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Gaia Data Access: Usage Scenarios: Request for Input from the Community
A Third Massive Star Component in the
sigma Orionis AB System
The
Photometric and Spectral Evolution of the 2008 Luminous Optical
Transient in NGC 300
A generalised
porosity formalism for isotropic and anisotropic effective opacity
and its effects on X-ray line attenuation in clumped O star
winds
Near- and Mid-Infrared colors
of evolved stars in the Galactic plane. The Q1 and Q2
parameters.
Constraining the
Absolute Orientation of Eta Carinae's Binary Orbit: A 3-D Dynamical
Model for the Broad [Fe III] Emission
Imaging
the time evolution of Eta Carinae's colliding winds with
HST
Recurrent dust formation by WR
48a on a 30-year timescale
He II
4686 in eta Carinae: collapse of the wind-wind collision region
during periastron passage
He II
4686 in eta Carinae: collapse of the wind-wind collision region
during periastron passage
Radiation-driven
winds of hot luminous stars
On the
stability of radiation-pressure-dominated cavities
The
first X-ray survey of Galactic Luminous Blue
Variables
High-resolution X-ray
spectroscopy of the magnetic Of?p star HD148937
Extended
Non-Thermal Emission Possibly Associated with Cyg OB2 #5
A
detailed X-ray investigation of zeta Puppis I. The dataset and some
preliminary results
Predictions for
mass-loss rates and terminal wind velocities of massive O-type
stars
In pursuit of gamma-ray burst
progenitors: the identification of a sub-population of rotating
Wolf-Rayet stars
Stellar envelope
inflation near the Eddington limit. Implications for the radii of
Wolf-Rayet stars and luminous blue variables
Yellow
supergiants as supernova progenitors: an indication of strong mass
loss for red supergiants?
The first
determination of the viscosity parameter in the circumstellar disk of
a Be Star
Grids of stellar models
with rotation
Observational
effects of magnetism in O stars: surface nitrogen abundances
Population Synthesis at the
Crossroads
Wind Models for Very
Massive Stars in the Local Universe
The
theory of stellar winds
The
Physical Basis of the Lx ~ Lbol Empirical Law for O-star X-rays
New
Galactic Candidate Luminous Blue Variables and Wolf-Rayet
Stars
Spectral Identification of
New Galactic cLBV and WR Stars
White paper on Massive Stars for 2010 CASCA/LRP
PhD position in stellar physics at IRSOL, Switzerland. Topic: Planet engulfing scenarios
IR View of
Massive stars - special session at IAU GA
Circumstellar
Dynamics at High Resolution (second announcement)
The
Mass Loss Return from Stars to Galaxies
Joint
Discussion on Very Massive Stars in the Local Universe
Circumstellar
Dynamics at High Resolution
As announced and discussed at
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(http://great.ast.cam.ac.uk/Greatwiki/GreatMeet-20110621) - the Gaia
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Products.
From this, the Gaia DPAC
(http://www.rssd.esa.int/gaia/dpac) will be implementing the systems
required to give access to the rich Gaia data products, through the
Gaia Archive.
The pages at
http://great.ast.cam.ac.uk/Greatwiki/GaiaDataAccess provide public
information as to the nature of Gaia data, the planning and
development of the Gaia archive and access systems, and give a chance
for the community to participate in the development process, through
for instance providing example science scenarios for how they might
wish to utilise and access the data.
If you wish to add your
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please visit http://great.ast.cam.ac.uk/Greatwiki/GaiaDataAccess and
add your data access scenario(s) to one of the topic areas:
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science
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scenarios
Those usage scenarios received before *Thursday 25
Nov 2011* will receive full consideration when developing the
technical requirements for the development of the Gaia Archive.
We
encourage you to add your use cases, and comments, to help us ensure
that the best possible Gaia archive is developed.
Yours,
Nicholas Walton, Timo Prusti, Francois Mignard
(GREAT
co-chair/ Gaia Project Scientist/ DPACE Chair)
Weblink:
http://great.ast.cam.ac.uk/Greatwiki/GaiaDataAccess
Email:
Ronny.Blomme@oma.be
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Simón-Díaz, S.(1,2);
Caballero, J. A.(3); Lorenzo, J.(4)
(1) Instituto de
Astrofísica de Canarias
(2) Departamento de Astrofísica,
Universidad de La Laguna
(3) Centro de Astrobiología (CSIC-INTA)
(4) Departamento de Física, Ingeniería de Sistemas y Teoría de
la Señal, Universidad de Alicante
We report on the detection
of a third massive star component in the σ Orionis AB system,
traditionally considered as a binary system. The system has been
monitored by the IACOB Spectroscopic Survey of Northern Massive Stars
program, obtaining 23 high-resolution FIES@NOT spectra with a time
span of ~2.5 years. The analysis of the radial velocity curves of the
two spectroscopic components observed in the spectra has allowed us
to obtain the orbital parameters of the system, resulting in a high
eccentric orbit (e ~ 0.78) with an orbital period of 143.5 ± 0.5
days. This result implies the actual presence of three stars in the σ
Orionis AB system when combined with previous results obtained from
the study of the astrometric orbit (with an estimated period of ~157
years).
Reference: 2011, ApJ, 742, 55S
Status:
Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2011ApJ...742...55S
Comments:
Email: ssimon@iac.es
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Roberta M. Humphreys (1),
Howard E. Bond (2) Luigi R. Bedin, (3) Alceste Z. Bonanos (4), Kris
Davidson (1), L. A. G. Berto Monard (5), Jose L. Prieto (6), and
Frederick M. Walter (7)
(1) University of Minnesota, (2)
Space Telescope Science Institute, (3) INAF-Osservatorio Astronomico
di Padova, (4) National Observatory of Athens, (5) Klein Karoo
Observatory, S. Africa, (6) Carnegie Observatories S. Africa, (7)
Stony Brook University
The 2008 optical transient in NGC 300
is one of a growing class of intermediate-luminosity transients that
brighten several orders ofmagnitude from a previously optically
obscured state. The origin of their
eruptions is not understood.
Our multi-wavelength photometry and spectroscopy
from maximum
light to more than a year later provide a record of its post-eruption
behavior. We describe its changing spectral-energy distribution, the
evolution of its absorption- and emission line-spectrum, the
development of a bipolar outflow, and the rapid transition from a
dense wind to an optically thin ionized wind. In addition to strong,
narrow hydrogen lines, the F-type
absorption-line spectrum of the
transient is characterized by strong Ca II and [Ca II] emission. The
very broad wings of the Ca II
triplet and the asymmetric [Ca II]
emission lines are due to strong Thomson scattering in the expanding
ejecta. Post-maximum, the hydrogen and Ca II lines developed
double-peaked emission profiles that we attribute to a bipolar
outflow. Between approximately 60 and 100 days after maximum, the
F-type absorption spectrum, formed in its dense wind, weakened and
the wind became transparent to ionizing radiation. We discuss the
probable evolutionary state of the transient and similar objects such
as SN~2008S, and conclude thatthey were most likely post-red
supergiants or post-AGB stars on a blue loop to warmer temperatures
when the eruption occurred. These objects are not LBVs.
Reference:
Asreophysical Journal
Status: Manuscript has been
accepted
Weblink: arXiv:1109.5131
Comments:
Email: roberta@umn.edu
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J.O. Sundqvist(1), S.P. Owocki(1), D.H. Cohen(2), M.A.
Leutenegger(3), R.H.D. Townsend(4)
1 - University of
Delaware, Bartol Research Institute, Newark, Delaware 19716, USA; 2 -
Swarthmore College, Department of Physics and Astronomy, Swarthmore,
Pennsylvania 19081, USA; 3 - CRESST and X-ray Astrophysics Laboratory
NASA/GSFC, Greenbelt, MD 20771, USA; 4 - University of Wisconsin,
Department of Astronomy, Madison, Wisconsin 53706, USA
We
present a generalised formalism for treating the porosity-associated
reduction in continuum opacity that occurs when individual clumps in
a stochastic medium become optically thick. As in previous work, we
concentrate on developing bridging laws between the limits of
optically thin and thick clumps. We consider geometries resulting in
either isotropic or anisotropic effective opacity, and, in addition
to an idealised model in which all clumps have the same local
overdensity and scale, we also treat an ensemble of clumps with
optical depths set by Markovian statistics. This formalism is then
applied to the specific case of bound-free absorption of X-rays in
hot star winds, a process not directly affected by clumping in the
optically thin limit. We find that the Markov model gives
surprisingly similar results to those found previously for the single
clump model, suggesting that porous opacity is not very sensitive to
details of the assumed clump distribution function. Further, an
anisotropic effective opacity favours escape of X-rays emitted in the
tangential direction (the `venetian blind' effect), resulting in a
'bump' of higher flux close to line centre as compared to profiles
computed from isotropic porosity models. We demonstrate how this
characteristic line shape may be used to diagnose the clump geometry,
and we confirm
previous results that for optically thick clumping
to significantly influence X-ray line profiles, very large porosity
lengths, defined as the mean free path between clumps, are required.
Moreover, we present the first X-ray line profiles computed directly
from line-driven instability simulations using a 3-D patch method,
and find that porosity effects from such models also are very small.
This further supports the view that porosity has, at most, a marginal
effect on X-ray line diagnostics in O stars, and therefore that these
diagnostics do indeed provide a good `clumping insensitive' method
for deriving O star mass-loss rates.
Reference: Accepted
for publication in MNRAS. Pre-print available at astro-ph.
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1111.1762
Comments:
Email: jon@bartol.udel.edu
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Maria Messineo, Karl Menten,
Ed Churchwell, and Harm Habing
Max-Planck-Institut f"ur
Radioastronomie (MPIfR), University of Leiden, and University of
Wisconsin-Madison
Mass-loss from evolved stars chemically
enriches the interstellar medium (ISM). Stellar winds from massive
stars and their explosions as supernovae shape the ISM
and
trigger star formation. Studying evolved stars is fundamental for
understanding galaxy formation and evolution at any redshift.
We
aim to establish a photometric classification scheme for Galactic
mass-losing evolved stars (e.g., WR, RSG, and AGB stars) with the
goal of identifying new ones, and subsequently to use these samples
as tracers of Galactic structure.
We searched for counterparts of
known Galactic WR, LBV, RSG, and O-rich AGB stars in the 2MASS,
GLIMPSE, and MSX catalogs, and we analyzed their properties with
near- and mid-infrared color-color diagrams.
We used the Q1
parameter, which is a measure of the deviation from the interstellar
reddening vector in the J-H versus H-Ks diagram, and we defined a new
parameter, Q2, which is a measure of the deviation from the
interstellar reddening vector in the J-Ks versus Ks-[8.0] diagram.
The latter plane enables to distinguish between interstellar and
circumstellar reddening, and to identify stars with circumstellar
envelopes. WR stars and late-type mass-losing stars (AGBs and RSGs)
are distributed in two different regions of the $Q1$ versus Ks-[8.0]
diagram. A sequence of increasing [3.6]-[4.5] and [3.6]-[8.0] colors
with increasing pulsation amplitudes (SRs, Miras, and OH/IR stars) is
found. Spectra of Miras and OH/IR stars have stronger water
absorption at 3.0 um than SR stars or most of the RSGs. Masing Miras
stars have water, but stronger SiO (~ 4 um) and CO2 absorption (~
4.25 um), as
suggested by their [3.6]-[4.5] colors, bluer than
those of non masing stars. A fraction of RSGs (22%) have the bluest
[3.6]-[4.5] colors, but small Q2 values. We propose a new set of
photometric criteria to distinguish among IR bright Galactic stars.
The GLIMPSE catalog is a powerful tool for photometric
classification of Galactic mass-losing evolved stars. Our new
criteria will yield many new RSGs and WRs.
Reference:
Accepted by A&A
Status: Manuscript has been
accepted
Weblink:
http://www.aanda.org/articles/aa/pdf/forth/aa17772-11.pdf
Comments:
Email: messineo@mpifr-bonn.mpg.de
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Thomas I. Madura(1), Theodore
R. Gull(2), Stanley P. Owocki(3), Jose H. Groh(1),
Atsuo T.
Okazaki(4), and Christopher M. P. Russell(3)
1 - Max
Planck Institute for Radio Astronomy, Bonn, Germany
2 -
NASA/GSFC, Greenbelt, MD, USA
3 - University of Delaware, Newark,
DE, USA
4 - Hokkai-Gakuen University, Toyohira-ku, Sapporo,
Japan
We present a three-dimensional (3-D) dynamical model for
the broad [Fe III] emission observed in Eta Carinae using the Hubble
Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS). This
model is based on full 3-D Smoothed Particle Hydrodynamics (SPH)
simulations of Eta Car's binary colliding winds. Radiative transfer
codes are used to generate synthetic spectro-images of [Fe III]
emission line structures at various observed orbital phases and STIS
slit position angles (PAs). Through a parameter study that varies the
orbital inclination i, the PA (theta) that the orbital plane
projection of the line-of-sight makes with the apastron side of the
semi-major axis, and the PA on the sky of the orbital axis, we are
able, for the first time, to tightly constrain the absolute 3-D
orientation of the binary orbit. To simultaneously reproduce the
blue-shifted emission arcs observed at orbital phase 0.976, STIS slit
PA = +38 degrees, and the temporal variations in emission seen at
negative slit PAs, the binary needs to have an i ~ 130 to 145
degrees, theta ~ -15 to +30 degrees, and an orbital axis projected on
the sky at a PA ~ 302 to 327 degrees east of north. This represents a
system with an orbital axis that is closely aligned with the inferred
polar axis of the Homunculus nebula, in 3-D. The companion star, Eta
B, thus orbits clockwise on the sky and is on the observer's side of
the system at apastron. This orientation has important implications
for theories for the formation of the Homunculus and helps lay the
groundwork for orbital modeling to determine the stellar
masses.
Reference: Accepted for publication in MNRAS.
Pre-print available on astro-ph.
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1111.2226
Comments:
Email: tmadura@mpifr-bonn.mpg.de
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Theodore R. Gull, Thomas I.
Madura, Jose H. Groh and Michael F. Corcoran
A: NASA/GSFC,
B,C: MPIR, D: CRESST & NASA/GSFC
We report new HST/STIS
observations that map the high-ionization forbidden line emission in
the inner arcsecond of Eta Car, the first that fully image the
extended wind-wind interaction region of the massive colliding wind
binary. These observations were obtained after the 2009.0 periastron
at orbital phases 0.084, 0.163, and 0.323 of the 5.54-year
spectroscopic cycle. We analyze the variations in brightness and
morphology of the emission, and find that blue-shifted emission (−400
to −200 km s−1) is symmetric and elongated along the
northeast-southwest axis, while the red-shifted emission (+100 to
+200 km s−1) is asymmetric and extends to the north- northwest.
Comparison to synthetic images generated from a 3-D dynamical model
strengthens the 3-D orbital orientation found by Madura et al.
(2011), with an inclination i ≈ 138◦, argument of periapsis ω ≈
270◦, and an orbital axis that is aligned at the same PA on the sky
as the symmetry axis of the Homunculus, 312◦. We discuss the
potential that these and future mappings have for constraining the
stellar parameters of the companion star and the long-term
variability of the system.
Reference: ApJ 743,
L3
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1110.6420
Comments:
Email: Ted.Gull@nasa.gov
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Peredur M. Williams (1),
Karel A. van der Hucht (2,3),
Francois van Wyk (4), Fred Marang
(4), Patricia A. Whitelock (4,5),
Patrice Bouchet (6) and
Diah Y. A. Setia Gunawan (7)
(1) Institute for Astronomy,
University of Edinburgh, Royal Observatory, Edinburgh; (2) Space
Research Organization Netherlands, Utrecht, The Netherlands; (3)
Astronomical Institute `Anton Pannekoek', University of Amsterdam,
The Netherlands; (4) South African Astronomical Observatory, South
Africa; (5) Astronomy, Cosmology and Gravity Centre, Astronomy
Department, University of Cape Town, Rondebosch, South Africa;
(6)
Service d'Astrophysique DSM/IRFU/SAp CEA - Saclay, Gif-sur-Yvette
France; (7) Atacama Large Millimetre/submillimetre Array (ALMA),
Santiago Chile
We present infrared photometry of the WC8
Wolf-Rayet system WR 48a observed with telescopes at ESO, the SAAO
and the AAT between 1982 and 2011 which show a slow decline in dust
emission from the previously reported outburst in 1978--79 until
about 1997, when significant dust emission was still evident. This
was followed by a slow rise, accelerating to reach and overtake the
first (1978) photometry, demonstrating that the outburst observed in
1978--79 was not an isolated event, but that they recur at intervals
of 32+ years. This suggests that WR 48a is a long-period dust maker
and colliding-wind binary (CWB). The locus of WR 48a in the (H-L), K
colour-magnitude diagram implies that the rate of dust formation fell
between 1979 and about 1997 and then increased steadily until 2011.
Superimposed on the long-term variation are secondary (`mini')
eruptions in (at least) 1990, 1994, 1997, 1999 and 2004,
characteristic of relatively brief episodes of additional dust
formation. Spectra show evidence for an Oe or Be companion to the WC8
star, supporting
the suggestion that WR 48a is a binary system
and indicating a system luminosity consistent with the association of
WR 48a and the young star clusters Danks 1 and Danks 2. The range of
dust formation suggests that these stars are in an elliptical orbit
having e ~ 0.6. The size of the orbit implied by the minimum period,
together with the WC wind velocity and likely mass-loss rate, implies
that the post-shock WC wind is adiabatic throughout the orbit -- at
odds with the observed dust formation. A similar conflict is observed
in the `pinwheel' dust-maker WR 112.
Reference:
MNRAS
Status: Manuscript has been accepted
Weblink:
http://www.roe.ac.uk/~pmw/WR48a3.pdf
Comments:
Email: pmw@roe.ac.uk
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M. Teodoro (1), A. Damineli (1), J. I. Arias (2), F. X. de
Araújo (3 and 4), R. H. Barbá (5), M. F. Corcoran (6), M. Borges
Fernandes (3), E. Fernández-Lajús (7 and 8), L. Fraga (9), R. C.
Gamen (7 and 8), J. F. González (5), J. H. Groh (10), J. L. Marshall
(11), P. J. McGregor (12), N. Morrell (13), D. C. Nicholls (12), E.
R. Parkin (12), C. B. Pereira (3), M. M. Phillips (13), G. R.
Solivella (7 and 8), J. E. Steiner (1), M. Stritzinger (14 and 15),
I. Thompson (16), C. A. O. Torres (17), M. A. P. Torres (18 and 19),
M. I. Zevallos-Herencia (3)
(1) IAG/USP, Brazil, (2)
Universidad de La Serena, Chile, (3) ON, Brazil, (4) in memoriam, (5)
ICATE-CONICET, Argentina, (6) CRESST/NASA, USA, (7) Universidad
Nacional de La Plata, Argentina, (8) Instituto de Astrofísica de La
Plata, Argentina, (9) SOAR, Chile, (10) MPIfR, Germany, (11) TAMU,
USA, (12) RSAA, Australia, (13) LCO, Chile, (14) Stockholm
University, Sweden, (15) University of Copenhagen, Denmark, (16)
Carnegie Institution, USA, (17) LNA, Brazil, (18) Harvard-Smithsonian
Center for Astrophysics, USA, (19) SRON, the Netherlands
The
periodic spectroscopic events in eta Carinae are now well established
and occur near the periastron passage of two massive stars in a very
eccentric orbit. Several mechanisms have been proposed to explain the
variations of different spectral features, such as an eclipse by the
wind-wind collision boundary, a shell ejection from the primary star
or accretion of its wind onto the secondary. All of them have
problems explaining all the observed phenomena. To better understand
the nature of the cyclic events, we performed a dense monitoring of
eta Carinae with 5 Southern telescopes during the 2009 low excitation
event, resulting in a set of data of unprecedented quality and
sampling. The intrinsic luminosity of the He II 4686 emission line
(L~310 Lsun) just before periastron reveals the presence of a very
luminous transient source of extreme UV radiation emitted in the
wind-wind collision (WWC) region. Clumps in the primary's wind
probably explain the flare-like behavior of both the X-ray and He II
4686 light-curves. After a short-lived minimum, He II 4686 emission
rises again to a new maximum, when X-rays are still absent or very
weak. We interpret this as a collapse of the WWC onto the "surface"
of the secondary star, switching off the hard X-ray source and
diminishing the WWC shock cone. The recovery from this state is
controlled by the momentum balance between the secondary's wind and
the clumps in the primary's wind.
Reference: Accepted
for publication in The Astrophysical Journal.
Status: Manuscript
has been accepted
Weblink:
Comments:
Two-column style; 18 pages, 10 figures, and 1 table.
Email:
mairan@astro.iag.usp.br
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contents
M. Teodoro (1), A. Damineli
(1), J. I. Arias (2), F. X. de Ara'ujo (3 and 4), R. H. Barb'a (5),
M. F. Corcoran (6), M. Borges Fernandes (3), E. Fern'andez-Laj'us (7
and 8), L. Fraga (9), R. C. Gamen (7 and 8), J. F. Gonz'alez (5), J.
H. Groh (10), J. L. Marshall (11), P. J. McGregor (12), N. Morrell
(13), D. C. Nicholls (12), E. R. Parkin (12), C. B. Pereira (3), M.
M. Phillips (13), G. R. Solivella (7 and 8), J. E. Steiner (1), M.
Stritzinger (14 and 15), I. Thompson (16), C. A. O. Torres (17), M.
A. P. Torres (18 and 19), M. I. Zevallos-Herencia (3)
(1)
IAG/USP, Brazil, (2) Universidad de La Serena, Chile, (3) ON, Brazil,
(4) in memoriam, (5) ICATE-CONICET, Argentina, (6) CRESST/NASA, USA,
(7) Universidad Nacional de La Plata, Argentina, (8) Instituto de
Astrof'isica de La Plata, Argentina, (9) SOAR, Chile, (10) MPIfR,
Germany, (11) TAMU, USA, (12) RSAA, Australia, (13) LCO, Chile, (14)
Stockholm University, Sweden, (15) University of Copenhagen, Denmark,
(16) Carnegie Institution, USA, (17) LNA, Brazil, (18)
Harvard-Smithsonian Center for Astrophysics, USA, (19) SRON, the
Netherlands
The periodic spectroscopic events in eta Carinae
are now well established and occur near the periastron passage of two
massive stars in a very eccentric orbit. Several mechanisms have been
proposed to explain the variations of different spectral features,
such as an eclipse by the wind-wind collision boundary, a shell
ejection from the primary star or accretion of its wind onto the
secondary. All of them have problems explaining all the observed
phenomena. To better understand the nature of the cyclic events, we
performed a dense monitoring of eta Carinae with 5 Southern
telescopes during the 2009 low excitation event, resulting in a set
of data of unprecedented quality and sampling. The intrinsic
luminosity of the He II 4686 emission line (L~310 Lsun) just before
periastron reveals the presence of a very luminous transient source
of extreme UV radiation emitted in the wind-wind collision (WWC)
region. Clumps in the primary's wind probably explain the flare-like
behavior of both the X-ray and He II 4686 light-curves. After a
short-lived minimum, He II 4686 emission rises again to a new
maximum, when X-rays are still absent or very weak. We interpret this
as a collapse of the WWC onto the "surface" of the
secondary star, switching off the hard X-ray source and diminishing
the WWC shock cone. The recovery from this state is controlled by the
momentum balance between the secondary's wind and the clumps in the
primary's wind.
Reference: Accepted for publication in
ApJ.
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1104.2276
Comments:
Two-column style; 18 pages, 10 figures, and 1 table.
Email:
mairan@astro.iag.usp.br
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contents
A.W.A. Pauldrach(1),
D.Vanbeveren(2,3), and T. L.Hoffmann(1)
1 Institut für
Astronomie und Astrophysik der Universität München, Scheinerstraße
1, 81679 München, Germany
e-mail: uh10107@usm.lmu.de, e-mail:
hoffmann@usm.lmu.de
2 Astrophysical Institute, Vrije Universiteit
Brussel, Pleinlaan 2, 1050 Brussels, Belgium
e-mail:
dvbevere@vub.ac.be
3 Leuven Engineering College, Groep T,
Association KU Leuven, Vessaliusstraat 13, 3000 Leuven,
Belgium
Context. Starbursts play an essential role in the
evolution of galaxies. In these environments, massive stars, with
their short lifetimes, are of particular importance. The stellar
winds ofmassive stars significantly influence not only on their
surroundings, but the associated mass loss also profoundly affects
the evolution of the stars themselves. The evolution of the dense
cores of massive starburst clusters is also affected by dynamical
processes induced by N-body interactions, in addition to the
evolution of each star, and the formation of very massive stars with
masses up to several thousand solar masses may be decisive for the
evolution of the cluster. The interpretation of the corresponding
observations relies mainly on the theoretical modeling of such
starbursts, which is a major challenge.
Aims. The primary
objective is to introduce an advanced diagnostic method of O-type
stellar atmospheres with winds, including an assessment of the
accuracy of the determinations of abundances, stellar and wind
parameters. Moreover, observational results are interpreted in the
framework of our stationary, one-dimensional theory of line driven
winds. Possible effects caused by nonhomogeneous time dependent
structures are also discussed.
Methods. We combine consistent
models of expanding atmospheres with stellar evolutionary
calculations of massive and very massive (up to several 1000 solar
masses) single stars with regard to the evolution of dense stellar
clusters. Essential in this context are accurate dynamic parameters
of the winds of very massive stars. Because the atmospheric mass
outflow has substantial influence on the radiation field and the
atomic occupation numbers, and the radiation field and the occupation
numbers in turn directly influence the radiative acceleration and
thus the strength and velocity of the outflow, the determination of
the hydrodynamic structures requires a highly consistent treatment of
the statistical equilibrium and the hydrodynamic and radiative
processes in the expanding atmospheres.
Results. We present
computed mass loss rates, terminal wind velocities, and spectral
energy distributions of massive and very massive stars of different
metallicities, calculated from atmospheric models with an improved
level of consistency. These computations have important implications
for (i) the primordial chemical enrichment of Population III very
massive stars; (ii) the age determination of globular clusters; and
(iii) the formation of intermediate mass black holes in dense stellar
clusters with respect to the importance of stellar wind mass loss for
the evolution of their progenitor stars.
Conclusions. Stellar
evolutionary calculations, using the mass loss rates of very massive
stars obtained in the present paper, show that very massive stars
with a low metallicity lose only a very small amount of their mass;
thus it is unlikely that very massive population III stars cause a
significant helium enrichment of the interstellar medium.
Solar-metallicity stars have higher mass-loss rates, but these are
not so high to exclude very massive stars of solar metallicity,
formed by dynamical processes in dense clusters, from ending their
life massive enough to form intermediate-mass black
holes.
Reference: Publication in A&A.
Pre-print
available on astro-ph.
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1107.0654
Comments:
Two-column style: 40 pages, 25 figures, and 15 tables.
Email:
uh10107@usm.uni-muenchen.de
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Rolf Kuiper^{1,2,3}, Hubert
Klahr^{2}, Henrik Beuther^{2}, Thomas Henning^{2}
1)
Argelander Institute for Astronomy, Bonn University, Auf dem Huegel
71, D-53121 Bonn, Germany
2) Max Planck Institute for Astronomy,
Koenigstuhl 17, D-69117 Heidelberg, Germany
3) Now: Jet
Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109,
USA
Context:
When massive stars exert a radiation pressure
onto their environment that is higher than their gravitational
attraction (super-Eddington condition), they launch a
radiation-pressure-driven outflow, which creates cleared cavities.
These cavities should prevent any further accretion onto the star
from the direction of the bubble, although it has been claimed that a
radiative Rayleigh-Taylor instability should lead to the collapse of
the outflow cavity and foster the growth of massive stars.
Aims:
We investigate the stability of idealized
radiation-pressure-dominated cavities, focusing on its dependence on
the radiation transport approach used in numerical simulations for
the stellar radiation feedback.
Methods:
We compare two
different methods for stellar radiation feedback: gray flux-limited
diffusion (FLD) and ray-tracing (RT).
Both methods are
implemented in our self-gravity radiation hydrodynamics simulations
for various initial density structures of the collapsing clouds,
eventually forming massive stars.
We also derive simple
analytical models to support our findings.
Results:
Both
methods lead to the launch of a radiation-pressure-dominated outflow
cavity.
However, only the FLD cases lead to prominent instability
in the cavity shell.
The RT cases do not show such instability;
once the outflow has started, it precedes continuously.
The FLD
cases display extended epochs of marginal Eddington equilibrium in
the cavity shell, making them prone to the radiative Rayleigh-Taylor
instability.
In the RT cases, the radiation pressure exceeds
gravity by 1-2 orders of magnitude.
The radiative Rayleigh-Taylor
instability is then consequently suppressed.
It is a fundamental
property of the gray FLD method to neglect the stellar radiation
temperature at the location of absorption and thus to underestimate
the opacity at the location of the cavity shell.
Conclusions:
Treating the stellar irradiation in the gray FLD approximation
underestimates the radiative forces acting on the cavity shell.
This
can lead artificially to situations that are affected by the
radiative Rayleigh-Taylor instability.
The proper treatment of
direct stellar irradiation by massive stars is crucial for the
stability of radiation-pressure-dominated cavities.
Reference:
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1111.5625v1
Comments:
Email: kuiper@mpia.de
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Yael Naze, Gregor Rauw,
Damien Hutsemekers
(Univ. of Liege)
Aims: The X-ray
emission of massive stars has been studied when these objects are in
their main-sequence phase, as well as in their Wolf-Rayet phase.
However, the X-ray properties of the transitional Luminous Blue
Variable (LBV) phase remain unknown.
Methods: Using a dedicated
but limited XMM survey as well as archival XMM and Chandra
observations, we performed the first X-ray survey of LBVs: about half
of the known LBVs or candidate LBVs are studied.
Results: Apart
from the well known X-ray sources eta Car and Cyg OB2 #12, four
additional LBVs are detected in this survey, though some doubt
remains on the association with the X-ray source for two of these.
For the other LBVs, upper limits on the flux were derived, down to
$log[L_{rm X}/L_{rm BOL}]-9.4$ for PCyg. This variety in the strength
of the X-ray emission is discussed, with particular emphasis on the
potential influence of binarity.
Reference: accepted by
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1111.6375
Comments:
Email: naze@astro.ulg.ac.be
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Y. Naze, S.A. Zhekov, N.R.
Walborn
(ULg, U of Col. and Space and solar-terrestrial
research inst., STScI)
High-resolution data of the peculiar
magnetic massive star HD148937 were obtained with Chandra-HETGS, and
are presented here in combination with a re-analysis of the older
XMM-RGS data. The lines of the high-Z elements (Mg, Si, S) were found
to be unshifted and relatively narrow (FWHM of about 800km/s), i.e.
narrower than the O line recorded by RGS, which possibly indicates
that the hot plasma is multi-thermal and has several origins. These
data further indicate a main plasma temperature of about 0.6keV and a
formation of the X-ray emission at about one stellar radius above the
photosphere. From the spectral fits and the H-to-He line ratios, the
presence of very hot plasma is however confirmed, though with a
smaller relative strength than for the prototype magnetic oblique
rotator $theta^1$,Ori,C. Both stars thus share many similarities, but
HD148937 appears less extreme than $theta^1$,Ori,C despite having
also a large magnetic confinement parameter.
Reference:
accepted by ApJ
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1111.7186
Comments:
Email: naze@astro.ulg.ac.be
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Gisela N. Ortiz-Leon(1), Luis
F. Rodriguez(1,2), and Mauricio Tapia(3)
1 - Centro de
Radioastronomia y Astrofisica, Universidad Nacional Autonoma de
Mexico, Campus Morelia; 2 - Astronomy Department, Faculty of Science,
King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi
Arabia; 3 - Instituto de Astronomia, Universidad Nacional Autonoma de
Mexico, Ensenada
Cyg OB2 #5 is a contact binary system
(O6.5-7+O5.5-6) with associated radio continuum emission. Two compact
(<=0.3") radio continuum components have been reported
previously: the primary one is associated with the contact binary and
the secondary one is an arc-like source 0.8" to the NE of the
primary. This arc-like source results from the interaction of the
winds of the contact binary and a B-type star in the region.In this
paper we report the detection of an extended (about 30"),
non-thermal component to the NE of the compact components. We propose
that this extended emission could be an unresolved background source
(i. e. a radio galaxy), extended galactic emission, or non-thermal
emission related with relativistic electrons that are produced in the
shock between the contact binary and the B-type star and that are
carried away to large distances by the wind from the contact
binary.
Reference: Revista Mexicana de Astronomia y
Astrofisica, in press.
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1111.6486
Comments:
Email: l.rodriguez@crya.unam.mx
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Yael Naze, Carlos Arturo
Flores, Gregor Rauw
ULg - Univ. Guanajuato - ULg
Aims:
zeta Puppis, one of the closest and brightest massive stars, was the
first early-type object observed by the current generation of X-ray
observatories. These data provided some surprising results,
confirming partly the theoretical predictions while simultaneously
unveiling some problematic mismatches with expectations. In this
series of papers, we perform a thorough study of zeta Puppis in
X-rays, using a decade of XMM observations.
Methods: zeta
Puppis was observed 18 times by XMM, totaling 1Ms in exposure. This
provides the highest-quality high-resolution X-ray spectrum of a
massive star to date, as well as a perfect dataset for studying X-ray
variability in an "archetype" object.
Results: This
first paper reports on the data reduction of this unique dataset and
provides a few preliminary results. On the one hand, the analysis of
EPIC low-resolution spectra shows the star to have a remarkably
stable X-ray emission from one observation to the next. On the other
hand, the fitting by a wind model of individual line profiles
recorded by RGS confirms the wavelength dependence of the line
morphology.
Reference: accepted for publication by
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1112.0862
Comments:
Email: naze@astro.ulg.ac.be
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L. E. Muijres (Amsterdam),
Jorick S. Vink (Armagh), A. de Koter (Amsterdam), P.E. Mueller
(Keele), N. Langer (Bonn)
Amsterdam, Armagh, Keele,
Bonn
Mass loss forms an important aspect of the evolution of
massive stars, as well as for the enrichment of the surrounding ISM.
Our goal is to predict accurate mass-loss rates and terminal wind
velocities. These quantities can be compared to empirical values,
thereby testing radiation-driven wind models. One specific issue is
that of the "weak-wind problem", where empirically derived
mass-loss rates fall orders of magnitude short of predicted values.
We employ an established Monte Carlo model and a recently suggested
new line acceleration formalism to solve the wind dynamics
consistently. We provide a new grid of mass-loss rates and terminal
wind velocities of O stars, and compare the values to empirical
results. Our models fail to provide mass-loss rates for main-sequence
stars below a luminosity of log(L/Lsun) = 5.2, where we run into a
fundamental limit. At luminosities below this critical value there is
insufficient momentum transferred in the region below the sonic point
to kick-start the acceleration. This problem occurs at the location
of the onset of the weak-wind problem. For O dwarfs, the boundary
between being able to start a wind, and failing to do so, is at
spectral type O6/O6.5. The direct cause of this failure is a
combination of the lower luminosity and a lack of Fe V lines at the
wind base. This might indicate that another mechanism is required to
provide the necessary driving to initiate the wind. For stars more
luminous than log(L/Lsun) = 5.2, our new mass-loss rates are in
excellent agreement with the mass-loss prescription by Vink et al.
2000. This implies that the main assumption entering the method of
the Vink et al. prescriptions - i.e. that the momentum equation is
not explicitly solved for - does not compromise the reliability of
the Vink et al. results for this part of parameter space
(Abridged).
Reference: Astronomy & Astrophysics (in
press)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1112.0944
Comments:
Email: jsv@arm.ac.uk
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Jorick S. Vink (Armagh), G.
Graefener (Armagh), T. J. Harries (Exeter)
Armagh
Observatory
Long gamma-ray bursts involve the most powerful
cosmic explosions since the Big Bang. Whilst it has been established
that GRBs are related to the death throes of massive stars, the
identification of their progenitors has proved challenging. Theory
suggests that rotating Wolf-Rayet stars are the best candidates, but
their strong stellar winds shroud their surfaces, preventing a direct
measurement of their rotation. Fortunately, linear spectropolarimetry
may be used to probe the flattening of their winds due to stellar
spin. Spectropolarimetry surveys show that an 80% majority of WR
stars have spherically symmetric winds and are thus rotating slowly,
yet a small 20% minority display a spectropolarimetric signature
indicative of rotation. Here we find a highly significant correlation
between WR objects that carry the signature of stellar rotation and
the subset of WR stars with ejecta nebulae that have only recently
transitioned from a red sugergiant or luminous blue variable phase.
As these youthful WR stars have yet to spin-down due to mass loss,
they are the best candidate GRB progenitors identified to date. When
we take recently published WR ejecta nebula numbers we find that five
out of the six line-effect WR stars are surrounded by ejecta nebulae.
The statistics imply that the null hypothesis of no correlation
between line-effect WR stars and ejecta nebulae can be rejected at
the 0.0004% level. Given that four line-effect and WR ejecta nebula
have spectroscopically been confirmed to contain nucleosynthetic
products, we argue that the correlation is both statistically
significant and physically convincing. The implication is that we
have identified a WR sub-population that fulfills the necessary
criteria for making GRBs. Finally, we discuss the potential of
identifying GRB progenitors via spectropolarimetry with extremely
large telescopes.
Reference: Astronomy &
Astrophysics Letters
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1111.5806
Comments:
Email: jsv@arm.ac.uk
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G. Gräfener (1), S.P. Owocki
(2), J.S. Vink (1)
(1) Armagh Observatory, College Hill,
Armagh, BT61 9DG, United Kingdom
(2) Bartol Research Institute,
University of Delaware, Newark, DE 19716, USA
Context: It has
been proposed that the envelopes of luminous stars may be subject to
substantial radius inflation. The peculiar structure of such inflated
envelopes, with an almost void, radiatively dominated region beneath
a thin, dense shell could mean that many in reality compact stars are
hidden below inflated envelopes, displaying much lower effective
temperatures. The inflation effect has been discussed in relation to
the radius problem of WR stars, but has yet failed to explain the
large observed radii of Galactic WR stars.
Aims: We wish to
obtain a physical perspective of the inflation effect, and study the
consequences for the radii of WR stars, and LBVs. For WR stars the
observed radii are up to an order of magnitude larger than predicted
by theory, whilst S Doradus-type LBVs are subject to humongous radius
variations, which remain as yet ill-explained.
Methods: We use a
dual approach to investigate the envelope inflation, based on
numerical models for stars near the Eddington limit, and a new
analytic formalism to describe the effect. An additional new aspect
is that we take the effect of density inhomogeneities (clumping)
within the outer stellar envelopes into account.
Results: Due to
the effect of clumping we are able to bring the observed WR radii in
agreement with theory. Based on our new formalism, we find that the
radial inflation is a function of a dimensionless parameter W, which
largely depends on the topology of the Fe-opacity peak, i.e., on
material properties. For W>1, we discover an instability limit,
for which the stellar envelope becomes gravitationally unbound, i.e.
there no longer exists a static solution. Within this framework we
are also able to explain the S Doradus-type instabilities for LBVs
like AG Car, with a possible triggering due to changes in stellar
rotation. The stellar effective temperatures in the upper HR diagram
are potentially strongly affected by the inflation effect.
Conclusions: This may have particularly strong effects on the
evolved massive LBV and WR stars just prior to their final collapse,
as the progenitors of SNe Ibc, SNe II, and long GRBs.
Reference:
Astronomy & Astrophysics
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1112.1910
Comments:
15 pages, 11 Figures
Email: ggr@arm.ac.uk
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Cyril Georgy
Centre
de Recherche Astrophysique de Lyon, ENS Lyon
The increasing
observed number of supernova events allows for finding ever more
frequently the progenitor star in archive images. In a few cases, the
progenitor star is a yellow supergiant star. The estimated position
in the Hertzsprung-Russell diagram of these stars is not compatible
with the theoretical tracks of classical single star models.
According to several authors, the mass-loss rates during the red
supergiant phase could be underestimated. We study the impact of an
increase of these mass-loss rates on the position of 12 to 15 Modot
stars at the end of their nuclear life, in order to reconcile the
theoretical tracks with the observed yellow supergiant progenitors.
We perform calculations of 12 to 15 Modot rotating stellar models
using the Geneva stellar evolution code. To account for the
uncertainties in the mass-loss rates during the RSG phase, we
increase the mass-loss rate of the star (between 3 and 10 times the
standard one) during that phase and compare the evolution of stars
undergoing such high mass-loss rates with models computed with the
standard mass-loss prescription. We show that the final position of
the models in the Hertzsprung-Russell diagram depends on the mass
loss they undergo during the red supergiant phase. With an increased
mass-loss rate, we find that some models end their nuclear life at
positions that are compatible with the observed position of several
supernova progenitors. We conclude that an increased mass-loss rate
(whom physical mechanism still need to be clarified) allows single
star models to reproduce simultaneously the estimated position in the
HRD of the YSG SN progenitors, as well as the SN type.
Reference:
A&A Letters (2011) in press, arXiv number 1111.7003
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1111.7003
Comments:
Email: Cyril.Georgy@ens-lyon.fr
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Alex C. Carciofi$^1$,
Jon
E. Bjorkman$^1,2$,
Sebastián A. Otero$^3$,
Atsuo T.
Okazaki$^4$,
Stanislav Stefl$^5$,
Thomas Rivinius$^5$,
Dietrich Baade$^6$,
and
Xavier Haubois$^1$
1 -
Instituto de Astronomia, Geofísica e Ciências Atmosféricas,
Universidade de São Paulo, Rua do Matão 1226, Cidade
Universit'aria, 05508-900, São Paulo, SP, BRAZIL, carciofi@usp.br
2
- Ritter Observatory, Department of Physics & Astronomy, Mail
Stop 113, University of Toledo, Toledo, OH 43606,
jon@physics.utoledo.edu
3 - AAVSO, American Association of
Variable Star Observers
4 - Faculty of Engineering, Hokkai-Gakuen
University, Toyohira-ku, Sapporo 062-8605, Japan
5 - European
Organization for Astronomical Research in the Southern Hemisphere,
Casilla 19001, Santiago 19, Chile
6 - European Organization for
Astronomical Research in the Southern Hemisphere,
Karl-Schwarzschild-Str.~2, 85748 Garching bei München, Germany
Be
stars possess gaseous circumstellar decretion disks, which are well
described using standard $alpha$-disk theory.
The Be star 28,CMa
recently underwent a long outburst followed by a long period of
quiescence, during which the disk dissipated. Here we present the
first time-dependent models of the dissipation of a viscous decretion
disk.
By modeling the rate of decline of the $V$-band excess, we
determine that the viscosity parameter $alpha=1.0pm0.2$,
corresponding to a mass injection rate $dot{M}=(3.5pm 1.3) times
10^{-8} M_sun,mathrm{yr}^{-1}$.
Such a large value of $alpha$
suggests that the origin of the turbulent viscosity is an instability
in the disk whose growth is limited by shock dissipation. The mass
injection rate is more than an order of magnitude larger than the
wind mass loss rate inferred from UV observations, implying that the
mass injection mechanism most likely is not the stellar wind, but
some other mechanism.
Reference: To appear in The
Astrophysical Journal Letters
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1112.0053
Comments:
Email: carciofi@usp.br
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S. Ekström (1), C. Georgy
(2), P. Eggenberger (1), G. Meynet (1), N. Mowlavi (1), A. Wyttenbach
(1), A. Granada (1,3), T. Decressin (1), R. Hirschi (4,5), U.
Frischknecht (4,6), C. Charbonnel (1,7), and A. Maeder (1)
1-
Geneva Observatory, University of Geneva, Maillettes 51, CH-1290
Sauverny, Switzerland
2- Centre de recherche astrophysique, Ecole
Normale Supérieure de Lyon, 46, allée d’Italie, F-69384 Lyon
cedex 07, France
3- Instituto de Astrofísica La Plata, CCT La
Plata, CONICET-UNLP, Paseo del Bosque S/N, La Plata, Buenos Aires,
Argentina
4- Astrophysics group, EPSAM, Keele University,
Lennard-Jones Labs, Keele, ST5 5BG, UK
5- Institute for the
Physics and Mathematics of the Universe, University of Tokyo, 5-1-5
Kashiwanoha, Kashiwa, 277-8583, Japan
6- Dept. of Physics,
University of Basel, Klingelbergstr. 82, CH-4056, Basel, Switzerland
7- IRAP, UMR 5277 CNRS and Université de Toulouse, 14, Av.
E.Belin, 31400 Toulouse, France
Many topical astrophysical
research areas, such as the properties of planet host stars, the
nature of the progenitors of different types of supernovae and gamma
ray bursts, and the evolution of galaxies, require complete and
homogeneous sets of stellar models at different metallicities in
order to be studied during the whole of cosmic history. We present
here a first set of models for solar metallicity, where the effects
of rotation are accounted for in a homogeneous way.
We
computed a grid of 48 different stellar evolutionary tracks, both
rotating and non-rotating, at Z = 0.014, spanning a wide mass range
from 0.8 to 120 Msun. For each of the stellar masses considered,
electronic tables provide data for 400 stages along the evolutionary
track and at each stage, a set of 43 physical data are given. These
grids thus provide an extensive and detailed data basis for
comparisons with the observations. The rotating models start on the
ZAMS with a rotation rate v_ini/v_crit = 0.4. The evolution is
computed until the end of the central carbon-burning phase, the early
AGB phase, or the core helium-flash for, respectively, the massive,
intermediate, and both low and very low mass stars. The initial
abundances are those deduced by Asplund and collaborators, which best
fit the observed abundances of massive stars in the solar
neighbourhood. We update both the opacities and nuclear reaction
rates, and introduce new prescriptions for the mass-loss rates as
stars approach the Eddington and/or the critical velocity. We account
for both atomic diffusion and magnetic braking in our low-mass star
models.
The present rotating models provide a good
description of the average evolution of non-interacting stars. In
particular, they reproduce the observed main-sequence width, the
positions of the red giant and supergiant stars in the HR diagram,
the observed surface compositions and rotational velocities. Very
interestingly, the enhancement of the mass loss during the
red-supergiant stage, when the luminosity becomes supra-Eddington in
some outer layers, help models above 15-20 Msun to lose a significant
part of their hydrogen envelope and evolve back into the blue part of
the HR diagram. This result has interesting consequences for the blue
to red supergiant ratio, the minimum mass for stars to become
Wolf-Rayet stars, and the maximum initial mass of stars that explode
as type II-P supernovae.
Reference: A&A, in press
arXiv:1110.5049
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1110.5049
Comments:
19 pages, 15 figures
Electronic tables on CDS
Email:
sylvia.ekstrom@unige.ch
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contents
F. Martins (1), C. Escolano (1),
G.A. Wade, (2), J.-F. Donati (3), J.-C. Bouret (4,5), the MiMeS
collaboration
(1) LUPM, CNRS and Universite Montpellier
II, (2) RMC, (3) IRAP, CNRS and Universite Paul Sabatier, (4) LAM,
CNRS and Universite de Provence, (5) NASA/GSFC
We investigate
the surface nitrogen content of the six magnetic O stars known to
date as well as of the early B-type star tau Sco. We compare these
abundances to predictions of evolutionary models to isolate the
effects of magnetic field on the transport of elements in stellar
interiors. We conduct a quantitative spectroscopic analysis of the
sample stars with state-of-the-art atmosphere models. We rely on high
signal-to-noise ratio, high resolution optical spectra obtained with
ESPADONS at CFHT and NARVAL at TBL. Atmosphere models and synthetic
spectra are computed with the code CMFGEN. Values of N/H together
with their uncertainties are determined and compared to predictions
of evolutionary models. We find that the magnetic stars can be
divided into two groups: one with stars displaying no N enrichment
(one object); and one with stars most likely showing extra N
enrichment (5 objects). For one star (Theta1 Ori C) no robust
conclusion can be drawn due to its young age. The star with no N
enrichment is the one with the weakest magnetic field, possibly of
dynamo origin. It might be a star having experienced strong magnetic
braking under the condition of solid body rotation, but its
rotational velocity is still relatively large. The five stars with
high N content were probably slow rotators on the zero age main
sequence, but they have surface N/H typical of normal O stars,
indicating that the presence of a (probably fossil) magnetic field
leads to extra enrichment. These stars may have a strong differential
rotation inducing shear mixing. Our results should be viewed as a
basis on which new theoretical simulations can rely to better
understand the effect of magnetism on the evolution of massive
stars.
Reference: Astronomy and Astrophysics
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1112.2497
Comments:
Email: fabrice.martins@univ-montp2.fr
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Claus Leitherer(1) &
Sylvia Ekstrom(2)
(1) STScI
(2) Geneva
Observatory
The current state-of-the-art of population
synthesis is reviewed. The field is currently undergoing major
revisions with the recognition of several key processes as new
critical ingredients. Stochastic effects can artificially enhance or
suppress certain evolutionary phases and/or stellar mass regimes and
introduce systematic biases in, e.g., the determination of the
stellar initial mass function. Post-main-sequence evolution is often
associated with irregular variations of stellar properties on
ultra-short time-scales. Examples are asymptotic giant branch stars
and luminous blue variables, both of which are poorly treated in the
models. Stars rarely form in isolation, and the fraction of truly
single stars may be very small. Therefore, stellar multiplicity must
be accounted for since many systems will develop tidal interaction
over the course of their evolution. Last but not least, stellar
rotation can drastically increase stellar temperatures and
luminosities, which in turn leads to revised mass-to-light ratios in
population synthesis models.
Reference: Review talk,
IAU Symp. 284, The Spectral Energy Distribution of Galaxies, Preston
(UK), September 2011, eds. R. J. Tuffs and C. C. Popescu
Status:
Conference proceedings
Weblink:
http://arxiv.org/abs/1111.5204
Comments:
Email: leitherer@stsci.edu
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Jorick S. Vink (Armagh), J.
M. Bestenlehner (Armagh), G. Graefener (Armagh), A. de Koter
(Amsterdam), N. Langer (Bonn)
Armagh Observatory
Some
studies have claimed the existence of a stellar upper-mass limit of
150 Msun. A factor that is often overlooked concerns the issue that
there might be a significant difference between the present-day and
the initial mass of the most massive stars - as a result of mass
loss. The upper-mass limit may be substantially higher, possibly
exceeding 200 Msun. The issue of the upper mass-limit will however
remain uncertain as long as there is only limited quantitative
knowledge of mass loss in close proximity to the Eddington (= Gamma)
limit. For this reason, we present mass-loss predictions from Monte
Carlo radiative transfer models for very massive stars up to 300
Msun. Using our new dynamical approach, we find an upturn or "kink"
in the mass-loss versus Gamma dependence, at the point where our
model winds become optically thick. These are the first mass-loss
predictions where the transition from optically thin O-star winds to
optically thick Wolf-Rayet winds has been resolved.
Reference:
To appear in Four Decades of Research on Massive Stars, ASP Conf.
Ser.
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1112.0936
Comments:
Email: jsv@arm.ac.uk
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Jorick S. Vink
Armagh Observatory
We
present a brief overview of the theory of stellar winds with a strong
emphasis on the radiation-driven outflows from massive stars. The
resulting implications for the evolution and fate of massive stars
are also discussed. Furthermore, we relate the effects of mass loss
to the angular momentum evolution, which is particularly relevant for
the production of long and soft gamma-ray bursts. Mass-loss rates are
not only a function of the metallicity, but are also found to depend
on temperature, particularly in the region of the bi-stability jump
at 21 000 Kelvin. We highlight the role of the bi-stability jump for
Luminous Blue Variable (LBV) stars, and discuss suggestions that LBVs
might be direct progenitors of supernovae. We emphasize that
radiation-driven wind studies rely heavily on the input opacity data
and linelists, and that these are thus of fundamental importance to
both the mass-loss predictions themselves, as well as to our overall
understanding of the lives and deaths of massive stars.
Reference:
Astrophysics and Space Science, Vol 336, Issue 1, pp. 163-167
(special HEDLA 2010 Issue)
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1112.0952
Comments:
Email: jsv@arm.ac.uk
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Stan Owocki^1, Jon
Sundqvist^1, David Cohen^2 and Ken Gayley^3
1-Bartol
Research Insitute, University of Delaware, Newark,DE 19716 USA
2-Department of Physics, Swarthmore College, Swarthmore, PA 19081
USA
3-Department of Physics, University of Iowa, Iowa City, IA
52242 USA
X-ray satellites since Einstein have empirically
established that the X-ray luminosity from single O-stars scales
linearly with bolometric luminosity, Lx~ 10^-7 Lbol. But
straightforward forms of the most favored model, in which X-rays
arise from instability-generated shocks embedded in the stellar wind,
predict a steeper scaling, either with mass loss rate Lx ~Mdot
Lbol^1.7 if the shocks are radiative, or with Lx ~Mdot^2 ~Lbol^3.4 if
they are adiabatic. We present here a generalized formalism that
bridges these radiative vs. adiabatic limits in terms of the ratio of
the shock cooling length to the local radius. Noting that the
thin-shell instability of radiative shocks should lead to extensive
mixing of hot and cool material, we then propose that the associated
softening and weakening of the X-ray emission can be parametrized by
the cooling length ratio raised to a power m, the “mixing
exponent.” For physically reasonable values m=0.4, this leads to an
X-ray luminosity Lx ~ Lbol that matches the empirical scaling. We
conclude by noting that such thin-shell mixing may also be important
for X-rays from colliding wind binaries, and that future numerical
simulation studies will be needed to test this thin-shell mixing
ansatz for X-ray emission.
Reference: To appear in
"Four Decades of Research on Massive Stars", proceedings of
a conference held 11-15 July 2011 in Saint-Michel-des-Saints, Quebec
to honor the retirement of Tony Moffat.
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1110.0891
Comments:
Email: owocki@udel.edu
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Guy S. Stringfellow (1),
Vasilii V. Gvaramadze (2), Yuri Beletsky (3) and Alexei Y. Kniazev
(4)
(1) Center for Astrophysics and Space Astronomy,
University of Colorado, 389 UCB,
Boulder, CO 80309-0389, USA;
(2) Sternberg Astronomical Institute, Moscow State University,
Universitetskij Pr. 13,
Moscow 119992, Russia;
(3) European
Southern Observatory, Alonso de Cordova 3107, Santiago, Chile;
(4)
South African Astronomical Observatory and Southern African Large
Telescope
Foundation, PO Box 9, 7935 Observatory, Cape Town,
South Africa
We have undertaken a near-infrared spectral
survey of stars associated with compact mid-IR
shells recently
revealed by the MIPSGAL (24 microns) and GLIMPSE (8 microns) Spitzer
surveys, whose morphologies are typical of circumstellar shells
produced by massive evolved
stars. Through spectral similarity
with known Luminous Blue Variable (LBV) and Wolf-Rayet
(WR)
stars, a large population of candidate LBVs (cLBVs) and a smaller
number of new WR
stars are being discovered. This significantly
increases the Galactic cLBV population and
confirms that nebulae
are inherent to most (if not all) objects of this class.
Reference:
To appear in the proceedings of IAU Symposium 282 "From
Interacting Binaries
to Exoplanets: Essential Modeling Tools",
eds. Mercedes Richards & Ivan Hubeny.
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1112.2685
Comments:
2 pages, 1 figure.
Email:
Guy.Stringfellow@colorado.edu
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contents
G. S. Stringfellow (1), V. V.
Gvaramadze (2), Y. Beletsky (3) and A.Y. Kniazev (4,2)
(1)
Center for Astrophysics and Space Astronomy, University of Colorado,
389 UCB,
Boulder, CO 80309-0389, USA;
(2) Sternberg
Astronomical Institute, Moscow State University, Universitetskij Pr.
13,
Moscow 119992, Russia;
(3) European Southern Observatory,
Alonso de Cordova 3107, Santiago, Chile;
(4) South African
Astronomical Observatory and Southern African Large Telescope
Foundation, PO Box 9, 7935 Observatory, Cape Town, South
Africa
We have undertaken a near-IR spectral survey of stars
associated with compact nebulae
recently revealed by the Spitzer
and WISE imaging surveys. These circumstellar nebulae,
produced
by massive evolved stars, display a variety of symmetries and shapes
and are
often only evident at mid-IR wavelengths. Stars
associated with ~50 of these nebulae have
been observed. We also
obtained recent spectra of previously confirmed (known) luminous
blue variables (LBVs) and candidate LBVs (cLBVs). The spectral
similarity of the stars
observed when compared directly to known
LBVs and Wolf-Rayet (WR) stars indicate
many are newly identified
cLBVs, with a few being newly discovered WR stars, mostly
of
WN8-9h spectral type. These results suggest that a large population
of previously
unidentified cLBVs and related transitional stars
reside in the Galaxy and confirm that circumstellar nebulae are
inherent to most (c)LBVs.
Reference: To appear in "Four
Decades of Research on Massive Stars: A Scientific
Meeting in
Honour of Anthony F. J. Moffat", ASP Conference series, 2012,
eds.
Laurent Drissen, Nicole St Louis, Carmelle Robert, and
Anthony F.J. Moffat.
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1112.2686
Comments:
3 pages, 2 figures
Email:
Guy.Stringfellow@colorado.edu
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contents
Anthony F.J. Moffat & Nicole
St-Louis
Dépt. de physique, Univ. de Montréal
Last
year we submitted a White Paper as input information to the Long
Range Plan Committee of the Canadian Astronomical Society. In this WP
we outlined several discovery highlights in the area of massive stars
involving Canadian astronomers during the past decade (2000-2009). We
thought this might be of interest to others in the general
massive-star community. A pdf version is available at the
accompanying web-site address.
Reference: Submitted to
CASCA/LRP
Status: Other
Weblink:
http://www.astro.umontreal.ca/~moffat/WP2010Canada/
Comments:
Email: moffat@astro.umontreal.ca
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Michele Bianda
Istituto
Ricerche Solari Locarno
IRSOL
via Patocchi 57
CH-6605
Locarno Monti
Switzerland
A Swiss-NSF-funded PhD position
is now open at the solar physics research institute Istituto Ricerche
Solari Locarno, IRSOL, located in Locarno in the Southern part of
Switzerland. The project will be carried out in collaboration with
the University of Geneva, and Kiepenheuer Institut in Freiburg,
Germany. The PhD student will be enrolled as a PhD student at the
University of Geneva.
The PhD student will have the
opportunity to work in a lively small group on a challenging and
cutting-edge topic. The work will address on planet engulfing
scenarios considering both theoretical and observational aspects. The
goal will be to study the consequences on the star involved in the
process of planet engulfing, through numerical modeling, and to find
corresponding observational signatures. The PhD student is expected
to get familiar with the instrumentation and the observational
techniques at the IRSOL observatory, where it will be possible to
carry out spectroscopy observations of bright stars and to perform
calibration observations on the Sun. Fainter stars will be observed
at the Gregor telescope in Tenerife or at other large telescopes.
We are seeking an outstanding and highly motivated candidate
with a MSc or equivalent degree in astrophysics, astronomy or physics
with interests in observational techniques and numerical modeling.
The candidates should send a letter of motivation, a CV, academic
transcripts and contact details of three potential referees by post
or by email to the address below. Electronic material should be sent
in a single PDF-file.
IRSOL - via Patocchi - CH-6605 Locarno
Monti – Switzerland
Email: info@irsol.ch with CC:
mbianda@irsol.ch
Links: www.irsol.ch
Gross annual salary:
~ 40000 CHF (ca. 34000 EUR)
Review of applications will begin
November 14, 2011. Start date: to be agreed
For more
information please contact:
Dr. Michele Bianda (IRSOL):
mbianda@irsol.ch, +41 91 743 42 26
Prof. Georges Meynet
(University of Geneva): Georges.Meynet@unige.ch
Prof. Svetlana
Berdjugina (KIS): sveta@kis.uni-freiburg.de
Attention/Comments:
Weblink:
http://www.irsol.ch/Concorso_dottorando.pdf
Email:
info@irsol.ch
Deadline:
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august 2012
Venue:
beijing, china
After the initial announcement sent some
weeks ago, please find below a link to be kept informed of the
meeting and possibly to be considered for an oral
presentation.
Weblink:
http://www.gaphe.ulg.ac.be/IAU_XXVIII/prereg.php
Email:
naze@astro.ulg.ac.be
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Feb. 27th to Mar. 02nd,
2012
Venue: Foz do Iguaçu, Brazil
Second
Announcement
(please circulate among your colleagues)
ESO
Workshop: Circumstellar Dynamics at High Resolution
Foz do
Iguaçu, Brazil, February 27 - March 02, 2012
http://www.eso.org/sci/meetings/2012/csdyn.html
Info:
csdyninfo@eso.org
This workshop aims at bringing together the
active community of hot stellar astrophysicists, both theoreticians
and observers, along the common topic of what can be learned from
high resolution observations. The key topics of the workshop are:
-
Circumstellar Disks & Outflows
- Delta Sco and Be stars as
laboratories for CS disk physics
- Dynamics of Circumstellar
Material and tidal interactions in hot binaries
- Massive star
formation out of a dynamic environment
- Magnetospheres of Hot
Stars
*** REGISTRATION ***
Registrations are open at
http://www.eso.org/sci/meetings/2012/csdyn.html. The deadline for
early registration is Dec. 17th. (200 USD). After this date, the
registration fee will amount to 250 USD (deadline for late
registration is Jan. 13th).
This workshop is co-sponsored by
ESO, Nara (Núcleo de Apoio à Pesquisa em Radioastronomia) and the
University of São Paulo.
We are looking forward to see you
in Brazil in February!
Alex C. Carciofi & Thomas
Rivinius, for the SOC
Weblink:
http://www.eso.org/sci/meetings/2012/csdyn.html
Email:
csdyninfo@eso.org
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March 28 - 30, 2012
Venue:
Space Telescope Science Institute, Baltimore, MD, USA
In
this small workshop of about 60 participants, we will discuss the
topic of mass-loss return to galaxies and the resulting dust and
metal enrichment process. The workshop will be about 2.5 days and
involve talks and audience wide discussions. We have plenty of room
for contributed talks and posters. As the title suggests, the focus
of our workshop is four areas:
1) The parameterizations of
mass-loss rates and their basis in fact for both massive stars and
intermediate mass stars.
2) The variations in mass loss due
to quiescent/smooth, eruptive/episodic, or explosive processes and to
the effects of binary companions.
3) How these
parameterizations affect both theoretical modeling of stellar
evolution and estimates for mass-loss return to galaxies from stellar
populations.
4) The composition in dust, metals and total gas
of the ejecta and how these are incorporated into dust and chemical
evolution of galaxies.
Weblink:
http://www.stsci.edu/institute/conference/mass-loss-return
Email:
fullerton@stsci.edu
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August 2012
Venue:
Beijing, China
Please find below a link to PRE-REGISTER.
(This helps the SOC with the distribution of
presentations)
Weblink: http://www.arm.ac.uk/IAU/
Email:
jsv@arm.ac.uk
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Feb. 27th - Mar. 02nd
Venue: Foz do
Iguaçu, Brazil
Last announcement
ESO Workshop:
Circumstellar Dynamics at High Resolution
Foz do Iguaçu, Brazil,
February 27 - March 02, 2012
http://www.eso.org/sci/meetings/2012/csdyn.html
Info:
csdyninfo@eso.org
The deadline for late registration is
approaching fast: Jan 13th.
Financial support
Support is
available to partially cover hotel expenses for a few students and
post-docs.
Applications can be submitted by via the registration
form.
Sessions will be held on:
1 - Circumstellar Disks &
Outflows: Theory
2 - Circumstellar Disks & Outflows:
Observations
3 - Delta Sco and Be stars as laboratories for CS
disk physics
4 - Dynamics of Circumstellar Material and tidal
interactions in hot binaries
5 - Massive star formation out of a
dynamic environment
6 - Magnetospheres of Hot Stars
Confirmed
invited speakers:
E. Alecian (Observatoire de Paris, France)
J.
Bjorkman (Univ. of Toledo, US)
D. Cohen (Swarthmore College)
W.
Dent (ALMA)
W.-J. de Wit (ESO)
J. Groh (Max-Planck-Institute
for Radioastronomy, Germany)
C. Jones (Univ. of Western Ontario,
Canada)
M. Krumholz (Univ. of California, US)
A. M. Magalhães
(Univ. of São Paulo, Brazil)
F. Millour (Univ. of Nice, France)
A. Miroshnichenko (Univ. of North Carolina at Greensboro, US)
A.
Okazaki (Hokkai-Gakuen Univ., Japan)
R. Oudmaijer (Univ. of
Leeds, UK)
S. Owocki (Univ. of Delaware, US)
R. Townsend
(Univ. of Wisconsin, US)
A. ud-Doula (Penn State W. Scranton, US)
SOC:
D. Baade
A. C. Carciofi (co-chair)
J. E.
Bjorkman
A. Daminelli
W. Dent
A. Domiciano de Souza
Th.
Rivinius (co-chair)
S. Stefl
J. Vink
G. Wade
Venue:
The workshop will take place in Foz do Iguaçu, Brazil, close to
the magnificent Iguaçu Waterfalls, a network of 275 waterfalls in
the Iguaçu River that lies in the border of Brazil and Argentina.
Tours:
Two visits to the waterfalls are planned during
the workshop. For more details, see
http://www.eso.org/sci/meetings/2012/csdyn/local.html#par_title
We
look forward to see you in Brazil next February!
Alex Carciofi,
for the SOC
Weblink:
http://www.eso.org/sci/meetings/2012/csdyn.html
Email:
csdyninfo@eso.org
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