138 research outputs found
Supernova Kicks and Misaligned Be Star Binaries
Be stars are rapidly spinning B stars surrounded by an outflowing disc of gas
in Keplerian rotation. Be star/X-ray binary systems contain a Be star and a
neutron star. They are found to have non-zero eccentricities and there is
evidence that some systems have a misalignment between the spin axis of the
star and the spin axis of the binary orbit. The eccentricities in these systems
are thought to be caused by a kick to the neutron star during the supernova
that formed it. Such kicks would also give rise to misalignments. In this paper
we investigate the extent to which the same kick distribution can give rise to
both the observed eccentricity distribution and the observed misalignments. We
find that a Maxwellian distribution of velocity kicks with a low velocity
dispersion, , is consistent with the observed
eccentricity distribution but is hard to reconcile with the observed
misalignments, typically . Alternatively a higher velocity kick
distribution, , is consistent with the observed
misalignments but not with the observed eccentricities, unless post-supernova
circularisation of the binary orbits has taken place. We discuss briefly how
this might be achieved.Comment: Accepted for publication in MNRA
Spectral signature of a free pulsar wind in the gamma-ray binaries LS 5039 and LSI +61\degr303
LS 5039 and LSI +61\degr303 are two binaries that have been detected in the
TeV energy domain. These binaries are composed of a massive star and a compact
object, possibly a young pulsar. The gamma-ray emission would be due to
particle acceleration at the collision site between the relativistic pulsar
wind and the stellar wind of the massive star. Part of the emission may also
originate from inverse Compton scattering of stellar photons on the unshocked
(free) pulsar wind. The purpose of this work is to constrain the bulk Lorentz
factor of the pulsar wind and the shock geometry in the compact pulsar wind
nebula scenario for LS 5039 and LSI +61\degr303 by computing the unshocked
wind emission and comparing it to observations. Anisotropic inverse Compton
losses equations are derived and applied to the free pulsar wind in binaries.
The unshocked wind spectra seen by the observer are calculated taking into
account the gamma-gamma absorption and the shock geometry. A pulsar wind
composed of monoenergetic pairs produces a typical sharp peak at an energy
which depends on the bulk Lorentz factor and whose amplitude depends on the
size of the emitting region. This emission from the free pulsar wind is found
to be strong and difficult to avoid in LS 5039 and LSI +61\degr303. If the
particles in the pulsar are monoenergetic then the observations constrain their
energy to roughly 10-100 GeV. For more complex particle distributions, the free
pulsar wind emission will be difficult to distinguish from the shocked pulsar
wind emission.Comment: 11 pages, 10 figures, accepted for publication in Astronomy and
Astrophysic
Runaway Massive Binaries and Cluster Ejection Scenarios
The production of runaway massive binaries offers key insights into the
evolution of close binary stars and open clusters. The stars HD 14633 and HD
15137 are rare examples of such runaway systems, and in this work we
investigate the mechanism by which they were ejected from their parent open
cluster, NGC 654. We discuss observational characteristics that can be used to
distinguish supernova ejected systems from those ejected by dynamical
interactions, and we present the results of a new radio pulsar search of these
systems as well as estimates of their predicted X-ray flux assuming that each
binary contains a compact object. Since neither pulsars nor X-ray emission are
observed in these systems, we cannot conclude that these binaries contain
compact companions. We also consider whether they may have been ejected by
dynamical interactions in the dense environment where they formed, and our
simulations of four-body interactions suggest that a dynamical origin is
possible but unlikely. We recommend further X-ray observations that will
conclusively identify whether HD 14633 or HD 15137 contain neutron stars.Comment: Accepted to ApJ, 11 page
Recommended from our members
Assessment of Maternal Posttraumatic Stress Disorder Following Childbirth: Psychometric Properties of the Swedish Version of City Birth Trauma Scale
Objective: City Birth Trauma Scale is an instrument designed to evaluate and diagnose postpartum posttraumatic stress disorder (PTSD) according to the 5th edition of Diagnostic and Statistical Manual of Mental Disorders (DSM-5). No validated Swedish instrument exists to measure postpartum PTSD according to DSM-5. Therefore, the objective of this study was to assess the psychometric properties of the Swedish version of the City BiTS (City BiTS-Swe) and to examine the latent factor structure of postpartum PTSD.
Method: A total of 619 women, who had given birth at five clinics in the past six to 16 weeks, completed an online version of City BiTS-Swe and the Edinburgh Postnatal Depression Scale (EPDS). Additionally, sociodemographic and medical data was collected. A second questionnaire was answered by 110 women to examine reliability over time.
Results: The confirmatory factor analysis using the two-factor model gave best fit to the data. We found a high internal consistency (α = 0.89-0.87) and good test-retest reliability (ICC = 0.53 - 0.90). Divergent reliability with EPDS showed significant correlations with satisfying results for the subscale birth-related symptoms (r=0.41). We also found discriminant validity concerning mode of birth, parity, gestational age, mental illness, history of traumatic childbirth and history of traumatic event as expected.
Conclusions: The City BiTS-Swe is a valid and reliable instrument to assess and diagnose PTSD following childbirth.
Clinical impact statement: PTSD following childbirth can cause considerable suffering for the affected woman, her partner and the child. Having a valid and reliable instrument to assess and diagnose childbirth-related PTSD is of great importance for the detection and treatment of the disease. The results of this study confirms that the Swedish version of City BiTS is a reliable and valid instrument that can be recommended for use in daily clinical practice and for research purposes
The Full Spectrum Galactic Terrarium: MHz to TeV Observations of Various Critters
Multi-wavelength studies at radio, infrared, optical, X-ray, and TeV
wavelengths have discovered probable counterparts to many Galactic sources of
GeV emission detected by EGRET. These include pulsar wind nebulae, high mass
X-ray binaries, and mixed morphology supernova remnants. Here we provide an
overview of the observational properties of Galactic sources which emit across
19 orders of magnitude in energy. We also present new observations of several
sources.Comment: 4 pages, 5 figures, Proceedings of the The 4th Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy, eds. Aharonian,
Hofmann, Riege
Impact of the orbital uncertainties on the timing of pulsars in binary systems
The detection of pulsations from an X-ray binary is an unambiguous signature
of the presence of a neutron star in the system. When the pulsations are missed
in the radio band, their detection at other wavelengths, like X-ray or
gamma-rays, requires orbital demodulation, since the length of the observations
are often comparable to, or longer than the system orbital period. The detailed
knowledge of the orbital parameters of binary systems plays a crucial role in
the detection of the spin period of pulsars, since any uncertainty in their
determination translates into a loss in the coherence of the signal during the
demodulation process. In this paper, we present an analytical study aimed at
unveiling how the uncertainties in the orbital parameters might impact on
periodicity searches. We find a correlation between the power of the signal in
the demodulated arrival time series and the uncertainty in each of the orbital
parameters. This correlation is also a function of the pulsar frequency. We
test our analytical results with numerical simulations, finding good agreement
between them. Finally, we apply our study to the cases of LS 5039 and LS I +61
303 and consider the current level of uncertainties in the orbital parameters
of these systems and their impact on a possible detection of a hosted pulsar.
We also discuss the possible appearance of a sideband ambiguity in real data.
The latter can occur when, due to the use of uncertain orbital parameters, the
power of a putative pulsar is distributed in frequencies lying nearby the
pulsar period. Even if the appearance of a sideband is already a signature of a
pulsar component, it may introduce an ambiguity in the determination of its
period. We present here a method to solve the sideband issue.Comment: Accepted 2012 September 08 by MNRAS. The paper contains 18 figures
and 5 table
A Spectroscopic Study of Mass Outflows in the Interacting Binary RY Scuti
The massive interacting binary RY Scuti is an important representative of an
active mass-transferring system that is changing before our eyes and which may
be an example of the formation of a Wolf-Rayet star through tidal stripping.
Utilizing new and previously published spectra, we present examples of how a
number of illustrative absorption and emission features vary during the binary
orbit. We identify spectral features associated with each component, calculate
a new, double-lined spectroscopic binary orbit, and find masses of 7.1 +/- 1.2
M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the hidden massive
companion. Through tomographic reconstruction of the component spectra from the
composite spectra, we confirm the O9.7 Ibpe spectral class of the bright
supergiant and discover a B0.5 I spectrum associated with the hidden massive
companion; however, we suggest that the latter is actually the spectrum of the
photosphere of the accretion torus immediately surrounding the massive
companion. We describe the complex nature of the mass loss flows from the
system in the context of recent hydrodynamical models for beta Lyr, leading us
to conclude RY Scuti has matter leaving the system in two ways: 1) a bipolar
outflow from winds generated by the hidden massive companion, and 2) mass from
the bright O9.7 Ibpe supergiant flowing from the region near the L2 point to
fill out a large, dense circumbinary disk. This circumbinary disk (radius ~ 1
AU) may feed the surrounding double-toroidal nebula (radius ~ 2000 AU).Comment: 41 pages with 7 tables and 11 figures, accepted to Ap
A Spectroscopic Study of Field and Runaway OB Stars
Identifying binaries among runaway O- and B-type stars offers valuable
insight into the evolution of open clusters and close binary stars. Here we
present a spectroscopic investigation of 12 known or suspected binaries among
field and runaway OB stars. We find new orbital solutions for five single-lined
spectroscopic binaries (HD 1976, HD 14633, HD 15137, HD 37737, and HD 52533),
and we classify two stars thought to be binaries (HD 30614 and HD 188001) as
single stars. In addition, we reinvestigate their runaway status using our new
radial velocity data with the UCAC2 proper motion catalogs. Seven stars in our
study appear to have been ejected from their birthplaces, and at least three of
these runaways are spectroscopic binaries and are of great interest for future
study.Comment: 21 pages, 1 figure, 7 tables; Accepted to Ap
A Spectroscopic Orbit for Regulus
We present a radial velocity study of the rapidly rotating B-star Regulus
that indicates the star is a single-lined spectroscopic binary. The orbital
period (40.11 d) and probable semimajor axis (0.35 AU) are large enough that
the system is not interacting at present. However, the mass function suggests
that the secondary has a low mass (M_2 > 0.30 M_sun), and we argue that the
companion may be a white dwarf. Such a star would be the remnant of a former
mass donor that was the source of the large spin angular momentum of Regulus
itself.Comment: 18 pages, 2 figures, ApJL in pres
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