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The super-orbital modulation of
supergiant high-mass X-ray binaries
Properties
of six short-period massive binaries: a study of the effects of
binarity on surface chemical abundances
X-rays
from the colliding wind binary WR 146
Emission
Lines in the Near-infrared Spectra of the Infrared Quintuplet Stars
in the Galactic Center
Close
binary evolution. III. Impact of tides, wind magnetic braking and
internal angular momentum transport
A
Tale of Two Impostors: SN2002kg and SN1954J in NGC 2403
Multi-epoch
VLTI-PIONIER imaging of the supergiant V766 Cen: Image of the close
companion in front of the primary
Forming
spectroscopic massive proto-binaries by disk fragmentation
A
dearth of OH/IR stars in the Small Magellanic Cloud
The
dusty aftermath of SN Hunt248: merger-burst remnant?
An
X-ray Study of Two B+B Binaries: AH Cep and CW Cep
Winds
from stripped low-mass Helium stars and Wolf-Rayet stars
Are
some CEMP-s stars the daughters of spinstars?
BRITE-Constellation
high-precision time-dependent photometry of the early-O-type
supergiant Zeta Puppis unveils the photospheric drivers of its small-
and large-scale wind structures
2D
wind clumping in hot, massive stars from hydrodynamical line-driven
instability simulations using a pseudo-planar approach
Fizeau exchange visitors program in
optical interferometry - call for applications
MUNI
Award in Science and Humanities
Imaging of
Stellar Surfaces
Star Formation
and Young Stars in Cygnus
E. Bozzo (1), L. Oskinova (2,3), A. Lobel (4), W.-R Hamann
(2)
1- Department of Astronomy, University of Geneva,
Switzerland; 2 - Institut für Physik und Astronomie, Universität
Potsdam, Germany; 3 - Kazan Federal University, Kazan, Russia), 4 -
Royal Observatory of Belgium, Brussels, Belgium)
The
long-term X-ray lightcurves of classical supergiant X-ray binaries
and supergiant fast X-ray transients show relatively similar
super-orbital modulations, which are still lacking a sound
interpretation. We propose that these modulations are related to the
presence of corotating interaction regions (CIRs) known to thread the
winds of OB supergiants. To test this hypothesis, we couple the
outcomes of 3-D hydrodynamic models for the formation of CIRs in
stellar winds with a simplified recipe for the accretion onto a
neutron star. The results show that the synthetic X-ray light curves
are indeed modulated by the presence of the CIRs. The exact period
and amplitude of these modulations depend on a number of parameters
governing the hydrodynamic wind models and on the binary orbital
configuration. To compare our model predictions with the
observations, we apply the 3-D wind structure previously shown to
well explain the appearance of discrete absorption components in the
UV time series of a prototypical B0.5I-type supergiant. Using the
orbital parameters of IGRJ16493-4348 which has the same B0.5I donor
spectral type, the period and modulations in the simulated X-ray
light-curve are similar to the observed ones, thus providing support
to our scenario. We propose, that the presence of CIRs in donor star
winds should be considered in future theoretical and simulation
efforts of wind-fed X-ray binaries.
Weblink:
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1710.01877
Email:
enrico.bozzo@unige.ch
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Fabrice Martins$^1$, Laurent Mahy$^2,3$, Anthony
Hervé$^1$
1- LUPM, CNRS & Montpellier University;
2- Space sciences, Technologies, and Astrophysics Research (STAR)
Institute, Liège University; 3- Instituut voor Sterrenkunde, KU
Leuven
A significant fraction of massive stars are found
in multiple systems. The effect of binarity on stellar evolution is
poorly constrained. In particular, the role of tides and mass
transfer on surface chemical abundances is not constrained
observationally. The aim of this study is to investigate the effect
of binarity on the stellar properties and surface abundances of
massive binaries. We perform a spectroscopic analysis of six Galactic
massive binaries. The spectra of individual components are obtained
from a spectral disentangling method and are subsequently analyzed by
means of atmosphere models. The stellar parameters and CNO surface
abundances are determined. Most systems are made of main-sequence
stars. Three systems are detached, two are in contact and no
information is available for the sixth system. For eleven out of the
twelve stars studied the surface abundances are only mildly affected
by stellar evolution and mixing. They are not different from those of
single stars, within the uncertainties. The secondary of XZ~Cep is
strongly chemically enriched. Considering previous determinations of
surface abundance in massive binary systems suggests that the effect
of tides on chemical mixing is limited, whereas mass transfer and
removal of outer layers of the mass donor leads to the appearance of
chemically processed material at the surface, although this is not
systematic. The evolutionary masses of the components of our six
systems are on average 16.5% higher than the dynamical masses. Some
systems seem to have reached synchronization, while others may still
be in a transitory phase.
Reference: Acepted in
Astronomy and Astrophysics
Status: Manuscript has been
accepted
Weblink:
https://arxiv.org/abs/1709.00937
Comments:
Email: fabrice.martins@umontpellier.fr
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Svetozar A. Zhekov
Institute of Astronomy
and National Astronomical Observatory,
72 Tsarigradsko Chaussee
Blvd., Sofia 1784, Bulgaria
The X-ray emission from the
massive binary WR 146R is analysed in the framework of the colliding
stellar wind (CSW) picture. The theoretical CSW model spectra match
well the shape of the observed
X-ray spectrum of WR 146R but
they overestimate considerably the observed X-ray flux (emission
measure). This is valid both in the case of complete temperature
equalization and in the case of partial electron heating at the shock
fronts (different electron and ion temperatures), but, there are
indications for a better correspondence between model predictions and
observations for the latter. To reconcile the model predictions and
observations, the mass-loss rate of WR 146 must be reduced by a
factor of 8 – 10 compared to the currently accepted value for this
object (the latter already takes clumping into account). No excess
X-ray absorption is derived from the CSW modelling.
Reference:
Accepted for publication in MNRAS
Status: Manuscript has
been accepted
Weblink:
https://arxiv.org/abs/1709.01023
Comments:
Email: szhekov@astro.bas.bg
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F. Najarro^1, T.R. Geballe^2, D.F. Figer^3 and D. de la
Fuente^4
^1 Centro de Astrobiologia
^2 Gemini
Observatory
^3 Rochester Institute of Technology
^4
Instituto de Astronomia, UNAM
We report the detection of a
number of emission lines in the 1.0--2.4$\mu$m spectra of four of the
five bright infrared dust-embedded stars at the center of the
Galactic center's Quintuplet Cluster. Spectroscopy of the central
stars of these objects is hampered not only by the large interstellar
extinction that obscures all objects in the Galactic center, but also
by the large amounts of warm circumstellar dust surrounding each of
the five. The pinwheel morphologies of the dust observed previously
around two of them are indicative of Wolf-Rayet colliding wind
binaries; however, infrared spectra of each of the five have until
now revealed only dust continua steeply rising to long wavelengths
and absorption lines and bands from interstellar gas and dust. The
emission lines detected, from ionized carbon and from helium, are
broad and confirm that the objects are dusty late-type carbon
Wolf-Rayet stars.
Reference: Published in ApJ Aug
20, 2017
Status: Manuscript has been accepted
Weblink:
http://lanl.arxiv.org/pdf/1707.06894v1
Comments:
Email: najarro@cab.inta-csic.es
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H.F. Song{1,2,3}, G. Meynet{2}, A. Maeder{2}, S.
Ekstrom{2}, P. Eggenberger{2}, C. Georgy{2}, Y. Qin{2,4}, T.
Fragos{2}, M. Soerensen{2}, F. Barblan{2}, G. A. Wade{5}
1-College
of Physics, Guizhou University, Guiyang City, Guizhou Province,
550025, P.R. China
2- Geneva Observatory, Geneva University,
CH-1290 Sauverny, Switzerland
3- Key Laboratory for the
Structure and Evolution of Celestial Objects, Chinese Academy of
Sciences, Kunming 650011
-4 Guangxi Key Laboratory for
Relativistic Astrophysics, Department of Physics, Guangxi University,
Nanning 530004, China
-5 Department of Physics, Royal Military
College of Canada, Ontario, Canada
We discuss the
evolution of a 10 M$_\odot$ star in a close binary system with a 7
M$_\odot$ companion using the Geneva stellar evolution code. The
initial orbital period is 1.2 days. The 10 M$_\odot$ star has a
surface magnetic field of 1 kG. Various initial rotations are
considered. We use two different approaches for the internal angular
momentum transport. In one of them angular momentum is transported by
shear and meridional currents. In the other, a strong internal
magnetic field imposes nearly perfect solid-body rotation. The
evolution of the primary is computed until the first mass transfer
episode occurs. The cases of different values for the magnetic
fields, for various orbital periods and mass ratios are briefly
discussed. We show that, independently of the initial rotation rate
of the primary and the efficiency of the internal angular momentum
transport, the surface rotation of the primary will converge, in a
time that is short with respect to the main-sequence lifetime,
towards a slowly-evolving velocity that is different from the
synchronization velocity. This "equilibrium angular velocity''
is always inferior to the angular orbital velocity. In a given close
binary system at this equilibrium stage, the difference between the
spin and the orbital angular velocities becomes larger when the mass
losses and/or the surface magnetic field increase. The treatment of
the internal angular momentum transport has a strong impact on the
evolutionary tracks in the Hertzsprung-Russell Diagram as well as on
the changes of the surface abundances resulting from rotational
mixing. Our modeling suggests that the presence of an undetected
close companion might explain rapidly-rotating stars with strong
surface magnetic fields, having ages well above the magnetic braking
timescale. Our models predict that the rotation of most stars of this
type increases as a function of time, except for a first initial
phase in spin-down systems. The measure of their surface abundances,
together when possible with their mass-luminosity ratio, provide
interesting constraints on the transport efficiencies of angular
momentum and chemical species. Close binaries, when studied at phases
predating any mass transfer, are key objects to probe the physics of
rotation and magnetic fields in stars.
Reference:
Astronomy and Astrophysics, in press
Status: Manuscript has
been accepted
Weblink:
https://arxiv.org/abs/1709.01902
Comments:
Email: georges.meynet@unige.ch
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Roberta M.. Humphreys(1), Kris Davidson(1), Schuyler D.
Van Dyk(2) and Michael S. Gordon(1)
(1) University of
Minnesota
(2) Caltech/IPAC
We describe new results
on two supernova impostors in NGC 2403, SN 1954J(V12) and SN
2002kg(V37). For the famous object SN 1954J we combine four critical
observations: its current SED, its Halpha emission line profile, the
Ca II triplet in absorption in its red spectrum, and the brightness
compared to its pre-event state. Together these strongly suggest that
the survivor is now a hot supergiant with T ~ 20000 K, a dense wind,
substantial circumstellar extinction, and a G-type supergiant
companion. The hot star progenitor of V12's giant eruption was likely
in the post-red supergiant stage and had already shed a lot of mass.
V37 is a classical LBV/S Dor variable. Our photometry and spectra
observed during and after its eruption show that its outburst was an
apparent transit on the HR Diagram due to enhanced mass loss and the
formation of a cooler, dense wind. V37 is an evolved hot supergiant
at ~10^6 Lsun with a probable initial mass of 60 -80
Msun.
Reference:
http://adsabs.harvard.edu/abs/2017arXiv170901528H
Status:
Manuscript has been accepted
Weblink:
Comments:
Email: roberta@umn.edu
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M. Wittkowski (1), F. J. Abellan (2), B. Arroyo-Torres
(3,4), A. Chiavassa (5), J. C. Guirado (2,6), J. M. Marcaide (2), A.
Alberdi (3), W. J. de Wit (7), K.-H. Hofmann (8), A. Meilland (5), F.
Millour (5), S. Mohamed (9,10,11), J. Sanchez-Bermudez (12)
(1)
European Southern Observatory, Garching, Germany
(2)
Universitat de Valencia, Burjassot, Spain
(3) Instituto de
Astrofisica de Andalucia, Granada, Spain
(4) Centro Astronomico
Hispano Aleman, Calar Alto, Spain
(5) Universite Cote d’Azur,
Nice, France
(6) Observatori Astronomic, Paterna, Spain
(7)
European Southern Observatory, Santiago Chile
(8)
Max-Planck-Institut fuer Radioastronomie, Bonn, Germany
(9)
South African Astronomical Observatory, South Africa
(10)
University of Cape Town, Rondebosch, South Africa
(11) National
Institute for Theoretical Physics, Matieland, South Africa
(12)
Max-Planck-Institut fuer Astronomie, Heidelberg, Germany
The
star V766 Cen (=HR 5171A) was originally classified as a yellow
hypergiant but lately found to more likely be a 27-36 Msun red
supergiant (RSG). Recent observations indicated a close eclipsing
companion in the contact or common-envelope phase. Here, we aim at
imaging observations of V766 Cen to confirm the presence of the close
companion. We used near-infrared H -band aperture synthesis imaging
at three epochs in 2014, 2016, and 2017, employing the PIONIER
instrument at the Very Large Telescope Interferometer (VLTI). The
visibility data indicate a mean Rosseland angular diameter of
4.1+/-0.8 mas, corresponding to a radius of 1575+/-400 Rsun. The data
show an extended shell (MOLsphere) of about 2.5 times the Rosseland
diameter, which contributes about 30% of the H-band flux. The
reconstructed images at the 2014 epoch show a complex elongated
structure within the photospheric disk with a contrast of about 10%.
The second and third epochs show qualitatively and quantitatively
different structures with a single very bright and narrow feature and
high contrasts of 20-30%. This feature is located toward the
south-western limb of the photospheric stellar disk. We estimate an
angular size of the feature of 1.7+/-0.3 mas, corresponding to a
radius of 650+/-150 Rsun, and giving a radius ratio of
0.42+0.35/-0.10} compared to the primary stellar disk. We interpret
the images at the 2016 and 2017 epochs as showing the close
companion, or a common envelope toward the companion, in front of the
primary. At the 2014 epoch, the close companion is behind the primary
and not visible. Instead, the structure and contrast at the 2014
epoch are typical of a single RSG harboring giant photospheric
convection cells. The companion is most likely a cool giant or
supergiant star with a mass of 5+15/-3 Msun.
Reference:
A&A, 606, L1
Status: Manuscript has been
accepted
Weblink:
https://www.aanda.org/articles/aa/full_html/2017/10/aa31569-17/aa31569-17.html
Comments:
See also the ESO picture of the week at
https://www.eso.org/public/images/potw1740a/
Email:
mwittkow@eso.org
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D. M.-A. Meyer (1), R. Kuiper (1) , W. Kley (1)
K. G.
Johnston (2)
E. Vorobyov (3,4,5)
(1) Institut
für Astronomie und Astrophysik, Universität Tübingen, Auf der
Morgenstelle 10, 72076 Tübingen, Germany,
(2) School of
Physics and Astronomy, E.C. Stoner Building, The University of Leeds,
Leeds LS2 9JT, UK,
(3) Institute of Fluid Mechanics and Heat
Transfer, TU Wien, Vienna, 1060, Austria,
(4) Department of
Astrophysics, The University of Vienna, Vienna, A-1180, Austria,
(5)
Research Institute of Physics, Southern Federal University, Stachki
194, Rostov-on-Don, 344090, Russia.
The surroundings of
massive protostars constitute an accretion disc which has numerically
been shown to be subject to fragmentation and responsible for
luminous accretion-driven outbursts. Moreover, it is suspected to
produce close binary companions which will later strongly influence
the star's future evolution in the Hertzsprung-Russell diagram. We
present three-dimensional gravitation-radiation-hydrodynamic
numerical simulations of 100 Mo pre-stellar cores. We find that
accretion discs of young massive stars violently fragment without
preventing the (highly variable) accretion of gaseous clumps onto the
protostars. While acquiring the characteristics of a nascent low-mass
companion, some disc fragments migrate onto the central massive
protostar with dynamical properties showing that its final Keplerian
orbit is close enough to constitute a close massive proto-binary
system, having a young high-mass and a low-mass component. We
conclude on the viability of the disc fragmentation channel for the
formation of such short-period binaries, and that both processes
--close massive binary formation and accretion bursts-- may happen at
the same time. FU-Orionis-type bursts, such as observed in the young
high-mass star S255IR-NIRS3, may not only indicate ongoing disc
fragmentation, but also be considered as a tracer for the formation
of close massive binaries -- progenitors of the subsequent massive
spectroscopic binaries -- once the high-mass component of the system
will enter the main-sequence phase of its evolution.
Reference:
Monthly Notices of the Royal Astronomical Society:stx2551
arXiv:1710.01162
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/abs/2017arXiv171001162M
Comments:
Accepted for publication at MNRAS
Email:
d.m.meyer@exeter.ac.uk
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Steven R. Goldman (1), Jacco Th. van Loon (1), José F.
Gómez (2), James A. Green (3,4), Albert A. Zijlstra (5), Ambra Nanni
(6), Hiroshi Imai (7), Patricia A. Whitelock (8,9), Martin A. T.
Groenewegen (10), Joana M. Oliveira (1)
1 -
Astrophysics Group, Lennard-Jones Laboratories, Keele University, ST5
5BG, UK
2 - Instituto de Astrofísica de Andalucía, CSIC,
Glorieta de la Astronomía s/n, 18008 Granada, Spain
3 - SKA
Organisation, Jodrell Bank Observatory, Lower Withington,
Macclesfield, Cheshire, SK11 9DL, UK
4 - CSIRO Astronomy and
Space Science, Australia Telescope National Facility, PO Box 76,
Epping, NSW 1710, Australia
5 - Jodrell Bank Centre for
Astrophysics, Alan Turing Building, School of Physics and Astronomy,
The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
6
- Dipartimento di Fisica e Astronomia Galileo Galilei, vicolo
dell'Osservatorio 3, 35122 Padova PD, Italy
7 - Department of
Physics and Astronomy, Kagoshima University, 1-21-35 Korimoto,
Kagoshima 890-0065, Japan
8 - South African Astronomical
Observatory (SAAO), PO Box 9, 7935 Observatory, South Africa
9
- Astronomy Department, University of Cape Town, 7701 Rondebosch,
South Africa
10 - Koninklijke Sterrenwacht van België,
Ringlaan 3, B-1180 Brussels, Belgium
We present the
results of targeted observations and a survey of 1612-, 1665-, and
1667-MHz circumstellar OH maser emission from asymptotic giant branch
(AGB) stars and red supergiants (RSGs) in the Small Magellanic Cloud
(SMC), using the Parkes and Australia Telescope Compact Array radio
telescopes. No clear OH maser emission has been detected in any of
our observations targeting luminous, long-period, large-amplitude
variable stars, which have been confirmed spectroscopically and
photometrically to be mid- to late-M spectral type. These
observations have probed 3 - 4 times deeper than any OH maser survey
in the SMC. Using a bootstrapping method with LMC and Galactic OH/IR
star samples and our SMC observation upper limits, we have calculated
the likelihood of not detecting maser emission in any of the two
sources considered to be the top maser candidates to be less than
0.05%, assuming a similar pumping mechanism as the LMC and Galactic
OH/IR sources. We have performed a population comparison of the
Magellanic Clouds and used Spitzer IRAC and MIPS photometry to
confirm that we have observed all high luminosity SMC sources that
are expected to exhibit maser emission. We suspect that, compared to
the OH/IR stars in the Galaxy and LMC, the reduction in metallicity
may curtail the dusty wind phase at the end of the evolution of the
most massive cool stars. We also suspect that the conditions in the
circumstellar envelope change beyond a simple scaling of abundances
and wind speed with metallicity.
Reference:
arXiv:1710.02184
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1710.02184
Comments:
accepted in MNRAS
Email: sgoldman@stsci.edu
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Jon C. Mauerhan, Schuyler D. Van Dyk, Joel Johansson, Ori
D. Fox, Alexei V. Filippenko, Melissa L. Graham
UC
Berkeley
SN Hun248 was classified as a nonterminal
eruption (a SN "impostor") from a directly identified and
highly variable cool hypergiant star. The 2014 outburst achieved peak
luminosity equivalent to that of the historic eruption of luminous
blue variable (LBV) Eta Car, and exhibited a multipeaked optical
light curve that rapidly faded after ~100 days. We report ultraviolet
(UV) through optical observations of SN Hunt248 with the Hubble Space
Telescope (HST) about 1 yr after the outburst, and mid-infrared
observations with the Spitzer Space Telescope before the burst and in
decline. The HST data reveal a source that is a factor of ~10 dimmer
in apparent brightness than the faintest available measurement of the
precursor star. The UV-optical spectral energy distribution (SED)
requires a strong Balmer continuum, consistent with a hot B4-B5
photosphere attenuated by grey circumstellar extinction. Substantial
mid-infrared excess of the source is consistent with thermal emission
from hot dust with a mass of 10^{-6} - 10^{-5} MSun and a geometric
extent that is comparable to the expansion radius of the ejecta from
the 2014 event. SED modeling indicates that the dust consists of
relatively large grains (>0.3 um), which could be related to the
grey circumstellar extinction that we infer for the UV-optical
counterpart. Revised analysis of the precursor photometry is also
consistent with grey extinction by circumstellar dust, and suggests
that the initial mass of the star could be twice as large as
previously estimated (nearly ~60 MSun). Reanalysis of the earlier
outburst data shows that the peak luminosity and outflow velocity of
the eruption are consistent with a trend exhibited by stellar merger
candidates, prompting speculation that SN Hunt248 may also have
stemmed from a massive stellar merger or common-envelope
ejection.
Reference: Mauerhan, J. et al.
2017, MNRAS, in press, arXiv:1702.00430
Status: Manuscript has
been accepted
Weblink:
https://arxiv.org/abs/1702.00430
Comments:
Email: mauerhan@astro.berkeley.edu
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Ignace, Hole, Oskinova, Rotter
East
Tennessee State University, Norwich University, University of
Potsdam
AH Cep and CW Cep are both early B-type binaries
with short orbital periods of 1.8 d and 2.7 d, respectively. All four
components are B0.5V types. The binaries are also double-lined
spectroscopic and eclipsing. Consequently, solutions for orbital and
stellar parameters make the pair of binaries ideal targets for a
study of the colliding winds between two B~stars. Chandra ACIS-I
observations were obtained to determine X-ray luminosities. AH Cep
was detected with an unabsorbed X-ray luminosity at a 90% confidence
interval of (9-33)e30 erg/s, or (0.5-1.7)e-7 LBol, relative to the
combined Bolometric luminosities of the two components. While
formally consistent with expectations for embedded wind shocks, or
binary wind collision, the near-twin system of CW Cep was a
surprising non-detection. For CW Cep, an upper limit was determined
with LX/LBol < 1e-8, again for the combined components. One
difference between these two systems is that AH Cep is part of a
multiple system. The X-rays from AH Cep may not arise from standard
wind shocks nor wind collision, but perhaps instead from magnetism in
any one of the four components of the system. The possibility could
be tested by searching for cyclic X-ray variability in AH Cep on the
short orbital period of the inner B stars.
Reference:
accepted to ApJ
Status: Manuscript has been
accepted
Weblink:
http://lanl.arxiv.org/abs/1710.05764
Comments:
Email: ignace@etsu.edu
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Jorick S Vink
Armagh Observatory and
Planetarium
We present mass-loss predictions from Monte
Carlo radiative transfer models for helium (He) stars as a function
of stellar mass, down to 2 Msun. Our study includes both massive
Wolf-Rayet (WR) stars and low-mass He stars that have lost their
envelope through interaction with a companion. For these low-mass
He-stars we predict mass-loss rates that are an order of magnitude
smaller than by extrapolation of empirical WR mass-loss rates. Our
lower mass-loss rates make it harder for these elusive stripped stars
to be discovered via line emission, and we should attempt to find
them through alternative methods instead. Moreover, lower mass-loss
rates will make it less likely that low-mass He stars provide
stripped-envelope supernovae (SNe) of type Ibc. We express our
mass-loss predictions as a function of L and Z, and not as a function
of the He abundance, as we do not consider this physically astute
given our earlier work. The exponent of the dM/dt vs. Z dependence is
found to be 0.61, which is less steep than relationships derived from
recent empirical atmospheric modelling. Our shallower exponent will
make it more challenging to produce "heavy" black holes of
order 40 Msun, as recently discovered in the gravitational wave event
GW 150914, making low metallicity for these types of events even more
necessary.
Reference: Astronomy & Astrophysics
Letters
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1710.02010
Comments:
Email: jsv@arm.ac.uk
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Arthur Choplin (1), Raphael Hirschi (2,3,4), Georges
Meynet (1) and Sylvia Ekstrom (1)
1 - Geneva
Observatory, University of Geneva, Maillettes 51, CH-1290 Sauverny,
Switzerland
2 - Astrophysics Group, Lennard-Jones Labs 2.09,
Keele University, ST5 5BG, Staffordshire, UK
3 - Kavli
Institute for the Physics and Mathematics of the Universe (WPI),
University of Tokyo, 5-1-5
Kashiwanoha, Kashiwa, 277-8583,
Japan
4 - UK Network for Bridging the Disciplines of Galactic
Chemical Evolution (BRIDGCE)
Carbon-Enhanced Metal-Poor
(CEMP)-s stars are long-lived low-mass stars with a very low iron
content as well as overabundances of carbon and s-elements. Their
peculiar chemical pattern is often explained by pollution from an
asymptotic giant branch (AGB) star companion.
Recent
observations have shown that most CEMP-s stars are in binary systems,
providing support to the AGB companion scenario. A few CEMP-s stars,
however, appear to be single. We inspect four apparently single
CEMP-s stars and discuss the possibility that they formed from the
ejecta of a previous-generation massive star, referred to as the
''source'' star. In order to investigate this scenario, we computed
low-metallicity massive-star models with and without rotation and
including complete s-process nucleosynthesis. We find that
non-rotating source stars cannot explain the observed abundance of
any of the four CEMP-s stars. Three out of the four CEMP-s stars can
be explained by a 25 $M_{\odot}$ source star with $v_{\rm ini} \sim
500$ km s$^{-1}$ (spinstar). The fourth CEMP-s star has a high Pb
abundance that cannot be explained by any of the models we computed.
Since spinstars and AGB predict different ranges of [O/Fe] and
[ls/hs], these ratios could be an interesting way to further test
these two scenarios.
Reference: arXiv:1710.05564,
Accepted in A&A
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/abs/2017arXiv171005564C
Comments:
Email: arthur.choplin@unige.ch
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Tahina Ramiaramanantsoa (1,2), Anthony F. J. Moffat
(1,2), Robert Harmon (3), Richard Ignace (4), Nicole St-Louis (1,2),
Dany Vanbeveren (5), Tomer Shenar (6), Herbert Pablo (1,2), Noel D.
Richardson (7), Ian D. Howarth (8), Ian R. Stevens (9), Caroline
Piaulet (1), Lucas St-Jean (1), Thomas Eversberg (10), Andrzej
Pigulski (11), Adam Popowicz (12), Rainer Kuschnig (13), Elzbieta
Zoclonska (14), Bram Buysschaert (15,16), Gerald Handler (14), Werner
W. Weiss (13), Gregg A. Wade (17), Slavek M. Rucinski (18), Konstanze
Zwintz (19), Paul Luckas (20), Bernard Heathcote (21), Paulo Cacella
(22), Jonathan Powles (23), Malcolm Locke (24), Terry Bohlsen (25),
André-Nicolas Chené (26), Brent Miszalski (27,28), Wayne L. Waldron
(29), Marissa M. Kotze (27,28), Enrico J. Kotze (27) and Torsten Böhm
(30,31)
(1) Université de Montréal, Canada
(2)
Centre de Recherche en Astrophysique du Québec, Canada
(3)
Ohio Wesleyan University, USA
(4) East Tennessee State
University, USA
(5) Vrije Universiteit Brussel, Belgium
(6)
Universität Potsdam, Germany
(7) University of Toledo, USA
(8) University College London, UK
(9) University of
Birmingham, UK
(10) Schnörringen Telescope Science Institute,
Germany
(11) Uniwersytet Wroclawski, Poland
(12) Instytut
Automatyki, Politechnika Slaska, Poland
(13) Universität Wien,
Austria
(14) Nicolaus Copernicus Astronomical Center, Poland
(15) LESIA, Observatoire de Paris, France
(16) KU Leuven,
Belgium
(17) Royal Military College of Canada, Canada
(18)
University of Toronto, Canada
(19) Universität Innsbruck,
Austria
(20) International Centre for Radio Astronomy Research,
The University of Western Australia, Australia
(21) SASER Team,
Domain Observatory, Australia
(22) SASER Team, Dogsheaven
Observatory, Brazil
(23) SASER Team, Latham Observatory,
Australia
(24) SASER Team, R. F. Joyce Observatory, New Zealand
(25) SASER Team, Mirranook Observatory, Australia
(26)
Gemini Observatory, Northern Operations Center, USA
(27) South
African Astronomical Observatory, South Africa
(28) South
African Large Telescope, South Africa
(29) Eureka Scientific
Inc., USA
(30) Université de Toulouse, France
(31)
Centre National de la Recherche Scientifique, Institut de Recherche
en Astrophysique et Planétologie, France
From 5.5 months
of dual-band optical photometric monitoring at the 1 mmag level,
BRITE-Constellation has revealed two simultaneous types of
variability in the O4I(n)fp star Zeta Puppis: one single periodic
non-sinusoidal component superimposed on a stochastic component. The
monoperiodic component is the 1.78 d signal previously detected by
Coriolis/SMEI, but this time along with a prominent first harmonic.
The shape of this signal changes over time, a behaviour that is
incompatible with stellar oscillations but consistent with rotational
modulation arising from evolving bright surface inhomogeneities. By
means of a constrained non-linear light curve inversion algorithm we
mapped the locations of the bright surface spots and traced their
evolution. Our simultaneous ground-based multi-site spectroscopic
monitoring of the star unveiled cyclical modulation of its He II 4686
wind emission line with the 1.78-day rotation period, showing
signatures of Corotating Interaction Regions (CIRs) that turn out to
be driven by the bright photospheric spots observed by BRITE. Traces
of wind clumps are also observed in the He II 4686 line and are
correlated with the amplitudes of the stochastic component of the
light variations probed by BRITE at the photosphere, suggesting that
the BRITE observations additionally unveiled the photospheric drivers
of wind clumps in Zeta Pup and that the clumping phenomenon starts at
the very base of the wind. The origins of both the bright surface
inhomogeneities and the stochastic light variations remain unknown,
but a subsurface convective zone might play an important role in the
generation of these two types of photospheric
variability.
Reference: To appear in MNRAS
Status:
Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1710.08414
Comments:
44 pages, 28 figures, 6 Tables
Email:
tahina@astro.umontreal.ca
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J.O. Sundqvist (1), S.P.
Owocki (2), J. Puls (3)
1 - KU Leuven; 2 - University
of Delaware; 3 - University of Munich
Context: Clumping in
the radiation-driven winds of hot, massive stars arises naturally due
to the strong, intrinsic instability of line-driving (the `LDI'). But
LDI wind models have so far mostly been limited to 1D, mainly because
of severe computational challenges regarding calculation of the
multi-dimensional radiation force. Aims: To simulate and examine the
dynamics and multi-dimensional nature of wind structure resulting
from the LDI. Methods: We introduce a `pseudo-planar',
`box-in-a-wind' method that allows us to efficiently compute the
line-force in the radial and lateral directions, and then use this
approach to carry out 2D radiation-hydrodynamical simulations of the
time-dependent wind. Results: Our 2D simulations show that the LDI
first manifests itself by mimicking the typical shell-structure seen
in 1D models, but how these shells then quickly break up into complex
2D density and velocity structures, characterized by small-scale
density `clumps' embedded in larger regions of fast and rarefied gas.
Key results of the simulations are that density variations in the
well-developed wind statistically are quite isotropic and that
characteristic length-scales are small; a typical clump size is
~0.01R at 2R, thus resulting also in rather low typical clump-masses
~10^17 g. Overall, our results agree well with the theoretical
expectation that the characteristic scale for LDI-generated
wind-structure is of order the Sobolev length. We further confirm
some earlier results that lateral `filling-in' of radially compressed
gas leads to somewhat lower clumping factors in 2D simulations than
in comparable 1D models. We conclude by discussing an extension of
our method toward rotating LDI wind models that exhibit an intriguing
combination of large- and small-scale structure extending down to the
wind base.
Reference: arXiv:1710.07780, Accepted
for A&A
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2017arXiv171007780S
Comments:
Email: jon.sundqvist@kuleuven.be
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Josef Hron & Peter Abraham
European
Interferometry Initiative
The Fizeau exchange visitors
program in optical interferometry funds (travel and accommodation)
visits of researchers to an institute of his/her choice (within the
European Community) to perform collaborative work and training on one
of the active topics of the European Interferometry Initiative. The
visits will typically last for one month, and strengthen the network
of astronomers engaged in technical, scientific and training work on
optical/infrared interferometry. The program is open for all levels
of astronomers (Ph.D. students to tenured staff), with priority given
to PhD students and young postdocs. Non-EU based missions will only
be funded if considered essential by the Fizeau Committee.
Applicants are strongly encouraged to seek also partial support
from their home or host institutions.
The deadline for
applications is October 15. Fellowships can be awarded for missions
to be carried out between December 2017 and May 2018!
Further
informations and application forms can be found at:
www.european-interferometry.eu
The program is funded by
OPTICON/H2020.
Please distribute this message also to
potentially interested colleagues outside of your community!
Looking forward to your applications,
Josef Hron &
Peter Abraham
(for the European Interferometry
Initiative)
Reference:
www.european-interferometry.eu
Status: Other
Weblink:
www.european-interferometry.eu
Comments:
Email: fizeau@european-interferometry.eu
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Jiri Krticka
Department
of Theoretical Physics and Astrophysics
Kotlarska 2
611
37 Brno
Czech Republic
Masaryk University, Brno,
Czech Republic opens a call for excellent scientists for working on
their own scientific projects. The award offers the opportunity to
get:
- 5 years long tenure-track professorship with a
possibility to gain a permanent contract.
- A budget of approx.
230 000 USD/ a year for a 5 year period.
- Associate or full
professorship.
- Laboratory and office space for the research
team.
- Welcome service and administrative support.
Scientists willing to work in the field of research of
individual DTPA members (massive stars, chemically peculiar stars,
binaries, open clusters, and related fields) may wish to contact
local person to get the support.
Attention/Comments:
Weblink: https://gamu.muni.cz/en/mash
Email:
krticka@physics.muni.cz
Deadline: November 3rd,
2017
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March 5 - 9, 2018
Venue: ESO
Headquarters, Garching, Germany
First Announcement
ESO
Workshop "Imaging of Stellar Surfaces"
http://www.eso.org/sci/meetings/2018/Imaging-Stellar-Surfaces.html
March 5 - 9, 2018
Venue: ESO Headquarters,
Garching, Germany
Maximum number of participants: 70
Scientific Rationale:
Until very recently, all
information about mechanisms affecting the stellar surface came
either from indirect observations or from studies of the Sun. The
stellar surface is the locus where we first interface with the
mechanisms happening at the interior of the stars such as convection,
magnetic field, and diffusion producing abundance anomalies. Studying
stellar surfaces is important for advancing our understanding of
these physical processes.
There is currently a tremendous
advance of different observational techniques that enable us to
resolve the surfaces of stars other than the sun. The Very Large
Telescope Interferometer (VLTI) is transitioning from its first
generation instruments, which focused on spectro-interferometry, to
the second generation instruments, which focus on spectro-imaging and
astrometry. The VLTI instrument PIONIER has already shown its
capabilities and great potential to resolve stellar surfaces, while
the instruments GRAVITY and MATISSE are coming into operations. The
VLT instrument SPHERE is resolving the surfaces of the apparently
largest stars as well. At the same time, ALMA observations have
suceeded to resolve stellar surfaces at millimetre wavelengths with
its long baselines. A number of other interferometers at optical and
radio wavelengths have been successful to resolve stellar surfaces as
well, including CHARA, VLA, e-MERLIN.
In the last one or
two years we have seen great progress in resolving surfaces of active
stars such as zet And, of red giants such as R Dor, of asymptotic
giant branch stars such as Mira or R Scl, and of red supergiants such
as Betelgeuse, Antares, VY CMa, with these different techniques at
multiple wavelengths from the visual to the radio.
Stellar
atmosphere models have also been advancing, during a similar time
frame, from 1D models to 3D models including the effects of
convection. Interaction between observations and theory of stellar
atmospheres is of utmost importance to constrain the models and to
advance our understanding of physical processes such as pulsation,
convection, chromospheric activity.
This workshop aims to
bring together observers from different techniques and wavelengths
and theoreticians working on stellar atmosphere and stellar
structure. Presentations will include recent individual results of
stellar surface mapping and the corresponding modelling.
Observational strategies to advance in this field will be discussed.
In addition, we will dedicate a session to the prospect of resolving
stellar surfaces of stars other than the sun with future facilities
such as the ELT or the JWST, or with intensity interfermetry/CTA.
We also aim to share technical, observational, and
modeling expertise with a larger community. We will discuss how the
different communities (VLT, VLTI, CHARA, ALMA, HST/JWST) deal with
the image reconstruction problem and with the physical interpretation
of the images.
We aim at a focused workshop with ample of
time for discussions on recent images of stellar surfaces and
atmospheres (out to below a few stellar radii), the observational
strategies, and the relevant physical processes. The number of
participants will be limited to 70.
SOC:
Bernd
Freytag (Uppsala University, Sweden), Xavier Haubois (ESO), Liz
Humphreys (ESO, co-chair), Lynn Matthews (MIT Haystack, USA), Claudia
Paladini (ESO), Oskar von der Luehe (Albert-Ludwigs-Universitat
Freiburg, Germany), Markus Wittkowski (ESO, co-chair)
Invited
Speakers: to be confirmed
Topics:
- The Sun as a
star: Physical processes affecting the Sun's surface and overviews of
recent observations at optical and sub-mm wavelengths
-
Physical processes
-- Convection
-- Pulsation
--
Magnetic fields
-- Chromospheric activity
-- Close
companions
-- Rotation
- Red giants including active
giants
- Asymptotic giant branch stars
- Red supergiants
- Imaging techniques and observational strategies
-
Future facilities
We plan to start the workshop on Monday
lunchtime and to finish on Friday lunchtime.
Contact:
ioss@eso.org
Weblink:
http://www.eso.org/sci/meetings/2018/Imaging-Stellar-Surfaces.html
Email:
ioss@eso.org
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31st January - 2nd February 2018
Venue:
Keele University, UK
The Cygnus star forming complex
is the nearest truly massive star forming region to the Sun. It is
home to hundreds of thousands of young stars and many thousands of
massive O and B-type stars, in multiple star clusters and OB
associations, including the prominent Cygnus OB2 association. In the
massive Cygnus X giant molecular cloud star formation is still
ongoing in numerous sites, particularly the DR21 molecular filament,
which is actively forming massive stars. The region has drawn
comparison with young massive clusters and star forming regions in
our galaxy and in neighbouring galaxies, yet at a distance of only
1.4 kpc it can be studied at a level of detail not accessible to more
distant regions.
Following many exciting results from
NASA’s Spitzer and Chandra space telescopes and ESA’s Herschel
Space Obser- vatory we are poised to enter a new era of discovery
thanks to upcoming data releases from ESA’s astrometric Gaia
satellite and forthcoming spectrosopic surveys with WEAVE/WHT. This
workshop will bring together experts in the Cygnus region to present
recent results and discuss our understanding of the entire Cygnus
star forming complex.
The final day of the meeting will
focus on planning the upcoming WHT/WEAVE survey of Cygnus (P.I. A.
Herrero) and will be open to survey members and interested
individuals from WEAVE member countries.
There is no
registration fee for this meeting, but the number of participants
will be limited so prior registration is required. If you would like
to attend please send an email to nick.nwright@gmail.com including
your full name and affiliation.
If you would like to
present an oral contribution at the meeting please also send a title
and brief abstract by 1st December 2017. We will endeavour to provide
all attendees with an opportunity to present their work.
Organisers: Nick Wright (Keele University) and Artemio
Herrero (Instituto de Astrofisica de Canarias)
Weblink:
http://www.astro.keele.ac.uk/cygnus
Email:
nick.nwright@gmail.com
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