ISSN 1783-3426
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IAU Symposia and Focus Meetings in 2018
Sub-mm free-free emission from the
winds of massive stars in the age of ALMA
Chandra
View of Magnetically Confined Wind in HD191612: Theory versus
Observations
Apsidal motion in
the massive binary HD152218
Characterisation
of red supergiants in the Gaia spectral range
On
the existence of accretion-driven bursts in massive star
formation
Bow shock nebulae of
hot massive stars in a magnetized medium
A
close encounter of the massive kind
VLTI/AMBER
spectro-interferometry of the late-type supergiants V766 Cen (=HR
5171 A), sigma Oph, BM Sco, and HD 206859
A
new prescription for the mass-loss rates of WC and WO
stars
Protostellar Outflows and
Radiative Feedback from Massive Stars. II. Feedback, Star Formation
Efficiency, and Outflow Broadening
Modeling
the early evolution of massive OB stars with an experimental wind
routine. The first bi-stability jump and the angular momentum loss
problem
A propelling neutron star
in the enigmatic Be-star gamma Cassiopeia
The
Tarantula Massive Binary Monitoring project: II. A first SB2 orbital
and spectroscopic analysis for the Wolf-Rayet binary R145
3D Hydrodynamic Simulations of Carbon Burning in Massive Stars
Evolution of intermediate mass and massive binary stars: physics, mass loss, and rotation.
Postdoc position in Sheffield: Massive
Stars in Starburst Galaxies
Postdoc
position in Theoretical Astrophysics
International Workshop on Spectral Stellar Libraries - 3rd Edition
Dear Members of IAU
Commission on Massive Stars and Massive Star Newsletter subscribers,
You have probably already received a reminder for the
submission of Letters of Interest for
- IAU Symposia in
2018
- IAU Focus Meetings in 2018
From the OC of
the Massive Stars Commission we would like to encourage our members
to submit proposals of interest for our community.
Below you
find some useful information.
9 IAU Symposia will be
selected for 2018, 6 of them for the IAU General Assembly in Vienna,
20-31 August 2018. About 15 IAU Focus Meetings (depending on
schedule) will be selected, all of them to be held during the GA.
Letters of Intent are due by September, 15th, 2016.
Full proposals are due by December, 15th, 2016.
The
electronic form for the submission is the same for Symposia and FM.
For letters of interest, the link is:
http://www.iau.org/science/meetings/proposals/loi/
and
for full proposals:
https://www.iau.org/science/meetings/proposals/lop/
Note that the LoI shall include the Coordinating
Division, and that the President shall be contacted previously. All
LoIs received by the deadline will be posted on the IAU web pages,
allowing prospective proposers to consider possible collaboration or
coordination before embarking in the preparation of the full-fledged
proposal. After that, draft proposals should be submitted to
Coordinating Divisions and other interested bodies (associated
Divisions, Commissions and Working Groups) for advice and letters of
endorsement, early enough to be included in the final form submitted
to IAU.
Symposia held during the GA last for 3.5 days.
Other IAU Symposia last for 5 days and cannot be held within 3 months
of the GA. FMs last for 1-2 days.
You find all the
information about IAU meetings in
http://www.iau.org/science/meetings/rules/
With
best regards,
Artemio Herrero
on behalf of the OC of the
IAU Commission G2 on Massive Stars
Weblink:
Email:
ahd@iac.es
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S. Daley-Yates, I. R. Stevens, T. D.
Crossland
University of Birmingham
The
thermal radio and sub-mm emission from the winds of massive stars is
investigated and the contribution to the emission due to the stellar
wind acceleration region and clumping of the wind is quantified.
Building upon established theory, a method for calculating the
thermal radio and sub-mm emission using results for a line-driven
stellar outflow according to Castor, Abbott & Klein (1975) is
presented. The results show strong variation of the spectral index
for 10 2 GHz < {\nu} < 10 4 GHz. This corresponds both to the
wind acceleration region and clumping of the wind, leading to a
strong dependence on the wind velocity law and clumping parameters.
The Atacama Large Millimeter/sub-mm Array (ALMA) is the first
observatory to have both the spectral window and sensitivity to
observe at the high frequencies required to probe the acceleration
regions of massive stars. The deviations in the predicted flux levels
as a result of the inclusion of the wind acceleration region and
clumping are sufficient to be detected by ALMA, through deviations in
the spectral index in different portions of the radio/sub-mm spectra
of massive stars, for a range of reasonable mass-loss rates and
distances. Consequently both mechanisms need to be included to fully
understand the mass-loss rates of massive stars.
Reference:
arXiv:1608.08380v2
Status: Manuscript has been
accepted
Weblink:
Comments:
Email:
sdaley@star.sr.bham.ac.uk
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Yael Naze (1), Asif ud-Doula (2), Svetozar A. Zhekov
(3)
1 - ULg, Belgium, 2 - Penn State, USA, 3 - Inst.
of Astro, Bulgaria
High-resolution spectra of the magnetic
star HD191612 were acquired using the Chandra X-ray observatory at
both maximum and minimum emission phases. We confirm the flux and
hardness variations previously reported with XMM-Newton,
demonstrating the great repeatability of the behavior of HD191612
over a decade. The line profiles appear typical for magnetic massive
stars: no significant line shift, relatively narrow lines for high-Z
elements, and formation radius at about 2R*. Line ratios confirm the
softening of the X-ray spectrum at the minimum emission phase. Shift
or width variations appear of limited amplitude at most (slightly
lower velocity and slightly increased broadening at minimum emission
phase, but within 1--2 sigma of values at maximum). In addition, a
fully self-consistent 3D magnetohydrodynamic (MHD) simulation of the
confined wind in HD191612 was performed. The simulation results were
directly fitted to the data leading to a remarkable agreement overall
between them.
Reference: accepted by ApJ
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1608.08741
Email:
naze@astro.ulg.ac.be
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Rauw G.(1), Rosu S.(1), Noels A.(1), Mahy L.(1), Schmitt
J.H.M.M.(2), Godart M.(1); Dupret M.-A.(1), Gosset E.(1)
1
- University of Liege, Belgium
2 - Hamburger Sternwarte,
Germany
Massive binary systems are important laboratories
in which to probe the properties of massive stars and stellar physics
in general. In this context, we analysed optical spectroscopy and
photometry of the eccentric short-period early-type binary HD 152218
in the young open cluster NGC 6231. We reconstructed the spectra of
the individual stars using a disentangling code. The individual
spectra were then compared with synthetic spectra obtained with the
CMFGEN model atmosphere code. We furthermore analysed the light curve
of the binary and used it to constrain the orbital inclination and to
derive absolute masses of 19.8 +/- 1.5 and 15.0 +/- 1.1 solar masses.
Combining radial velocity measurements from over 60 years, we show
that the system displays apsidal motion at a rate of
(2.04^{+.23}_{-.24}) degree/year. Solving the Clairaut-Radau
equation, we used stellar evolution models, obtained with the CLES
code, to compute the internal structure constants and to evaluate the
theoretically predicted rate of apsidal motion as a function of
stellar age and primary mass. In this way, we determine an age of 5.8
+/- 0.6 Myr for HD 152218, which is towards the higher end of, but
compatible with, the range of ages of the massive star population of
NGC 6231 as determined from isochrone fitting.
Reference:
Astronomy & Astrophysics, in press
Status: Manuscript
has been accepted
Weblink:
http://arxiv.org/abs/1609.02735
Comments:
Email: rauw@astro.ulg.ac.be
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Ricardo Dorda$^1$,
Carlos González-Fernández$^2$,
Ignacio Negueruela$^1$,
1- Universidad de
Alicante;
2- Institute of Astronomy - University of
Cambridge
The infrared Calcium Triplet and its nearby
spectral region have been used for spectral and luminosity
classification of late-type stars, but the samples of cool
supergiants (CSGs) used have been very limited (in size, metallicity
range, and spectral types covered). The spectral range of the Gaia
Radial Velocity Spectrograph (RVS) covers most of this region but
does not reach the main TiO bands in this region, whose depths define
the M sequence. We study the behaviour of spectral features around
the Calcium Triplet and develop effective criteria to identify and
classify CSGs, comparing their efficiency with other methods
previously proposed. We measure the main spectral features in a large
sample (almost 600) of CSGs from three different galaxies, and we
analyse their behaviour through a principal component analysis. Using
the principal components, we develop an automatised method to
differentiate CSGs from other bright late-type stars, and to classify
them. The proposed method identifies a high fraction of the
supergiants (SGs) in our test sample, which cover a wide metallicity
range (SGs from the SMC, the LMC, and the Milky Way) and with
spectral types from G0 up to late-M. In addition, it is capable to
separate most of the non-SGs in the sample, identifying as SGs only a
very small fraction of them. A comparison of this method with other
previously proposed shows that it is more efficient and selects less
interlopers. A way to automatically assign a spectral type to the SGs
is also developed. We apply this study to spectra at the resolution
and spectral range of the Gaia RVS, with a similar success rate. The
method developed identifies and classifies CSGs in large samples,
with high efficiency and low contamination, even in conditions of
wide metallicity and spectral-type ranges.
Reference:
Astronomy & Astrophysics
Status: Manuscript has been
accepted
Weblink:
https://arxiv.org/abs/1609.04063
Comments:
Email: ri.dorda@gmail.com
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D. M.-A. Meyer (1), E.I. Vorobyov (2,3), R. Kuiper (1),
W. Kley (1)
(1) Institut fuer Astronomie und
Astrophysik, Universitaet Tuebingen
(2) Department of
Astrophysics, The University of Vienna
(3) Research Institute
of Physics, Southern Federal University
Accretion-driven
luminosity outbursts are a vivid manifestation of variable mass
accretion onto protostars. They are known as the so-called FU Orionis
phenomenon in the context of low-mass protostars. More recently, this
process has been found in models of primordial star formation. Using
numerical radiation hydrodynamics simulations, we stress that
present-day forming massive stars also experience variable accretion
and show that this process is accompanied by luminous outbursts
induced by the episodic accretion of gaseous clumps falling from the
circumstellar disk onto the protostar. Consequently, the process of
accretion-induced luminous flares is also conceivable in the
high-mass regime of star formation and we propose to regard this
phenomenon as a general mechanism that can affect protostars
regardless of their mass and/or the chemical properties of the parent
environment in which they form. In addition to the commonness of
accretion-driven outbursts in the star formation machinery, we
conjecture that luminous flares from regions hosting forming
high-mass star may be an observational implication of the
fragmentation of their accretion disks.
Reference:
MNRAS Letters (2016) doi: 10.1093/mnrasl/slw187
Status:
Manuscript has been accepted
Weblink:
http://mnrasl.oxfordjournals.org/content/early/2016/09/15/mnrasl.slw187.abstract
Comments:
Email: dominique.meyer@uni-tuebingen.de
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D. M.-A. Meyer (1), A. Mignone (2), R. Kuiper (1), A.
Raga (3) and W. Kley (1)
(1) Institut fuer Astronomie
und Astrophysik, Universitaet Tubingen, Auf der Morgenstelle 10,
72076 Tubingen, Germany
(2) Dipartimento di Fisica Generale
Facolta di Scienze M.F.N., Universita degli Studi di Torino, Via
Pietro Giuria 1, 10125 Torino, Italy
(3) Instituto de Ciencias
Nucleares, Universidad Nacional Autonoma de Mexico, Ap. 70-543, 04510
D.F., Mexico
A significant fraction of OB-type,
main-sequence massive stars are classified as run-away and move
supersonically through the interstellar medium (ISM). Their strong
stellar winds interact with their surroundings where the typical
strength of the local ISM magnetic field is about 3.5-7 microG, which
can result in the formation of bow shock nebulae. We investigate the
effects of such magnetic fields, aligned with the motion of the flow,
on the formation and emission properties of these circumstellar
structures. Our axisymmetric, magneto-hydrodynamical simulations with
optically-thin radiative cooling, heating and anisotropic thermal
conduction show that the presence of the background ISM magnetic
field affects the projected optical emission our bow shocks at Ha and
[OIII] lambda 5007 which become fainter by about 1-2 orders of
magnitude, respectively. Radiative transfer calculations against dust
opacity indicate that the magnetic field slightly diminishes their
projected infrared emission and that our bow shocks emit brightly at
60 micron. This may explain why the bow shocks generated by ionizing
runaway massive stars are often difficult to identify. Finally, we
discuss our results in the context of the bow shock of Zeta Ophiuchi
and we support the interpretation of its imperfect morphology as an
evidence of the presence of an ISM magnetic field not aligned with
the motion of its driving star.
Reference: doi:
10.1093/mnras/stw2537
Status: Manuscript has been
accepted
Weblink:
http://mnras.oxfordjournals.org/content/early/2016/10/05/mnras.stw2537.abstract?keytype=ref&ijkey=uLtsP0ASPYyc8RF
Comments:
Email: dominique.meyer@uni-tuebingen.de
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J. Maíz Apellániz, H. Sana, R. H. Barbá, J.-B. Le
Bouquin, & R. C. Gamen
[1] CAB, CSIC-INTA; [2] KU
Leuven; [3] ULS; [4] IPAG; [5] IALP, CONICET-UNLP.
We have
used (a) HST ACS imaging and STIS spectroscopy, (b) ground-based
PIONIER/VLT long-baseline interferometry, and (c) ground-based
spectroscopy from different instruments to study the orbit of the
extreme multiple system HD 93 129 Aa,Ab, which is composed of (at
least) two very massive stars in a long-period orbit with e>0.92
that will pass through periastron in 2017/2018. In several ways, the
system is an eta Car precursor. Around the time of periastron passage
the two very strong winds will collide and generate an outburst of
non-thermal hard X-ray emission without precedent in an O+O binary
since astronomers have been able to observe above Earth's atmosphere.
A coordinated multiwavelength monitoring in the next two years will
enable a breakthrough understanding of the wind interactions in such
extreme close encounters. Furthermore, we have found evidence that HD
93 129 Aa may be a binary system itself. In that case, we could
witness a three-body interaction that may yield a runaway star or a
stellar collision close to or shortly after the periastron passage.
Either of those outcomes would be unprecedented, as they are
predicted to be low-frequency events in the Milky Way.
Reference:
Accepted for publication in MNRAS
Status: Manuscript has
been accepted
Weblink:
https://arxiv.org/abs/1609.08521
Comments:
Email: jmaiz@cab.inta-csic.es
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M. Wittkowski (1), B. Arroyo-Torres (2,3,4), J. M.
Marcaide (2), F. J. Abellan (2), A. Chiavassa (5), J. C. Guirado
(2,6)
1: European Southern Observatory, Garching,
Germany
2: Dpt. Astronomia i Astrofisica, Universitat de
Valencia, Burjassot, Spain
3: Instituto de Astrofisica de
Andalucia (IAA-CSIC), Granada, Spain
4: Centro Astronomico
Hispano Aleman, Calar Alto, Spain
5: Laboratoire Lagrange,
Universite de Nice Sophia-Antipolis, Nice, France
6:
Observatorio Astronomico, Universidad de Valencia, Spain
Aims:
We add four warmer late-type supergiants to our previous
spectro-interferometric studies of red giants and supergiants.
Methods: We measure the near-continuum angular diameter, derive
fundamental parameters, discuss the evolutionary stage, and study
extended atmospheric atomic and molecular layers.
Results: V766
Cen (=HR 5171 A) is found to be a high-luminosity (log
L/L_sun=5.8+-0.4) source of effective temperature 4290+-760 K and
radius 1490+-540 R_sun, located in the Hertzsprung-Russell (HR)
diagram close to both the Hayashi limit and Eddington limit; this
source is consistent with a 40 M_sun evolutionary track without
rotation and current mass 27-36 M_sun. V766 Cen exhibits NaI in
emission arising from a shell of radius 1.5 R_Phot and a photocenter
displacement of about 0.1 R_Phot. It shows strong extended molecular
(CO) layers and a dusty circumstellar background component. The other
three sources are found to have lower luminosities of about log
L/L_sun=3.4-3.5, corresponding to 5-9 M_sun evolutionary tracks. They
cover effective temperatures of 3900 K to 5300 K and radii of 60-120
R_sun. They do
not show extended molecular layers as observed
for higher luminosity red supergiants of our sample. BM Sco shows an
unusually strong contribution by an over-resolved circumstellar dust
component.
Conclusions: V766 Cen is a red supergiant located
close to the Hayashi limit instead of a yellow hypergiant already
evolving back toward warmer effective temperatures as discussed in
the literature. Our observations of the NaI line and the extended
molecular layers suggest an optically thick pseudo-photosphere at
about 1.5 R_Phot at the onset of the wind. The stars sigma Oph, BM
Sco, and HD 206859 are more likely high-mass red giants instead of
red supergiants as implied by their luminosity class Ib. This leaves
us with an unsampled locus in the HR diagram corresponding to
luminosities log L/L_sun of 3.8-4.8 or masses 10-13 M_sun, possibly
corresponding to the mass region where stars explode as (type II-P)
supernovae during the red supergiant stage. With V766 Cen, we now
confirm that our previously found relation of increasing strength of
extended molecular layers with increasing luminosities extends to
double our previous luminosities and up to the Eddington limit. This
might further point to steadily increasing radiative winds with
increasing luminosity.
Reference: Astronomy &
Astrophysics (A&A), accepted
arXiv:1610.01927
Status:
Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2016arXiv161001927W
Comments:
Email: mwittkow@eso.org
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F. Tramper, H. Sana, A. de Koter
European
Space Astronomy Centre, KU Leuven, University of Amsterdam
We
present a new empirical prescription for the mass-loss rates of
carbon and
oxygen sequence Wolf-Rayet stars as a function of
their luminosity, surface
chemical composition, and initial
metallicity. The new prescription is based on
results of
detailed spectral analyses of WC and WO stars, and improves the
often applied Nugis & Lamers (2000) relation. We find that
the mass-loss rates
of WC and WO stars (with $X=0$ and $Y <
0.98$) can be expressed as
$\log{\dot{M}} = -9.20 +
0.85\log{(L/L_{\odot})} + 0.44\log{Y} +
0.25\log{(Z_{\mathrm{Fe}}/Z_{\mathrm{Fe}, \odot})}$. This
relation is based on
mass-loss determinations that assume a
volume-filling factor of 0.1, but the
prescription can easily
be scaled to account for other volume-filling factors.
The
residual of the fit is $\sigma = 0.06$ dex. We investigated whether
the
relation can also describe the mass loss of hydrogen-free
WN stars and showed
that it can when an adjustement of the
metallicty dependence ($\log{\dot{M}}
\propto
1.3\log{(Z_{\mathrm{Fe}}/Z_{\mathrm{Fe}, \odot})}$) is applied.
Compared to Nugis & Lamers (2000), $\dot{M}$ is less
sensitive to the
luminosity and the surface abundance, implying
a stronger mass loss of massive
stars in their late stages of
evolution. The modest metallicity dependence
implies that if WC
or WO stars are formed in metal deficient environments,
their
mass-loss rates are higher than currently anticipated. These effects
may
result in a larger number of type Ic supernovae and less
black holes to be
formed, and may favour the production of
superluminous type Ic supernovae
through interaction with C and
O rich circumstellar material or the dense
stellar
wind.
Reference: ApJ
Status: Manuscript has
been accepted
Weblink:
https://arxiv.org/abs/1610.03800
Comments:
Email: ftramper@sciops.esa.int
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Rolf Kuiper, Neal J. Turner, Harold W. Yorke
Institute
of Astronomy and Astrophysics, University of Tübingen, Auf der
Morgenstelle 10, D-72076 Tübingen, Germany
Jet Propulsion
Laboratory, California Institute of Technology, 4800 Oak Grove Drive,
Pasadena, CA 91109, USA
We perform two-dimensional axially
symmetric radiation-hydrodynamic simulations to assess the impact of
outflows and radiative force feedback from massive protostars by
varying when the protostellar outflow starts, the ratio of ejection
to accretion rates, and the strength of the wide angle disk wind
component. The star formation efficiency, i.e. the ratio of final
stellar mass to initial core mass, is dominated by radiative forces
and the ratio of outflow to accretion rates. Increasing this ratio
has three effects: First, the protostar grows slower with a lower
luminosity at any given time, lowering radiative feedback. Second,
bipolar cavities cleared by the outflow are larger, further
diminishing radiative feedback on disk and core scales. Third, the
higher momentum outflow sweeps up more material from the collapsing
envelope, decreasing the protostar’s potential mass reservoir via
entrainment. The star formation efficiency varies with the ratio of
ejection to accretion rates from 50% in the case of very weak
outflows to as low as 20% for very strong outflows. At latitudes
between the low density bipolar cavity and the high density accretion
disk, wide angle disk winds remove some of the gas, which otherwise
would be part of the accretion flow onto the disk; varying the
strength of these wide angle disk winds, however, alters the final
star formation efficiency by only ±6%. For all cases, the opening
angle of the bipolar outflow cavity remains below 20 degree during
early protostellar accretion phases, increasing rapidly up to 65
degree at the onset of radiation pressure feedback.
Reference:
Kuiper, Turner, & Yorke (2016), eprint
arXiv:1609.05208
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2016arXiv160905208K
Comments:
accepted for publication at ApJ
Email:
rolf.kuiper@uni-tuebingen.de
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Z. Keszthelyi (1,2,3), J. Puls (1), G.A. Wade (2)
(1)
LMU Munich, Universitätssternwarte, Scheinerstr. 1, 81679 München,
Germany
(2) Royal Military College of Canada, PO Box 17000
Station Forces, Kingston, Ontario, Canada, K7K 7B4
(3) Queen's
University, Stirling Hall, Kingston, Ontario, Canada, K7L
3N6
Context. Stellar evolution models of massive stars are
very sensitive
to the adopted mass-loss scheme. The magnitude
and evolution of
mass-loss rates significantly affect the main
sequence evolution, and
the properties of post-main sequence
objects, including their
rotational velocities.
Aims.
Driven by potential discrepancies between theoretically predicted and
observationally derived mass-loss rates in the OB star range,
we
particularly aim to investigate the response to mass-loss
rates that
are lower than currently adopted, in parallel with
the mass-loss
behavior at the ``first'' bi-stability jump.
Methods. We perform 1D hydrodynamical model calculations
of single $20 - 60 \,
M_{\odot}$ Galactic ($Z = 0.014$) stars
where the effects of stellar
winds are already significant
during the main sequence phase. We
develop an experimental wind
routine to examine the behavior and
response of the models
under the influence of different mass-loss
rates. This
observationally guided, simple and flexible wind routine
is not
a new mass-loss description but a useful tool based on the
Wind-momentum Luminosity Relation and other scaling relations,
and
provides a meaningful base for various tests and
comparisons.
Results. The main result of this study
indicates a dichotomy when accounting
for currently debated
problems regarding mass-loss rates of hot
massive stars. In a
fully diffusive approach, and for commonly
adopted initial
rotational velocities, lower mass-loss rates than
theoretically
predicted require to invoke an additional source of
angular
momentum loss (either due to bi-stability braking, or yet
unidentified) to brake down surface rotational velocities. On
the
other hand, a large jump in the mass-loss rates due to the
bi-stability mechanism (a factor 5 - 7 predicted by Vink et al.
(2000,
Astronomy \& Astrophysics, 362, 295), but a factor
10 - 20 in modern
models of massive stars) is challenged by
observational results, and
might be avoided if the early
mass-loss rates agreed with the
theoretically predicted values.
Conclusions. We conclude that simultaneously adopting
lower mass-loss rates and a
significantly smaller jump in the
mass-loss rates over the
bi-stability region (both compared to
presently used prescriptions)
would require an additional
mechanism for angular momentum loss to be
present in massive
stars. Otherwise, the observed rotational
velocities of a large
population of B supergiants, that are thought to
be the
evolutionary descendants of O stars, would remain
unexplained.
Reference: Astronomy &
Astrophysics. astro-ph:1610.04812
Status: Manuscript has been
accepted
Weblink:
https://arxiv.org/abs/1610.04812
Comments:
Email: zsolt.keszthelyi@rmc.ca
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K. Postnov, L. Oskinova, J. M. Torrejon
SAI
MSU, U. Potsdam, U. Alicante
The enigmatic X-ray emission
from the bright optical star, gamma Cassiopeia, is a long-standing
problem. gamma Cas is known to be a binary system consisting of a
Be-type star and a low-mass (M~1Msun) companion of unknown nature
orbiting in the Be-disk plane. Here we apply the quasi-spherical
accretion theory onto a compact magnetized star and show that if the
low-mass companion of gamma Cas is a fast spinning neutron star, the
key observational signatures of gamma Cas are remarkably well
reproduced. Direct accretion onto this fast rotating neutron star is
impeded by the propeller mechanism. In this case, around the neutron
star magnetosphere a hot shell is formed that emits thermal X-rays in
qualitative and quantitative agreement with observed properties of
the X-ray emission from gamma Cas. We suggest that gamma Cas and its
analogs constitute a new subclass of Be-type X-ray binaries hosting
rapidly rotating neutron stars formed in supernova explosions with
small kicks. The subsequent evolutionary stage of gamma Cas and its
analogs should be the X Per-type binaries comprising low-luminosity
slowly rotating X-ray pulsars. The model explains the enigmatic X-ray
emission from gamma Cas, and also establishes evolutionary
connections between various types of rotating magnetized neutron
stars in Be-binaries.
Reference: MNRAS
Status:
Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1610.07799
Comments:
Email: kpostnov@gmail.com
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T. Shenar, N. D. Richardson, D.
P. Sablowski, R. Hainich, H. Sana, A. F. J. Moffat, H. Todt, W.-R.
Hamann, L. M. Oskinova, A. Sander, F. Tramper, N. Langer, A. Z.
Bonanos, S. E. de Mink, G. Graefener, P. A. Crowther, J. S. Vink, L.
A. Almeida, A. de Koter, R. Barba, A. Herrero, K. Ulaczyk
University
of Potsdam
We present the first SB2 orbital solution and
disentanglement of the massive Wolf-Rayet binary R145 (P = 159d)
located in the Large Magellanic Cloud. The primary was claimed to
have a stellar mass greater than 300Msun, making it a candidate for
the most massive star known. While the primary is a known late type,
H-rich Wolf-Rayet star (WN6h), the secondary could not be so far
unambiguously detected. Using moderate resolution spectra, we are
able to derive accurate radial velocities for both components. By
performing simultaneous orbital and polarimetric analyses, we derive
the complete set of orbital parameters, including the inclination.
The spectra are disentangled and spectroscopically analyzed, and an
analysis of the wind-wind collision zone is conducted.
The
disentangled spectra and our models are consistent with a WN6h type
for the primary, and suggest that the secondary is an O3.5 If*/WN7
type star. We derive a high eccentricity of e = 0.78 and minimum
masses of M1 sin^3 i ~ M2 sin^3 i ~ 13 +- 2 Msun, with q = M2 / M1 =
1.01 +- 0.07. An analysis of emission excess stemming from a
wind-wind collision yields a similar inclination to that obtained
from polarimetry (i = 39 +- 6deg). Our analysis thus implies M1 =
53^{+40}_{-20} and M2 = 54^{+40}_{-20} Msun, excluding M1 >
300Msun. A detailed comparison with evolution tracks calculated for
single and binary stars, as well as the high eccentricity, suggest
that the components of the system underwent quasi-homogeneous
evolution and avoided mass-transfer. This scenario would suggest
current masses of ~ 80 Msun and initial masses of Mi,1 ~ 105 and Mi,2
~ 90Msun, consistent with the upper limits of our derived orbital
masses, and would imply an age of ~2.2 Myr.
Reference:
A&A, in press
Status: Manuscript has been
accepted
Weblink:
https://arxiv.org/abs/1610.07614
Email:
shtomer@astro.physik.uni-potsdam.de
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Andrea Cristini (1), Casey
Meakin (2,3,4), Raphael Hirschi (1,5), David Arnett (2), Cyril Georgy
(1,6), Maxime Viallet (7)
1 - Astrophysics Group,
Keele University, Lennard-Jones Laboratories, Keele, ST5 5BG, UK; 2 -
Department of Astronomy, University of Arizona, Tucson, AZ 85721,
USA; 3 - New Mexico Consortium, Los Alamos, NM 87544, USA; 4 -
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM
87545, USA; 5 - Kavli IPMU (WPI), The University of Tokyo, Kashiwa,
Chiba 277-8583, Japan; 6 - Geneva Observatory, University of Geneva,
Maillettes 51, 1290 Versoix, Switzerland; 7 - Max-Planck-Institut für
Astrophysik, Karl Schwarzschild Strasse 1, Garching, D-85741,
Germany
We present the first detailed three-dimensional
(3D) hydrodynamic implicit large eddy simulations of turbulent
convection of carbon burning in massive stars. The simulations start
with initial radial profiles mapped from a carbon burning shell
within a 15 solar mass 1D stellar evolution model. We consider 4
resolutions from 128^3 to 1024^3 zones. The turbulent flow properties
of these carbon burning simulations are very similar to the oxygen
burning case. We performed a mean field analysis of the kinetic
energy budgets within the Reynolds-averaged Navier-Stokes framework.
For the upper convective boundary region, we find that the inferred
numerical dissipation is insensitive to resolution for linear mesh
resolutions between 512 and 1,024 grid points. For the stiffer and
more stratified lower boundary, our highest resolution model still
shows signs of decreasing dissipation suggesting that it is not yet
fully resolved numerically. We estimate the widths of the upper and
lower boundaries to be roughly 30% and 10% of the local pressure
scale heights, respectively. The shape of the boundaries is
significantly different from those used in stellar evolution models,
which assume strict Ledoux or Schwarzschild boundaries. Entrainment
rates derived for the carbon shell are consistent with those derived
for the oxygen shells and with the entrainment law commonly used in
the meteorological and atmosphere science communities. The
entrainment rate is roughly inversely proportional to the bulk
Richardson number. We thus suggest the use of the bulk Richardson
number as a means to apply the results of 3D hydrodynamics
simulations to 1D stellar evolution modelling.
Reference:
MN-16-3621-MJ
Status: Manuscript has been
submitted
Weblink:
https://arxiv.org/abs/1610.05173
Comments:
Email: a.j.cristini@keele.ac.uk
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Dany Vanbeveren & Nicki
Mennekens
Vrije Universiteit Brussels, Belgium
In
the present review we discuss the past and present status of the
interacting OB-type binary frequency. We critically examine the
popular idea that Be-stars and supergiant sgB[e] stars are binary
evolutionary products. The effects of rotation on stellar evolution
in general, stellar population studies in particular, and the link
with binaries will be evaluated. Finally a discussion is presented of
massive double compact star binary mergers as possible major sites of
chemical enrichment of r-process elements and as the origin of recent
aLIGO GW events.
Reference: Invited paper to appear
in the proceedings of the June 2016 conference 'The B[e] Phenomenon:
Forty Years of Studies'.
Status: Conference
proceedings
Weblink: arXiv:
1609.02401
Comments:
Email:
dvbevere@vub.ac.be
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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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6th to 10th Feb 2017
Venue: Campos
do Jordao, Brazil
Libraries of stellar spectra play an
important role in different
fields of astrophysics. They can
serve as reference for the
classification and automatic
analysis of large stellar spectroscopic
surveys, or be employed
in the spectral modelling of galaxies, among
other
applications. These libraries may either consist of observed
or
theoretical spectra, and vary by their wavelength coverage,
parameter space domain and resolution.
The goals of
this workshop are to present the recent efforts in this
area,
in particular in four domains: Stellar Libraries as Templates
for
Stars, SLs for Chemical Evolution, SLs for Stellar Population
studies and SLs in the Big Data Era.
This is the
3rd Edition of this workshop, following the editions in
Delhi
in 2011 and Lyon in 2013.
Registration is now open. For
more information, please visit
https://sites.google.com/site/iwssl2017/
Weblink:
https://sites.google.com/site/iwssl2017/
Email:
pcoelho@usp.br
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