35 Msun). It is proposed that the low-mass, low-kick neutron stars are formed by the electron capture of degenerate O-Ne-Mg cores of stars with initial masses below about 12-14 Msun, while the high-kick neutron stars originated from the photo-disintegration collapse of the iron cores of stars which started out with masses larger than this limit. The latter group may be further subdivided into two classes of different mass.