ISSN 1783-3426
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Self Regulated Shocks in Massive Star
Binary Systems
Blue supergiant
progenitor models of Type II supernovae
The
Photometric variability of the WC9-type Wolf-Rayet star WR
103
Spectral modelling of massive
binary systems
Populations of
rotating stars. - I. Models from 1.7 to 15 M⊙ at Z = 0.014, 0.006,
and 0.002
A Bake-Off Between
CMFGEN and FASTIND: Modeling the Physical Properties of SMC and LMC
O-type Stars
The H-band Emitting
Region of the Luminous Blue Variable P Cygni: Spectrophotometry and
Interferometry of the Wind
Evidence
for quasi-chemically homogeneous evolution of massive stars up to
solar metallicity
Three-dimensional
orbits of the triple-O stellar system HD 150136
R144
revealed as a double-lined spectroscopic binary
The
X-ray under-luminosity of the O-type supergiants HD16691 and HD14947
revealed by XMM-Newton
Three-Dimensional
Modelling of Ionized Gas. I. Did very massive stars of different
metallicities drive the second cosmic reionization?
Betelgeuse and the red supergiants
Very
Massive Stars in the Local Universe
PhD Position in Astrophysics
Tenure
Track Position in Stellar Astrophysics
Putting A
Stars into Context: Evolution, Environment, and Related Stars
Massive
Stars: From α to Ω
IAU Symposium
302
E. R. Parkin (1) & S. A.
Sim (1,2)
(1) Research School of Astronomy and
Astrophysics, The Australian National University, Australia
(2)
Astrophysics Research Centre, School of Mathematics and Physics,
Queen’s University Belfast, Belfast
In an early-type,
massive star binary system, X-ray bright shocks result from the
powerful collision of stellar winds driven by radiation pressure on
spectral line transitions. We examine the influence of the X-rays
from the wind-wind collision shocks on the radiative driving of the
stellar winds using steady state models that include a parameterized
line force with X-ray ionization dependence. Our primary result is
that X-ray radiation from the shocks inhibits wind acceleration and
can lead to a lower pre-shock velocity, and a correspondingly lower
shocked plasma temperature, yet the intrinsic X-ray luminosity of the
shocks, LX remains largely unaltered, with the exception of a modest
increase at small binary separations. Due to the feedback loop
between the ionizing X-rays from the shocks and the wind-driving, we
term this scenario as self regulated shocks. This effect is found to
greatly increase the range of binary separations at which a
wind-photosphere collision is likely to occur in systems where the
momenta of the two winds are significantly different. Furthermore,
the excessive levels of X-ray ionization close to the shocks
completely suppresses the line force, and we suggest that this may
render radiative braking less effective. Comparisons of model results
against observations reveals reasonable agreement in terms of
log(LX/Lbol). The inclusion of self regulated shocks improves the
match for kT values in roughly equal wind momenta systems, but there
is a systematic offset for systems with unequal wind momenta (if
considered to be a wind-photosphere collision).
Reference:
ApJ, in press
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2013arXiv1302.6228P
Comments:
16 pages, 13 figures
Email: parkin@mso.anu.edu.au
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D. Vanbeveren, N. Mennekens,
W. Van Rensbergen, C. De Loore
Astrophysical Institute,
Vrije Universiteit Brussel
In the present paper we show that
within all the uncertainties that govern the process of Roche lobe
overflow in Case Br type massive binaries, it can not be excluded
that a significant fraction of them merge and become single stars. We
demonstrate that at least some of them will spend most of their core
helium burning phase as hydrogen rich blue stars, populating the
massive blue supergiant region and/or the massive Be type star
population. The evolutionary simulations let us suspect that these
mergers will explode as luminous hydrogen rich stars and it is
tempting to link them to at least some super luminous
supernovae.
Reference: A&A (in press)
Status:
Manuscript has been accepted
Weblink: arXiv:
1212.4285
Email: dvbevere@vub.ac.be
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A.M. van Genderen1$^1$,
S.R.G. Veijgen2$^1$, K.A. van der Hucht3$^2,3$
1 - Leiden
Observatory, Leiden University, Postbus 9513, 2300RA Leiden, The
Netherlands;
2 - Leiden Observatory, Leiden University, Postbus
9513, 2300RA Leiden, The Netherlands;
3 - SRON Netherlands
Institute for Space Research, Sorbonnelaan 2, 3584CA Utrecht, The
Netherlands,
and Astronomical Institute Anton Pannekoek,
University of Amsterdam, Science Park 904, 1098XH Amsterdam, The
Netherlands
We discuss a collection of archival multi-colour
photometric data of the variable WC9-type Wolf-Rayet star WR 103 = HD
164270 observed over a time interval of eleven years. The photometric
systems used are Walraven $VBLUW$, Bessel $UBV$ and Strömgren
$uvby$. The purpose is to search for periodicity and to disentangle
continuum and line emission variations.
The star turns out to
be stochastically variable in all time intervals under
considerations. The time scale of the variations hovers between a few
hours to a few days. The continuum light amplitude varies from
$sim$~0fm1 in the visual to $sim$~0fm2 in the UV.
Emission-line
variations at the level of
1--5% are detectable in all pass
bands, but are largest in the Strömgren $b$ and Walraven $V$
filters, due to the prominent presence of the C{sc iii} emission
lines (blended with a much weaker O{sc ii} line) at 4650 and 5696 AA
emission lines, respectively.
The relative large light
amplitude of WR 103 resembles that of WN8-type stars; a possible link
between the two is discussed.
Stellar (multi-mode) pulsations are
likely the cause of the photometric variability.
We also
discuss the exceptional status of WR,103 within the class of WC9-type
stars which are almost photometrically stable.
A striking
phenomenon observed for the first time in WR 103: a three days
lasting flux enhancement of the C{sc iii} line by at least 10% was
observed in August 1998. Such strong spectroscopic flare-like events
are very seldom observed in WR stars. So far, the one of WR,103 had
the longest duration ever observed.
Reference: Astrophys.
Space Sci, 2013,
Status: Manuscript has been accepted
Weblink:
http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s10509-013-1381-x
Email:
genderen@strw.leidenuniv.nl
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M. Palate(1), G. Rauw(1), G.
Koenigsberger(2), & E. Moreno(3)
(1)Institut
d'Astrophysique & Geophysique, Liege, Belgium
(2)Instituto de
Ciencias Fisicas, Universidad Nacional Autonoma de Mexico,
Cuernavaca, Mexico
(3)Instituto de Astronomia, Universidad
Nacional Autionoma de Mexico, Mexico D.F., Mexico
Context: The
spectra of massive binaries may be affected by interactions between
the stars in the system. These are believed to produce observational
phenomena such as the Struve-Sahade effect.
Aims: We simulate the
spectra of massive binaries at different phases of the orbital cycle,
accounting for the gravitational influence of the companion star on
the shape and physical properties of the stellar surface.
Methods:
We used the Roche potential modified to account for radiation
pressure to compute the stellar surface of close circular systems. We
further more used the tidal interactions with dissipation of energy
through shear code for surface computation of eccentric systems. In
both cases, we accounted for gravity darkening and mutual heating
generated by irradiation to compute the surface temperature. We then
interpolated non-local thermodynamic equilibrium (NLTE)
plane-parallel atmosphere model spectra in a grid to obtain the local
spectrum at each surface point. We finally summed all contributions,
accounting for the Doppler shift, limb-darkening, and visibility to
obtain the total synthetic spectrum. We computed different orbital
phases and different sets of physical and orbital parameters.
Results: Our models predict line strength variations through the
orbital cycle, but fail to completely reproduce the Struve-Sahade
effect. Including radiation pressure allows us to reproduce a surface
temperature distribution that is consistent with observations of
semi-detached binary systems.
Conclusions: Radiation pressure
effects on the stellar surface are weak in (over)contact binaries and
well-detached systems but can become very significant in
semi-detached systems. The classical von Zeipel theorem is sufficient
for the spectral computation. Broad-band light curves derived from
the spectral computation are different from those computed with a
model in which the stellar surfaces are equipotentials of the Roche
potential scaled by the instantaneous orbital separation. In many
cases, the fit of two Gaussian/Lorentzian profiles fails to properly
measure the equivalent width of the lines and leads to apparent
variations that could explain some of the effects reported in the
literature.
Reference: Astronomy &
Astrophysics
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1302.5201
Email:
palate@astro.ulg.ac.be
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Cyril Georgy$^{1,2}$, Sylvia
Ekström$^3$, Anahí Granada$^3$, Georges Meynet$^3$, Nami
Mowlavi$^3$, Patrick Eggenberger$^3$ and André Maeder$^3$
1
- Astrophysics group, EPSAM, Keele University, Lennard-Jones Labs,
Keele, ST5 5BG, UK
2 - Centre de Recherche Astrophysique de Lyon,
Ecole Normale Supérieure de Lyon, 46, allée d’Italie, F-69384
Lyon cedex 07, France
3 - Geneva Observatory, University of
Geneva, Maillettes 51, CH-1290 Sauverny, Switzerland
B-type
stars are known to rotate at various velocities, including very fast
rotators near the critical velocity as the Be stars. In this paper,
we provide stellar models covering the mass range between 1.7 to 15
M⊙, which includes the typical mass of known Be stars, at Z =
0.014, 0.006, and 0.002 and for an extended range of initial
velocities on the zero-age main sequence.
We used the Geneva
stellar-evolution code, including the effects of shellular rotation,
with a numerical treatment that has been improved so the code can
precisely track the variation in the angular momentum content of the
star as it changes under the influence of radiative winds and/or
mechanical mass loss.
We discuss the impact of the initial
rotation rate on the tracks in the Hertzsprung-Russell diagram, the
main-sequence (MS) lifetimes, the evolution of the surface rotation
and abundances, as well as on the ejected masses of various isotopes.
Among the new results obtained from the present grid we find that 1)
fast-rotating stars with initial masses around 1.7 M⊙ present at
the beginning of the core hydrogen-burning phase quite small
convective cores with respect to their slowly rotating counterparts.
This fact may be interesting to keep in mind in the framework of the
asteroseismic studies of such stars. 2) The contrast between the core
and surface angular velocity is higher in slower rotating stars. Our
results are in agreement with the very few values obtained for B-type
stars from asteroseismology. 3) At Z = 0.002, the stars in the mass
range of 1.7 to 3 M⊙ with a mean velocity on the MS of the order of
150 km · s−1 show N/H enhancement superior to 0.2 dex at mid-MS,
and superior to 0.4 dex at the end of the MS phase. At solar
metallicity the corresponding values are below 0.2 dex at any time in
the MS.
An extended database of stellar models containing 270
evolutionary tracks is provided to the community.
Reference:
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1303.2321
Email:
c.georgy@keele.ac.uk
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Philip Massey (1), Kathryn F.
Neugent (1), D. John Hillier (2), and Joachim Puls (3)
(1)
Lowell Observatory, (2) Dept of Astronomy, University of Pittsburgh,
(3) Universitatssternwarte Munchen
The model atmosphere
programs FASTWIND and CMFGEN are both elegantly designed to perform
non-LTE analyses of the spectra of hot massive stars, and include
sphericity and mass-loss. The two codes differ primarily in their
approach towards line blanketing, with CMFGEN treating all of the
lines in the co-moving frame and FASTWIND taking an approximate
approach which speeds up execution times considerably. Although both
have been extensively used to model the spectra of O-type stars, no
studies have used the codes to independently model the same spectra
of the same stars and compare the derived physical properties. We
perform this task on ten O-type stars in the Magellanic Clouds. For
the late-type O supergiants, both CMFGEN and FASTWIND have trouble
fitting some of the He I lines, and we discuss causes and cures. We
find that there is no difference in the average effective
temperatures found by the two codes for the stars in our sample,
although the dispersion is large, due primarily to the various
difficulties each code has with He I. The surface gravities
determined using FASTWIND are systematically lower by 0.12~dex
compared to CMFGEN, a result we attribute to the better treatment of
electron scattering by CMFGEN. This has implications for the
interpretation of the origin of the so-called mass discrepancy, as
the masses derived by FASTWIND are on average lower than inferred
from stellar evolutionary models, while those found by CMFGEN are in
better agreement.
Reference: Astrophysical Journal, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1303.5469
Email:
phil.massey@lowell.edu
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N. D. Richardson, G. H.
Schaefer, D. R. Gies, O. Chesneau, J. D. Monnier, F. Baron, X. Che,
J. R. Parks, R. A. Matson, Y. Touhami, D. P. Clemens, E. J.
Aldoretta, N. D. Morrison, T. A. ten Brummelaar, H. A. McAlister, S.
Kraus, S. T. Ridgway, J. Sturmann, L. Sturmann, B. Taylor, N. H.
Turner, C. D. Farrington, and P. J. Goldfinger
Universite
de Montreal, Georgia State University (and others, see paper)
We
present the first high angular resolution observations in the
near-infrared H-band (1.6 microns) of the Luminous Blue Variable star
P Cygni. We obtained six-telescope interferometric observations with
the CHARA Array and the MIRC beam combiner. These show that the
spatial flux distribution is larger than expected for the stellar
photosphere. A two component model for the star (uniform disk) plus a
halo (two-dimensional Gaussian) yields an excellent fit of the
observations, and we suggest that the halo corresponds to flux
emitted from the base of the stellar wind. This wind component
contributes about 45% of the H-band flux and has an angular FWHM =
0.96 mas, compared to the predicted
stellar diameter of 0.41 mas.
We show several images reconstructed from the interferometric
visibilities and closure phases, and they indicate a generally
spherical geometry for the wind. We also obtained near-infrared
spectrophotometry of P Cygni from which we derive the flux excess
compared to a purely photospheric spectral energy distribution. The
H-band flux excess
matches that from the wind flux fraction
derived from the two component fits to
the interferometry. We
find evidence of significant near-infrared flux variability over the
period from 2006 to 2010 that appears similar to the variations in
the H-alpha emission flux from the wind. Future interferometric
observations may be capable of recording the spatial variations
associated with temporal changes in the wind structure.
Reference:
ApJ, in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1304.1560
Comments:
34 pages, 8 figures, 5 tables
Email:
richardson@astro.umontreal.ca
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F. Martins$^1$, E.
Depagne$^2$, D. Russeil$^3$, L. Mahy$^4$
1- LUPM, CNRS &
Montpellier University, 2- Leibniz-Institut fur Astrophysik Potsdam,
3- LAM, CNRS & Marseille University, 4- Liège University
Long
soft gamma ray bursts (LGRBs) are usually associated with the death
of the most massive stars. A large amount of core angular momentum in
the phases preceding the explosion is required to form LGRBs. A very
high initial rotational velocity can provide this angular momentum.
Such a velocity strongly influences the way the star evolves: it is
chemically homogeneously mixed and evolves directly towards the blue
part of the HR diagram from the main sequence. We have shown that
chemically homogeneous evolution (CHE) takes place in the SMC, at low
metallicity. We want to see if there is a metallicity threshold above
which such an evolution does not exist. We perform a spectroscopic
analysis of H-rich early-type WN stars in the LMC and the Galaxy. We
use the code CMFGEN to determine the fundamental properties and the
surface composition of the target stars. We then place the stars in
the HR diagram and determine their evolution. We show that both the
LMC and Galactic WNh stars we selected cannot be explained by
standard stellar evolution. They are located on the left of the main
sequence but show surface abundances typical of CN equilibrium. In
addition, they still contain a large amount of hydrogen. They are
thus core-H burning objects. Their properties are consistent with
CHE. We determine the metallicity of the Galactic stars from their
position and Galactic metallicity gradients, and conclude that they
have 0.6
Reference: Accepted in Astronomy and
Astrophysics
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1304.3337
Email: fabrice.martins@univ-montp2.fr
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H. Sana [1], J.-B. Le Bouquin [2], L. Mahy [3], O. Absil
[3], M. De Becker [3], E. Gosset [3]
1. Astronomical
Institute Anton Pannekoek, Amsterdam University, Science Park 904,
1098 XH, Amsterdam, The Netherlands
2. UJF-Grenoble 1 /
CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble
(IPAG) UMR 5274, Grenoble, France
3. Département
d’Astrophysique, Géophysique et Océanographie, Université de
Liège, Allée du 6 Août 17, B-4000 Liège, Belgium
Context.
HD 150136 is a triple hierarchical system and a non-thermal radio
emitter. It is formed by an O3-3.5 V + O5.5-6 V close binary and a
more distant O6.5-7 V tertiary. So far, only the inner orbital
properties have been reliably constrained.
Aims. To
quantitatively understand the non-thermal emission process, accurate
knowledge of the physical and orbital properties of the object is
crucial. Here, we aim to investigate the orbital properties of the
wide system and to constrain the inclinations of the inner and outer
binaries, and with these the absolute masses of the system
components.
Methods. We used the PIONIER combiner at the Very
Large Telescope Interferometer to obtain the very first
interferometric measurements of HD 150136. We combines the
interferometric observations with new and existing high-resolution
spectroscopic data to derive the orbital solution of the outer
companion in the three-dimensional space.
Results. The wide
system is clearly resolved by PIONIER, with a projected separation on
the plane of the sky of about 9 milli-arcsec. The best-fit orbital
period, eccentricity, and inclination are 8.2 yr, 0.73, and 108
degrees. We constrain the masses of the three stars of the system to
63 +/- 10, 40 +/- 6, and 33 +/- 12 Msun for the O3-3.5 V, O5.5-6
V, and O6.5-7 V components.
Conclusions. The dynamical masses
agree within errors with the evolutionary masses of the components.
Future interferometric and spectroscopic monitoring of HD 150136
should allow one to reduce the uncertainties to a few per cent only
and to accurately constrain the distance to the system. This makes HD
150136 an ideal system to quantitatively test evolutionary models of
high-mass stars as well as the physics of non-thermal processes
occurring in O-type systems.
Reference: Astronomy &
Astrophysics
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1304.3457
Email:
H.Sana@uva.nl
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H. Sana [1], T. van Boeckel
[1], F. Tramper [1], L.E. Ellerbroek [1], A. de Koter [1,2,3], L.
Kaper [1], A.F.J. Moffat [4], O. Schnurr [5], F.R.N. Schneider [6],
D.R. Gies [7]
1. Astronomical Institute Anton Pannekoek,
Amsterdam University, Science Park 904, 1098 XH, Amsterdam, The
Netherlands
2. Utrecht University, Princetonplein 5, 3584CC,
Utrecht, The Netherlands
3. Instituut voor Sterrenkunde,
Universiteit Leuven, Celestijnenlaan 200 D, 3001, Leuven, Belgium
4.
Department de Physique, Universite de Montreal and Centre de
Recherche en Astrophysique du Quebec, C. P. 6128, succ.
centre-ville, Montreal (Qc) H3C 3J7, Canada
5. Leibniz Institut
fur Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam,
Germany
6. Argelander-Institut fur Astronomie, Universitat
Bonn, Auf dem Hugel 71, 53121 Bonn, Germany
7. Center for High
Angular Resolution Astronomy and Department of Physics and Astronomy,
Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106,
USA
R144 is a WN6h star in the 30 Doradus region. It is
suspected to be a binary because of its high luminosity and its
strong X-ray ux, but no periodicity could be established so far.
Here, we present new X-shooter multi-epoch spectroscopy of R144
obtained at the ESO Very Large Telescope (VLT). We detect variability
in position and/or shape of all the spectral lines. We measure radial
velocity variations with an amplitude larger than 250 km/s in Niv and
Nv lines. Furthermore, the Niii and Nv line Doppler shifts are
anti-correlated and the Niv lines show a double-peaked profile on six
of our seven epochs. We thus conclude that R144 is a double-lined
spectroscopic binary. Possible orbital periods range from 2 to 6
months, although a period up to one year is allowed if the orbit is
highly eccentric. We estimate the spectral types of the components to
be WN5-6h and WN6-7h, respectively. The high luminosity of the system
(log Lbol/Lsun ~ 6.8) suggests a present-day total mass content in
the range of about 200 to 300 Msun, depending on the evolutionary
stage of the components. This makes R144 the most massive binary
identified so far, with a total mass content at birth possibly as
large as 400 Msun. We briefly discuss the presence of such a massive
object 60 pc away from the R136 cluster core in the context of star
formation and stellar dynamics.
Reference: MNRAS
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1304.4591
Email:
H.Sana@uva.nl
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M. De Becker
Department
of Astrophysics, Geophysics and Oceanography, University of Liège,
Belgium
The members of the scarce category of Of^+ supergiants
present properties that are intermediate between regular O-stars and
Wolf-Rayet (WR) stars. Significant similarities between these
transitional stars and WN-type objects are now clearly established,
at least in the visible and near-infrared domains, pointing to common
stellar wind properties. In this study, we report on the first
dedicated X-ray observations of HD16691 (O4If^+) and HD14947 (O5f^+),
revealing a soft thermal spectrum in agreement with the expected
X-ray emission from a single O-type star. However, the X-ray
luminosity of our targets is slightly lower than expected for single
O-type stars, suggesting that the particular properties of their
stellar wind has also a significant impact on the X-ray emission of
these objects on the way to the WN category. We argue that the X-ray
under-luminosity of HD16691 and HD14947 may be interpreted as the
signature in X-rays of the intermediate stage between O and WR stars,
as a consequence of enhanced wind density.
Reference: 2013,
New Astronomy, in press
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1304.4253
Email:
debecker@astro.ulg.ac.be
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J. A. Weber, A. W. A. Pauldrach,
J. S. Knogl, T. L. Hoffmann
Institut fuer Astronomie und
Astrophysik der Universitaet Muenchen, Scheinerstraße 1, 81679
Muenchen, Germany
Context. The first generation of stars,
which formed directly from the primordial gas, is believed to have
played a crucial role in the early phase of the epoch of reionization
of the universe. Theoretical studies indicate that the initial mass
function (IMF) of this first stellar population differs significantly
from the present IMF, being top-heavy and thus allowing for the
presence of supermassive stars with masses up to several thousand
solar masses. The first generation of population III stars was
therefore not only very luminous, but due to its lack of metals its
emission of UV radiation considerably exceeded that of present stars.
Because of the short lifetimes of these stars the metals produced in
their cores were quickly returned to the environment, from which
early population II stars with a different initial mass function and
different spectral energy distributions (SEDs) were formed, already
much earlier than the time at which the universe became completely
reionized (at a redshift of z > 6).
Aims. Using a
state-of-the-art model atmosphere code we calculate realistic SEDs of
very massive stars (VMSs) of different metallicities to serve as
input for the 3-dimensional radiative transfer code we have developed
to simulate the temporal evolution of the ionization of the
inhomogeneous interstellar and intergalactic medium, using multiple
stellar clusters as sources of ionizing radiation. The ultimate
objective of these simulations is not only to quantify the processes
which are believed to have lead to the reionized state of the
universe, but also to determine possible observational diagnostics to
constrain the nature of the ionizing sources.
Methods. The
multi-frequency treatment in our combination of 3d radiative transfer
– based on ray-tracing – and time-dependent simulation of the
ionization structure of hydrogen and helium allows, in principle, to
deduce information about the spectral characteristics of the first
generations of stars and their interaction with the surrounding gas
on various scales.
Results. As our tool can handle distributions
of numerous radiative sources characterized by high resolution
synthetic SEDs, and also yields occupation numbers of the required
energy levels of the most important elements which are treated in
NLTE and are calculated consistently with the 3d radiative transfer,
the ionization state of an inhomogeneous gaseous density structure
can be calculated accurately. We further demonstrate that the
increasing metallicity of the radiative sources in the transition
from population III stars to population II stars has a strong impact
on the hardness of the emitted spectrum, and hence on the
reionization history of helium.
Conclusions. A top-heavy stellar
mass distribution characterized by VMSs forming in chemically evolved
clusters of high core mass density may not only provide the
progenitors of intermediate-mass and supermassive black holes
(SMBHs), but also play an important role for the reionization of He
II. The number of VMSs required to reionize He II by a redshift of z
~ 2.5 is astonishingly close to the number of VMSs required to
explain galactic SMBHs if one assumes that these have been formed by
mergers of smaller black holes.
Reference: 2013, A&A,
in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1304.4824
Comments:
23 pages, 26 figures
Email: uh10107@usm.lmu.de
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Jacco Th. van Loon
Keele
University, UK
Betelgeuse is one of the most magnificent stars
in the sky, and one of the
nearest red supergiants. Astronomers
gathered in Paris in the Autumn of 2012
to decide what we know
about its structure, behaviour, and past and future
evolution,
and how to place this in the general context of the class of red
supergiants. Here I reflect on the discussions and propose a
synthesis of the
presented evidence. I believe that, in those
four days, we have achieved to
solve a few riddles.
Reference:
European Astronomical Society Publications Series, editors:
Pierre Kervella, Thibaut Le Bertre and Guy Perrin
Status:
Conference proceedings
Weblink:
http://arxiv.org/abs/1303.0321
Comments:
Summary talk of the Betelgeuse workshop, November 2012,
Paris.
Email: j.t.van.loon@keele.ac.uk
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Jorick S. Vink^1, Alexander Heger, Mark
R. Krumholz, Joachim Puls, S. Banerjee, N. Castro, K.-J. Chen, A.-N.
Chene, P.A. Crowther, A. Daminelli, G. Grafener, J. H. Groh, W.-R.
Hamann, S. Heap, A. Herrero, L. Kaper, F. Najarro, L. M. Oskinova, A.
Roman-Lopes, A. Rosen, A. Sander, M. Shirazi, Y. Sugawara, F.
Tramper, D. Vanbeveren, R. Voss, A. Wofford, Y. Zhang (and the other
participants of Joint Discussion 2 IAU-GA)
^1 Armagh
Observatory, College Hill, BT61 9DG, Armagh, United Kingdom
Recent
studies have claimed the existence of very massive stars (VMS) up to
300 solar masses in the local Universe. As this finding may represent
a paradigm shift for the canonical stellar upper-mass limit of 150
Msun, it is timely to discuss the status of the data, as well as the
far-reaching implications of such objects.
We held a Joint
Discussion at the General Assembly in Beijing to discuss:
(i)
the determination of the current masses of the most massive stars,
(ii) the formation of VMS,
(iii) their mass loss, and
(iv)
their evolution and final fate.
Reference: Astro-ph
1302.2021
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1302.2021
Comments:
29 pages. To be published in Highlights of Astronomy
Email:
jsv@arm.ac.uk
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Panos Boumis
Institute
of Astronomy, Astrophysics, Space Applications and Remote Sensing
National Observatory of Athens
Greece
Applications are
invited for a 3-year PhD position, combining optical instrumentation
with studies of the interstellar medium (ISM). Applicants with
previous experience in optical instrumentation, observing and
analysis of data, and the field of evolved stars and/or supernova
remnants (SNRs) are particularly encouraged to apply.
The
successful candidate is expected to be highly motivated and will work
under the supervision of Dr. P. Boumis at the Institute of Astronomy,
Astrophysics, Space Applications and Remote Sensing of the National
Observatory of Athens. A master's degree in astrophysics or optics is
a prerequisite for the PhD position. The appointment is part of a
large program that involves the construction, testing and use of a
new wide field camera (AWFC) for the 2.3m Aristarchos telescope, at
Helmos Observatory, Greece. The position will be funded by the
“KRIPIS” program of the Greek Secreteriat of Research and
Technology.
Applications should include a curriculum vitae, a
brief statement of current and future research interests (in PDF
format) and three letters of reference, sent directly by e-mail to
Dr. P. Boumis. Consideration of applications will begin on April 5th,
2013 and will continue until the position is filled. A starting date
in May or June of 2013 is anticipated. The gross monthly salary is
¤1500.
Submission and inquiries should be addressed to Dr.
P. Boumis (e-mail: ptb@astro.noa.gr, tel.: +30 2108109162, fax: +30
2108040453).
Attention/Comments:
Weblink:
http://www.astro.noa.gr/iaa_news.htm
Email:
bonanos@astro.noa.gr
Deadline: April 5, 2013
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Dr. Salvador Curiel
Instituto
de Astronomía, Universidad Nacional Autónoma de México, Mexico
City, iasacad@astro.unam.mx
The Instituto de Astronomía of
the Universidad Nacional Autónoma de México (IA-UNAM) has an
opening for a tenure track position in stellar astrophysics at the
Mexico City campus. Applicants should hold a Ph.D. degree in
astronomy or physics, have at least two years of postdoctoral
experience and preferably be less than 40 years old by October 2013.
A background in the study of stellar physics, stellar formation
and evolution is preferred. Experience with optical and infrared
wavelength observational projects (such as HST, VLT, HERSCHEL,
SPITZER), radiative transfer modeling, the interaction between
stellar winds, binaries and multiple systems, knowledge or
participation in instrumentation projects and experience in parallel
computing will be valuable assets.
The main selection criteria
will be outstanding research accomplishments and promise of future
achievement. The successful candidate is expected to carry out
original research, to collaborate with faculty members and teach
astronomy courses at the graduate and/or undergraduate level, as well
as mentor students. The level of the appointment will depend on the
curriculum of the candidate.
Candidates must send a complete
curriculum vitae including a full list of publications, as well as a
statement of previous experience and current and future professional
interests, and arrange for three letters of recommendation to be sent
to Dr. Salvador Curiel at the IA-UNAM (iasacad@astro.unam.mx) by May
27th 2013. Unsigned material can be sent by e-mail; letters can be
sent by e-mail (scanned) or by courier. Please do not use regular
post mail.
You can find further information using these
links:
IA Main Web Page: www.astroscu.unam.mx
Additional Job
Information: www.astroscu.unam.mx/job_ia
AAS Job Register:
jobregister.aas.org/job_view?JobID=44810
Attention/Comments:
Weblink:
Email:
gloria@astro.unam.mx
Deadline: 27 May 2013
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June 3-7, 2013
Venue:
Moscow, Russia
This is the third announcement for the
upcoming conference:
Putting A Stars into Context: Evolution,
Environment, and Related Stars,
June 3-7, 2013
Moscow,
Russia
We remind all potential participants that the deadline
for registration and submission of abstracts is April 1, 2013.
Registration
To register for the meeting and submit
your abstract, please, point your browser to
http://agora.guru.ru/astars2013/ and follow the instructions
The
registration fee covers all regular meeting costs including abstract
book, welcome party, coffee breaks, conference banquet, Moskva-river
cruise tour, and classical music concert. Full conference
registration costs 280 Euros (11 300 Rubles). Participants who pay
the registration fee before April 1, 2013, benefit from a discount of
30 Euros. Payments can be made via credit card.
Program:
Overview introductory talk (John D. Landstreet)
Session
1: A-star formation
1a. Big clouds to open clusters
Invited
talks:
1.1. Chemically peculiar tepid stars in the Milky Way and
beyond (Martin Netopil)
1.2. Elemental abundances in open cluster
A-type and related stars (Luca Fossati)
1b. Small clouds to
stars
Invited talks:
1.3. Discs around A-type and related
stars (Helmut Abt)
1.4. Accretion discs around magnetic stars
(Caroline D'Angelo)
1.5. Planets around A stars (David
Mkrtichian)
1.6. Distant sub-stellar companions of A-type and
related stars
1.7. Multiplicity of A-type and related stars
(Pierre North)
1c. Magnetic field generation
Invited
talks:
1.8. Magnetic fields in Herbig Ae/Be stars (Evelyne
Alecian)
1.9. Generation and evolution of stable stellar magnetic
fields (Rainer Arlt)
1.10. The protostar merger scenario of Ap
star magnetic field generation (Lilia Ferrario)
Session 2:
Properties of A-type stars
Invited talks:
2.1. Determinations
of fundamental parameters of (chemically peculiar) A stars through
optical interferometry (Karine Perraut)
2.2. Recent results and
current challenges in normal and chemically peculiar A-star model
atmospheres (Denis Shulyak)
2.3. Simultaneous mapping of chemical
abundances and magnetic field structure in Ap stars (Theresa
Lueftinger)
2.4. Element spots in HgMn stars (Heidi Korhonen)
2.5. The origin of light variability in Ap stars (Jiri Krticka)
2.6. Vertical abundance gradients in Ap-star atmospheres (Tatyana
Ryabchikova)
Session 3: Rotation and hydrodynamics of A-type
and related stars
Invited talks:
3.1. Time-dependent
diffusion and abundance stratification in A- and B-type stars(with
and without mass-loss)
3.2. A-star rotation (Frederic Royer)
3.3. Ap stars with variable rotation periods (Zdenek Mikulasek)
3.4. Rotation and hydrodynamical processes in upper main-sequence
stars (Stephane Mathis)
Session 4: Pulsation of A-type and
related stars
Invited talks:
4.1. A- and B-type star
pulsations in the Kepler and CoRoT era: observational results
(Katrien Uytterhoeven)
4.2. A- and B-type star pulsations in the
Kepler and CoRoT era: theoretical considerations (Hideyuki Saio)
4.3. Observational studies of roAp stars (Mikhail Sachkov)
4.4.
Stochastic oscillations in A-type and related stars (Victoria Antoci)
Session 5: Magnetic fields from O to early F stars
Invited
talks:
5.1. Magnetic fields in O stars
5.2. Magnetic fields
in beta Cep, SPB and Be stars
5.3. Recent results and current
challenges in observations of Ap/Bp star magnetic fields (Iosif
Romanyuk)
5.4. Magnetic fields in A stars besides Ap stars (Oleg
Kochukhov)
5.5. Non-pulsational variability of A- and B-type
stars as observed by Kepler (Luis Balona)
5.6. X-ray emission of
Ap stars and of other A stars (Jan Robrade)
5.7. Bp star
magnetospheres (Asif ud-Doula)
Session 6: A-stars at
post-main-sequence stages
Invited talks:
6.1. Descendants of
magnetic and non-magnetic A-type and related stars
6.2. White
dwarf magnetic fields (Gennady Valyavin)
6.3. A-type blue
stragglers
6.4. Horizontal-Branch A stars
6.5. Non-LTE
studies of A supergiants (Maria-Fernanda Nieva)
6.6. A
supergiants in the Local Group of galaxies and beyond (Miguel
Urbaneja)
Summary talk and closing discussion (Charles
Cowley)
Invited Speakers (confirmed):
Helmut Abt,
Evelyne Alecian, Victoria Antoci, Rainer Arlt, Luis Balona, Charles
Cowley, Caroline D'Angelo, Lilia Ferrario, Luca Fossati, Oleg
Kochukhov, Heidi Korhonen, Jiri Krticka, John D. Landstreet, Theresa
Lueftinger, Stephane Mathis, Zdenek Mikulasek, David Mkrtichian,
Martin Netopil, Maria-Fernanda Nieva, Pierre North, Karine Perraut,
Jan Robrade, Iosif Romanyuk, Frederic Royer, Tatyana Ryabchikova,
Mikhail Sachkov, Hideyuki Saio, Denis Shulyak, Asif ud-Doula, Miguel
Urbaneja, Katrien Uytterhoeven, Gennady Valyavin
Abstract
submission
Contributed talks will be selected from the
submitted abstracts, and there will also be a poster session.
Scientific Organizing Committee:
Gautier Mathys
(chair), Maryline Briquet, Margarida Cunha, Oleg Kochukhov, Friedrich
Kupka, Francis LeBlanc, Lyudmila Mashonkina, Richard Monier, Olga
Pintado, Hiromoto Shibahashi, Kazimierz Stepien, Glenn
Wahlgren
Weblink: http://agora.guru.ru/astars2013/
Email:
astars2013@inasan.ru
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June 10-14, 2013
Venue:
Rhodes, Greece
The 'Massive Stars' meetings have enjoyed
more than 40 years of startling success since the first meeting in
Argentina in 1971. Held every 4 to 5 years, these meetings aim to
encapsulate the current state-of-the-art of our understanding of the
physics of Massive Stars and their role in the Universe. For this
10th meeting in the Massive Stars series the Institute of Astronomy,
Astrophysics, Space Applications and Remote Sensing of the National
Observatory of Athens, invites you to the island of Rhodes, once home
to one of the greatest astronomers of antiquity, Hipparchos, who is
generally acknowledged as the founder of trigonometry, discoverer of
precession and publisher of the first modern star catalog around 135
BC.
The conference will build on results from ongoing
large-scale multi-wavelength surveys of massive stars which are being
coupled with new theoretical advances dealing with stellar evolution
and the processes which effect that evolution: mass-loss, rotation,
convection, magnetic fields, multiplicity and environment. It will
tackle important problems from birth, through main sequence evolution
and until core collapse.
There will be a strong focus on
relating the major theoretical uncertainties afflicting stellar
evolution through these phases to the current observational picture.
The impetus for this focus is derived from the realization that our
understanding of massive star evolution is severely challenged by new
observations powered largely by technological advances in telescopes
and instrumentation. This has enabled new ways of looking at old
long-standing problems enabling large-scale high-quality surveys of
resolved stellar populations. As theoretical approaches try to keep
pace with this increase in information the cracks in our assumptions
concerning stellar evolution have become more apparent, even glaring.
Whereas before it might have been possible to understand some of the
stars some of the time it is now clear that understanding stellar
populations is a considerable challenge and will require substantial
efforts to resolve.
This is an exciting time as observations
have revealed large gaps in understanding of the formation and
evolution of massive stars. The huge impact that massive stars have
on their immediate environment, parent galaxies, and through the
Universe, demands better understanding of massive star evolution from
alpha to Omega.
Looking forward to seeing you in
Rhodes!
Weblink: http://a2omega-conference.net
Email:
a2omega@astro.noa.gr
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26-30 August 2013
Venue: Biarritz,
France
This is the second announcement for the Symposium 302
of the International Astronomical Union, entitled "Magnetic
fields throughout stellar evolution". The conference will be
held in Biarritz (France), 26-30 August 2013.
--
Presentation:
Magnetic fields are key actors in the evolution
of all stellar objects, through their ability to influence the
angular momentum evolution, internal mixing or mass-loss of stars, as
well as their activity phenomena or star-planet interactions. The
present Symposium is aimed at offering a synthetic view of recent
progresses in the young and growing domain of stellar magnetism. This
research area is now benefiting from the rapid, combined development
of observations and numerical simulations, enabling stellar
physicists to take magnetic fields into account in most models of
stellar structure and evolution.
-- Topics:
- Stellar
structure and evolution
- Magnetized accretion and outflows in
young stellar objects
- Magnetic braking of PMS stars
- Solar
and stellar activity in photospheres, chromospheres and coronae, and
stellar cycles
- Magnetism in very low-mass stars and brown
dwarfs
- Star-planet interaction
- Stellar dynamos across the
HR diagram
- Magnetic field origin and stability in massive stars
- Magnetically-confined winds of massive stars
- Cool active
subgiants and giants
- Dynamo and mass-loss in giant and
supergiant stars
- Final phases of stellar evolution : magnetism
in compact objects
-- Scientific Organizing Committee:
-
Gibor Basri (Univ. California, USA)
- Matthew Browning (Univ.
Toronto,Canada)
- Corinne Charbonnel (Geneva Observatory,
Switzerland)
- Jose-Dias do Nascimento (Univ. Natal, Brazil)
-
Siraj Hasan (IIA, India)
- Moira Jardine (Univ. Saint Andrews,
Scotland, co-chair)
- Oleg Kochukhov (Univ. Uppsala, Sweden)
-
Renada Konstantinova-Antova (Bulgarian Academy of Sciences, Bulgaria)
- Hiroaki Isobe (Univ. Kyoto, Japan)
- Stephen Marsden (James
Cook University, Australia)
- Pascal Petit (Univ. Toulouse,
France, chair)
- Sami Solanki (MPS, Germany)
- Henk Spruit
(MPA, Germany, co-chair)
- Klaus Strassmeier (AIP, Germany)
-
Asif ud-Doula (Penn State, USA)
- Gregg Wade (RMC, Canada)
--
Confirmed speakers:
Jonathan Braithwaite - Sacha Brun - Rim
Fares - Jason Grunhut - Gaitee Hussain - Oleg Kochukhov - Heidi
Korhonen - Ryuichi Kurosawa - Norbert Langer - François Lignières -
Stuart Littlefair - Stan Owocki - Ralph Pudritz - Nanda Rea - Ansgar
Reiners - Andreas Reisenegger - Karel Schrijver - Saku Tsuneta -
Aline Vidotto - Wouter Vlemmings - Lucianne Walkowicz
--
Venue:
The conference will be held at Casino Municipal,
Biarritz (France). Situated on the French Atlantic coast, at the
western end of the Pyrénées mountain range, Biarritz is a friendly
and attractive town benefiting from the mild weather of southern
France. It can be easily reached by plane or train and offers more
than 2,300 hotel rooms. With 6 km of beaches, Biarritz is the
historical capital of surfing in Europe. You can also find there the
secondoldest golf course in Europe, 5 thalassotherapy centres and a
casino.
The town is just a stone’s throw away from Spain
and is less than 150 km away from Bilbao and its famous Guggenheim
museum. Biarritz is also located at less than 200 km from Bordeaux
and its world-famous wineries. It is a perfect starting point to
explore the Basque country, with its authentic countryside and
charming villages. A half-day excursion will bring the participants
to selected spots around the town, and the symposium diner will be
the opportunity to enjoy French gastronomy.
-- Accommodation:
Biarritz is very attractive during the month of August, and
hotels get fully booked very early. We therefore very strongly
recommend to book your hotel as soon as possible! A list of hotels is
available here: http://iaus302.sciencesconf.org/resource/page/id/9
-- Social events:
The conference dinner will take
place on Thursday night (29 Aug 2013), at Salle des Ambassadeurs
(Casino Municipal). The banquet cost is 40€ per person.
Three
optional wednesday tours are proposed, to be chosen between a visit
of Domaine Brana (winery), a discovery of the Basque coast by boat,
and a visit of Château-Observatory Abbadia. Additional fees of 20€
per person apply for the tours.
-- Registration:
Registration fee is 350€ per participant. The fee allows
access to the conference venue, the welcome cocktail on Sunday night,
the coffee breaks, four lunches, and a hard copy of proceedings.
Addditionnal fee is requested for conference dinner (40€) and
Wednesday tours (20€).
The online payment interface is
available here: http://iaus302.irap.omp.eu
Cancellations:
Requests for cancellation with a 50% fee refund will only be accepted
through 01 Jul 2013.
-- Abstract submission:
Abstracts
can be submitted at the following address:
http://iaus302.sciencesconf.org/submission/submit
-- Visa
information:
General information for preparing your entry in
France and applying to a French Visa is available here:
http://www.diplomatie.gouv.fr/en/france/coming-to-france/getting-a-visa/
Invitation letters will be provided to registered participants
whenever needed. Should you require a letter, we invite you to
contact the organizers by email (iaus302@sciencesconf.org).
--
Proceedings:
The proceedings of the Symposium will be
published by Cambridge University Press. A hardcopy of the
proceedings will be sent to each registered participant. Further
information will follow about page limits and LaTeX templates. The
deadline for submission of the proceedings is 30 Sep 2013.
--
Important dates:
- Abstract deadline for contributed talks:
13 May 2013
- Abstract deadline for posters: 21 Jun 2013
-
Deadline for registration: 15 Jul 2013
- Deadline for proceedings
submission: 30 Sep 2013
-- Contact:
Any inquiry about
the conference should be addressed to iaus302@sciencesconf.org
We
hope to see as many of you as possible in Biarritz this summer!
Best regards,
the SOC and LOC
Weblink:
http://iaus302.sciencesconf.org
Email:
iaus302@sciencesconf.org
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