ISSN 1783-3426
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Fizeau exchange visitors program in optical interferometry - supplemental call for applications
The Wind of Rotating B Supergiants.
Spectral type, temperature and
evolutionary stage in cool supergiants
The
Red Supergiant Content of M31
Modelling
the Central Constant Emission X-ray component of η Carinae
The
Prevalence and Impact of Wolf-Rayet Stars in Emerging Massive Star
Clusters
Multiple short-lived
stellar prominences on O stars: The O6.5I(n)fp star lambda Cephei
Research Associate in Theoretical Stellar Astrophysics
J. Hron, L. Mosoni
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 June 15. Fellowships can be awarded for
missions carried out until the end of 2016! For missions in 2017
please wait for further announcements!
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 your community!
Looking forward to your
applications,
Josef Hron & Laszlo Mosoni
(for the
European Interferometry Initiative)
Reference:
www.european-interferometry.eu
Status: Other
Weblink:
www.european-interferometry.eu
Comments:
Email: fizeau@european-interferometry.eu
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R. O. J. Venero(1), M. Curé(2), L. S. Cidale(1), I.
Araya(2)
1 - Departamento de Espectroscopía,
Facultad
de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La
Plata (UNLP), and Instituto de Astrofísica La Plata, CCT La Plata,
CONICET-UNLP, Paseo del Bosque S/N, 1900 La Plata, Argentina.
2
- Instituto de Física y Astronomía, Facultad de Ciencias,
Universidad de Valparaíso -
Av. Gran Bretaña 1111, Casilla
5030, Valparaíso, Chile.
In the scenario of rotating
radiation-driven wind theory for massive stars, three types of
hydrodynamic solutions are currently known: the classical "fast"
m-CAK solution, the "Omega-slow" solution that arises for
fast rotators, and the so-called "delta-slow" solution for
high values of the delta line-force parameter are allowed
independently of the rotation speed. Compared to the "fast"
solutions, both "slow solutions" have lower terminal
velocities.
As the study of the "slow" solution
parameters domain is still incomplete, we perform a comprehensive
analysis of the distinctive solution regimes for B supergiants that
emerge from a fine grid of rotation values, Omega, and various
ionization conditions in the wind, the delta parameter. The wind
ionization defines two domains: one for "fast" outflowing
winds and the other for "slow" expanding flows. Both
domains are clear-cut by a gap, where no solution is found for a
finite interval of delta. The location and width of the forbidden
region depend on Teff and Omega. There is a smooth and continuous
transition between the "Omega-slow" and "delta-slow"
regimes, a single "Omega-delta-slow" regime.
We discuss
different situations where the "slow" solutions can be
found and the possibility of a switch between "fast" and
"slow" solutions in the B supergiant winds. We compare the
theoretical terminal velocity with observations of B and A
supergiants and find that the "fast" regime prevails mostly
for early B supergiants while the "slow" wind regime
matches better for A and B mid- and late-type
supergiants.
Reference: ApJ, 822, 28.
Status:
Manuscript has been accepted
Weblink:
Comments:
Email: roberto@fcaglp.unlp.edu.ar
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Ricardo Dorda (1), Ignacio Negueruela (1), Carlos
González-Fernández (2), Hugo M. Tabernero (1 and 3)
(1)
DFISTS, Universidad de Alicante, (2) Institute of Astronomy,
University of Cambridge, (3) Departamento de Astrofísica,
Universidad Complutense de Madrid
In recent years, temperature
scales in cool supergiants (CSGs) have been disputed, and the
possibility that spectral types (SpTs) do not depend primarily on
temperature has been raised. We explore the relations between
different observed parameters and the capability of deriving accurate
intrinsic stellar parameters from them through the analysis of the
largest spectroscopic sample of CSGs to date from SMC and LMC. We
explore possible correlations between different observational
parameters, also making use of near- and mid-infrared colours and
literature on photometric variability. Direct comparison between the
behaviour of atomic lines (Fe I, Ti I, and Ca II) in the observed
spectra and synthetic atmospheric models provides compelling evidence
that effective temperature is the prime underlying variable driving
the SpT sequence in CSGs. However, there is a clear correlation
between SpT and luminosity, with later ones tending to correspond to
more luminous stars with heavier mass loss. The population of CSGs in
the SMC is characterised by a higher degree of spectral variability,
early spectral types (centred on type K1) and low mass-loss rates (at
least as measured by dust-sensitive mid-infrared colours). The
population in the LMC displays less spectroscopic variability and
later spectral types. The distribution of spectral types is not
single-peaked. Instead, the brightest CSGs have a significantly
different distribution from less luminous objects, presenting mostly
M subtypes (centred on M2), and increasing mass-loss rates for later
types. In conclusion, the observed properties of CSGs in the SMC and
the LMC cannot be described correctly by standard evolutionary
models. The very strong correlation between spectral type and
bolometric luminosity, supported by all data from the Milky Way,
cannot be reproduced at all by current evolutionary
tracks.
Reference: Accepted for subscription for
publication in Astronomy and Astrophysics
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1605.03239
Comments:
Email: ricardo.dorda@ua.es
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Philip Massey (1), Kate Anne Evans (1, 2)
(1)
Lowell Observatory, (2) Caltech
We investigate the red
supergiant (RSG) population of M31, obtaining radial
velocities
of 255 stars. These data substantiate membership of our
photometrically-selected sample, demonstrating that Galactic
foreground stars
and extragalactic RSGs can be distinguished on
the basis of B-V, V-R two-color
diagrams. In addition, we use
these spectra to measure effective temperatures
and assign
spectral types, deriving physical properties for 192 RSGs.
Comparison with the solar-metallicity Geneva evolutionary tracks
indicates
astonishingly good agreement. The most luminous RSGs in
M31 are likely evolved
from 25-30 Mo stars, while the vast
majority evolved from stars with initial
masses of 20 Mo or less.
There is an interesting bifurcation in the
distribution of RSGs
with effective temperatures that increases with higher
luminosities,
with one sequence consisting of early K-type supergiants, and
with
the other consisting of M-type supergiants that become later (cooler)
with
increasing luminosities. This separation is only partially
reflected in the
evolutionary tracks, although that might be due
to the mis-match in
metallicities between the solar Geneva models
and the higher-than-solar
metallicity of M31. As the luminosities
increase the median spectral type also
increases; i.e., the
higher mass RSGs spend more time at cooler temperatures
than do
those of lower luminosities, a result which is new to this study.
Finally we discuss what would be needed observationally to
successfully build a
luminosity function that could be used to
constrain the mass-loss rates of RSGs
as our Geneva colleagues
have suggested.
Reference: AJ, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1605.07900
Comments:
Email: phil.massey@lowell.edu
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Christopher M. P. Russell (1), Michael F. Corcoran (2,3),
Kenji Hamaguchi (2,4),
Thomas I. Madura (3,5), Stanley P. Owocki
(6), and D. John Hillier (7)
1 - X-ray Astrophysics
Laboratory, Code 662, NASA/Goddard Space Flight Center, Greenbelt, MD
20771, USA
2 - CRESST and X-ray Astrophysics Laboratory,
NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
3 -
Universities Space Research Association, 7178 Columbia Gateway Drive,
Columbia, MD 21044, USA
4 - Department of Physics, University of
Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250,
USA
5 - CRESST and Astrophysics Science Division, Code 667,
NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
6 -
Bartol Research Institute, Department of Physics and Astronomy,
University of Delaware, Newark, DE 19716, USA
7 - Department of
Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA
15260, USA
The X-ray emission of η Carinae shows multiple
features at various spatial and temporal scales. The central constant
emission (CCE) component is centred on the binary and arises from
spatial scales much smaller than the bipolar Homunculus nebula, but
likely larger than the central wind–wind collision region between
the stars as it does not vary over the ∼2–3 month X-ray minimum
when it can be observed. Using large-scale 3D smoothed particle
hydrodynamics (SPH) simulations, we model both the colliding-wind
region between the stars, and the region where the secondary wind
collides with primary wind ejected from the previous periastron
passage. The simulations extend out to one hundred semimajor axes and
make two limiting assumptions (strong coupling and no coupling) about
the influence of the primary radiation field on the secondary wind.
We perform 3D radiative transfer calculations on the SPH output to
synthesize the X-ray emission, with the aim of reproducing the CCE
spectrum. For the preferred primary mass-loss rate $\dot{M}_A \approx
8.5 \times 10^{-4} M_\odot$\,yr$^{-1}$, the model spectra well
reproduce the observation as the strong- and no-coupling spectra
bound the CCE observation for longitude of periastron ω ≈ 252◦,
and bound/converge on the observation for ω ≈ 90◦. This suggests
that η Carinae has moderate coupling between the primary radiation
and secondary wind, that both the region between the stars and the
comoving collision on the backside of the secondary generate the CCE,
and that the CCE cannot place constraints on the binary’s line of
sight. We also discuss comparisons with common X-ray fitting
parameters.
Reference: MNRAS, 458, 3
Status:
Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2016MNRAS.458.2275R
Comments:
Email: crussell@udel.edu
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Kimberly R. Sokal$^(1, 2}$, Kelsey E. Johnson$^1$, R\'{e}my
Indebetouw$^1$, and Philip Massey$^{2,3}$
1-Department of
Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA
22903, USA; krs9tb@virginia.edu.
2-Visiting astronomer, Kitt Peak
National Observatory, National Optical Astronomy Observatory, which
is operated by the Association of Universities for Research in
Astronomy (AURA) under a cooperative agreement with the National
Science Foundation.
3-Lowell Observatory, 1400 W Mars Hill Road,
Flagstaff, AZ 86001, USA.
We investigate Wolf-Rayet (WR) stars
as a source of feedback contributing to the removal of natal material
in the early evolution of massive star clusters. Despite previous
work suggesting that massive star clusters clear out their natal
material before the massive stars evolve into the WR phase, WR stars
have been detected in several emerging massive star clusters. These
detections suggest that the timescale for clusters to emerge can be
at least as long as the time required to produce WR stars (a few
million years), and could also indicate that WR stars may be
providing the tipping point in the combined feedback processes that
drive a massive star cluster to emerge. We explore the potential
overlap between the emerging phase and the WR phase with an
observational survey to search for WR stars in emerging massive star
clusters hosting WR stars. We select candidate emerging massive star
clusters from known radio continuum sources with thermal emission and
obtain optical spectra with the 4m Mayall Telescope at Kitt Peak
National Observatory and the 6.5m MMT. We identify 21 sources with
significantly detected WR signatures, which we term ``emerging WR
clusters.'' WR features are detected in ~50\% of the radio-selected
sample, and thus we find that WR stars are commonly present in
massive star clusters currently emerging. The observed extinctions
and ages suggest that clusters without WR detections remain embedded
for longer periods of time, and may indicate that WR stars can aid,
and therefore accelerate, the emergence process.
Reference:
ApJ (in press)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1605.08044
Comments:
Email: krs9tb@virginia.edu
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N.P. Sudnik (1,2), H.F. Henrichs
(1)
(1) University of Amsterdam, (2) Saint-Petersburg
State University
Most O-type stars and many B stars show
unexplained cyclical variability in their spectral lines, i.e.,
modulation on the rotational timescale, but not strictly periodic.
The variability occurs in the so-called discrete absorption
components (DACs) that accelerate through the UV-wind line profiles
and also in many optical lines. For such OB stars no dipolar magnetic
fields have been detected with upper limits of ~ 300 G.
We
investigate whether multiple magnetic loops on the surface rather
than non-radial pulsations (NRPs) or a dipolar magnetic field can
explain the observed cyclical UV and optical spectral line
variability.
We present time-resolved, high-resolution optical
spectroscopy of the O6.5I(n)fp star lambda Cephei. We apply a
simplified phenomenological model in which multiple spherical blobs
attached to the surface represent magnetic-loop structures, which we
call stellar prominences, by analogy with solar prominences. We
compare the calculated line profiles as a function of rotational
phase, adopting a rotation period of 4.1 d, with observed relative
changes in subsequent quotient spectra.
We identify many
periodicities in spectral lines, almost none of which is stable over
timescales from months to years. We show that the relative changes in
various optical absorption and emission lines are often very similar.
Our proposed model applied to the He II 4686 line can typically be
fitted with 2--5 equatorial blobs with lifetimes between ~ 1 and 24
h.
Given the irregular timescales involved, we propose that the
azimuthal distribution of DACs correspond to the locations of stellar
prominences attached to the surface. This could explain the observed
variability of optical and UV lines, and put constraints on the
strength and lifetime of these structures, which can be compared with
recent theoretical predictions, in which bright magnetic surface
spots are formed by the action of the subsurface convection
zone.
Reference: A&A (in press)
Status:
Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1606.00404
Comments:
Accepted May 02, 2016, 30 pages, 48 figures
Email:
h.f.henrichs@uva.nl
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Raphael Hirschi
Keele University, UK
Faculty
of Natural Sciences
Faculty Research Office
Research
Associate in Theoretical Stellar Astrophysics
Fixed Term
until October 2017
Starting salary: Grade 7 £31,656
Keele
University wishes to appoint a Research Associate starting in October
2016, in order to conduct research on theoretical stellar
astrophysics.
The appointed Research Associate will work in
the group of Dr Raphael Hirschi within the Astrophysics Group at
Keele University as part of an ERC-funded project entitled “Stellar
HYdrodynamics, Nucleosynthesis and Evolution” (SHYNE). The ERC
starting grant awarded to Dr Hirschi provides funding for a dedicated
1200+-CPU-core computer cluster, including 288 CPU-cores sharing
memory via numascale technology.
You will lead the component
of this project related to 3D-1D modelling of stellar interiors. This
will include a range of computer simulations including 1D stellar
evolution and 3D hydrodynamics simulations with as main goal to
improve modelling of convection and rotation in stellar evolution.
The Research Associate will also contribute to the other components
of the project and be encouraged to develop their own research
program and their leadership skills. The post holder will work
closely with a collaborator in America and the appointment will
involve frequent travel to the USA.
Applicants should have or
expect to obtain a PhD in theoretical stellar astrophysics or a
related area and should have a demonstrated aptitude for research.
Experience in stellar evolution modelling and 3D hydrodynamic
simulations 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 please visit:
www.keele.ac.uk/vacancies
Keele University employees wishing
to apply should login to Employee Self Service and click on the 'View
current vacancies' link.
Closing date for applications: 4
August 2016
Interviews will most probably be conducted
remotely (via skype or similar technology)
Post reference:
KU00000093
Attention/Comments:
Weblink:
https://forums.keele.ac.uk/viewtopic.php?f=14&t=15679
Email:
r.hirschi@keele.ac.uk
Deadline: 4 August 2016
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