410 research outputs found
Formation of the binary pulsars PSR B2303+46 and PSR J1141-6545 - young neutron stars with old white dwarf companions
We have investigated the formation of the binary radio pulsars PSR B2303+46
and PSR J1141-6545 via Monte Carlo simulations of a large number of interacting
stars in binary systems. PSR B2303+46 has recently been shown (van Kerkwijk &
Kulkarni 1999) to be the first neutron star - white dwarf binary system
observed, in which the neutron star was born after the formation of the white
dwarf. We discuss the formation process for such a system and are able to put
constraints on the parameters of the initial ZAMS binary. We present
statistical evidence in favor of a white dwarf companion to the binary pulsar
PSR J1141-6545, just recently discovered in the Parkes Multibeam Survey. If
this is confirmed by observations this system will be the second one known in
which the neutron star was born after its white dwarf companion. We also
predict a minimum space velocity of 150 km/s for PSR J1141-6545, and show it
must have experienced an asymmetric SN in order to explain its low
eccentricity. Finally, we estimate the birthrate of these systems relative to
other binary pulsar systems and present the expected distribution of their
orbital periods, eccentricities and velocities.Comment: 9 pages, 4 figures, 2 tables, some revisions, accepted for
publication in A&A Main Journa
The case of PSR J1911-5958A in the outskirts of NGC 6752: signature of a black hole binary in the cluster core?
We have investigated different scenarios for the origin of the binary
millisecond pulsar PSR J1911-5958A in NGC 6752, the most distant pulsar
discovered from the core of a globular cluster to date. The hypothesis that it
results from a truly primordial binary born in the halo calls for
accretion-induced collapse and negligible recoil speed at the moment of neutron
star formation. Scattering or exchange interactions off cluster stars are not
consistent with both the observed orbital period and its offset position. We
show that a binary system of two black holes with (unequal) masses in the range
of 3-100 solar masses can live in NGC 6752 until present time and can have
propelled PSR J1911-5958A into an eccentric peripheral orbit during the last ~1
Gyr.Comment: Accepted by ApJ Letter. 5 pages, 1 figure, 1 tabl
Formation of undermassive single white dwarfs and the influence of planets on late stellar evolution
We propose a scenario to form low-mass, single, slow rotating white dwarfs
from a solar-like star accompanied by a massive planet, or a brown dwarf, in a
relatively close orbit (e.g. HD 89707). Such white dwarfs were recently found
by Maxted & Marsh (1998). When the solar-like star ascends the giant branch it
captures the planet and the subsequent spiral-in phase expels the envelope of
the giant leaving a low-mass helium white dwarf remnant. In case the planet
evaporizes, or fills its own Roche-lobe, the outcome is a single undermassive
white dwarf. The observed distribution of planetary systems supports the
applicability of this scenario.Comment: 4 pages, accepted for publication in A&A letter
Formation of millisecond pulsars. I. Evolution of low-mass X-ray binaries with P > 2 days
We have performed detailed numerical calculations of the non-conservative
evolution of close binary systems with low-mass (1.0-2.0 M_sun) donor stars and
a 1.3 M_sun accreting neutron star. Rather than using analytical expressions
for simple polytropes, we calculated the thermal response of the donor star to
mass loss, in order to determine the stability and follow the evolution of the
mass transfer. Tidal spin-orbit interactions and Reimers wind mass-loss were
also taken into account. We have re-calculated the correlation between orbital
period and white dwarf mass in wide binary radio pulsar systems. Furthermore,
we find an anti-correlation between orbital period and neutron star mass under
the assumption of the "isotropic re-emission" model and compare this result
with observations. We conclude that the accretion efficiency of neutron stars
is rather low and that they eject a substantial fraction of the transferred
material even when accreting at a sub-Eddington level. The mass-transfer rate
is a strongly increasing function of initial orbital period and donor star
mass. For relatively close systems with light donors (P < 10 days and M_2 < 1.3
M_sun) the mass-transfer rate is sub-Eddington, whereas it can be highly
super-Eddington by a factor of 10^4 for wide systems with relatively heavy
donor stars (1.6 - 2.0 M_sun) as a result of their deep convective envelopes.
We briefly discuss the evolution of X-ray binaries with donor stars in excess
of 2 M_sun.
Based on our calculations we present evidence that PSR J1603-7202 evolved
through a phase with unstable mass transfer from a relatively heavy donor star
and therefore is likely to host a CO white dwarf companion.Comment: Accepted for publication in A&A. 18 pages, 6 figures, 2 table
Recycling Pulsars: spins, masses and ages
Although the first millisecond pulsars (MSPs) were discovered 30 years ago we
still do not understand all details of their formation process. Here, we
present new results from Tauris, Langer & Kramer (2012) on the recycling
scenario leading to radio MSPs with helium or carbon-oxygen white dwarf
companions via evolution of low- and intermediate mass X-ray binaries (LMXBs,
IMXBs). We discuss the location of the spin-up line in the (P,Pdot)-diagram and
estimate the amount of accreted mass needed to obtain a given spin period and
compare with observations. Finally, we constrain the true ages of observed
recycled pulsars via calculated isochrones in the (P,Pdot)-diagram.Comment: Contributed talk, Proceedings of IAUS 291 "Neutron Stars and Pulsars:
Challenges and Opportunities after 80 years", J. van Leeuwen (ed.); 4 pages,
2 figure
PSR J2019+2425: A Unique Testing Ground for Binary Evolution
If the theoretical relationship between white dwarf mass and orbital period
for wide-orbit binary radio pulsars is assumed to be correct, then the neutron
star mass of PSR J2019+2425 is shown to be ~1.20 M_sun. Hence the mass of the
neutron star in this system prior to the mass transfer phase is expected to
have been < 1.1 M_sun. Alternatively this system descends from the accretion
induced collapse (AIC) of a massive white dwarf. We estimate the magnetic
inclination angles of all the observed wide-orbit low-mass binary pulsars in
the Galactic disk using the core-mass period relation and assuming that the
spin axis of an accreting neutron star aligns with the orbital angular momentum
vector in the recycling process of the pulsar. The large estimated magnetic
inclination angle of PSR J2019+2425, in combination with its old age, gives for
this system evidence against alignment of the magnetic field axis with the
rotational spin axis. However, in the majority of the similar systems the
distribution of magnetic inclination angles is concentrated toward low values
(if the core-mass period relation is correct) and suggests that alignment has
taken place.Comment: 4 pages, 2 figures, accepted for publication in A&A Letter
New Direct Observational Evidence for Kicks in SNe
We present an updated list of direct strong evidence in favour of kicks being
imparted to newborn neutron stars. In particular we discuss the new cases of
evidence resulting from recent observations of the X-ray binary Circinus X-1
and the newly discovered binary radio pulsar PSR J1141-6545. We conclude that
the assumption that neutron stars receive a kick velocity at their formation is
unavoidable (van den Heuvel & van Paradijs 1997).Comment: 2 pages, to appear in the proceedings of the IAU Colloq. 177 "Pulsar
Astronomy - 2000 and beyond
Spin frequency distributions of binary millisecond pulsars
Rotation-powered millisecond radio pulsars have been spun up to their present
spin period by a - yr long X-ray-bright phase of accretion of
matter and angular momentum in a low-to-intermediate mass binary system.
Recently, the discovery of transitional pulsars that alternate cyclically
between accretion and rotation-powered states on time scales of a few years or
shorter, has demonstrated this evolutionary scenario. Here, we present a
thorough statistical analysis of the spin distributions of the various classes
of millisecond pulsars to assess the evolution of their spin period between the
different stages. Accreting sources that showed oscillations exclusively during
thermonuclear type I X-ray bursts (nuclear-powered millisecond pulsars) are
found to be significantly faster than rotation-powered sources, while accreting
sources that possess a magnetosphere and show coherent pulsations (accreting
millisecond pulsars) are not. On the other hand, if accreting millisecond
pulsars and eclipsing rotation-powered millisecond pulsars form a common class
of transitional pulsars, these are shown to have a spin distribution
intermediate between the faster nuclear-powered millisecond pulsars and the
slower non-eclipsing rotation-powered millisecond pulsars. We interpret these
findings in terms of a spin-down due to the decreasing mass-accretion rate
during the latest stages of the accretion phase, and in terms of the different
orbital evolutionary channels mapped by the various classes of pulsars. We
summarize possible instrumental selection effects, showing that even if an
unbiased sample of pulsars is still lacking, their influence on the results of
the presented analysis is reduced by recent improvements in instrumentation and
searching techniques.Comment: Accepted for publication in A&A (6 pages, 4 figures
On the pre-RLO spin-orbit couplings in LMXBs
We investigate the effect of orbital decay caused by nuclear expansion of a (sub)giant star in synchronous binary system. We compare this effect with the presence of a magnetic stellar wind and show that the additional transfer of orbital angular momentum into spin angular momentum is relatively important -- especially since it has been shown that the effect of magnetic braking saturates at short orbital periods
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