ISSN 1783-3426
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IAU Working Group --> New IAU Massive
Stars Commission
New Massive Stars
Commission -- Reminder
Radiation-driven winds of hot luminous
stars
B fields in OB stars (BOB):
FORS2 spectropolarimetric follow-up of the two rare rigidly rotating
magnetosphere stars HD23478 and HD345439
The
flux-weighted gravity-luminosity relationship of blue supergiant
stars as a constraint for stellar evolution
A
Modern Search for Wolf-Rayet Stars in the Magellanic Clouds. II. A
Second Year of Discoveries
An
infrared diagnostic for magnetism in hot stars
Revisiting
the Rigidly Rotating Magnetosphere model for σ Ori E - II. Magnetic
Doppler imaging, arbitrary field RRM, and light
variability
Simultaneous X-ray and
optical spectroscopy of the Oef supergiant lambda Cep
Tight
asteroseismic constraints on core overshooting and diffusive mixing
in
Massive stars in the W33 giant
molecular complex
Tentative insight
into the multiplicity of the persistent dust maker WR106 from X-ray
observations
Long-term XMM-Newton
investigation of two particle-accelerating colliding-wind binaries in
NGC6604: HD168112 and HD167971
Observational
signatures of convectively driven waves in massive stars
X-rays
from the oxygen-type Wolf-Rayet binary WR30a
Asymmetric
supernova remnants generated by Galactic, massive runaway stars
Waves inside Stars: Theory, Simulations, Observational Signatures, and Lab Experiments
dear friends,
this is our
last Massive Star Newsletter as an IAU Working Group. The next will
be the first one distributed under the new IAU Commission on Massive
Stars. On behalf of the Organizing Committee I would like to thank
all people that contributed to the success of the Working Group and
its Newsletter, its preparation and distribution. Thanks to all
former chairs and members of the Organizing Committee, the editors of
the Newsletter, Philippe Eenens and Raphael Hirschi, and the
Universidad Nacional Autonoma de Mexico team that supports its
distribution and our webpage. Thanks finally to all members of the
Working Group for its daily effort in favour of this exciting field
of massive stars.
with best regards,
Artemio Herrero,
chair, on behalf of the Massive Stars Working Group
Weblink:
Email: ahd@iac.es
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dear friends,
this is a
kind remind for those of you interested in joining the new Massive
Stars Commission but that still didn't. Do it asap, as the
registration closes after May, 15. To register you have to be an
official IAU member and follow the instructions sent by General
Secretary on his email from April 29.
with best regards,
Artemio Herrero,
chair, on behalf of the Massive Stars
Working Group
Weblink:
Email:
ahd@iac.es
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T. L. Hoffmann, A. W. A. Pauldrach, and C. B.
Kaschinski
Institut fuer Astronomie und Astrophysik der
Universitaet Muenchen, Scheinerstrasse 1, 81679 Muenchen,
Germany
Context. The uncertainty in the degree to which
radiation-driven winds of hot stars might be affected by small
inhomogeneities in the density leads to a corresponding uncertainty
in the determination of the atmospheric mass loss rates from the
strength of optical recombination lines and – since the mass loss
rate is not a free parameter but a function of the stellar parameters
mass, radius, luminosity, and abundances – in principle also in the
determination of these stellar parameters. Furthermore, the optical
recombination lines also react sensitively to even small changes in
the density structure resulting from the (often assumed instead of
computed) velocity law of the outflow. This raises the question of
how reliable the parameter determinations from such lines are.
Aims.
The currently existing severe discrepancy between CSPN (central stars
of planetary nebulae) stellar and wind parameters derived from model
fits to the optical spectra and those derived using hydrodynamically
consistent model fits to the UV spectra is to be reassessed via a
simultaneous optical/UV analysis using a state-of-the-art model
atmosphere code.
Methods. We have modified our hydrodynamically
consistent model atmosphere code with an implementation of the usual
ad-hoc treatment of clumping (small inhomogeneities in the density)
in the wind. This allows us to re-evaluate, with respect to their
influence on the appearance of the UV spectra and their compatibility
with the observations, the parameters determined in an earlier study
that had employed clumping in its models to achieve a fit to the
observed optical spectra.
Results. The discrepancy between the
optical and the UV analyses is confirmed to be the result of a
missing consistency between stellar and wind parameters in the
optical analysis. While clumping in the wind does significantly
increase the emission in the optical hydrogen and helium
recombination lines, the influence of the density (velocity field) is
of the same order as that of moderate clumping factors.Moderate
clumping factors leave the UV spectra mostly unaffected, indicating
that the influence on the ionization balance, and thus on the
radiative acceleration, is small. Instead of the erratic behavior of
the clumping factors claimed fromthe optical analyses, our analysis
based on the velocity field computed from radiative driving yields
similar clumping factors for all CSPNs, with a typical value of f_cl
= 4. With and without clumping, wind strengths and terminal
velocities consistent with the stellar parameters from the optical
analysis give spectra incompatible with both optical and UV
observations, whereas a model that consistently implements the
physics of radiation driven winds achieves a good fit to both the
optical and UV observations with a proper choice of stellar
parameters. The shock temperatures and the ratios of X-ray to
bolometric luminosity required to reproduce the highly ionized Ovi
line in the FUSE spectral range agree with those known from massive O
stars (LX/Lbol ~ 10-7 . . . 10-6), again confirming the similarity of
O-type CSPN and massive O star atmospheres and further strengthening
the claim that both have identical wind driving mechanisms.
Conclusions. The similarity of the winds of O-type CSPNs and
those of massive O stars justifies using the same methods based on
the dynamics of radiation-driven winds in their analysis, thus
supporting the earlier result that several of the CSPNs in the sample
have near-Chandrasekhar-limit masses and may thus be possible
single-star progenitors of type Ia supernovae.
Reference:
Publication in A&A.
Pre-print available on
astro-ph.
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1307.2948
Comments:
17 figures, and 3 tables
Email:
uh10107@usm.uni-muenchen.de
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contents
S. Hubrig(1), M. Schoeller(2), L. Fossati(3), T. Morel(4),
N. Castro(3), L.M. Oskinova(5), N. Przybilla(6), S.S. Eikenberry(7),
M.F. Nieva(6), N. Langer(3), the BOB collaboration
(1)
Leibniz-Institut fuer Astrophysik Potsdam (AIP), An der Sternwarte
16, 14482 Potsdam, Germany,
(2) European Southern Observatory,
Karl-Schwarzschild-Str. 2, 85748 Garching, Germany,
(3)
Argelander-Institut fuer Astronomie, Universitaet Bonn, Auf dem
Huegel 71, 53121 Bonn, Germany,
(4) Institut d'Astrophysique et
de Geophysique, Universite de Liege, Allee du 6 Aout, Bat. B5c, 4000
Liege, Belgium,
(5) Universitaet Potsdam, Institut fuer Physik
und Astronomie, 14476 Potsdam, Germany,
(6) Institute for Astro-
and Particle Physics, University of Innsbruck, Technikerstr. 25/8,
6020 Innsbruck, Austria,
(7) Department of Astronomy, University
of Florida, 2011 Bryant Space Center, Gainesville, FL 32611
Massive
B-type stars with strong magnetic fields and fast rotation are very
rare and pose a mystery for theories of star formation and magnetic
field evolution. Only two such stars, called sigma Ori E analogues,
were known until recently. A team involved in APOGEE, one of the
Sloan Digital Sky Survey III programs, announced the discovery of two
additional rigidly rotating magnetosphere stars, HD23478 and
HD345439. The magnetic fields in these newly discovered sigma Ori E
analogues have not been investigated so far.
In the framework
of our ESO Large Programme and one normal ESO programme, we carried
out low-resolution FORS2 spectropolarimetric observations of HD23478
and HD345439.
In the measurements of hydrogen lines, we
discover a rather strong longitudinal magnetic field of up to 1.5kG
in HD23478 and up to 1.3kG using the entire spectrum. The analysis of
HD345439 using four subsequent spectropolarimetric subexposures does
not reveal a magnetic field at a significance level of 3sigma. On the
other hand, individual subexposures indicate that HD345439 may host a
strong magnetic field that rapidly varies over 88 minutes. The fast
rotation of HD345439 is also indicated by the behaviour of several
metallic and He I lines in the low-resolution FORS2 spectra that show
profile variations already on this short time-scale.
Reference:
Accepted for publication as a letter to A&A.
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1505.02447
Comments:
Email: shubrig@aip.de
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Georges Meynet (1), Rolf-Peter Kudritzki (2, 3), and Cyril
Georgy (4)
(1) Geneva Observatory, University of Geneva,
Maillettes 51, CH-1290 Sauverny, Switzerland
(2) Institute
for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu,
HI 96822, USA
(3) University Observatory Munich, Scheinerstr.
1, D-81679 Munich, Germany
(4) Astrophysics, Lennard-Jones
Laboratories, EPSAM, Keele University, Staffordshire ST5 5BG, UK
The
flux-weighted gravity-luminosity relationship (FGLR) of blue
supergiant stars (BSG) links their absolute magnitude to the
spectroscopically determined flux-weighted gravity log(g/Teff^4). BSG
are the brightest stars in the universe at visual light and the
application of the FGLR has become a powerful tool to determine
extragalactic distances.
Observationally, the FGLR is a tight
relationship with only small scatter. It is, therefore, ideal to be
used as a constraint for stellar evolution models. The goal of this
work is to investigate whether stellar evolution can reproduce the
observed FGLR and to develop an improved foundation of the FGLR as an
extragalactic distance indicator. We use different grids of stellar
models for initial masses between 9 and 40 Msun, for metallicities
between Z=0.002 and 0.014, with and without rotation, computed with
various mass loss rates during the red supergiant phase. For each of
these models we discuss the details of post-main sequence evolution
and construct theoretical FGLRs by means of population synthesis
models which we then compare with the observed FGLR.In general, the
stellar evolution model FGLRs agree reasonably well with the observed
one. There are, however, differences between the models, in
particular with regard to the shape and width (scatter) in the
flux-weighted gravity-luminosity plane. The best agreement is
obtained with models which include the effects of rotation and assume
that the large majority, if not all the observed BSG evolve towards
the red supergiant phase and only a few are evolving back from this
stage. The effects of metallicity on the shape and scatter of the
FGLR are small. The shape, scatter and metallicity dependence of the
observed FGLR are well explained by stellar evolution models. This
provides a solid theoretical foundation for the use of this
relationship as a robust extragalactic distance
indicator.
Reference: Astronomy and Astrophysics, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1505.00603
Email:
georges.meynet@unige.ch
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Philip Massey (1), Kathryn F. Neugent (1), Nidia Morrell
(2)
(1) Lowell Observatory, (2) Las Campanas
Observatory
The numbers and types of evolved massive stars
found in nearby galaxies provide an exacting test of stellar
evolution models. Because of their proximity and rich massive star
populations, the Magellanic Clouds have long served as the linchpins
for such studies. Yet the continued accidental discoveries of
Wolf-Rayet (WR) stars in these systems demonstrate that our knowledge
is not as complete as usually assumed. Therefore, we undertook a
multi-year survey for WRs in the Magellanic Clouds. Our results from
our first year (reported previously) confirmed nine new LMC WRs. Of
these, six were of a type never before recognized, with WN3-type
emission combined with O3-type absorption features. Yet these stars
are 2-3 magnitudes too faint to be WN3+O3~V binaries. Here we report
on the second year of our survey, including the discovery of four
more WRs, two of which are also WN3/O3s, plus two ``slash" WRs.
This brings the total of LMC WRs known to 152, 13 (8.2%) of which
were found by our survey, which is now ~60% complete. We find that
the spatial distribution of the WN3/O3s is similar to that of other
WRs in the LMC, suggesting that they are descended from the same
progenitors. We call attention to the fact that five of the 12 known
SMC WRs may in fact be similar WN3/O3s rather than the binaries they
have often been assumed to be. We also discuss our other discoveries:
a newly found Onfp-type star, and a peculiar emission-line object.
Finally, we consider the completeness limits of our
survey.
Reference: ApJ, in press
Status: Manuscript
has been accepted
Weblink:
http://arxiv.org/abs/1505.06265
Comments:
Email: phil.massey@lowell.edu
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M. E. Oksala, J. H. Grunhut, M. Kraus, M. Borges Fernandes,
C. Neiner, C. A. H. Condori, J. C. N. Campagnolo, T. B.
Souza
Observatoire de Paris-Meudon, ESO, Astronomical
Institute ASCR, Tartu Observatory, Observatorio
Nacional
Magnetospheric observational proxies are used for
indirect detection of magnetic fields in hot stars in the X-ray, UV,
optical, and radio wavelength ranges. To determine the viability of
infrared (IR) hydrogen recombination lines as a magnetic diagnostic
for these stars, we have obtained low-resolution (R~1200), near-IR
spectra of the known magnetic B2V stars HR 5907 and HR 7355, taken
with the Ohio State Infrared Imager/Spectrometer (OSIRIS) attached to
the 4.1m Southern Astrophysical Research (SOAR) Telescope. Both stars
show definite variable emission features in IR hydrogen lines of the
Brackett series, with similar properties as those found in optical
spectra, including the derived location of the detected
magnetospheric plasma. These features also have the added advantage
of a lowered contribution of stellar flux at these wavelengths,
making circumstellar material more easily detectable. IR diagnostics
will be useful for the future study of magnetic hot stars, to detect
and analyze lower-density environments, and to detect magnetic
candidates in areas obscured from UV and optical observations,
increasing the number of known magnetic stars to determine basic
formation properties and investigate the origin of their magnetic
fields.
Reference: A&A, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1505.01739
Comments:
Email: meo@udel.edu
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M. E. Oksala, O. Kochukhov, J. Krticka, R. H. D. Townsend,
G. A. Wade, M. Prvak, Z. Mikulasek, J. Silvester, S. P.
Owocki
Observatoire de Paris-Meudon, University of
Delaware, Astronomical Insitute ASCR, Uppsala Univeristy, University
of Wisconsin-Madison, RMC, Masaryk Univeristy, Queen's
University
The initial success of the Rigidly Rotating
Magnetosphere (RRM) model application to the B2Vp star sigma Ori E by
Townsend, Owocki & Groote (2005) triggered a renewed era of
observational monitoring of this archetypal object. We utilize
high-resolution spectropolarimetry and the magnetic Doppler imaging
(MDI) technique to simultaneously determine the magnetic
configuration, which is predominately dipolar, with a polar strength
Bd = 7.3-7.8 kG and a smaller non-axisymmetric quadrupolar
contribution, as well as the surface distribution of abundance of He,
Fe, C, and Si. We describe a revised RRM model that now accepts an
arbitrary surface magnetic field configuration, with the field
topology from the MDI models used as input. The resulting synthetic
Ha emission and broadband photometric observations generally agree
with observations, however, several features are poorly fit. To
explore the possibility of a photospheric contribution to the
observed photometric variability, the MDI abundance maps were used to
compute a synthetic photospheric light curve to determine the effect
of the surface inhomogeneities. Including the computed photospheric
brightness modulation fails to improve the agreement between the
observed and computed photometry. We conclude that the discrepancies
cannot be explained as an effect of inhomogeneous surface abundance.
Analysis of the UV light variability shows good agreement between
observed variability and computed light curves, supporting the
accuracy of the photospheric light variation calculation. We thus
conclude that significant additional physics is necessary for the RRM
model to acceptably reproduce observations of not only sigma Ori E,
but also other similar stars with significant stellar wind-magnetic
field interactions.
Reference: MNRAS, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1505.04839
Email:
meo@udel.edu
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G. Rauw$^1$, A. Herve$^2$, Y. Naze$^1$, J.N.
Gonzalez-Perez$^3$, A. Hempelmann$^3$, M. Mittag$^3$, J.H.M.M.
Schmitt$^3$, K.-P. Schroeder$^4$, E. Gosset$^1$, P. Eenens$^4$, J.M.
Uuh-Sonda$^4$
1 - University of Liege, Belgium; 2 -
University of Montpellier, France; 3 - Hamburger Sternwarte, Germany;
4 - University of Guanajuato, Mexico
Probing the structures of
stellar winds is of prime importance for the understanding of massive
stars. Based on their optical spectral morphology and variability,
the stars of the Oef class have been suggested to feature large-scale
structures in their wind. High-resolution X-ray spectroscopy and
time-series of X-ray observations of presumably-single O-type stars
can help us understand the physics of their stellar winds. We have
collected XMM-Newton observations and coordinated optical
spectroscopy of the O6Ief star lambda Cep to study its X-ray and
optical variability and to analyse its high-resolution X-ray
spectrum. We investigate the line profile variability of the He II
4686 and H-alpha emission lines in our time series of optical
spectra, including a search for periodicities. We further discuss the
variability of the broadband X-ray flux and analyse the
high-resolution spectrum of lambda Cep using line-by-line fits as
well as a code designed to fit the full high-resolution X-ray
spectrum consistently. During our observing campaign, the He II
lambda 4686 line varies on a timescale of ~18 hours. On the contrary,
the H-alpha line profile displays a modulation on a timescale of 4.1
days which is likely the rotation period of the star. The X-ray flux
varies on time-scales of days and could in fact be modulated by the
same 4.1 days period as H-alpha, although both variations are shifted
in phase. The high-resolution X-ray spectrum reveals broad and skewed
emission lines as expected for the X-ray emission from a distribution
of wind-embedded shocks. Most of the X-ray emission arises within
less than 2 R* above the photosphere.
Reference: Astronomy
& Astrophysics, in press
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1505.07714
Comments:
Email: rauw@astro.ulg.ac.be
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Ehsan Moravveji $^1$, Conny Aerts $^{1,2}$, Peter I. Papics
$^1$, Santiago Andres Triana $^1$, Bram Vandoren $^1$
1 -
Institute of Astronomy, KU,Leuven, Celestijnenlaan 200D, B-3001
Leuven, Belgium
2 - Department of Astrophysics, IMAPP, Radboud
University Nijmegen, PO Box 9010, 6500 GL, Nijmegen, The
Netherlands
KIC 10526294 was recently discovered to be a very
slowly rotating and slowly pulsating late B-type star. Its 19
consecutive dipole gravity modes constitute a series with almost
constant period spacing. This unique collection of identified modes
probes the near-core environment of this star and holds the potential
to reveal the size and structure of the overshooting zone above the
convective core, as well as the mixing properties of the star.
We
revisit the asteroseismic modelling of this star with specific
emphasis on the properties of the core overshooting, while
considering additional diffusive mixing throughout the radiative
envelope of the star.
We pursued forward seismic modelling
based on adiabatic eigenfrequencies of equilibrium models for eight
extensive evolutionary grids tuned to KIC 10526294 by varying the
initial mass, metallicity, chemical mixture, and the extent of the
overshooting layer on top of the convective core. We examined models
for both OP and OPAL opacities and tested the occurrence of extra
diffusive mixing throughout the radiative interior.
We find a
tight mass-metallicity relation within the
ranges M from 3.13 to
3.25 M_sun and Z from 0.014 to 0.028. We deduce that an exponentially
decaying diffusive core overshooting prescription
describes the
seismic data better than a step function formulation and derive a
value of f_ov between 0.017 and 0.018. Moreover, the inclusion of
extra diffusive mixing with a value of log D_{mix} between 1.75 and
2.00 dex (with D_{mix} in cm^2/sec) improves the goodness-of-fit
based on the observed and modelled frequencies by a factor 11
compared to the case where no extra mixing is considered,
irrespective of the (M,Z) combination within the allowed seismic
range.
The inclusion of diffusive mixing in addition to core
overshooting is essential to explain the structure in the observed
period spacing pattern of this star. Moreover, for the input physics
and chemical mixtures we investigated, we deduce that an
exponentially decaying prescription for the core overshooting is to
be preferred over a step function, regardless of the adopted mixture
or choice of opacity tables. Our best models for KIC 10526294
approach the seismic data to a level that they can serve future
inversion of its stellar structure.
Reference: A&A
in press
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2015arXiv150506902M
Comments:
:-)
Email: Ehsan.Moravveji@ster.kuleuven.be
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Maria Messineo(1,2), J. Simon Clark(3), Donald F. Figer(4),
Rolf-Peter Kudritzki(5,11), Francisco Najarro(6), R. Michael Rich(7),
Karl M. Menten(1), Valentin D. Ivanov(8,9), Elena Valenti(9),
Christine Trombley(4), C.-H. Rosie Chen(1), Ben Davies(10)
(1)
MPIfR, (2) ESA, (3) The Open University,
(4) RIT, (5) University
of Hawaii, (6) CSIC-INTA, (7) University of California, (8) ESO
Santiago, (9) ESO Munich, (10) Liverpool John Moores University, (11)
MPA
Rich in HII regions, giant molecular clouds are natural
laboratories to study massive stars and sequential star formation.
The Galactic star forming complex W33 is located at l=~12.8deg and at
a distance of 2.4 kpc, has a size of ~10 pc and a total mass of (~0.8
- ~8.0) X 10^5 Msun. The integrated radio and IR luminosity of W33 -
when combined with the direct detection of methanol masers, the
protostellar object W33A, and protocluster embedded within the radio
source W33 main - mark the region out as a site of vigorous ongoing
star formation. In order to assess the long term star formation
history, we performed an infrared spectroscopic search for massive
stars, detecting for the first time fourteen early-type stars,
including one WN6 star and four O4-7 stars. The distribution of
spectral types suggests that this population formed during the last
~2-4 Myr, while the absence of red supergiants precludes extensive
star formation at ages 6-30 Myr. This activity appears distributed
throughout the region and does not appear to have yielded the dense
stellar clusters that characterize other star forming complexes such
as Carina and G305. Instead, we anticipate that W33 will eventually
evolve into a loose stellar aggregate, with Cyg OB2 serving as a
useful, albeit richer and more massive, comparator. Given recent
distance estimates, and despite a remarkably similar stellar
population, the rich cluster Cl 1813-178 located on the north-west
edge of W33 does not appear to be physically associated with
W33.
Reference: 2015, ApJ, 805, 110
Status:
Manuscript has been accepted
Weblink:
http://cdsads.u-strasbg.fr/abs/2015ApJ...805..110M
Comments:
Email: messineo@mpifr-bonn.mpg.de
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De Becker, M.
Liège University
This
paper presents the results of the analysis of the very first
dedicated X-ray observation with XMM-Newton of WR106. This
carbon-rich WC9d Wolf-Rayet star belongs to the category of
persistent dust makers (WCd stars). The issue of the multiplicity of
these dust makers is pivotal to understand the dust formation
process, and in this context X-ray observations may allow to reveal
an X-ray emission attributable to colliding-winds in a binary system.
The main result of this analysis is the lack of detection of X-rays
coming from WR106. Upper limits on the X-ray flux are estimated, but
the derived numbers are not sufficient to provide compelling
constraints on the existence or not of a colliding-wind region.
Detailed inspection of archive data bases reveals that persistent
dust makers have been poorly investigated by the most sensitive X-ray
observatories. Certainly, the combination of several approaches to
indirectly constrain their multiplicity should be applied to lift a
part of the veil on the nature of these persistent dust
makers.
Reference: 2015, New Astronomy, in
press
Status: Manuscript has been accepted
Weblink:
http://orbi.ulg.ac.be/handle/2268/182251
Comments:
Email: debecker@astro.ulg.ac.be
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De Becker, M.
Liège University
The
long-term (over more than one decade) X-ray emission from two massive
stellar systems known to be particle accelerators is investigated
using XMM-Newton. Their X-ray properties are interpreted taking into
account recent information about their multiplicity and orbital
parameters. The two targets, HD168112 and HD167971 appear to be
overluminous in X-rays, lending additional support to the idea that a
significant contribution of the X-ray emission comes from
colliding-wind regions. The variability of the X-ray flux from
HD168112 is interpreted in terms of varying separation expected to
follow the 1/D rule for adiabatic shocked winds. For HD167971,
marginal decrease of the X-ray flux in September 2002 could
tentatively be explained by a partial wind eclipse in the close pair.
No long-term variability could be demonstrated despite the
significant difference of separation between 2002 and 2014. This
suggests the colliding-wind region in the wide orbit does not
contribute a lot to the total X-ray emission, with a main
contribution coming from the radiative shocked winds in the eclipsing
pair. The later result provides evidence that shocks in a
colliding-wind region may be efficient particle accelerators even in
the absence of bright X-ray emission, suggesting particle
acceleration may operate in a wide range of conditions. Finally, in
hierarchical triple O-type systems, thermal X-rays do not necessarily
constitute an efficient tracer to detect the wind-wind interaction in
the long period orbit.
Reference: 2015, MNRAS, 451,
5589-5599
Status: Manuscript has been accepted
Weblink:
http://orbi.ulg.ac.be/handle/2268/182374
Comments:
Email: debecker@astro.ulg.ac.be
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C. Aerts & T. M. Rogers
Instituut voor
Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
Department of Mathematics and Statistics, Newcastle
University, UK
We demonstrate observational evidence for the
occurrence of convectively driven internal gravity waves (IGW) in
young massive O-type stars observed with high-precision CoRoT space
photometry. This evidence results from a comparison between velocity
spectra based on 2D hydrodynamical simulations of IGW in a
differentially-rotating massive star and the observed spectra.We also
show that the velocity spectra caused by IGW may lead to detectable
line-profile variability and explain the occurrence of
macroturbulence in the observed line profiles of OB stars. Our
findings provide predictions that can readily be tested by including
a sample of bright slowly and rapidly rotating OB-type stars in the
scientific programme of the K2 mission accompanied by high-precision
spectroscopy and their
confrontation with multi-dimensional
hydrodynamic simulations of IGW for various masses and
ages.
Reference: ApJ Letters, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1505.06648
Comments:
Email: conny.aerts@ster.kuleuven.be
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S.A.Zhekov (1) and S.L.Skinner (2)
(1) Institute
of Astronomy and National Astronomical observatory, Sofia, Bulgaria
(2) CASA, University of Colorado, Boulder, USA
We present
an analysis of XMM-Newton X-ray data of WR30a (WO+O),
a close
massive binary that harbours an oxygen-rich Wolf-Rayet star.
Its
spectrum is characterized by the presence of two well-separated
broad peaks, or `bumps', one peaking at energies between 1 and 2
keV
and the other between 5 and 7 keV. A two-component model is
required
to match the observed spectrum. The higher energy
spectral peak is
considerably more absorbed and dominates the
X-ray luminosity.
For the currently accepted distance of 7.77
kpc, the X-ray
luminosity of WR30a is L_X > 10^{34} erg
s^{-1}, making it one of the
most X-ray luminous WR+O binary
amongst those in the Galaxy with
orbital periods less than ~20 d.
The X-ray spectrum can be acceptably
fitted using either thermal
or nonthermal models, so the X-ray
production mechanism is yet
unclear.
Reference: Monthly Notices of the Royal
Astronomical Society
Status: Manuscript has been
accepted
Weblink:
http://xxx.lanl.gov/abs/1506.04634
Comments:
Email: szhekov@astro.bas.bg
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D. M.-A.~Meyer (1), N.~Langer
(1), J.~Mackey (1), P.~F.~Vel'azquez (2) and A.~Gusdorf (3)
(1)
Argelander-Institut f"ur Astronomie der Universit"at Bonn,
Auf dem H"ugel 71, 53121, Bonn, Germany
(2) Instituto de
Ciencias Nucleares, UNAM, Apartado Postal 70-543, 04510 Mexico, DF,
Mexico
(3) LERMA, UMR 8112 du CNRS, Observatoire de Paris, Ecole
Normale Sup' erieure, 24 rue Lhomond, 75231 Paris Cedex 05,
France
After the death of a runaway massive star, its
supernova shock wave interacts with the bow shocks produced by its
defunct progenitor, and may lose its spherical symmetry before
expanding into the local interstellar medium (ISM). We investigate
whether the initial mass and space velocity of these progenitors can
be associated with asymmetric supernova remnants. We run
hydrodynamical models of supernovae exploding in the pre-shaped
medium of moving Galactic core-collapse progenitors. We find that bow
shocks that accumulate more than about 1.5 Mo generate asymmetric
remnants. The shock wave collides 160-750 yr up to 830-4900 yr after
the supernova with these bow shocks then located at about 1.35-5 pc
from the center of the explosion. It expands freely into the ISM
whereas it is channelled into the region of undisturbed wind material
moving in the opposite direction. This applies to an initially 20 Mo
progenitor moving with velocity 20 km/s and to our initially 40 Mo
progenitor. These remnants generate mixing of ISM gas, stellar wind
and supernova ejecta that is particularly important upstream from the
center of the explosion. Their lightcurves are dominated by emission
from optically-thin cooling and by X-ray emission of the shocked ISM
gas. We find that these remnants are likely to be observed in the
[OIII] 5007 spectral line emission or in the soft energy-band of
X-rays. Finally, we discuss our results in the context of observed
Galactic supernova remnants such as 3C391 and the Cygnus
Loop.
Reference: Meyer D. et al., MNRAS (450)
2015
Status: Manuscript has been accepted
Weblink:
http://cdsads.u-strasbg.fr/abs/2015MNRAS.450.3080M
Comments:
Email: dominique.meyer@uni-tuebingen.de
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Monday 31 August 2015
Venue: Freiburg
Waves
inside Stars: Theory, Simulations, Observational Signatures, and Lab
Experiments
Splinter session, Monday 31 August, 10h -
12h30, during
SOLARNET III / HELAS VII / SpaceInn Conference
"The Sun, the stars, and solar-stellar relations"
http://www.iac.es/congreso/solarnet-3meeting/
Organisers:
Tamara Rogers (Newcastle University, UK)
Conny Aerts
(Leuven University, B)
Abstract:
Waves are as
ubiquitous in stars as they are on Earth. Just as on Earth, waves
can transport angular momentum and mix species within stellar
interiors,
steering their rotational and chemical evolution.
Waves also set up standing
modes which can be observed through
helio- and asteroseismology.
Helioseismology has revolutionized
our picture of the Sun, constraining the
internal rotation
profile and convective undershooting in the solar interior.
Asteroseismology is not far behind, recently constraining
core-envelope
differential rotation and core convective
overshooting in more massive stars.
Indeed, the observations of
waves through helio- and asteroseismology places the
tightest
constraints on the dynamical evolution those same waves induce.
This 2.5 hour splinter session aims to bring together
researchers doing theory,
simulations, and observations of waves
in stars (gravity, pressure and mixed)
with the hope that the
synergy between the three (often disparate) fields could
lead to
tests and comparisons which would further our understanding of
stellar
interiors. Moreover, we include also studies of wave
generation by convection
in laboratory experiments to search for
connections between those and stellar
physics. We begin this
session with four short talks on each of the sub-topics
and will
then continue with a guided discussion on how these fields can work
together to advance our understanding.
Programme:
Monday 31 August, 10:00 - 12:30
10:00 - 10:30 Theory:
Stephane Mathis (Saclay, France)
10:30 - 11:00 Simulations: Tami
Rogers (Newcastle, UK)
11:00 - 11:15 Observational Signatures:
Conny Aerts (Leuven, B)
11:15 - 11:30 Lab Experiments: Santiago
Andres Triana (Leuven, B)
11:30 - 11:45 Short Coffee Break
11:45 - 12:25 Guided discussion, participants are encouraged
to bring 1 slide
12:25 - 12:30 Summary of Synergies & Future
Steps
Weblink:
http://www.iac.es/congreso/solarnet-3meeting/
Email:
conny.aerts@ster.kuleuven.be
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