377 research outputs found
Recipes for bolometric corrections and Gaia luminosities of B-type stars: Application to an asteroseismic sample
We provide three statistical model prescriptions for the bolometric
corrections appropriate for B-type stars as a function of: 1) T_eff, 2) T_eff,
log g, and 3) T_eff, log g, [M/H]. These statistical models have been
calculated for 27 different filters, including those of the Gaia space mission,
and were derived based on two different grids of bolometric corrections
assuming LTE and LTE+NLTE, respectively. Previous such work has mainly been
limited to a single photometric passband without taking into account NLTE
effects on the bolometric corrections. Using these statistical models, we
calculate the luminosities of 34 slowly pulsating B-type (SPB) stars with
available spectroscopic parameters, to place them in the Hertzsprung-Russell
diagram and compare their position to the theoretical SPB instability strip. We
find that excluding NLTE effects has no significant impact on the derived
luminosities for the temperature range 11500-21000 K. We conclude that
spectroscopic parameters are needed in order to achieve meaningful luminosities
of B-type stars. The three prescriptions for the bolometric corrections are
valid for any galactic B-type star with effective temperatures and surface
gravities in the ranges 10000-30000 K and 2.5-4.5 dex, respectively, covering
regimes below the Eddington limit.Comment: 17 pages, 12 figures, accepted for publication in MNRA
Lederutdanning - hva lærer man egentlig? - Subjektivt opplevde læringseffekter av to lederutdanninger
Masteroppgave i samfunnsvitenskap - Universitetet i Nordland, 201
What asteroseismology can do for exoplanets
We describe three useful applications of asteroseismology in the context of
exoplanet science: (1) the detailed characterisation of exoplanet host stars;
(2) the measurement of stellar inclinations; and (3) the determination of
orbital eccentricity from transit duration making use of asteroseismic stellar
densities. We do so using the example system Kepler-410 (Van Eylen et al.
2014). This is one of the brightest (V = 9.4) Kepler exoplanet host stars,
containing a small (2.8 Rearth) transiting planet in a long orbit (17.8 days),
and one or more additional non-transiting planets as indicated by transit
timing variations. The validation of Kepler-410 (KOI-42) was complicated due to
the presence of a companion star, and the planetary nature of the system was
confirmed after analyzing a Spitzer transit observation as well as ground-based
follow-up observations.Comment: 4 pages, Proceedings of the CoRoT Symposium 3 / Kepler KASC-7 joint
meeting, Toulouse, 7-11 July 2014. To be published by EPJ Web of Conference
Asteroseismology of massive stars with the TESS mission: the runaway Beta Cep pulsator PHL 346 = HN Aqr
We report an analysis of the first known Beta Cep pulsator observed by the
TESS mission, the runaway star PHL 346 = HN Aqr. The star, previously known as
a singly-periodic pulsator, has at least 34 oscillation modes excited, 12 of
those in the g-mode domain and 22 p modes. Analysis of archival data implies
that the amplitude and frequency of the dominant mode and the stellar radial
velocity were variable over time. A binary nature would be inconsistent with
the inferred ejection velocity from the Galactic disc of 420 km/s, which is too
large to be survivable by a runaway binary system. A kinematic analysis of the
star results in an age constraint (23 +- 1 Myr) that can be imposed on
asteroseismic modelling and that can be used to remove degeneracies in the
modelling process. Our attempts to match the excitation of the observed
frequency spectrum resulted in pulsation models that were too young. Hence,
asteroseismic studies of runaway pulsators can become vital not only in tracing
the evolutionary history of such objects, but to understand the interior
structure of massive stars in general. TESS is now opening up these stars for
detailed asteroseismic investigation.Comment: accepted for ApJ
Haemodynamic consequences of changing bicarbonate and calcium concentrations in haemodialysis fluids
Background. In a previous study we demonstrated that mild metabolic alkalosis resulting from standard bicarbonate haemodialysis induces hypotension. In this study, we have further investigated the changes in systemic haemodynamics induced by bicarbonate and calcium, using non-invasive procedures
A self-consistent quantum master equation approach to molecular transport
We propose a self-consistent generalized quantum master equation (GQME) to
describe electron transport through molecular junctions. In a previous study
[M.Esposito and M.Galperin. Phys. Rev. B 79, 205303 (2009)], we derived a
time-nonlocal GQME to cure the lack of broadening effects in Redfield theory.
To do so, the free evolution used in the Born-Markov approximation to close the
Redfield equation was replaced by a standard Redfield evolution. In the present
paper, we propose a backward Redfield evolution leading to a time-local GQME
which allows for a self-consistent procedure of the GQME generator. This
approach is approximate but properly reproduces the nonequilibrium steady state
density matrix and the currents of an exactly solvable model. The approach is
less accurate for higher moments such as the noise.Comment: 9 pages, 4 figure
Weighing stars from birth to death: mass determination methods across the HRD
The mass of a star is the most fundamental parameter for its structure,
evolution, and final fate. It is particularly important for any kind of stellar
archaeology and characterization of exoplanets. There exists a variety of
methods in astronomy to estimate or determine it. In this review we present a
significant number of such methods, beginning with the most direct and
model-independent approach using detached eclipsing binaries. We then move to
more indirect and model-dependent methods, such as the quite commonly used
isochrone or stellar track fitting. The arrival of quantitative
asteroseismology has opened a completely new approach to determine stellar
masses and to complement and improve the accuracy of other methods. We include
methods for different evolutionary stages, from the pre-main sequence to
evolved (super)giants and final remnants. For all methods uncertainties and
restrictions will be discussed. We provide lists of altogether more than 200
benchmark stars with relative mass accuracies between for the
covered mass range of M\in [0.1,16]\,\msun, of which are stars burning
hydrogen in their core and the other covering all other evolved stages.
We close with a recommendation how to combine various methods to arrive at a
"mass-ladder" for stars.Comment: Invited review article for The Astronomy and Astrophysics Review. 146
pages, 16 figures, 11 tables. Accepted version by the Journal. It includes
summary figure of accuracy/precision of methods for mass ranges and summary
table for individual method
Weighing stars from birth to death : mass determination methods across the HRD
Funding: C.A., J.S.G.M., and M.G.P. received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 670519: MAMSIE). N.B. gratefully acknowledge financial support from the Royal Society (University Research Fellowships) and from the European Research Council (ERC-CoG-646928, Multi-Pop).The mass of a star is the most fundamental parameter for its structure, evolution, and final fate. It is particularly important for any kind of stellar archaeology and characterization of exoplanets. There exist a variety of methods in astronomy to estimate or determine it. In this review we present a significant number of such methods, beginning with the most direct and model-independent approach using detached eclipsing binaries. We then move to more indirect and model-dependent methods, such as the quite commonly used isochrone or stellar track fitting. The arrival of quantitative asteroseismology has opened a completely new approach to determine stellar masses and to complement and improve the accuracy of other methods. We include methods for different evolutionary stages, from the pre-main sequence to evolved (super)giants and final remnants. For all methods uncertainties and restrictions will be discussed. We provide lists of altogether more than 200 benchmark stars with relative mass accuracies between [0.3 ,2 ]% for the covered mass range of M ∈[0.1 ,16 ] M⊙ , 75 % of which are stars burning hydrogen in their core and the other 25 % covering all other evolved stages. We close with a recommendation how to combine various methods to arrive at a "mass-ladder" for stars.PostprintPeer reviewe
Genetics of Type A Behavior in Two European Countries: Evidence for Sibling Interaction
Young male twins in The Netherlands and England completed the Jenkins Activity Survey (Dutch and English versions, respectively), a measure of Type A behavior. Separate model fitting analysis revealed a similar pattern of variance estimates and associated goodness of fit across the two countries. The data were then analyzed concurrently, with a scalar parameter included to account for differences in variance due to the disparity of the measurement scales. A model including additive genetic and individual environmental effects gave a good explanation to the data. The heritability estimate was 0.28. Models of social interaction and dominance explained the data even better, the former being preferred. The twins' parents were included in the analysis to examine population variation for Type A behavior intergenerationally. There was evidence for individual environmental experiences having a greater influence on Type A behavior in the older generation. © 1991 Plenum Publishing Corporation
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