688 research outputs found
The first orbital solution for the massive colliding-wind binary HD93162 (=WR25)
Since the discovery, with the EINSTEIN satellite, of strong X-ray emission
associated with HD93162 (=WR25), this object has been predicted to be a
colliding-wind binary system. However, radial-velocity variations that would
prove the suspected binary nature have yet to be found. We spectroscopically
monitored this object to investigate its possible variability to address this
discordance. We compiled the largest available radial-velocity data set for
this star to look for variations that might be due to binary motion. We derived
radial velocities from spectroscopic data acquired mainly between 1994 and
2006, and searched these radial velocities for periodicities using different
numerical methods. For the first time, periodic radial-velocity variations are
detected. Our analysis definitively shows that the Wolf-Rayet star WR25 is an
eccentric binary system with a probable period of about 208 days.Comment: 7 pages, 4 figures, accepted by A+
Evidence of magnetic field decay in massive main-sequence stars
A significant fraction of massive main-sequence stars show strong,
large-scale magnetic fields. The origin of these fields, their lifetimes, and
their role in shaping the characteristics and evolution of massive stars are
currently not well understood. We compile a catalogue of 389 massive
main-sequence stars, 61 of which are magnetic, and derive their fundamental
parameters and ages. The two samples contain stars brighter than magnitude 9 in
the V band and range in mass between 5 and 100 Msun. We find that the
fractional main-sequence age distribution of all considered stars follows what
is expected for a magnitude limited sample, while that of magnetic stars shows
a clear decrease towards the end of the main sequence. This dearth of old
magnetic stars is independent of the choice of adopted stellar evolution
tracks, and appears to become more prominent when considering only the most
massive stars. We show that the decreasing trend in the distribution is
significantly stronger than expected from magnetic flux conservation. We also
find that binary rejuvenation and magnetic suppression of core convection are
unlikely to be responsible for the observed lack of older magnetic massive
stars, and conclude that its most probable cause is the decay of the magnetic
field, over a time span longer than the stellar lifetime for the lowest
considered masses, and shorter for the highest masses. We then investigate the
spin-down ages of the slowly rotating magnetic massive stars and find them to
exceed the stellar ages by far in many cases. The high fraction of very slowly
rotating magnetic stars thus provides an independent argument for a decay of
the magnetic fields.Comment: Accepted for publication on A&A; 9 pages, 8 figure
The VLT-FLAMES Tarantula Survey. VII. A low velocity dispersion for the young massive cluster R136
Detailed studies of resolved young massive star clusters are necessary to
determine their dynamical state and evaluate the importance of gas expulsion
and early cluster evolution. In an effort to gain insight into the dynamical
state of the young massive cluster R136 and obtain the first measurement of its
velocity dispersion, we analyse multi-epoch spectroscopic data of the inner
regions of 30 Doradus in the Large Magellanic Cloud (LMC) obtained as part of
the VLT-FLAMES Tarantula Survey. Following a quantitative assessment of the
variability, we use the radial velocities of non-variable sources to place an
upper limit of 6 km/s on the line-of-sight velocity dispersion of stars within
a projected distance of 5 pc from the centre of the cluster. After accounting
for the contributions of undetected binaries and measurement errors through
Monte Carlo simulations, we conclude that the true velocity dispersion is
likely between 4 and 5 km/s given a range of standard assumptions about the
binary distribution. This result is consistent with what is expected if the
cluster is in virial equilibrium, suggesting that gas expulsion has not altered
its dynamics. We find that the velocity dispersion would be ~25 km/s if
binaries were not identified and rejected, confirming the importance of the
multi-epoch strategy and the risk of interpreting velocity dispersion
measurements of unresolved extragalactic young massive clusters.Comment: 18 pages, 7 figures, accepted by A&
The BinaMIcS project: understanding the origin of magnetic fields in massive stars through close binary systems
It is now well established that a fraction of the massive (M>8 Msun) star
population hosts strong, organised magnetic fields, most likely of fossil
origin. The details of the generation and evolution of these fields are still
poorly understood. The BinaMIcS project takes an important step towards the
understanding of the interplay between binarity and magnetism during the
stellar formation and evolution, and in particular the genesis of fossil
fields, by studying the magnetic properties of close binary systems. The
components of such systems are most likely formed together, at the same time
and in the same environment, and can therefore help us to disentangle the role
of initial conditions on the magnetic properties of the massive stars from
other competing effects such as age or rotation. We present here the main
scientific objectives of the BinaMIcS project, as well as preliminary results
from the first year of observations from the associated ESPaDOnS and Narval
spectropolarimetric surveys.Comment: To appear in New Windows on Massive Stars, proceedings of the IAU
Symposium 30
The VLT-FLAMES Tarantula Survey XXI. Stellar spin rates of O-type spectroscopic binaries
The initial distribution of spin rates of massive stars is a fingerprint of
their elusive formation process. It also sets a key initial condition for
stellar evolution and is thus an important ingredient in stellar population
synthesis. So far, most studies have focused on single stars. Most O stars are
however found in multiple systems. By establishing the spin-rate distribution
of a sizeable sample of O-type spectroscopic binaries and by comparing the
distributions of binary sub-populations with one another as well as with that
of presumed single stars in the same region, we aim to constrain the initial
spin distribution of O stars in binaries, and to identify signatures of the
physical mechanisms that affect the evolution of the massive stars spin rates.
We use ground-based optical spectroscopy obtained in the framework of the
VLT-FLAMES Tarantula Survey (VFTS) to establish the projected equatorial
rotational velocities (\vrot) for components of 114 spectroscopic binaries in
30 Doradus. The \vrot\ values are derived from the full-width at half-maximum
(FWHM) of a set of spectral lines, using a FWHM vs. \vrot\ calibration that we
derive based on previous line analysis methods applied to single O-type stars
in the VFTS sample. The overall \vrot\ distribution of the primary stars
resembles that of single O-type stars in the VFTS, featuring a low-velocity
peak (at \vrot < 200 kms) and a shoulder at intermediate velocities (200 <
\vrot < 300 kms). The distributions of binaries and single stars however
differ in two ways. First, the main peak at \vrot \sim100 kms is broader and
slightly shifted toward higher spin rates in the binary distribution compared
to that of the presumed-single stars. Second, the \vrot distribution of
primaries lacks a significant population of stars spinning faster than 300 kms
while such a population is clearly present in the single star sample.Comment: 16 pages, 16 figures, paper accepted in Astronomy & Astrophysic
The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud: spectroscopy, orbital analysis, formation, and evolution
Massive Wolf-Rayet (WR) stars dominate the radiative and mechanical energy
budget of galaxies and probe a critical phase in the evolution of massive stars
prior to core-collapse. It is not known whether core He-burning WR stars
(classical WR, cWR) form predominantly through wind-stripping (w-WR) or binary
stripping (b-WR). With spectroscopy of WR binaries so-far largely avoided due
to its complexity, our study focuses on the 44 WR binaries / binary candidates
of the Large Magellanic Cloud (LMC, metallicity Z~0.5 Zsun), identified on the
basis of radial velocity variations, composite spectra, or high X-ray
luminosities. Relying on a diverse spectroscopic database, we aim to derive the
physical and orbital parameters of our targets, confronting evolution models of
evolved massive stars at sub-solar metallicity, and constraining the impact of
binary interaction in forming them. Spectroscopy is performed using the Potsdam
Wolf-Rayet (PoWR) code and cross-correlation techniques. Disentanglement is
performed using the code Spectangular or the shift-and-add algorithm.
Evolutionary status is interpreted using the Binary Population and Spectral
Synthesis (BPASS) code, exploring binary interaction and chemically-homogeneous
evolution.
No obvious dichotomy in the locations of apparently-single and binary WN
stars on the Hertzsprung-Russell diagram is apparent. According to commonly
used stellar evolution models (BPASS, Geneva), most apparently-single WN stars
could not have formed as single stars, implying that they were stripped by an
undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing
(e.g., during the red supergiant phase) are strongly underestimated in standard
stellar evolution models.Comment: accepted to A&A on 10.05.2019; 69 pages (25 main paper + 44
appendix); Corrigendum: Shenar et al. 2020, A&A, 641, 2: An unfortunate typo
in the implementation of the "transformed radius" caused errors of up to
~0.5dex in the derived mass-loss rates. This has now been correcte
The VLT-FLAMES Tarantula Survey XV. VFTS 822: A candidate Herbig B[e] star at low metallicity
We report the discovery of the B[e] star VFTS 822 in the 30 Doradus star-forming region of the Large Magellanic Cloud, classified by optical spectroscopy from the VLT-FLAMES Tarantula Survey and complementary infrared photometry. VFTS 822 is a relatively low-luminosity (log L = 4.04 ± 0.25 L⊙) B8[e] star. In this Letter, we evaluate the evolutionary status of VFTS 822 and discuss its
candidacy as a Herbig B[e] star. If the object is indeed in the pre-main sequence phase, it would present an exciting opportunity to
spectroscopically measure mass accretion rates at low metallicity, to probe the effect of metallicity on accretion rates
Presenilin-1 processing of ErbB4 in fetal type II cells is necessary for control of fetal lung maturation
AbstractMaturation of pulmonary fetal type II cells to initiate adequate surfactant production is crucial for postnatal respiratory function. Little is known about specific mechanisms of signal transduction controlling type II cell maturation. The ErbB4 receptor and its ligand neuregulin (NRG) are critical for lung development. ErbB4 is cleaved at the cell membrane by the γ-secretase enzyme complex whose active component is either presenilin-1 (PSEN-1) or presenilin-2. ErbB4 cleavage releases the 80kDa intracellular domain (4ICD), which associates with chaperone proteins such as YAP (Yes-associated protein) and translocates to the nucleus to regulate gene expression. We hypothesized that PSEN-1 and YAP have a development-specific expression in fetal type II cells and are important for ErbB4 signaling in surfactant production. In primary fetal mouse E16, E17, and E18 type II cells, PSEN-1 and YAP expression increased at E17 and E18 over E16. Subcellular fractionation showed a strong cytosolic and a weaker membrane location of both PSEN-1 and YAP. This was enhanced by NRG stimulation. Co-immunoprecipitations showed ErbB4 associated separately with PSEN-1 and with YAP. Their association, phosphorylation, and co-localization were induced by NRG. Confocal immunofluorescence and nuclear fractionation confirmed these associations in a time-dependent manner after NRG stimulation. Primary ErbB4-deleted E17 type II cells were transfected with a mutant ErbB4 lacking the γ-secretase binding site. When compared to transfection with wild-type ErbB4, the stimulatory effect of NRG on surfactant protein mRNA expression was lost. We conclude that PSEN-1 and YAP have crucial roles in ErbB4 signal transduction during type II cell maturation
The VLT-FLAMES Tarantula Survey XVII. Physical and wind properties of massive stars at the top of the main sequence
The evolution and fate of very massive stars (VMS) is tightly connected to
their mass-loss properties. Their initial and final masses differ significantly
as a result of mass loss. VMS have strong stellar winds and extremely high
ionising fluxes, which are thought to be critical sources of both mechanical
and radiative feedback in giant Hii regions. However, how VMS mass-loss
properties change during stellar evolution is poorly understood. In the
framework of the VLT-Flames Tarantula Survey (VFTS), we explore the mass-loss
transition region from optically thin O to denser WNh star winds, thereby
testing theoretical predictions. To this purpose we select 62 O, Of, Of/WN, and
WNh stars, an unprecedented sample of stars with the highest masses and
luminosities known. We perform a spectral analysis of optical VFTS as well as
near-infrared VLT/SINFONI data using the non-LTE radiative transfer code CMFGEN
to obtain stellar and wind parameters. For the first time, we observationally
resolve the transition between optically thin O and optically thick WNh star
winds. Our results suggest the existence of a kink between both mass-loss
regimes, in agreement with recent MC simulations. For the optically thick
regime, we confirm the steep dependence on the Eddington factor from previous
theoretical and observational studies. The transition occurs on the MS near a
luminosity of 10^6.1Lsun, or a mass of 80...90Msun. Above this limit, we find
that - even when accounting for moderate wind clumping (with f = 0.1) - wind
mass-loss rates are enhanced with respect to standard prescriptions currently
adopted in stellar evolution calculations. We also show that this results in
substantial helium surface enrichment. Based on our spectroscopic analyses, we
are able to provide the most accurate ionising fluxes for VMS known to date,
confirming the pivotal role of VMS in ionising and shaping their environments.Comment: Accepted for publication in A&A, 19 pages, 14 figures, 6 tables, (74
pages appendix, 68 figures, 4 tables
Applying Patient-Reported Outcome Methodology to Capture Patient-Reported Health Data: Report From an NIH Collaboratory Roundtable
Patient-reported health data provide information for pragmatic clinical trials that may not be readily available from electronic health records or administrative claims data. In this report, we present key considerations for collecting patient-reported health information in pragmatic clinical trials, which are informed by best practices from patient-reported outcome research. We focus on question design and administration via electronic data collection platforms with respect to 3 types of patient-reported health data: medication use, utilization of health care services, and comorbid conditions. We summarize key scientific literature on the accuracy of these patient-reported data compared with electronic health record data. We discuss question design in detail, specifically defining the concept to be measured, patient understanding of the concept, recall periods of the question, and patient willingness to report. In addition, we discuss approaches for question administration and data collection platforms, which are key aspects of successful patient-reported data collection
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