ISSN 1783-3426
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The two components of the evolved
massive binary LZ Cep. Testing the effects of binarity on stellar
evolution
Variability in the CoRoT
photometry of three hot O-type stars. HD 46223, HD 46150 and HD
46966.
Confirmation of the magnetic
oblique rotator model for the Of?p star HD 191612
The
Eddington factor as the key to understand the winds of the most
massive stars. Evidence for a Gamma-dependence of Wolf-Rayet type
mass loss
The bi-stability jump as
the origin for multiple P-Cygni absorption components in Luminous
Blue Variables
The strong magnetic
field of the large-amplitude $beta$,Cephei pulsator V1449,Aql
N
II 5668-5712, a New Class of Spectral Features in Eta
Carinae
Critical Differences and
Clues in Eta Car's 2009 Event
On
the Origin of the Salpeter Slope for the Initial Mass Function
Jet
formation from massive young stars: Magnetohydrodynamics versus
radiation pressure
L-band
spectroscopy of Galactic OB-stars
Further
Results from the Galactic O-Star Spectroscopic Survey: Rapidly
Rotating Late ON Giants
Circumstellar Dynamics at High Resolution
L. Mahy (1), F. Martins (2),
C. Machado (2), J.-F. Donati (3), J.-C. Bouret (4,5)
1:
Institut d’Astrophysique et de Géophysique, Université de Liège,
Belgium
2: LUPM–UMR 5299, CNRS & Université
Montpellier II, France
3: IRAP–UMR 5277, CNRS &
Université. de Toulouse, France
4: LAM–UMR 6110, CNRS &
Université de Provence, France
5: NASA/GSFC, USA
Aims.
We present an in-depth study of the two components of the binary
system LZCep in order to constrain the effects of binarity on the
evolution of massive stars.
Methods. We use a set of
high-resolution, high signal–to-noise ratio optical spectra
obtained over the orbital period of the system to perform a
spectroscopic disentangling and derive an orbital solution. We
subsequently determine the stellar properties of each component
through an analysis with the CMFGEN atmosphere code. Finally, with
the derived stellar parameters, we model the Hipparcos photometric
light curve using the program NIGHTFALL to obtain the inclination and
the real stellar masses.
Results. LZCep is a O9III+ON9.7V binary.
It is as a semi-detached system in which either the primary or the
secondary star almost fills up its Roche lobe. The dynamical masses
are about 16.0 M⊙ (primary) and 6.5 M⊙ (secondary). The latter is
lower than the typical mass of late–type O stars. The secondary
component is chemically more evolved than the primary (which barely
shows any sign of CNO processing), with strong helium and nitrogen
enhancements as well as carbon and oxygen depletions. These
properties (surface abundances and mass) are typical of Wolf-Rayet
stars, although the spectral type is ON9.7V. The luminosity of the
secondary is consistent with that of core He–burning objects. The
preferred, tentative evolutionary scenario to explain the observed
properties involves mass transfer from the secondary – which was
initially more massive– towards the primary. The secondary is now
almost a core He–burning object, probably with only a thin envelope
of H–rich and CNO processed material. A very inefficient mass
transfer is necessary to explain the chemical appearance of the
primary. Alternative scenarios are discussed but they suffer from
more uncertainties.
Reference: A&A, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1106.6162
Comments:
11 pages, 10 figures, 3 tables
Email:
mahy@astro.ulg.ac.be
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R. Blomme (1), L. Mahy (2),
C. Catala (3), J. Cuypers (1), E. Gosset (2), M. Godart (2), J.
Montalban (2), P. Ventura (4), G. Rauw (2), T. Morel (2), P. Degroote
(5), C. Aerts (5,6), A. Noels (2), E. Michel (3), F. Baudin (7), A.
Baglin (3), M. Auvergne (3), R. Samadi (3)
(1) Royal
Observatory of Belgium, Belgium
(2) Institut d'Astrophysique et
de Geophysique, University of Liege, Belgium
(3) LESIA,
Observatoire de Paris, France
(4) INAF, Osservatorio Astronomico
di Roma, Italy
(5) Instituut voor Sterrenkunde, K.U. Leuven,
Belgium
(6) Department of Astrophysics, University of Nijmegen,
The Netherlands
(7) Institut d'Astrophysique Spatiale, Universite
Paris-Sud, France
The detection of pulsational frequencies in
stellar photometry is required as input for asteroseismological
modelling. The second short run (SRa02) of the CoRoT mission has
provided photometric data of unprecedented quality and time-coverage
for a number of O-type stars.
We analyse the CoRoT data
corresponding to three hot O-type stars, describing the properties of
their light curves and we search for pulsational frequencies, which
we then compare to theoretical model predictions.
We determine
the amplitude spectrum of the data, using the Lomb-Scargle and a
multifrequency HMM-like technique. Frequencies are extracted by
prewhitening, and their significance is evaluated under the
assumption that the light curve is dominated by red noise. We search
for harmonics, linear combinations and regular spacings among these
frequencies. We use simulations with the same time sampling as the
data as a powerful tool to judge the significance of our results.
From the theoretical point of view, we use the MAD non-adiabatic
pulsation code to determine the expected frequencies of excited
modes.
A substantial number of frequencies is listed, but none
can be convincingly identified as being connected to pulsations. The
amplitude spectrum is dominated by red noise. Theoretical modelling
shows that all three O-type stars can have excited modes but the
relation between the theoretical frequencies and the observed
spectrum is not obvious.
The dominant red noise component in the
hot O-type stars studied here clearly points to a different origin
than the pulsations seen in cooler O stars. The physical cause of
this red noise is unclear, but we speculate on the possibility of
sub-surface convection, granulation, or stellar wind inhomogeneities
being responsible.
Reference: A&A, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1107.0267
Comments:
13 pages, 8 figures. Tables 2, 3 and 4 available on
ftp://omaftp.oma.be/dist/astro/Blomme.R/CoRoT/
Email:
Ronny.Blomme@oma.be
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G.A. Wade, I.D. Howarth,
R.H.D. Townsend, J.H. Grunhut, M. Shultz, J.-C. Bouret, A. Fullerton,
W. Marcolino, F. Martins, Y. Naze, A. ud Doula, N.R. Walborn, J.-F.
Donati, and the MiMeS Collaboration
Dept. of Physics,
Royal Military College of Canada, PO Box 17000, Stn Forces, Kingston,
Ontario K7K 7B4, Canada
Dept. of Physics and Astronomy, UCL,
Gower Place, London WC1E 6BT, United Kingdom
Dept. of Astronomy,
University of Wisconsin-Madison, 475 N. Charter Street, Madison WI
53706-1582, USA
Dept. of Physics, Engineering Physics and
Astronomy, Queen’s University, 99 University Avenue, Kingston,
Ontario K7L 3N6, Canada
LAM-UMR 6110, CNRS & Universitd ́e
Provence, rue Fre ́de ́ric Joliot-Curie, F-13388 Marseille Cedex
13, France
NASA/GSFC, Code 665, Greenbelt, MD 20771, USA
Space
Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD
21218, USA
Observato ́rio do Valongo, Universidade Federal do
Rio de Janeiro, Rio de Janeiro, Brazil
LUPM-UMR5299, CNRS &
Universite ́ Montpellier II, Place Euge`ne Bataillon, F-34095,
Montpellier, France
FNRS-Institut d’Astrophysique et de Ge
́ophysique, Universite ́ de Lie`ge, Belgium
Penn State
Worthington Scranton, 120 Ridge View Drive, Dunmore, PA, USA 18512
Observatoire Midi-Pyre ́n ́e ́es, 14 avenue E ́douard Belin,
F-31400, Toulouse, France
This paper reports high-precision
Stokes V spectra of HD 191612 acquired using the ESPaDOnS
spectropolarimeter at the Canada-France-Hawaii Telescope, in the
context of the Magnetism in Massive stars (MiMeS) Project. Using
measurements of the equivalent width of the Hα line and radial
velocities of various metallic lines, we have updated both the
spectroscopic and orbital ephemerides of this star. We confirm the
presence of a strong magnetic field in the photosphere of HD 191612,
and detect its variability. We establish that the longitudinal field
varies in a manner consistent with the spectroscopic period of 537.6
d, in an approximately sinusoidal fashion. The phases of minimum and
maximum longitudinal field are respectively coincident with the
phases of maximum and minimum Hα equivalent width and Hp magnitude.
This demonstrates a firm connection between the magnetic field and
the processes responsible for the line and continuum variability.
Interpreting the variation of the longitudinal magnetic field within
the context of the dipole oblique rotator model, and adopting an
inclination i = 30◦ obtained assuming alignment of the orbital and
rotational angular momenta, we obtain a best-fit surface magnetic
field model with obliquity β = 67 ± 5◦ and polar strength Bd =
2450 ± 400 G . The inferred magnetic field strength implies an
equatorial wind magnetic confinement parameter η∗ ≃ 50,
supporting a picture in which the Hα emission and photometric
variability have their origin in an oblique, rigidly rotating
magnetospheric structure resulting from a magnetically channeled
wind. This interpretation is supported by our successful Monte Carlo
radiative transfer modeling of the photometric variation, which
assumes the enhanced plasma densities in the magnetic equatorial
plane above the star implied by such a picture, according to a
geometry that is consistent with that derived from the magnetic
field. Predictions of the continuum linear polarisation resulting
from Thompson scattering from the magnetospheric material indicate
that the Stokes Q and U variations are highly sensitive to the
magnetospheric geometry, and that expected amplitudes are in the
range of current instrumentation.
Reference: MNRAS,
accepted and in press
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/pdf/1106.3008v1
Comments:
Email: wade-g@rmc.ca
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G. Gräfener^1, J.S. Vink^1,
A. de Koter^2,4, N. Langer^3,4
(1) Armagh Observatory,
College Hill, Armagh BT61 9DG, United Kingdom
(2) Astronomical
Institute “Anton Pannekoek”, University of Amsterdam, Science
Park XH, Amsterdam, The Netherlands
(3) Argelander-Institut f¨ur
Astronomie der Universit¨at Bonn, Auf dem H¨ugel 71, 53121 Bonn,
Germany
(4) Astronomical Institute, Utrecht University,
Princetonplein 5, 3584 CC Utrecht, The Netherlands
The most
massive stars are thought to be hydrogen-rich Wolf-Rayet stars of
late spectral subtype (WNh stars). In previous theoretical studies
the enhanced mass loss of these stars has been attributed to their
proximity to the Eddington limit. Here we investigate observed trends
in the mass-loss properties of such young, very massive stars. We
derive theoretical mass-luminosity relations for very massive stars,
based on a large grid of stellar structure models. Using these
relations, we estimate Eddington factors for a sample of stars, under
different assumptions of their evolutionary status. We evaluate the
resulting mass-loss relations, and compare them with theoretical
predictions. We find observational evidence that the mass loss in the
WR regime is dominated by the Eddington parameter Gamma_e, which has
important consequences for the way we understand Wolf-Rayet stars and
their mass loss. In addition, we derive wind masses that support the
picture that the WNh stars in young stellar clusters are very
massive, hydrogen-burning stars. Our findings suggest that the
proximity to the Eddington limit is the physical reason for the onset
of Wolf-Rayet type mass loss. This means that, e.g. in stellar
evolution models, the Wolf-Rayet stage should be identified by large
Eddington parameters, instead of a helium-enriched surface
composition. The latter is most likely only a consequence of strong
mass loss, in combination with internal mixing. For very massive
stars, the enhanced Gamma-dependent mass loss is responsible for the
formation of late WNh subtypes with high hydrogen surface abundances,
partly close to solar. Because mass loss dominates the evolution of
very massive stars, we expect a strong impact of this effect on their
end products, in particular on the potential formation of black
holes, and Gamma-Ray Bursts, as well as the observed upper mass limit
of stars.
Reference: A&A
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1106.5361
Comments:
Email: ggr@arm.ac.uk
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Jose H. Groh (1) and Jorick
S. Vink (2)
(1) Max-Planck-Institute for Radioastronomy,
Germany; (2) Armagh Observatory, UK
Luminous Blue Variables
(LBVs) oftentimes show double-troughed absorption in their strong
Halpha lines, which are as yet not understood. Intriguingly, the
feature has also been seen in the interacting supernova SN 2005gj,
which was for this reason suggested to have an LBV progenitor. Our
aims are to understand the double-troughed absorption feature in LBVs
and investigate whether this phenomenon is related to wind
variability. To this purpose, we perform time-dependent radiative
transfer modeling using CMFGEN. We find that abrupt changes in the
wind-terminal velocity - as expected from the bi-stability jump - are
required to explain the double-troughed absorption profiles in LBVs.
This strengthens scenarios that discuss the link between LBVs and SNe
utilizing the progenitor's wind variability resulting from the
bi-stability jump. We also discuss why the presence of
double-troughed P-Cygni components may become an efficient tool to
detect extra-galactic LBVs and how to analyze their mass-loss history
on the basis of just one single epoch of spectral
observations.
Reference: A&A 531, 10
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1106.3007
Comments:
Email: jgroh@mpifr.de
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S.~Hubrig$^1$, I.~Ilyin$^1$,
M.~Briquet$^{2,3}$, M.~Sch"oller$^4$, J.~F.~Gonz'alez$^5$,
N.~Nu~nez$^5$, P. De Cat$^6$, T. Morel$^7$
$^1$
Leibniz-Institut f"ur Astrophysik Potsdam (AIP), An der
Sternwarte 16, 14482 Potsdam, Germany
$^2$ Instituut voor
Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D,
3001~Leuven, Belgium
$^3$ LESIA, Observatoire de Paris, CNRS,
UPMC, Universit'e Paris-Diderot, 92195 Meudon, France
$^4$
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748
Garching bei M"unchen, Germany
$^5$ Instituto de Ciencias
Astronomicas, de la Tierra, y del Espacio (ICATE), 5400 San Juan,
Argentina
$^6$ Koninklijke Sterrenwacht van Belgi"e,
Ringlaan 3, 1180 Brussel, Belgium
$^7$ Institut d'Astrophysique
et de G'eophysique, Universit'e de Li`ege, All'ee du 6 Ao^ut, B^at.
B5c, 4000~Li`ege, Belgium
Only for very few $beta$~Cephei
stars has the behaviour of the magnetic field
been studied over
the rotation cycle. During the past two years we have obtained
multi-epoch polarimetric spectra of the $beta$~Cephei star
V1449,Aql with
SOFIN at the Nordic Optical Telescope to search
for a rotation period and to
constrain the geometry of the
magnetic field.
The mean longitudinal magnetic field is
measured at 13 different epochs. The new
measurements, together
with the previous FORS,1 measurements, have been used
for the
frequency analysis and the characterization of the magnetic field.
V1449,Aql so far possesses the strongest longitudinal
magnetic field of up to
700,G among the $beta$,Cephei stars. The
resulting periodogram displays three
dominant peaks with the
highest peak at $f=0.0720$,d$^{-1}$ corresponding to a
period
$P=13fd893$. The magnetic field geometry can likely be described by a
centred dipole with a polar magnetic field strength $B_{rm d}$
around 3,kG and
an inclination angle $beta$ of the magnetic axis
to the rotation axis of
76$pm$4$^{circ}$. As of today, the
strongest longitudinal magnetic fields are
detected in the
$beta$,Cephei stars V1449,Aql and $xi^1$,CMa with large
radial
velocity amplitudes. Their peak-to-peak amplitudes reach
$sim$90,km,s$^{-1}$ and $sim$33,km,s$^{-1}$, respectively.
Concluding, we
briefly discuss the position of the currently
known eight magnetic
$beta$,Cephei and candidate $beta$,Cephei
stars in the Hertzsprung-Russell
(H-R) diagram.
Reference:
A&A 531, L20 (2011)
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1107.0883
Comments:
Email: mschoell@eso.org
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Andrea Mehner(1), Kris
Davidson(1), Gary J. Ferland(2)
(1) Department of
Astronomy, University of Minnesota, Minneapolis, MN 55455
(2)
Department of Physics & Astronomy, University of Kentucky,
Lexington, KY 40506
We report on the N II 5668-5712 emission
and absorption lines in the spectrum of eta Carinae. Spectral lines
of the stellar wind regions can be classified into four physically
distinct categories: 1) low-excitation emission such as H I and Fe
II, 2) higher excitation He I features, 3) the N II lines discussed
in this paper, and 4) He II emission. These categories have different
combinations of radial velocity behavior, excitation processes, and
dependences on the secondary star. The N II lines are the only known
features that originate in “normal” undisturbed zones of the
primary wind but depend primarily on the location of the hot
secondary star. N II probably excludes some proposed models, such as
those where He I lines originate in the secondary star’s wind or in
an accretion disk.
Reference: ApJ
Status: Manuscript
has been accepted
Email: mehner@astro.umn.edu
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Andrea Mehner(1), Kris
Davidson(1), John C. Martin(2), Roberta M. Humphreys(1), Kazunori
Ishibashi(3), Gary J. Ferland(4)
1 - Department of
Astronomy, University of Minnesota, Minneapolis, MN 55455, USA; 2 -
University of Illinois Springfield, Springfield, IL 62703, USA; 3 -
Department of Physics, Nagoya University, Nagoya 464-8602, Japan; 4 -
Department of Physics & Astronomy, University of Kentucky,
Lexington, KY 40506, USA
We monitored Eta Carinae with {it
HST/} WFPC2 and {it Gemini/} GMOS throughout the 2009 spectroscopic
event, which was expected to differ from its predecessor in 2003.
Here we report major observed differences between events, and their
implications. Some of these results were quite unexpected. (1) The UV
brightness minimum was much deeper in 2009. This suggests that
physical conditions in the early stages of an event depend on
different parameters than the ``normal'' inter-event wind. Extra mass
ejection from the primary star is one possible cause. (2) The
expected ion{He}{2} $lambda$4687 brightness maximum was followed
several weeks later by another. We explain why this fact, and the
timing of the $lambda$4687 maxima, strongly support a ``shock
breakup'' hypothesis for X-ray and $lambda$4687 behavior as proposed
5--10 years ago. (3) We observed a polar view of the star via light
reflected by dust in the Homunculus nebula. Surprisingly, at that
location the variations of emission-line brightness and Doppler
velocities closely resembled a direct view of the star; which should
not have been true for any phenomena related to the orbit. This
result casts very serious doubt on all the proposed velocity
interpretations that depend on the secondary star's orbital motion.
(4) Latitude-dependent variations of ion{H}{1}, ion{He}{1} and
ion{Fe}{2} features reveal aspects of wind behavior during the event.
In addition, we discuss implications of the observations for several
crucial unsolved problems.
Reference: ApJ
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1106.5869
Comments:
Email: mehner@astro.umn.edu
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M. S. Oey
University
of Michigan
We suggest that the intrinsic, stellar initial
mass function (IMF) follows a power-law slope gamma=2, inherited from
hierarchical fragmentation of molecular clouds into clumps and clumps
into stars. The well-known, logarithmic Salpeter slope GAMMA=1.35 in
clusters is then the aggregate slope for all the star-forming clumps
contributing to an individual cluster, and it is steeper than the
intrinsic slope within individual clumps because the smallest
star-forming clumps contributing to any given cluster are unable to
form the highest-mass stars. Our Monte Carlo simulations demonstrate
that the Salpeter power-law index is the limiting value obtained for
the cluster IMF when the lower-mass limits for allowed stellar masses
and star-forming clumps are effectively equal, m_lo = M_lo. This
condition indeed is imposed for the high-mass IMF tail by the
turn-over at the characteristic value $m_csim 1 rm M_sun. IMF slopes
of GAMMA ~ 2 are obtained if the stellar and clump upper-mass limits
are also equal, m_up = M_up ~ 100 M_sun, and so our model explains
the observed range of IMF slopes between GAMMA ~ 1 to 2. Flatter
slopes of GAMMA = 1 are expected when M_lo > m_up, which is a
plausible condition in starbursts, where such slopes are suggested to
occur. While this model is a simplistic parameterization of the
star-formation process, it seems likely to capture the essential
elements that generate the Salpeter tail of the IMF for massive
stars. These principles also likely explain the IGIMF effect seen in
low-density star-forming environments.
Reference: ApJ
Letters, in press
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2011arXiv1108.2287O
Comments:
Email: msoey@umich.edu
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Bhargav Vaidya [1], Christian
Fendt [1], Henrik Beuther [1] and Oliver Porth[1]
[1] Max
Planck Institute for Astronomy, Heidelberg
Observations
indicate that outflows from massive young stars are more collimated
during their early
evolution compared to later stages.
Our
paper investigates various physical processes that impacts the
outflow dynamics, i.e. its acceleration and collimation.
We
perform axisymmetric MHD simulations particularly considering the
radiation
pressure exerted by the star and the disk.
We have
modified the PLUTO code to include radiative forces
in the
line-driving approximation.
We launch the outflow from the
innermost disk region ($r < 50$,AU)
by magneto-centrifugal
acceleration.
In order to disentangle MHD effects from radiative
forces, we start the
simulation in pure MHD, and later switch on
the radiation force.
We perform a parameter study considering
different stellar masses (thus luminosity),
magnetic flux, and
line-force strength.
For our reference simulation - assuming a
$30msun$ star, we find substantial de-collimation of 35%
due to
radiation forces.
The opening angle increases from $20^circ$ to
$32^circ$ for stellar masses from
$20msun$ to $60msun$.
A
small change in the line-force parameter $alpha$ from 0.60 to 0.55
changes the opening angle
by $sim 8^circ$.
We find that it is
mainly the stellar radiation which affects the jet
dynamics.
Unless the disk extends very close to the star, its pressure is too
small to have much impact.
Essentially, our parameter runs with
different stellar mass can be understood
as a proxy for the time
evolution of the star-outflow system.
Thus, we have shown that
when the stellar mass (thus luminosity) increases
(with age), the
outflows become less collimated.
Reference: Accepted
for publication in ApJ
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1108.4924
Comments:
Email: vaidya@mpia.de
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F. Najarro$^1$, M.M.
Hanson$^2$ and J. Puls$^3$
$^1$Centro de Astrobiología,
(CSIC-INTA), Ctra. Torrejón Ajalvir km4, 28850 Torrejón de Ardoz,
Spain
$^2$Department of Physics, University of Cincinnati, PO Box
21001, Cincinnati, Ohio, 45221-0011, USA
$^3$Universitätssternwarte
München, Scheinerstr. 1, D-81679 München, Germany
Context.
Mass-loss, occurring through radiation driven supersonic winds, is a
key issue throughout the evolution of massive stars. Two outstanding
problems are currently challenging the theory of radiation-driven
winds: wind clumping and the weak-wind problem. Aims. We seek to
obtain accurate mass-loss rates of OB stars at different evolutionary
stages to constrain the impact of both problems in our current
understanding of massive star winds. Methods. We perform a
multi-wavelength quantitative analysis of a sample of ten Galactic
OB-stars by means of the atmospheric code CMFGEN, with special
emphasis on the L-band window. A detailed investigation is carried
out on the potential of Bralpha and Pfgamma as mass-loss and clumping
diagnostics. Results. For objects with dense winds, Bralpha samples
the intermediate wind while Pfgamma maps the inner one. In
combination with other indicators (UV, Halpha, Brgamma) these lines
enable us to constrain the wind clumping structure and to obtain
"true" mass-loss rates. For objects with weak winds,
Bralpha emerges as a reliable diagnostic tool to constrain the
mass-loss rates. The emission component at the line Doppler-core
superimposed on the rather shallow Stark absorption wings reacts very
sensitively to mass loss already at very low mass-loss values. On the
other hand, the line wings display similar sensitivity to mass loss
as Halpha, the classical optical mass loss diagnostics. Conclusions.
Our investigation reveals the great diagnostic potential of L-band
spectroscopy to derive clumping properties and mass-loss rates of hot
star winds. We are confident that Bralpha will become the primary
diagnostic tool to measure very low mass-loss rates with
unprecedented accuracy
Reference: A&A
Status:
Manuscript has been accepted
Weblink:
http://es.arxiv.org/abs/1108.5752v1
Comments:
Email: najarro@cab.inta-csic.es
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Nolan R. Walborn$^1$, Jesús
Maíz Apellániz$^2$, Alfredo Sota$^2$, Emilio J. Alfaro$^2$, Nidia
I. Morrell$^3$, Rodolfo H. Barbá$^4$, Julia I. Arias$^4$, and
Roberto C. Gamen$^5$
1 - STScI, Baltimore, USA; 2 -
IAA-CSIC, Granada, Spain; 3 - Carnegie Observatories, La Serena,
Chile; 4 - Universidad de La Serena, La Serena, Chile; 5 -
IALP-CONICET, La Plata, Argentina
With new data from the
Galactic O-Star Spectroscopic Survey, we confirm and expand the ONn
category of late-O, nitrogen-enriched (N), rapidly rotating (n)
giants. In particular, we have discovered two ``clones'' (HD 102 415
and HD 117 490) of one of the most rapidly rotating O stars
previously known (HD 191 423, ``Howarth’s Star''). We compare the
locations of these objects in the theoretical HR Diagram to those of
slowly rotating ON dwarfs and supergiants. All ON giants known to
date are rapid rotators, whereas no ON dwarf or supergiant is; but
all ON stars are small fractions of their respective spectral-
type/luminosity-class/rotational subcategories. The ONn giants,
displaying both substantial processed material and high rotation at
an intermediate evolutionary stage, may provide significant
information about the development of those prop- erties. They may
have preserved high initial rotational velocities or been spun up by
TAMS core contraction; but alternatively and perhaps more likely,
they may be products of binary mass transfer. At least some of them
are also runaway stars.
Reference: To appear in the
November 2011 issue of AJ
Status: Manuscript has been
accepted
Weblink:
Comments:
Email:
jmaiz@iaa.es
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February 27th - March 02nd, 2012
Venue: Foz
do Iguaçu,
Brazil
*************************************************************************
*
* First Announcement
*
* Workshop
*
*
Circumstellar Dynamics at High Resolution
*
* Foz do Iguaçu,
Brazil, February 27 - March 02, 2012
*
* ESO - Univ. of São
Paulo
*
*************************************************************************
This is the first announcement of a conference on "Circumstellar
Dynamics at High Resolution" to be held February 27 to March 02,
2012. The venue of the meeting will be in Foz do Iguaçu, Brazil.
The Workshop is sponsored by ESO and the University of São
Paulo. More detailed information is available on our web page:
http://www.eso.org/sci/meetings/2012/csdyn.html
or by
email to csdyninfo@eso.org.
We encourage you to circulate the
announcement among your colleagues.
On behalf of the
organizers,
Alex Carciofi
*************************************************************************
*** SCOPE ***
The dynamics of circumstellar (CS)
envelopes is an active research frontier that has benefited greatly
from the advent of high-resolution observational techniques in the
spectral, spatial and temporal domains. The observational discoveries
and theoretical results emerging from this field have broad
implications for many astrophysical topics, ranging from cosmology
(via a better understanding of the progenitors of GRBs, for
instance), to star and planet formation (through a better description
of CS disk dynamics in which viscosity plays a key role).
The
diverse and complex CS environments revealed by these observational
techniques are particularly evident near hot high-mass stars, where
stellar radiation plays a large if not crucial role in continuously
shaping the immediate environment.
High-resolution
observations (spatial, spectral, and temporal) have provided
important information in several frontline research topics. For
example, many hot stars have been shown to be very rapidly rotating,
in a regime where geometric deformation and gravity darkening become
important. CS structures have not only been resolved spatially, but
have been followed over characteristic variation timescales. This
dynamical evolution has been modeled for disks and winds: we are now
directly observing and measuring the consequence of the physical
mechanisms operating within the CS environments. As a result, current
observing facilities have allowed the field to progress from a static
picture of the CS environment towards understanding its dynamics and
concomitant impact on the evolution of the central star.
This
workshop aims at bringing together the active community of hot
stellar astrophysics, both theoreticians and observers, along the
common topic of what can be learned from high resolution
observations.
*** PROGRAM ***
Oral sessions during the
meeting 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
*** 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. The
site was designated World Heritage by UNESCO. Tourist attractions
include visits to both the Brazilian and Argentinian sides of the
Falls, natural parks, and the dam of the Itaipu Hydroeletric
Facility. In 1994, the American Society of Civil Engineers elected
the Itaipu Dam as one of the seven modern Wonders of the World.
The
Meeting will take place in the Rafain Hotel and Convention Centers
(http://www.rafainpalace.com.br/v2/home/). Special rates are
available for the period of the conference. Hotel costs are 274 BRL
(170 USD) for single occupancy and 171 BRL (106 USD) per person for
double occupancy. Those rates include full board (breakfast, morning
coffebreak, lunch, afternoon coffebreak and dinner).
IMPORTANT
NOTE: all participants are encouraged to register in this hotel for
two reasons. First, those low rates will only be secured if a minimum
of 50 rooms is booked. Second, the hotel is far from the city (10km)
and there are no restaurants nearby.
*** PRE-REGISTRATION ***
If you intend to participate in the workshop please fill in the
pre-registration form in our web page. This is not a formal
registration, and requires no commitment from you. Our goal is to
have an idea about the number of participants for organization
purposes.
*** PROCEEDINGS ***
We will have online
conference proceedings, whether these will be published in print
depends on funding decisions made towards the end of 2011 only.
***
FINANCIAL MATTERS ***
The workshop fee will be 200 USD. We will
have some limited financial support for students and young
researchers. Money will be requested for the Brazilian students that
do not have research contingency funds.
*** DEADLINES ***
Requests for financial support must be submitted by Nov. 1st at
the latest, together with the abstract of the intended contribution.
The deadline for the final registration and abstracts is Dec. 17th.
*** CONTACT ***
- Website:
http://www.eso.org/sci/meetings/2012/csdyn.html
- Mail:
csdyninfo@eso.org
SOC: A. C. Carciofi (co-chair), D. Baade,
J. E. Bjorkman, A. Damineli, W. Dent, A. Domiciano de Souza, Th.
Rivinius (co-chair), S. Stefl, J. Vink, G. Wade
LOC: A.
Carciofi (chair), A. Damineli, M. Borges, M. Teodoro, C. Barbosa, D.
M. Faes, M.E. Gomez, Th. Rivinius and C. Martayan
Weblink:
http://www.eso.org/sci/meetings/2012/csdyn.html
Email:
carciofi@usp.br
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