220 research outputs found
The origin of runaway stars
Milli-arcsecond astrometry provided by Hipparcos and by radio observations
makes it possible to retrace the orbits of some of the nearest runaway stars
and pulsars to determine their site of origin. The orbits of the runaways AE
Aurigae and mu Columbae and of the eccentric binary iota Orionis intersect each
other about 2.5 Myr ago in the nascent Trapezium cluster, confirming that these
runaways were formed in a binary-binary encounter. The path of the runaway star
zeta Ophiuchi intersects that of the nearby pulsar PSR J1932+1059, about 1 Myr
ago, in the young stellar group Upper Scorpius. We propose that this neutron
star is the remnant of a supernova that occurred in a binary system which also
contained zeta Oph, and deduce that the pulsar received a kick velocity of
about 350 km/s in the explosion. These two cases provide the first specific
kinematic evidence that both mechanisms proposed for the production of runaway
stars, the dynamical ejection scenario and the binary-supernova scenario,
operate in nature.Comment: 5 pages, including 2 eps-figures and 1 table, submitted to the ApJ
Letters. The manuscript was typeset using aaste
De invloed van verschillende verpakkingen op de bewaarbaarheid in de koelcel van enkele boomkwekerijgewassen
Onderzoek is verricht naar de invloed van verpakking op de kwaliteit van twee rozenrassen, een forsythia en een ribes tijdens bewaring bij 0 tot 1 graad Celsius en 95% relatieve vochtigheid. De onderzochte verpakkingen zijn een geperforeerde polyethyleen folie, halfdoorlatend folie en gasdichte folie. De bewaring duurde 1 tot 3 maanden. Ribes bleek absoluut niet bewaarbaar, forsythia en de rozenrassen wel, ongeacht de verpakking. Bij een van de rozenrassen gaf de halfdoorlatende folie betere resultate
X-ray Light Curves and Accretion Disk Structure of EX Hydrae
We present X-ray light curves for the cataclysmic variable EX Hydrae obtained
with the Chandra High Energy Transmission Grating Spectrometer and the Extreme
Ultraviolet Explorer Deep Survey photometer. We confirm earlier results on the
shape and amplitude of the binary light curve and discuss a new feature: the
phase of the minimum in the binary light curve, associated with absorption by
the bulge on the accretion disk, increases with wavelength. We discuss several
scenarios that could account for this trend and conclude that, most likely, the
ionization state of the bulge gas is not constant, but rather decreases with
binary phase. We also conclude that photoionization of the bulge by radiation
originating from the white dwarf is not the main source of ionization, but that
it is heated by shocks originating from the interaction between the inflowing
material from the companion and the accretion disk. The findings in this paper
provide a strong test for accretion disk models in close binary systems.Comment: 19 pages, 4 figures, accepted for publication in the Ap
Open Clusters IC 4665 and Cr 359 and a Probable Birthplace of the Pulsar PSR B1929+10
Based on the epicyclic approximation, we have simulated the motion of the
young open star clusters IC 4665 and Collinder 359. The separation between the
cluster centers is shown to have been minimal 7 Myr ago, 36 pc. We have
established a close evolutionary connection between IC 4665 and the
Scorpius-Centaurus association -- the separation between the centers of these
structures was pc 15 Myr ago. In addition, the center of IC 4665
at this time was near two well-known regions of coronal gas: the Local Bubble
and the North Polar Spur. The star HIP 86768 is shown to be one of the
candidates for a binary (in the past) with the pulsar PSR B1929+10. At the
model radial velocity of the pulsar km s, a close
encounter of this pair occurs in the vicinity of IC 4665 at a time of -1.1 Myr.
At the same time, using currently available data for the pulsar B1929+10 at its
model radial velocity km s, we show that the hypothesis
of Hoogerwerf et al. (2001) about the breakup of the Oph--B1929+10
binary in the vicinity of Upper Scorpius (US) about 0.9 Myr ago is more
plausible.Comment: 19 pages, 8 figure
High-mass X-ray binaries and OB-runaway stars
High-mass X-ray binaries (HMXBs) represent an important phase in the
evolution of massive binary systems. HMXBs provide unique diagnostics to test
massive-star evolution, to probe the physics of radiation-driven winds, to
study the process of mass accretion, and to measure fundamental parameters of
compact objects. As a consequence of the supernova explosion that produced the
neutron star (or black hole) in these systems, HMXBs have high space velocities
and thus are runaways. Alternatively, OB-runaway stars can be ejected from a
cluster through dynamical interactions. Observations obtained with the
Hipparcos satellite indicate that both scenarios are at work. Only for a
minority of the OB runaways (and HMXBs) a wind bow shock has been detected.
This might be explained by the varying local conditions of the interstellar
medium.Comment: 15 pages, latex (sty file included) with 5 embedded figures (one in
jpg format), to appear in Proc. "Influence of binaries on stellar population
studies", Eds. Vanbeveren, Van Rensberge
The proper motion of the isolated neutron star RX J1605.3+3249
We obtained deep optical imaging of the thermally emitting X-ray bright and
radio-quiet isolated neutron star RX J1605.3+3249 with the Subaru telescope in
1999 and 2003. Together with archival HST images acquired in 2001 these data
reveal a proper motion of mu = 144.5 +/- 13.2 mas/yr. This implies a relatively
high spatial velocity and indicates that the star is unlikely to be re-heated
by accretion of matter from the interstellar medium. Assuming that RX
J1605.3+3249 is a young (10^5-10^6 yr) cooling neutron star, its apparent
trajectory is consistent with a birth in the nearby Sco OB2 OB association at a
location close to that derived for RX J1856.5-3754 and perhaps also to that of
RX J0720.4-3125. This suggests that the X-ray bright part of ROSAT-discovered
isolated neutron stars is dominated by the production of the Sco OB2 complex
which is the closest OB association and a part of the Gould belt. The B and R
magnitudes of the faint optical counterpart did not vary from 1999 to 2003 at B
= 27.22 +/- 0.10. Its B-R colour index of +0.32 +/- 0.17 is significantly
redder than that of other isolated neutron stars and the optical flux lies a
factor 11.5 above the extrapolation of the X-ray blackbody-like spectrum. The
red optical colour reveals the presence of an additional emitting component in
the optical regime over the main neutron star thermal emission. We also
discovered a small elongated Halpha nebula approximately centered on the
neutron star and aligned with the direction of motion. The width of the nebula
is unresolved and smaller than ~ 0.4" for a length of about 1". The shape of
the Balmer emitting nebula is very different from those seen close to other
neutron stars and should be confirmed by follow-up observations. We shortly
discuss the possible mechanisms which could give rise to such a geometry.Comment: 9 pages, 6 figures, resolution of some figures reduced to meet
astro-ph file size restriction, accepted for publication in A&
Precision Astrometry with the Very Long Baseline Array: Parallaxes and Proper Motions for 14 Pulsars
Astrometry can bring powerful constraints to bear on a variety of scientific
questions about neutron stars, including their origins, astrophysics,
evolution, and environments. Using phase-referenced observations at the VLBA,
in conjunction with pulsar gating and in-beam calibration, we have measured the
parallaxes and proper motions for 14 pulsars. The smallest measured parallax in
our sample is 0.13+-0.02 mas for PSR B1541+09, which has a most probable
distance of 7.2+1.3-1.1 kpc. We detail our methods, including initial VLA
surveys to select candidates and find in-beam calibrators, VLBA
phase-referencing, pulsar gating, calibration, and data reduction. The use of
the bootstrap method to estimate astrometric uncertainties in the presence of
unmodeled systematic errors is also described. Based on our new
model-independent estimates for distance and transverse velocity, we
investigate the kinematics and birth sites of the pulsars and revisit models of
the Galactic electron density distribution. We find that young pulsars are
moving away from the Galactic plane, as expected, and that age estimates from
kinematics and pulsar spindown are generally in agreement, with certain notable
exceptions. Given its present trajectory, the pulsar B2045-16 was plausibly
born in the open cluster NGC 6604. For several high-latitude pulsars, the
NE2001 electron density model underestimates the parallax distances by a factor
of two, while in others the estimates agree with or are larger than the
parallax distances, suggesting that the interstellar medium is irregular on
relevant length scales. The VLBA astrometric results for the recycled pulsar
J1713+0747 are consistent with two independent estimates from pulse timing,
enabling a consistency check between the different reference frames.Comment: 16 pages, 9 figures, 4 tables; results unchanged; revised version
accepted by Ap
Association between prehospital end-tidal carbon dioxide levels and mortality in patients with suspected severe traumatic brain injury
Purpose: Severe traumatic brain injury is a leading cause of mortality and morbidity, and these patients are frequently intubated in the prehospital setting. Cerebral perfusion and intracranial pressure are influenced by the arterial partial pressure of CO2 and derangements might induce further brain damage. We investigated which lower and upper limits of prehospital end-tidal CO2 levels are associated with increased mortality in patients with severe traumatic brain injury. Methods: The BRAIN-PROTECT study is an observational multicenter study. Patients with severe traumatic brain injury, treated by Dutch Helicopter Emergency Medical Services between February 2012 and December 2017, were included. Follow-up continued for 1 year after inclusion. End-tidal CO2 levels were measured during prehospital care and their association with 30-day mortality was analyzed with multivariable logistic regression. Results: A total of 1776 patients were eligible for analysis. An L-shaped association between end-tidal CO2 levels and 30-day mortality was observed (p = 0.01), with a sharp increase in mortality with values below 35 mmHg. End-tidal CO2 values between 35 and 45 mmHg were associated with better survival rates compared to < 35 mmHg. No association between hypercapnia and mortality was observed. The odds ratio for the association between hypocapnia (< 35 mmHg) and mortality was 1.89 (95% CI 1.53–2.34, p < 0.001) and for hypercapnia (≥ 45 mmHg) 0.83 (0.62–1.11, p = 0.212). Conclusion: A safe zone of 35–45 mmHg for end-tidal CO2 guidance seems reasonable during prehospital care. Particularly, end-tidal partial pressures of less than 35 mmHg were associated with a significantly increased mortality.</p
Epidemiology, Prehospital Characteristics and Outcomes of Severe Traumatic Brain Injury in The Netherlands:The BRAIN-PROTECT Study
Objective: A thorough understanding of the epidemiology, patient characteristics, trauma mechanisms, and current outcomes among patients with severe traumatic brain injury (TBI) is important as it may inform potential strategies to improve prehospital emergency care. The aim of this study is to describe the prehospital epidemiology, characteristics and outcome of (suspected) severe TBI in the Netherlands. Methods: The BRAIN-PROTECT study is a prospective observational study on prehospital management of patients with severe TBI in the Netherlands. The study population comprised all consecutive patients with clinical suspicion of TBI and a prehospital GCS score ≤ 8, who were managed by one of the 4 Helicopter Emergency Medical Services (HEMS). Patients were followed-up in 9 trauma centers until 1 year after injury. Planned sub-analyses were performed for patients with “confirmed” and “isolated” TBI. Results: Data from 2,589 patients, of whom 2,117 (81.8%) were transferred to a participating trauma center, were analyzed. The incidence rate of prehospitally suspected and confirmed severe TBI were 3.2 (95% CI: 3.1;3.4) and 2.7 (95% CI: 2.5;2.8) per 100,000 inhabitants per year, respectively. Median patient age was 46 years, 58.4% were involved in traffic crashes, of which 37.4% were bicycle related. 47.6% presented with an initial GCS of 3. The median time from HEMS dispatch to hospital arrival was 54 minutes. The overall 30-day mortality was 39.0% (95% CI: 36.8;41.2). Conclusion: This article summarizes the prehospital epidemiology, characteristics and outcome of severe TBI in the Netherlands, and highlights areas in which primary prevention and prehospital care can be improved
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