ISSN 1783-3426
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Atmospheric NLTE-Models for the
Spectroscopic Analysis of Blue Stars with Winds.
Two
bi-stability jumps in theoretical wind models for massive stars and
the implications for luminous blue variable supernovae
Measuring
the stellar wind parameters in IGR J17544-2619 and Vela X-1
constrains the accretion physics in Supergiant Fast X-ray Transient
and classical Supergiant X-ray Binaries
Searching
for a magnetic field in Wolf-Rayet stars using FORS2
spectropolarimetry
Surface
abundances of OC supergiants
A test
for the theory of colliding winds: the periastron passage of 9
Sagittarii
Direct Detection of
Lyman Continuum Escape from Local Starburst Galaxies with the Cosmic
Origins Spectrograph
Searching for
Cool Dust in the Mid-to-far Infrared: The Mass-loss Histories of the
Hypergiants μ Cep, VY CMa, IRC+10420, and ρ Cas
Star-formation
history and X-ray binary populations: the case of the Large
Magellanic Cloud
A Spectroscopic
Survey of Massive Stars in M31 and M33
Wolf-Rayet
stars in the Small Magellanic Cloud: II. Analysis of the binaries
The
first spectropolarimetric monitoring of the peculiar O4Ief supergiant
zeta Puppis
The X-ray light curve
of the massive colliding wind Wolf-Rayet + O binary WR21a
Alpha
Virginis: line-profile variations and orbital elements
On
the Social Traits of Luminous Blue Variables
Luminous
and Variable Stars in M31 and M33. III. The Yellow and Red
Supergiants and Post-Red Supergiant Evolution
Complete proceedings of the Potsdam
Wolf-Rayet Workshop 2015 now available
Giant
eruptions of very massive stars
11 postdoc positions at Instituto de
Astrofisica de Canarias
Two 3-year
postdoctoral positions in stellar modelling
Postdoctoral position on Gaia and massive stars
IAUS 329: The Lives and Death-Throes of Massive Stars
Luiz P. Carneiro (1), J. Puls (1), J.O. Sundqvist (2,3),
and T.L. Hoffmann (1)
(1) LMU Munich,
Universitätssternwarte, Scheinerstr. 1, 81679 München, Germany
(2)
Centro de Astrobiología, CSIC-INTA, Ctra. Torrejón a Ajalvir km.4,
28850 Madrid, Spain
(3) Instituut voor Sterrenkunde, KU Leuven,
Celestijnenlaan 200D, 3001 Leuven, Belgium
Context. X-rays/EUV
radiation emitted from wind-embedded shocks in hot, massive stars can
affect the ionization balance in their outer atmospheres, and can be
the mechanism responsible for the production of highly ionized atomic
species detected in stellar wind UV spectra.
Aims. To allow
for these processes in the context of spectral analysis, we have
implemented the emission from wind-embedded shocks and related
physics into our unified, NLTE model atmosphere/spectrum synthesis
code FASTWIND.
Methods. The shock structure and corresponding
emission is calculated as a function of user-supplied parameters
(volume filling factor, radial stratification of shock strength, and
radial onset of emission). We account for a temperature and density
stratification inside the post-shock cooling zones, calculated for
radiative and adiabatic cooling in the inner and outer wind,
respectively. The high-energy absorption of the cool wind is
considered by adding important K-shell opacities, and corresponding
Auger ionization rates have been included into the NLTE network. To
test our implementation and to check the resulting effects, we
calculated a comprehensive model grid with a variety of X-ray
emission parameters.
Results. We tested and verified our
implementation carefully against corresponding results from various
alternative model atmosphere codes, and studied the effects from
shock emission for important ions from He, C, N, O, Si, and P.
Surprisingly dielectronic recombination turned out to play an
essential role for the ionization balance of OIV/OV in stars
(particularly dwarfs) with Teff approx. 45,000 K. Finally, we
investigated the frequency dependence and radial behavior of the mass
absorption coefficient, kappa_nu(r), important in the context of
X-ray line formation in massive star winds.
Conclusions. In
almost all considered cases, direct ionization is of major influence
(because of the enhanced EUV radiation field), and Auger ionization
significantly affects only NVI and OVI. The approximation of a
radially constant kappa_nu is justified for r > 1.2 Rstar and
lambda < 18 A, and also for many models at longer wavelengths. To
estimate the actual value of this quantity, however, the HeII
opacities need to be calculated from detailed NLTE modeling, at least
for wavelengths longer than 18 to 20 A, and information on the
individual CNO abundances has to be present.
Reference:
Astronomy and Astrophysics, in press
astro-ph,
1603.01177
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1603.01177
Comments:
accepted by A&A
Email:
luiz@usm.uni-muenchen.de
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Blagovest Petrov (1); Jorick S. Vink(2); Götz Gräfener
(2)
(1) Institute of Astronomy with NAO, BAS, Sofia,
Bulgaria
(2) Armagh Observatory, College Hill, Armagh BT61 9DG,
Northern Ireland
Luminous Blue Variables have been suggested
to be the direct progenitors of supernova types IIb and IIn, with
enhanced mass loss prior to explosion. However, the mechanism of this
mass loss is not yet known. Here, we investigate the qualitative
behaviour of theoretical stellar wind mass-loss as a function of Teff
across two bi-stability jumps in blue supergiant regime and also in
proximity to the Eddington limit, relevant for LBVs. To investigate
the physical ingredients that play a role in the radiative
acceleration we calculate blue supergiant wind models with the CMFGEN
non-LTE model atmosphere code over an effective temperature range
between 30 000 and 8 800 K. Although our aim is not to provide new
mass-loss rates for BA supergiants, we study and confirm the
existence of two bi-stability jumps in mass-loss rates predicted by
Vink, de Koter, & Lamers (1999). However, they are found to occur
at somewhat lower Teff (20 000 and 9 000 K, respectively) than found
previously, which would imply that stars may evolve towards lower
Teff before strong mass-loss is induced by the bi-stability jumps.
When the combined effects of the second bi-stability jump and the
proximity to Eddington limit are accounted for, we find a dramatic
increase in the mass-loss rate by up to a factor of 30. Further
investigation of both bi-stability jumps is expected to lead to a
better understanding of discrepancies between empirical modelling and
theoretical mass-loss rates reported in the literature, and to
provide key inputs for the evolution of both normal AB supergiants
and LBVs, as well as their subsequent supernova type II
explosions.
Reference: MNRAS in press
astro-ph,
1602.05868
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1602.05868
Comments:
Email: bpetrov@astro.bas.bg
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A. Gimenez-Garcia(1), T. Shenar(2), J. M. Torrejon(1), L.
Oskinova(2), S. Martinez-Nunez(1), W.-R. Hamann(2), J. J.
Rodes-Roca(1), A. Gonzalez-Galan(2), J. Alonso-Santiago(1), C.
Gonzalez-Fernandez(3), G. Bernabeu(1), and A. Sander(2)
1)
Departamento de Física, Ingeniería de Sistemas y
Teoría de la
Señal,
University of Alicante, P.O. Box 99, E03080 Alicante,
Spain.
2) Institut für Physik und Astronomie, Universität
Potsdam,
Karl-Liebknecht-Str. 24/25, D-14476 Potsdam, Germany
3)
Institute of Astronomy, University of Cambridge, Madingly
Road,
Cambridge, CB3 0HA, UK
Classical Supergiant X-ray Binaries
(SGXBs) and Supergiant Fast X-ray Transients (SFXTs) are two types of
High-mass X-ray Binaries (HMXBs) that present similar donors but, at
the same time, show very different behavior in the X-rays. The reason
for this dichotomy of wind-fed HMXBs is still a matter of debate.
Among the several explanations that have been proposed, some of them
invoke specific stellar wind properties of the donor stars. Only
dedicated empiric analysis of the donors' stellar wind can provide
the required information to accomplish an adequate test of these
theories. However, such analyses are scarce. To close this gap, we
perform a comparative analysis of the optical companion in two
important systems: IGR J17544-2619 (SFXT) and Vela X-1 (SGXB). We
analyse the spectra of each star in detail and derive their stellar
and wind properties. We compare the wind parameters, giving us an
excellent chance of recognizing key differences between donor winds
in SFXTs and SGXBs. We find that the stellar parameters derived from
the analysis generally agree well with the spectral types of the two
donors: O9I (IGR J17544-2619) and B0.5Iae (Vela X-1). An important
difference between the stellar winds of the two stars is their
terminal velocities v_inf=1500km/s in IGR J17544-2619 and
v_inf=700km/s in Vela~X-1, which has important consequences on the
X-ray luminosity of these sources. Their specific combination of wind
speed and pulsar spin favours an accretion regime with a persistently
high luminosity in Vela X-1, while it favours an inhibiting accretion
mechanism in IGR~J17544-2619. Our study demonstrates that the wind
relative velocity is critical in the determination of the class of
HMXBs hosting a supergiant donor, given that it may shift the
accretion mechanism from direct accretion to propeller regimes when
combined with other parameters.
Reference: Astronomy
and Astrophysics, Section 8: Stellar atmospheres
Status:
Manuscript has been accepted
Weblink:
Comments:
Email: garciagimenezangel@gmail.com
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S. Hubrig(1), K. Scholz(2), W.-R. Hamann(2), M.
Schoeller(3), R. Ignace(4), I. Ilyin(1), K.G. Gayley(5), L.M.
Oskinova(2)
(1) Leibniz-Institut fuer Astrophysik Potsdam
(AIP), An der Sternwarte 16, 14482 Potsdam, Germany
(2)
Universitaet Potsdam, Institut fuer Physik und Astronomie, 14476
Potsdam, Germany
(3) European Southern Observatory,
Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
(4) Department
of Physics and Astronomy, East Tennessee State University, Johnson
City, TN 37663, USA
(5) Department of Physics and Astronomy,
University of Iowa, Iowa City, IA 52242, USA
To investigate if
magnetic fields are present in Wolf-Rayet stars, we selected a few
stars in the Galaxy and one in the Large Magellanic Cloud (LMC). We
acquired low-resolution spectropolarimetric observations with the ESO
FORS2 instrument during two different observing runs. During the
first run in visitor mode, we observed the LMC Wolf-Rayet star BAT99
7 and the stars WR6, WR7, WR18, and WR23 in our Galaxy. The second
run in service mode was focused on monitoring the star WR6. Linear
polarization was recorded immediately after the observations of
circular polarization. During our visitor observing run, the magnetic
field for the cyclically variable star WR6 was measured at a
significance level of 3.3sigma ( = 258+-78G). Among the other
targets, the highest value for the longitudinal magnetic field, =
327+-141G, was measured in the LMC star BAT99 7. Spectropolarimetric
monitoring of the star WR6 revealed a sinusoidal nature of the
variations with the known rotation period of 3.77d, significantly
adding to the confidence in the detection. The presence of the
rotation-modulated magnetic variability is also indicated in our
frequency periodogram. The reported field magnitude suffers from
significant systematic uncertainties at the factor 2 level, in
addition to the quoted statistical uncertainties, owing to the
theoretical approach used to characterize it. Linear polarization
measurements showed no line effect in the stars, apart from WR6.
BAT99 7, WR7, and WR,23 do not show variability of the linear
polarization over two nights.
Reference: Accepted for
publication in MNRAS
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1603.01441
Comments:
Email: shubrig@aip.de
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F. Martins$^1$, S. Foschino$^1$, J.-C. Bouret$^2$, R.
Barba$^3$, I. Howarth$^4$
1- LUPM, CNRS & Montpellier
University; 2- LAM, CNRS & Aix-Marseille University; 3- La Serena
University; 4- University College London
Some O and B stars
show unusually strong or weak lines of carbon and/or nitrogen. These
objects are classified as OBN or OBC stars. It has recently been
shown that nitrogen enrichment and carbon depletion are the most
likely explanations for the existence of the ON class. We investigate
OC stars (all being supergiants) to check that surface abundances are
responsible for the observed anomalous line strengths. We perform a
spectroscopic analysis of three OC supergiants using atmosphere
models. A fourth star was previously studied by us. Our sample thus
comprises all OC stars known to date in the Galaxy. We determine the
stellar parameters and He, C, N, and O surface abundances. We show
that all stars have effective temperatures and surface gravities
fully consistent with morphologically normal O supergiants. However,
OC stars show little, if any, nitrogen enrichment and carbon surface
abundances consistent with the initial composition. OC supergiants
are thus barely chemically evolved, unlike morphologically normal O
supergiants.
Reference: Research Note in Astronomy &
Astrophysics
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1603.02027
Comments:
Email: fabrice.martins@umontpellier.fr
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G. Rauw (1), R. Blomme (2), Y. Naze (1), M. Spano (3), L.
Mahy (1), E. Gosset (1), D. Volpi (2), H. van Winckel (4), G. Raskin
(4), C. Waelkens (4)
(1) Institut d'Astrophysique et de
Geophysique, Liege University, Belgium
(2) Royal Observatory of
Belgium, Brussels, Belgium
(3) Observatoire de Geneve, Geneva,
Switzerland
(4) Instituut voor Sterrenkunde, Katholieke
Universiteit Leuven, Belgium
The long-period, highly eccentric
O-star binary 9 Sgr, known for its non-thermal radio emission and its
relatively bright X-ray emission, went through its periastron in
2013. Such an event can be used to observationally test the
predictions of the theory of colliding stellar winds over a broad
range of wavelengths. We have conducted a multi-wavelength monitoring
campaign of 9 Sgr around the 2013 periastron. In this paper, we focus
on X-ray observations and optical spectroscopy. The optical spectra
allow us to revisit the orbital solution of 9 Sgr and to refine its
orbital period to 9.1 years. The X-ray flux is maximum at periastron
over all energy bands, but with clear differences as a function of
energy. The largest variations are observed at energies above 2 keV,
whilst the spectrum in the soft band (0.5 - 1.0 keV) remains mostly
unchanged indicating that it arises far from the collision region, in
the inner winds of the individual components. The level of the hard
emission at periastron clearly deviates from the 1/r relation
expected for an adiabatic wind interaction zone, whilst this relation
seems to hold at the other phases covered by our observations. The
spectra taken at phase 0.946 reveal a clear Fe xxv line at 6.7 keV,
but no such line is detected at periastron although a simple model
predicts a strong line that should be easily visible in the data. The
peculiarities of the X-ray spectrum of 9 Sgr could reflect the impact
of radiative inhibition as well as a phase-dependent efficiency of
particle acceleration on the shock properties.
Reference:
Astronomy & Astrophysics, in press
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1603.06745
Email:
rauw@astro.ulg.ac.be
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Claus Leitherer (1), Svea Hernandez (2), Janice C. Lee (1),
M. S. Oey (3)
1 - STScI, Baltimore, 2 - Radboud Univ.
Nijmegen, 3 - Univ. of Michigan
We report on the detection of
Lyman continuum radiation in two nearby starburst galaxies. Tol
0440-381, Tol 1247-232 and Mrk 54 were observed with the Cosmic
Origins Spectrograph onboard the Hubble Space Telescopes. The three
galaxies have radial velocities of ~13,000 km/s, permitting a ~35 A
window on the restframe Lyman continuum shortward of the Milky Way
Lyman edge at 912 A. The chosen instrument configuration using the
G140L grating covers the spectral range from 912 to 2,000 A. We
developed a dedicated background subtraction method to account for
temporal and spatial background variations of the detector, which is
crucial at the low flux levels around 912 A. This modified pipeline
allowed us to significantly improve the statistical and systematic
detector noise and will be made available to the community. We detect
Lyman continuum in all three galaxies. However, we conservatively
interpret the emission in Tol 0440-381 as an upper limit due to
possible contamination by geocoronal Lyman series lines. We
determined the current star-formation properties from the
far-ultraviolet continuum and spectral lines and used synthesis
models to predict the Lyman continuum radiation emitted by the
current population of hot stars. We discuss the various model
uncertainties such as, among others, atmospheres and evolution
models. Lyman continuum escape fractions were derived from a
comparison between the observed and predicted Lyman continuum fluxes.
Tol 1247-232, Mrk 54 and Tol 0440-381 have absolute escape fractions
of (4.5 +/- 1.2)%, (2.5 +/- 0.72)% and <(7.1 +/- 1.1)%,
respectively.
Reference: The Astrophysical Journal, in
press
Status: Manuscript has been accepted
Weblink:
http://lanl.arxiv.org/abs/1603.06779
Comments:
Email: leitherer@stsci.edu
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Dinesh Shenoy(1), Roberta M. Humphreys(1), Terry J.
Jones(1), Massimo Marengo(2) et al.
(1) University of
Minnesota
(2) Iowa State University
We present mid- and
far-IR imaging of four famous hypergiant stars: the red supergiants μ
Cep and VY CMa, and the warm hypergiants IRC +10420 and ρ Cas. Our
11–37 μm SOFIA/FORCAST imaging probes cool dust not detected in
visual and near-IR imaging studies. Adaptive optics 8–12 μm
imaging of μ Cep and IRC +10420 with MMT/MIRAC reveals extended
envelopes that are the likely sources of these stars’ strong
silicate emission features. We find μ Cep’s mass-loss rate to have
declined by about a factor of five over a 13,000 year history,
ranging from 5 × 10‑6 down to ∼1× 10‑6 M⊙ yr‑1.
The morphology of VY CMa indicates a cooler dust component coincident
with the highly asymmetric reflection nebulae seen in the visual and
near-IR. The lack of cold dust at greater distances around VY CMa
indicates that its mass-loss history is limited to the last ∼1200
years, with an average rate of 6 × 10‑4 M⊙ yr‑1. We
find two distinct periods in the mass-loss history of IRC +10420 with
a high rate of 2 × 10‑3 M⊙ yr‑1 until approximately
2000 years ago, followed by an order of magnitude decrease in the
recent past. We interpret this change as evidence of its evolution
beyond the RSG stage. Our new infrared photometry of ρ Cas is
consistent with emission from the expanding dust shell ejected in its
1946 eruption, with no evidence of newer dust formation from its more
recent events.
Reference: Astronomical Journal, 151,
51, 2016
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2016AJ....151...51S
Email:
roberta@umn.edu
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Vallia Antoniou$^1$ and Andreas Zezas$^2,3,1$
1
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,
Cambridge, MA 02138, USA
2 - Physics Department \& Institute
of Theoretical \& Computational Physics, University of Crete,
71003 Heraklion, Crete, Greece
3 - Foundation for Research and
Technology-Hellas, 71110 Heraklion, Crete, Greece
In the
present work we investigate the link between high-mass X-ray binaries
(HMXBs) and star formation in the Large Magellanic Cloud (LMC), our
nearest star-forming galaxy. Using optical photometric data, we
identify the most likely counterpart of 44 X-ray sources. Among the
40 HMXBs classified in this work, we find 33 Be/X-ray binaries, and 4
supergiant XRBs. Using this census and the published spatially
resolved star-formation history map of the LMC, we find that the
HMXBs (and as expected the X-ray pulsars) are present in regions with
star-formation bursts ~6-25 Myr ago, in contrast to the Small
Magellanic Cloud (SMC), for which this population peaks at later ages
(~25-60 Myr ago). We also estimate the HMXB production rate to be
equal to 1 system per ~(23.0+4.4-4.1) x 10^{-3} Mo/yr or 1 system per
~143 Mo of stars formed during the associated star-formation episode.
Therefore, the formation efficiency of HMXBs in the LMC is ~17 times
lower than that in the SMC. We attribute this difference primarily in
the different ages and metallicity of the HMXB populations in the two
galaxies. We also set limits on the kicks imparted on the neutron
star during the supernova explosion. We find that the time elapsed
since the supernova kick is ~3 times shorter in the LMC than the SMC.
This in combination with the average offsets of the HMXBs from their
nearest star clusters results in ~4 times faster transverse
velocities for HMXBs in the LMC than in the SMC.
Reference:
MNRAS in press, arXiV: 1603.08011
Status: Manuscript has been
accepted
Weblink:
http://xxx.lanl.gov/abs/1603.08011
Comments:
44 pages, 10 figures, 10 tables, MNRAS in press (accepted on Jan
17, 2016)
Email: vantoniou@cfa.harvard.edu
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Philip Massey (1,2), Kathryn F. Neugent (1,2), and Brianna
M. Smart (1,3)
(1) Lowell Observatory; (2) Dept of Physics
and Astronomy, Northern Arizona University; (3) Dept of Astronomy,
University of Wisconsin-Madison
We describe our spectroscopic
follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31
and M33. We have obtained new spectroscopy of 1895 stars, allowing us
to classify 1496 of them for the first time. Our study has identified
many foreground stars, and established membership for hundreds of
early- and mid-type supergiants. We have also found 9 new candidate
Luminous Blue Variables and a previously unrecognized Wolf-Rayet
star. We republish the LGGS M31 and M33 catalogs with improved
coordinates and including spectroscopy from the literature and our
new results. The spectroscopy in this paper is responsible for the
vast majority of the stellar classifications in these two nearby
spiral neighbors. The most luminous (and hence massive) of the stars
in our sample are early-type B supergiants, as expected; the more
massive O stars will be fainter visually, and thus mostly remain
unobserved so far. The majority of the unevolved stars in our sample
are in the 20-40Mo range.
Reference: AJ, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1604.00112
Comments:
Full copies of revised LGGS catalogs may be downloaded from
http://www.lowell.edu/users/massey/table5full.txt and
http://wwwllowell.edu/users/massey/table6full.txt
Email:
phil.massey@lowell.edu
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T. Shenar(1), R. Hainich(1), H. Todt(1), A. Sander(1),
W.-R. Hamann(1), A. F. J. Moffat(2), J. J. Eldridge(3), H. Pablo(2),
L. M. Oskinova(1), N. D. Richardson(4)
1- Potsdam
Universität, Potsdam, Germany
2- Université de Montréal,
Montreal, Canada
3- University of Auckland, Auckland, New Zealand
4- University of Toledo, Toledo, USA
Massive WR stars are
evolved massive stars characterized by strong mass-loss.
Hypothetically, they can form either as single stars or as mass
donors in close binaries. About 40% of the known WR stars are
confirmed binaries, raising the question as to the impact of binarity
on the WR population. By performing a spectral analysis of all
multiple WR systems in the SMC, we obtain the full set of stellar
parameters for each individual component. Mass-luminosity relations
are tested, and the importance of the binary evolution channel is
assessed. The spectral analysis is performed with the PoWR model
atmosphere code by superimposing model spectra that correspond to
each component. Evolutionary channels are constrained using the BPASS
evolution tool. Significant Hydrogen mass fractions (0.1 - 0.4) are
detected in all WN components. A comparison with mass-luminosity
relations and evolutionary tracks implies that the majority of the WR
stars in our sample are not chemically homogeneous. The WR component
in the binary AB 6 is found to be very luminous (Log L ~ 6.3 [Lsun])
given its orbital mass (~10 Msun), presumably because of
observational contamination by a third component. Evolutionary paths
derived for our objects suggest that Roche lobe overflow had occurred
in most systems, affecting their evolution. However, the implied
initial masses are large enough for the primaries to have entered the
WR phase, regardless of binary interaction. Together with the results
for the putative single SMC WR stars, our study suggests that the
binary evolution channel does not dominate the formation of WR stars
at SMC metallicity.
Reference: A&A, in press.
astroph: 1604.01022
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1604.01022
Comments:
Email: shtomer@astro.physik.uni-potsdam.de
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S. Hubrig(1), A. Kholtygin(2), I. Ilyin(1), M. Schöller(3),
L.M. Oskinova(4)
(1) Leibniz-Institut fuer Astrophysik
Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
(2)
Astronomical Institute, St. Petersburg State University,
Universitetski pr. 28, 198504, St. Petersburg, Russia
(3)
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748
Garching, Germany
(4) Universitaet Potsdam, Institut fuer Physik
und Astronomie, 14476 Potsdam, Germany
The origin of the
magnetic field in massive O-type stars is still under debate. To
model the physical processes responsible for the generation of O star
magnetic fields, it is important to understand whether correlations
between the presence of a magnetic field and stellar evolutionary
state, rotation velocity, kinematical status, and surface composition
can be identified. The O4Ief supergiant zeta Pup is a fast rotator
and a runaway star, which may be a product of a past binary
interaction, possibly having had an encounter with the cluster
Trumper 10 some 2Myr ago. The currently available observational
material suggests that certain observed phenomena in this star may be
related to the presence of a magnetic field. We acquired
spectropolarimetric observations of zeta Pup with FORS2 mounted on
the 8-m Antu telescope of the VLT to investigate if a magnetic field
is indeed present in this star. We show that many spectral lines are
highly variable and probably vary with the recently detected period
of 1.78d. No magnetic field is detected in zeta Pup, as no magnetic
field measurement has a significance level higher than 2.4sigma.
Still, we studied the probability of a single sinusoidal explaining
the variation of the longitudinal magnetic field
measurements.
Reference: Accepted for publication in
ApJ
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1604.01068
Comments:
Email: shubrig@aip.de
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Eric Gosset & Yael Naze
University of
Liege
Our dedicated XMM-Newton monitoring, as well as archival
Chandra and Swift datasets, were used to examine the behaviour of the
WN5h+O3V binary WR21a at high energies. For most of the orbit, the
X-ray emission exhibits few variations. However, an increase in
strength of the emission is seen before periastron, following a 1/D
relative trend, where D is the separation between both components.
This increase is rapidly followed by a decline due to strong
absorption as the Wolf-Rayet (WR) comes in front. The fitted local
absorption value appears to be coherent with a mass-loss rate of
about 1$\times$10$^{-5}$ M$_{\odot}$/yr for the WR component.
However, absorption is not the only parameter affecting the X-ray
emission at periastron as even the hard X-ray emission decreases,
suggesting a possible collapse of the colliding wind region near to
or onto the photosphere of the companion just before or at
periastron. An eclipse may appear as another potential scenario, but
it would be in apparent contradiction with several lines of evidence,
notably the width of the dip in the X-ray light curve and the absence
of variations in the UV light curve. Afterwards, the emission slowly
recovers, with a strong hysteresis effect. The observed behaviour is
compatible with predictions from general wind-wind collision models
although the absorption increase is too shallow.
Reference:
accepted by A&A
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1604.01536
Comments:
Email: gosset@astro.ulg.ac.be
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David Harrington^1,2,3, Gloria Koenigsberger^4, Enrique
Olguin^7,lya Ilyin^5, Svetlana V. Berdyugina^1,2, Bruno Lara^7, and
Edmundo Moreno^6
1) Kiepenheuer-Institut für
Sonnenphysik, Schöneckstr. 6, D-79104 Freiburg, Germany; 2)Institute
for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu,
HI, 96822, USA; 3)Applied Research Labs, University of Hawaii, 2800
Woodlawn Drive, Honolulu, HI, 96822, USA; 4) Instituto de Ciencias
Físicas, Universidad Nacional Autónoma de México, Ave. Universidad
S/N, Cuernavaca, Morelos, 62210, México; 5) Leibniz-institut für
Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam,
Germany; 6) instituto de Astronomía, Universidad Nacional Autónoma
de México, Apdo. Postal 70-264, México, D.F. 04510, México; 7)
Centro de Investigación en Ciencias, Universidad Autónoma del
Estado de Morelos, Cuernavaca, 62210, México.
Alpha Virginis
is a binary system whose proximity and brightness allow detailed
investigations of the internal structure and evolution of stars
undergoing time-variable tidal interactions. Previous studies have
led to the conclusion that the internal structure of Spica's primary
star may be more centrally condensed than predicted by theoretical
models of single stars, raising the possibility that the interactions
could lead to effects that are currently neglected in structure and
evolution calculations. The key parameters in confirming this result
are the values of the orbital eccentricity e, the apsidal period U,
and the primary star's radius, R1. We analyze the impact that line
profile variability has on the derivation of its orbital elements and
R1. We use high SNR observations obtained in 2000, 2008, and 2013 to
derive the orbital elements from fits to the radial velocity curves.
We produce synthetic line profiles using an ab initio tidal
interaction model. Results: The variations in the line profiles can
be understood in terms of the tidal flows, whose large-scale
structure is relatively fixed in the rotating binary system reference
frame. Fits to the radial velocity curves yield e=0.108+/-0.014.
However, the analogous RV curves from theoretical line profiles
indicate that the distortion in the lines causes the fitted value of
e to depend on the argument of periastron; i.e., on the epoch of
observation. As a result, the actual value of e may be as high as
0.125. We find that U=117.9+/-1.8, which is in agreement with
previous determinations. Using the value R1=6.8 Ro derived by Palate
et al. (2013) the value of the observational internal structure
cinstant k_{2,obs} is consistent with theory. We confirm the presence
of variability in the line profiles of the secondary
star.
Reference: A&A
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1604.02057
Comments:
Email: gloria@astro.unam.mx
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Roberta M. Humphreys(1), Kerstin Weis(2), Kris Davidson(1),
and Michael S. Gordon(1)
1. Minnesota Institute for
Astrophysics, University of Minnesota
2. Astronomical Institute,
Ruhr-Universitaet Bochum, Germany
In a recent paper, Smith and
Tombleson (2015) state that the Luminous Blue Variables (LBVs) in the
Milky Way and the Magellanic Clouds are isolated; that they are not
spatially associated with young O-type stars. They propose a novel
explanation that would overturn the standard view of LBVs. In this
paper we test their hypothesis for the LBVs in M31 and M33 as well as
the LMC and SMC. In M31 and M33, the LBVs are associated with
luminous young stars and supergiants appropriate to their
luminosities and positions on the HR Diagram. Moreover, in the Smith
and Tombleson scenario most of the LBVs should be runaway stars, but
the stars' velocities are consistent with their positions in the
respective galaxies. In the Magellanic Clouds, those authors' sample
was a mixed population. We reassess their analysis, removing seven
stars that have no clear relation to LBVs. When we separate the more
massive classical and the less luminous LBVs, the classical LBVs have
a distribution similar to the late O-type stars, while the less
luminous LBVs have a distribution like the red supergiants. None of
the confirmed LBVs have high velocities or are candidate runaway
stars. These results support the accepted description of LBVs as
evolved massive stars that have shed a lot of mass, and are now close
to their Eddington limit.
Reference: The Astrophysical
Journal
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1603.01278
Comments:
Email: roberta@umn.edu
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Michael S. Gordon, Roberta M.
Humphreys, and Terry J. Jones
Minnesota Institute for
Astrophysics, University of Minnesota
Recent supernova and
transient surveys have revealed an increasing number of non-terminal
stellar eruptions. Though the progenitor class of these eruptions
includes the most luminous stars, little is known of the
pre-supernova mechanics of massive stars in their most evolved state,
thus motivating a census of possible progenitors. From surveys of
evolved and unstable luminous star populations in nearby galaxies, we
select a sample of yellow and red supergiant candidates in M31 and
M33 for review of their spectral characteristics and spectral energy
distributions. Since the position of intermediate and late-type
supergiants on the color-magnitude diagram can be heavily
contaminated by foreground dwarfs, we employ spectral classification
and multi-band photometry from optical and near-infrared surveys to
confirm membership. Based on spectroscopic evidence for mass loss and
the presence of circumstellar dust in their SEDs, we find that 30-40%
of the yellow supergiants are likely in a post-red supergiant state.
Comparison with evolutionary tracks shows that these mass-losing,
post-RSGs have initial masses between 20-40 Msun. More than half of
the observed red supergiants in M31 and M33 are producing dusty
circumstellar ejecta. We also identify two new warm hypergiants in
M31, J004621.05+421308.06 and J004051.59+403303.00, both of which are
likely in a post-RSG state.
Reference: The
Astrophysical Journal
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1603.08003
Comments:
Email: roberta@umn.edu
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W.-R. Hamann, A. Sander, and H. Todt
Institut
fuer Physik und Astronomie, Universitaet Potsdam, Germany
After
careful editing and printing, the complete proceedings of the
Wolf-Rayet Workshop 2015 in Potsdam are now available online. For all
participants, a printed copy has been sent out.
Apart from
the total volume, each of the single contributions are also available
for free via ADS or the university publisher interface at
https://publishup.uni-potsdam.de/solrsearch/index/search/searchtype/collection/id/17262
Proceedings abstract:
---------------------
Nearly
150 years ago, the French astronomers Charles Wolf and Georges Rayet
described stars with very conspicuous spectra that are dominated by
bright and broad emission lines. Meanwhile termed Wolf-Rayet Stars
after their discoverers, those objects turned out to represent
important stages in the life of massive stars.
As the first
conference in a long time that was specifically dedicated to
Wolf-Rayet stars, an international workshop was held in Potsdam,
Germany, from 1.-5. June 2015. About 100 participants, comprising
most of the leading experts in the field as well as as many young
scientists, gathered for one week of extensive scientific exchange
and discussions. Considerable progress has been reported throughout,
e.g. on finding such stars, modeling and analyzing their spectra,
understanding their evolutionary context, and studying their
circumstellar nebulae. While some major questions regarding
Wolf-Rayet stars still remain open 150 years after their discovery,
it is clear today that these objects are not just interesting stars
as such, but also keystones in the evolution of galaxies.
These
proceedings summarize the talks and posters presented at the Potsdam
Wolf-Rayet workshop. Moreover, they also include the questions,
comments, and discussions emerging after each talk, thereby giving a
rare overview not only about the research, but also about the current
debates and unknowns in the field. The Scientific Organizing
Committee (SOC) included Alceste Bonanos (Athens), Paul Crowther
(Sheffield), John Eldridge (Auckland), Wolf-Rainer Hamann (Potsdam,
Chair), John Hillier (Pittsburgh), Claus Leitherer (Baltimore),
Philip Massey (Flagstaff), George Meynet (Geneva), Tony Moffat
(Montreal), Nicole St-Louis (Montreal), and Dany Vanbeveren
(Brussels).
Reference: Electronic publication by the
Universitätsverlag Potsdam (Potsdam University Press)
Status:
Conference proceedings
Weblink:
http://adsabs.harvard.edu/abs/2015wrs..conf.....H
Comments:
The total volume contains 378 pages and 84 articles including the
questions/discussions after each talk.
Email:
ansander@astro.physik.uni-potsdam.de
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Kris Davidson
University
of Minnesota
Giant eruptions or supernova-impostor events are
far more mysterious than true supernovae. An extreme example can
release as much radiative energy as a SN, ejecting several M_sun of
material. These events involve continuous radiation-driven outflows
rather than blast waves. They constitute one of the main unsolved
problems in stellar astrophysics, but have received surprisingly
little theoretical effort. Here I note some aspects that are not yet
familiar to most astronomers.
Reference: To appear in
Phys. Chem. Late Stages Stellar Evol., 11th Pacific Rim Conf., Hong
Kong 2015
Status: Conference proceedings
Email:
kd@astro.umn.edu
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Dr. Enric Palle, IAC Research Head
Instituto de
Astrofisica de Canarias
C/ Via Lactea s/n
E-38205 La Laguna,
Tenerife
Spain
The IAC offers 11 postdoc positions in the
frame of the Severo Ochoa program for excellence research centers in
Spain.
Some of the positions are for five years (so-called Severo
Ochoa Advanced Fellowships).
The positions cover many different
fields in Astrophysics.
Attention/Comments: see the
link below for details of each position
Weblink:
http://www.iac.es/info.php?op1=26〈=en
Email:
corinv@iac.es
Deadline: may 31, 2016 or july 31,
2016
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Conny Aerts and Tami Rogers
Institute
of Astronomy, University of Leuven, Belgium
Department of
Mathematics and Statistics, Newcastle University, UK
Thanks to
STFC & ERC funding, Profs Tami Rogers (Newcastle University, UK)
and Conny Aerts (Leuven University, B) welcome applications for two
postdoctoral positions of 3 years each to work on 3D hydrodynamical
simulations of massive stars and their signature in modern
observations and in 1D stellar models. The postdocs will work in
close collaboration with the two PIs and with four PhD students (2 in
Newcastle and 2 in Leuven).
Application deadline: 1 July
2016.
Start of the positions: ideally between 1 September and
1 December 2016.
Review of applications will start early July
2016.
Attention/Comments: The two positions require
separate applications.
Postdoc vacancy at Newcastle
University, UK:
https://vacancies.ncl.ac.uk/ViewVacancyV2.aspx?enc=mEgrBL4XQK0+ld8aNkwYmARQe8VyurAyTH4BnG2cTVTglCZNptYX3gaQgAQkznbZUDvoIjA3C94RqL5R7p005vlMgM4/4/6eGL5lwEzMOAosVtYZT35LeankA+JWKVhHec+zs2jkqKzMwnhf5exSao8lw9nkPCUpD9mF24s4T1sF2L5YCUK1j2ftceTmiHDn
Postdoc vacancy at Leuven University, B:
http://jobregister.aas.org/job_view?JobID=53969
Weblink:
Email: conny.aerts@ster.kuleuven.be
Deadline:
1 July 2016
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Dr. Eric Gosset and Prof. Gregor
Rauw
Institute of Astrophysics and Geophysics
Quartier
Agora, Batiment B5c
Allee du 6 Aout, 19c
4000 Liege
Belgium
The High-Energy Astrophysics Group
(http://www.gaphe.ulg.ac.be/index_e.html) of the Department of
Astrophysics, Geophysics and Oceanography
(http://www.ago.ulg.ac.be/index_e.php) of the University of Liege
(Belgium) is offering a postdoctoral position to participate in the
development of projects related to massive stars and the ESA
cornerstone mission Gaia. The position is funded by Concerted
Research Actions (ARC) programme.
The High-Energy
Astrophysics Group (GAPHE) carries out a variety of research projects
aiming at studying single and binary massive stars (OB, Wolf-Rayet,
Luminous Blue Variables, ...) and the interactions with their
environment based on data obtained with world-class, space-borne
(XMM, Chandra, ...) or ground-based (ESO, ...) facilities.
The
Gaia satellite is currently performing an all-sky survey providing
astrometry and photometry for about one billion stars, and
spectroscopy for a subsample. The first data are due to be released
to the whole community in summer 2016. This release will include
parallaxes and proper motions of unprecedented accuracy for about 2.5
million bright sources (see
http://www.cosmos.esa.int/web/gaia/release), among which a large
number of massive stars. On the other hand, members of the GAPHE are
involved in the Gaia-ESO survey (https://www.gaia-eso.eu/), whose
main goal is to complement the Gaia data by providing precise
chemical abundances. As part of this survey, spectroscopic data are
being collected for numerous hot stars in young open clusters (Carina
Nebula, ...).
The successful candidate will develop projects
making use of the data for hot stars from the first (2016) and second
(2017) Gaia data releases. In parallel, he/she is expected to analyse
the data for OB stars obtained by the Gaia-ESO survey, with a
particular emphasis on the determination of the atmospheric
parameters, chemical composition and wind properties.
Applicants
with interest and previous experience in massive star research are
invited to apply. Expertise in the determination of fundamental
parameters and abundances of massive stars, analysis of spectroscopic
data, knowledge of model atmosphere codes for hot stars (CMFGEN,
TLUSTY, ...) and astronomical softwares (IRAF, MIDAS, ...) are an
advantage but are not mandatory.
Applicants should have a
record of publications in peer-reviewed journals, demonstrated
creativity, independence, high motivation, good communication skills,
and the ability to work independently as well as in collaboration
with other members of our research group.
The appointment is
initially for one year with a possible extension for a second year
subject to funding and performance. The starting date is negotiable
but preferably before June 1st, 2016. To be eligible, the applicant
should not have lived or worked in the 'Federation
Wallonie-Bruxelles' for more than 24 months over the last three
years. The salary is on the official Belgian public employee pay
scale for a young Post-Doc. Funding for travel and research equipment
is available.
Interested persons should send their
application material including a curriculum vitae, a summary (one
page at most) of past and current research activities, a letter of
interest, a full publication list and a list of three reference
persons by e-mail to: Eric Gosset/Gregor Rauw, Institute of
Astrophysics and Geophysics, Quartier Agora, Batiment B5c, Allee du 6
Aout, 19c, 4000 Liege, Belgium (e-mail: gosset@astro.ulg.ac.be,
rauw@astro.ulg.ac.be). The application deadline is May 1st, 2016. For
any further inquiry, please e-mail:
gosset@astro.ulg.ac.be.
Attention/Comments:
Weblink:
http://www.ago.ulg.ac.be/Edu/Jobs/Job_54.pdf
Email:
gosset@astro.ulg.ac.be
Deadline: May 1st,
2016
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28th November to 2nd December 2016
Venue: The
Spencer on Byron Hotel, Takapuna, Auckland, New Zealand
Dear
colleagues,
This is the second announcement of the
forthcoming IAU symposium to be held in Auckland, New Zealand
entitled
"IAUS 329: The Lives and Death-Throes of Massive
Stars".
Dates: 28th November to 2nd December 2016
Location: Auckland, New Zealand
Venue: The Spencer on Byron
Hotel, Takapuna
Registration, abstract submission and
application for IAU travel grants are now open.
Abstract
Submission closes: 30th May 2016
IAU travel grant Submission
closes: 30th May 2016
Early-bird registration closes: 30th August
2016
Conference website: http://nzstars2016.nz
Contact
for questions about the meeting scientific program:
nzstars2016@auckland.ac.nz
The meeting will summarize recent
progress and establish stronger links between the massive star
community and closely-linked fields, particularly those studying end
stages of massive star evolution and massive star cosmic
implications.
Topics to be covered:
Death throes:
supernovae, stellar deaths and progenitors
Observations and
surveys of massive stars: hot stars, cool stars, transition objects
and binaries
Theory of stellar evolution & atmospheres:
beyond standard physics, rotation, duplicity, mass loss and magnetic
fields and instabilities
Massive stars and their supernovae as
galactic building blocks and engines: Milky Way, nearby galaxies and
the early Universe
Invited Speakers
Evelyne Alecian,
Rodolfo Barba, Kris Belczynski, Melina Bersten, Saida
Caballero-Nieves, Luc Dessart, Morgan Fraser, Miriam Garcia, Cyril
Georgy, Goetz Grafener, Jose Groh, Stephen Justham, Emily Levesque,
Georges Meynet, Shazrene Mohamed, Bernhard Muller, Ignacio
Negureruela, Maria Fernanda Nieva, Keiichi Ohnaka, Hugues Sana,
Andreas Sander, Sergio Simon-Diaz, Alicia Soderberg, Elizabeth
Stanway, Miguel Urbaneja
Travel, accommodation and support
New Zealand is a significant distance to travel, particularly
due to the location of the international date line causing many
attendees to "lose-a-day" when travelling to the
conference. We advise our most distant attendees to arrive two days
early, if possible, but at least 1 day before the Monday morning, so
they are able to enjoy the first full day of the conference.
Rooms
can be booked directly at the hotel as described on the conference
website. It is possible for two or three people to share one room. We
suggest attendees organise their own groups. We will attempt to
provide a way to find roommates on the conference website shortly,
this can also be done via the conference's facebook group.
We
are also attempting to obtain access to discounts on flights. We will
update the conference website with details of this hopefully in the
next few weeks.
We have limited funds from the IAU to provide
support for attendees that have limited travel funding. Details on
how to apply for this are on the conference website.
If you
require a letter of invitation to visit New Zealand, you must first
register for and pay all applicable registration fees. Full details
of how to apply for this letter and a list of visa-free countries are
listed on the conference website.
Nationwide public symposium
In the weekend following the conference, Dec 3rd, we are
planning to run a large one day public symposium with as many
speakers as possible talking about their latest research. We also
hope to have these talks streamed live onto the internet and recorded
so there is a lasting impact of the meeting in New Zealand. If you
would like to be involved, or perhaps to travel to a city within New
Zealand to give a talk please email nztars2016@auckland.ac.nz and
outline your previous outreach experience.
Splinter Meetings
It may be possible to run a few splinter meetings during the
conference in the evenings, or during the weekend after the main
conference. If you would like to run a splinter meeting please email
nztars2016@auckland.ac.nz with a short outline of the topic, an
estimated number of participants, and the names of organizers before
the 30th May 2016.
Conference Excursions
There are
currently two excursions planned for the Wednesday afternoon of the
conference. One is a trip to Rangitoto Island, the volcano that is
visible from the hotel. This costs NZ$92 and lasts from11.45am to
approximately 5.15pm - includes round trip coach transfers (from the
hotel to Ferry Terminal, Ferry to the island and tour escort. While
it’s not a walk for the faint-hearted, it is family friendly. Make
sure you arrive prepared – there are no shops or transport on the
island and limited drinking water. Bring sunblock and a hat and wear
comfortable walking shoes. Alternatively there is a trip to the
Auckland War Memorial Museum which will cost NZ$72. The trip runs
from 1.15pm to approximately 4.15pm - includes round trip coach
transfers, tour guide and entry to museum.
Social Media
The
hashtag for the meeting is #NZstars2016. We have also setup a
Facebook group for the meeting which can be found at:
https://www.facebook.com/groups/1015095635200645/
Conference
Equity and Anti-Harassment Statement
#NZstars2016 is
dedicated to providing an equitable and harassment-free conference
experience for everyone regardless of gender, gender identity and
expression, sexual orientation, disability, physical appearance, body
size, race, age or religion. We do not tolerate harassment of
conference participants in any form. Conference participants
violating these rules may be sanctioned at the discretion of the
conference organizers and the conference equity committee.
Weblink:
nzstars2016.nz
Email:
nzstars2016@auckland.ac.nz
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