ISSN 1783-3426
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Spectroscopy, MOST photometry, and
interferometry of MWC 314: is it an LBV or an interacting binary?
To
v∞ and beyond! The He I absorption variability across the 2014.6
periastron passage of η Carinae
The
CHARA Array resolves the long-period Wolf-Rayet binaries WR 137 and
WR 138
Stellar wind models of
subluminous hot stars
The X-ray
emission of the gamma Cassiopeiae stars
e-MERLIN
21cm constraints on the mass-loss rates of OB stars in Cyg
OB2
Tracing back the evolution of
the candidate LBV HD 168625
X-ray
emission from interacting massive binaries: a review of 15 years of
progress
X-ray and optical
spectroscopy of the massive young open cluster IC1805
G11.92-0.61
MM1: A Keplerian disc around a massive young proto-O star
The
nature of the light variability of magnetic Of?p star HD 191612
The
IACOB project: IV. New predictions for high-degree non-radial mode
instability domains in massive stars and connection with
macroturbulent broadening
The
IACOB project: III. New observational clues to understand
macroturbulent broadening in massive O- and B-type stars
Postdoc position in Sheffield: Massive
Stars in Starburst Galaxies
Postdoc
position in Theoretical Astrophysics
Research
Associate in Theoretical Stellar Astrophysics
2-yr
postdoctoral position on Massive Stars at IAC
The special issue of
Advances in Space Research ``X-rays from hot stars'' is
now
available on-line.
http://www.sciencedirect.com/science/journal/02731177/58/5
ALL PAPERS CAN BE DOWNLOADED FREE OF CHARGE UNTIL
SEPTEMBER 9, 2016
This special issue is aimed at
summarizing our current knowledge of X-ray
emission from hot
stars as well as at opening new avenues for investigation in
anticipation of the next generation of X-ray telescopes. In
this volume we
assembled a collection of review papers and
original contributions covering
the wide range of topics on
X-ray emission from hot stars. All interested
members of the
community were invited to contribute. Each submitted paper was
peer
reviewed by at least two anonymous referees, whom we would like to
thank
for their very important work. Please find below some
links to the individual
papers for a (time-limited) free
download:
http://authors.elsevier.com/a/1TPuE~6OiOeh2
http://authors.elsevier.com/a/1TPuE~6OiSQrP
http://authors.elsevier.com/a/1TPuE~6OiTavT
http://authors.elsevier.com/a/1TPuE~6OiOeuZ
http://authors.elsevier.com/a/1TPuE~6OiOeM9
http://authors.elsevier.com/a/1TPuE~6OiSQqf
http://authors.elsevier.com/a/1TPuE~6OiSQqr
Weblink:
http://www.sciencedirect.com/science/journal/02731177/58/5
Email:
lida@astro.physik.uni-potsdam.de
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Noel Richardson et al.
Universite de
Montreal
MWC 314 is a bright candidate luminous blue
variable (LBV) that resides in a fairly close binary system, with an
orbital period of 60.753 ± 0.003 d. We observed MWC 314 with a
combination of optical spectroscopy, broad-band ground- and
space-based photometry, as well as with long baseline, near-infrared
interferometry. We have revised the single-lined spectroscopic orbit
and explored the photometric variability. The orbital light curve
displays two minima each orbit that can be partially explained in
terms of the tidal distortion of the primary that occurs around the
time of periastron. The emission lines in the system are often
double-peaked and stationary in their kinematics, indicative of a
circumbinary disc. We find that the stellar wind or circumbinary disc
is partially resolved in the K'-band with the longest baselines of
the CHARA Array. From this analysis, we provide a simple, qualitative
model in an attempt to explain the observations. From the assumption
of Roche Lobe overflow and tidal synchronization at periastron, we
estimate the component masses to be M1 ≈ 5 M⊙ and M2 ≈ 15 M⊙,
which indicates a mass of the LBV that is extremely low. In addition
to the orbital modulation, we discovered two pulsational modes with
the MOST satellite. These modes are easily supported by a low-mass
hydrogen-poor star, but cannot be easily supported by a star with the
parameters of an LBV. The combination of these results provides
evidence that the primary star was likely never a normal LBV, but
rather is the product of binary interactions. As such, this system
presents opportunities for studying mass-transfer and binary
evolution with many observational techniques.
Reference:
2016, MNRAS, 455, 244
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1510.00324
Comments:
Email: noel.richardson@UToledo.edu
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Noel Richardson et al.
University of
Toledo
We have monitored the massive binary star η
Carinae with the CTIO/SMARTS 1.5~m telescope and CHIRON spectrograph
from the previous apastron passage of the system through the recent
2014.6 periastron passage. Our monitoring has resulted in a large,
homogeneous data set with an unprecedented time-sampling, spectral
resolving power, and signal-to-noise. This allowed us to investigate
temporal variability previously unexplored in the system and discover
a kinematic structure in the P Cygni absorption troughs of neutral
helium wind lines. The features observed occurred prior to the
periastron passage and are seen as we look through the trailing arm
of the wind-wind collision shock cone. We show that the bulk of the
variability is repeatable across the last five periastron passages,
and that the absorption occurs in the inner 230 AU of the system. In
addition, we found an additional, high-velocity absorption component
super-imposed on the P Cygni absorption troughs that has been
previously un-observed in these lines, but which bears resemblance to
the observations of the He~I λ10830 \AA\ feature across previous
cycles. Through a comparison of the current smoothed particle
hydrodynamical simulations, we show that the observed variations are
likely caused by instabilities in the wind-wind collision region in
our line-of-sight, coupled with stochastic variability related to
clumping in the winds.
Reference: MNRAS, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1606.03655
Comments:
Email: noel.richardson@UToledo.edu
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Noel Richardson et al.
University of
Toledo
We report on interferometric observations with the
CHARA Array of two classical Wolf-Rayet stars in suspected binary
systems, namely WR 137 and WR 138. In both cases, we resolve the
component stars to be separated by a few milliarcseconds. The data
were collected in the H-band, and provide a measure of the fractional
flux for both stars in each system. We find that the WR star is the
dominant H-band light source in both systems ($f_{\rm WR, 137} =
0.59\pm0.04$; $f_{\rm WR, 138} = 0.67\pm0.01$), which is confirmed
through both comparisons with estimated fundamental parameters for WR
stars and O dwarfs, as well as through spectral modeling of each
system. Our spectral modeling also provides fundamental parameters
for the stars and winds in these systems. The results on WR 138
provide evidence that it is a binary system which may have gone
through a previous mass-transfer episode to create the WR star. The
separation and position of the stars in the WR 137 system together
with previous results from the IOTA interferometer provides evidence
that the binary is seen nearly edge-on. The possible edge-on orbit of
WR 137 aligns well with the dust production site imaged by the Hubble
Space Telescope during a previous periastron passage, showing that
the dust production may be concentrated in the orbital
plane.
Reference: MNRAS, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1606.09586
Comments:
Email: noel.richardson@UToledo.edu
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J. Krticka, J. Kubat, I. Krtickova
Masaryk
University, Brno
Astronomical Institute, Ondrejov
Mass-loss
rate is one of the most important stellar parameters. We aim to
provide mass-loss rates as a function of subdwarf parameters and to
apply the formula for individual subdwarfs, to predict the wind
terminal velocities, to estimate the influence of the magnetic field
and X-ray ionization on the stellar wind, and to study the
interaction of subdwarf wind with mass loss from Be and cool
companions. We used our kinetic equilibrium (NLTE) wind models with
the radiative force determined from the radiative transfer equation
in the comoving frame (CMF) to predict the wind structure of
subluminous hot stars. Our models solve stationary hydrodynamical
equations, that is the equation of continuity, equation of motion,
and energy equation and predict basic wind parameters. We predicted
the wind mass-loss rate as a function of stellar parameters, namely
the stellar luminosity, effective temperature, and metallicity. The
derived wind parameters (mass-loss rates and terminal velocities)
agree with the values derived from the observations. The radiative
force is not able to accelerate the homogeneous wind for stars with
low effective temperatures and high surface gravities. We discussed
the properties of winds of individual subdwarfs. The X-ray
irradiation may inhibit the flow in binaries with compact components.
In binaries with Be components, the winds interact with the disk of
the Be star. Stellar winds exist in subluminous stars with low
gravities or high effective temperatures. Despite their low mass-loss
rates, they are detectable in the ultraviolet spectrum and cause
X-ray emission. Subdwarf stars may lose a significant part of their
mass during the evolution. The angular momentum loss in magnetic
subdwarfs with wind may explain their low rotational velocities.
Stellar winds are especially important in binaries, where they may be
accreted on a compact or cool companion.
Reference:
A&A, in press
Status: Manuscript has been
accepted
Weblink:
http://lanl.arxiv.org/abs/1607.04445
Comments:
Email: krticka@physics.muni.cz
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Myron A. Smith$^1$, Raimundo. Lopes de Oliveira$^2$, and
Christian Motch$^3$
1 - National Optical Astronomical
Observatory, USA, 2 - Universidad Fedeeralde Sergipe, Departamento de
F\'isica, Brazil - 3 - Observatoire Astronomique, Universit\'e de
Strasbourg,
Long considered as the "odd man out"
among X-ray emitting Be stars, gamma Cas (B0.5e\,IV) is now
recognized as the prototype of a class of stars that emit hard
thermal X-rays. Our classification differs from the historical use of
the term "gamma Cas stars" defined from optical properties
alone. The luminosity output of this class contributes significantly
to the hard X-ray production of massive stars in the Galaxy. The
gamma Cas stars have light curves showing variability on a few
broadly-defined timescales and spectra indicative of an optically
thin plasma consisting of one or more hot thermal components. By now
9--13 Galactic $\approx$B0-1.5e main sequence stars are judged to be
members or candidate members of the gamma Cas class. Conservative
criteria for this designation are for a $\approx$B0-1.5e III-V star
to have an X-ray luminosity of10$^{32}$--10$^{33}$ ergs\,s$^{-1}$, a
hot thermal spectrum containing the short wavelength Ly$\alpha$
Fe\,XXV and Fe\,XXVI lines and the fluorescence FeK feature all in
emission. If thermality cannot be demonstrated, for example from
either the presence of these Ly$\alpha$ lines or curvature of the
hard continuum; these are the gamma Cas {\it candidates.} We discuss
the history of the discovery of the complicated characteristics of
the variability in the optical, UV, and X-ray domains, leading to
suggestions for the physical cause of the production of hard X-rays.
These include scenarios in which matter from the Be star accretes
onto a degenerate secondary star and interactions between magnetic
fields on the Be star and its decretion disk. The greatest aid to the
choice of the causal mechanism is the temporal correlations of X-ray
light curves and spectra with diagnostics in the optical and UV
wavebands. We show why the magnetic star-disk interaction scenario is
the most tenable explanation for the creation of hard X-rays on these
stars.
Reference: Advances in Space Research, 58,
782-808, 2016
Status: Manuscript has been accepted
Weblink:
Comments:
Email:
myronmeister@gmail.com
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Jack Morford(1), Danielle Fenech(1), Raman Prinja(1),
Ronnie Blomme(2), Jeremy Yates(1)
1. Dept. of Physics
& Astronomy, University College London, Gower Street, London,
WC1E 6BT.
2. Royal Observatory of Belgium, Ringlaan 3, 1180
Brussel, Belgium
We present e-MERLIN 21 cm (L-band)
observations of single luminous OB stars in the Cygnus OB2
association, from the COBRaS Legacy programme. The radio observations
potentially offer the most straightforward, least model-dependent,
determinations of mass-loss rates, and can be used to help resolve
current discrepancies in mass-loss rates via clumped and structured
hot star winds. We report here that the 21 cm flux densities of O3 to
O6 supergiant and giant stars are less than ~70 microJy. These fluxes
may be translated into 'smooth' wind mass-loss upper limits of ~ 4.4
- 4.8 x 10^(-6) M_sol/yr for O3 supergiants and < 2.9 x 10^(-6)
M_sol/yr for B0 to B1 supergiants. The first ever resolved 21 cm
detections of the hypergiant (and LBV candidate) Cyg OB2 #12 are
discussed; for multiple observations separated by 14 days, we detect
a ~ 69% increase in its flux density. Our constraints on the upper
limits for the mass-loss rates of evolved OB stars in Cyg OB2 support
the model that the inner wind region close to the stellar surface
(where Halpha forms) is more clumped than the very extended geometric
region sampled by our radio observations.
Reference:
10.1093/mnras/stw1914
Status: Manuscript has been
accepted
Email: jmorford@star.ucl.ac.uk
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L. Mahy (1), D. Hutsemékers (1), P. Royer (2), C. Waelkens
(2)
(1): Institut d’Astrophysique et de
Géophysique, Université de Liège, Quartier Agora, Allée du 6
Août 19C, B-4000, Liège 1, Belgium
(2): Instituut voor
Sterrenkunde, KU Leuven, Celestijnenlaan 200D, Bus 2401, B-3001
Leuven, Belgium
Context. The luminous blue variable phase
is a crucial transitory phase that is not clearly understood in the
massive star evolution.
Aims. We have obtained far-infrared
Herschel/PACS imaging and spectroscopic observations of the nebula
surrounding the candidate LBV HD168625. By combining these data with
optical spectra of the central star, we want to constrain the
abundances in the nebula and in the star and compare them to trace
back the evolution of this object.
Methods. We use the CMFGEN
atmosphere code to determine the fundamental parameters and the CNO
abundances of the central star whilst the abundances of the nebula
are derived from the emission lines present in the Herschel/PACS
spectrum.
Results. The far-infrared images show a nebula
composed of an elliptical ring/torus of ejecta with a ESE-WNW axis
and of a second perpendicular bipolar structure composed of empty
caps/rings. We detect equatorial shells composed of dust and ionized
material with different sizes when observed at different wavelengths,
and bipolar caps more of less separated from the central star in
Halpha and mid-IR images. This complex global structure seems to show
two different inclinations: ~40° for the equatorial torus and ~60°
for the bipolar ejections. From the Herschel/PACS spectrum, we
determine nebular abundances of N/H = 4.1 +/- 0.8 x 10^-4 and C/H =
1.6^{+1.16}_{-0.35} x 10^-4, as well as a mass of ionized gas of 0.17
+/- 0.04 Msun and a neutral hydrogen mass of about 1.0 +/- 0.3 Msun
which dominates. Analysis of the central star reveals Teff = 14000
+/- 2000K, log g = 1.74 +/- 0.05 and log(L/Lsun) = 5.58 +/- 0.11. We
derive stellar CNO abundances of about N/H = 5.0 +/- 1.5 x 10^-4, C/H
= 1.4 +/- 0.5 x 10^-4 and O/H = 3.5 +/- 1.0 x 10^-4, not
significantly different from nebular abundances. All these
measurements taken together are compatible with the evolutionary
tracks of a star with an initial mass between 28 and 33 Msun and with
a critical rotational rate between 0.3 and 0.4 that has lost its
material during or just after the Blue Supergiant phase.
Reference:
14 pages, 16 figures, A&A, in press
Status: Manuscript
has been accepted
Weblink:
http://arxiv.org/abs/1608.01087
Comments:
Email: mahy@astro.ulg.ac.be
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Gregor Rauw, Yael Naze
University of
Liege, Belgium
Previous generations of X-ray observatories
revealed a group of massive binaries that were relatively bright
X-ray emitters. This was attributed to emission of shock-heated
plasma in the wind-wind interaction zone located between the stars.
With the advent of the current generation of X-ray observatories, the
phenomenon could be studied in much more detail. In this review, we
highlight the progress that has been achieved in our understanding of
the phenomenon over the last 15 years, both on theoretical and
observational grounds. All these studies have paved the way for
future investigations using the next generation of X-ray satellites
that will provide crucial information on the X-ray emission formed in
the innermost part of the wind-wind interaction.
Reference:
Advances in Space Research, 58, 761-781
Status: Manuscript
has been accepted
Weblink:
http://authors.elsevier.com/a/1TPuE~6OiOeML
Comments:
Paper can be downloaded free of charge until September 9,
2016
Email: rauw@astro.ulg.ac.be
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Gregor Rauw, and Yael Naze
University of
Liege, Belgium
Very young open clusters are ideal places
to study the X-ray properties of a homogeneous population of
early-type stars. In this respect, the IC1805 open cluster is very
interesting as it hosts the O4If+ star HD15570 thought to be in an
evolutionary stage intermediate between a normal O-star and a
Wolf-Rayet star. Such a star could provide a test for theoretical
models aiming at explaining the empirical scaling relation between
the X-ray and bolometric luminosities of O-type stars. We have
observed IC1805 with XMM-Newton and further collected optical
spectroscopy of some of the O-star members of the cluster. The
optical spectra allow us to revisit the orbital solutions of BD+60°
497 and HD15558, and provide the first evidence of binarity for
BD+60° 498. X-ray emission from colliding winds does not appear to
play an important role among the O-stars of IC1805. Notably, the
X-ray fluxes do not vary significantly between archival X-ray
observations and our XMM-Newton pointing. The very fast rotator
BD+60° 513, and to a lesser extent the O4If+ star HD15570 appear
somewhat underluminous. Whilst the underluminosity of HD15570 is only
marginally significant, its amplitude is found to be compatible with
theoretical expectations based on its stellar and wind properties. A
number of other X-ray sources are detected in the field, and the
brightest objects, many of which are likely low-mass pre-main
sequence stars, are analyzed in detail.
Reference: A&A
in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1608.04499
Comments:
Email: rauw@astro.ulg.ac.be
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J. D. Ilee (1), C. J. Cyganowski (2), P. Nazari (2), T.
R. Hunter (3), C. L. Brogan (3), D. H. Forgan (2) and Q. Zhang
(4)
(1) Institute of Astronomy, Madingley Road,
Cambridge CB3 0HA, UK;
(2) SUPA, School of Physics &
Astronomy, University of St Andrews, North Haugh, St Andrews,
Scotland, KY16 9SS, UK;
(3) NRAO, 520 Edgemont Rd,
Charlottesville, VA 22903, USA;
(4) Harvard-Smithsonian Center
for Astrophysics, Cambridge, MA 02138, USA
The formation
process of massive stars is not well understood, and advancement in
our understanding benefits from high resolution observations and
modelling of the gas and dust surrounding individual high-mass
(proto)stars. Here we report sub-arcsecond (<1550 au) resolution
observations of the young massive star G11.92-0.61 MM1 with the SMA
and VLA. Our 1.3 mm SMA observations reveal consistent velocity
gradients in compact molecular line emission from species such as
CH$_3$CN, CH$_3$OH, OCS, HNCO, H$_2$CO, DCN and CH$_3$CH$_2$CN,
oriented perpendicular to the previously reported bipolar molecular
outflow from MM1. Modelling of the compact gas kinematics suggests a
structure undergoing rotation around the peak of the dust continuum
emission. The rotational profile can be well fit by a model of a
Keplerian disc, including infall, surrounding an enclosed mass of
30-60M$_{\odot}$, of which 2-3M$_{\odot}$ is attributed to the disc.
From modelling the CH$_3$CN emission, we determine that two
temperature components, of 150 K and 230 K, are required to
adequately reproduce the spectra. Our 0.9 and 3.0cm VLA continuum
data exhibit an excess above the level expected from dust emission;
the full centimetre-submillimetre wavelength spectral energy
distribution of MM1 is well reproduced by a model including dust
emission, an unresolved hypercompact H{\i}{\i} region, and a compact
ionised jet. In combination, our results suggest that MM1 is an
example of a massive proto-O star forming via disc accretion, in a
similar way to that of lower mass stars.
Reference:
MNRAS, in press.
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/abs/2016arXiv160805561I
Comments:
Email: jdilee@ast.cam.ac.uk
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J. Krticka
Masaryk University, Brno, Czech
Republic
A small fraction of hot OBA stars host global
magnetic fields with field strengths of the order of 0.1-10 kG. This
leads to the creation of persistent surface structures (spots) in
stars with sufficiently weak winds as a result of the radiative
diffusion. These spots become evident in spectroscopic and
photometric variability. This type of variability is not expected in
stars with strong winds, where the wind inhibits the radiative
diffusion. Therefore, a weak photometric variability of the magnetic
Of?p star HD 191612 is attributed to the light absorption in the
circumstellar clouds. We study the nature of the photometric
variability of HD 191612. We assume that the variability results from
variable wind blanketing induced by surface variations of the
magnetic field tilt and modulated by stellar rotation. We used our
global kinetic equilibrium (NLTE) wind models with radiative force
determined from the radiative transfer equation in the comoving frame
(CMF) to predict the stellar emergent flux. Our models describe the
stellar atmosphere in a unified manner and account for the influence
of the wind on the atmosphere. The models are calculated for
different wind mass-loss rates to mimic the effect of magnetic field
tilt on the emergent fluxes. We integrate the emergent fluxes over
the visible stellar surface for individual rotational phases, and
calculate the rotationally modulated light curve of HD 191612. The
wind blanketing that varies across surface is able to explain a part
of the observed light variability in this star. The mechanism is able
to operate even at relatively low mass-loss rates. The remaining
variability is most likely caused by the flux absorption in
circumstellar clouds. The variable wind blanketing is an additional
source of the light variability in massive stars. The presence of the
rotational light variability may serve as a proxy for the magnetic
field.
Reference: accepted for publication in
A&A
Status: Manuscript has been accepted
Weblink:
http://lanl.arxiv.org/abs/1608.07157
Comments:
Email: krticka@physics.muni.cz
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Godart, M.; Simón-Díaz, S.; Herrero, A.; Dupret, M. A.;
Grötsch-Noels, A.; Salmon, S. J. A. J.; Ventura, P.
IAC,
ULL, IAG-Liege, CEA/DSM-CNRS, INAF
Asteroseismology is a
powerful tool to access the internal structure of stars. Apart from
the important impact of theoretical developments, progress in this
field has been commonly associated with the analysis of time-resolved
observations. Recently, the so-called macroturbulent broadening has
been proposed to be a complementary and less expensive way -- in
terms of observational time -- to investigate pulsations in massive
stars. We assess to what extent this ubiquitous non-rotational
broadening component shaping the line profiles of O stars and B
supergiants is a spectroscopic signature of pulsation modes driven by
a heat mechanism. We compute stellar main sequence and post-main
sequence models from 3 to 70Msun with the ATON stellar evolution code
and determine the instability domains for heat-driven modes for
degrees l=1-20 using the adiabatic and non-adiabatic codes LOSC and
MAD. We use the observational material presented in Sim\'on-D\'iaz et
al. (2016) to investigate possible correlations between the single
snapshot line-broadening properties of a sample of ~260 O and B-type
stars and their location inside/outside the various predicted
instability domains. We present an homogeneous prediction for the
non-radial instability domains of massive stars for degree l up to
20. We provide a global picture of what to expect from an
observational point of view in terms of frequency range of excited
modes, and investigate the behavior of the instabilities with stellar
evolution and increasing degree of the mode. Furthermore, our
pulsational stability analysis, once compared to the empirical
results of Sim\'on-D\'iaz et al. (2016), indicates that stellar
oscillations originated by a heat mechanism can not explain alone the
occurrence of the large non-rotational line-broadening component
commonly detected in the O star and B supergiant domain.
Reference:
A&A accpeted
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/abs/2016arXiv160805520G
Comments:
Email: melanie.godart@gmail.com
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Simón-Díaz, S.; Godart, M.;
Castro, N.; Herrero, A.; Aerts, C.; Puls, J.; Telting, J.;
Grassitelli, L.
IAC/ULL, AIfA-Bonn, IvS-KULeuven,
LMU-USM-Munich, NOT
We aim to provide new empirical clues
about macroturbulent spectral line broadening in O- and B-type stars
to evaluate its physical origin. We use high-resolution spectra of
~430 stars with spectral types in the range O4-B9 (all luminosity
classes). We characterize the line-broadening of adequate diagnostic
metal lines using a combined FT and GOF technique. We perform a
quantitative spectroscopic analysis of the whole sample using
automatic tools coupled with a huge grid of FASTWIND models. We also
incorporate quantitative information about line asymmetries to our
observational description of the characteristics of the
line-profiles, and present a comparison of the shape and type of
line-profile variability found in a small sample of O stars and B
supergiants with still undefined pulsational properties and B main
sequence stars with variable line-profiles. We present a homogeneous
and statistically significant overview of the (single snapshot)
line-broadening properties of stars in the whole O and B star domain.
We find empirical evidence of the existence of various types of
non-rotational broadening agents acting in the realm of massive
stars. Even though all of them could be quoted and quantified as a
macroturbulent broadening from a practical point of view, their
physical origin can be different. Contrarily to the early- to late-B
dwarfs/giants, which present a mixture of cases in terms of
line-profile shape and variability, the whole O-type and B supergiant
domain (or, roughly speaking, stars with M_ZAMS > 15 M_sol) is
fully dominated by stars with a remarkable non-rotational broadening
component and very similar profiles (including type of variability).
We provide some examples illustrating how this observational dataset
can be used to evaluate scenarios aimed at explaining the existence
of sources of non-rotational broadening in massive stars.
Reference:
A&A accepted
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/abs/2016arXiv160805508S
Comments:
Email: ssimon@iac.es
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Augusto Damineli (1), Leonerdo
A. Almeida (1), Robert D. Blum (2), Daniel S.C.Damineli (3,4), Felipe
Navarete (1), Marcelo S. Rubinho (1), Miran Teodoro(5,6)
1-Instituto
de Astronomia, Geofísica e Ciências Atmosféricas da USP, Rua do
Matão 1226, Cidade Universitária São Paulo-SP, 05508-090, Brasil
2-NOAO, 950 N Cherry Ave., Tucson, AZ 85719 USA
3-Cell
Biology and Molecular Genetics Department, University of Maryland,
College Park, Maryland 20742-5815, USA
4-PhD Program in
Computational Biology, Instituto Gulbenkian de Ciência, 2780-156
Oeiras, Portugal
5-Astrophysics Science Division, Code 667,
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
6-Universities Space Research Association, 7178 Columbia
Gateway Dr., Columbia, MD 20146, USA
The young stellar
cluster Westerlund 1 (Wd 1: l =339.6, b= 0.4 deg) is one of the most
massive in the local Universe, but accurate parameters are pending on
better determination of its extinction and distance. Based on our
photometry and data collected from other sources, we have derived a
reddening law for the cluster line-of-sight representative of the
Galactic Plane (-5< b< +5 deg ) in the window 0.4-4.8 micron.
The power low exponent alpha=2.13 is much steeper than those
published a decade ago (1.6-1.8) and our index RV=2.50 is also
discrepant from them, but in very good agreement with recent results
based on large deep surveys in the inner Galaxy. As a consequence,
the total extinction AKs=0.74 is substantially smaller than in
previous works (AKs =0.91 - 1.13), from which the interstellar
component was found to be AKs=0.63 (AV=9.66). The extinction to the
cluster members spans a range of AV=8.7, with a gradient increasing
from SW to NE across the cluster face, following the same general
trend as the warm dust distribution. The map of J-Ks colour index
also shows a trend in this direction. We measured the equivalent
width of the diffuse interstellar band at 8620A (the GAIA DIB) for Wd
1 cluster members, which supplemented with data taken from different
sources results in the relation AKs =0.612EW - 0.191EW^2 . This
extends the Munari et al. (2008 ) relation, valid for EB-V < 1, to
the non-linear regime (AV > 4).
Reference: To
appear in MNRAS
Status: Manuscript has been submitted
Weblink:
http://arxiv.org/abs/1607.04639
Comments:
Email: augusto.damineli@gmail.com
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Prof Paul Crowther
Dept of Physics &
Astronomy, University of Sheffield, Sheffield, S3 7RH, UK
Postdoc
position to work on a STFC-funded project entitled “Massive Stars
in Starburst Regions” with Prof Paul Crowther to support an
observational programme based upon ground- and space-based datasets
from VLT, HST and Chandra. Key questions to be addressed involve the
contribution of individual stars to the integrated light in starburst
regions, the binary fraction of massive stars in starburst regions
and the origin of very massive stars.
You will take a
lead role in the analysis of existing spectroscopic datasets, and
should have a PhD in astrophysics or a closely related field.
Preference will be given to applicants with observational or
theoretical experience in one or more of the following fields:
stellar atmospheres, evolution of massive stars, young star clusters.
A good track record of published research is also
expected.
Attention/Comments: The post is
fixed-term for 17 months from January 2017 in the first instance. Job
Reference UOS014506
Weblink:
http://www.sheffield.ac.uk/jobs
Email:
Paul.crowther@sheffield.ac.uk
Deadline: 31 Oct
2016
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Raphael Hirschi
Keele
University, UK
Fixed Term for 6 months
Keele
University wishes to appoint a Research Associate in order to conduct
research on theoretical stellar astrophysics.
The appointed
Research Associate will work in the group of Dr Raphael Hirschi
within the Astrophysics Group at Keele University as part of an
ERC-funded project entitled "Stellar HYdrodynamics,
Nucleosynthesis and Evolution" (SHYNE). The ERC starting grant
awarded to Dr Hirschi provides funding for a dedicated 1000+-CPU-core
computer cluster, including 288 CPU-cores sharing memory via
numascale technology.
You will lead the component of this
project related to 3D-1D modelling of stellar interiors. This will
include a range of computer simulations including 1D stellar
evolution and 3D hydrodynamics simulations with as main goal to
improve modelling of convection and rotation in stellar evolution.
The PDRA will also contribute to the other components of the project
and be encouraged to develop their own research program and their
leadership skills.
Applicants should have or expect to
obtain a PhD in theoretical stellar astrophysics or a related area
and should have a demonstrated aptitude for research. Experience in
stellar evolution modelling, 3D hydrodynamic simulations or parallel
programming (CUDA/MPI/OpenMP) is highly desirable.
For
more details of this post and the Keele Astrophysics Group, and for
information on how to apply, see
http://www.astro.keele.ac.uk.
For further enquiries please contact Dr Raphael Hirschi
at r.hirschi@keele.ac.uk.
Attention/Comments:
Weblink:
http://www.astro.keele.ac.uk/shyne
Email:
r.hirschi@keele.ac.uk
Deadline: 31 October
2016
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Raphael Hirschi
Keele University,
UK
Faculty of Natural Sciences
Faculty
Research Office
Research Associate in Theoretical Stellar
Astrophysics
Fixed Term until October 2017
Starting
salary: Grade 7 £31,656
Keele University wishes to
appoint a Research Associate starting in October 2016, in order to
conduct research on theoretical stellar astrophysics.
The
appointed Research Associate will work in the group of Dr Raphael
Hirschi within the Astrophysics Group at Keele University as part of
an ERC-funded project entitled “Stellar HYdrodynamics,
Nucleosynthesis and Evolution” (SHYNE). The ERC starting grant
awarded to Dr Hirschi provides funding for a dedicated 1200+-CPU-core
computer cluster, including 288 CPU-cores sharing memory via
numascale technology.
You will lead the component of this
project related to 3D-1D modelling of stellar interiors. This will
include a range of computer simulations including 1D stellar
evolution and 3D hydrodynamics simulations with as main goal to
improve modelling of convection and rotation in stellar evolution.
The Research Associate will also contribute to the other components
of the project and be encouraged to develop their own research
program and their leadership skills. The post holder will work
closely with a collaborator in America and the appointment will
involve frequent travel to the USA.
Applicants should
have or expect to obtain a PhD in theoretical stellar astrophysics or
a related area and should have a demonstrated aptitude for research.
Experience in stellar evolution modelling and 3D hydrodynamic
simulations is highly desirable.
For more details of this
post and the Keele Astrophysics Group, and for information on how to
apply, see http://www.astro.keele.ac.uk.
For further
enquiries please contact Dr Raphael Hirschi at r.hirschi@keele.ac.uk.
Keele University is committed to the principles of the
Athena SWAN charter, and values equality and diversity across our
workforce. We strive to ensure that our workforce is representative
of broader society, and therefore, we would actively welcome
applications from women for this role.
For full post
details please visit: www.keele.ac.uk/vacancies
Keele
University employees wishing to apply should login to Employee Self
Service and click on the 'View current vacancies' link.
Closing
date for applications: 4 August 2016
Interviews will most
probably be conducted remotely (via skype or similar technology)
Post reference: KU00000093
Attention/Comments:
Weblink:
https://forums.keele.ac.uk/viewtopic.php?f=14&t=15679
Email:
r.hirschi@keele.ac.uk
Deadline: 4 August
2016
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Prof. Artemio Herrero
Instituto de
Astrofisica de Canarias
C/ Via Lactea s/n
E-38205 La
Laguna
Tenerife
The IAC (Tenerife) invites
applications for ONE postdoctoral contract to work on topics within
the “Massive stars in the Local Universe” (AYA2015-68012-C2-1-P)
project, led by Prof. Artemio Herrero Davó.
Duties:
The selected candidate will pursue research on massive stars
currently underway in the group: multiwavelength observations and
analysis of massive stars in the Milky Way, and nearby galaxies,
comparison of results with the evolutionary model predictions, update
of atomic and atmosphere models, influence of rotation, and other
velocity fields in the structure and evolution of massive stars.
Expertise in the following topics will be highly
valued:
· Astronomical observing, reduction and stellar
analysis of massive stars, and use of model atmospheres.
·
Use or calculation of evolutionary models.
· Knowledge
of numerical and statistical techniques.
· Analysis of
stellar pulsations, particularly when appropriate for massive stars.
Qualification requirements: To be eligible for
admission, applicants must have obtained a Ph.D. degree in
Astrophysics or Physics, within the application deadline (September
20, 2016). A copy of your degree or corresponding stamped certificate
(issued on behalf of the University where you have obtained the
degree), must be included. If the applicant has not completed the
Ph.D. degree within the application deadline, will not be considered.
Duration: The starting date is expected to be in
the first quarter of 2017. In any case the contract will not be
extended later than December 31, 2018 (finalization of the project).
Remuneration: The gross annual salary is 32,886
Euros, subject to up to 20% tax and Social Security deductions
(depending on the personal situation of the candidate). Medical
insurance under the Spanish National Health Service will be provided
for the candidate and will also cover spouse or registered partner
(de facto partner) and children (if relevant).
Attention/Comments:
Instructions on how to apply may be found in the weblink address.
For administrative questions, please send an email to
secinv@iac.es
Weblink:
http://www.iac.es/info.php?op1=26&id=603
Email:
ahd@iac.es
Deadline: September 20th, 2016
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