ISSN 1783-3426
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Revisiting the Rigidly Rotating
Magnetosphere model for $sigma$ Ori E. I. Observations and Data
Analysis
WR 38/38a and the ratio of
total-to-selective extinction in Carina
Near-infrared
study of the stellar population of Sh2-152
Spectral
modeling of circular massive binary systems: Towards an understanding
of the Struve-Sahade effect?
A
spectroscopic investigation of early-type stars in the young open
cluster Westerlund 2
Nitrogen line
spectroscopy of O-stars -- I. Nitrogen III emission line formation
revisited
The massive star binary
fraction in young open clusters - III. IC 2944 and the Cen OB2
association
A double detached shell
around a post-Red Supergiant:IRAS 17163-3907, the Fried Egg
nebula
Radio Continuum Emission
from FS CMa Stars
Wind structure
and luminosity variations in the WR/LBV HD 5980
A
Binary Orbit for the Massive, Evolved Star HDE 326823, a WR+O System
Progenitor
A multi-epoch XMM-Newton
campaign on the core of the massive Cyg OB2 association
Nitrogen
line spectroscopy in O-stars -- II. Surface nitrogen abundances for
O-stars in the Large Magellanic Cloud
A
quantitative study of O stars in NGC2244 and the Mon OB2
association
An obscured cluster
associated with the H II region RCW173
X-ray
emission from massive stars with magnetic fields
Completing the Massive Star Population:
Striking Into the Field
CoRoT
observations of O stars: diverse origins of variability
The
IMF of Field OB Stars in the Small Magellanic Cloud
Discovery
of a new Wolf-Rayet star using SAGE-LMC
Sparse
Aperture Masking of Massive Stars
The
nature and consequences of clumping in hot, massive star winds
Astrophysics
at Extremely High Angular Resolution: Optical and Infrared
Interferometry
The Physics of
Astronomical Transients
The
Evolution of Massive Stars and Progenitors of GRBs
The
IR view of massive stars: the main sequence and beyond
Very
Massive Stars in the Local Universe
On-line database of Milky Way
Wolf-Rayet stars, updated with respect to VIIth WR Catalogue (van der
Hucht 2001, 2006). Catalogue currently includes 547 WR stars, as of
October 2011, and is intended to be complementary to Galactic O-star
catalog http://gosc.iaa.es/ Please send updates to Paul
Crowther.
Weblink:
http://pacrowther.staff.shef.ac.uk/WRcat/
Email:
Paul.Crowther@sheffield.ac.uk
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M.E. Oksala$^{1,2}$, G.A.
Wade$^2$, R.H.D. Townsend$^{3}$, S.P. Owocki$^{1}$, O.
Kochukhov$^{4}$, C. Neiner$^{5}$, E. Alecian$^{5}$, J.
Grunhut$^{2,6}$, and the MiMeS Collaboration
1 - Bartol
Research Institute, University of Delaware, USA;
2 - Royal
Military College of Canada;
3 - University of Wisconsin-Madison,
USA;
4 - Uppsala University, Sweden;
5 - LESIA, France;
6
- Queen's University, Canada
We have obtained 18 new
high-resolution spectropolarimetric observations of the B2Vp star
$sigma$ Ori E with both the Narval and ESPaDOnS spectropolarimeters.
The aim of these observations is to test, with modern data, the
assumptions of the Rigidly Rotating Magnetosphere (RRM) model of
Townsend & Owocki (2005), applied to the specific case of $sigma$
Ori E by Townsend et al. (2005). This model includes a substantially
offset dipole magnetic field configuration, and approximately
reproduces previous observational variations in longitudinal field
strength, photometric brightness, and H$alpha$ emission. We analyze
new spectroscopy, including H~{sc i}, He~{sc i}, C~{sc ii}, Si~{sc
iii} and Fe~{sc iii} lines, confirming the diversity of variability
in photospheric lines, as well as the double S-wave variation of
circumstellar hydrogen. Using the multiline analysis method of
Least-Squares Deconvolution (LSD), new, more precise longitudinal
magnetic field measurements reveal a substantial variance between the
shapes of the observed and RRM model time-varying field. The phase
resolved Stokes~$V$ profiles of He{sc i} 5876 AA~and 6678 AA~lines
are fit poorly by synthetic profiles computed from the magnetic
topology assumed by Townsend et al. (2005). These results challenge
the offset dipole field configuration assumed in the application of
the RRM model to $sigma$ Ori E, and indicate that future models of
its magnetic field should also include complex, higher-order
components.
Reference: MNRAS
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1109.0328
Comments:
Email: meo@udel.edu
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David G. Turner
Saint
Mary's University, Halifax, Nova Scotia, Canada.
A reanalysis
of the (seemingly very distant) open cluster Shorlin 1, the group of
stars associated with WR 38 and WR 38a, is made on the basis of
existing UBV and JHKs observations for cluster members. The 2MASS
observations, in particular, imply a mean cluster reddening of
E(B-V)=1.45+-0.07 and a distance of 2.94+-0.12 kpc. The reddening
agrees with the UBV results provided that the local reddening slope
is described by E(U-B)/E(B-V)=0.64+-0.01, but the distance estimates
in the 2MASS and UBV systems agree only if the ratio of
total-to-selective extinction for the associated dust is
R=Av/E(B-V)=4.0+-0.1. Both results are similar to what has been
obtained for adjacent clusters in the Eta Carinae region by similar
analyses, which suggests that `anomalous' dust extinction is
widespread through the region, particularly for groups reddened by
relatively nearby dust. Dust associated with the Eta Carinae complex
itself appears to exhibit more `normal' qualities. The results have
direct implications for the interpretation of distances to optical
spiral arm indicators for the Galaxy at l=287-291 degrees, in
particular the Carina arm here is probably little more than ~2 kpc
distant, rather than 2.5-3 kpc distant as implied in previous
studies. Newly-derived intrinsic parameters for the two cluster
Wolf-Rayet stars WR 38 (WC4) and WR 38a (WN5) are in good agreement
with what is found for other WR stars in Galactic open clusters,
which was not the case previously.
Reference: Ap&SS
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1108.3567
Comments:
Email: turner@ap.smu.ca
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S. Ramírez Alegría (1,2),
A. Herrero (1,2), A. Marín-Franch (3,4), E. Puga (5), F. Najarro
(5), J. A. Acosta Pulido (1,2), S. L. Hidalgo (1,2), and S.
Simón-Díaz (1,2)
1- Instituto de Astrofísica de
Canarias, Tenerife, Spain; 2- Departamento de Astrofísica, ULL,
Tenerife, Spain; 3- Centro de Estudios de Física del Cosmos de
Aragón (CEFCA), Teruel, Spain; 4- Departamento de Astrofísica,
Universidad Complutense de Madrid, Spain; 5- Centro de Astrobiología
(CSIC-INTA), Madrid, Spain.
Context: The discovery of new
massive star clusters and massive stellar populations in previously
known clusters in our Galaxy by means of infrared studies has changed
our view of the Milky Way from an inactive to an active star-forming
machine. Within this scenario, we present a near-infrared
spectrophotometric study of the stellar content of the compact H II
region Sh2-152.
Aims: We aim to determine the distance,
extinction, age, and mass of Sh2-152, using for the first time
near-infrared stellar classification for several sources in the
region.
Methods: Using our near-infrared (J, H, and Ks)
photometry and the colour-magnitude diagram for the cluster field, we
selected 13 bright stars, candidate members of the reddened cluster's
main sequence, for H- and K- spectroscopy and spectral
classification. This near-infrared information was complemented with
an optical spectrum of the ionizing central star to confirm its
spectral nature.
Results: From the 13 spectroscopically
observed stars, 5 were classified as B-type, 3 as G-type, 2 were
young stellar objects (YSOs), and 3 remained unclassified (because of
the poor data quality). The cluster's extinction varies from
A_(Ks)=0.5 to 2.6 magnitudes (A_V=4.5 to 24 magnitudes) and the
distance is estimated to be 3.21±0.21 kpc. The age of the cluster is
younger than 9.4 Myr and the lower limit to the total mass of the
cluster is (2.45±0.79)·10³ M_(Sun). We compare the number of
ionizing photons emitted from the OB-type stars with the Lyman
continuum photons derived from the radio observations and conclude
that both quantities are consistent for the central region of
Sh2-152. In contrast, the main ionizing source of the lower region
remains unidentified.
Reference: A&A, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1108.6258
Comments:
Email: sramirez@iac.es
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Matthieu Palate, Gregor
Rauw
Institut d'Astrophysique & Geophysique, Liege,
Belgium
Context: Some secondary effects are known to introduce
variations in spectra of massive binaries. These phenomena (such as
the Struve-Sahade effect, difficulties to determine properly the
spectral type,...) have been reported and documented in the
literature. Aims: We simulate the spectra of circular massive
binaries at different phases of the orbital cycle and accounting for
the gravitational influence of the companion star on the shape and
physical properties of the stellar surface. Methods: We use the Roche
potential to compute the stellar surface, von Zeipel theorem and
reflection effects to compute the surface temperature. We then
interpolate in a grid of NLTE plan-parallel atmosphere model spectra
to obtain the local spectrum at each surface point. We finally sum
all the contributions (accounting for the Doppler shift,
limb-darkening, ...) to obtain the total spectrum. The computation is
done for different orbital phases and for different sets of physical
and orbital parameters. Results: Our first models reproduce the
Struve-Sahade effect for several lines. Another effect, surface
temperature distribution is visible but the distribution predicted by
our current model is not yet consistent with observations.
Conclusions: In some cases, the Struve-Sahade effect as well as more
complex line intensity variations could be linked to blends of
intrinsically asymmetric line profiles that are not appropriately
treated by the deblending routine. Systematic variations of lines for
(nearly) contact systems are also predicted by the model.
Reference:
Astronomy & Astrophysics
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1109.1103
Comments:
Email: palate@astro.ulg.ac.be
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Gregor Rauw (1), Hugues Sana
(2), Yaël Nazé (1)
1 - Institut d'Astrophysique &
Geophysique, Liege, Belgium; 2 - Sterrenkundig Instituut 'Anton
Pannekoek', Amsterdam, The Netherlands
The distance of the
very young open cluster Westerlund 2, which contains the very massive
binary system WR 20a and is likely associated with a TeV source, has
been the subject of much debate. We attempt a joint analysis of
spectroscopic and photometric data of eclipsing binaries in the
cluster to constrain its distance. A sample of 15 stars, including
three eclipsing binaries (MSP 44, MSP 96, and MSP 223) was monitored
with the FLAMES multi-object spectrograph. The spectroscopic data are
analysed together with existing BV photometry. The analysis of the
three eclipsing binaries clearly supports the larger values of the
distance, around 8 kpc, and rules out values of about 2.4 - 2.8 kpc
that have been suggested in the literature. Furthermore, our
spectroscopic monitoring reveals no clear signature of binarity with
periods shorter than 50 days in either the WN6ha star WR 20b, the
early O-type stars MSP 18, MSP 171, MSP 182, MSP 183, MSP 199, and
MSP 203, or three previously unknown mid O-type stars. The only newly
identified candidate binary system is MSP 167. The absence of a
binary signature is especially surprising for WR 20b and MSP 18,
which were previously found to be bright X-ray sources. The distance
of Westerlund 2 is confirmed to be around 8 kpc as previously
suggested based on the spectrophotometry of its population of O-type
stars and the analysis of the light curve of WR 20a. Our results
suggest that short-period binary systems are not likely to be common,
at least not among the population of O-type stars in the
cluster.
Reference: Astronomy &
Astrophysics
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1109.1086
Comments:
Email: rauw@astro.ulg.ac.be
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J.G. Rivero Gonzalez(1), J.
Puls(1), and F. Najarro(2)
(1) Universitätssternwarte
München, Scheinerstr. 1, 81679 München, Germany
(2) Centro de
Astrobiologia (CSIC-INTA), Ctra. Torrejon a Ajalvir km 4, 28850
Torrejon de Ardoz, Spain
Context: Evolutionary models of
massive stars predict a surface enrichment of Nitrogen, due to
rotational mixing. Recent studies within the VLT-FLAMES survey of
massive stars have challenged (part of) these predictions. Such
systematic determinations of Nitrogen abundances, however, have been
mostly performed only for cooler (B-type) objects. For the most
massive and hottest stars, corresponding results are scarce.
Aims:
This is the first paper in a series dealing with optical Nitrogen
spectroscopy of O-type stars, aiming at the analysis of Nitrogen
abundances for stellar samples of significant size, to place further
constraints on the early evolution of massive stars. Here we
concentrate on the formation of the optical NIII lines at lambda
lambda 4634/40/42 A that are fundamental for the definition of the
different morphological `f'-classes.
Methods: We implement a
new Nitrogen model atom into the NLTE atmosphere/spectrum synthesis
code FASTWIND, and compare the resulting optical NIII spectra with
other predictions, mostly from the seminal work by Mihalas &
Hummer (1973, ApJ 179, 827, `MH'), and from the alternative code
CMFGEN.
Results: Using similar model atmospheres as MH (not
blanketed and wind-free), we are able to reproduce their results, in
particular the optical triplet emission lines. According to MH, these
should be strongly related to dielectronic recombination and the
drain by certain two-electron transitions. However, using realistic,
fully line-blanketed atmospheres at solar abundances, the key role of
the dielectronic recombinations controlling these emission features
is superseded -- for O-star conditions -- by the strength of the
stellar wind and metallicity. Thus, in the case of wind-free (weak
wind) models, the resulting lower ionizing EUV-fluxes severely
suppress the emission. As the mass loss rate is increased, pumping
through the NIII resonance line(s) in the presence of a
near-photospheric velocity field (i.e., the Swings-mechanism) results
in a net optical triplet line emission. A comparison with results
from CMFGEN is mostly satisfactory, except for the range 30,000 K <
Teff < 35,000 K, where CMFGEN triggers the triplet emission at
lower Teff than FASTWIND. This effect could be traced down to line
overlap effects between the NIII and OIII resonance lines that cannot
be simulated by FASTWIND so far, due to the lack of a detailed OIII
model atom.
Conclusions: Since the efficiency of dielectronic
recombination and `two electron drain' strongly depends on the degree
of line-blanketing/-blocking, we predict the emission to become
stronger in a metal-poor environment, though lower wind-strengths and
Nitrogen abundances might counteract this effect. Weak winded stars
(if existent in the decisive parameter range) should display less
triplet emission than their counterparts with `normal'
winds.
Reference: Astronomy and Astrophysics, in
press
Status: Manuscript has been accepted
Weblink:
http://www.usm.uni-muenchen.de/people/puls/papers/paper_niii.pdf
Comments:
Email: jorge@usm.uni-muenchen.de
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H. Sana^1, G. James^2, E.
Gosset^3
1. Sterrenkundig Instituut Anton Pannekoek,
Universiteit van Amsterdam, Science Park 904, 1098 XH Amsterdam, The
Netherlands
2. European Southern Observatory,
Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen, Germany
3. Astrophysical Institute, Liege University, Bat. B5c, Allee
du 6 Aout 17, B-4000 Liege, Belgium
Using an extended set of
multi-epoch high-resolution high signal-to-noise ratio optical
spectra, we readdress the multiplicity properties of the O-type stars
in IC 2944 and in the Cen OB2 association. We present new evidence of
binarity for five objects and we confirm the multiple nature of
another two. We derive the first orbital solutions for HD 100099, HD
101436 and HD 101190 and we provide additional support for HD 101205
being a quadruple system. The minimal spectroscopic binary fraction
in our sample is f_min= 0.57. Using numerical simulations, we show
that the detection rate of our observational campaign is close to 90
per cent, leaving thus little room for undetected spectroscopic
binary systems. The statistical properties of the O-star population
in IC 2944 are similar, within the uncertainties, to the results
obtained in the earlier papers in this series despite the fact that
sample size effects limit the significance of the comparison. Using
newly derived spectroscopic parallaxes, we reassess the distance to
IC 2944 and obtained 2.3 +/- 0.3 kpc, in agreement with previous
studies. We also confirm that, as far as the O stars are concerned,
the IC 2944 cluster is most likely a single entity.
Reference:
Published in MNRAS, 416, 817
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1109.2899
Comments:
Email: h.sana@uva.nl
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Lagadec E.(1), Zijlstra A.
A.(2), Oudmaijer R. D.(3), Verhoelst T.(4), Cox N. L. J.(4), Szczerba
R.(5), Mekarnia D.(6), van Winckel H.(4)
1: ESO Garching
2: JBCA Manchester
3: University of Leeds
4: KU Leuven
5: NCAC Torun
6: OCA Nice
We performed a mid-infrared
imaging survey of evolved stars in order to study the dust
distribution in circumstellar envelopes around these objects and to
better understand the mass-loss mechanism responsible for the
formation of these envelopes. During this survey, we resolved for the
first time the circumstellar environment of IRAS 17163-3907
(hereinafter IRAS17163), which is one of the brightest objects in the
mid-infrared sky, but is surprisingly not well studied. Our aim is to
determine the evolutionary status of IRAS 17163 and study its
circumstellar environment in order to understand its mass-loss
history. We obtained diffraction-limited images of IRAS 17163 in the
mid-infrared using VISIR on the VLT. Optical spectra of the object
allowed us to determine its spectral type and estimate its distance
via the presence of diffuse interstellar bands. We show that IRAS
17163 is a Post-Red Supergiant, possibly belonging to the rare class
of Yellow Hypergiants, and is very similar to the well studied object
IRC +10420. Our mid-infrared images of IRAS 17163 are the first
direct images of this bright mid-infrared source. These images
clearly show the presence of a double dusty detached shell around the
central star, due to successive ejections of material with a
timescale of the order of 400 years and a total circumstellar mass
larger than 4 M$_{odot}$. This indicates that non quiescent mass-loss
occurs during this phase of stellar evolution.
Reference:
arXiv:1109.5947
Accepted for publication in A&A
Letters
Status: Manuscript has been accepted
Weblink:
Comments:
Email: elagadec@eso.org
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Luis F. Rodriguez(1,2),
Alejandro Baez-Rubio(3,1), and Anatoly S. Miroshnichenko(4)
1-
Centro de Radiostronomia y Astrofisica, UNAM, A. P. 3-72, (Xangari),
58089 Morelia, Michoacan, Mexico; 2- Astronomy Department, Faculty of
Science, King Abdulaziz University, P.O.Box 80203, Jeddah 21589,
Saudi Arabia; 3- Centro de Astrobiologia (CSIC/INTA), Ctra. de
Torrejon a Ajalvir km 4, 28850 Torrejon de Ardoz, Madrid, Spain; 4-
Department of Physics and Astronomy, University of North
Carolina,Greensboro, NC 27402 USA
The FS CMa stars exhibit
bright optical emission-line spectra and strong IR excesses. Very
little is known of their radio characteristics.We analyzed archive
Very Large Array data to search for radio continuum emission in a
sample of them. There are good quality data for seven of the $sim$40
known FS CMa stars. Of these seven stars, five turn out to have
associated radio emission. Two of these stars, CI Cam and MWC 300,
have been previously reported in the literature as radio emitters. We
present and briefly discuss the radio detection of the other three
sources: FS CMa (the prototype of the class), AS 381, and MWC 922.
The radio emission is most probably of a free-free nature but
additional observations are required to better characterize
it.
Reference: To appear in Revista Mexicana de
Astronomia y Astrofisica
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1109.5939
Comments:
Email: l.rodriguez@crya.unam.mx
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Leonid N Georgiev^1, Gloria
Koenigsberger^2, D John Hillier^3, Nidia Morrell^4, Rodolfo Barba^5,
Roberto Gamen^6
1) Instituto de Astronom'{i}a, Universidad
Nacional Aut'onoma de M'exico, Apdo. Postal 70-264, M'exico D.F.,
04510
2) Instituto de Ciencias F'{i}sicas, Universidad Nacional
Aut'onoma de M'exico, Apdo. Postal 48-3, Cuernavaca, Mor. 62210
3)
Department of Astronomy, 3941 O'Hara Street, University of Pittsburg,
Pittsburg, PA 15260, USA
4) Las Campanas Observatory, The
Carnegie Observatories, Colina El Pino s/n, Casillas 601, La Serena,
Chile
5) Departamento de F'{i}sica, Universidad de la Serena,
Benavente 980, La Serena, Chile; ICATE-CONICET, San Juan Argentina
6) Facultad de Ciencias Astron'omicas y Geof'{i}sicas,
Universidad Nacional de La Plata, and Instituto de Astrof'{i}sica de
La Plata (CCT La Plata CONICET), Paseo del Bosque S/N, B1900FWA, La
Plata, Argentina
Over the past 40 years, the massive LBV/WR
system HD 5980 in the Small Magellanic Cloud has undergone a
long-term S Doradus type variability cycle and two brief and violent
eruptions in 1993 and 1994. In this paper we analyze a collection of
UV and optical spectra obtained between 1979 and 2009 and perform
CMFGEN model fits to spectra of 1994, 2000, 2002 and 2009. The
results are as follows:
a) The long term S Dor-type variability
is associated with changes of the hydrostatic radius;
b) The 1994
eruption involved changes in its bolometric luminosity and wind
structure;
c) the emission-line strength, the wind velocity and
the continuum luminosity underwent correlated variations in the sense
that a decreasing V$_infty$ is associated with increasing emission
line and continuum levels; and d) The spectrum of the third star in
the system ({it Star C}) is well-fit by a T$_{eff}$=32 K model
atmosphere with SMC chemical abundances.
For all epochs, the
wind of the erupting star is optically thick at the sonic point and
is thus driven mainly by the continuum opacity. We speculate that the
wind switches between two stable regimes driven by the ``hot"
(during the eruption) and the ``cool" (post-eruption) iron
opacity bumps as defined by Lamers & Nugis (2002) and Gr"afener
and Hamann (2008), and thus the wind may undergo a bi-stability jump
of a different nature from that which occurs in OB-stars.
Reference:
Astronomical Journal
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1109.5942
Comments:
Email: georgiev@astro.unam.mx
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Noel D. Richardson, Douglas
R. Gies, Stephen J. Williams
Georgia State University
The
hot star HDE 326823 is a candidate transition-phase object that is
evolving into a nitrogen-enriched Wolf-Rayet star. It is also a known
low-amplitude, photometric variable with a 6.123 d period. We present
new, high and moderate resolution spectroscopy of HDE 326823, and we
show that the absorption lines show coherent Doppler shifts with this
period while the emission lines display little or no velocity
variation. We interpret the absorption line shifts as the orbital
motion of the apparently brighter star in a close, interacting
binary. We argue that this star is losing mass to a mass gainer star
hidden in a thick accretion torus and to a circumbinary disk that is
the source of the emission lines. HDE 326823 probably belongs to a
class of objects that produce short-period WR+O binaries.
Reference:
AJ, in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1110.1548
Comments:
32 pages, including 3 tables and 10 figures.
Email:
richardson@chara.gsu.edu
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Gregor Rauw
Institut
d'Astrophysique & Geophysique, Liege University, Belgium
Cyg
OB2 is one of the most massive associations of O-type stars in our
Galaxy. Despite the large interstellar reddening towards Cyg OB2,
many studies, spanning a wide range of wavelengths, have been
conducted to more clearly understand this association. X-ray
observations provide a powerful tool to overcome the effect of
interstellar absorption and study the most energetic processes
associated with the stars in Cyg OB2. We analyse XMM-Newton data to
investigate the X-ray and UV properties of massive O-type stars as
well as low-mass pre-main sequence stars in Cyg OB2. We obtained six
XMM-Newton observations of the core of Cyg OB2. In our analysis, we
pay particular attention to the variability of the X-ray bright OB
stars, especially the luminous blue variable candidate Cyg OB2 #12.
We find that X-ray variability is quite common among the stars in Cyg
OB2. Whilst short-term variations are restricted mostly to low-mass
pre-main sequence stars, one third of the OB stars display long-term
variations. The X-ray flux of Cyg OB2 #12 varies by 37%, over
timescales from days to years, whilst its mean log(L_X/L_bol) amounts
to -6.10. These properties suggest that Cyg OB2 #12 is either an
interacting-wind system or displays a magnetically confined wind. Two
other X-ray bright O-type stars (MT91 516 and CPR2002 A11) display
variations that suggest they are interacting wind binary
systems.
Reference: Astronomy &
Astrophysics
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1110.4223
Comments:
Email: rauw@astro.ulg.ac.be
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J.G. Rivero Gonzalez (1), J.
Puls (1), F. Najarro(2), and I. Brott(3)
(1)
Universitätssternwarte München, Scheinerstr. 1, 81679 München,
Germany
(2) Centro de Astrobiologia, (CSIC-INTA), Ctra. Torrejon
a Ajalvir km 4, 28850 Torrejon de Ardoz, Spain
Context.
Nitrogen is a key element to test the impact of rotational mixing on
evolutionary models of massive stars. Recent studies of the nitrogen
surface abundance in B-type stars within the VLT-FLAMES survey of
massive stars have challenged part of the corresponding predictions.
To obtain a more complete picture of massive star evolution, and to
allow for further constraints, these studies need to be extended to
O-stars.
Aims. This is the second paper in a series aiming at
the analysis of nitrogen abundances in O-type stars, to enable
further constraints on the early evolution of massive stars. In this
paper, we investigate the NIV lambda4058 emission line formation,
provide nitrogen abundances for a substantial O-star sample in the
Large Magellanic Cloud, and compare our (preliminary) findings with
recent predictions from stellar evolutionary models.
Methods.
Stellar and wind parameters of our sample stars are determined by
line profile fitting of hydrogen, helium and nitrogen lines,
exploiting the corresponding ionization equilibria. Synthetic spectra
are calculated by means of the NLTE atmosphere/spectrum synthesis
code FASTWIND, using a new nitrogen model atom. We derive nitrogen
abundances for 20 O- and 5 B-stars, by analyzing all nitrogen lines
(from different ionization stages) present in the
available
optical spectra.
Results. The dominating process responsible
for emission at NIV lambda 4058 in O-stars is the strong depopulation
of the lower level of the transition, which increases as a function
of Mdot. Unlike the NIII triplet emission, resonance lines do not
play a role for typical mass-loss rates and below. We find (almost)
no problem in fitting the nitrogen lines, in particular the `f'
features. Only for some objects, where lines from NIII/NIV/NV are
visible in parallel, we need to opt for a compromise solution.
For
five objects in the early B-/late O-star domain which have been
previously analyzed by different methods and model atmospheres, we
derive consistent nitrogen abundances. The bulk of our sample O-stars
seems to be strongly nitrogen-enriched, and a clear correlation of
nitrogen and helium enrichment is found. By comparing the nitrogen
abundances as a function of vsini ('Hunter-plot') with tailored
evolutionary calculations, we identify a considerable number of
highly enriched objects at low rotation.
Conclusions. Our
findings seem to support the basic outcome of previous B-star studies
within the VLT-FLAMES survey. Due to the low initial abundance, the
detection of strong Nitrogen enrichment in the bulk of O-stars
indicates that efficient mixing takes place already during the very
early phases of stellar evolution of LMC O-stars. For tighter
constraints, however, upcoming results from the VLT-FLAMES Tarantula
survey need to be waited for, comprising a much larger number of
O-stars that will be analyzed based on similar methods as presented
here.
Reference: Astronomy & Astrophysics
Status:
Manuscript has been accepted
Weblink:
http://www.usm.uni-muenchen.de/people/puls/electronic_prints.html
Comments:
Email: uh101aw@usm.uni-muenchen.de
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F. Martins$^1$, L. Mahy$^2$,
G. Rauw$^2$, D.J. Hillier$^3$
1- LUPM-CNRS-Montpellier
University; 2- Liege University; 3- Pittsburgh University
Our
goal is to determine the stellar and wind properties of seven O stars
in the cluster NGC2244 and three O stars in the OB association
MonOB2. These properties give us insight into the mass loss rates of
O stars, allow us to check the validity of rotational mixing in
massive stars, and to better understand the effects of the ionizing
flux and wind mechanical energy release on the surrounding
interstellar medium and its influence on triggered star formation. We
collect optical and UV spectra of the target stars which are analyzed
by means of atmosphere models computed with the code CMFGEN. The
spectra of binary stars are disentangled and the components are
studied separately. All stars have an evolutionary age less than 5
million years, with the most massive stars being among the youngest.
Nitrogen surface abundances show no clear relation with projected
rotational velocities. Binaries and single stars show the same range
of enrichment. This is attributed to the youth and/or wide separation
of the binary systems in which the components have not (yet)
experienced strong interaction. A clear trend of larger enrichment in
higher luminosity objects is observed, consistent with what
evolutionary models with rotation predict for a population of O stars
at a given age. We confirm the weakness of winds in late O dwarfs. In
general, mass loss rates derived from UV lines are lower than mass
loss rates obtained from Ha. The UV mass loss rates are even lower
than the single line driving limit in the latest type dwarfs. These
issues are discussed in the context of the structure of massive stars
winds. The evolutionary and spectroscopic masses are in agreement
above 25 Msun but the uncertainties are large. Below this threshold,
the few late-type O stars studied here indicate that the mass
discrepancy still seems to hold.
Reference: Astronomy
and Astrophysics, in press
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1110.4509
Comments:
Email: fabrice.martins@univ-montp2.fr
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Amparo Marco, Ignacio
Negueruela
Universidad de Alicante, Spain
The
discovery of several clusters of red supergiants towards l = 24°−30°
has triggered interest in this area of the Galactic plane, where
lines of sight are very complex and previous explorations of the
stellar content were very preliminary.
We attempt to
characterise the stellar population associated with the HII region
RCW 173 (=Sh2-60), located at , as previous studies have suggested
that this population could be beyond the Sagittarius arm.
We
obtained UBV photometry of a stellar field to the south of the
brightest part of RCW 173, as well as spectroscopy of about twenty
stars in the area. We combined our new data with archival 2MASS
near-infrared photometry and Spitzer/GLIMPSE imaging and photometry,
to achieve a more accurate characterisation of the stellar sources
and the associated cloud.
We find a significant population of
early-type stars located at d = 3.0 kpc, in good agreement with the
“near” dynamical distance to the H II region. This population
should be located at the near intersection of the Scutum-Crux arm. A
luminous O7 II star is likely to be the main source of ionisation.
Many stars are concentrated around the bright nebulosity, where
GLIMPSE images in the mid infrared show the presence of a bubble of
excited material surrounding a cavity that coincides spatially with a
number of B0-1 V stars. We interpret this as an emerging cluster,
perhaps triggered by the nearby O7 II star. We also find a number
of B-type giants. Some of them are located at approximately the same
distance, and may be part of an older population in the same area,
characterised by much lower reddening. A few have shorter distance
moduli and are likely to be located in the Sagittarius arm.
The
line of sight in this direction is very complex. Optically visible
tracers delineate two spiral arms, but seem to be absent beyond d ≈
3 kpc. Several HII regions in this area suggest that the Scutum-Crux
arm contains thick clouds actively forming stars. All these
populations are projected on top of the major stellar complex
signposted by the clusters of red supergiants.
Reference:
Astronomy & Astrophysics, Vol 534, A114
Status: Manuscript
has been accepted
Weblink:
http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/abs/2011/10/aa17142-11/aa17142-11.html
Comments:
Email: ignacio.negueruela@ua.es
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L. M. Oskinova, W. -R. Hamann, J.
P. Cassinelli, J. C. Brown, H. Todt
University of Potsdam,
Germany
University of Wisconsin-Madison, US
University of
Glasgow, UK
We investigate the connections between the
magnetic fields and the X-ray emission from massive stars. Our study
shows that the X-ray properties of known strongly magnetic stars are
diverse: while some comply to the predictions of the magnetically
confined wind model, others do not. We conclude that strong, hard,
and variable X-ray emission may be a sufficient attribute of magnetic
massive stars, but it is not a necessary one. We address the general
properties of X-ray emission from "normal" massive stars,
especially the long standing mystery about the correlations between
the parameters of X-ray emission and fundamental stellar properties.
The recent development in stellar structure modeling shows that small
scale surface magnetic fields may be common. We suggest a "hybrid"
scenario which could explain the X-ray emission from massive stars by
a combination of magnetic mechanisms on the surface and shocks in the
stellar wind. The magnetic mechanisms and the wind shocks are
triggered by convective motions in sub-photospheric layers. This
scenario opens the door for a natural explanation of the well
established correlation between bolometric and X-ray
luminosities.
Reference: Accepted AN. 2011 Potsdam
Thinkshop "Magnetic Fields in Stars and Exoplanets"
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1110.5345
Comments:
Email: lida@astro.physik.uni-potsdam.de
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M. S. Oey and J. B.
Lamb
University of Michigan
As a population, field
massive stars are relatively enigmatic, and this review attempts to
illuminate this sector of the high-mass stellar population, which
comprises 20 -- 25% of the massive stars in star-forming galaxies.
The statistical properties of the field population are vital
diagnostics of star formation theory, cluster dynamical evolution,
and stellar evolution.
We present evidence that field massive
stars originate both in situ and as runaways from clusters, based on
the clustering law, IMF, rotation velocities, and individual observed
in situ candidate field stars. We compare the known properties of
field and cluster massive stars from studies in the Magellanic Clouds
and the Galaxy, including our RIOTS4 complete spectroscopic survey of
SMC OB stars. In addition to the origin of the field massive stars,
we discuss additional properties including binarity, runaway
mechanisms, and some evolved spectral types.
Reference:
Four Decades of Research on Massive Stars, eds. L. Drissen, C.
Robert, and N. St.-Louis, ASP Conference Series
Status: Conference
proceedings
Weblink:
http://adsabs.harvard.edu/abs/2011arXiv1109.0759
Comments:
Invited review
Email: msoey@umich.edu
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R. Blomme, M. Briquet, P.
Degroote, L. Mahy, C. Aerts, J. Cuypers, M. Godart, E. Gosset, M.
Hareter, J. Montalban, T. Morel, M.F. Nieva, A. Noels, R. Oreiro, E.
Poretti, N. Przybilla, M. Rainer, G. Rauw, F. Schiller, S.
Simon-Diaz, K. Smolders, P. Ventura, M. Vuckovic, M. Auvergne, A.
Baglin, F. Baudin, C. Catala, E. Michel and R. Samadi
R.
Blomme: Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussel,
Belgium
Six O-type stars were observed continuously by the
CoRoT satellite during a 34.3-day run. The unprecedented quality of
the data allows us to detect even low-amplitude stellar pulsations in
some of these stars (HD 46202 and the binaries HD 46149 and
Plaskett's star). These cover both opacity-driven modes and
solar-like stochastic oscillations, both of importance to the
asteroseismological modelling of O stars. Additional effects can be
seen in the CoRoT light curves, such as binarity and rotational
modulation. Some of the hottest O-type stars (HD 46223, HD 46150 and
HD 46966) are dominated by the presence of red-noise: we speculate
that this is related to a sub-surface convection zone.
Reference:
To be published in "Four decades of Research on Massive
Stars", Astronomical Society of the Pacific. Eds. C. Robert, N.
St-Louis and L. Drissen
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1109.1999
Comments:
Email: Ronny.Blomme@oma.be
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J. B. Lamb, M. S. Oey, A. S.
Graus, and D. M. Segura-Cox
University of Michigan
Department of Astronomy, 830 Dennison Bldg., Ann Arbor, MI
48109-1042, USA
The population of field OB stars are an
important component of a galaxy's stellar content, representing
20-30% of the massive stars. To study this population, we have
undertaken the Runaways and Isolated O Type Star Spectroscopic Survey
of the SMC (RIOTS4). RIOTS4 surveys a spatially complete sample of
>350 field OB stars in the Small Magellanic Cloud and will serve
as a key probe of runaways, binaries, and the stellar IMF in the
field massive star population. Here, we focus on the field IMF, which
provides an empirical probe of the star-forming process and is a
fundamental property of a stellar population. Together with
photometry from the OGLE survey, RIOTS4 will yield a definitive
stellar IMF for the SMC field massive star population. We present
preliminary results that suggests the field IMF is much steeper,
Gamma = 2.9, than the canonical stellar IMF of Gamma = 1.35. Despite
the steep slope, we see no evidence of a stellar upper mass limit, up
to our highest mass star of 65 solar masses.
Reference:
Four Decades of Research on Massive Stars, eds. L. Drissen, C.
Robert, and N. St-Louis, ASP Conference Series
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1109.6655
Comments:
Email: joellamb@umich.edu
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V.V. Gvaramadze (1), A.-N.
Chené (2,3), A.Y. Kniazev (4,1), O. Schnurr (5)
(1)
Sternberg Astronomical Institute, Moscow State University, Russia,
(2) Departamento de Astronomia, Univ. de Concepcion, Chile, (3) Univ.
de Valparaiso, Departamento de Fisica y Astronomia, Chile, (4) South
African Astronomical Observatory and Southern African Large Telescope
Foundation, South Africa, (5) AIP, An der Sternwarte, Germany
We
report the first-ever discovery of an extragalactic Wolf-Rayet (WR)
star with Spitzer. A new WR star in the Large Magellanic Cloud
(LMC) was revealed
via detection of its circumstellar shell using
24 μm images obtained in the framework of
the Spitzer Survey of
the Large Magellanic Cloud (SAGE-LMC). Subsequent spectroscopic
observations with the Gemini South resolved the central star in
two components,
one of which is a WN3b+abs star, while the second
one is a B0V star. We consider
the lopsided brightness
distribution over the circumstellar shell as an indication that the
WR star is a runaway and use this interpretation to identify a
possible parent cluster of
the star.
Reference: To
be published in the proceedings of the meeting 'Four decades of
research on massive stars' in honor of Tony Moffat, 11-15 July 2011,
Saint-Michel-des-Saints, Quebec
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1110.0126
Comments:
Email: achene@astro-udec.cl
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H. Sana [1], S. Lacour [2],
J.-B. Le Bouquin [3], A. de Koter [1,4], C. Moni Bidin [5], L.
Muijres[1], O. Schnurr[6], H. Zinnecker [7,8]
1.
Astronomical Institute `Anton Pannekoek', University of Amsterdam,
Postbus 94249, 1090 GE, Amsterdam, The Netherlands
2. LESIA,
Observatoire de Paris, Universite Paris Diderot, Meudon, France
3.
Institut de Planetologie et d'Astrophysique de Grenoble (IPAG),
France
4. Astronomical Institute, Utrecht University, Utrecht,
The Netherlands
5. Departamento de Astronomia, Universidad de
Concepcion, Chile
6. Leibniz-Institut für Astrophysik Potsdam
(AIP), Potsdam, Germany
7. Deutsches SOFIA Institute, Stuttgart,
Germany
8. SOFIA Science Center, NASA-Ames Research Center,
Moffett Field, CA, USA
We present the earliest results of our
NACO/VLT sparse aperture masking (SAM) campaign to search for
binarity in a sample of 60 O-type stars. We detect Delta Ks < 5
mag companions for 20-25% of our targets with separations in the
range 30-100 mas (typically, 40 - 200 A.U.). Most of these companions
were unknown, shedding thus new light on the multiplicity properties
of massive stars in a separation and brightness regime that has been
difficult to explore so far. Adding detections from other techniques
(spectroscopy, interferometry, speckle, lucky imaging, AO), the
fraction of O stars with at least one companion is 85% (51/60
targets). This is the largest multiplicity fraction ever
found.
Reference: To be published in the proceedings of
the meeting 'Four decades of research on massive stars' in honor of
Tony Moffat, 11-15 July 2011, Saint-Michel-des-Saints, Quebec
Status:
Conference proceedings
Weblink:
http://arxiv.org/abs/1109.6654
Comments:
Email: h.sana@uva.nl
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Jon O. Sundqvist(1), Stanley P.
Owocki(1), and Joachim Puls(2)
1 - University of Delaware,
Bartol Research Institute, Newark, Delaware 19716, USA; 2 -
Universitaetssternwarte Muenchen, Scheinerstr. 1, 81679
Muenchen
This review describes the evidence for small scale
structure, `clumping', in the radiation line-driven winds of hot,
massive stars. In particular, we focus on examining to what extent
simulations of the strong instability inherent to line-driving can
explain the multitude of observational evidence for wind clumping, as
well as on how to properly account for extensive structures in
density and velocity when interpreting the various wind diagnostics
used to derive mass-loss rates.
Reference: Invited
review to appear in "Four Decades of Research on Massive Stars"
in honor of Tony Moffat, ASP Conf. Ser.
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1110.0485
Comments:
8 pages, 3 figures
Email: jon@bartol.udel.edu
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Friday November 11 2011,
10:30-15:30
Venue: The Geological Society,
Burlington House, LONDON,W1J 0BG, UK
We'd like to announce a
one day RAS Specialist Discussion meeting on Astrophysics at
Extremely High Angular Resolution: Optical and Infrared
Interferometry
The new century has seen a quantum leap in the
field of optical and infrared long-baseline interferometry, with
facilities such as the CHARA and VLTI arrays now routinely producing
images with milliarcsecond resolution. As a result, over the past ten
years, ground-based optical/IR interfometry has transitioned to
become a mainstream, common-user, technique offering unprecedented
insights into a wide range of astrophysical phenomena. These include
asteroseismology, YSO accretion, photosphere dynamics, exoplanet
characterization, and the structure of AGN cores.
This
meeting will bring together experts and novices in the field to
present their latest scientific results, and to highlight the
existing and upcoming capabilities at facility class arrays such as
the VLTI. We hope to attract not only attendees who are excited by
the possibilities that interferometric methods can bring to their
research, but also those who wish to find out more and assess the
investment of their time needed to best exploit the UK's access to
European and American interferometric arrays.
You can find
more information, including a preliminary program on the website.
Rene Oudmaijer (Leeds) roud at ast.leeds.ac.uk
Ettore
Pedretti (St Andrews, ESO) ep41 at st-and.ac.uk
Chris Haniff
(Cambridge) cahm at rao.cam.ac.uk
Weblink:
http://www.ast.leeds.ac.uk/~roud/rasmeet2012.htm
Email:
r.d.oudmaijer@leeds.ac.uk
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Jan 21 - 27, 2012
Venue: Aspen Center for
Physics
This meeting will focus on issues related to the
physics and discovery of astronomical transients. Topics will range
from the extragalactic: detection of gamma-ray bursts, and supernovae
in distant galaxies, variable AGN, to the galactic: variable stars,
novae, and other cataclysmic events.
We have now set up the
webpage for registration and abstract submission:
http://www.aspenphys.org/
You may also express a preference
for either an oral or poster presentation. All talks will be invited
talks, selected by the organizers from the submitted abstracts.
Registration and abstracts are due by October 30, 2011.
We
look forward to seeing you in Aspen, CO, for a lively scientific
program and an upbeat discussion on innovative exploration strategies
and novel theoretical work.
Sincerely
Organizers
Enrico Ramirez-Ruiz, University of California, Santa Cruz
Fred
Rasio, Northwestern University
Natalia Ivanova, University of
Alberta
Shri Kulkarni, California Institute of
Technology
Weblink: http://www.aspenphys.org/
Email:
enrico@ucolick.org
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June 17 - July 1
Venue:
Aspen Center for Physics, Aspen, CO
Long-duration
gamma-ray bursts (LGRBs), associated with the core-collapse deaths of
unusual massive stars, are the fleeting signatures of extraordinarily
high-energy events occurring throughout our universe. These phenomena
hold enormous promise as cosmological tools, but the full potential
of LGRBs cannot be realized without first gaining a thorough
understanding of their massive stellar progenitors. Recent advances
in the massive star community on binarity, mass loss, and the effects
of metallicity are all critical to current debates surrounding the
nature of LGRB progenitors. Simultaneously, new results in the LGRB
community have yielded important insights into the physical
properties, environmental dependences, and interior structures of the
most extreme massive stars. However, the study of massive stellar
evolution and the study of LGRBs have long been seen as separate
pursuits within astronomy, with only limited communication between
the two subfields. This multi-disciplinary workshop will bring
together leaders in these complementary disciplines, offering an
opportunity for participants to exchange expertise, share recent
results, and consider the most pressing current questions that will
shape the future of LGRB and massive star research for years to
come.
Weblink:
http://casa.colorado.edu/~emle6425/aspen/
Email:
Emily.Levesque@colorado.edu
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August 2012
Venue:
IAU GA in Beijing
Though multiwavelength astronomy was
born about fifty years ago, the full use of multiwavelength
diagnostics is quite recent. Even in the last decade, astronomers
still mostly relied on the optical domain. This is certainly going to
change, as most current and future instruments are dedicated to the
infrared, from the near- to the far-IR bands.
While this
domain is a known "must" for low-mass stars, especially the
very low-mass ones, the infrared emission of high-mass stars has been
often neglected. Many advantages of the infrared must however be
underlined, like its strong potential for circumstellar material and
atmosphere diagnostics, and its insensitivity to obscuration. Its
interest with regards to the first generation of stars, thought to be
very massive, is also well known.
It is thus important to
discuss the results obtained for massive stars from existing IR
facilities (VLTs/VLTI, Spitzer, Herschel, CRIRES, GAIA, ...) as well
as tools for interpreting IR data (e.g. atmosphere modeling) and
observing capabilities of future facilities (ELTs, JWST, ...). To
this aim, we will hold a 1.5-day special session (SpS) at the next
IAU General Assembly meeting in Beijing.
Topics to be
presented during this special session:
- Obscured and distant
clusters
- Stellar and wind parameters
- Matter ejection and
feedback
Note there will also be a joint discussion on 'Very
Massive Stars in the Local Universe' during the same GA.
Weblink:
http://www.gaphe.ulg.ac.be/IAU_XXVIII/index.html
Email:
naze@astro.ulg.ac.be
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August 2012
Venue: IAU GA in
Beijing
While Very Massive Stars (VMS) with over 100 solar
masses have been claimed to exist in the early Universe, recent
studies discussing the existence and deaths of stars up to 300 solar
masses in the local Universe came as a surprise to many workers both
inside and outside the field. Before the full implications of these
findings can be explored, it is imperative to discuss the various
lines of evidence for VMS.
We hold a 1.5-day Joint Discussion
-- spread over 3 days -- at the next IAU GA to discuss the
determination of both the current and final masses of VMS. The aim is
to reach broad consensus between observers and theorists on how to
identify and quantify the importance of the dominant physical
processes.
Topics to be presented during the JD:
-
Weighing the most massive stars from their binary motions
-
Stellar spectra of O and Wolf-Rayet stars
- Mass determinations
from stellar spectroscopy and model atmosphere analysis
-
Formation of the most massive stars
- Mass loss mechanisms, incl.
eruptions of Luminous Blue Variables
- Stellar structure and
evolution modelling
- The fate of the most massive stars (over
cosmological time)
- Mass and energy return to the interstellar
medium (ISM)
Note there will also be a special session on
'The infrared view of massive stars
' during the same
GA.
Weblink: http://www.arm.ac.uk/IAU/
Email:
jsv@arm.ac.uk
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