2,394 research outputs found
Evolution of Neutron-Star, Carbon-Oxygen White-Dwarf Binaries
At least one, but more likely two or more, eccentric neutron-star,
carbon-oxygen white-dwarf binaries with an unrecycled pulsar have been
observed. According to the standard scenario for evolving neutron stars which
are recycled in common envelope evolution we expect to observe \gsim 50 such
circular neutron star-carbon oxygen white dwarf binaries, since their formation
rate is roughly equal to that of the eccentric binaries and the time over which
they can be observed is two orders of magnitude longer, as we shall outline. We
observe at most one or two such circular binaries and from that we conclude
that the standard scenario must be revised. Introducing hypercritical accretion
into common envelope evolution removes the discrepancy by converting the
neutron star into a black hole which does not emit radio waves, and therefore
would not be observed.Comment: 25 pages, 1 figure, accepted in Ap
Stability Criteria for Mass Transfer in Binary Stellar Evolution
The evolution of a binary star system by various analytic approximations of
mass transfer is discussed, with particular attention payed to the stability of
these processes against runaway on the thermal and dynamical timescales of the
mass donating star. Mass transfer in red giant - neutron star binary systems is
used as a specific example of such mass transfer, and is investigated.
Hjellming and Webbink's (1987) results on the dynamic timescale response of a
convective star with a core to mass loss are applied, with new results.
It is found that mass transfer is usually stable, so long as the the wind's
specific angular momentum does not exceed the angular momentum per reduced mass
of the system. This holds for both dynamical and thermal timescales. Those
systems which are not stable will usually transfer mass on the thermal
timescale. Included are graphs illustrating the variation of the Roche radius
exponent with mass ratio in the binary, for various parameters in the
non-conservative mass transfer, as well as evolutionary paths of interacting
red giant neutron star binaries.Comment: 18 pages, 11 figures, LaTeX, l-aa.sty and psfig.sty macros incl. to
appear in Astronomy and Astrophysic
A Massive White Dwarf Companion to the Eccentric Binary Pulsar System PSR B2303+46
Pulsars in close, eccentric binary systems are usually assumed to have
another neutron star as a companion. These double neutron star binaries have
proven to be the best laboratories for experimental General Relativity and are
the most secure candidates for gravitational wave interferometers. We present
deep B, V, and R images of the field containing the eccentric binary pulsar
system PSR B2303+46. We find a faint, blue object (B=26.60+/-0.09;
(B-R)_0=-0.4+/-0.2) coincident with the timing position. We suggest this object
is the optical counterpart to the PSR B2303+46 system. The counterpart is too
bright to reflect emission from the pulsar or a neutron star companion. Most
likely, the companion of PSR B2303+46 is not a neutron star but a massive white
dwarf. We show that the observations are consistent with a hot white dwarf
companion (T_eff>~5*10^4 K) with cooling age equal the characteristic age of
the pulsar (t_cool~30 Myr) and mass within the range set by timing observations
and the Chandrasekhar mass (1.2<M_C<1.4 M_sun). Given the eccentric orbit, the
white dwarf must have formed before the neutron star, from what was originally
the more massive star in the binary. Due to mass transfer, the originally less
massive star could become sufficiently massive to end its life in a supernova
explosion and form the radio pulsar. We constrain the mass of the pulsar to be
in the range 1.24<M_psr<1.44 M_sun.Comment: Revised version, with only very small changes. 6 pages, 1 figure,
uses aas4pp2.sty, psfig.sty. Accepted for publication in Astrophysical
Journal Letter
Neutron Star Mass Measurements. I. Radio Pulsars
There are now about fifty known radio pulsars in binary systems, including at
least five in double neutron star binaries. In some cases, the stellar masses
can be directly determined from measurements of relativistic orbital effects.
In others, only an indirect or statistical estimate of the masses is possible.
We review the general problem of mass measurement in radio pulsar binaries, and
critically discuss all current estimates of the masses of radio pulsars and
their companions. We find that significant constraints exist on the masses of
twenty-one radio pulsars, and on five neutron star companions of radio pulsars.
All the measurements are consistent with a remarkably narrow underlying
gaussian mass distribution, m = 1.35 +- 0.04 solar masses. There is no evidence
that extensive mass accretion (delta m >~ 0.1 solar mass) has occurred in these
systems. We also show that the observed inclinations of millisecond pulsar
binaries are consistent with a random distribution, and thus find no evidence
for either alignment or counteralignment of millisecond pulsar magnetic fields.Comment: 35 pages, 5 figures, submitted to the Astrophys. J. Also available at
http://pulsar.princeton.edu/pulsar/publications.shtm
The formation of the eccentric-orbit millisecond pulsar J1903+0327 and the origin of single millisecond pulsars
The millisecond pulsar J1903+0327 is accompanied by an ordinary G-dwarf star
in an unusually wide (\,days) and eccentric () orbit. The standard model for producing MSPs fails to explain the
orbital characteristics of this extraordinary binary, and alternative binary
models are unable to explain the observables. We present a triple-star model
for producing MSPs in relatively wide eccentric binaries with a normal
(main-sequence) stellar companion. We start from a stable triple system
consisting of a Low-Mass X-ray Binary (LMXB) with an orbital period of at least
1 day, accompanied by a G-dwarf in a wide and possibly eccentric orbit.
Variations in the initial conditions naturally provide a satisfactory
explanation for the unexplained triple component in the eclipsing soft X-ray
transient 4U~2129+47 or the cataclysmic variable EC 19314-5915. The best
explanation for J1903, however, results from the expansion of the orbit of the
LMXB, driven by the mass transfer from the evolving donor star to its neutron
star companion, which causes the triple eventually to becomes dynamically
unstable. Using numerical computations we show that, depending on the precise
system configuration at the moment the triple becomes dynamically unstable, the
ejection of each of the three components is possible. If the donor star of the
LMXB is ejected, a system resembling J1903, will result. If the neutron star is
ejected, a single MSP results. This model therefore also provides a
straightforward mechanism for forming single MSP in the Galactic disk. We
conclude that the Galaxy contains some 30--300 binaries with characteristics
similar to J1903, and about an order of magnitude fewer single millisecond
pulsars produced with the proposed triple scenario.Comment: ApJ accepted for publicatio
The mass of the neutron star in Cyg X-2 (V1341 Cyg)
Cygnus X-2 is one of the brightest and longest known X-ray sources. We
present high resolution optical spectroscopy of Cyg X-2 obtained over 4 years
which gives an improved mass function of 0.69 +/- 0.03 Msun (1 sigma error). In
addition, we resolve the rotationally broadened absorption features of the
secondary star for the first time, deriving a rotation speed of vsin(i) = 34.2
+/- 2.5 km per s (1 sigma error) which leads to a mass ratio of q = M_c/M_x =
0.34 +/- 0.04 (1 sigma error), assuming a tidally-locked and Roche lobe-filling
secondary). Hence with the lack of X-ray eclipses (i.e. i <~ 73 degrees) we can
set firm 95% confidence lower limits to the neutron star mass of M_x > 1.27
Msun and to the companion star mass of M_c > 0.39 Msun. However, by
additionally requiring that the companion must exceed 0.75 Msun (as required
theoretically to produce a steady low-mass X-ray binary), then M_x > 1.88 Msun
and i < 61 degrees (95% confidence lower and upper limit, respectively),
thereby making Cyg X-2 the highest mass neutron star measured to date. If
confirmed this would set significant constraints on the equation of state of
nuclear matter.Comment: 16 pages, 4 figures, ApJ Letters, accepted, LaTeX, aasms4.st
Expected Coalescence Rate of Double Neutron Stars for Ground Based Interferometers
In this paper we present new estimates of the coalescence rate of neutron
star binaries in the local universe and we discuss its consequences for the
first generations of ground based interferometers. Our approach based on both
evolutionary and statistical methods gives a galactic merging rate of 1.7
10 yr, in the range of previous estimates 10 - 10
yr. The local rate which includes the contribution of elliptical
galaxies is two times higher, in the order of 3.4 10 yr. We
predict one detection every 148 and 125 years with initial VIRGO and LIGO, and
up to 6 events per year with their advanced configuration. Our recent detection
rate estimates from investigations on VIRGO future improvements are quoted.Comment: talk given at the GWDAW9 (Annecy, 2004) to be published in CQ
Loss of Productivity Due to Neck/Shoulder Symptoms and Hand/Arm Symptoms: Results from the PROMO-Study
Introduction: The objective of the present study is to describe the extent of productivity loss among computer workers with neck/shoulder symptoms and hand/arm symptoms, and to examine associations between pain intensity, various physical and psychosocial factors and productivity loss in computer workers with neck/shoulder and hand/arm symptoms. Methods: A cross-sectional design was used. The study population consisted of 654 computer workers with neck/shoulder or hand/arm symptoms from five different companies. Descriptive statistics were used to describe the occurrence of self-reported productivity loss. Logistic regression analyses were used to examine the associations. Results: In 26% of all the cases reporting symptoms, productivity loss was involved, the most often in cases reporting both symptoms (36%). Productivity loss involved sickness absence in 11% of the arm/hand cases, 32% of the neck/shoulder cases and 43% of the cases reporting both symptoms. The multivariate analyses showed statistically significant odds ratios for pain intensity (OR: 1.26; CI: 1.12-1.41), for high effort/no low reward (OR: 2.26; CI: 1.24-4.12), for high effort/low reward (OR: 1.95; CI: 1.09-3.50), and for low job satisfaction (OR: 3.10; CI: 1.44-6.67). Physical activity in leisure time, full-time work and overcommitment were not associated with productivity loss. Conclusion: In most computer workers with neck/shoulder symptoms or hand/arm symptoms productivity loss derives from a decreased performance at work and not from sickness absence. Favorable psychosocial work characteristics might prevent productivity loss in symptomatic workers. © 2007 Springer Science+Business Media, LLC
Cygnus X-3 and the problem of the missing Wolf-Rayet X-ray binaries
Cygnus X-3 is a strong X-ray source (L_X about 10^38 erg/s) which is thought
to consist of a compact object, accreting matter from a helium star. We find
analytically that the estimated ranges of mass-loss rate and orbital-period
derivative for Cyg X-3 are consistent with two models: i) the system is
detached and the mass loss from the system comes from the stellar wind of a
massive helium star, of which only a fraction that allows for the observed
X-ray luminosity is accreted, or ii) the system is semidetached and a
Roche-lobe-overflowing low- or moderate-mass helium donor transfers mass to the
compact object, followed by ejection of its excess over the Eddington rate from
the system. These analytical results appear to be consistent with evolutionary
calculations. By means of population synthesis we find that currently in the
Galaxy there may exist ~1 X-ray binary with a black hole that accretes from a
>~ 7 MSun Wolf-Rayet star and ~1 X-ray binary in which a neutron star accretes
matter from a Roche-lobe-overflowing helium star with mass <~ 1.5 MSun. Cyg X-3
is probably one of these systems.Comment: 12 pages, 6 figures, accepted by A&
Structural subnetwork evolution across the life-span: rich-club, feeder, seeder
The impact of developmental and aging processes on brain connectivity and the
connectome has been widely studied. Network theoretical measures and certain
topological principles are computed from the entire brain, however there is a
need to separate and understand the underlying subnetworks which contribute
towards these observed holistic connectomic alterations. One organizational
principle is the rich-club - a core subnetwork of brain regions that are
strongly connected, forming a high-cost, high-capacity backbone that is
critical for effective communication in the network. Investigations primarily
focus on its alterations with disease and age. Here, we present a systematic
analysis of not only the rich-club, but also other subnetworks derived from
this backbone - namely feeder and seeder subnetworks. Our analysis is applied
to structural connectomes in a normal cohort from a large, publicly available
lifespan study. We demonstrate changes in rich-club membership with age
alongside a shift in importance from 'peripheral' seeder to feeder subnetworks.
Our results show a refinement within the rich-club structure (increase in
transitivity and betweenness centrality), as well as increased efficiency in
the feeder subnetwork and decreased measures of network integration and
segregation in the seeder subnetwork. These results demonstrate the different
developmental patterns when analyzing the connectome stratified according to
its rich-club and the potential of utilizing this subnetwork analysis to reveal
the evolution of brain architectural alterations across the life-span
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