253 research outputs found
The properties of dynamically ejected runaway and hyper-runaway stars
Runaway stars are stars observed to have large peculiar velocities. Two
mechanisms are thought to contribute to the ejection of runaway stars, both
involve binarity (or higher multiplicity). In the binary supernova scenario a
runaway star receives its velocity when its binary massive companion explodes
as a supernova (SN). In the alternative dynamical ejection scenario, runaway
stars are formed through gravitational interactions between stars and binaries
in dense, compact clusters or cluster cores. Here we study the ejection
scenario. We make use of extensive N-body simulations of massive clusters, as
well as analytic arguments, in order to to characterize the expected ejection
velocity distribution of runaways stars. We find the ejection velocity
distribution of the fastest runaways (>~80 km s^-1) depends on the binary
distribution in the cluster, consistent with our analytic toy model, whereas
the distribution of lower velocity runaways appears independent of the binaries
properties. For a realistic log constant distribution of binary separations, we
find the velocity distribution to follow a simple power law; Gamma(v) goes like
v^(-8/3) for the high velocity runaways and v^(-3/2) for the low velocity ones.
We calculate the total expected ejection rates of runaway stars from our
simulated massive clusters and explore their mass function and their binarity.
The mass function of runaway stars is biased towards high masses, and depends
strongly on their velocity. The binarity of runaways is a decreasing function
of their ejection velocity, with no binaries expected to be ejected with v>150
km s^-1. We also find that hyper-runaways with velocities of hundreds of km
s^-1 can be dynamically ejected from stellar clusters, but only at very low
rates, which cannot account for a significant fraction of the observed
population of hyper-velocity stars in the Galactic halo.Comment: Now matching published ApJ versio
HD 69686: A Mysterious High Velocity B Star
We report on the discovery of a high velocity B star, HD 69686. We estimate
its space velocity, distance, surface temperature, gravity, and age. With these
data, we are able to reconstruct the trajectory of the star and to trace it
back to its birthplace. We use evolutionary tracks for single stars to estimate
that HD 69686 was born 73 Myr ago in the outer part of our Galaxy (
kpc) at a position well below the Galactic plane ( kpc), a very
unusual birthplace for a B star. Along the star's projected path in the sky, we
also find about 12 other stars having similar proper motions, and their
photometry data suggest that they are located at the same distance as HD 69686
and probably have the same age. We speculate on the origin of this group by
star formation in a high velocity cloud or as a Galactic merger fragment.Comment: 28 pages, 6 figures, accepted for publication in Ap
Electrophysiological findings during re-do procedures after single-shot pulmonary vein isolation for atrial fibrillation with pulsed field ablation
Background: Pulsed field ablation (PFA) is a novel ablation technology recently adopted in the treatment of atrial fibrillation (AF). Currently, little is known about the durability of PFA ablation lesions. Methods: We investigated patients who underwent redo-ablation due to recurrent AF/atrial-flutter or tachycardia (AFL/AT) following PVI with PFA. We report electrophysiological findings and ablation strategy during redo-ablation. Results: Of 447 patients undergoing index PVI with PFA, 14 patients (age: 61.9±10.8 years; 7 (50.0%) males; left atrial volume index (n=10): 39.4±14.6 mL/m2) were referred for redo-ablation. Initial indication was paroxysmal-AF in 7 patients, persistent-AF in 6 and long-standing-persistent-AF in one patient. Mean time-to-recurrence was 4.9±1.9 months. Three patients received additional posterior-wall-isolation during index PFA. Twelve (85.7%) patients suffered AF recurrence and 5/12 had concomitant AFL. In the remaining 2 patients, one had a (box-dependent) AFL, and one had an atypical AT. No patients had all PVs reconnected. Reconnection in zero, one, two or three PVs was found in 35.7%, 21.4%, 14.3%, and 28.6% of patients, respectively. All 7 patients with zero or one reconnection with AF recurrence received additional/repeat posterior-wall-isolation during re-ablation, while in the others, PVs were re-isolated. Patients with only AFL/AT had no reconnection of PVs, and the substrate was successfully ablated. Conclusions: Durable PVI (all PV’s isolated) was observed in over one-third of patients at re-do. The predominant recurrent arrhythmia following PVI-only was AF. Concomitant (35.7%) or isolated (14.3%) AFL/AT recurrence was observed in 50% of patients.</p
Heated Disc Stars in the Stellar Halo
Minor accretion events with mass ratio M_sat : M_host ~ 1:10 are common in
the context of LCDM cosmology. We use high-resolution simulations of
Galaxy-analogue systems to show that these mergers can dynamically eject disk
stars into a diffuse light component that resembles a stellar halo both
spatially and kinematically. For a variety of orbital configurations, we find
that ~3-5e8 M_sun of primary stellar disk material is ejected to a distance
larger than 5 kpc above the galactic plane. This ejected contribution is
similar to the mass contributed by the tidal disruption of the satellite galaxy
itself, though it is less extended. If we restrict our analysis to the
approximate solar neighborhood in the disk plane, we find that ~1% of the
initial disk stars in that region would be classified kinematically as halo
stars. Our results suggest that the inner parts of galactic stellar halos
contain ancient disk stars and that these stars may have been liberated in the
very same events that delivered material to the outer stellar halo.Comment: 9 pages, 5 figures; MNRAS accepte
Long-term outcomes of the pentaspline pulsed field ablation catheter for the treatment of paroxysmal atrial fibrillation: Results of the prospective, multicenter FARA-Freedom Study.
INTRODUCTION/OBJECTIVES
Pulmonary vein isolation (PVI) is well-established strategy for the treatment of paroxysmal atrial fibrillation (PAF). Despite randomized controlled trials and real-world data showing the promise of pulsed-field ablation (PFA) for this treatment, long term efficacy and safety data demonstrating single procedure outcomes off antiarrhythmic drugs remain limited. The aim of the FARA-Freedom Study was to evaluate long-term efficacy and safety of PFA using the pentaspline catheter for PAF.
METHODS
FARA-Freedom, a prospective, non-randomized, multicenter study, enrolled patients with PAF undergoing de novo PVI with PFA, which were followed for 12 months with weekly transtelephonic monitoring (TTMs) and 72-hr Holter ECG at 6 and 12 months. The primary safety endpoint was a composite of device- or procedure-related serious adverse events out to 7 days post-ablation and PV stenosis or atrioesophageal (AE) fistula out to 12 months. Treatment success is a composite of acute PVI and chronic success; which includes freedom from any documented atrial tachyarrhythmia longer than 30 s, use of antiarrhythmic drugs or cardioversion after a 3-month blanking period, or use of amiodarone or repeat ablation at any time.
RESULTS
The study enrolled 179 PAF patients (62 ± 10 yr, 39% female) at 13 centers. At index procedure, all PVs were successfully isolated with the pentaspline PFA catheter. Procedure and left atrial dwell times, with a 20 min waiting period, were 71.9 ± 17.6 and 41.0 ± 13.3 min, respectively. Fluoroscopy time was 11.5 ± 7.4 min. Notably, monitoring compliance was high with 88.4% and 90.3% with weekly event and 72-hour Holter monitors, respectively. Freedom from composite primary effectiveness endpoint was 66.6%, 41 patients had atrial tachyarrhythmia recurrence: mostly recurrent atrial fibrillation (31 patients). The composite safety endpoint occurred in 2 patients (1.1%), 1 tamponade and 1 TIA. There was no coronary spasm, PV stenosis, or AE fistula. There were 4 cases of transient phrenic nerve palsy, but all resolved during index procedure.
CONCLUSIONS
In this prospective, non-randomized, multicenter study, PVI using a pentaspline PFA catheter was effective in treating PAF patients despite rigorous endpoint definitions and high monitoring compliance and demonstrated favorable safety
Runaway stars as progenitors of supernovae and gamma-ray bursts
When a core collapse supernova occurs in a binary system, the surviving star
as well as the compact remnant emerging from the SN, may reach a substantial
space velocity. With binary population synthesis modelling at solar and one
fifth of solar metallicity, we predict the velocities of such runaway stars or
binaries. We compile predictions for runaway OB stars, red supergiants and
Wolf-Rayet stars. For those stars or binaries which undergo a second stellar
explosion we compute their further evolution and the distance travelled until a
Type II or Type Ibc SN or a long or short gamma-ray burst occurs. We find our
predicted population of OB runaway stars broadly matches the observed
population of stars but, to match the fastest observed WR runaway stars, we
require that black holes receive an asymmetric kick upon formation. We find
that at solar metallicity Type Ic SN progenitors travel shorter distances than
the progenitors of other SN types because they are typically more massive and
thus have shorter lifetimes. Those of Type IIP SN can fly farthest about 48 pc
on average at solar metallicity. In considering the consequences of assuming
that the progenitors of long GRBs are spun-up secondary stars that experience
quasi-homogeneous evolution, we find that such evolution has a dramatic effect
on the population of runaway WR stars and that some 30 per cent of GRBs could
occur a hundred parsecs or more from their initial positions. We also consider
mergers of double compact object binaries consisting of neutron stars and/or
black holes. We find the most common type of visible mergers are neutron
star--black hole mergers that are roughly ten times more common than neutron
star--neutron star mergers. We also find that there may be a population of
low-velocity neutron stars that are ejected from a binary rather than by their
own natal kick.Comment: Accepted for publication in MNRAS, 23 pages, 17 figures and 11
tables. Abstract was editted to fit within arXiv.org submission requirement
A catalogue of young runaway Hipparcos stars within 3kpc from the Sun
Traditionally runaway stars are O and B type stars with large peculiar
velocities.We want to extend this definition to young stars (up to ~50 Myr) of
any spectral type and identify those present in the Hipparcos catalogue
applying different selection criteria such as peculiar space velocities or
peculiar one-dimensional velocities. Runaway stars are important to study the
evolution of multiple star systems or star clusters as well as to identify
origins of neutron stars. We compile distances, proper motions, spectral types,
luminosity classes, V magnitudes and B-V colours and utilise evolutionary
models from different authors to obtain star ages and study a sample of 7663
young Hipparcos stars within 3 kpc from the Sun. Radial velocities are obtained
from the literature. We investigate the distributions of the peculiar spatial
velocity, the peculiar radial velocity as well as the peculiar tangential
velocity and its one-dimensional components and obtain runaway star
probabilities for each star in the sample. In addition, we look for stars that
are situated outside any OB association or OB cluster and the Galactic plane as
well as stars of which the velocity vector points away from the median velocity
vector of neighbouring stars or the surrounding local OB association/ cluster
although the absolute velocity might be small. We find a total of 2547 runaway
star candidates (with a contamination of normal Population I stars of 20 per
cent at most). Thus, after subtraction of those 20 per cent, the runaway
frequency among young stars is about 27 per cent. We compile a catalogue of
runaway stars which will be available via VizieR.Comment: 12 pages, 8 figures, 7 tables, accepted for publication in MNRAS old
version replaced due to change of the title after journal proof-readin
Abundance analysis of prime B-type targets for asteroseismology I. Nitrogen excess in slowly-rotating beta Cephei stars
We present the results of a detailed NLTE abundance study of nine beta Cephei
stars, all of them being prime targets for theoretical modelling: gamma Peg,
delta Cet, nu Eri, beta CMa, xi1 CMa, V836 Cen, V2052 Oph, beta Cep and DD (12)
Lac. The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S
and Fe. Our abundance analysis is based on a large number of time-resolved,
high-resolution optical spectra covering in most cases the entire oscillation
cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four
stars, three of which have severe constraints on their equatorial rotational
velocity, \Omega R, from seismic or line-profile variation studies: beta Cep
(\Omega R~26 km/s), V2052 Oph (\Omega R~56 km/s), delta Cet (\Omega R < 28
km/s) and xi1 CMa (\Omega R sin i < 10 km/s). The existence of core-processed
material at the surface of such largely unevolved, slowly-rotating objects is
not predicted by current evolutionary models including rotation. We draw
attention to the fact that three stars in this subsample have a detected
magnetic field and briefly discuss recent theoretical work pointing to the
occurrence of diffusion effects in beta Cephei stars possibly capable of
altering the nitrogen surface abundance. On the other hand, the abundances of
all the other chemical elements considered are, within the errors,
indistinguishable from the values found for OB dwarfs in the solar
neighbourhood. Despite the mild nitrogen excess observed in some objects, we
thus find no evidence for a significantly higher photospheric metal content in
the studied beta Cephei stars compared to non-pulsating B-type stars of similar
characteristics.Comment: Accepted for publication in A&A, 21 pages, 7 figure
Inter- and Intraobserver Variation in the Assessment of Preoperative Colostograms in Male Anorectal Malformations: An ARM-Net Consortium Survey
Aim: Male patients with anorectal malformations (ARM) are classified according to
presence and level of the recto-urinary fistula. This is traditionally established by a
preoperative high-pressure distal colostogram that may be variably interpreted by
different surgeons. The aim of this study was to evaluate the inter- and intraobserver
variation in the assessment by pediatric surgeons of preoperative colostograms with
respect to the level of the recto-urinary fistula.
Materials and Methods: Sixteen pediatric surgeons from 14 European centers
belonging to the ARM-Net Consortium twice scored 130 images of distal colostograms
taken in sagittal projection at a median age of 66 days of life (range: 4–1,106 days).
Surgeons were asked to classify the fistula in bulbar, prostatic, bladder-neck, no
fistula, and “unclear anatomy” example. Their assessments were compared with the
intraoperative findings (kappa) for two scoring rounds with an interval of 6 months
(intraobserver variation). Agreement among the surgeons’ scores (interobserver variation)
was also calculated using Krippendorff’s alpha. A kappa over 0.75 is considered
excellent, between 0.40 and 0.75 fair to good, and below 0.40 poor. Surgeons were
asked to score the images in “poor” and “good” quality and to provide their years of
experience in ARM treatment.
Results: Agreement between the image-based rating of surgeons and the intraoperative
findings ranges from 0.06 to 0.45 (mean 0.31). Interobserver variation is higher
(Krippendorff’s alpha between 0.40 and 0.45). Years of experience in ARM treatment
does not seem to influence the scoring. The mean intraobserver variation between
the two rounds is 0.64. Overall, the quality of the images is considered poor. Images
categorized as having a good quality result in a statistically significant higher kappa
(mean: 0.36 and 0.37 in the first and second round, respectively) than in the group of
bad-quality images (mean: 0.25 and 0.23, respectively).
Conclusions: There is poor agreement among experienced pediatric colorectal
surgeons on preoperative colostograms. Techniques and analyses of images need to be
improved in order to generate a homogeneous series of patients and make comparison
of outcomes reliable
Women have less progression of paroxysmal atrial fibrillation:data from the RACE V study
BACKGROUND: Sex differences in atrial fibrillation (AF) are observed in terms of comorbidities, symptoms, therapies received, AF progression and cardiovascular complications.METHODS: We assessed the differences in prevalence and the determinants of AF progression, as well as the clinical characteristics and quality of life (QoL), between women and men with paroxysmal AF included in the RACE V (Reappraisal of Atrial Fibrillation: Interaction between hyperCoagulability, Electrical remodeling, and Vascular Destabilisation in the Progression of AF) study. At baseline, extensive phenotyping was done. To assess AF progression, implantable loop recorder (ILR) monitoring was used throughout follow-up. AF progression was defined as (1) progression to persistent or permanent AF or (2) progression of paroxysmal AF (>3% burden increase).RESULTS: 417 patients were included, 179 (43%) of whom were women. Women were older (median 67 years vs 63 years, p<0.001), less often had coronary artery disease (n=11 (6%) vs n=36 (16%), p=0.003), had more obesity (n=57 (32%) vs n=50 (21%), p=0.013), had less epicardial and pericardial fat (median 144 (interquartile range [IQR] 94-191) mL vs 199 (IQR 146-248) mL, p<0.001; and median 89 (ICQ 61-121) mL vs 105 (IQR 83-133) mL, p<0.001, respectively) and had more impaired left atrial function. The median follow-up was 2.2 (1.6-2.8) years. 51 of 417 patients (5.5% per year) showed AF progression (15/179 (8.4%) women and 36/238 (15.1%) men, p=0.032). Multivariable analysis showed tissue factor pathway inhibitor, N-terminal prohormone brain natriuretic peptide (NT-proBNP) and PR interval being associated with AF progression in women and factor XIIa:C1 esterase, NT-proBNP and proprotein convertase subtilisin/kexin type 9 in men. QoL was not different between sexes.CONCLUSION: Despite older age, the incidence of AF progression was lower in women. Parameters associated with AF progression varied in part between sexes, suggesting different underlying pathophysiological mechanisms.</p
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