ISSN 1783-3426
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Fundamental parameters of massive stars in
multiple systems: The cases of HD17505A and HD206267A
A
Runaway Yellow Supergiant Star in the Small Magellanic Cloud
Subsonic structure and optically thick
winds from Wolf-Rayet stars
Polarization
simulations of stellar wind bow shock nebulae. I. The case of
electron scattering
Co-existence and
switching between fast and Omega-slow wind solutions in rapidly
rotating massive stars
Very Massive Stars: a
metallicity-dependent upper-mass limit, slow winds, and the
self-enrichment of Globular Clusters
Searching
for cool dust: ii. Infrared imaging of the OH/IR supergiants, NML
Cyg, VX Sgr, S Per and the normal red supergiants RS Per and T
Per
Lucky Spectroscopy, an equivalent
technique to Lucky Imaging. Spatially resolved spectroscopy of
massive close visual binaries using the William Herschel
Telescope
Spin rates and spin evolution of O
components in WR+O binaries
A search for
Galactic runaway stars using Gaia Data Release 1 and Hipparcos proper
motions
Post-doctoral position in stellar physics in
Tartu Observatory, Estonia
Two PhD positions
in stellar physics at Geneva Observatory
F. Raucq(1), G. Rauw(1), L. Mahy(2), S. Simon-Diaz(3,4)
(1) Liege University, Belgium
(2) KU Leuven,
Belgium
(3) IAC, Tenerife, Spain
(4) Universidad de La
Laguna, Spain
Many massive stars are part of binary or
higher multiplicity systems. The present work focusses on two higher
multiplicity systems: HD17505A and HD206267A. Determining the
fundamental parameters of the components of the inner binary of these
systems is mandatory to quantify the impact of binary or triple
interactions on their evolution. We analysed high-resolution optical
spectra to determine new orbital solutions of the inner binary
systems. After subtracting the spectrum of the tertiary component, a
spectral disentangling code was applied to reconstruct the individual
spectra of the primary and secondary. We then analysed these spectra
with the non-LTE model atmosphere code CMFGEN to establish the
stellar parameters and the CNO abundances of these stars. The inner
binaries of these systems have eccentric orbits with e ~ 0.13 despite
their relatively short orbital periods of 8.6 and 3.7 days for
HD17505Aa and HD206267Aa, respectively. Slight modifications of the
CNO abundances are found in both components of each system. The
components of HD17505Aa are both well inside their Roche lobe, whilst
the primary of HD206267Aa nearly fills its Roche lobe around
periastron passage. Whilst the rotation of the primary of HD206267Aa
is in pseudo-synchronization with the orbital motion, the secondary
displays a rotation rate that is higher. The CNO abundances and
properties of HD17505Aa can be explained by single star evolutionary
models accounting for the effects of rotation, suggesting that this
system has not yet experienced binary interaction. The properties of
HD206267Aa suggest that some intermittent binary interaction might
have taken place during periastron passages, but is apparently not
operating anymore.
Reference: A&A, in press
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1803.00243
Comments:
Email:
rauw@astro.ulg.ac.be
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Kathryn Neugent (1,2), Phil Massey (1), Nidia Morrell
(3), Brian Skiff (1), Cyril Georgy (4)
1 - Lowell
Observatory; 2 - University of Washington; 3 - Las Campanas
Observatory; 4 - Geneva University
We recently discovered
a yellow supergiant (YSG) in the Small Magellanic Cloud (SMC) with a
heliocentric radial velocity of ~300 km/s which is much larger than
expected for a star in its location in the SMC. This is the first
runaway YSG ever discovered and only the second evolved runaway star
discovered in a different galaxy than the Milky Way. We classify the
star as G5-8I, and use de-reddened broad-band colors with model
atmospheres to determine an effective temperature of 4700+/-250K,
consistent with what is expected from its spectral type. The star's
luminosity is then L/Lo ~ 4.2+/-0.1, consistent with it being a
~30Myr 9Mo star according to the Geneva evolution models. The star is
currently located in the outer portion of the SMC's body, but if the
star's transverse peculiar velocity is similar to its peculiar radial
velocity, in 10Myr the star would have moved 1.6 degrees across the
disk of the SMC, and could easily have been born in one of the SMC's
star-forming regions. Based on its large radial velocity, we suggest
it originated in a binary system where the primary exploded as a
supernovae thus flinging the runaway star out into space. Such stars
may provide an important mechanism for the dispersal of heavier
elements in galaxies given the large percentage of massive stars that
are runaways. In the future we hope to look into additional evolved
runaway stars that were discovered as part of our other past surveys.
Reference: AJ
Status: Manuscript has been
accepted
Weblink: https://arxiv.org/abs/1803.02859
Comments:
Email:
kneugent@lowell.edu
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L.Grassitelli (1), N.Langer (1), N.J. Grin (1), J. Mackey
(2), J.M. Bestenlehner (3), G.Graefener (1)
(1)
Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel
71, 53121 Bonn, Germany
(2) Dublin Institute for Advanced
Studies, Dunsink Observatory, Dunsink Lane, Castleknock, Dublin 15,
Ireland
(3) Department of Physics and Astronomy, University of
Sheffield, Hicks Building, Hounsfield Rd, Sheffield, S3 7RH, UK
Mass loss by stellar wind is a key agent in the evolution
and spectroscopic appearance of massive main sequence and post-main
sequence stars. In Wolf–Rayet stars the winds can be so dense and
so optically thick that the photosphere appears in the highly
supersonic part of the outflow, veiling the underlying subsonic part
of the star, and leaving the initial acceleration of the wind
inaccessible to observations. Here we investigate the conditions and
the structure of the subsonic part of the outflow of Galactic
Wolf–Rayet stars, in particular of the WNE subclass; our focus is
on the conditions at the sonic point of their winds. We compute 1D
hydrodynamic stellar structure models for massive helium stars
adopting outer boundaries at the sonic point. We find that the
outflows of our models are accelerated to supersonic velocities by
the radiative force from opacity bumps either at temperatures of the
order of 200 kK by the iron opacity bump or of the order of 50 kK by
the helium-II opacity bump. For a given mass-loss rate, the diffusion
approximation for radiative energy transport allows us to define the
temperature gradient based purely on the local thermodynamic
conditions. For a given mass-loss rate, this implies that the
conditions in the subsonic part of the outflow are independent from
the detailed physical conditions in the supersonic part. Stellar
atmosphere calculations can therefore adopt our hydrodynamic models
as ab initio input for the subsonic structure. The close proximity to
the Eddington limit at the sonic point allows us to construct a Sonic
HR diagram, relating the sonic point temperature to the
luminosity-to-mass ratio and the stellar mass-loss rate, thereby
constraining the sonic point conditions, the subsonic structure, and
the stellar wind mass-loss rates of WNE stars from observations. The
minimum stellar wind mass-loss rate necessary to have the flow
accelerated to supersonic velocities by the iron opacity bump is
derived. A comparison of the observed parameters of Galactic WNE
stars to this minimum mass-loss rate indicates that these stars have
their winds launched to supersonic velocities by the radiation
pressure arising from the iron opacity bump. Conversely, stellar
models which do not show transonic flows from the iron opacity bump
form low-density extended envelopes. We derive an analytic criterion
for the appearance of envelope inflation and of a density inversion
in the outer sub-photospheric layers.
Reference: A&A,
in press
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1803.03033
Comments:
Email:
luca@astro.uni-bonn.de
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Manisha Shrestha$^1$, Hilding R. Neilson$^2$, Jennifer L.
Hoffman$^1$, Richard Ignace$^3$
1-University of
Denver, 2-University of Toronto, 3-East Tennessee State
University
Bow shocks and related density enhancements
produced by the winds of massive stars moving through the
interstellar medium provide important information regarding the
motions of the stars, the properties of their stellar winds, and the
characteristics of the local medium. Since bow shock nebulae are
aspherical structures, light scattering within them produces a net
polarization signal even if the region is spatially unresolved.
Scattering opacity arising from free electrons and dust leads to a
distribution of polarized intensity across the bow shock structure.
That polarization encodes information about the shape, composition,
opacity, density, and ionizsation state of the material within the
structure. In this paper we use the Monte Carlo radiative transfer
code SLIP to investigate the polarization created when photons
scatter in a bow shock-shaped region of enhanced density surrounding
a stellar source. We present results for electron scattering, and
investigate the polarization behaviour as a function of optical
depth, temperature, and source of photons for two different cases:
pure scattering and scattering with absorption. In both regimes we
consider resolved and unresolved cases. We discuss the implications
of these results as well as their possible use along with
observational data to constrain the properties of observed bow shock
systems. In different situations and under certain assumptions, our
simulations can constrain viewing angle, optical depth and
temperature of the scattering region, and the relative luminosities
of the star and shock.
Reference: MNRAS in press
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1712.04958
Comments:
Email:
manisha.shrestha9@du.edu
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Ignacio Araya (1,2), Michel Curé (1), Asif ud-Doula
(3,4), Alfredo Santillán (5) and Lydia Cidale (6,7,1)
1-
Instituto de Física y Astronomía, Facultad de Ciencias, Universidad
de Valparaíso, Av. Gran Bretaña 1111, Casilla 5030, Valparaíso,
Chile
2- Núcleo de Matemáticas, Física y Estadística,
Facultad de Ciencias, Universidad Mayor, Chile
3- Penn State
Worthington Scranton, Dunmore, PA 18512, USA
4- Dept A.G.O.,
Universite de Liege, Belgium
5-Dirección General de Cómputo y
Tecnologías de la Información y Comunicación, Universidad Nacional
Autónoma de México, Ciudad Universitaria, C.P. 04510, Mexico City,
Mexico
6-Departamento de Espectroscopía, Facultad de Ciencias
Astronómicas y Geofísicas, Universidad Nacional de La Plata (UNLP),
Paseo del Bosque S/N, 1900 La Plata, Argentina
7-Instituto de
Astrofísica La Plata, CCT La Plata, CONICET-UNLP, Paseo del Bosque
S/N, 1900 La Plata, Argentina
Most radiatively-driven
massive star winds can be modelled with m-CAK theory resulting in so
called fast solution. However, those most rapidly rotating among
them, especially when the stellar rotational speed is higher than ~
75% of the critical rotational speed, can adopt a different solution
called Omega-slow solution characterized by a dense and slow wind.
Here, in this work we study the transition region of the solutions
where the fast solution changes to the Omega-slow. Using both
time-steady and time-dependent numerical codes, we study this
transition region for different equatorial models of B-type stars. In
all the cases, at certain range of rotational speeds, we found a
region where the fast and Omega-slow solution can co-exist. We find
that the type of solution obtained in this co-existence region
depends heavily on the initial conditions of our models. We also test
the stability of the solutions within the co-existence region by
performing base density perturbations in the wind. We find that under
certain conditions, the fast solution can switch to a Omega-slow
solution, or vice versa. Such solution switching may be a possible
contributor of material injected into the circumstellar environment
of Be stars, without requiring rotational speeds near critical
values.
Reference: accepted for publication in
MNRAS
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1803.07572
Comments:
Email:
ignacio.araya@umayor.cl
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Jorick S. Vink
Armagh Observatory and
Planetarium
One of the key questions in Astrophysics
concerns the issue of whether there exists an upper-mass limit to
stars, and if so, what physical mechanism sets this limit, which
might also determine if the upper-mass limit is metallicity (Z)
dependent. We argue that mass loss by radiation-driven winds mediated
by line opacity is one of the prime candidates setting the upper-mass
limit. We present mass-loss predictions (dM/dt_wind) from Monte Carlo
radiative transfer models for relatively cool (Teff = 15kK) inflated
very massive stars (VMS) with large Eddington Gamma factors in the
mass range 100-1000 Msun as a function of metallicity down to 1/100
Z/Zsun. We employ a hydrodynamic version of our Monte Carlo method,
allowing us to predict the rate of mass loss (dM/dt_wind) and the
terminal wind velocity (vinf) simultaneously. Interestingly, we find
wind terminal velocities (vinf) that are low (100-500 km/s) over a
wide Z-range, and we propose that the slow winds from VMS are an
important source of self-enrichment in globular clusters. We also
find mass-loss rates (dM/dt_wind), exceeding the typical
mass-accretion rate (dM/dt_accr) of 0.001 Msun/yr during massive-star
formation. We express our mass-loss predictions as a function of mass
and Z, finding log dM/dt = -9.13 + 2.1 log(M/Msun) + 0.74 log(Z/Zsun)
(Msun/yr). Even if stellar winds would not directly halt &
reverse mass accretion during star formation, if the most massive
stars form by stellar mergers stellar wind mass loss may dominate
over the rate at which stellar growth takes place. We therefore argue
that the upper-mass limit is effectively Z-dependent due to the
nature of radiation-driven winds. This has dramatic consequences for
the most luminous supernovae, gamma-ray bursts, and other black hole
formation scenarios at different Cosmic epochs.
Reference:
Astronomy & Astrophysics
Status: Manuscript has been
accepted
Weblink: https://arxiv.org/abs/1803.08042
Comments: Accepted by A&A
Email:
jsv@arm.ac.uk
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Michael S. Gordon^1, Roberta M. Humphreys^1, Terry J.
Jones^1, Dinesh Shenoy^1, Robert D. Gehrz^2, L. Andrew Helton^2,
Massimo Marengo^3, Philip M. Hinz^4, William F. Hoffman^4
1.
University of Minnesota, 2. USRA-SOFIA, 3. Iowa State Univsersity, 4.
University of Arizona
New
MMT/MIRAC(9–11μm),SOFIA/FORCAST(11–37μm), and Herschel/PACS (70
and 160μm) infrared(IR) imaging and photometry is presented for
three famous OH/IR red supergiants(NML Cyg, VX Sgr, and S Per) and
two normal red supergiants (RS Per and T Per). We model the observed
spectral energy distributions (SEDs) using radiative transfer code
DUSTY. Azimuthal average profiles from the SOFIA/FORCAST imaging, in
addition to dust mass distribution profiles from DUSTY, constrain the
mass-loss histories of these supergiants. For all of our observed
supergiants, the DUSTY models suggest that constant mass-loss rates
do not produce enough dust to explain the observed infrared emission
in the stars’ SEDs. Combining our results with Shenoy et al.(2016)
(Paper I) we find mixed results with some red supergiants showing
evidence for variable and high mass-loss events while others have
constant mass loss over the past few thousand years.
Reference:
AJ, in press
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1708.00018
Comments: To appear in the Astronomical Journal
Email: roberta@umn.edu
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J. Maíz Apellániz (1), R. H. Barbá (2), S. Simón-Díaz
(3,4), A. Sota (5), E. Trigueros Páez (1,6), J. A. Caballero (1), E.
J. Alfaro (5)
(1) CAB, (2) ULS, (3) ULL, (4) IAC, (5)
IAA, (6) UA
CONTEXT: Many massive stars have nearby
companions whose presence hamper their characterization through
spectroscopy. AIMS: We want to obtain spatially resolved spectroscopy
of close massive visual binaries to derive their spectral types.
METHODS: We obtain a large number of short long-slit spectroscopic
exposures of five close binaries under good seeing conditions, select
those with the best characteristics, extract the spectra using
multiple-profile fitting, and combine the results to derive spatially
separated spectra. RESULTS: We demonstrate the usefulness of Lucky
Spectroscopy by presenting the spatially resolved spectra of the
components of each system, in two cases with separations of only
~0.3". Those are delta Ori Aa+Ab (resolved in the optical for
the first time) and sigma Ori AaAb+B (first time ever resolved). We
also spatially resolve 15 Mon AaAb+B, zeta Ori AaAb+B (both
previously resolved with GOSSS, the Galactic O-Star Spectroscopic
Survey), and eta Ori AaAb+B, a system with two spectroscopic B+B
binaries and a fifth visual component. The systems have in common
that they are composed of an inner pair of slow rotators orbited by
one or more fast rotators, a characteristic that could have
consequences for the theories of massive star formation.
Reference:
Accepted for publication in A&A
Status: Manuscript has
been accepted
Weblink: https://arxiv.org/abs/1804.03133
Comments:
Email:
jmaiz@cab.inta-csic.es
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D. Vanbeveren (*), N. Mennekens, M. M. Shara and A. F. J.
Moffat
(*) Vrije Universiteit Brussel, Dept. of
physics and Astrophysics, AARG, Pleinlaan 2, 1050 Brussels, Belgium
Despite 50 years of extensive binary research we must
conclude that the Roche lobe overflow/mass transfer process that
governs close binary evolution is still poorly understood. It is the
scope of the present paper to lift the edge of the veil by studying
the spin-up and spin-down processes of the O-type components of WR+O
binaries. We critically analyzed the available observational data of
rotation speeds of the O-type components in WR+O binaries. By
combining a binary evolutionary code and a formalism that describes
the effects of tides in massive stars with an envelope in radiative
equilibrium, we computed the corresponding rotational velocities
during the Roche lobe overflow of the progenitor binaries. In all the
WR+O binaries studied, we find that the O-type stars were affected by
accretion of matter during Roche lobe overflow (RLOF) of the
progenitor. This means that common envelope evolution, which excludes
any accretion onto the secondary O star, has not played an important
role in explaining WR+O binaries. Moreover, although it is very
likely that the O-type star progenitors were spun up by mass
transfer, many ended the RLOF (and mass transfer) phase with a
rotational velocity that is significantly smaller than the critical
rotation speed. This may indicate that during the mass transfer phase
there is a spin-down process that is of the same order, although
significantly less, than that of the spin-up process. We propose a
Spruit-Tayler type dynamo spin-down suggested in the past to explain
the rotation speeds of the mass gainers in long-period Algols.
Reference: Astronomy and Astrophysics
Status:
Manuscript has been accepted
Weblink: arXiv:
1711.05989
Comments:
Email:
dvbevere@vub.be
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J. Maíz Apellániz (1), M. Pantaleoni González (1,2),
R. H. Barbá (3), S. Simón-Díaz (4,5), I. Negueruela (6), D. J.
Lennon (7), A. Sota (8), E. Trigueros Páez (1,6)
(1)
CAB, CSIC-INTA, (2) UCM, (3) ULS, (4) IAC, (5) ULL, (6) UA, (7) ESA,
(8) IAA
CONTEXT.The first Gaia Data Release (DR1)
significantly improved the previously available proper motions for
the majority of the Tycho-2 stars. AIMS. We want to detect runaway
stars using Gaia DR1 proper motions and compare our results with
previous searches. METHODS. Runaway O stars and BA supergiants are
detected using a 2-D proper-motion method. The sample is selected
using Simbad, spectra from our GOSSS project, literature spectral
types, and photometry processed using CHORIZOS. RESULTS. We detect 76
runaway stars, 17 (possibly 19) of them with no prior identification
as such, with an estimated detection rate of approximately one half
of the real runaway fraction. An age effect appears to be present,
with objects of spectral subtype B1 and later having travelled for
longer distances than runaways of earlier subtypes. We also
tentatively propose that the fraction of runaways is lower among BA
supergiants that among O stars but further studies using future Gaia
data releases are needed to confirm this. The frequency of fast
rotators is high among runaway O stars, which indicates that a
significant fraction of them (and possibly a majority) is produced in
supernova explosions.
Reference: Accepted for
publication in A&A
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1804.06915
Comments:
Email:
jmaiz@cab.inta-csic.es
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Anna Aret
Tartu Observatory
University
of Tartu
Observatooriumi 1
Tõravere
61602
Estonia
Applications are invited for a
post-doctoral position in the Department of Stellar Physics of Tartu
Observatory, University of Tartu. The successful applicant will work
with Drs. Indrek Kolka, Laurits Leedjärv and Anna Aret on
investigating massive stars in post-main sequence evolution phases,
their pulsation habits, and mass-loss behaviour. The ideal candidate
will have a background in stellar physics (massive star evolution,
stellar winds, and/or circumstellar discs) and have experience with
observations (spectroscopy, photometry and/or interferometry), data
reduction, and data analysis of optical and/or infrared data. The
applicant must hold a PhD degree in the field (max 6 years from PhD)
by the date of employment.
Tartu Observatory is the
largest professional astronomical organization in Estonia conducting
research in the fields of astronomy, remote sensing, and space
technology. It is located in Tõravere, approximately 20 km out of
Tartu. The main building of Tartu Observatory has been completely
renovated in 2011 - 2012, providing a modern research environment.
The department offers excellent computing facilities and fast
internet connection. In 2015, Estonia became a full member of the
European Space Agency. The Department of Stellar Physics operates a
1.5m telescope with a single-slit spectrograph, 0.6m and 0.3m
telescopes with CCD photometers.
Salary will be based on
the domestic level and it includes health insurance. Starting salary
will be in the range 1700 - 2400 EUR. See
http://www.numbeo.com/cost-of-living/comparison.jsp to compare cost
of living.
The appointment is initially for one year, an
extension for another year is expected upon satisfactory scientific
performance. The preferred starting date shall be between June 1st
2018 and September 1st 2018 but can be negotiated.
Applicants
should submit:
1) a curriculum vitae with a full publication
list,
2) a statement of interest (max. 2 pages),
3) a
summary of the research experience (max. 2 pages).
Applicants
must also provide the names and contact details of two referees who
would be prepared to send confidential recommendation letters should
they be requested to do so. The selection committee will send out
requests for such letters for those applicants on the short-list
after an initial ranking. The short-listed applicants will be invited
for an interview (live or via Skype). Applications can be submitted
before finishing PhD, in which case a statement from the supervisor
stating the planned date of the defence should be included.
The
application materials should be sent by email to: info@to.ee
(subject: "postdoc 2018", pdf file please), to arrive no
later than 23:59 EET on April 15, 2018. Interviews will be held
during May 2018 and the selected candidate will be contacted at the
latest by May 31, 2018.
Additional information may be
obtained by contacting Dr. Anna Aret (anna.aret@to.ee).
Attention/Comments:
Weblink:
https://www.to.ee/eng/vacancies/post_doctoral_position_in_stellar_physics
Email:
anna.aret@to.ee
Deadline: April 15, 2018
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Georges Meynet
Geneva
University
Applications are invited for 2 PhD student
positions in theoretical and computational astrophysics at the
Department of Astronomy of the University of Geneva to start in fall
2018. The successful candidates will work within the group of Prof.
Georges Meynet on the fields of the evolution of massive stars and
star-planet interactions
The potential research projects
are along two different lines of research. A first line is focused on
the physics of massive stars with a strong emphasis on the nature of
the core collapse supernova progenitors. A second line will focus on
smaller initial mass stars, studying various effects in relation with
star-planet interactions and asteroseismology. In both lines of
researches, nucleosynthetic aspects will be explored (for instance
chemical composition of the ejecta for the core-collapse supernovae,
change of the surface abundances of stars engulfing planet).
The
Geneva Observatory and the associated Laboratory of Astrophysics of
the Swiss Federal Institute of Technology in Lausanne (EPFL) carry
out observational, interpretative, and theoretical research in the
fields of extra-solar planets, stellar physics, high energy
astrophysics, galaxy evolution and dynamics, and observational
cosmology, providing a rich and vibrant research environment.
These
PhD projects will run in parallel to the COST Action entitled
“Chemical Elements as Tracers of the Evolution of the Cosmos”
(ChETEC, see http://www.chetec.eu for more details). The ChETEC COST
Action will offer great opportunities (training, networking,
collaborations with both academic and industrial partners) for the
successful candidate.
Applications are invited from
candidates with a solid background in physics or astronomy and should
consist of a cover letter explaining the motivation for seeking a PhD
in theoretical and computational astrophysics and especially the
aforementioned research fields, a statement outlining any research
experience so far (<1 page each), a CV, and a copy of the Bachelor
and Master academic record (exams, theses, and grades). Candidates
should also provide names and e-mail addresses of at least two
references. Applications should be sent as a single PDF file to
georges.meynet@unige.ch
Complete applications received by
15 May 2018 will receive full consideration, but the search will
remain open until the positions are filled. Preliminary inquiries may
be addressed via e-mail to georges.meynet@unige.ch
Included
Benefits:
Generous Salary (~50’000-60’000 CHF),
Standard Swiss Social Security, Accident Insurance, Pension
contributions, Maternal leave and access to family support programs
(see:
http://www.snf.ch/en/funding/supplementary-measures/flexibility-grant/Pages/default.aspx#)
Attention/Comments:
Weblink:
http://www.unige.ch/sciences/astro/en/research/stars/
Email:
georges.meynet@unige.ch
Deadline: 15 May
2018
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