708 research outputs found
Formation of the binary pulsars J1141-6545 and B2023+46
The binaries PSR J1141-6545 and PSR B2303+46 each appear to contain a white
dwarf which formed before the neutron star. We describe an evolutionary pathway
to produce these two systems. In this scenario, the primary transfers its
envelope onto the secondary which is then the more massive of the two stars,
and indeed sufficiently massive later to produce a neutron star via a
supernova. The core of the primary produces a massive white dwarf which enters
into a common envelope with the core of the secondary when the latter evolves
off the main sequence. During the common envelope phase, the white dwarf and
the core of the secondary spiral together as the envelope is ejected. The
evolutionary history of PSR J1141-6545 and PSR B2303+46 differ after this
phase. In the case of PSR J1141--6545, the secondary (now a helium star)
evolves into contact transferring its envelope onto the white dwarf. We propose
that the vast majority of this material is in fact ejected from the system. The
remains of the secondary then explode as a supernova producing a neutron star.
Generally the white dwarf and neutron star will remain bound in tight, often
eccentric, systems resembling PSR J1141-6545. These systems will spiral in and
merge on a relatively short timescale and may make a significant contribution
to the population of gamma ray burst progenitors. In PSR B2303+46, the
helium-star secondary and white dwarf never come into contact. Rather the
helium star loses its envelope via a wind, which increases the binary
separation slightly. Only a small fraction of such systems will remain bound
when the neutron star is formed (as the systems are wider). Those systems which
are broken up will produce a population of high-velocity white dwarfs and
neutron stars.Comment: 9 pages, 10 figures; MNRAS in pres
Irradiation-driven mass transfer cycles in compact binaries
We elaborate on the analytical model of Ritter, Zhang, and Kolb (2000, A&A
360, 959) which describes the basic physics of irradiation-driven mass transfer
cycles in semi-detached compact binary systems. In particular, we take into
account a contribution to the thermal relaxation of the donor star which is
unrelated to irradiation and which was neglected in previous studies. We
present results of simulations of the evolution of compact binaries undergoing
mass transfer cycles, in particular also of systems with a nuclear evolved
donor star. These computations have been carried out with a stellar evolution
code which computes mass transfer implicitly and models irradiation of the
donor star in a point source approximation, thereby allowing for more realistic
simulations than were hitherto possible. We find that low-mass X-ray binaries
and cataclysmic variables with orbital periods less than about 6 hours can
undergo mass transfer cycles only for low angular momentum loss rates. CVs
containing a giant donor or one near the terminal age main sequence are more
stable than previously thought, but can possibly also undergo mass transfer
cycles.Comment: 6 pages, LaTeX, one eps figure, requires asp2004.sty, to appear in:
The Astrophysics of Cataclysmic Variables and Related Objects, ASP Conf.
Ser., Vol. ?, 2005, J.M. Hameury and J.P. Lasota (eds.
Recommended from our members
Classification and clustering: models, software and applications
We are pleased to present the report on the 30th Fall Meeting of the working group ``Data Analysis and Numerical Classification'' (AG-DANK) of the German Classification Society. The meeting took place at the Weierstrass Institute for Applied Analysis and Stochastics (WIAS), Berlin, from Friday Nov. 14 till Saturday Nov. 15, 2008. Already 12 years ago, WIAS had hosted a traditional Fall Meeting with special focus on classification and multivariate graphics (Mucha and Bock, 1996). This time, the special topics were stability of clustering and classification, mixture decomposition, visualization, and statistical software
Properties of discontinuous and nova-amplified mass transfer in CVs
We investigate the effects of discontinuous mass loss in recurrent outburst
events on the long-term evolution of cataclysmic variables (CVs). Similarly we
consider the effects of frictional angular momentum loss (FAML), i.e.
interaction of the expanding nova envelope with the secondary. Numerical
calculations of CV evolution over a wide range of parameters demon- strate the
equivalence of a discontinuous sequence of nova cycles and the corresponding
mean evolution (replacing envelope ejection by a continuous wind), even close
to mass transfer instability. A formal stability analysis of discontinuous mass
transfer confirms this, independent of details of the FAML model. FAML is a
consequential angular momentum loss which amplifies the mass transfer rate
driven by systemic angular momentum losses such as magnetic braking. We show
that for a given v_exp and white dwarf mass the amplification increases with
secondary mass and is significant only close to the largest secondary mass
consistent with mass transfer stability. The amplification factor is
independent of the envelope mass ejected during the outburst, whereas the mass
transfer amplitude induced by individual nova outbursts is proportional to it.Comment: 16 pages, 19 figures; to appear in MNRA
trans-Ethylenedi-p-phenylene diacetate
The centrosymmetric title compound, C18H26O4, was prepared in high yield from 4-acetoxystyrene via Ru-catalysed homo-olefin metathesis. Exclusive formation of the E-configurated isomer was observed. In the crystal, a strong C—H⋯π intermolecular interaction links the molecules together
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