ISSN 1783-3426
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Non-standard s process in low
metallicity massive rotating stars
A
Lighthouse Effect in Eta Carinae
Strongly
star forming galaxies in the local universe with nebular He II 4686
emission
Asteroseismology of the
Nearby SN-II Progenitor: Rigel Part I. The MOST High Precision
Photometry and Radial Velocity Monitoring
Photometric
and Spectroscopic Studies of Massive Binaries in the Large Magellanic
Cloud. I. Introduction and Orbits for Two Detached Systems: Evidence
for a Mass Discrepancy?
Global
modelling of X-ray spectra produced in O-type star winds
On
the Eddington limit and WR Stars
The
Galactic WC stars: Stellar parameters from spectral analyses indicate
a new evolutionary sequence
X-rays
from Colliding Stellar Winds: the case of close WR+O binary
systems
High-resolution X-ray
spectroscopy reveals the special nature of Wolf-Rayet star winds
The
relationship between gamma Cassiopeiae's X-ray
The
G305 star-forming complex: the central star clusters Danks 1 and
Danks 2
A newly discovered young
massive star cluster at the far end of the Galactic Bar
Yellow
and Red Supergiants in the Large Magellanic Cloud
Asteroseismology
of the Nearby SN-II Progenitor Rigel
Variability
in X-ray line ratios in helium-like ions of massive stars: the
radiation-driven case
X-ray
Emission Line Profiles from Wind Clump Bow Shocks in Massive
Stars
HST/STIS spectroscopy of the
magnetic Of?p star HD 108: the low state at ultraviolet
wavelengths
3-D radiative transfer
in clumped hot star winds
Evidence
for a physically bound third component in HD 150136
The IR view
of massive stars: the main sequence and beyond
The
Evolution of Massive Stars and Progenitors of GRBs
IAU-general
assembly
U. Frischknecht (1,2), R.
Hirschi (2,3), F.-K. Thielemann (1)
1 - Department of
Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel,
Switzerland
2 - Astrophysics Group, EPSAM, University of Keele,
Lennard-Jones Labs, Keele ST5 5BG, UK
3 - Institute for the
Physics and Mathematics of the Universe, University of Tokyo, 5-1-5
Kashiwanoha, Kashiwa 277-8583, Japan
Context. Rotation is
known to have a strong impact on the nucleosynthesis of light
elements in massive stars, mainly by inducing mixing in radiative
zones. In particular, rotation boosts the primary nitrogen
production, and models of rotating stars are able to reproduce the
nitrogen observed in low-metallicity halo stars.
Aims. Here
we present the first grid of stellar models for rotating massive
stars at low metallicity, where a full s-process network is used to
study the impact of rotation-induced mixing on the neutron capture
nucleosynthesis of heavy elements.
Methods. We used the
Geneva stellar evolution code that includes an enlarged reaction
network with nuclear species up to bismuth to calculate 25 solar mass
models at three different metallicities (Z = 1e-3, 1e-5, and 1e-7)
and with different initial rotation rates.
Results. First, we
confirm that rotation-induced mixing (shear) between the convective
H-shell and He-core leads to a large production of primary $^{22}$Ne
(0.1 to 1% in mass fraction), which is the main neutron source for
the s process in massive stars. Therefore rotation boosts the s
process in massive stars at all metallicities. Second, the
neutron-to-seed ratio increases with decreasing Z in models including
rotation, which leads to the complete consumption of all iron seeds
at metallicities below Z = 1e-3 by the end of core He-burning. Thus
at low Z, the iron seeds are the main limitation for this boosted s
process. Third, as the metallicity decreases, the production of
elements up to the Ba peak increases at the expense of the elements
of the Sr peak. We studied the impact of the initial rotation rate
and of the highly uncertain $^{17}$O$(alpha,gamma)$ rate (which
strongly affects the strength of $^{16}$O as a neutron poison) on our
results. This study shows that rotating models can produce
significant amounts of elements up to Ba over a wide range of Z,
which has important consequences for our understanding of the
formation of these elements in low-metallicity environments like the
halo of our galaxy and globular clusters. Fourth, compared to the
He-core, the primary $^{22}$Ne production induced by rotation in the
He-shell is even higher (greater than 1% in mass fraction at all
metallicities), which could open the door for an explosive neutron
capture nucleosynthesis in the He-shell, with a primary neutron
source.
Reference: A&A, letter to the editor,
accepted
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2011arXiv1112.5548F
Comments:
Email: urs.frischknecht@unibas.ch
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Thomas I. Madura and Jose H.
Groh
Max Planck Institute for Radio Astronomy, Bonn,
Germany
We present a new model for the behavior of scattered
time-dependent, asymmetric near-UV emission from the nearby ejecta of
Eta Car. Using a 3-D hydrodynamical simulation of Eta Car's binary
colliding winds, we show that the 3-D binary orientation derived by
Madura et al. (2012) is capable of explaining the asymmetric near-UV
variability observed in the Hubble Space Telescope Advanced Camera
for Surveys/High Resolution Camera (HST ACS/HRC) F220W images of
Smith et al. (2004b). Models assuming a binary orientation with i ~
130 to 145 degrees, {omega} ~ 230 to 315 degrees, PAz ~ 302 to 327
degrees are consistent with the observed F220W near-UV images. We
find that the hot binary companion does not significantly contribute
to the near-UV excess observed in the F220W images. Rather, we
suggest that a bore-hole effect and the reduction of Fe II optical
depths inside the wind-wind collision cavity carved in the extended
photosphere of the primary star lead to the time-dependent
directional illumination of circum-binary material as the companion
moves about in its highly elliptical orbit.
Reference:
Accepted for publication in ApJL. Pre-print available on
astro-ph.
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1201.1848
Comments:
Email: tmadura@mpifr-bonn.mpg.de
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Maryam Shirazi and Jarle
Brinchmann
Leiden Observatory, Leiden University, P.O. Box
9513, 2300 RA Leiden, The Netherlands
We present a sample of
2865 emission line galaxies with strong nebular He II 4686 emissions
in Sloan Digital Sky Survey Data Release 7 and use this sample to
investigate the origin of this line in star-forming galaxies. We show
that star-forming galaxies and galaxies dominated by an active
galactic nucleus form clearly separated branches in the He II
4686/H{beta} versus [N II] 6584/H{alpha} diagnostic diagram and
derive an empirical classification scheme which separates the two
classes. We also present an analysis of the physical properties of
189 star forming galaxies with strong He II 4686 emissions. These
star-forming galaxies provide constraints on the hard ionizing
continuum of massive stars. To make a quantitative comparison with
observation we use photoionization models and examine how different
stellar population models affect the predicted He II 4686 emission.
We confirm previous findings that the models can predict He II 4686
emission only for instantaneous bursts of 20% solar metallicity or
higher, and only for ages of ~ 4 - 5 Myr, the period when the
extreme-ultraviolet continuum is dominated by emission from
Wolf-Rayet stars. We find however that 83 of the star-forming
galaxies (40%) in our sample do not have Wolf-Rayet features in their
spectra despite showing strong nebular He II 4686 emission. We
discuss possible reasons for this and possible mechanisms for the He
II 4686 emission in these galaxies.
Reference: MNRAS,
2081 (in press)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1201.1290
Comments:
Email: shirazi@strw.leidenuniv.nl
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Ehsan Moravveji, Edward F.
Guinan, Matt Shultz, Michael H. Williamson, Andres Moya
1-
Department of Physics, Institute for Advanced Studies in Basic
Sciences (IASBS), Zanjan 45137-66731, Iran
2- Department of
Astronomy, Villanova University, 800 Lancaster Ave, Villanova, PA
19085, USA
3- Royal Military College of Canada, PO Box 17000,
Station Forces, Kingston, ON K7K 4B4, Canada
4- Center of
Excellence in Information Systems, Tennessee State University,
Nashville, USA
5- Departamento de Astrof'{i}sica, Centro de
Astrobiolog'ia (INTA-CSIC), PO BOX 78, 28691
Villanueva de la
Ca~nada, Madrid, Spain
Rigel (beta Ori, B8 Ia) is a nearby
blue supergiant displaying alpha Cyg type variability, and is one of
the nearest type-II supernova progenitors. As such it is an excellent
test bed to study the internal structure of pre core-collapse stars.
In this study, for the first time, we present 28 days of high
precision MOST photometry and over 6 years of spectroscopic
monitoring. We report nineteen significant pulsation modes of SNR>4.6
from radial velocities, with variability time scales ranging from
1.21 to 74.7 days, which are associated with high order low degree
gravity modes. While the radial velocity variations show a degree of
correlation with the flux changes, there is no clear interplay
between the equivalent widths of different metallic and Halpha
lines.
Reference: ApJ, 745 (in press)
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1201.0843
Comments:
Email: moravveji@iasbs.ac.ir
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Philip Massey (1), Nidia I. Morrel l(2), Kathryn F. Neugent
(1), Laura R. Penny (3), Kathleen-DeGioia Eastwood (4), and Douglas
R. Gies (5)
(1) Lowell Observatory; (2) Las Campanas
Observatories, Carnegie Observatory; (3) Dept of Physics and
Astronomy, College of Charleston; (4) Dept of Physics and Astronomy,
Northern Arizona University; (5) CHARA and Department of Physics and
Astronomy, Georgia State University
The stellar
mass-luminosity relation is poorly constrained by observations for
high mass stars. We describe our program to find eclipsing massive
binaries in the Magellanic Clouds using photometry of regions rich in
massive stars, and our spectroscopic follow-up to obtain radial
velocities and orbits. Our photometric campaign identified 48
early-type periodic variables, of which only 15 (31%) were found as
part of the microlensing surveys. Spectroscopy is now complete for 17
of these systems, and in this paper we present analysis of the first
two, LMC 172231 and ST2-28, simple detached systems of late-type O
dwarfs of relatively modest masses. Our orbit analysis yields very
precise masses (about 2%), and we use tomography to separate the
components and determine effective temperatures by model fitting,
necessary for determining accurate (0.05 0.07 dex) bolometric
luminosities in combination with the light-curve analysis. Our
approach allows more precise comparisons with evolutionary theory
than previously possible. To our considerable surprise, we find a
small, but significant, systematic discrepancy: all of the stars are
slightly under-massive, by typically 11% (or over luminous by 0.2
dex) compared to that predicted by the evolutionary models. We
examine our approach for systematic problems, but find no
satisfactory explanation. The discrepancy is in the same sense as the
long-discussed and elusive discrepancy between the masses measured
from stellar atmosphere analysis with the stellar evolutionary
models, and might suggest that either increased rotation or
convective overshooting is needed in the models. Additional systems
will be discussed in future papers of this series, and will hopefully
confirm or refute this trend.
Reference: ApJ, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1201.3280
Comments:
Email: phil.massey@lowell.edu
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A. Hervé, G. Rauw, Y. Nazé
and A. Foster
GAPHE, Département AGO, Université de
Liège
and
Smithsonian Astrophysical
Observatory
High-resolution X-ray spectra of O-type stars
revealed less wind absorption than expected from smooth winds with
conventional mass-loss rates. Various solutions have been proposed,
including porous winds, optically thick clumps or an overall
reduction of the mass-loss rates. The latter has a strong impact on
the evolution of the star. Our final goal is to analyse high
resolution X-ray spectra of O-type stars with a multi temperature
plasma model in order to determine crucial stellar and wind
parameters such as the mass loss rate, the CNO abundances and the
X-ray temperature plasma distribution in the wind. In this context we
are developing a modelling tool to calculate synthetic X-ray spectra.
We present, here, the main ingredients and physics necessary for a
such work. Our code uses the most recent version of the AtomDB
emissivities to compute the intrinsic emissivity of the hot plasma as
well as the CMFGEN model atmosphere code to evaluate the opacity of
the cool wind. Following the comparison between two formalisms of
stellar wind fragmentation, we introduce, for the first time in
X-rays, the effects of a tenuous inter-clump medium. We then explore
the quantitative impact of different model parameters on the X-ray
spectra such as the position in the wind of the X-ray emitting
plasma. For the first time, we also show that the two formalisms of
stellar wind fragmentation yield different results, although the
differences for individual lines are small and can probably not be
tested with the current generation of X-ray telescopes.
As an
illustration of our method, we compare various synthetic line
profiles to the observed O VIII λ 18.97 Å line in the spectrum of ζ
Puppis. We illustrate how different combinations of parameters can
actually lead to the same morphology of a single line, underlining
the need to analyse the whole spectrum in a consistent way when
attempting to constrain the parameters of the wind.
Reference:
Astrophysical Journal
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1201.4716
Comments:
Email: herve@astro.ulg.ac.be
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André Maeder (1), Cyril
Georgy (2), Georges Meynet (1), Sylvia Ekström (1)
1)
Geneva Observatory, Geneva University, CH--1290 Sauverny, Switzerland
2) Centre de Recherche Astrophysique, Ecole Normale Supérieure
de Lyon, 46, allée d'Italie, F-69384 Lyon cedex 07, France
We
examine some properties of stars evolving close to the classical
Eddington limit for electron-scattering opacity, when these stars
maintain a chemically homogeneous structure as a result of mixing
and/or mass loss.
We consider analytical relations and models
computed with the Geneva code.
Homologous, chemically
homogeneous stars evolving with a constant Eddington factor obey a
relation of the form mu^2 M = const. This applies, for example, to
Wolf-Rayet (WR) stars in stages without hydrogen. The value of the
constant may depend on the metallicity, initial mass, evolutionary
stage, and physical processes included in the considered homologous
evolutionary sequence. An average value of the constant between 20
and 40 in solar units is consistent with the masses of Galactic WR
stars.
Reference: A&A
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1201.5013
Comments:
Email: Andre.Maeder@unige.ch
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A. Sander, W.-R. Hamann, H.
Todt
University of Potsdam, Germany
CONTEXT: The
life cycles of massive stars from the main sequence to their
explosion as supernova or gamma ray burst are not yet fully clear,
and the empirical results from spectral analyses are partly in
conflict with current evolutionary models. The spectral analysis of
Wolf-Rayet stars requires the detailed modeling of expanding stellar
atmospheres in non-LTE. The Galactic WN stars have been
comprehensively analyzed with such models in their latest stage
of sophistication, while a similarly comprehensive study of the
Galactic WC sample is still missing.
AIMS: The stellar parameters
and mass-loss rates of the GalacticWC stars shall be established.
These data shall provide the empirical basis for studies of (i) the
role of WC stars in the evolution of massive stars, (ii) the
wind-driving mechanisms, and (iii) the feedback of WC stars as input
for the chemical and dynamical evolution of galaxies.
METHODS: We
analyze the nearly complete sample of un-obscured Galactic WC stars,
using optical spectra as well as UV spectra if available. The
observations are fitted with theoretical spectra, using the Potsdam
Wolf-Rayet (PoWR) model atmosphere code. A large grid of line-blanked
models has been established for the range of WC subtypes WC4 - WC8,
and smaller grids for the WC9 parameter domain. WO stars and WN/WC
transit types are covered as well using special models.
RESULTS:
Stellar and atmospheric parameters have been derived for more than 50
Galactic WC and two WO stars, covering almost the whole Galactic WC
population as far as the stars are single, and un-obscured in the
visual. In the Hertzsprung-Russell diagram, the WC stars reside
between the hydrogen and the helium zero-age main sequences, having
luminosities L from 10^4.9 to 10^5.6 Lsun The mass-loss rates scale
very tightly with L^0.8. The two WO stars in our sample turned out to
be outstandingly hot (~200 kK) and do not fit into the WC scheme.
CONCLUSIONS: From comparing the empirical WC positions in the
Hertzsprung-Russell diagram with evolutionary models, and from recent
supernova statistics, we conclude thatWC stars have evolved from
initial masses between 20 and 45 Msun. In contrast to previous
assumptions, it seems that WC stars in general do not descend from
the most-massive stars. Only the WO stars might stem from progenitors
that have been more massive than 45 Msun initially.
Reference:
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1201.6354
Comments:
PoWR grid models are available online at
http://www.astro.physik.uni-potsdam.de/PoWR.html
Email:
ansander@astro.physik.uni-potsdam.de
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Svetozar A. Zhekov
Space and Sollar-Terrestrial
Research Institute, 6 Moskovska str.,
Sofia-1000, Bulgaria
We
have analysed the X-ray emission from a sample of close WR+O binaries
using data from the public Chandra and XMM-Newton archives. Global
spectral fits show that two-temperature plasma is needed to match the
X-ray emission from these objects as the hot component (kT > 2
keV) is an important ingredient of the spectral models. In close WR+O
binaries, X-rays likely originate in colliding stellar wind (CSW)
shocks driven by the massive winds of the binary components. CSW
shocks in these objects are expected to be radiative due to the high
density of the plasma in the interaction region. Opposite to this,
our analysis shows that the CSW shocks in the sample of close WR+O
binaries are adiabatic. This is possible only if the mass-loss rates
of the stellar components in the binary are at least one order of
magnitude smaller than the values currently accepted. The most likely
explanation for the X-ray properties of close WR+O binaries could be
that their winds are two-component flows. The more massive component
(dense clumps) play role for the optical/UV emission from these
objects, while the smooth rarefied component is a key factor for
their X-ray emission.
Reference: MNRAS
Status:
Manuscript has been accepted
Weblink:
http://xxx.lanl.gov/abs/1202.1386
Comments:
Email: szhekov@space.bas.bg
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L. M. Oskinova, K. G. Gayley,
W.-R. Hamann, D. P. Huenemoerder, R. Ignace, A. M. T.
Pollock
University of Potsdam, University of Iowa, MIT,
ETSU, XMM-Newton SOC
We present the first high-resolution
X-ray spectrum of a putatively single Wolf-Rayet star. 400 ks
observations of WR 6 by the XMM-Newton-telescope resulted in a superb
quality high-resolution X-ray spectrum. Spectral analysis reveals
that the X-rays originate far out in the stellar wind, more than 30
stellar radii from the photosphere, and thus outside the wind
acceleration zone where the line-driving instability could create
shocks. The X-ray emitting plasma reaches temperatures up to 50 MK,
and is embedded within the un-shocked, "cool" stellar wind
as revealed by characteristic spectral signatures. We detect a
fluorescent Fe line at approx 6.4 keV. The presence of fluorescence
is consistent with a two-component medium, where the cool wind is
permeated with the hot X-ray emitting plasma. The wind must have a
very porous structure to allow the observed amount of X-rays to
escape. We find that neither the line-driving instability nor any
alternative binary scenario can explain the data. We suggest a
scenario where X-rays are produced when the fast wind rams into slow
"sticky clumps" that resist acceleration. Our new data show
that the X-rays in single WR-star are generated by some special
mechanism different from the one operating in the O-star
winds.
Reference: ApJL
Status: Manuscript has been
accepted
Weblink:
http://de.arxiv.org/abs/1202.1525
Comments:
Email: lida@astro.physik.uni-potsdam.de
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M. A. Smith(1),
R. Lopes de Oliveira(2,3),
C.
Motch(4),
G. W. Henry(5},
N. D. Richardson(6),
K. S.
Bjorkman(7),
Ph. Stee(8), D. Mourard(8),
J. D. Monnier(9), X.
Che(9),
R. Buecke(10),
E. Pollmann(11)
D. R. Gies(6), G.
H., Schaefer(6), T. ten Brummelaar(6),
H. A. McAlister(6), N. H.
Turner(6), J. Sturmann(6),
L. Sturmann(6), and S. T.
Ridgway(12)
(1)Catholic University of America,
(2)
Departmento de Fisica, Universidade Federal de Sergipe, (3)
Departmento de Fisica, Universidade de Sao Paulo,
(4)
Observatoire Astronomique, Universit'e de Strasbourg,
(5)Center
of Excellence in Information Systems, Tennessee State University,
(6)Center for High Angular Resolution Astronomy and Department of
Physics
and Astronomy, Georgia State University,
(7)Ritter
Astrophysical Research Center, Department of Physics and
Astronomy,
(8)Laboratoire Lagrange, l'Observatorie, Universite de Nice,
(9)
Department of Astronomy, University of Michigan
(10)
Anna-von-Gierke-Ring 147, Hamburg,
(11)Emil-Nolde-Str. 12,
Leverkusen,
(12) National Optical Astronomical Observatory,
Tucson.
gamma Cas is the prototypical classical Be star and is
best known for its variable hard X-ray emission. To elucidate the
reasons for this emission, we mounted a multiwavelength campaign in
2010 centered around 4 XMM-Newtonobservations. The observational
techniques included Long Baseline Optical Interferometry (LBOI),
monitoring by an Automated Photometric Telescope and Halpha
observations. Because gamma Cas is also known to be in a binary, we
measured Halpha radial velocities and redetermined its period as
203.55+/-0.2 days and an eccentricity near zero. The LBOI
observations suggest that the star's decretion disk was axisymmetric
in 2010, has an inclination angle near 45^o, and a larger radius than
previously reported. The Be star began an "outburst" at the
beginning of our campaign, made visible by a disk brightening and
reddening during our campaign. Our analyses of the new high
resolution spectra disclosed many attributes found from spectra
obtained in 2001 (Chandra) and 2004 (XMM). As well as a dominant hot
14 keV thermal component, these familiar ones included: (i) a
fluorescent feature of Fe K stronger than observed at previous times,
(ii) strong lines of N VII and Ne XI lines indicative of
overabundances, and (iii) a subsolar Fe abundance from K-shell lines
but a solar abundance from L-shell ions. We also found that 2
absorption columns are required to fit the continuum. While the first
column maintained its historical average of 1x10^21 cm^-2, the second
was very large and doubled to 7.4x10^23 cm^-2 during our X-ray
observations. Although we found no clear relation between this column
density and orbital phase, it correlates well with the disk
brightening and reddening both in the 2010 and earlier observations.
Thus, the inference from this study is that much (perhaps all?) of
the X-ray emission from this source originates behind matter ejected
by gamma Cas into our line of sight.
Reference: Astronomy
and Astrophysics
Status: Manuscript has been accepted
Weblink:
http://xxx.lanl.gov/abs/1201.6415
Comments:
Email: msmith@stsci.edu
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Davies, Ben; Clark, J. S.;
Trombley, Christine; Figer, Donald F.; Najarro, Francisco; Crowther,
Paul A.; Kudritzki, Rolf-Peter; Thompson, Mark; Urquhart, James S.;
Hindson, Luke
Cambridge, Open University, RIT, RIT,
Madrid, Sheffield, Hawaii, UHerts, ATNF, UHerts
The G305 H II
complex (G305.4+0.1) is one of the most massive star-forming
structures yet identified within the Galaxy. It is host to many
massive stars at all stages of formation and evolution, from embedded
molecular cores to post-main-sequence stars. Here, we present a
detailed near-infrared analysis of the two central star clusters
Danks 1 and Danks 2, using Hubble Space Telescope+NICMOS imaging and
Very Large Telescope+ISAAC spectroscopy. We find that the
spectrophotometric distance to the clusters is consistent with the
kinematic distance to the G305 complex, an average of all
measurements giving a distance of 3.8 ± 0.6 kpc. From analysis of
the stellar populations and the pre-main-sequence stars, we find that
Danks 2 is the elder of the two clusters, with an age of 3+3- 1 Myr.
Danks 1 is clearly younger with an age of 1.5+1.5- 0.5 Myr, and is
dominated by three very luminous H-rich Wolf-Rayet stars which may
have masses ≳100 Msun. The two clusters have mass functions
consistent with the Salpeter slope, and total cluster masses of 8000
± 1500 and 3000 ± 800 Msun for Danks 1 and Danks 2, respectively.
Danks 1 is significantly the more compact cluster of the two, and is
one of the densest clusters in the Galaxy with log (ρ/Msun pc-3) =
5.5+0.5- 0.4. In addition to the clusters, there is a population of
apparently isolated Wolf-Rayet stars within the molecular cloud's
cavity. Our results suggest that the star-forming history of G305
began with the formation of Danks 2, and subsequently Danks 1, with
the origin of the diffuse evolved population currently uncertain.
Together, the massive stars at the centre of the G305 region appear
to be clearing away what is left of the natal cloud, triggering a
further generation of star formation at the cloud's
periphery.
Reference: Published in MNRAS
Status:
Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2012MNRAS.419.1871D
Comments:
Email: bdavies@ast.cam.ac.uk
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Davies, Ben; de La Fuente,
Diego; Najarro, Francisco; Hinton, Jim A.; Trombley, Christine;
Figer, Donald F.; Puga, Elena
Cambridge, Madrid, Madrid,
Leicester, RIT, RIT, ESA
We present a near-infrared study of
the candidate star cluster Mercer 81, located at the centre of the
G338.4+0.1 H II region and close to the TeV gamma-ray source HESS
1640-465. Using Hubble Space Telescope/NICMOS imaging and VLT/ISAAC
spectroscopy, we have detected a compact and highly reddened cluster
of stars, although the bright stars in the centre of the field are in
fact foreground objects. The cluster contains nine stars with strong
Pα emission, one of which we identify as a Wolf-Rayet (WR) star, as
well as an A-type supergiant. The line-of-sight extinction is very
large, AV˜ 45, illustrating the challenges of locating young star
clusters in the Galactic plane. From a quantitative analysis of the
WR star, we argue for a cluster age of 3.7? Myr, and, assuming that
all emission-line stars are WR stars, a cluster mass of ≳104 Msun.
A kinematic analysis of the cluster's surrounding H II region shows
that the cluster is located in the Galactic disc at a distance of 11
± 2 kpc. This places the cluster close to where the far end of the
Bar intersects the Norma spiral arm. This cluster, as well as the
nearby cluster [DBS2003]179, represents the first detections of
active star cluster formation at this side of the Bar, in contrast to
the near side which is well known to have recently undergone a ˜106
Msun starburst episode.
Reference: Published in
MNRAS
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2012MNRAS.419.1860D
Comments:
Email: bdavies@ast.cam.ac.uk
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Kathryn F. Neugent, Philip
Massey, Brian Skiff, Georges Meynet
Lowell Observatory,
Lowell Observatory, Lowell Observatory, Geneva University
Due
to their transitionary nature, yellow supergiants provide a critical
challenge for evolutionary modeling. Previous studies within M31 and
the SMC show that the Geneva evolutionary models do a poor job at
predicting the lifetimes of these short-lived stars. Here we extend
this study to the LMC while also investigating the galaxy's red
supergiant content. This task is complicated by contamination by
Galactic foreground stars that color and magnitude criteria alone
cannot weed out. Therefore, we use proper motions and the LMC's large
systemic radial velocity (~278 km/s) to separate out these foreground
dwarfs. After observing nearly 2,000 stars, we identified 317
probable yellow supergiants, 6 possible yellow supergiants and 505
probable red supergiants. Foreground contamination of our yellow
supergiant sample was ~80%, while that of the the red supergiant
sample was only 3%. By placing the yellow supergiants on the H-R
diagram and comparing them against the evolutionary tracks, we find
that new Geneva evolutionary models do an exemplary job at predicting
both the locations and the lifetimes of these transitory
objects.
Reference: Accepted for publication in the
ApJ
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1202.4225
Comments:
Email: KNeugent@lowell.edu
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Moravveji Ehsan, Moya Andy,
Guinan Edward F
Department of Physics, Institute for
Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
Departamento de Astrof'{i}sica, Centro de Astrobiolog'ia
(INTA-CSIC), PO BOX 78, 28691 Villanueva de la Ca~nada, Madrid, Spain
Department of Astronomy, Villanova University, 800 Lancaster
Ave, Villanova PA, USA
The cores of luminous B and A-type (BA)
supergiant stars are the seeds of later core collapse supernovae.
Thus, constraining the near-core conditions in this class of
stars can place tighter constraints on the size, mass and chemical
composition of supernova remnants.
Asteroseismology of these
massive stars is one possible approach into such investigations.
Recently, Moravveji et al. (2012, hereafter Paper I) extracted 19
significant frequencies from a 6-year radial velocity monitoring or
Rigel ($beta$ Ori, B8 Ia).
The periods they determined broadly
range from 1.22 to 74.74 days.
Based on our differentially
rotating stellar structure and evolution model, Rigel, at it’s
current evolutionary state, is undergoing core He burning and shell H
burning.
Linear fully non-adiabatic non-radial stability analyses
result in the excitation of a dense spectrum of non-radial
gravity-dominated mixed modes.
The fundamental radial mode
($ell=0$) and its overtones are all stable.
When the hydrogen
burning shell is located even partially in the radiative zone, a
favorable condition for destabilization of
g-modes through the
so-called $epsilon-$mechanism becomes viable.
Only those g-modes
that have high relative amplitudes in the hydrogen burning
(radiative) zone can survive the strong radiative damping.
From
the entire observed range of variability periods of Rigel (found in
Paper I), and based on our model, only those modes with periods
ranging between 21 to 127 days can be theoretically explained by the
$epsilon-$mechanism.
The origin of the short-period variations
(found in Paper I) still remain unexplained.
Because Rigel is
similar to other massive BA supergiants, we believe that the
$epsilon-$mechanism may be able to explain the long-period variations
in $alpha$ Cygni class of pulsating stars.
Reference:
Accepted for publication in The Astrophysical Journal, Volume
747
Status: Manuscript has been accepted
Weblink:
Comments:
Email:
moravveji@iasbs.ac.ir
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K. T. Hole and R.
Ignace
East Tennessee State University
Line ratios
in "fir" triplets of helium-like ions have proven to be a
powerful diagnostic of conditions in X-ray emitting gas surrounding
massive stars. Recent observations indicate that these ratios can be
variable with time.
The possible causes of variation in line
ratios are limited: changes in the radiation field or changes in
density, and changes in mass-loss or geometry. In this paper, we
investigate the ability of changes in the radiation field to induce
variability in the ratio R=f/i.
To isolate the radiative effect,
we use a heuristic model of temperature and radius changes in
variable stars in the B and O range with low-density, steady-state
winds. We model the changes in emissivity of X-ray emitting gas close
to the star due to differences in level-pumping from available UV
photons at the location of the gas.
We find that under these
conditions, variability in R is dominated by the stellar temperature.
Although the relative amplitude of variability is roughly comparable
for most lines at most temperatures, detectable variations are
limited to a few lines for each spectral type. We predict that
variable values in R due to stellar variability must follow
predictable trends found in our simulations.
Our model uses
radial pulsations as a mode of stellar variability that maximizes the
amplitude of variation in R. This model is robust enough to show
which ions will provide the best opportunity for observing
variability in the f/i ratio at different stellar temperatures, and
the correlation of that variability with other observable parameters.
In real systems, the effects would be more complex than in our model,
with differences in phase and suppressed amplitude in the presence of
non-radial pulsations. This suggests that changes in R across many
lines concurrently are not likely to be produced by a variable
radiation field.
Reference: astro-ph (accepted to
A&A)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1202.3193
Comments:
Email: kth.astro@gmail.com
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R. Ignace^1, W.L. Waldron^2,
J.P. Cassinelli^3
1 East Tennessee State U
2 Eureka
Scientific
3 U of Wisconsin
The consequences of structured
flows continue to be a pressing topic in relating spectral data to
physical processes occurring in massive star winds. In a preceding
paper, our group reported on hydrodynamic simulations of hypersonic
flow past a rigid spherical clump to explore the structure of bow
shocks that can form around wind clumps. Here we report on profiles
of emission lines that arise from such bow shock morphologies. To
compute emission line profiles, we adopt a two component flow
structure of wind and clumps using two "beta" velocity
laws. While individual bow shocks tend to generate double horned
emission line profiles, a group of bow shocks can lead to line
profiles with a range of shapes with blueshifted peak emission that
depends on the degree of X-ray photoabsorption by the interclump wind
medium, the number of clump structures in the flow, and the radial
distribution of the clumps. Using the two beta law prescription, the
theoretical emission measure and temperature distribution throughout
the wind can be derived. The emission measure tends to be power law,
and the temperature distribution broad in terms of wind velocity.
Although restricted to the case of adiabatic cooling, our models
highlight the influence of bow shock effects for hot plasma
temperature and emission measure distributions in stellar winds and
their impact on X-ray line profile shapes. Previous models have
focused on geometrical considerations of the clumps and their
distribution in the wind. Our results represent the first time that
the temperature distribution of wind clump structures are explicitly
and self-consistently accounted in modeling X-ray line profile shapes
for massive stars.
Reference: to appear in ApJ
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1202.5492
Comments:
Email: ignace@etsu.edu
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W. L. F. Marcolino, J. -C.
Bouret, N. R. Walborn, I. D. Howarth, Y. Naze, A. W. Fullerton, G. A.
Wade, D. J. Hillier, A. Herrero
...
We present the
first ultraviolet spectrum of the peculiar, magnetic Of?p star HD 108
obtained in its spectroscopic low state. The new data, obtained with
the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space
Telescope, reveal significant changes compared to IUE spectra
obtained in the high state: N V 1240, Si IV 1400, and C IV 1550
present weaker P-Cygni profiles (less absorption) in the new data,
while N IV 1718 absorption is deeper, without the clear wind
signature evident in the high state. Such changes contrast with those
found in other magnetic massive stars, where more absorption is
observed in the resonance doublets when the sightline is close to the
plane of the magnetic equator. The new data show also that the
photospheric Fe IV forest, at 1600--1700 angstroms, has strengthened
compared to previous observations. The ultraviolet variability is
large compared to that found in typical, non-magnetic O stars, but
moderate when compared to the high-/low-state changes reported in the
optical spectrum of HD 108 over several decades. We use non-LTE
expanding-atmosphere models to analyze the new STIS observations.
Overall, the results are in accord with a scenario in which the
optical variability is mainly produced by magnetically constrained
gas, close to the photosphere. The relatively modest changes found in
the main ultraviolet wind lines suggest that the stellar wind is not
substantially variable on a global scale. Nonetheless,
multidimensional radiative-transfer models may be needed to
understand some of the phenomena observed.
Reference:
MNRAS
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1202.6041
Comments:
9 pages, 8 figures
Email: wagner@astro.ufrj.br
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Šurlan, Brankica(1,2,3);
Hamann, Wolf-Rainer(4); Kubát Jiří(1); Oskinova, Lidia M.(4);
Feldmeier, Achim(4)
1 - Astronomický ústav, Akademie věd
České Republiky, CZ-251 65 Ondřejov, Czech Republic
2 -
Matematicko fyzikální fakulta, Univerzita Karlova, Praha, Czech
Republic
3 - Matematički Institut SANU, Kneza Mihaila 36, 11001
Beograd, Republic of Serbia
4 - Institut für Physik und
Astronomie, Universität Potsdam, Karl-Liebknecht-Straße 24/25,
14476 Potsdam-Golm, Germany
The true mass-loss rates from
massive stars are important for many branches of astrophysics. For
the correct modeling of the resonance lines, which are among the key
diagnostics of stellar mass-loss, the stellar wind clumping turned
out to be very important. In order to incorporate clumping into
radiative transfer calculation, 3-D models are required. Various
properties of the clumps may have strong impact on the resonance line
formation and, therefore, on the determination of empirical mass-loss
rates.
We incorporate the 3-D nature of the stellar wind clumping
into radiative transfer calculations and investigate how different
model parameters influence the resonance line formation. We develop a
full 3-D Monte Carlo radiative transfer code for inhomogeneous
expanding stellar winds. The number density of clumps follows the
mass conservation. For the first time, realistic 3-D models that
describe the dense as well as the tenuous wind components are used to
model the formation of resonance lines in a clumped stellar wind. At
the same time, non-monotonic velocity fields are accounted for.
The
3-D density and velocity wind inhomogeneities show very strong impact
on the resonance line formation. The different parameters describing
the clumping and the velocity field results in different line
strengths and profiles. We present a set of representative models for
various sets of model parameters and investigate how the resonance
lines are affected. Our 3-D models show that the line opacity is
reduced for larger clump separation and for more shallow velocity
gradients within the clumps.
Our new model demonstrates that to
obtain empirically correct mass-loss rates from the UV resonance
lines, the wind clumping and its 3-D nature must be taken into
account.
Reference: arXiv:1202.4787
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1202.4787
Comments:
Astronomy and Astrophysics, accepted for publication
Email:
surlan@sunstel.asu.cas.cz
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Mahy, L.(1), Gosset, E.(1), Sana, H.(2), Damerdji, Y.(1),
De Becker, M.(1), Rauw, G.(1), Nitschelm, C.(3)
(1)
Institut d’Astrophysique et de Géophysique, Université de Liège,
Bât. B5C, Allée du 6 Août 17, B-4000, Liège, Belgium
(2)
Sterrenkundig Instituut "Anton Pannekoek", University of
Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, The Netherlands
(3)
Instituto de Astronomía, Universidad Católica del Norte, Avenida
Angamos 0610, Antofagasta, Chile
Context. HD 150136 is one of
the nearest systems harbouring an O3 star. Although this system was
for a long time considered as
binary, more recent investigations
have suggested the possible existence of a third component.
Aims.
We present a detailed analysis of HD 150136 to confirm the triple
nature of this system. In addition, we investigate the physical
properties of the individual components of this system.
Methods.
We analysed high-resolution, high signal-to-noise data collected
through multi-epoch runs spread over ten years. We applied a
disentangling program to refine the radial velocities and to obtain
the individual spectra of each star. With the radial velocities, we
computed the orbital solution of the inner system, and we describe
the main properties of the orbit of the outer star such as the
preliminary mass ratio, the eccentricity, and the orbital-period
range. With the individual spectra, we determined the stellar
parameters
of each star by means of the CMFGEN atmosphere code.
Results. We offer clear evidence that HD150136 is a triple system
composed of an O3V((f*))–3.5V((f+)), an O5.5–6V((f)), and an
O6.5–7V((f)) star. The three stars are between 0–3 Myr old.
We derive dynamical masses of about 64, 40, and 35 Msun for the
primary, the secondary and the third components by assuming an
inclination of 49° (sin^3 i = 0.43). It currently corresponds to one
of the most massive systems in our galaxy. The third star moves with
a period in the range of 2950 to 5500 d on an outer orbit with an
eccentricity of at least 0.3. However, because of the long orbital
period, our dataset is not sufficient to constrain the orbital
solution of the tertiary
component with high accuracy.
Conclusions. We confirm the presence of a tertiary star in the
spectrum of HD 150136 and show that it is physically bound to the
inner binary system. This discovery makes HD 150136 the first
confirmed triple system with an O3 primary star.
Reference:
arXiv:1202.6215
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1202.6215
Comments:
13 pages, 11 figures, 4 tables
Astronomy & Astrophysics,
accepted for publication
Email: mahy@astro.ulg.ac.be
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Paul.Crowther@sheffield.ac.uk
Dept
of Physics & Astronomy,
University of Sheffield,
Hounsfield
Road,
Sheffield, S3 7RH
United Kingdom
A PDRA
position, funded by the UK Science and Technology Facilities Council,
is available for three years from 1 Jul 2012 to support a HST/STIS
programme http://pacrowther.staff.shef.ac.uk/R136_stis.html which
seeks to construct the mass function of very massive stars within the
young, rich star cluster R136 via a comprehensive census of the
central parsec at UV and optical wavelengths.
The successful
applicant will take a lead role in the reduction and analysis of the
HST datasets, and should have a PhD in astronomy or a closely related
field. Preference will be given to applicants with observational or
theoretical experience in one or more of the following fields:
stellar atmospheres, evolution of massive stars, young star clusters.
A good track record of published research is also expected.
Applications (including CV, list of publications and a
statement of research interests) should be submitted via weblink,
with three reference letters sent separately. On-line application
queries to e-Recruitment@sheffield.ac.uk
Salary:
£28,401 per annum
Attention/Comments: Reference Number
UOS 004056
Weblink: http://www.sheffield.ac.uk/jobs
Email:
Paul.Crowther@sheffield.ac.uk
Deadline: 30 Apr
2012
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23-24 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.
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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June 17 - July 1
Venue:
Aspen Center for Physics, Aspen, CO
APPLICATION DEADLINE:
TUESDAY, JAN 31, 2012
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: Beijing,
China
Deadline for early registration has been extended to
March 17 ; abstract submission is requested before Feb 29. For info,
there are two massive stars meetings at the GA...
Weblink:
http://www.astronomy2012.org/dct/page/65615
Email:
naze@astro.ulg.Ac.be
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