ISSN 1783-3426
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Massive Star Workshop 2016/17 -- Announcement and input request
The wind of Variable C in M33 (an LBV
in eruption)
3D Radiative Transfer
in η Carinae: Application of the SimpleX Algorithm to 3D SPH
Simulations of Binary Colliding Winds
Luminous
and Variable Stars in M31 and M33. II. Luminous Blue
Variables,Candidate LBVs, Fe II Emission Line Stars, and Other
Supergiants
The VLT-FLAMES
Tarantula Survey XVII. Physical and wind properties of massive stars
at the top of the main sequence
On
the use of the Fourier Transform to determine the projected
rotational velocity of line-profile variable B stars
Investigating
the origin of cyclical wind variability in hot, massive stars - I. On
the dipolar magnetic field hypothesis
Time-dependent
modeling of extended thin decretion disks of critically rotating
stars
The HD5980 multiple system:
Masses and evolutionary status
Magnetic
braking of stellar cores in red giants and supergiants
The
three-dimensional structure of the Eta Carinae Homunculus
MOST
Detects Corotating Bright Spots On The Mid-O-Type Giant xi Persei
A New Class of Wolf-Rayet Stars:
WN3/O3s
Massive Star
Asteroseismology in Action
The B
Fields in OB Stars (BOB) Survey
Physics
of rotation: problems and challenges
Faculty
Position: Numerical Modelling of Stellar Interiors
Research
Associate in Theoretical Stellar Astrophysics
Fizeau
exchange visitors program: call for applications
dear colleagues,
the Organizing
Committee of the Massive Star Working Group, together with John
Eldridge (in the following, OC refers to both) is preparing the
proposal for our next Massive Stars Workshop, that will take place in
New Zealand.
After some discussion, the OC decided to have the
meeting at the end of 2016, in the week from November 28 to December
2.
As we want to get support from the IAU, we have to write a
Letter of Interest. For Symposia to be held in 2016, the deadline for
LoIs is September 15, 2014.
This LoI has to contain some
information, in particular about the scientific content of the
Symposium.
We are a group interested on massive stars, so
massive stars will be our main scientific focus. But massive stars
have many related or adjacent fields,and to remain an open community,
involved with the rest of Astrophysics,we want to also dedicate some
time (1-1,5 out of our 4,5 workshop days) to one of these fields. The
OC thought that participation of the whole group in this decission
would be a positive innitiative.
Therefore we ask you to send
comments and opinions about which field of astrophysics should
complement our meeting. To mention just a few examples, you could
support to have some time for Supernovae, the cosmic reionization,
starburst, HII regions, massive star forming regions... (or a
combination of them).
Comments can be sent through the
massive stars facebook page or to a dedicated email account we have
set:
massivestarmeeting2017@yahoo.com
In the first case, OC
members already in facebook will collect and synthesize the input and
in the second case, the whole OC will have direct acces to the emails
received. After input by the community, the OC will take a decision
on the complementary subject and write a proposal for the IAU.
As
the IAU deadline is September 15, we ask those interested in
participating to send their comments before August 15.
best
regards,
Artemio Herrero
chair, on behalf of the Massive
Stars Organizing Committee
Weblink:
Email:
massivestarmeeting2017@yahoo.com
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Roberta M. Humphreys (1), Kris Davidson(1), Michael S.
Gordon(1), Kerstin Weis(2), Birgitta Burggraf(2), D. J. Bomans(2),
and John C. Martin(3)
(1) University of Minnesota
(2)
Ruhr Universitaet, Bochum
(3) University of Illinois,
Springfield
We discuss the spectrum of Var C in M33 obtained
just before the onset of its current brightening and recent spectra
during its present "eruption" or optically thick wind
stage. These spectra illustrate the typical LBV transition in
apparent spectral type or temperature that characterizes the
classical LBV or S Dor-type variability. LBVs are known to have slow,
dense winds during their maximum phase. Interestingly, Var C had a
slow wind even during its hot, quiescent stage in comparison with the
normal hot supergiants with similar temperatures. Its outflow or wind
speeds also show very little change between these two
states.
Reference: Astrophysical Journal Letters, 2014,
782, L21
Status: Manuscript has been accepted
Weblink:
Comments:
Email: roberta@umn.edu
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N. Clementel (1), T. I. Madura (2), C. J. H. Kruip (1), V.
Icke (1), T. R. Gull (2)
(1) Leiden Observatory, Leiden
University, P.O. Box 9513, 2300 RA Leiden, the Netherlands
(2)
Astrophysics Science Division, Code 667, NASA Goddard Space Flight
Center, Greenbelt, MD 20771, USA
Eta Carinae is an ideal
astrophysical laboratory for studying massive binary interactions and
evolution, and stellar wind-wind collisions. Recent three-dimensional
(3D) simulations set the stage for understanding the highly complex
3D flows in η Car. Observations of different broad high- and
low-ionization forbidden emission lines provide an excellent tool to
constrain the orientation of the system, the primary’s mass-loss
rate, and the ionizing flux of the hot secondary. In this work we
present the first steps towards generating synthetic observations to
compare with available and future HST/STIS data. We present initial
results from full 3D radiative transfer simulations of the
interacting winds in η Car. We use the SimpleX algorithm to
post-process the output from 3D SPH simulations and obtain the
ionization fractions of hy- drogen and helium assuming three
different mass-loss rates for the primary star. The resultant
ionization maps of both species constrain the regions where the
observed forbidden emission lines can form. Including collisional
ionization is necessary to achieve a better description of the
ionization states, especially in the areas shielded from the
secondary’s radiation. We find that reducing the primary’s
mass-loss rate increases the volume of ionized gas, creating larger
areas where the forbidden emission lines can form. We conclude that
post processing 3D SPH data with SimpleX is a viable tool to create
ionization maps for η Car.
Reference: Clementel et
al., 2014, MNRAS (accepted)
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1406.7240
Comments:
Email: clementel@strw.leidenuniv.nl
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Roberta M. Humphreys(1), Kerstin Weis(2),
Kris
Davidson(1), D.~J.Bomans(2), and
Birgitta Burggraf(2)
1.
University of Minnesota
2. Ruhr-Universitaet Bochum, Germany
An
increasing number of non-terminal eruptions are being found in the
numerous
surveys for optical transients. Very little is known
about these giant eruptions, their progenitors and their evolutionary
state. A greatly improved census of the likely progenitor class,
including the most luminous evolved stars, the Luminous Blue
Varaibles (LBVs), and the warm and cool hypergiants is now needed for
a complete picture of the final pre-SN stages of very massive stars.
We have begun a survey of the evolved and unstable luminous star
populations in several nearby resolved galaxies. In this second
paper on M31 and M33, we review the spectral characteristics,
spectral energy distributions, circumstellar ejecta, and evidence for
mass loss for 82 luminous and variable stars. We show that many of
these stars have warm circumstellar dust including several of the Fe
II emission line stars, but conclude that the confirmed LBVs in M31
and M33 do not. The confirmed LBVs have relatively low wind speeds
even in their hot, quiescent or visual minimum state compared to the
B-type supergiants and Of/WN stars which they spectroscopically
resemble. The nature of the Fe II emission line stars and their
relation to the LBV state remains uncertain, but some have properties
in common with the warm hypergiants and the sgB[e] stars. Several
individual stars are discussed in detail. We identify three possible
candidate LBVs and three additional post-red supergiant candidates.
We suggest that M33-013406.63 (UIT301,B416) is not an LBV/S Dor
variable, but is a very luminous late O-type supergiant and one of
the most luminous stars or pair of stars in M33.
Reference:
Astrophysical Journal, 790, 48
Status: Manuscript has been
accepted
Weblink:
Comments:
Email:
roberta@umn.edu
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Joachim M. Bestenlehner(1), Götz Gräfener(1), Jorick S.
Vink(1), F. Najarro(2), A. de Koter(3,4), H. Sana(5), C. J. Evans(6),
P. A. Crowther(7), V. Hénault-Brunet(8), A. Herrero(9,10), N.
Langer(11), F. R. N. Schneider(11), S. Simón-Díaz(9,10), W. D.
Taylor(6), and N. R. Walborn(12)
1 - Armagh Observatory,
College Hill, Armagh BT61 9DG, United Kingdom; 2 - Centro de
Astrobiología (CSIC-INTA), Ctra. de Torrejón a Ajalvir km-4,
E-28850 Torrejón de Ardoz, Madrid, Spain; 3 - Astronomical Institute
Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH,
Amsterdam, The Netherlands; 4 - Instituut voor Sterrenkunde,
Universiteit Leuven, Celestijnenlaan 200 D, 3001, Leuven, Belgium; 5
- ESA/STScI, 3700 San Martin Drive, Baltimore, MD21210, USA; 6 - UK
Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford
Hill, Edinburgh, EH9 3HJ, UK; 7 - Dept. of Physics & Astronomy,
Hounsfield Road, University of Sheffield, S3 7RH, UK; 8 - Department
of Physics, Faculty of Engineering and Physical Sciences, University
of Surrey, Guildford, GU2 7XH, UK; 9 - Instituto de Astrofísica de
Canarias, E-38200 La Laguna, Tenerife, Spain;10 - Departamento de
Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife,
Spain; 11 - Argelander-Institut für Astronomie der Universität
Bonn, Auf dem Hügel 71, 53121 Bonn, Germany; 12 - Space Telescope
Science Institute, 3700 San Martin Drive, Baltimore, MD 21218,
USA
The evolution and fate of very massive stars (VMS) is
tightly connected to their mass-loss properties. Their initial and
final masses differ significantly as a result of mass loss. VMS have
strong stellar winds and extremely high ionising fluxes, which are
thought to be critical sources of both mechanical and radiative
feedback in giant H ii regions. However, how VMS mass-loss properties
change during stellar evolution is poorly understood. In the
framework of the VLT-Flames Tarantula Survey (VFTS), we explore the
mass-loss transition region from optically thin O star winds to
denser WNh Wolf-Rayet star winds, thereby testing theoretical
predictions. To this purpose we select 62 O, Of, Of/WN, and WNh
stars, an unprecedented sample of stars with the highest masses and
luminosities known. We perform a spectral analysis of optical VFTS as
well as near-infrared VLT/SINFONI data using the non-LTE radiative
transfer code CMFGEN to obtain both stellar and wind parameters. For
the first time, we observationally resolve the transition between
optically thin O star winds and optically thick hydrogen-rich WNh
Wolf-Rayet winds. Our results suggest the existence of a ``kink''
between both mass-loss regimes, in agreement with recent Monte Carlo
simulations. For the optically thick regime, we confirm the steep
dependence on the classical Eddington factor Gamma_e from previous
theoretical and observational studies. The transition occurs on the
main sequence near a luminosity of 10^6.1 Lsun, or a mass of 80...90
Msun. Above this limit, we find that -- even when accounting for
moderate wind clumping (with f_v = 0.1) -- wind mass-loss rates are
enhanced with respect to standard prescriptions currently adopted in
stellar evolution calculations. We also show that this results in
substantial helium surface enrichment. Finally, based on our
spectroscopic analyses, we are able to provide the most accurate
ionising fluxes for VMS known to date, confirming the pivotal role of
VMS in ionising and shaping their environments.
Reference:
Accepted for publication in A&A
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1407.1837
Comments:
Email: jbl@astro.uni-bonn.de
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C. Aerts, S. Simon-Diaz, P. G. Groot, P.
Degroote
Institute of Astronomy, KULeuven, Belgium
Dept.
of Astrophysics, IMAPP, Radboud University Nijmegen, the Netherlands
Instituto de Astrofisica de Canarias, 38200, La Laguna,
Tenerife, Spain
Departamento de Astrofisica, Universidad de
La Laguna, 38205, La Laguna,
Tenerife, Spain
The Fourier
Transform method is a popular tool to derive the rotational
velocities of stars from their spectral line profiles. However, its
domain of validity does not include line-profile variables with
time-dependent profiles. We investigate the performance of the
method for
such cases, by interpreting the line-profile
variations of spotted B stars, and
of pulsating B stars, as if
their spectral lines were caused by uniform surface
rotation
along with macroturbulence. We perform time-series analysis and
harmonic least-squares fitting of various line diagnostics and of
the outcome
of several implementations of the Fourier Transform
method. We find that
the projected rotational velocities derived
from the Fourier Transform vary
appreciably during the pulsation
cycle whenever the pulsational and rotational
velocity fields are
of similar magnitude. The macroturbulent velocities
derived while
ignoring the pulsations can vary with tens of km/s
during the
pulsation cycle. The temporal behaviour of the deduced rotational
and macroturbulent velocities are in antiphase with each other.
The
rotational velocity is in phase with the second moment of the
line profiles.
The application of the Fourier method to stars
with considerable pulsational
line broadening may lead to an
appreciable spread in the values of the
rotation velocity, and,
by implication, of the deduced value of the
macroturbulence.
These two quantities should therefore not be derived from
single
snapshot spectra if the aim is to use them as a solid diagnostic for
the evaluation of stellar evolution models of slow to moderate
rotators.
Reference: Accepted for publication in
A&A
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2014arXiv1407.6611A
Comments:
Email: conny.aerts@ster.kuleuven.be
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A. David-Uraz$^{1,2}$, G. A. Wade$^1$, V. Petit$^3$, A.
ud-Doula$^4$, J. O. Sundqvist$^{3,5}$, J. Grunhut$^6$, M.
Shultz$^{1,2,7}$, C. Neiner$^8$, E. Alecian$^{9,8}$, H. F.
Henrichs$^10$, J.-C. Bouret$^{11,12}$ and the MiMeS Collaboration
1
- Department of Physics, Royal Military College of Canada, PO Box
17000, Stn Forces, Kingston, Canada, K7K 4B4
2 - Department of
Physics, Engineering Physics and Astronomy, Queen’s University, 99
University Avenue, Kingston, Canada, K7L 3N6
3 - Bartol Research
Institute, University of Delaware, Newark, DE 19716, USA
4 - Penn
State Worthington Scranton, Dunmore, PA 18512, USA
5 - Institut
fur Astronomie und Astrophysik der Universitat Munchen, Scheinerstr.
1, D-81679 Munchen, Germany
6 - European Organisation for
Astronomical Research in the Southern Hemisphere,
Karl-Schwarzschild-Str. 2, 85748,
Garching bei Munchen, Germany
7 - European Organisation for Astronomical Research in the
Southern Hemisphere, Casilla 19001, Santiago 19, Chile
8 - LESIA,
UMR 8109 du CNRS, Observatoire de Paris, UPMC, Universit´e Paris
Diderot, 5 place Jules Janssen, F-92195
Meudon Cedex, France
9
- UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et
d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041,
France
10 - Astronomical Institute Anton Pannekoek, University of
Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
11 - Laboratoire d’Astrophysique de Marseille, CNRS-Universite
de Provence, Pole de l’Etoile Site de Chateau-Gombert, ´
38,
rue Frederic Joliot-Curie 13388 Marseille cedex 13, France
12 -
NASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA
OB
stars exhibit various types of spectral variability associated with
wind structures, including the apparently ubiquitous discrete
absorption components (DACs). These are proposed to be caused by
either magnetic fields or non-radial pulsations (NRPs). In this
paper, we evaluate the possible relation between large-scale, dipolar
magnetic fields and the DAC phenomenon by investigating the magnetic
properties of a sample of 13 OB stars exhibiting well-documented DAC
behaviour.
Using high-precision spectropolarimetric data acquired
in part in the context of the Magnetism in Massive Stars (MiMeS)
project, we find no evidence for surface dipolar magnetic fields in
any of these stars.
Using Bayesian inference, we compute
upper limits on the strengths of the fields and use these limits to
assess two potential mechanisms by which the field may influence wind
outflow: magnetic wind confinement and local photospheric brightness
enhancements. Within the limits we derive, both mechanisms fail to
provide a systematic process capable of producing DACs in all of the
stars of our sample. Therefore, this implies that dipolar fields are
highly unlikely to be responsible for these structures in all massive
stars, meaning that some other mechanism must come into
play.
Reference: arXiv:1407.6417 (accepted in
MNRAS)
Status: Manuscript has been accepted
Weblink:
Comments:
Email:
adavid-uraz@astro.queensu.ca
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P. Kurfürst (1), A. Feldmeier (2), J. Krtička
(1)
1-Department of Theoretical Physics and Astrophysics,
Masaryk University, Kotlářská 2, CZ-611,37 Brno, Czech Republic;
2-Institut für Physik und Astronomie, Universität Potsdam,
Karl-Liebknecht-Strasse 24/25,
14476 Potsdam-Golm,
Germany
During their evolution massive stars can reach the
phase of critical rotation when a further increase in rotational
speed is no longer possible. Direct centrifugal ejection from a
critically or near-critically rotating surface forms a gaseous
equatorial decretion disk. Anomalous viscosity provides the efficient
mechanism for transporting the angular momentum outwards.
The
outer part of the disk can extend up to a very large distance from
the parent star. We study the evolution of density, radial and
azimuthal velocity, and angular momentum loss rate of equatorial
decretion disks out to very distant regions. We investigate how the
physical characteristics of the disk depend on the distribution of
temperature and viscosity.
We calculated stationary models using
the Newton-Raphson method. For time-dependent hydrodynamic modeling
we developed the numerical code based on an explicit finite
difference scheme on an Eulerian grid including full Navier-Stokes
shear viscosity.
The sonic point distance and the maximum angular
momentum loss rate strongly depend on the temperature profile and are
almost independent of viscosity. The rotational velocity at large
radii rapidly drops accordingly to temperature and viscosity
distribution. The total amount of disk mass and the disk angular
momentum increase with decreasing temperature and viscosity. The
time-dependent one-dimensional models basically confirm the results
obtained in the stationary models as well as the assumptions of the
analytical approximations. Including full Navier-Stokes viscosity we
systematically avoid the rotational velocity sign change at large
radii. The unphysical drop of the rotational velocity and angular
momentum
loss at large radii (present in some models) can be
avoided in the models with decreasing temperature and
viscosity.
Reference: AA/2014/24272
Status:
Manuscript has been accepted
Weblink:
Comments:
Email: petrk@physics.muni.cz
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Gloria Koenigsberger, Nidia Morrell, D. John Hiller, Fabian
R.N. Schneider, Nicolas Gonzalez-Jimenez,
Norbert Langer, and
Rodolfo Barba
1) Instituto de Ciencias Fisicas,
Universidad Nacional Autonoma de Mexico; 2) Las Campanas Observatory,
The Carnegie Observatories; 3) Department of Physics and Astronomy, &
Pittsburgh Partile Physis, Astrophysics and Cosmology Center,
University of Pittsburgh; 4) Facultad de Ciencias Astronomicas y
Geofisicas, Universidad Nacional de La Plata, and Instituto de
Astrofisica de La Plata; 5) Argelander-Institut fur Astronomie; 6)
Departamento de Fisica, Universidad de la Serena
New
spectroscopic observations of the LBV/WR multiple system HD5980 in
the Small Magellanic Cloud are used to address the question of the
masses and evolutionary status of the two very luminous stars in the
19.3d eclipsing binary system. Two distinct components of the N V
4944 A line are detected in emission and their radial velocity
variations are used to derive masses of 61 and 66 Mo, under the
assumption that binary interaction effects on this atomic transition
are negligible. We propose that this binary system is the product of
quasi-chemically homogeneous evolution with little or no mass
transfer. Thus, both of these binary stars may be candidates for
gamma-ray burst progenitors or even pair instability supernovae.
Analysis of the photospheric absorption lines belonging to the
third-light object in the system confirm that it consists of an
O-type star in a 96.56d eccentric orbit (e=0.82) around an unseen
companion. The 5:1 period ratio and high eccentricities of the two
binaries suggest that they may constitute a hierarchical quadruple
system.
Reference: Astronomical Journal (in
press)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1408.0556
Comments:
Email: gloria@astro.unam.mx
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Andre Maeder and Georges
Meynet
Geneva Observatory, Geneva University
Magnetic
configurations, stable on the long term, appear to exist in various
evolutionary phases, from Main-Sequence stars to white dwarfs and
neutron stars. The large scale ordered nature of these fields, often
approximately dipolar, and their scaling according to the flux
conservation scenario favor the model of a fossil field Duez et al.
(2010). We make some first estimates of the
magnetic coupling
between the stellar cores and the outer layers in red giants and
supergiants. Analytical expressions of the truncation radius of the
field coupling are established for a convective envelope and for a
rotating radiative zone with horizontal turbulence. The timescales of
the internal exchanges of angular momentum are considered.
Numerical estimates are made on the basis of recent model
grids. The direct magnetic coupling of the core to the extended
convective envelope of red giants and supergiants appears unlikely.
However, we find that the intermediate radiative zone is fully
coupled to the core during the He-burning and later phases. This
coupling is able to produce a strong spin down of the core of red
giants and supergiants, also leading to relatively slowly rotating
stellar remnants, like white dwarfs and pulsars. Some angular
momentum is also transferred to the outer convective envelope of red
giants and supergiants during the He-burning phase and
later.
Reference: in press for Astrophysical
Journal
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1408.1192
Comments:
Email: georges.meynet@unige.ch
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W. Steffen$^1$, M. Teodoro$^2$, T. I. Madura$^2$, J. H.
Groh$^3$, T. R. Gull$^2$, A. Mehner$^4$, M. F. Corcoran$^{5,6}$, A.
Damineli$^7$, and K. Hamaguchi$^{5,8}$
1 - Instituto de
Astronomía, Universidad Nacional Autónoma de México, Apdo Postal
106, Ensenada 22800, Baja California, México; 2 - Astrophysics
Science Division, Code 667, NASA Goddard Space Flight Center,
Greenbelt, MD 20771, USA; 3 - Geneva Observatory, Geneva University,
Chemin des Maillettes 51, CH-1290 Sauverny, Switzerland; 4 - ESO,
Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile; 5 -
CRESST and X-ray Astrophysics Laboratory, NASA Goddard Space Flight
Center, Greenbelt, MD 20771, USA; 6 - Universities Space Research
Association, 7178 Columbia Gateway Drive, Columbia, MD 21046, USA; 7
- Instituto de Astronomia, Geofísica e Ciências Atmosféricas,
Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária,
São Paulo 05508-900, Brazil; 8 - Department of Physics, University
of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD
21250, USA
We investigate, using the modelling code SHAPE, the
three-dimensional structure of the bipolar Homunculus nebula
surrounding Eta Carinae as mapped by new ESO Very Large
Telescope/X-Shooter observations of the H2 λ = 2.121 25 μm
emission line. Our results reveal for the first time important
deviations from the axisymmetric bipolar morphology: (1) circumpolar
trenches in each lobe positioned point symmetrically from the centre
and (2) off-planar protrusions in the equatorial region from each
lobe at longitudinal (∼55°) and latitudinal (10°-20°) distances
from the projected apastron direction of the binary orbit. The
angular distance between the protrusions (∼110°) is similar to the
angular extent of each polar trench (∼130°) and nearly equal to
the opening angle of the wind–wind collision cavity (∼110°). As
in previous studies, we confirm a hole near the centre of each polar
lobe and no detectable near-IR H2 emission from the thin optical
skirt seen prominently in visible imagery. We conclude that the
interaction between the outflows and/or radiation from the central
binary stars and their orientation in space has had, and possibly
still has, a strong influence on the Homunculus. This implies that
prevailing theoretical models of the Homunculus are incomplete as
most assume a single-star origin that produces an axisymmetric
nebula. We discuss how the newly found features might be related to
the Homunculus ejection, the central binary, and the interacting
stellar winds.
Reference: Published on MNRAS (August
11, 2014) 442 (4): 3316-3328.
doi: 10.1093/mnras/stu1088
First
published online July 7, 2014
Status: Other
Weblink:
http://mnras.oxfordjournals.org/content/442/4/3316
Comments:
Email: mairan.teodoro@gmail.com
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Tahina Ramiaramanantsoa [1,2],
Anthony F. J. Moffat [1,2], Andre-Nicolas Chene [3,4,5], Noel D.
Richardson [1,2], Huib F. Henrichs [6], Sebastien Desforges [1,2],
Victoria Antoci [7], Jason F. Rowe [8], Jaymie M. Matthews [9],
Rainer Kuschnig [9,10], Werner W. Weiss [10], Dimitar Sasselov [11],
Slavek M. Rucinski [12] and David B. Guenther [13]
[1]
Departement de physique, Universite de Montreal, C.P. 6128, Succ.
Centre-Ville, Montreal, QC H3C 3J7, Canada
[2] Centre de
Recherche en Astrophysique du Quebec (CRAQ), Canada
[3] Gemini
Observatory, Northern Operations Centre, 670 North A'ohoku Place,
Hilo, HI 96720, USA
[4] Departamento de Fisica y Astronomia,
Universidad de Valparaiso, Av. Gran Bretana 1111, Playa Ancha,
Casilla 5030, Chile
[5] Departamento de Astronomia, Universidad
de Concepcion, Casilla 160-C, Chile
[6] Astronomical Institute
'Anton Pannekoek', University of Amsterdam, Science Park 904, NL-1098
XH Amsterdam, the Netherlands
[7] Stellar Astrophysics Centre,
Department of Physics and Astronomy, Aarhus University, Ny Munkegade
120, DK-8000 Aarhus C, Denmark
[8] NASA Ames Research Center,
Moffett Field, CA 94035, USA
[9] Department of Physics and
Astronomy, University of British Columbia, 6224 Agricultural Road,
Vancouver, BC V6T 1Z1, Canada
[10] Institute for Astronomy,
University of Vienna, Turkenschanzstrasse 17, A-1180 Vienna, Austria
[11] Harvard–Smithsonian Center for Astrophysics, 60 Garden
Street, Cambridge, MA 02138, USA
[12] Department of Astronomy and
Astrophysics, University of Toronto, 50 St George Street, Toronto, ON
M5S 3H4, Canada
[13] Institute for Computational Astrophysics,
Department of Astronomy and Physics, St Mary’s University, Halifax,
NS B3H 3C3, Canada
We have used the MOST (Microvariability and
Oscillations of STars) microsatellite to obtain four weeks of
contiguous high-precision broad-band visual photometry of the
O7.5III(n)((f)) star xi Persei in November 2011. This star is well
known from previous work to show prominent DACs (discrete absorption
components) on time-scales of about 2 d from UV spectroscopy and
non-radial pulsation with one (l = 3) p-mode oscillation with a
period of 3.5 h from optical spectroscopy. Our MOST-orbit (101.4 min)
binned photometry fails to reveal any periodic light variations above
the 0.1 mmag 3 sigma noise level for periods of a few hours, while
several prominent Fourier peaks emerge at the 1 mmag level in the
two-day period range. These longer period variations are unlikely due
to pulsations, including gravity modes. From our simulations based
upon a simple spot model, we deduce that we are seeing the
photometric modulation of several corotating bright spots on the
stellar surface. In our model, the starting times (random) and
lifetimes (up to several rotations) vary from one spot to another yet
all spots rotate at the same period of 4.18 d, the best-estimated
rotation period of the star. This is the first convincing reported
case of corotating bright spots on an O star, with important
implications for drivers of the DACs (resulting from corotating
interaction regions) with possible bright-spot generation via a
breakout at the surface of a global magnetic field generated by a
subsurface convection zone.
Reference: Published in
MNRAS (June 11, 2014) 441, 910-917. DOI:10.1093/mnras/stu619
Status:
Other
Weblink:
http://adsabs.harvard.edu/abs/2014MNRAS.441..910R
Comments:
Email: tahina@astro.umontreal.ca
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Philip Massey(1), Kathryn F. Neugent (1), Nidia Morrell
(2), and D. John Hillier (3)
1) Lowell Observatory, (2)
Las Campanas Observatory, Carnegie Observatories, (3) Department of
Physics and Astronomy & Pittsburgh Particle Physics,
Astrophysics, and Cosmology Center, University of Pittsburgh
Our
new survey for Wolf-Rayet stars in the Magellanic Clouds is only 15%
complete but has already found 9 new WRs in the LMC. This suggests
that the total WR population in the LMC may be underestimated by
10-40%. Eight of the nine are WNs, demonstrating that the "observed"
WC to WN ratio is too large, and is biased towards WC stars. The
ninth is another rare WO star, the second we have found in the LMC in
the past two years. Five (and possibly six) of the 8 WNs are of a new
class of WRs, which pose a significant challenge to our
understanding. Naively we would classify these stars as "WN3+O3V,"
but there are several reasons why such a pairing is unlikely, not the
least of which is that the absolute visual magnitudes of these stars
are faint, with M_V~ -2.3 to -3.1. We have performed a preliminary
analysis with CMFGEN, and we find that (despite the faint visual
magnitudes) the bolometric luminosities of these stars are normal for
early-type WNs. Our fitting suggests that these stars are evolved,
with significantly enriched N and He. Their effective temperatures
are also normal for early-type WNs. What is unusual about these stars
is that they have a surprisingly small mass-loss rate compared to
other early-type WNs. How these stars got to be the way they are
(single star evolution? binary evolution?) remains an open question.
For now, we are designating this class as WN3/O3, in analogy to the
late-type WN "slash" stars.
Reference: To
appear in IAU 307, New Windows on Massive Stars: Asteroseismology,
Interferometry, and Spectropolarimetry
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1407.4659
Comments:
Email: phil.massey@lowell.edu
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Conny Aerts
Institute of Astronomy, KULeuven,
Belgium
Department of Astrophysic/IMAPP, Radboud University
Nijmegen, the Netherlands
After highlighting the principle and
power of asteroseismology for stellar physics, we briefly emphasize
some recent progress in this research for various types of stars. We
give an overview of high-precision high duty-cycle space photometry
of OB-type stars. Further, we update the overview of seismic
estimates of stellar parameters of OB dwarfs, with specific emphasis
on convective core overshoot. We discuss connections between
pulsational, rotational, and magnetic variability of massive stars
and end with future prospects for asteroseismology of evolved OB
stars.
Reference: Invited review paper to appear in
Proc. IAU307: New windows on massive stars: asteroseismology,
interferometry, and
Status: Conference proceedings
Weblink:
http://adsabs.harvard.edu/abs/2014arXiv1407.6479A
Comments:
Email: conny.aerts@ster.kuleuven.be
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T. Morel (1), N. Castro (2), L. Fossati (2), S. Hubrig (3),
N. Langer (2), N. Przybilla (4), M. Schoeller (5), T. Carroll (3), I.
Ilyin (3), A. Irrgang (6), L. Oskinova (7), F. R. N. Schneider (2),
S. Simon Diaz (8,9), M. Briquet (1), J. F. Gonzalez (10), N.
Kharchenko (11), M.-F. Nieva (4,6), R.-D. Scholz (3), A. de Koter
(12,13), W.-R. Hamann (7), A. Herrero (8,9), J. Maiz Apellaniz (14),
H. Sana (15), R. Arlt (3), R. Barba (16), P. Dufton (17), A.
Kholtygin (18), G. Mathys (19), A. Piskunov (20), A. Reisenegger
(21), H. Spruit (22), S.-C. Yoon (23)
(1) Institut
d'Astrophysique et de Geophysique, Liege, Belgium
(2)
Argelander-Institut fuer Astronomie, Bonn, Germany
(3)
Leibniz-Institut fuer Astrophysik Potsdam (AIP), Potsdam, Germany
(4) Institute for Astro- and Particle Physics, University of
Innsbruck, Austria
(5) European Southern Observatory, Garching,
Germany
(6) Dr. Remeis Observatory & ECAP, Bamberg, Germany
(7) Institut fuer Physik und Astronomie der Universitat Potsdam,
Germany
(8) Instituto de Astrofisica de Canarias, La Laguna,
Spain
(9) Universidad de La Laguna, Dpto. de Astrofisica, La
Laguna, Spain
(10) Instituto de Ciencias Astronomicas, de la
Tierra, y del Espacio (ICATE), San Juan, Argentina
(11) Main
Astronomical Observatory, Kiev, Ukraine
(12) Astronomical
Institute Anton Pannekoek, Amsterdam, The Netherlands
(13)
Instituut voor Sterrenkunde, Universiteit Leuven, Belgium
(14)
Instituto de Astrofisica de Andalucia-CSIC, Granada, Spain
(15)
ESA/Space Telescope Science Institute, Baltimore, USA
(16)
Departamento de Fisica, La Serena, Chile
(17) Astrophysics
Research Centre, Belfast, UK
(18) Chair of Astronomy,
Saint-Petersburg State University, Russia
(19) European Southern
Observatory, Santiago, Chile
(20) Institute of Astronomy of the
Russian Acad. Sci., Moscow, Russia
(21) Pontificia Universidad
Catolica de Chile, Santiago, Chile
(22) Max-Planck-Institut fuer
Astrophysik, Garching, Germany
(23) Department of Physics and
Astronomy, Seoul National University, Seoul, Republic of Korea
The
B fields in OB stars (BOB) survey is an ESO large programme
collecting spectropolarimetric observations for a large number of
early-type stars in order to study the occurrence rate, properties,
and ultimately the origin of magnetic fields in massive stars. As of
July 2014, a total of 98 objects were observed over 20 nights with
FORS2 and HARPSpol. Our preliminary results indicate that the
fraction of magnetic OB stars with an organised, detectable field is
low. This conclusion, now independently reached by two different
surveys, has profound implications for any theoretical model
attempting to explain the field formation in these objects. We
discuss in this contribution some important issues addressed by our
observations (e.g., the lower bound of the field strength) and the
discovery of some remarkable objects.
Reference: To
appear in proceedings of IAU Symposium 307, New Windows on Massive
Stars (Geneva, June 2014)
Status: Conference proceedings
Weblink:
http://www.astro.ulg.ac.be/~morel/articles/IAUS307_morel_talk.pdf
Comments:
Email: morel@astro.ulg.ac.be
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Andre Maeder and Georges Meynet
Geneva
Observatory, University of Geneva
We examine some debated
points in current discussions about rotating stars: the shape, the
gravity darkening, the critical velocities, the mass loss rates, the
hydrodynamical instabilities, the internal mixing and N--enrichments.
The study of rotational mixing requires high quality data and careful
analysis. From recent studies where such conditions are fulfilled,
rotational mixing is well confirmed. Magnetic coupling with stellar
winds may produce an apparent contradiction, i.e. stars with a low
rotation and a high N--enrichment. We point out that it rather
confirms the large role of shears in differentially rotating stars
for the transport processes. New models of interacting binaries also
show how shears and mixing may be enhanced in close binaries which
are either spun up or down by tidal interactions.
Reference:
IAU Symposium 307, New windows on massive stars:
asteroseismology, interferometry, and spectropolarimetry, G. Meynet,
C. Georgy, J.H. Groh & Ph. Stee, eds.
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1408.1768
Comments:
10 pages, 4 figures
Email:
georges.meynet@unige.ch
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Conny Aerts
Institute of Astronomy
University
of Leuven
Celestijnenlaan 200D
3001 Leuven
Belgium
http://fys.kuleuven.be/ster/vacancies/numerical-modelling-of-stellar-interiors
Attention/Comments:
Online applications only.
Weblink:
http://fys.kuleuven.be/ster/vacancies/numerical-modelling-of-stellar-interiors
Email:
conny.aerts@ster.kuleuven.be
Deadline: 30 September
2014
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Raphael Hirschi
Keele University, Keele, ST5
5BG, United Kingdom
Fixed Term for 2 Years
Starting
salary: Grade 7 £31,342
Keele University wishes to appoint a
Research Associate for a duration of 2 years starting 1 January 2015,
in order to conduct research on theoretical stellar astrophysics.
You will work in the group led by Dr Raphael Hirschi within
the Astrophysics Group at Keele University as part of an ERC-funded
project entitled “Stellar HYdrodynamics, Nucleosynthesis and
Evolution” (SHYNE).
You will lead the explosive
nucleosynthesis component of this project, which includes grids of
models as well as impact studies of key nuclear reactions. You will
also contribute to the other components of the project and be
encouraged to develop your own research program and your leadership
skills.
You should have or be expecting to obtain a PhD in
astrophysics or a related area within a year of appointment and
should have a demonstrated aptitude for research. Experience in
theoretical stellar astrophysics is essential and experience with
parallel computer programming is highly desirable.
For more
details of this post and the Keele Astrophysics Group, and for
information on how to apply, see http://www.astro.keele.ac.uk.
For
further enquiries please contact Dr Raphael Hirschi at
r.hirschi@keele.ac.uk.
Keele University is committed to the
principles of the Athena SWAN charter, and values equality and
diversity across our workforce. We strive to ensure that our
workforce is representative of broader society, and therefore, we
would actively welcome applications from women for this role.
For
full post details and to apply, please visit:
http://tinyurl.com/RE14-10
Shortlisting will take place on
8th October 2014
Closing date for applications: 1st October
2014
Interviews may be conducted remotely if needed (via
skype or similar technology)
Post reference:
RE14/10
Attention/Comments:
Weblink:
http://tinyurl.com/RE14-10
Email:
r.hirschi@keele.ac.uk
Deadline: 1 October
2014
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J. Hron & L. Misoni
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), 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
September 15. Fellowships can be awarded for missions starting in
November 2014.
Further informations and application forms can
be found at
www.european-interferometry.eu
The program is
funded by OPTICON/FP7.
Please distribute this message also to
potentially interested colleagues outside of the your community!
Looking forward to your applications,
Josef Hron &
Laszlo Mosoni
(for the European Interferometry
Initiative)
Reference: Deadline Sept. 15
Status:
Other
Weblink: www.european-interferometry.eu
Comments:
Please circulate not later than Sept. 1
Email:
fizeau@european-interferometry.eu
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