ISSN 1783-3426
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The XMM-Newton view of the yellow
hypergiant IRC +10420 and its surroundings
Suppression
of X-rays from radiative shocks by their thin-shell instability
The
impact of rotation on the line profiles of Wolf-Rayet stars
The
yellow hypergiant HR 5171 A: Resolving a massive interacting binary
in the common envelope phase
Epoch-dependent
absorption line profile variability in lambda Cep
The
VLT-FLAMES Tarantula Survey. XV. VFTS,822: a candidate Herbig B[e]
star at low metallicity
Identification
of red supergiants in nearby galaxies with mid-IR photometry
A
High Angular Resolution Survey of Massive Stars in Cygnus OB2:
Variability of Massive Stars with
Known Spectral Types in the Small Magellanic Cloud Using 8 Years of
OGLE-III Data
Kinematics of massive
star ejecta in the Milky Way as traced by 26Al
The
Wolf-Rayet stars in the Large Magellanic Cloud: A comprehensive
analysis of the WN class
Near-Infrared
Evidence for a Sudden Temperature Increase in Eta Carinae
X-ray
Emission from Eta Carinae near Periastron in 2009 I: A Two State
Solution
The evolution of massive
stars and their spectra I. A non-rotating 60 Msun star from the
zero-age main sequence to the pre-supernova stage
Non-LTE
models for synthetic spectra of type Ia supernovae. III. An
accelerated lambda iteration procedure for the mutual interaction of
strong spectral lines in SN Ia models with and without energy
deposition
Non-LTE models for
synthetic spectra of type Ia supernovae. IV. A modified Feautrier
scheme for opacity-sampled pseudo-continua at high expansion
velocities and application to synthetic SN Ia spectra
X-ray
emission from massive stars in Cyg OB2
A
Chandra Grating Observation of the Dusty Wolf-Rayet Star
WR48a
Optical and infrared
observations of the young SMC "blob" N26 and its
environment
The Wolf-Rayet stars
in M31: I. Analysis of the late-type WN stars
The
VLT-FLAMES Tarantula Survey XVI. The optical+NIR extinction laws in
30 Doradus and the photometric determination of the effective
temperatures of OB stars
Measuring
mass-loss rates and constraining shock physics using X-ray line
profiles of O stars from the Chandra archive
Disk-Loss
and Disk-Renewal Phases in Classical Be Stars II. Contrasting with
Stable and Variable Disks
Rotating
massive O stars with non-spherical 2D winds
Interacting winds in massive
binaries
New Stellar Models - Boon
or Bane?
Closed (original deadline passed):
Research Position at the Astronomical
Institute of the Academy of Sciences of the Czech Republic
Stellar
evolution and asteroseismology of massive stars
Postdoctoral
position in extragalactic stellar spectroscopy
Researcher
position in astrophysics
Open:
Research Professorship in Time-Domain Astronomy of Variable Stars
Magnetism
and Variability in O stars
Why
Galaxies Care About AGB Stars III
This message concerns the published
paper
ApJ, Vol. 781, id.88
announced earlier through
the Massive Star Newsletter.
Following a concrete
question: Data Table 3 was too small to be allowed to publish it as
Machine-Readable Table by ApJ. An electronic version of this Table is
available to the community upon request.
Weblink:
http://adsabs.harvard.edu/abs/2014ApJ...781...88A
Email:
conny.aerts@ster.kuleuven.be
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De Becker M., Hutsemékers D., Gosset, E.
Department
of Astrophysics, Geophysics and Oceanography, University of
Liège
Among evolved massive stars likely in transition to the
Wolf-Rayet phase, IRC +10420 is probably one of the most enigmatic.
It belongs to the category of yellow hypergiants and it is
characterized by quite high mass loss episodes. Even though IRC
+10420 benefited of many observations in several wavelength domains,
it has never been a target for an X-ray observatory. We report here
on the very first dedicated observation of IRC +10420 in X-rays,
using the XMM-Newton satellite. Even though the target is not
detected, we derive X-ray flux upper limits of the order of 1--3
10^-14 erg cm^-2 s^-1 (between 0.3 and 10.0 keV), and we discuss the
case of IRC +10420 in the framework of emission models likely to be
adequate for such an object. Using the Optical/UV Monitor on board
XMM-Newton, we present the very first upper limits of the flux
density of IRC +10420 in the UV domain (between 1800 and 2250 A, and
between 2050 and 2450 A). Finally, we also report on the detection in
this field of 10 X-ray and 7 UV point sources, and we briefly discuss
their properties and potential counterparts at longer
wavelengths.
Reference: 2014, New Astronomy (in
press)
Status: Manuscript has been accepted
Weblink:
http://hdl.handle.net/2268/160591
Comments:
ArXiv link: http://arxiv.org/abs/1401.0707
Email:
debecker@astro.ulg.ac.be
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N. D. Kee^1, S. Owocki^1, A. ud-Doula^2
1.
University of Delaware
2. Penn State Worthington Scranton
We
examine X-rays from radiatively cooled shocks, focusing on how their
thin-shell instability reduces X-ray emission. For 2D simulations of
collision between equal expanding winds, we carry out a parameter
study of such instability as a function of the ratio of radiative vs.
adiabatic-expansion cooling lengths. In the adiabatic regime, the
extended cooling layer suppresses instability, leading to planar
shock compression with X-ray luminosity that follows closely the
expected (Lx ∼ M^2) quadratic scaling with mass-loss rate M . In
the strongly radiative limit, the X-ray emission now follows an
expected linear scaling with mass loss (Lx ∼ M), but the
instability deforms the shock compression into extended shear layers
with oblique shocks along fingers of cooled, dense material. The
spatial dispersion of shock thermalization limits strong X-ray
emission to the tips and troughs of the fingers, and so reduces the
X-ray emission (here by about a factor 1/50) below what is expected
from analytic radiative-shock models without unstable structure.
Between these two limits, X-ray emission can switch between a
high-state associated with extended shock compression, and a
low-state characterized by extensive shear. Further study is needed
to clarify the origin of this “shear mixing reduction factor” in
X-ray emission, and its dependence on parameters like the shock Mach
number.
Reference: MNRAS, In Press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1401.2063
Comments:
Email: dkee@udel.edu
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T. Shenar, W.-R. Hamann, H. Todt
University of
Potsdam
Massive Wolf-Rayet stars are recognized today to be in
a very common, but short, evolutionary phase of massive stars. While
our understanding of Wolf-Rayet stars has increased dramatically over
the past decades, it remains unclear whether rapid rotators are among
them. There are various indications that rapidly rotating Wolf-Rayet
stars should exist. Unfortunately, due to their expanding
atmospheres, rotational velocities of Wolf-Rayet stars are very
difficult to measure. However, recently observed spectra of several
Wolf-Rayet stars reveal peculiarly broad and round emission lines.
Could these spectra imply rapid rotation?
In this work, we
model the effects of rotation on the atmospheres of Wolf-Rayet stars.
We further investigate whether the peculiar spectra of five
Wolf-Rayet stars may be explained with the help of stellar rotation,
infer appropriate rotation parameters, and discuss the implications
of our results. We make use of the Potsdam Wolf-Rayet (PoWR) non-LTE
model atmosphere code. Since the observed spectra of Wolf-Rayet stars
are mainly formed in their expanding atmospheres, rotation must be
accounted for with a 3D integration scheme of the formal integral.
For this purpose,
we assume a rotational velocity field
consisting of an inner co-rotating domain and an outer domain, where
the angular momentum is conserved. We find that rotation can
reproduce the unique spectra analyzed here. However, the inferred
rotational velocities at the stellar surface are large (~200 km/s),
and the inferred co-rotation radii (~10 stellar radii) suggest the
existence of very strong photospheric magnetic fields (~20
kG).
Reference: A&A, accepted
Status: Manuscript
has been accepted
Weblink:
http://arxiv.org/abs/1401.2159
Comments:
Email: shtomer@astro.physik.uni-potsdam.de
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O. Chesneau^1, A. Meilland^1, E. Chapellier^1, F.
Millour^1, A.M. Van Genderen^2, Y. Naz'e^3, N. Smith^4, A. Spang^1,
J.V. Smoker^5, L. Dessart^6, S. Kanaan^7, Ph. Bendjoya^1, M.W.
Feast^8, J.H. Groh^9, A. Lobel^10, N. Nardetto^1, S. Otero^11, R.D.
Oudmaijer^12, A.G. Tekola^8,13, P.A. Whitelock^8, C. Arcos^7, M.
Cur'e^7, L. Vanzi^14
^1 Univ. Nice Sophia-Antipolis, CNRS,
OCA, France, ^2 Leiden Observatory, The Netherlands, ^3 FNRS,
Universit'e de Li`ege, Belgium, ^4 Steward Observatory, USA, ^5
ESO-Chile, ^6 Aix Marseille Universit'e, CNRS, France, ^7 Universidad
de Valpara'iso, Chile, ^8 SAAO + University of Cape Town, South
Africa, ^9 Geneva Observatory, Switzerland, ^10 Royal Observatory of
Belgium, ^11 AAVSO, USA
^12 University of Leeds, UK, ^13 Las
Cumbres Observatory, USA, ^14 Pontificia Universidad Catolica de
Chile.
We initiated long-term optical interferometry
monitoring of the diameters of unstable yellow hypergiants (YHG) with
the goal of detecting both the long-term evolution of their radius
and shorter term formation related to large mass-loss events. We
observed HR5171 A with AMBER/VLTI. We also examined archival
photometric data in the visual and near-IR spanning more than 60
years, as well as sparse spectroscopic data. HR5171A exhibits a
complex appearance. Our AMBER data reveal a surprisingly large star
for a YHG R*=1315+/-260Rsun (~6.1AU) at the distance of 3.6+/-0.5kpc.
The source is surrounded by an extended nebulosity, and these data
also show a large level of asymmetry in the brightness distribution
of the system, which we attribute to a newly discovered companion
star located in front of the primary star. The companion's signature
is also detected in the visual photometry, which indicates an orbital
period of Porb=1304+/-6d. Modeling the light curve with the NIGHTFALL
program provides clear evidence that the system is a contact or
possibly over-contact eclipsing binary. A total current system mass
of 39^{+40}_{-22} solar mass and a high mass ratio q>10 is
inferred for the system. The low-mass companion of HR5171 A is very
close to the primary star that is embedded within its dense wind.
Tight constraints on the inclination and vsini of the primary are
lacking, which prevents us from determining its influence precisely
on the mass-loss phenomenon, but the system is probably experiencing
a wind Roche-Lobe overflow. Depending on the amount of angular
momentum that can be transferred to the stellar envelope, HR5171 A
may become a fast-rotating B[e]/Luminous Blue Variable
(LBV)/Wolf-Rayet star. In any case, HR5171 A highlights the possible
importance of binaries for interpreting the unstable YHGs and for
massive star evolution in general.
Reference: accepted
by A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1401.2628
Comments:
Email: Olivier.Chesneau@oca.eu
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Uuh-Sonda, J.M.$^1$; Rauw, G.$^2$; Eenens, P.$^1$; Mahy,
L.$^2$; Palate, M.$^2$; Gosset, E.$^2$; Flores, C.A.$^1$
1
- Departamento de Astronomia, Universidad de Guanajuato, Mexico
2
- Institut d’Astrophysique et de Geophysique, Liege University,
Belgium
We present the analysis of a multi-epoch spectroscopic
monitoring campaign of the O6Ief star lambda Cep. Previous
observations reported the existence of two modes of non-radial
pulsations in this star. Our data reveal a much more complex
situation. The frequency content of the power spectrum considerably
changes from one epoch to the other. We find no stable frequency that
can unambiguously be attributed to pulsations. The epoch-dependence
of the frequencies and variability patterns are similar to what is
seen in the wind emission lines of this and other Oef stars,
suggesting that both phenomena likely have the same, currently still
unknown, origin.
Reference: Revista Mexicana de
Astronomia y Astrofisica, in press
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1401.2875
Comments:
Email: rauw@astro.ulg.ac.be
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V. M. Kalari (1,2), J. S. Vink (1), P. L. Dufton (2), C. J.
Evans (3), P. R. Dunstall (2), H. Sana (4), J. S. Clark (5), L.
Ellerbroek (6), A. de Koter (6,7), D. J. Lennon (8), W. D. Taylor
(3)
(1) Armagh Observatory, College Hill, Armagh, BT619DG,
UK,
(2) Department of Physcis ,& Astronomy, Queen's
University Belfast, BT71NN, UK ,
(3) UK Astronomy Technology
Centre, Royal Observatory, Edinburgh, Blackford Hill, Edinburgh,
EH93HJ, UK ,
(4) ESA/STScI, 3700 San Martin Drive, Baltimore,
MD21218, USA ,
(5) Department of Physics Astronomy, The Open
University, Walton Hall, Milton Keynes, MK76AA, UK ,
(6)
Astronomical Institute Anton Pannekoek, Amsterdam University, Science
Park 904, 1098XH, Amsterdam, The Netherlands ,
(7) Instituut voor
Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium,
(8) European Space Astronomy Centre, Camino bajo del Castillo,
Villanueva de la Canada, E-28692 Madrid, Spain
We report the
discovery of the B[e] star VFTS 822 in the 30 Doradus star-forming
region of the Large Magellanic Cloud, classified by optical
spectroscopy from the VLT-FLAMES Tarantula Survey and complementary
infrared photometry. VFTS 822 is a relatively low-luminosity (log ? =
4.04 ± 0.25 ?¬ハル)
B8[e] star. In this Letter, we evaluate the evolutionary status of
VFTS 822 and discuss its candidacy as a Herbig B[e] star. If the
object is indeed in the pre-main sequence phase, it would present an
exciting opportunity to measure mass accretion rates at low
metallicity spectroscopically, to understand the effect of
metallicity on accretion rates.
Reference: Astronomy &
Astrophysics Letters
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1401.3149
Comments:
Email: vek@arm.ac.uk
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N. E. Britavskiy, A. Z. Bonanos, A. Mehner, D.
Garcia-Alvarez, J. L. Prieto, N.I. Morrell
National
Observatory of Athens, Greece
The role of episodic mass loss
in massive star evolution is one of the most important open questions
of current stellar evolution theory. Episodic mass loss produces dust
and therefore causes evolved massive stars to be very luminous in the
mid-infrared and dim at optical wavelengths. We aim to increase the
number of investigated luminous mid-IR sources to shed light on the
late stages of these objects. To achieve this we employed mid-IR
selection criteria to identity dusty evolved massive stars in two
nearby galaxies. The method is based on mid-IR colors, using 3.6
{mu}m and 4.5 {mu}m photometry from archival Spitzer Space Telescope
images of nearby galaxies and J-band photometry from 2MASS. We
applied our criteria to two nearby star-forming dwarf irregular
galaxies, Sextans A and IC 1613, selecting eight targets, which we
followed up with spectroscopy. Our spectral classification and
analysis yielded the discovery of two M-type supergiants in IC 1613,
three K-type supergiants and one candidate F-type giant in Sextans A,
and two foreground M giants. We show that the proposed criteria
provide an independent way for identifying dusty evolved massive
stars, that can be extended to all nearby galaxies with available
Spitzer/IRAC images at 3.6 {mu}m and 4.5 {mu}m.
Reference:
A&A in press
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1309.6320
Comments:
8 pages, 4 figures
Email: bonanos@noa.gr
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S. M. Caballero-Nieves (1,10), E. P. Nelan (2), D. R. Gies
(1), D. J. Wallace (3), K. DeGioia-Eastwood (4), A. Herrero (5,6),
W.-C. Jao (1), B. D. Mason (7), P. Massey (8), A. F. J. Moffat (9),
and N. R. Walborn (2)
(1) Center for High Angular
Resolution Astronomy, Department of Physics and Astronomy, Georgia
State University, P.O. Box 4106, Atlanta, GA 30302-4106, USA
(2)
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore,
MD 21218, USA
(3) Department of Natural Sciences, University of
South Carolina Beaufort, 1 University Boulevard, Bluffton, SC 29909,
USA
(4) Department of Physics and Astronomy, Northern Arizona
University, P.O. Box 6010, Flagstaff, AZ 86011-6010, USA
(5)
Instituto de Astrofísica de Canarias, C/ Via Lactea s/n, E-38280 La
Laguna, Spain
(6) Departamento de Astrofísica, Universidad de La
Laguna, Avda. Astrofísico Francisco Sánchez, 2, E-38205 La Laguna,
Spain
(7) U. S. Naval Observatory, 3450 Massachusetts Avenue, NW,
Washington, DC 20392-5420, USA
(8) Lowell Observatory, 1400 West
Mars Hill Road, Flagstaff, AZ 86001, USA
(9) Département de
physique, Université de Montréal, CP 6128, Succ. Centre-Ville,
Montréal, QC H3C 3J7, Canada
(10) Current Address: Department of
Physics and Astronomy University of Sheffield, Hounsfield Road,
Sheffield S3 7RH, UK.
We present results of a high angular
resolution survey of massive OB stars in the Cygnus OB2 association
that we conducted with the fine guidance sensor 1R (FGS1r) on the
Hubble Space Telescope. FGS1r is able to resolve binary systems with
a magnitude difference delta-V < 4 down to separations as small as
0.''01. The sample includes 58 of the brighter members of Cyg OB2,
one of the closest examples of an environment containing a large
number of very young and massive stars. We resolved binary companions
for 12 targets and confirmed the triple nature of one other target,
and we offer evidence of marginally resolved companions for two
additional stars. We confirm the binary nature of 11 of these systems
from complementary adaptive optics imaging observations. The overall
binary frequency in our study is 22% to 26% corresponding to orbital
periods ranging from 20 to 20,000 yr. When combined with the known
short-period spectroscopic binaries, the results support the
hypothesis that the binary fraction among massive stars is >60%.
One of the new discoveries is a companion to the hyper giant star MT
304 = Cyg OB2-12, and future measurements of orbital motion should
provide mass estimates for this very luminous star.
Reference:
AJ, 147, 40
Status: Manuscript has been accepted
Weblink:
http://stacks.iop.org/1538-3881/147/40
Comments:
Email: s.caballero@shef.ac.uk
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M. Kourniotis, A.Z. Bonanos, I. Soszynski, R. Poleski, G.
Krikelis, A. Udalski, M.K. Szymanski, M. Kubiak, G. Pietrzynski, L.
Wyrzykowski, K. Ulaczyk, S. Kozlowski, P. Pietrukowicz
IAASARS,
National Observatory of Athens, Greece & Section of Astrophysics,
Astronomy and Mechanics, Faculty of Physics, University of Athens,
Greece.
We present a variability study of 4646 massive stars
in the Small Magellanic Cloud (SMC) with known spectral types from
the catalog of Bonanos et al. (2010) using the light curves from the
OGLE-III database. The goal is to exploit the time domain information
available through OGLE-III to gain insight into the processes that
govern the evolution of massive stars. This variability survey of
massive stars with known spectral types is larger than any previous
survey by a factor of 7. We find that 60% of our sample (2766 stars)
show no significant variability and 40% (1880 stars) exhibit
variability distributed as follows: 807 stars display low-amplitude
stochastic variability with fluctuations in I-band of up to 0.05 mag,
443 stars present irregular variability of higher amplitude (76% of
these are reported as variables for the first time), 205 are
eclipsing binaries (including 101 newly discovered systems), 50 are
candidate rotating variables, 126 are classical Cepheids, 188 stars
exhibit short-term sinusoidal periodicity (P < 3 days) making them
candidate "slowly pulsating B stars" and non-radial Be
pulsators, and 61 periodic stars exhibit longer periods. We
demonstrate the wealth of information provided in the time domain, by
doubling the number of known massive eclipsing binary systems and
identifying 189 new candidate early-type Be and 20 Oe stars in the
SMC. In addition, we find that ~80% of Be stars are photometrically
variable in the OGLE-III time domain and provide evidence that
short-term pulsating stars with additional photometric variability
are rotating close to their break-up velocity.
Reference:
A&A in press.
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1310.5701
Comments:
46 pages, 18 figures, 11 tables.
Email:
mkourniotis@astro.noa.gr
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contents
Kretschmer, Karsten; Diehl, Roland; Krause, Martin;
Burkert, Andreas; Fierlinger, Katharina; Gerhard, Ortwin; Greiner,
Jochen; Wang, Wei
François Arago Centre, APC, Université
Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne
Paris Cité, 10 rue Alice Domon et Léonie Duquet, 75205, Paris Cedex
13, France AND Max-Planck-Institut für extraterrestrische Physik,
Giessenbachstrasse 1, 85741, Garching, Germany)
Context.
Massive stars form in groups and their winds and supernova explosions
create superbubbles up to kpc in size. The fate of their ejecta is of
vital importance for the dynamics of the interstellar medium, for
chemical evolution models, and the chemical enrichment of galactic
halos and the intergalactic medium. However, ejecta kinematics and
the characteristic scales in space and time have not been explored in
great detail beyond ~10 Ka.
Aims: Through measurement of
radioactive 26Al with its decay time constant at ~106 years, we aim
to trace the kinematics of cumulative massive-star and supernova
ejecta independent of the uncertain gas parameters over million-year
time scales. Our goal is to identify the mixing time scale and the
spatio-kinematics of such ejecta from the pc to kpc scale in our
Milky Way.
Methods: We use the SPI spectrometer on the INTEGRAL
observatory and its observations along the Galactic ridge to trace
the detailed line shape systematics of the 1808.63 keV gamma-ray line
from 26Al decay. We determine line centroids and compare these to
Doppler shift expectations from large-scale systematic rotation
around the Galaxy centre, as observed in other Galactic objects.
Results: We measure the radial velocities of gas traced by 26Al,
averaged over the line of sight, as a function of Galactic longitude.
We find substantially higher velocities than expected from Galactic
rotation, the average bulk velocity being ~200 km s-1 larger than
predicted from Galactic rotation. The observed radial velocity spread
implies a Doppler broadening of the gamma-ray line that is consistent
with our measurements of the overall line width. We can reproduce the
observed characteristics with 26Al sources located along the inner
spiral arms, when we add a global blow-out preference into the
forward direction away from arms into the inter-arm region, as is
expected when massive stars are offset towards the spiral-arm leading
edge. With the known connection of superbubbles to the gaseous halo,
this implies angular-momentum transfer in the disk-halo system and
consequently also radial gas flows. The structure of the interstellar
gas above the disk affects how ionizing radiation may escape and
ionize intergalactic gas
Reference: Astronomy and
Astrophysics, Vol 559, A99 (2013)
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/abs/2013A%26A...559A..99K
Comments:
Accepted, and identified as "highlight paper" by
A&A
Email: rod@mpe.mpg.de
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R. Hainich(1), U. Ruehling(1), H. Todt(1), L. M.
Oskinova(1), A. Liermann(2), G. Graefener(3), C. Foellmi, O.
Schnurr(2), W.-R. Hamann(1)
1 - Institut fuer Physik und
Astronomie, Universitaet Potsdam, Germany
2 - Leibniz-Institut
für Astrophysik Potsdam, Germany
3 - Armagh Observatory,
UK
Context: Massive stars, although being important building
blocks of galaxies, are still not fully understood. This holds
especially for Wolf-Rayet stars with their strong mass loss, whose
spectral analysis requires adequate model atmospheres.
Aims:
Following our comprehensive studies of the WR stars in the Milky Way,
we now present spectroscopic analyses of almost all known WN stars in
the Large Magellanic Cloud (LMC).
Methods: For the quantitative
analysis of the wind-dominated emission-line spectra we employ the
Potsdam Wolf-Rayet (PoWR) model atmosphere code. By fitting synthetic
spectra to the observed spectral energy distribution and the
available spectra (ultraviolet and optical), we obtain the physical
properties of 107 stars.
Results: We present the fundamental
stellar and wind parameters for an almost complete sample of WN stars
in the LMC. Among those stars which are putatively single, two
different groups can be clearly distinguished. While 12% of our
sample are more luminous than 10^6 Lsun and contain a significant
amount of hydrogen, 88% of the WN stars, with little or no hydrogen,
populates the luminosity range between log (L/Lsun) = 5.3...5.8.
Conclusions: While the few extremely luminous stars (log (L/Lsun)
> 6), if indeed single stars, descended directly from the main
sequence at very high initial masses, the bulk of WN stars have gone
through the red-supergiant phase. According to their luminosities in
the range of log (L/Lsun) = 5.3...5.8, these stars originate from
initial masses between 20 and 40 Msun. This mass range is similar to
the one found in the Galaxy, i.e. the expected metallicity dependence
of the evolution is not seen. Current stellar evolution tracks, even
when accounting for rotationally induced mixing, still partly fail to
reproduce the observed ranges of luminosities and initial masses.
Moreover, stellar radii are generally larger, and effective
temperatures correspondingly lower, than predicted from stellar
evolution models, probably due to subphotospheric
"inflation".
Reference: A&A,
accepted
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1401.5474
Comments:
17+126 pages, 10+108 figures
Email:
rhainich@astro.physik.uni-potsdam.de
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Andrea Mehner (1), Kazunori Ishibashi (2), Patricia
Whitelock (3,4), Takahiro Nagayama (2), Michael Feast (3,4), Francois
van Wyk (3), and Willem-Jan de Wit (1)
1 - ESO, Alonso de
Cordova 3107, Vitacura, Santiago de Chile, Chile; 2 - Division of
Elementary Particle Physics and Astrophysics, Graduate School of
Science, Nagoya University, Nagoya, 464-8602, Japan; 3 - South
African Astronomical Observatory, PO Box 9, Observatory, South
Africa; 4 - Astronomy, Cosmology and Gravity Centre, Astronomy
Department, University of Cape Town, 7701, Rondebosch, South
Africa
Aims. Eta Car's ultra-violet, optical, and X-ray light
curves and its spectrum suggest a physical change in its stellar wind
over the last decade. It was proposed that the mass-loss rate
decreased by a factor of about 2 in the last 15 years. We complement
these recent results by investigating the past evolution and the
current state of eta Car in the near-infrared (IR).
Methods. We
present JHKL photometry of eta Car obtained at SAAO Sutherland from
2004-2013 with the Mk II photometer at the 0.75-m telescope and JHKs
photometry with SIRIUS at the 1.4-m IRSF telescope from 2012-2013.
The near-IR light curves since 1972 are analyzed.
Results. The
long-term brightening trends in eta Car's JHKL light curves were
discontinuous around the 1998 periastron passage. After 1998, the
star shows excess emission above the extrapolated trend from earlier
dates, foremost in J and H, and the blueward, cyclical progression in
its near-IR colors is accelerated. The near-IR color evolution is
strongly correlated with the periastron passages. After correcting
for the secular trend we find that the color evolution matches an
apparent increase in blackbody temperature of an optically thick
near-IR emitting plasma component from about 3500 to 6000 K over the
last 20 years.
Conclusions. We suggest that the changing near-IR
emission may be caused by variability in optically thick
bremsstrahlung emission. Periastron passages play a key role in the
observed excess near-IR emission after 1998 and the long-term color
evolution. We thus propose as a hypothesis that angular momentum
transfer (via tidal acceleration) during periastron passages leads to
sudden changes in eta Car's atmosphere resulting in a long-term
decrease in the mass-loss rate.
Reference: A&A,
accepted
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1401.4999
Comments:
Email: amehner@eso.org
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Kenji Hamaguchi(1,2), Michael F. Corcoran(1,3), Christopher
Russell(4), Andrew M.T. Pollock(5), Theodore R. Gull(6), Mairan
Teodoro(6,7), Thomas I. Madura(6,8), Augusto Damineli(9), Julian M.
Pittard(10)
(1)CRESST NASA/GSFC, (2)UMBC, (3)USRA,
(4)Hokkai-Gakuen University, (5)ESAC, (6)NASA/GSFC, (7)CNPq, (8)NPP,
(9)Universidade de S~ao Paulo, (10)The University of Leeds
X-ray
emission from the supermassive binary system Eta Carinae declines
sharply around periastron. This X-ray minimum has two distinct phases
- the lowest flux phase in the first ~3 weeks and a brighter phase
thereafter. In 2009, the Chandra X-ray Observatory monitored the
first phase five times and found the lowest observed flux at ~1.9e-12
ergs cm-2 s-1 (3-8 keV). The spectral shape changed such that the
hard band above ~4 keV dropped quickly at the beginning and the soft
band flux gradually decreased to its lowest observed value in ~2
weeks. The hard band spectrum had begun to recover by that time. This
spectral variation suggests that the shocked gas producing the
hottest X-ray gas near the apex of the wind-wind collision (WWC) is
blocked behind the dense inner wind of the primary star, which later
occults slightly cooler gas downstream. Shocked gas previously
produced by the system at earlier orbital phases is suggested to
produce the faint residual X-ray emission seen when the emission near
the apex is completely blocked by the primary wind. The brighter
phase is probably caused by the re-appearance of the WWC plasma,
whose emissivity significantly declined during the occultation. We
interpret this to mean that the X-ray minimum is produced by a hybrid
mechanism of an occultation and a decline in emissivity of the WWC
shock.
Reference: Astrophysical Journal
http://arxiv.org/abs/1401.5870
Status: Manuscript has been
accepted
Weblink:
Comments:
Email:
Kenji.Hamaguchi@nasa.gov
Back to
contents
Jose Groh (1), Georges Meynet (1), Sylvia Ekstrom (1),
Cyril Georgy (2)
(1) Geneva Observatory, Switzerland
(2)
Keele University, UK
For the first time, the interior and
spectroscopic evolution of a massive star is analyzed from the
zero-age main sequence (ZAMS) to the pre-supernova (SN) stage. For
this purpose, we combined stellar evolution models using the Geneva
code and atmospheric models using CMFGEN. With our approach, we were
able to produce observables, such as a synthetic high-resolution
spectrum and photometry, aiding the comparison between evolution
models and observed data. Here we analyze the evolution of a
non-rotating 60 Msun star and its spectrum throughout its lifetime.
Interestingly, the star has a supergiant appearance (luminosity class
I) even at the ZAMS. We find the following evolutionary sequence of
spectral types: O3 I (at the ZAMS), O4 I (middle of the H-core
burning phase), B supergiant (BSG), B hypergiant (BHG), hot luminous
blue variable (LBV; end of H-core burning), cool LBV (H-shell burning
through the beginning of the He-core burning phase), rapid evolution
through late WN and early WN, early WC (middle of He-core burning),
and WO (end of He-core burning until core collapse). We find the
following spectroscopic phase lifetimes: 3.22e6 yr for the O-type,
0.34e5 yr (BSG), 0.79e5 yr (BHG), 2.35e5 yr (LBV), 1.05e5 yr (WN),
2.57e4 yr (WC), and 3.80e4 yr (WO). Compared to previous studies, we
find a much longer (shorter) duration for the early WN (late WN)
phase, as well as a long-lived LBV phase. We show that LBVs arise
naturally in single-star evolution models at the end of the MS when
the mass-loss rate increases as a consequence of crossing the
bistability limit. We discuss the evolution of the spectra,
magnitudes, colors, and ionizing flux across the star's lifetime, and
the way they are related to the evolution of the interior. We find
that the absolute magnitude of the star typically changes by ~6 mag
in optical filters across the evolution, with the star becoming
significantly fainter in optical filters at the end of the evolution,
when it becomes a WO just a few 10e4 years before the SN explosion.
We also discuss the origin of the different spectroscopic phases
(i.e., O-type, LBV, WR) and how they are related to evolutionary
phases (H-core burning, H-shell burning, He-core burning)
Reference:
A&A, in press
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1401.7322
Comments:
Email: jose.groh@unige.ch
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A. W. A. Pauldrach, T. L. Hoffmann, and P. J. N.
Hultzsch
Universitaets-Sternwarte Muenchen, Scheinerstr.
1, 81679 M¨unchen, Germany
Context. In type Ia supernova
(SNIa) envelopes a huge number of lines of different elements overlap
within their thermal Doppler widths, and this problem is exacerbated
by the circumstance that up to 20% of these lines can have a line
optical depth greater than 1. The stagnation of the lambda iteration
in such optically thick cases is one of the fundamental physical
problems inherent in the iterative solution of the non-LTE problem,
and the failure of a lambda iteration to converge is a point of
crucial importance whose physical significance must be understood
completely.
Aims. We discuss a general problem related to
radiative transfer under the physical conditions of supernova ejecta
that involves a failure of the usual non-LTE iteration scheme to
converge when multiple strong opacities belonging to different
physical transitions come together, similar to the well-known
situation where convergence is impaired even when only a single
process attains large optical depths. The convergence problem is
independent of the chosen frequency and depth grid spacing,
independent of whether the radiative transfer is solved in the
comoving or observer’s frame, and independent of whether a common
complete-linearization scheme or a conventional accelerated lambda
iteration (ALI) is used. The problem appears when all millions of
line transitions required for a realistic description of SNIa
envelopes are treated in the frame of a comprehensive non-LTE model.
The only way out of this problem is a complete-linearization approach
which considers all ions of all elements simultaneously, or an
adequate generalization of the established ALI technique which
accounts for the mutual interaction of the strong spectral lines of
different elements and which thereby unfreezes the “stuck” state
of the iteration.
Methods. The physics of the atmospheres of SNIa
are strongly affected by the high-velocity expansion of the ejecta,
dominating the formation of the spectra at all wavelength ranges.
Thus, hydrodynamic explosion models and realistic model atmospheres
that take into account the strong deviation from local thermodynamic
equilibrium are necessary for the synthesis and analysis of the
spectra. In this regard one of the biggest challenges we have found
in the modeling of the radiative transfer in SNIa is the fact that
the radiative energy in the UV has to be transferred only via
spectral lines into the optical regime in order to be able to leave
the ejecta. However, convergence of the model toward a state where
this is possible is impaired when using the standard procedures. We
report on improvements in our approach of computing synthetic spectra
for SNIa with respect to (i) an improved and sophisticated treatment
of many thousands of strong lines that interact intricately with the
“pseudo-continuum” formed entirely by Doppler-shifted spectral
lines, (ii) an improved and expanded atomic database, and (iii) the
inclusion of energy deposition within the ejecta arising from the
radioactive decay of mostly 56Ni and 56Co.
Results. We show that
an ALI procedure we have developed for the mutual interaction of
strong spectral lines appearing in the atmospheres of SNe Ia solves
the longstanding problem of transferring the radiative energy from
the UV into the optical regime. Our new method thus constitutes a
foundation for more refined models, such as those including energy
deposition. In this regard we further show synthetic spectra obtained
with various methods adopted for the released energy and compare them
to observations. In detail we discuss applications of the diagnostic
technique by example of a standard type Ia supernova, where the
comparison of calculated and observed spectra revealed that in the
early phases the consideration of the energy deposition within the
spectrum-forming regions of the ejecta does not qualitatively alter
the shape of the emergent spectra.
Conclusions. The results of
our investigation lead to an improved understanding of how the shape
of the spectrum changes radically as function of depth in the ejecta,
and show how different emergent spectra are formed as a result of the
particular physical properties of SNe Ia ejecta and the resulting
peculiarities in the radiative transfer. This knowledge provides an
important insight into the process of extracting information from
observed SNIa spectra, since these spectra are a complex product of
numerous unobservable SNIa spectral features which are thus analyzed
in parallel to the observable SNIa spectral features.
Reference:
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1307.3067v2
Comments:
27 pages
Email: uh10107@usm.lmu.de
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T. L. Hoffmann, D. N. Sauer, A. W. A. Pauldrach, P. J. N.
Hultzsch
Universitaets-Sternwarte Muenchen, Scheinerstr.
1, 81679 Muenchen, Germany
Context. Type Ia supernovae (SN Ia)
have become an invaluable cosmological tool as their exceptional
brightness makes them observable even at very large distances (up to
redshifts around z~1). To investigate possible systematic differences
between local and distant SN Ia requires detailed models whose
synthetic spectra can be compared to observations, and in which the
solution of the radiative transfer is a key ingredient. One commonly
employed method is the Feautrier scheme, which is generally very
robust, but which can yield wrong results under certain conditions
that frequently occur in the modelling of supernova ejecta or even in
the radiatively driven expanding atmospheres of hot stars.
Methods.
We use a sophisticated model atmosphere code which takes into account
the non-LTE effects and high velocity gradients that strongly affect
the physics of SN Ia atmospheres at all wavelengths to simulate the
formation of SN Ia spectra by the thousands of strong spectral lines
which intricately interact with the "pseudo-continuum"
formed entirely by these Doppler-shifted lines themselves. We focus
to an investigation of the behavior of the Feautrier scheme under
these conditions.
Results. Synthetic spectra of SN Ia, a complex
product of computer models replicating numerous physical processes
that determine the conditions of matter and radiation in the ejecta,
are affected by large spatial jumps of the line-dominated opacities
and source functions for which the application of even
well-established methods may harbor certain pitfalls. We analyze the
conditions that can lead to a breakdown of conventional procedures
and we derive for the Feautrier radiative transfer solver a modified
description which yields more accurate results in the given
circumstances.
Reference: A&A
Status: Manuscript
has been accepted
Weblink:
http://arxiv.org/abs/1307.3105
Comments:
11 pages
Email: hoffmann@usm.lmu.de
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G. Rauw (1), Y. Naze (1), N.J. Wright (2), J.J. Drake (2),
M.G. Guarcello (2), R.K. Prinja (3), L.W. Peck (3), J.F. Albacete
Colombo (4), A. Herrero (5), H.A. Kobulnicky (6), S. Sciortino (7),
J.S. Vink (8)
(1) - Institut d’Astrophysique &
Geophysique, University of Liege, Belgium
(2) - Smithsonian
Astrophysical Observatory, Cambridge, USA
(3) - Department of
Physics & Astronomy, University College London, United Kingdom
(4) - Centro regional Zona Atlantica, Universidad Nacional del
Comahue, Viedma, Argentina
(5) - Instituto de Astrofısica de
Canarias, Universidad de La Laguna, La Laguna, Spain
(6) -
Department of Physics & Astronomy, University of Wyoming,
Laramie, USA
(7) - INAF - Osservatorio Astronomico di Palermo,
Italy
(8) - Armagh Observatory, College Hill, Armagh, Northern
Ireland
We report on the analysis of the Chandra-ACIS data of
O, B and WR stars in the young association Cyg OB2. X-ray spectra of
49 O-stars, 54 B-stars and 3 WR-stars are analyzed and for the
brighter sources, the epoch dependence of the X-ray fluxes is
investigated. The O-stars in Cyg,OB2 follow a well-defined scaling
relation between their X-ray and bolometric luminosities:
log(Lx/Lbol) = -7.2 +/- 0.2. This relation is in excellent agreement
with the one previously derived for the Carina OB1 association.
Except for the brightest O-star binaries, there is no general X-ray
overluminosity due to colliding winds in O-star binaries. Roughly
half of the known B-stars in the surveyed field are detected, but
they fail to display a clear relationship between Lx and Lbol. Out of
the three WR stars in Cyg OB2, probably only WR144 is itself
responsible for the observed level of X-ray emission, at a very low
log(Lx/Lbol) = -8.8 +/- 0.2. The X-ray emission of the other two
WR-stars (WR145 and 146) is most probably due to their O-type
companion along with a moderate contribution from a wind-wind
interaction zone.
Reference: Accepted for an ApJS
Special Issue devoted to the Chandra Cygnus OB2 Legacy Survey
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1401.8098
Comments:
Email: rauw@astro.ulg.ac.be
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Svetozar A. Zhekov, Marc Gagne and Stephen L.
Skinner
Space Research and Technology Institute, Sofia,
Bulgaria; Department of Geology and Astronomy, West Chester
University, West Chester, Pennsylvania, USA; CASA, University of
Colorado, Boulder, Colorado, USA
We present results of a
Chandra High Energy Transmission Grating (HETG) observation of the
carbon-rich Wolf-Rayet (WR) star WR48a. These are the first
high-resolution spectra of this object in X-rays. Blue-shifted
centroids of the spectral lines of about -360 km/s and line widths of
1000 - 1500 km/s (FWHM) were deduced from the analysis of the line
profiles of strong emission lines. The forbidden line of Si XIII is
strong and not suppressed, indicating that the rarefied 10-30 MK
plasma forms far from strong sources of far-UV emission, most likely
in a wind collision zone. Global spectral modeling showed that the
X-ray spectrum of WR48a suffered higher absorption in the October
2012 Chandra observation compared to a previous January 2008
XMM-Newton observation. The emission measure of the hot plasma in
WR48a decreased by a factor ~ 3 over the same period of time. The
most likely physical picture that emerges from the analysis of the
available X-ray data is that of colliding stellar winds in a wide
binary system with an elliptical orbit. We propose that the unseen
secondary star in the system is another WR star or perhaps a luminous
blue variable.
Reference: The Astrophysical
Journal
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1402.1280
Comments:
Email: zhekovs@jila.colorado.edu
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G. Testor (1), M. Heydari-Malayeri (1), C.H. R. Chen (2,3),
J.L. Lemaire (1,4) M. Sewilo (5,6), S. Diana (4)
1 LERMA,
UMR 8112 du CNRS, Observatoire de Paris, 92195 Meudon, France
2
Department of Astronomy, University of Virginia , PO Box 400325,
Charlottesville, VA 22904, USA
3 Max-Planck-Institut fur
Radioastronomie, D-53121 Bonn, Germany
4 Universit'e de
Cergy-Pontoise, 95031 Cergy Cedex, France
5 The Johns Hopkins
University, Department of Physics and Astronomy, 366 Bloomberg
Center, 3400 N. Charles Street, Baltimore, MD 21218, USA
6
Space Science Institute, 4750 Walnut St. Suite 205, Boulder, CO
80301, USA
High-excitation compact HII regions of the
Magellanic Clouds are sites of recent massive star formation in low
metallicity environments.
Detailed study of these regions and
their environments using high-spatial resolution observations is
necessary to better understand massive star formation, which is still
an unsolved problem. We aim at a detailed study of the Small
Magellanic Cloud compact HII region N26, which is only $sim$4"
in diameter.
This study is based on high spatial resolution
imaging ($sim$ 0".1-0".3) in JHKs and $L'$ bands, using the
VLT equipped with the NAOS adaptive optics system. A larger region
($sim$ 50 $times$ 76 pc) was also imaged at medium-spatial
resolution, using the ESO 2.2m telescope in optical wavelengths. We
also used the textit{JHKs} archival data from the IRSF survey and the
textit{Spitzer} Space Telescope SAGE-SMC survey.
Our
high-resolution textit{JHKs} data of the compact high-excitation HII
region N26 reveal a new, bright component (C) between the two already
known optical components A and B. Components A and C are resolved
into several stars. Component A is the main ionization source of N26
and coincides with the radio continuum source B0046-7333. A new
compact HII region with very faint oiii $lambda$5007 emission is
discovered. In the mid-IR, our field resembles a shell formed by
filaments and dust clumps, coinciding with the molecular cloud SMCB2.
N22, located in the center of the shell, is the most excited HII
region of the complex and seems to have created a cavity in SMCB2. We
derive nebular parameters from spectra, and using color-magnitude and
color-color diagrams, we identify stellar sources that show
significant near-IR excess emission, in order to identify the best
YSO candidates.
Reference: Astronomy and
Astrophysics
Status: Manuscript has been accepted
Weblink:
http://aramis.obspm.fr/~heydari/n26-fin.pdf
Comments:
Email: gerard.testor@obspm.fr
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Andreas Sander, Helge Todt, Rainer Hainich, Wolf-Rainer
Hamann
Institut fuer Physik und Astronomie, Universitaet
Potsdam, Germany
CONTEXT: Comprehensive studies of Wolf-Rayet
stars were performed in the past for the Galactic and the LMC
population. The results revealed significant differences, but also
unexpected similarities between the WR populations of these different
galaxies. Analyzing the WR stars in M31 will extend our understanding
of these objects in different galactic environments.
AIMS: The
present study aims at the late-type WN stars in M31. The stellar and
wind parameters will tell about the formation of WR stars in other
galaxies with different metallicity and star formation histories. The
obtained parameters will provide constraints to the evolution of
massive stars in the environment of M31.
METHODS: We used the
latest version of the Potsdam Wolf-Rayet model atmosphere code to
analyze the stars via fitting optical spectra and photometric data.
To account for the relatively low temperatures of the late WN10 and
WN11 subtypes, our WN models have been extended into this temperature
regime.
RESULTS: Stellar and atmospheric parameters are derived
for all known late-type WN stars in M31 with available spectra. All
of these stars still have hydrogen in their outer envelopes, some of
them up to 50% by mass. The stars are located on the cool side of the
zero age main sequence in the Hertzsprung-Russell diagram, while
their luminosities range from 10^5 to 10^6 Lsun. It is remarkable
that no star exceeds 10^6 Lsun.
CONCLUSIONS: If formed via
single-star evolution, the late-type WN stars in M31 stem from an
initial mass range between 20 and 60 Msun. From the very late-type
WN9-11 stars, only one star is located in the S Doradus instability
strip. We do not find any late-type WN stars with the high
luminosities known in the Milky Way.
Reference: A&A,
in Press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1402.2282
Comments:
11+11 pages, 13+18 figures
Email:
ansander@uni-potsdam.de
Back to
contents
J. Maíz Apellániz, C. J. Evans, R. H. Barbá, G.
Gräfener, J. M. Bestenlehner, P. A. Crowther, M. García, A.
Herrero, H. Sana, S. Simón-Díaz, W. D. Taylor, J. Th. van Loon, J.
S. Vink, and N. R. Walborn
IAA-CSIC, UKATC, ULS, AO, US,
CAB, IAC, STScI, IAC, UKATC, KU, AO, and STScI
Context: The
commonly used extinction laws of Cardelli et al. (1989) have
limitations that, among other issues, hamper the determination of the
effective temperatures of O and early B stars from optical+NIR
photometry.
Aims: We aim to develop a new family of extinction
laws for 30 Doradus, check their general applicability within that
region and elsewhere, and apply them to test the feasibility of using
optical+NIR photometry to determine the effective temperature of OB
stars.
Methods: We use spectroscopy and NIR photometry from the
VLT-FLAMES Tarantula Survey and optical photometry from HST/WFC3 of
30 Doradus and we analyze them with the software code CHORIZOS using
different assumptions such as the family of extinction laws.
Results: We derive a new family of optical+NIR extinction laws
for 30 Doradus and confirm its applicability to extinguished Galactic
O-type systems. We conclude that by using the new extinction laws it
is possible to measure the effective temperatures of OB stars with
moderate uncertainties and only a small bias, at least up to
E(4405-5495) ~ 1.5 mag.
Reference: Accepted in
A&A
Status: Manuscript has been accepted
Weblink:
http://jmaiz.iaa.es/files/MaízApellánizetal14.pdf
Comments:
Email: jmaiz@iaa.es
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David H. Cohen(1), Emma E. Wollman(1,2), Maurice A.
Leutenegger(3,4), Jon O. Sundqvist(5,6), Alex W. Fullerton(7), Janos
Zsarg'{o}(8), Stanley P. Owocki(5)
(1) Swarthmore College,
(2) Caltech, (3) NASA/GSFC, (4) CRESST and UMBC, (5) Bartol/U.
Delaware, (6) Munich, (7) STScI, (8) IPN
We quantitatively
investigate the extent of wind absorption signatures in the X-ray
grating spectra of all non-magnetic, effectively single O stars in
the Chandra archive via line profile fitting. Under the usual
assumption of a spherically symmetric wind with embedded shocks, we
confirm previous claims that some objects show little or no wind
absorption. However, many other objects do show asymmetric and blue
shifted line profiles, indicative of wind absorption. For these
stars, we are able to derive wind mass-loss rates from the ensemble
of line profiles, and find values lower by an average factor of 3
than those predicted by current theoretical models, and consistent
with H-alpha if clumping factors of f_cl ~ 20 are assumed. The same
profile fitting indicates an onset radius of X-rays typically at r ~
1.5 Rstar, and terminal velocities for the X-ray emitting wind
component that are consistent with that of the bulk wind. We explore
the likelihood that the stars in the sample that do not show
significant wind absorption signatures in their line profiles have at
least some X-ray emission that arises from colliding wind shocks with
a close binary companion. The one clear exception is zeta Oph, a
weak-wind star that appears to simply have a very low mass-loss rate.
We also reanalyse the results from the canonical O supergiant zeta
Pup using a solar-metallicity wind opacity model and find Mdot = 1.8
X 10^{-6} solar masses per year, consistent with recent
multi-wavelength determinations.
Reference: Monthly
Notices of the Royal Astronomical Society
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1401.7995
Comments:
Email: dcohen1@swarthmore.edu
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Zachary H. Draper(1,2), John P. Wisniewski(3), Karen S.
Bjorkman(4), Marilyn R. Meade(5), Xavier Haubois(6,7), Bruno C.
Mota(6), Alex C. Carciofi(6), Jon E. Bjorkman(4)
(1)
University of Victoria; (2) HIA-NRC Canada; (3) University of
Oklahoma; (4) University of Toledo; (5) University of Wisconsin; (6)
Universitaria de Sao Paulo; (7) University of Sydney
Recent
observational and theoretical studies of classical Be stars have
established the utility of polarization color diagrams (PCD) in
helping to constrain the time-dependent mass decretion rates of these
systems. We expand on our pilot observational study of this
phenomenon, and report the detailed analysis of a long-term
(1989-2004) spectropolarimetric survey of 9 additional classical Be
stars, including systems exhibiting evidence of partial
disk-loss/disk-growth episodes as well as systems exhibiting
long-term stable disks. After carefully characterizing and removing
the interstellar polarization along the line of sight to each of
these targets, we analyze their intrinsic polarization behavior. We
find that many steady-state Be disks pause at the top of the PCD, as
predicted by theory. We also observe sharp declines in the Balmer
jump polarization for later spectral type, near edge-on steady-state
disks, again as recently predicted by theory, likely caused when the
base density of the disk is very high, and the outer region of the
edge-on disk starts to self absorb a significant number of Balmer
jump photons. The intrinsic V-band polarization and polarization
position angle of gamma Cas exhibits variations that seem to phase
with the orbital period of a known one-armed density structure in
this disk, similar to the theoretical predictions of Halonen &
Jones. We also observe stochastic jumps in the intrinsic polarization
across the Balmer jump of several known Be+sdO systems, and speculate
that the thermal inflation of part of the outer region of these disks
could be responsible for producing this observational phenomenon.
Finally, we estimate the base densities of this sample of stars to be
between ~8x10^{-11} to ~4 times 10^{-12} g cm^{-3} during quasi
steady state periods given there maximum observed
polarization.
Reference: ApJ, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1402.5240
Comments:
Email: wisniewski@ou.edu
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Patrick E. Müller (1,2), Jorick
S. Vink (1)
(1) Armagh Observatory, Armagh,
Northern-Ireland, UK,
(2) School of Physical and Geographical
Sciences, Keele University, Staffordshire, UK
We present
solutions for the velocity field and mass-loss rates for 2D
axisymmetric outflows, as well as for the case of mass accretion
through the
use of the Lambert W-function. For the case of a
rotating radiation-driven wind
the velocity field is obtained
analytically using a parameterised description
of the line
acceleration that only depends on radius r at any given latitude
theta. The line acceleration g(r) is obtained from Monte-Carlo
multi-line
radiative transfer calculations. The critical/sonic
point of our equation of
motion varies with latitude theta.
Furthermore, an approximate analytical
solution for the
supersonic flow of a rotating wind is derived, which is found
to
closely resemble the exact solution. For the simultaneous solution of
the
mass-loss rate and velocity field, we use the iterative
method of our 1D method
extended to the non-spherical 2D case. We
apply the new theoretical expressions
with our iterative method
to the stellar wind from a differentially rotating 40
M_sun O5-V
main sequence star as well as to a 60 M_sun O-giant star,
and we
compare our results to previous studies that are extensions of the
Castor et al. (1975, ApJ, 195, 157) CAK formalism. Next, we
account for the
effects of oblateness and gravity darkening. Our
numerical results predict an
equatorial decrease of the mass-loss
rate, which would imply that
(surface-averaged) total mass-loss
rates are lower than for the spherical 1D
case, in contradiction
to the Maeder & Meynet (2000, A&A, 361, 159) formalism
that
is oftentimes employed in stellar evolution calculations for rotating
massive stars. To clarify the situation in nature we discuss
observational
tests to constrain the shapes of large-scale 2D
stellar winds.
Reference: A&A, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1402.5929
Comments:
20 pages, 4 figures, 7 tables
Email:
p.e.mueller@gmx.com
Back to contents
Gregor Rauw
Institut d’Astrophysique et de
Geophysique, Liege University, Belgium
Massive stars feature
highly energetic stellar winds that interact whenever two such stars
are bound in a binary system. The signatures of these interactions
are nowadays found over a wide range of wavelengths, including the
radio domain, the optical band, as well as X-rays and even
gamma-rays. A proper understanding of these effects is thus important
to derive the fundamental parameters of the components of massive
binaries from spectroscopic and photometric observations.
Reference:
Proceedings of the conference "Setting a new standard in the
analysis of binary stars", Leuven, Sept 2013, EAS Publication
Series, in press
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1401.3508
Comments:
Email: rauw@astro.ulg.ac.be
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Claus Leitherer
STScI
The
impact of new stellar evolution models with rotation on the
predictions of population synthesis models is discussed. Massive
rotating stars have larger convective cores than their non-rotating
counterparts, and their outer layers are chemically enriched due to
increased mixing. Together, these two effects lead to hotter and more
luminous stars, in particular during later evolutionary phases. As a
result, stellar populations containing massive stars are predicted to
become more luminous for a given mass and to emit more ionizing
photons. Depending on the assumed rotation velocity, rotation causes
profound changes in the properties of young stellar populations.
These changes are most noticeable at later evolutionary phases and at
shorter wavelengths of the spectral energy distribution. Most
strikingly, the Lyman continuum luminosity increases by up to a
factor of five in O- and Wolf-Rayet stars. Care is required when
comparing these models to observations, and some fine-tuning of the
models is still required before recalibrations of star-formation
indicators should be attempted.
Reference: Proc.
"Massive Young Star Clusters Near and Far: From the Milky Way to
Re-ionization", eds. D. Rosa, D. Mayya, & E. Terlevich,
Puebla (2014)
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1402.0824
Comments:
Email: leitherer@stsci.edu
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(original deadline passed)
Jiri Kubat
Astronomical Institute
251 65
Ondrejov
Czech Republic
The Astronomical Institute of the
Academy of Sciences of the Czech Republic (www.asu.cas.cz) opens one
temporary position in its Stellar department in the field of NLTE
radiative transfer to work on a project "Transfer of polarized
radiation in stellar atmospheres". The applicant is expected to
have experience in the field of the proposed project and to have a
university degree, preferably PhD, at the time of arrival.
The
Stellar Department of the Astronomical Institute
(http://www.asu.cas.cz) is located on the observatory campus in
Ondrejov, which is situated approximately 30 km south-east of Prague.
The stellar department (http://stelweb.asu.cas.cz) operates a
2m telescope with a coude spectrograph, which is suitable for studies
of bright objects (e.g., B stars, hot subdwarfs). Czech Republic is a
member state of both ESO and ESA, and has access to ESO facilities.
The department includes about a dozen active researchers, with a
total of about 60 scientists working at the Astronomical Institute.
The department offers excellent computing facilities, running under
Linux. Researchers of the stellar department also have free access to
the computer cluster (http://wave.asu.cas.cz/ocas/).
The
salary will be based on the standard domestic scale. The starting
date is as soon as possible and the appointment is initially for 1
year. Further extension will be possible upon satisfactory scientific
results, publication output, and availability of funding.
The
candidates should send their applications (list of publications,
curriculum vitae, and summary of their research work) and arrange two
letters of recommendation to be sent to Dr. J. Kubat, Astronomical
Institute, Fricova 298, 251 65 Ondrejov, Czech Republic; (phone +420
323620328, fax +420 323620250), preferrably via e-mail
kubat@sunstel.asu.cas.cz. Applications should be received before 20th
January 2014.
Attention/Comments:
Weblink:
http://www.asu.cas.cz/news/497_konkurz-na-misto-post-doktoranda-ve-stelarnim-oddeleni/
Email:
kubat@sunstel.asu.cas.cz
Deadline: 20th January
2014
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Marc-Antoine Dupret
Department of Astrophysics,
Geophysics and Oceanography
Liege University
Allee du 6 Aout,
17, 4000 Liege, Belgium
The group ASTA (Theoretical Stellar
Astrophysics and Asteroseismology) of the University of Liège,
Belgium offers a postdoctoral grant of 18 months to work on stellar
evolution and asteroseismology of massive stars (see details below).
The postdoc should begin between April and December 2014. The
administrative eligibility criterium for this postdoctoral grant
requires that the candidate must have worked more than 1 year out of
Belgium during the 3 years before this postdoc.
Applicants are
invited to send to Marc-Antoine Dupret (MA.Dupret@ulg.ac.be) before
1st of March:
- A motivation letter
- A CV
- At least two
recommendation letters
Details of the postdoc.
The postdoc is
expected to contribute to the characterization of poorly modeled
processes in massive stars evolution such as the transport of
chemicals and angular momentum, mass loss and exchanges in binaries,
magnetic field, … using e.g. asteroseismology. He/she will work on
the improvement of current numerical codes modeling the evolution and
oscillations of massive stars, and apply these tools by confronting
their predictions to current observations. Candidates are expected to
have a strong experience in the modeling of stellar interiors and
their oscillations.
Attention/Comments:
Weblink:
Email: MA.Dupret@ulg.ac.be
Deadline: 1
March 2014
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Ben Davies
Astrophysics Research Institute
Liverpool John Moores University
Liverpool Science Park ic2
146 Brownlow Hill
Liverpool L3 5RF
United
Kingdom
Applications are invited for a postdoctoral research
position working with Ben Davies at the Astrophysics Research
Institute, Liverpool John Moores University. The aim of the project
is to develop and exploit the use of massive stars as probes of their
host galaxy's abundances and chemical evolution. This will be done
using state-of-the-art model atmospheres in conjunction with near-IR
spectroscopy from the VLT and Keck.
Candidates should have a
PhD in astronomy/astrophysics or a closely related field. Experience
with model atmospheres of cool stars, massive stars, near-infrared
spectroscopy, and automated spectral fitting is especially desirable.
The position is guaranteed for a period of two years in the
first instance, with a possibility of extension subject to funding.
The expected start date will be from 1 April 2014 or as near as
possible. The salary will be in the range £30,727 - £36,661 per
annum
For further information, and to apply for this position
on-line, please visit http://www.ljmu.ac.uk/working-at-ljmu/ and
enter the vacancy reference number 708. Alternatively contact the HR
Department on 0151 904 6130/6131, or email: jobs@ljmu.ac.uk
For
informal inquires, please contact Ben Davies at b.davies@ljmu.ac.uk
LJMU is committed to achieving equality of
opportunity.
Attention/Comments:
Weblink:
http://jobregister.aas.org/job_view?JobID=47667
Email:
b.davies@ljmu.ac.uk
Deadline: 28 Feb 2014
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Anna Aret
Tartu Observatory
Observatooriumi
1
Tõravere 61602
Tartu county
Estonia
Tartu
Observatory (Estonia) invites applications for a researcher position
in astrophysics.
The position is initially for 2 years, but
has good prospects of developing into a long-term career, depending
on the performance of the applicant and on the availability of
funding. The starting time is negotiable, but not earlier than
September 2014.
Applicants must possess a Ph.D. in
astrophysics, or a closely related area, and should have spent at
least 2 years as a postdoc at an internationally recognised research
institution. Candidates with the background in any of the following
topics: early or late evolutionary stages of stars, massive stars,
first stars, stellar population synthesis, chemical enrichment of the
Universe, interstellar matter, intergalactic matter, galaxy formation
and evolution, galactic structure, are especially encouraged to
apply. The successful candidate will be able to conduct his or her
own research as well as participate in the current research at Tartu
Observatory and in the national and European funding schemes.
The
deadline for applications is March 10th 2014. Applications including
a CV, publications list and a statement of research interests (max. 5
pages in total) should be sent to jobs@to.ee.
Tartu
Observatory is among the leading astronomical research institutes in
North-Eastern Europe, its strongest research being carried out in the
field of the large-scale structure of the Universe. It offers a
modern and friendly work environment and conducts research in wide
international collaboration. It currently hosts 20 staff members and
6 PhD students in astrophysics. The new position is intended to
develop the stellar and/or galaxy physics research at Tartu
Observatory to an internationally competitive level through
broadening the collaboration network and through advancing the local
teamwork.
The successful applicant is offered a gross salary
starting from 2000 Euros per month (subject to 21% income tax and 2%
unemployment security tax), depending on his/her work experience.
Further uprating is possible.
Please feel free to send
inquiries to: jobs@to.ee.
Attention/Comments:
Weblink:
http://www.to.ee/en/researcher-position-astrophysics
Email:
jobs@to.ee
Deadline: March 10, 2014
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Conny Aerts
Institute
of Astronomy
KULeuven
Celestijnenlaan 200D
300q Leuven
Belgium
The recent past has seen an immense revolution in
stellar physics, driven by asteroseismic studies performed with the
spacemissionsMOST, CoRoT, and Kepler in combination with ground-based
high-precision spectroscopy and interferometry. This area of research
will get further boosts the coming decade thanks to the K2, Gaia,
TESS, and PLATO space missions as well as ground-based astronomy
projects.
In light of these future activities, we are
searching for a motivated scientist with international recognition in
observational astronomy, and with outstanding capabilities of
independent fundraising and people-management, to apply for a
Research Professorship at KULeuven and join the Institute of
Astronomy to build up his/her own team. Applicants need to have a PhD
degree in astrophysics and at least three years of postdoctoral
experience
by 1 October 2015, which is the starting date of the
position. We expect applicants to be well embedded in international
instrument consortia of relevance for studies of variability of
stars, binaries, clusters, associations, and other time-variable
phenomena in the Milky Way.
A KULeuven Research Professorship
is a tenure-track or a permanent faculty position with a limited
teaching assignment during the first five years, which gradually
increases to a full teaching assignment after ten years.
This
mail is a call for an Expression of Interest (EoI) to apply for such
a position. Interested applicants should send a one-page motivation
letter, the name and email address of three reference persons, and a
full CV as a single PDF file to the director of IoA: Prof. Conny
Aerts:
conny@ster.kuleuven.be, by 22 May 2014.
The staff
members of IoA and the Board of the Department of Physics and
Astronomy will
screen the EoIs, organise interviews, and select
maximally three candidates to go through the university-wide
competition led by the Research Council of KULeuven. The final
decision whether the post will actually be filled depends on the
ranking of candidates across all the faculties of the university.
This decision will be taken in February 2015.
Attention/Comments:
Weblink: http://fys.kuleuven.be/ster
Email:
conny@ster.kuleuven.be
Deadline: 22 May 2014
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* SCIENTIFIC ORGANISING COMMITTEE:
Huib Henrichs
Ed van den Heuvel
Lex Kaper (chair)
Alex de Koter
Tony
Moffat (Montreal, Canada)
Stan Owocki (Delaware, USA)
Gregg
Wade (Kingston, Canada)
* LOCAL ORGANISING COMMITTEE:
Susan
Franzen
Olga Hartoog
Martin Heemskerk
Milena Hoekstra
Lex Kaper (chair)
Bertrand
Lemasle
---
=============================================================================================
FIRST ANNOUNCEMENT
Magnetism and Variability in O stars
17-19 September 2014
Amsterdam (Netherlands)
=============================================================================================
* CONTACT:
email: h.f.henrichs@uva.nl
webpage:
www.astro.uva.nl/ostars/
* IMPORTANT DATES:
First
announcement and pre-registration: December 20th, 2013
Second
announcement and registration: February 15th, 2014
Early payment
fee (275 €): before May 1st, 2014
Regular payment fee (325 €)
Registration closed: June 15th, 2014
Conference: 17 -19
September 2014
* SCIENTIFIC RATIONALE:
For more
than 30 years, spectroscopic observations from space have shown that
wind variability in massive OB stars is a widespread phenomenon. This
variability is not strictly periodic, but cyclic (like sunspots) with
a dominant quasi period that scales with the estimated rotation
period. The underlying cause or trigger of this variability is not
known. The major time-variable wind features likely find their origin
close to, or at the surface and have been suggested to be connected
to non-radial pulsations or bright magnetic star spots.
The
past few years have shown very promising new developments, both
observationally and theoretically. High-precision space-based
photometry reveals rapid variations, incompatible with pulsations,
but consistent with the continuous presence of a multitude of
co-rotating bright spots that live at most a few days. These spots
are suggested to be of magnetic origin and could trigger large-scale
wind variability. Theoretical studies show that magnetic fields can
be generated with a short estimated turnover time in sub-surface
convective layers in massive stars. These may lead to magnetic spots.
Understanding the role of magnetic fields and
variability in O and early B stars is a major challenge in massive
star research. This is the focus of a 3-day conference to be held in
Amsterdam, organized to mark the formal retirement of Huib Henrichs,
who has worked in this field throughout his scientific life.
This
conference will be organized in a somewhat different way. Rather than
having a skeleton with specific names of invited speakers, the
community is invited to come forward on their own accord, thus giving
more people a chance to provide their input. From this, a list of
speakers and topics will be drawn up, with ample time for discussion.
The aim is 25 and 15 min talks (each including discussion) and
posters.
Reference: N/A
Status: Other
Weblink:
http://www.astro.uva.nl/ostars/
Comments:
Email:
h.f.henrichs@uva.nl
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July 28 - August 1, 2014
Venue: Vienna
Stars
are conspicuous components of galaxies, and the sites of the creation
of most chemical elements. Due to their high luminosity and their
production of heavy elements, stars on the Asymptotic Giant Branch
(AGB) play an important role in understanding stellar and galactic
evolution.
This conference aims to build a bridge between AGB
research and its application to the modelling of stellar populations
and the chemical evolution of galaxies and the universe as a whole.
Current developments and challenges on both sides will be discussed
to reach an understanding
of possibilities, limitations, and
needs in both areas, and hence to improve our knowledge about the
role of AGB stars in the context of galaxies. This is another
follow-up meeting to the successful Viennese conferences on similar
topics in 2006 and 2010.
The conference will be hosted by the
Austrian Society for Astronomy and Astrophysics and the Department of
Astrophysics at the University of Vienna. The meeting is supported by
the Robert F. Wing Support Fund at Ohio State University.
This
time the focus of the meeting will be:
1) Complex
Atmospheres: Observation and theoretical understanding
2) Living
together: Binarity, disks, ISM interaction
3) What is left: Dust,
yields, AGBs in the cosmic matter cycle
4) Resolved and
unresolved: AGB star populations in external stellar systems
5)
Perspectives: ALMA, SKA, SOFIA, JWST, VLTI+, ELT
INVITED
SPEAKERS
J. Blommaert, G. Bono, I. Cherchneff, O. Chesneau, A.
Chiavassa, N. Cox, L. Girardi, S. Höfner, R. Izzard, M. Maercker, M.
Marengo, P. Marigo, J. Menzies, S. Mohamed, K. Ohnaka, G. Perrin, A.
Renzini, R. Riffel, R. Schneider, S. Srinivasan, O. Straniero, W.
Vlemmings
SCIENTIFIC ORGANIZING COMMITTEE
H. Olofsson
(chair), I. Cherchneff, M. Groenewegen, S. Höfner, R.M. Humphreys,
A. Jorissen, A. Karakas, F. Kerschbaum (co-chair), T. Lebzelter, C.
Maraston, M. Meixner, B. Plez, P. Whitelock, H. van Winckel, R. Wing,
M. Wittkowski
LOCAL ORGANIZING COMMITTEE
F. Kerschbaum
(chair), J. Hron (co-chair), T. Lebzelter, W. Nowotny, R. Ottensamer,
T. Posch, et al.
MEETING FORMAT
The five sub-topics of
the meeting will be presented and discussed in a series of oral and
poster contributions. The sessions will be centred on invited reviews
supplemented by contributed talks offering opportunities to highlight
exciting new results. Posters will be on display throughout the
meeting.
IMPORTANT DEADLINES
Registration for the
conference is now open via our webpage http://www.univie.ac.at/galagb
including the possibility to submit abstracts for invited and
contributed talks and posters. Registration fee is 200 EUR for early
registration and 240 EUR for late registration.
- Deadline
for abstract submission for contributed talks: April 30, 2014
-
Deadline for applications for financial support: April 30, 2014
-
End of early registration: May 31, 2014
- Deadline for abstract
submission for posters: June 15, 2014
CONTRIBUTIONS
The
SOC will select a limited number of contributions for oral
presentation on the basis of the submitted abstracts. Proposed oral
contributions not selected for the programme can be converted to
poster presentations at the author's discretion. Deadline for the
submission of abstracts for oral contributions is April 30, 2014.
REGISTRATION FEE
The registration fee will be 200 EUR for
early registration and 240 EUR for late registration (after May 31)
and includes welcome reception, coffee breaks and a copy of the
conference proceedings.
CONFERENCE PROCEEDINGS
Proceedings
of the conference will be published in a similar way as 2006
and
2010 (see ASP Conf. Ser. Vols. 378 and 445).
FINANCIAL
ASSISTANCE
Limited support for PhD students and young researchers
will be available.
If you wish to apply for a supporting grant,
please send an email justifying its need to
galagb.astro@univie.ac.at. Students are asked to arrange a letter of
support from their advisor to be sent independently by email.
Deadline for applications is April 30, 2014. Supporting letters have
to be received by that time as well. Applicants will be informed
about the outcome not later than May 20. Please note that the grant
can cover only the registration fee.
CONFERENCE VENUE AND
FACILITIES
The conference will be held at the campus of the
University of Vienna located close to the city centre. Video and
computer display facilities will be available in the lecture room.
WIFI is available to all participants. Special needs can be
accommodated if we are advised well in advance.
SOCIAL
ACTIVITIES
We invite you to our welcome reception on Sunday
evening at the conference venue. Moreover there will be an evening
city walk on Tuesday, a trip to the beautiful Wachau valley including
a ship cruise on Wednesday afternoon and the conference dinner at the
old observatory on Thursday.
CHILDCARE
We are happy to
offer childcare (fee required) during the session hours of our
conference. The kid’s age range must be 3-12 years (from 0 upon
special arrangement).
TRAVEL INFORMATION
Vienna can be
reached
1) By Air: Vienna airport is located about 20 km
south-east of the town. There are shuttle trains and buses to the
city centre at least every half hour. A second airport close to
Vienna is Bratislava which is connected to Vienna by bus (1 hour) or
by boat.
2) By Train: Vienna is connected to any major city
in Europe.
3) By Road: two major European highways (E59, E60)
lead to Vienna.
ABOUT VIENNA
Vienna, the capital of
Austria, with 1.8 million inhabitants, situated on the banks of the
Danube, is a metropolis with a unique charm and flair. The influx of
visitors from all over the world has made Vienna the most popular
urban tourist destination in Austria. Wander along narrow, medieval
alleyways or across imperial squares, view Schönbrunn Palace or the
Imperial Palace (Hofburg) and marvel at the majestic architecture
along the Ring Boulevard. Vienna possesses a lively and vast array of
cultural attractions. The city has been synonymous with music for
centuries, and was home to Mozart, Beethoven, Schubert, Johann
Strauss, Mahler, and Berg. This outstanding musical heritage has been
preserved right to the present day. Down the centuries, Vienna has
always produced and nurtured world-famous artists. The collecting
passion of art-loving rulers and monarchs has made Vienna a treasure
house par excellence. In order to supplement these high cultural
aspects you can visit one of Vienna's famous coffee houses or
traditional wine taverns ("Heurige") and work your way
through famous culinary specialties.
LANGUAGE
The
language of the conference will be English. The spoken language in
Vienna is the Austrian flavour of German. Nevertheless, there should
be no difficulty in finding people with at least a basic knowledge of
English outside the conference.
WEB SITE
Please visit our
website for more information!
www.univie.ac.at/galagb
If
you have any questions, please contact us at
galagb.astro@univie.ac.at
We are looking forward to seeing you in
Vienna in 2014!
Weblink:
http://www.univie.ac.at/galagb
Email:
galagb.astro@univie.ac.at
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