94 research outputs found
The IACOB project VIII. Searching for empirical signatures of binarity in fast-rotating O-type stars
The empirical distribution of projected rotational velocities (vsini) in
massive O-type stars is characterized by a dominant slow velocity component and
a tail of fast rotators. Binary interaction has been proposed to play a
dominant role in the formation of this tail. We perform a complete and
homogeneous search for empirical signatures of binarity in a sample of 54
fast-rotating stars with the aim of evaluating this hypothesis. This working
sample has been extracted from a larger sample of 415 Galactic O-type stars
which covers the full range of vsini values. We use new and archival
multi-epoch spectra in order to detect spectroscopic binary systems. We
complement this information with Gaia proper motions and TESS photometric data
to aid in the identification of runaway stars and eclipsing binaries,
respectively. The identified fraction of single-lined spectroscopic binary
(SB1) systems and apparently single stars among the fast-rotating sample is
18% and 70%, respectively. When comparing these percentages with
those corresponding to the slow-rotating sample we find that our sample of fast
rotators is characterized by a slightly larger percentage of SB1 systems
(18% vs. 13%) and a considerably smaller fraction of clearly
detected SB2 systems (8% vs. 33%). Overall, there seems to be a clear deficit
of spectroscopic binaries (SB1+SB2) among fast-rotating O-type stars (26%
vs. 46%). On the contrary, the fraction of runaway stars is significantly
higher in the fast-rotating domain (33-50%) than among those stars with
vsini < 200 km/s. Lastly, almost 65% of the apparently single fast-rotating
stars are runaways. Our empirical results seem to be in good agreement with the
idea that the tail of fast-rotating O-type stars (with vsini > 200 km/s) is
mostly populated by post-interaction binary products.Comment: 33 pages, 16 figures, accepted for publication in "Astronomy and
Astrophysics
Photometric detection of internal gravity waves in upper main-sequence stars. II. Combined TESS photometry and high-resolution spectroscopy
Context. Massive stars are predicted to excite internal gravity waves (IGWs)
by turbulent core convection and from turbulent pressure fluctuations in their
near-surface layers. These IGWs are extremely efficient at transporting angular
momentum and chemical species within stellar interiors, but they remain largely
unconstrained observationally. Aims. We aim to characterise the photometric
detection of IGWs across a large number of O and early-B stars in the
Hertzsprung-Russell diagram, and explain the ubiquitous detection of stochastic
variability in the photospheres of massive stars. Methods. We combined
high-precision time-series photometry from the NASA Transiting Exoplanet Survey
Satellite with high-resolution ground-based spectroscopy of 70 stars with
spectral types O and B to probe the relationship between the photometric
signatures of IGWs and parameters such as spectroscopic mass, luminosity, and
macroturbulence. Results. A relationship is found between the location of a
star in the spectroscopic Hertzsprung-Russell diagram and the amplitudes and
frequencies of stochastic photometric variability in the light curves of
massive stars. Furthermore, the properties of the stochastic variability are
statistically correlated with macroturbulent velocity broadening in the
spectral lines of massive stars. Conclusions. The common ensemble morphology
for the stochastic low-frequency variability detected in space photometry and
its relationship to macroturbulence is strong evidence for IGWs in massive
stars, since these types of waves are unique in providing the dominant
tangential velocity field required to explain the observed spectroscopy.Comment: Accepted for publication in A&A. 10 pages and 5 figures (and an
additional 7 pages of appendix tables and figures). Resolution of appendix
figures have been downgraded to meet arXiv's maximum file size of 15Mb. This
version (2ver) is post A&A language editin
New β Cep pulsators discovered with K2 space photometry
Contains fulltext :
207549.pdf (publisher's version ) (Open Access
Reliability and correlation analysis of computed methods to convert conventional 2D radiological hindfoot measurements to 3D equivalents using weight bearing CT
A calibration point for stellar evolution from massive star asteroseismology
Massive stars are progenitors of supernovae, neutron stars and black holes.
During the hydrogen-core burning phase their convective cores are the prime
drivers of their evolution, but inferences of core masses are subject to
unconstrained boundary mixing processes. Moreover, uncalibrated transport
mechanisms can lead to strong envelope mixing and differential radial rotation.
Ascertaining the efficiency of the transport mechanisms is challenging because
of a lack of observational constraints. Here we deduce the convective core mass
and robustly demonstrate non-rigid radial rotation in a supernova progenitor,
the solar-mass hydrogen-burning star HD 192575, using
asteroseismology, TESS photometry, high-resolution spectroscopy, and Gaia
astrometry. We infer a convective core mass (
solar masses), and find the core to be rotating between 1.4 and 6.3 times
faster than the stellar envelope depending on the location of the rotational
shear layer. Our results deliver a robust inferred core mass of a massive star
using asteroseismology from space-based photometry. HD 192575 is a unique
anchor point for studying interior rotation and mixing processes, and thus also
angular momentum transport mechanisms inside massive stars.Comment: 41 pages, 5 figures, 1 table. Version comment: updated erroneous
affiliatio
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Metalloproteinases and their inhibitors—diagnostic and therapeutic opportunities in orthopedics
Matrix metalloproteinases (MMPs) and related enzymes (ADAMs, ADAMTS) and their inhibitors control matrix turnover and function. Recent advances in our understanding of musculoskeletal conditions such as tendinopathy, arthritis, Dupuytren's disease, degenerative disc disease, and bone and soft tissue healing suggest that MMPs have prominant roles. Importantly, MMPs are amenable to inhibition by cheap, safe, and widely available drugs such as the tetracycline antibiotics and the bisphosphonates. This indicates that these MMP inhibitors, if proven effective for any novel indication, may be quickly brought into clinical practice
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