ISSN 1783-3426
|
Selma de Mink awarded the EAS MERAC
Prize -- Congratulations
Webpage
of EWASS SS10 "Winds from massive stars: What are the real
rates?"
Call for proposals
to organize the next massive star meeting -- Reminder
MULTI-EPOCH BVRI PHOTOMETRY OF LUMINOUS
STARS IN M31 AND M33
Luminous and
Variable Stars in M31 and M33 V. The Upper HR Diagram}
A
modern study of HD166734: a massive supergiant system
An
X-ray view of HD166734, a massive supergiant system
CMF
models of hot star winds II. Reduction of O star wind mass-loss rates
in global models
The variability
of the BRITE-est Wolf-Rayet binary, $\gamma^2$ Velorum I. Photometric
and spectroscopic evidence for colliding winds
Exact
Analytic Solutions for a Ballistic Orbiting Wind
A
deep near-infrared spectroscopic survey of the Scutum-Crux arm for
Wolf-Rayet stars
A combined HST
and XMM-Newton campaign for the magnetic O9.7 V star HD 54879:
constraining the weak-wind problem of massive stars
Variable
millimetre radiation from the colliding-wind binary Cyg OB2 #8A
Properties of O dwarf stars in 30 Doradus
Our colleague, Dr. Selma de Mink from the University
of Amsterdam was awarded the MERAC Prize in Theoretical Astrophysics
of the European Astronomical Society (EAS) for her contributions to
the understanding of the role of massive binaries. The Executive
Committee of the Massive Stars Commission proudly congratulates Selma
for this well deserved achievement, that enlightens our whole field
of research. Selma gave an excellent & inspiring talk during the
European Week of Astronomy and Space Science (EWASS) in Prague,
emphasizing to a broad audience of Astrophysicists, the role of
massive stars for our understanding of the Universe. Thanks, Selma,
and congratulations!
the Massive Stars Commission
Executive Committee
(A. Herrero, J. Vink, N. St-Louis, G. Rauw,
A. ud-Doula, Y. Hua-Chu, J. Groh)
Weblink:
Email:
ahd@iac.es
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The presentations from EWASS SS10 "Winds from
massive stars: What are the real rates?" are available
online.
Weblink:
http://space.asu.cas.cz/~ewass17-soc/Presentations/SS10.html
Email:
krticka@physics.muni.cz
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contents
Dear Colleagues,
After
the fantastic meeting in Auckland (thanks to JJ Eldridge and the
whole organizing team) we have to start preparing the next Massive
Stars Meeting. We expect this to take place some time in 2020.
With
this call the Organizing Committee (OC) of our Massive Stars
Commission invites any interested individuals/institutions to send an
email before September 1st, 2017 expressing an interest in organizing
the next meeting. IAU has the final authority to select a symposium,
but the Massive Star Commission OC will support one application based
on a number of criteria. Once selected, the OC will assist the
meeting organizer in the whole application to IAU process, including
preparation and submission, SOC selection, etc. Our criteria for
selection include:
- the meeting location (traditionally,
our group prefers locations near a beach with a relaxed atmosphere
that encourages personal contacts)
- the availability of hotels
with large conference rooms (at least 200 people) and meeting
facilities at affordable prices
- the support of a local
astronomical community
- the balance of locations hosting all
our previous meetings
If possible, your email to the OC
should contain the following information:
- A list of
local volunteers willing to help organizing the meeting
- A
list of hotels that can guarantee accommodation of at least 200
participants, and with appropriate conference facilities
-
Approximate hotel room prices
- Approximate distance from the
nearest airport to the meeting venue/hotel
- Alternative
sponsors or ways to support the meeting
- The best dates for
the meeting, and/or black out dates
(because of school holidays
or high touristic season, etc.)
- Add any other information you
consider will be useful to OC.
The email should be sent
directly to the President of the Commission, Artemio Herrero
(ahd-at-iac.es).
The massive stars meeting is one of the
central pillars of
our community and therefore the OC thanks in
advance anyone interested in organizing this important meeting.
with best regards,
Artemio Herrero,
on behalf
of the Organizing Committee of the G2 Commission
Weblink:
Email: ahd@iac.es
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John C. Martin^1 and Roberta M. Humphreys^2
1.
University of Illinois Springfield
2. University of
Minnesota
We present the first four years of BVRI
photometry from an on-going survey to annually monitor the
photometric behavior of evolved luminous stars in M31 and M33.
Photometry was measured for 199 stars at multiple epochs, including 9
classic Luminous Blue Variables (LBVs), 22 LBV candidates, 10
post-RGB A/F type hypergiants, and 18 B[e] supergiants. At all epochs
the brightness is measured in V and at least one other band to a
precision of 0.04 – 0.10 magnitudes down to a limiting magnitude of
19.0 – 19.5. Thirty three (33) stars in our survey exhibit
significant variability, including at least two classic LBVs caught
in S Doradus type outbursts. A hyper-linked version of the photometry
catalog is at http://go.uis.edu/m31m33photcat.
Reference:
To appear in the Astronomical Journal
Status: Manuscript has
been accepted
Weblink:
Comments:
Email: roberta@umn.edu
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Roberta M Humphreys^1, Kris Davidson^1, David Hahn^1,
John C. Martin^2 and Kerstin Weis^3
1. University of
Minnesota
2. University of Illinois, Springfield
3.
Ruhr-Universitaet Bochum, Germany
We present HR Diagrams
for the massive star populations in M31 and M33 including several
different types of emission-line stars: the confirmed Luminous Blue
Variables (LBVs), candidate LBVs, B[e] supergiants and the warm
hypergiants. We estimate their apparent temperatures and luminosities
for comparison with their respective massive star populations and to
evaluate the possible relationships of these different classes of
evolved, massive stars, and their evolutionary state. Several of the
LBV candidates lie near the LBV/S Dor instability strip which
supports their classification. Most of the B[e] supergiants, however,
are less luminous than the LBVs. Many are very dusty with the
infrared flux contributing one-third or more to their total flux.
They are also relatively isolated from other luminous OB stars.
Overall, their spatial distribution suggests a more evolved state.
Some may be post-RSGs like the warm hypergiants, and there may be
more than one path to becoming a B[e] star. There are sufficient
differences in the spectra, luminosities, spatial distribution, and
the presence or lack of dust between the LBVs and B[e] supergiants to
conclude that one group does not evolve into the other.
Reference:
To appear in the Astrophysical Journal
Status: Manuscript
has been accepted
Weblink:
Comments:
Email: roberta@umn.edu
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L. Mahy (1,5), Y. Damerdji (2,1), E. Gosset (1), C.
Nitschelm (3), P. Eenens (4), H. Sana (5), and A. Klotz (6)
(1)
Space sciences, Technologies, and Astrophysics Research (STAR)
Institute, Université de Liège, Quartier Agora, Bât B5c, Allée du
6 août, 19c, B-4000 Liège, Belgium
(2) Centre de Recherche en
Astronomie, Astrophysique et Géophysique, route de l’Observatoire
BP 63 Bouzareah, 16340 Algiers, Algeria
(3) Unidad de
Astronomía, Facultad de Ciencias Básicas, Universidad de
Antofagasta, Antofagasta, Chile
(4) Departamento de Astronomía,
Universidad de Guanajuato, Apartado 144, 36000 Guanajuato, GTO,
Mexico
(5) Instituut voor Sterrenkunde, KU Leuven,
Celestijnenlaan 200D, Bus 2401, B-3001 Leuven, Belgium
(6)
Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
Aims.
HD166734 is an eccentric eclipsing binary system composed of two
supergiant O-type stars, orbiting with a 34.5-day period. In this
rare configuration for such stars, the two objects mainly evolve
independently, following single-star evolution so far. This system
provides a chance to study the individual parameters of two
supergiant massive stars and to derive their real masses.
Methods.
An intensive monitoring was dedicated to HD166734.We analyzed mid-
and high-resolution optical spectra to constrain the orbital
parameters of this system. We also studied its light curve for the
first time, obtained in the VRI filters. Finally, we disentangled the
spectra of the two stars and modeled them with the CMFGEN atmosphere
code in order to determine the individual physical parameters.
Results. HD166734 is a O7.5If+O9I(f) binary.We confirm its
orbital period but we revise the other orbital parameters. In
comparison to what we found in the literature, the system is more
eccentric and, now, the hottest and the most luminous component is
also the most massive one. The light curve exhibits only one eclipse
and its analysis indicates an inclination of 63.0° ± 2.7°. The
photometric analysis provides us with a good estimation of the
luminosities of the stars, and therefore their exact positions in the
Hertzsprung-Russell diagram. The evolutionary and the spectroscopic
masses show good agreement with the dynamical masses of 39.5 M⊙ for
the primary and 33.5 M⊙ for the secondary, within the
uncertainties. The two components are both enriched in helium and in
nitrogen and depleted in carbon. In addition, the primary also shows
a depletion in oxygen. Their surface abundances are however not
different from those derived from single supergiant stars, yielding,
for both components, an evolution similar to that of single
stars.
Reference: A&A accepted
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1707.02060
Comments:
13 pages, 13 figures
Email:
mahy@astro.ulg.ac.be
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Yael Naze, Eric Gosset, Laurent Mahy, Elliot Ross
Parkin
Univ. Liege, Belgium
The X-ray
emission of the O+O binary HD166734 was monitored using Swift and
XMM-Newton observatories, leading to the discovery of phase-locked
variations. The presence of an f line in the He-like triplets further
supports a wind-wind collision as the main source of the X-rays in
HD166734. While temperature and absorption do not vary significantly
along the orbit, the X-ray emission strength varies by one order of
magnitude, with a long minimum state (Delta(phi)~0.1) occurring after
a steep decrease. The flux at minimum is compatible with the
intrinsic emission of the O-stars in the system, suggesting a
possible disappearance of colliding wind emission. While this minimum
cannot be explained by eclipse or occultation effects, a shock
collapse may occur at periastron in view of the wind properties.
Afterwards, the recovery is long, with an X-ray flux proportional to
the separation d (in hard band) or to d^2 (in soft band). This is
incompatible with an adiabatic nature for the collision (which would
instead lead to "F_X propto 1/d"), but could be reconciled
with a radiative character of the collision, though predicted
temperatures are lower and more variable than in observations. An
increase in flux around phi~0.65 and the global asymmetry of the
light curve remain unexplained, however.
Reference:
A&A, in press
Status: Manuscript has been
accepted
Weblink:
https://arxiv.org/abs/1707.02064
Comments:
Email: naze@astro.ulg.ac.be
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Jiri Krticka, Jiri Kubat
Institute of
Theoretical Physics and Astrophysics, Masaryk University, Brno, Czech
Republic
Astronomical Institute, Academy of Sciences of the
Czech Republic, Ondrejov, Czech Republic
We calculate
global (unified) wind models of main-sequence, giant, and supergiant
O stars from our Galaxy. The models are calculated by solving
hydrodynamic, kinetic equilibrium (also known as NLTE) and
comoving-frame (CMF) radiative transfer equations from the (nearly)
hydrostatic photosphere to the supersonic wind. For given stellar
parameters, our models predict the photosphere and wind structure and
in particular the wind mass-loss rates without any free parameters.
Our predicted mass-loss rates are by a factor of 2--5 lower than the
commonly used predictions. A possible cause of the difference is
abandoning of the Sobolev approximation for the calculation of the
radiative force, because our models agree with predictions of CMF
NLTE radiative transfer codes. Our predicted mass-loss rates agree
nicely with the mass-loss rates derived from observed near-infrared
and X-ray line profiles and are slightly lower than mass-loss rates
derived from combined UV and Halpha diagnostics. The empirical
mass-loss rate estimates corrected for clumping may therefore be
reconciled with theoretical predictions in such a way that the
average ratio between individual mass-loss rate estimates is not
higher than about 1.6. On the other hand, our predictions are by
factor of 4.7 lower than pure Halpha mass-loss rate estimates and can
be reconciled with these values only assuming a microclumping factor
of at least eight.
Reference: A&A, in
press
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2017arXiv170606194K
Comments:
Email: krticka@physics.muni.cz
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Noel Richardson et al.
University of
Toledo
We report on the first multi-color precision light
curve of the bright Wolf-Rayet binary $\gamma^2$ Velorum, obtained
over six months with the nanosatellites in the BRITE- Constellation
fleet. In parallel, we obtained 488 high-resolution optical spectra
of the system. In this first report on the datasets, we revise the
spectroscopic orbit and report on the bulk properties of the
colliding winds. We find a dependence of both the light curve and
excess emission properties that scales with the inverse of the binary
separation. When analyzing the spectroscopic properties in
combination with the photometry, we find that the phase dependence is
caused only by excess emission in the lines, and not from a changing
continuum. We also detect a narrow, high-velocity absorption
component from the He I $\lambda$5876 transition, which appears twice
in the orbit. We calculate smoothed-particle hydrodynamical
simulations of the colliding winds and can accurately associate the
absorption from He I to the leading and trailing arms of the wind
shock cone passing tangentially through our line of sight. The
simulations also explain the general strength and kinematics of the
emission excess observed in wind lines such as C III $\lambda$5696 of
the system. These results represent the first in a series of
investigations into the winds and properties of $\gamma^2$ Velorum
through multi-technique and multi-wavelength observational
campaigns.
Reference: MNRAS, in press
Status:
Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1707.03390
Comments:
Email: noel.richardson@UToledo.edu
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Francis P. Wilkin, Harry Hausner
Union
College, University of Wisconsin
Much theoretical and
observational work has been done on stellar winds within binary
systems. We present a new solution for a ballistic wind launched from
a source in a circular orbit. Our method emphasizes the curved
streamlines in the corotating frame, where the flow is steady-state,
allowing us to obtain an exact solution for the mass density at all
pre-shock locations. Assuming an initially isotropic wind, fluid
elements launched from the interior hemisphere of the wind will be
the first to cross other streamlines, resulting in a spiral structure
bounded by two shock surfaces. Streamlines from the outer wind
hemisphere later intersect these shocks as well. An analytic solution
is obtained for the geometry of the two shock surfaces. Although the
inner and outer shock surfaces asymptotically trace Archimedean
spirals, our tail solution suggests many crossings where the shocks
overlap, beyond which the analytic solution cannot be continued. Our
solution can be readily extended to an initially anisotropic
wind.
Reference: Published in ApJ July 20,
2017
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/pdf/1707.02505.pdf
Comments:
Email: wilkinf@union.edu
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C K Rosslowe, Paul A Crowther
University
of Sheffield
We present an NTT/SOFI spectroscopic survey
of infrared selected Wolf-Rayet candidates in the Scutum-Crux spiral
arm (298 < l < 340, |b| < 0.5). We obtained near-IR spectra
of 127 candidates, revealing 17 Wolf-Rayet stars - a ~13% success
rate - of which 16 are newly identified here. The majority of the new
Wolf-Rayet stars are classified as narrow-lined WN5-7 stars, with 2
broad-lined WN4-6 stars and 3 WC6-8 stars. The new stars, with
distances estimated from previous absolute magnitude calibrations,
have no obvious association with the Scutum-Crux arm. Refined
near-infrared (YHJK) classification criteria based on over a hundred
Galactic and Magellanic Cloud WR stars, providing diagnostics for
hydrogen in WN stars, plus the identification of WO stars and
intermediate WN/C stars. Finally, we find that
only a quarter
of WR stars in the survey region are associated with star clusters
and/or HII regions, with similar statistics found for Luminous Blue
Variables in the Milky Way. The relative isolation of evolved massive
stars is discussed, together with the significance of the co-location
of LBVs and WR stars in young star clusters.
Reference:
MNRAS in press
Status: Manuscript has been
accepted
Weblink:
Comments:
Supplementary information incl. near-IR spectroscopic
classification of Wolf-Rayet stars
Email:
Paul.Crowther@sheffield.ac.uk
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T. Shenar(1), L. M. Oskinova, S. P. Järvinen, P. Luckas,
R. Hainich, H. Todt, S. Hubrig, A. A. C. Sander, I. Ilyin, W.-R.
Hamann
1 - University of Potsdam, Germany
Context:
HD 54879 (O9.7 V) is one of a dozen O-stars for which an organized
atmospheric magnetic field has been detected. To gain insights into
the interplay between atmospheres, winds, and magnetic fields of
massive stars, we acquired UV and X-ray data of HD 54879 using the
Hubble Space Telescope and the XMM-Newton satellite. In addition, 35
optical amateur spectra were secured to study the variability of HD
54879. A multiwavelength (X-ray to optical) spectral analysis is
performed using the Potsdam Wolf-Rayet (PoWR) model atmosphere code
and the xspec software.
Results: The photospheric parameters
are typical for an O9.7 V star. The microturbulent, macroturbulent,
and projected rotational velocities are lower than previously
suggested (<4 km/s). An initial mass of 16 M⊙ and an age of 5
Myr are inferred from evolutionary tracks. We derive a mean X-ray
emitting temperature of log TX = 6.7 [K] and an X-ray luminosity of
log LX = 32 [erg/s]. Short- and long-scale variability is seen in the
H-alpha line, but only a very long period of P ≈ 5yr could be
estimated. Assessing the circumstellar density of HD 54879 using UV
spectra, we can roughly estimate the mass-loss rate HD 54879 would
have in the absence of a magnetic field as log Mdot(B=0) ≈ −9.0
[M⊙/yr]. The magnetic field traps the stellar wind up to the
Alfv\'en radius > 12 R⊙, implying that its true mass-loss rate
is log Mdot < −10.2[M⊙/yr]. Hence, density enhancements around
magnetic stars can be exploited to estimate mass-loss rates of
non-magnetic stars of similar spectral types, essential for resolving
the weak wind problem.
Conclusions: Our study confirms that
strongly magnetized stars lose little or no mass, and supplies
important constraints on the weak-wind problem of massive main
sequence stars.
Reference: A&A, in
press
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1708.01261
Comments:
Email: shtomer@astro.physik.uni-potsdam.de
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R. Blomme (1), D. M. Fenech
(2), R. K. Prinja (2), J. M. Pittard (3), J. C. Morford (2)
1
- Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels, Belgium
2 - Department of Physics and Astronomy, University College
London, Gower Street, London WC1E 6BT, UK
3 - School of Physics
& Astronomy, E.C. Stoner Building, The University of Leeds,
Leeds, LS2 9JT, UK
Massive binaries have stellar winds
that collide. In the colliding-wind region, various physically
interesting processes occur, leading to enhanced X-ray emission,
non-thermal radio emission, as well as non-thermal X-rays and
gamma-rays. Non-thermal radio emission (due to synchrotron radiation)
has so far been observed at centimetre wavelengths. At millimetre
wavelengths, the stellar winds and the colliding-wind region emit
more thermal free-free radiation, and it is expected that any
non-thermal contribution will be difficult or impossible to detect.
We aim to determine if the material in the colliding-wind region
contributes substantially to the observed millimetre fluxes of a
colliding-wind binary. We also try to distinguish the synchrotron
emission from the free-free emission. We monitored the massive binary
Cyg OB2 #8A at 3 mm with the NOrthern Extended Millimeter Array
(NOEMA) interferometer of the Institut de Radioastronomie
Millimetrique (IRAM). The data were collected in 14 separate
observing runs (in 2014 and 2016), and provide good coverage of the
orbital period. The observed millimetre fluxes range between 1.1 and
2.3 mJy, and show phase-locked variability, clearly indicating that a
large part of the emission is due to the colliding-wind region. A
simple synchrotron model gives fluxes with the correct order of
magnitude, but with a maximum that is phase-shifted with respect to
the observations. Qualitatively this phase shift can be explained by
our neglect of orbital motion on the shape of the colliding-wind
region. A model using only free-free emission results in only a
slightly worse explanation of the observations. Additionally, on the
map of our observations we also detect the O6.5 III star Cyg OB2 #8B,
for which we determine a 3 mm flux of 0.21 +- 0.033 mJy. The question
of whether synchrotron radiation or free-free emission dominates the
millimetre fluxes of Cyg OB2 #8A remains open. More detailed
modelling of this system, based on solving the hydrodynamical
equations, is required to give a definite answer.
Reference:
A&A, in press
Status: Manuscript has been
accepted
Weblink:
https://arxiv.org/abs/1708.04834
Comments:
Email: Ronny.Blomme@oma.be
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Carolina Sab\'in-Sanjuli\'an
(1)
Departamento de F\'sica y Astronom\'a, Universidad de La Serena, Av.
Cisternas 1200 Norte, La Serena, Chile
(2) Instituto de
Investigaci\'on Multidisciplinar en Ciencia y Tecnolog\'ia,
Universidad de La Serena, Ra\'ul Bitr\'an 1305, La Serena, Chile
We
perform a quantitative spectroscopic analysis of 105 presumably
single O dwarf stars in 30 Doradus, located within the Large
Magellanic Cloud. We use mid-to-high resolution multi-epoch optical
spectroscopic data obtained within the VLT-FLAMES Tarantula Survey.
Stellar and wind parameters are derived by means of the automatic
tool IACOB-GBAT, which is based on a large grid of FASTWIND models.
We also benefit from the Bayesian tool BONNSAI to estimate
evolutionary masses. We provide a spectral calibration for the
effective temperature of O dwarf stars in the LMC, deal with the mass
discrepancy problem and investigate the wind properties of the
sample.
Reference: arXiv1707.04209
Status:
Conference proceedings
Weblink:
Comments:
Email: cssj@dfuls.cl
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