ISSN 1783-3426
|
Candidates and nominations for Organization Committee of IAU Working Group on Massive Stars
A Detailed Far-Ultraviolet Spectral
Atlas of O-Type Stars
The
Wolf-Rayet Content of M31
The
nature of the high Galactic latitude O-star HD93521: new results from
X-ray and optical spectroscopy
Discovery
of New, Dust-Poor B[e] Supergiants in the Small Magellanic
Cloud
Multi-D models of
circumstellar shells around evolved massive stars
The
Fundamental Parameters of Four Massive Eclipsing Binaries in
Westerlund 1
The 2.35 year itch of
Cyg OB2 #9 - I. Optical and X-ray monitoring
The
Discovery of a Rare WO-type Wolf-Rayet Star in the Large Magellanic
Cloud
Clumping in the inner winds
of hot, massive stars from hydrodynamical line-driven instability
simulations
A companion as the
cause of latitude-dependent effects in the wind of Eta Carinae
An
XMM-Newton view of the M17 nebula
Rotating
Wolf-Rayet stars in a post RSG/LBV phase. An evolutionary channel
towards long-duration GRBs?
On the
influence of the companion star in Eta Carinae: 2D radiative transfer
modeling of the ultraviolet and optical spectra
First
3D MHD simulation of a massive-star magnetosphere with application to
Hα emission from θ1 Ori C
Rotational
and Cyclical Variability in $gamma$
MHD
Modeling of a Disk-Wind from a High-Mass Protobinary: the case of
Orion Source I
The Unprecedented Third Outburst of SN
2009ip: A Luminous Blue Variable Becomes a Supernova
Proceedings
business meeting IAU WG on Massive Stars during GA Beijing 2012
IAUS 302 -
Magnetic Fields Throughout Stellar Evolution
Massive
Stars: From Alpha to Omega
Dear members of the Working Group on
Massive Stars,
time is running fast, and three years since
the last election for our Organization Committee (OC) have past.
According to our by-laws, 5 members have to leave (though they can be
re-elected if nominated), namely
Paul Crowther
Claus
Leitherer
Stan Owocki
Nicole St. Louis
and myself (Jo
Puls, Chair)
Remaining OC members for the next three years
are
Margaret Hanson
Artemio Herrero
Norbert Langer
Gegor Rauw
Rich Townsend
We are looking now for
candidates!!!!
If you are interested in promoting our
science, please step forward. Also, if you know suited candidates
(and have insured yourself that they would agree to 'serve'), please
nominate them.
Please note that OC members *must* be IAU
members!!!
For candidates and nominations, please contact me
via email:
uh101aw AT usm.uni-muenchen.de
latest
until Nov. 7th.
The election will take place during mid
November, and the new OC will begin its work with the new year. First
action will be voting for a new chair.
Hope to receive lots
of responses,
with best regards,
Jo Puls (Chair of OC
MSWG)
Weblink:
Email:
uh101aw@usm.uni-muenchen.de
Back to
contents
Myron A. Smith
Catholic
University of America
In this paper we present a spectral
atlas covering the wavelength interval 930--1188A for O2--O9.5 stars
using Far Ultraviolet Spectroscopic Explorer archival data. The stars
selected for the atlas were drawn from three populations: Galactic
main sequence (class III-V) stars, supergiants, and main sequence
stars in the Magellanic Clouds, which have low metallicities. For
each of these stars we have prepared FITS files comprised of paris of
merged spectra for user access via the Multi-Mission Archives at
Space Telescope. We chose spectra from the first population with
spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile
tables and figures with identifications of all possible atmospheric
and ISM lines in the region 949-1188A. Our identified line totals for
these six representative spectra are 821 (500), 992 (663), 1077
(749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively,
where the numbers in parentheses are the totals of lines formed in
the atmospheres, according to spectral synthesis models.
The
total number of unique atmospheric identifications for the six main
sequence O star template spectra is 1792, whereas the number of
atmospheric lines in common to these spectra is 300. The number of
identified lines decreases toward earlier types (increasing effective
temperature), the whlle percentages of "missed" features
(lines not predicted from our spectral syntheses) drops from a high
of 8% at type B0.2, from our recently published B star far-UV atlas,
to 1--3% for type O spectra. The percentages of overpredicted lines
are similar, despite their being much higher for B star spectra. We
also discuss the statistics of line populations among the various
elemental ionization states. Finally, as an aid to users we list
those isolated lines that can be used to determine stellar
temperatures and the presence of possible chemical
anomalies.
Reference: Astrophysical Journal Supplements
(October, 2012)
Status: Manuscript has been accepted
Weblink:
Comments: The full set of plots and line
identification tables will be available very shortly in the MAST
archives at http://archive.stsci.edu/prepds/fuvostars/ .
Email:
msmith@stsci.edu
Back to contents
Kathryn F. Neugent (1),
Philip Massey (1), and Cyril Georgy (2)
(1) Lowell
Observatory, (2) Centre de Recherche Astrophysique de Lyon, E ́cole
Normale Sup ́erieure de Lyon
Wolf-Rayet stars are evolved
massive stars, and the relative number of WC-type and WN-type WRs
should vary with the metallicity of the host galaxy, providing a
sensitive test of stellar evolutionary theory. However, past studies
of the WR content of M31 have been biased towards detecting WC stars,
as their emission line signatures are much stronger than those of
WNs. Here we present the results of a survey covering all of M31's
optical disk (2.2 deg^2), with sufficient sensitivity to detect the
weaker-lined WN-types. We identify 107 newly found WR stars, mostly
of WN-type. This brings the total number of spectroscopically
confirmed WRs in M31 to 154, a number we argue is complete to about
95%, except in regions of unusually high reddening. This number is
consistent with what we expect from the integrated Halpha luminosity
compared to that of M33. The majority of these WRs formed in OB
associations around the Population I ring, although 5% are truly
isolated. Both the relative number of WC to WN-type stars as well as
the WC subtype distribution suggest that most WRs exist in
environments with higher-than-solar metallicities, which is
consistent with studies of M31's metallicity. Although the WC-to-WN
ratio we find for M31 is much lower than that found by previous
studies, it is still higher than what the Geneva evolutionary models
predict. This may suggest that Roche-lobe overflow produces the
excess of WC stars observed at high metallicity, or that the assumed
rotational velocities in the models are too high.
Reference:
ApJ, in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1209.1177
Comments:
Email: phil.massey@lowell.edu
Back
to contents
G. Rauw, T. Morel, M.
Palate
Institut d'Astrophysique et de Geophysique,
Universite de Liege, Belgium
Owing to its unusual location and
its isolation, the nature of the high Galactic latitude O9.5Vp object
HD93521 is still uncertain. We have collected X-ray and optical
observations to characterize the star and its surroundings. X-ray
images and spectra are analyzed to search for traces of a recent star
formation event around HD93521 and to search for the signature of a
possible compact companion. Optical echelle spectra are analysed with
plane-parallel model atmosphere codes, assuming either a spherical
star or a gravity darkened rotationally flattened star, to infer the
effective temperature and surface gravity, and to derive the He, C, N
and O abundances of HD93521. The X-ray images reveal no traces of a
population of young low-mass stars coeval with HD93521. The X-ray
spectrum of HD93521 is consistent with a normal late O-type star
although with subsolar metallicity. No trace of a compact companion
is found in the X-ray data. In the optical spectrum, He and N are
found to be overabundant, in line with the effect of rotational
mixing in this very fast rotator, whilst C and O are subsolar. A
critical comparison with the properties of subdwarf OB stars,
indicates that, despite some apparent similarities, HD93521 does not
belong to this category. Despite some ambiguities on the runaway
status of the star, the most likely explanation is that HD93521 is a
Population I massive O-type star that was ejected from the Galactic
plane either through dynamical interactions or a result of a
supernova event in a binary system.
Reference: A&A
(in press)
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2012arXiv1209.2606R
Comments:
Email: rauw@astro.ulg.ac.be
Back
to contents
A. S. Graus, J. B. Lamb, M.
S. Oey
U. Michigan, UC Irvine
We present the
discovery of three new B[e] supergiants (sgB[e] stars) in the Small
Magellanic Cloud (SMC). All three stars (R15, R38, and R48) were
identified in the course of our Runaways and Isolated O Type Star
Spectroscopic Survey of the SMC (RIOTS4). The stars show optical
spectra that closely resemble those of previously known B[e] stars,
presenting numerous low-ionization forbidden and permitted emission
lines such as [Fe II] and Fe II. Furthermore, our stars have
luminosities of log(L/L_sun) > 4, demonstrating that they are
supergiants. However, we find lower infrared excesses and weaker
forbidden emission lines than for previously identified B[e]
supergiants. Thus our stars appear to either have less material in
their circumstellar disks than other sgB[e] stars, or the
circumstellar material has lower dust content. We suggest that these
may constitute a new subclass of dust-poor sgB[e] stars.
Reference:
Graus, A. S., Lamb, J. B., & Oey M. S., ApJ, in press;
astro-ph/1208.5486
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1208.5486
Comments:
Email: agraus@uci.edu
Back
to contents
Allard Jan van Marle$^{1,2}$,
Rony Keppens$^1$
1-Centre for Plasma Astrophysics, KU
Leuven;
2-Institute of Astronomy, KU Leuven
Massive stars
shape their surrounding medium through the force of their stellar
winds, which collide with the circumstellar medium. Since the
characteristics of these stellar winds vary over the course of the
evolution of the star, the circumstellar matter becomes a reflection
of the stellar evolution and can be used to determine the
characteristics of the progenitor star. In particular, whenever a
fast wind phase follows a slow wind phase, the fast wind sweeps up
its predecessor in a shell, which is observed as a circumstellar
nebula. We make 2-D and 3-D numerical simulations of fast stellar
winds sweeping up their slow predecessors to investigate whether
numerical models of these shells have to be 3-D, or whether 2-D
models are sufficient to reproduce the shells correctly. We focus on
those situations where a fast Wolf-Rayet (WR) star wind sweeps up the
slower wind emitted by its predecessor, being either a red supergiant
or a luminous blue variable. As the fast WR wind expands, it creates
a dense shell of swept up material that expands outward, driven by
the high pressure of the shocked WR wind. These shells are subject to
a fair variety of hydrodynamic-radiative instabilities. If the WR
wind is expanding into the wind of a luminous blue variable phase,
the instabilities will tend to form a fairly small-scale, regular
filamentary lattice with thin filaments connecting knotty features.
If the WR wind is sweeping up a red supergiant wind, the
instabilities will form larger interconnected structures with less
regularity. Our results show that 3-D models, when translated to
observed morphologies, give realistic results that can be compared
directly to observations. The 3-D structure of the nebula will help
to distinguish different progenitor scenarios.
Reference:
A&A, accepted
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1209.4496
Comments:
Email: AllardJan.vanMarle@ster.kuleuven.be
Back
to contents
E. Koumpia (1,2), A. Z.
Bonanos (2)
(1) University of Groningen, The Netherlands
(2) National Observatory of Athens, Greece
Context. Only a
small number of high mass stars (> 30M⊙) have fundamental
parameters (i.e. masses and radii) measured with high enough accuracy
from eclipsing binaries to constrain formation and evolutionary
models of massive stars.
Aims. This work aims to increase this
limited sample, by studying the four massive eclipsing binary
candidates discovered by Bonanos in the young massive cluster
Westerlund 1.
Methods. We present new follow-up echelle
spectroscopy of these binaries and models of their light and radial
velocity curves.
Results. We obtain fundamental parameters for
the eight component stars, finding masses that span a range of 10 −
40M⊙, and contributing accurate fundamental parameters for one
additional very massive star, the 33 M⊙ component of W13. WR77o is
found to have a ∼ 40 M⊙ companion, which provides a second
dynamical constraint on the mass of the progenitor of the magnetar
known in the cluster. We also use W13 to estimate the first, direct,
eclipsing binary distance to Westerlund 1 and therefore the magnetar
and find it to be at 3.7 ± 0.6 kpc.
Conclusions. Our results
confirm previous evidence for a high mass for the progenitor of the
magnetar. In addition, the availability of eclipsing binaries with
accurate parameters opens the way for direct, independent, high
precision eclipsing binary distance measurements to Westerlund
1.
Reference: A&A, in press
Status: Manuscript
has been accepted
Weblink:
http://arxiv.org/abs/1205.1369
Comments:
11 pages, 11 figures, 7 tables
Email:
bonanos@astro.noa.gr
Back to contents
Y. Naze, L. Mahy, Y.
Damerdji, H.A. Kobulnicky, J.M. Pittard, E.R. Parkin, O. Absil, R.
Blomme
Univ. Liege (1, 2, 3, 7), Univ. Wyoming (4), Univ
Leeds (5), Austr. Nat. Univ (6), Royal Obs. Belg. (8)
Context:
Nonthermal radio emission in massive stars is expected to arise in
wind-wind collisions occurring inside a binary system. One such case,
the O-type star Cyg OB2 #9, was proven to be a binary only four years
ago, but the orbital parameters remained uncertain. The periastron
passage of 2011 was the first one to be observable under good
conditions since the discovery of binarity. Aims: In this context, we
have organized a large monitoring campaign to refine the orbital
solution and to study the wind-wind collision. Methods: This paper
presents the analysis of optical spectroscopic data, as well as of a
dedicated X-ray monitoring performed with Swift and XMM. Results: In
light of our refined orbital solution, Cyg OB2 #9 appears as a
massive O+O binary with a long period and high eccentricity; its
components (O5-5.5I for the primary and O3-4III for the secondary)
have similar masses and similar luminosities. The new data also
provide the first evidence that a wind-wind collision is present in
the system. In the optical domain, the broad Ha line varies,
displaying enhanced absorption and emission components at periastron.
X-ray observations yield the unambiguous signature of an adiabatic
collision because, as the stars approach periastron, the X-ray
luminosity closely follows the 1/D variation expected in that case.
The X-ray spectrum appears, however, slightly softer at periastron,
which is probably related to winds colliding at slightly lower speeds
at that time. Conclusions: It is the first time that such a variation
has been detected in O+O systems, and the first case where the
wind-wind collision is found to remain adiabatic even at periastron
passage.
Reference: accepted by A&A
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1209.5622
Comments:
Email: naze@astro.ulg.ac.be
Back
to contents
Kathryn F. Neugent (1),
Philip Massey (1), Nidia Morrell (2)
(1) Lowell
Observatory
(2) Las Campanas Observatory, Carnegie
Observatories
While observing OB stars within the most crowded
regions of the Large Magellanic Cloud, we happened upon a new
Wolf-Rayet star in Lucke-Hodge 41, the rich OB association that
contains S Doradus and numerous other massive stars. At first glance
the spectrum resembled that of a WC4 star, but closer examination
showed strong OVI λλ 3811, 34 lines, leading us to classify it as a
WO4. This is only the second known WO in the LMC, and the first known
WO4 (the other being a WO3). This rarity is to be expected due to
these stars’ short lifespans as they represent the most advanced
evolutionary stage in a massive star’s life before exploding as
SNe. This discovery shows that while the majority of WRs within the
LMC have been discovered, there may be a few WRs left to be
found.
Reference: Astronomical Journal, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1210.0062
Comments:
Email: phil.massey@lowell.edu
Back
to contents
Jon O. Sundqvist(1), Stanley
P. Owocki(1)
1: University of Delaware, Bartol Research
Institute, Newark, DE 19716, USA
We investigate the effects of
stellar limb-darkening and photospheric perturbations for the onset
of wind structure arising from the strong, intrinsic line-deshadowing
instability (LDI) of a line-driven stellar wind. A linear
perturbation analysis shows that including limb-darkening reduces the
stabilizing effect of the diffuse radiation, leading to a net
instability growth rate even at the wind base. Numerical
radiation-hydrodynamics simulations of the non-linear evolution of
this instability then show that, in comparison with previous models
assuming a uniformly bright star without base perturbations, wind
structure now develops much closer ($r la 1.1 R_star$) to the
photosphere. This is in much better agreement with observations of
O-type stars, which typically indicate the presence of strong
clumping quite near the wind base.
Reference: Accepted
for publication in MNRAS. Pre-print on astro-ph.
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1210.1861
Comments:
Email: jon@bartol.udel.edu
Back
to contents
Jose H. Groh (1, 2), Thomas
I. Madura (2), D. J. Hillier (3), C. J. H. Kruip (4), and G. Weigelt
(2)
(1) Geneva Observatory, Switzerland
(2)
Max-Planck-Institute for Radioastronomy, Bonn
(3) University of
Pittsburgh, USA
(4) Leiden University, Netherlands
We
analyze spatially resolved spectroscopic observations of the Eta
Carinae binary system obtained with HST/STIS. Eta Car is enshrouded
by the dusty Homunculus nebula, which scatters light emitted by the
central binary and provides a unique opportunity to study a massive
binary system from different vantage points. We investigate the
latitudinal and azimuthal dependence of H$alpha$ line profiles caused
by the presence of a wind-wind collision (WWC) cavity created by the
companion star. Using two-dimensional radiative transfer models, we
find that the wind cavity can qualitatively explain the observed line
profiles around apastron. Regions of the Homunculus which scatter
light that propagated through the WWC cavity show weaker or no H
alpha absorption. Regions scattering light that propagated through a
significant portion of the primary wind show stronger P Cygni
absorption. Our models overestimate the H alpha absorption formed in
the primary wind, which we attribute to photoionization by the
companion, not presently included in the models. We can qualitatively
explain the latitudinal changes that occur during periastron,
shedding light on the nature of Eta Car's spectroscopic events. Our
models support the idea that during the brief period of time around
periastron when the primary wind flows unimpeded toward the observer,
H alpha absorption occurs in directions toward the central object and
Homunculus SE pole, but not toward equatorial regions close to the
Weigelt blobs. We suggest that observed latitudinal and azimuthal
variations are dominated by the companion star via the WWC cavity,
rather than by rapid rotation of the primary star.
Reference:
Groh et al. 2012, ApJ, 759, L2
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1210.2709
Comments:
Email: jose.groh@unige.ch
Back
to contents
Francois Mernier, Gregor
Rauw
Institut d'Astrophysique, Liege University,
Belgium
We present the analysis of an XMM-Newton observation
of the M17 nebula. The
X-ray point source population consists of
massive O-type stars and a population
of probable low-mass
pre-main sequence stars. CEN1a,b and OI352, the X-ray
brightest
O-type stars in M17, display hard spectra (kT of 3.8 and 2.6 keV)
consistent with a colliding wind origin in binary/multiple
systems. We show
that the strong interstellar reddening towards
the O-type stars of M17 yields
huge uncertainties on their
Lx/Lbol values. The low-mass pre-main sequence
stars exhibit hard
spectra resulting from a combination of high plasma
temperatures
and very large interstellar absorption. We find evidence for
considerable long term (months to years) variability of these
sources. M17 is
one of the few star formation complexes in our
Galaxy producing diffuse X-ray
emission. We analyze the spectrum
of this emission and compare it with previous
studies. Finally,
we discuss the Optical Monitor UV data obtained
simultaneously
with the X-ray images. We find very little correspondence
between
the UV and X-ray sources, indicating that the majority of the UV
sources are foreground stars, whilst the bulk of the X-ray
sources are deeply
embedded in the M17 complex.
Reference:
New Astronomy
Status: Manuscript has been accepted
Weblink:
arXiv:1210:2936
Comments:
Email: rauw@astro.ulg.ac.be
Back
to contents
G. Gräfener^1, J. S. Vink^1,
T. J. Harries^2, and N. Langer^3
1) Armagh Observatory,
College Hill, Armagh BT61 9DG, UK
2) School of Physics and
Astronomy, University of Exeter, Stocker Rd, Exeter EX4 4QL, UK
3)
Argelander-Institut für Astronomie der Universität Bonn, Auf dem
Hügel 71, 53121 Bonn, Germany
(shortened) We investigate the
properties of Galactic Wolf-Rayet (WR) stars and their circumstellar
(CS) environment to identify evolutionary channels that may lead to
the formation of long-duration Gamma-Ray bursts (LGRBs). To this
purpose we compile available information on the spectropolarimetric
properties, the presence of CS ejecta, and the CS velocities in the
environment of Galactic WR stars. We use linear line-depolarization
as an indicator of rotation, nebular morphology as an indicator of
stellar ejecta, and velocity patterns in UV absorption features as an
indicator of increased velocities in the CS environment. We find that
the ~23% WR stars with "possible ejecta nebulae" dominate
the population of WR stars with spectropolarimetric signatures of
rotation, while WR stars without such nebulae only rarely show
indications of rotation. The corresponding objects are most likely in
an early stage after a preceding RSG or LBV phase, and have not yet
lost their angular momenta due to the strong mass-loss in the WR
phase. From their photometric periods we estimate rotation parameters
in the range omega = 0.04...0.25, corresponding to moderate rotation
speeds of 36...120 km/s. These values are very uncertain, but comply
with the specific surface angular momentum requirement for LGRB
progenitors. Our results indicate that, in the Galaxy, mainly "young"
WR stars shortly after a RSG/LBV phase show spectropolarimetric
signatures of rotation. Their rotation rates are thus likely enhanced
with respect to the majority of Galactic WR stars. According to their
estimated specific surface angular momenta, a subgroup of stars
exploding in this phase may represent an evolutionary channel towards
LGRBs at high metallicities, comparable to the Galaxy.
Reference:
Astronomy & Astrophysics
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1210.1153
Comments:
Email: ggr@arm.ac.uk
Back
to contents
Jose H. Groh (1), D. John
Hillier (2), Thomas I. Madura (1), Gerd Weigelt (1)
(1)
Max-Planck-Institute for Radioastronomy, Germany, (2) Univ. of
Pittsburgh, USA
We present 2D radiative transfer modeling of
the Eta Carinae binary system accounting for the presence of a
wind-wind collision (WWC) cavity carved in the optically-thick wind
of the primary star. By comparing synthetic line profiles with
HST/STIS spectra obtained near apastron, we show that the WWC cavity
has a strong influence on multi-wavelength diagnostics. This
influence is regulated by the modification of the optical depth in
the continuum and spectral lines. We find that H-alpha, H-beta, and
Fe II lines are the most affected by the WWC cavity, since they form
over a large volume of the primary wind. These spectral lines depend
on latitude and azimuth since, according to the orientation of the
cavity, different velocity regions of a spectral line are affected.
For 2D models with orientation corresponding to orbital inclination
angle 110deg < i < 140deg and longitude of periastron 210deg <
omega < 330deg, the blueshifted and zero-velocity regions of the
line profiles are the most affected. These orbital orientations are
required to simultaneously fit the UV and optical spectrum of Eta
Car, for a half-opening angle of the cavity in the range 50-70deg. We
find that the excess P-Cygni absorption seen in H-alpha, H-beta and
optical Fe II lines in spherical models becomes much weaker or absent
in the 2D models, in agreement with the observations. The observed UV
spectrum of Eta Car, dominated by Fe II absorption lines, is superbly
reproduced by our 2D cavity models. Small discrepancies still remain,
as H-gamma and H-delta absorptions are overestimated by our models.
We suggest that photoionization of the wind of the primary by the hot
companion star is responsible for the weak absorption seen in these
lines. Our CMFGEN models indicate that the primary star has a
mass-loss rate of 8.5x10e-4 Msun/yr and wind terminal velocity of 420
km/s around the 2000 apastron.
Reference: Groh et al.
(2012), MNRAS, 423, 1623
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/abs/2012MNRAS.423.1623G
Comments:
Email: jose.groh@unige.ch
Back
to contents
A. ud-Doula, J. O. Sundqvist,
S. P. Owocki, V. Petit and R.H.D. Townsend
Penn State W.
Scranton
We present the first fully 3D MHD simulation for
magnetic channeling and confinement of a radiatively driven,
massive-star wind. The specific parameters are chosen to represent
the prototypical slowly rotating magnetic O star θ1 Ori C, for which
centrifugal and other dynamical effects of rotation are negligible.
The computed global structure in latitude and radius resembles that
found in previous 2D simulations, with unimpeded outflow along open
field lines near the magnetic poles, and a complex equatorial belt of
inner wind trapping by closed loops near the stellar surface, giving
way to outflow above the Alfv ́en radius. In contrast to this
previous 2D work, the 3D simulation described here now also shows how
this complex structure fragments in azimuth, forming distinct clumps
of closed loop infall within the Alfv ́en radius, transitioning in
the outer wind to radial spokes of enhanced density with
characteristic azimuthal separation of 15 − 20◦. Applying these
results in a 3D code for line radiative transfer, we show that
emission from the associated 3D ‘dynamical magnetosphere’ matches
well the observed Hα emission seen from θ1 Ori C, fitting both its
dynamic spectrum over rotational phase, as well as the observed level
of cycle to cycle stochastic variation. Comparison with previously
developed 2D models for Balmer emission from a dynamical
magnetosphere generally confirms that time-averaging over 2D
snapshots can be a good proxy for the spatial averaging over 3D
azimuthal wind structure. Nevertheless, fully 3D simulations will
still be needed to model the emission from magnetospheres with
non-dipole field components, such as suggested by asymmetric features
seen in the Hα equivalent-width curve of θ1 Ori C.
Reference:
Accepted for publication in MNRAS. Pre-print on astro-ph.
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1210.5298
Comments:
Email: auu4@psu.edu
Back
to contents
G. W. Henry$^1$ and M. A.
Smith$^2$
1 - Center of Excellence in Information Systems,
Tennessee State University, 3500 John A. Merritt Blvd., Box 9501,
Nashville,
TN 37209 USA; 2 - Catholic University of America, 3700
San Martin Dr., Baltimore, MD 21218 USA
The B0.5IVe star
$gamma$ Cass is of great interest because it is the prototype of a
small group of classical Be stars having hard X-ray emission of
unknown origin. We discuss results from ongoing B and V observations
of the gamma Cas star-disk system acquired with an Automated
Photometric Telescope during the observing seasons 1997--2011. In an
earlier study Smith, Henry, Vishniac showed that light variations in
gamma Cas are dominated by a series of comparatively prominent cycles
with amplitudes of 0.02--0.03 mag and lengths of 2--3 months,
superimposed on a 1.21-day periodic signal some five times smaller,
which they attributed to rotation. The cycle lengths clustered around
70 days, with a total range of 50--91 days. Changes in both cycle
length and amplitude were observed from year to year. These authors
also found the $V$-band cycles to be 30--40% larger than the B-band
cycles. In the present study we find a continuation of these
variability patterns and that the distribution of the
$Delta(B)/Delta(V)$ amplitude ratios in the long cycles to be
bimodal. During the 2010 observing season, gamma Cas underwent a mass
loss event ("outburst"), as evidenced by the brightening
and reddening seen in our new photometry. This episode coincided with
a waning of the amplitude in the ongoing cycle. The Be outburst ended
the following year, and the light-curve amplitude returned to
pre-outburst levels. This behavior reinforces the interpretation that
cycles arise from a global disk instability. We have determined a
more precise value of the rotation period, 1.215767${pm 0.00001}$
days, using the longer 15-season dataset and combining solutions from
the $V$ and $B$ band light curves. Remarkably, we also find that both
the amplitude and the asymmetry of the rotational waveform changed
over the years. We review arguments for this modulation arising from
transits of a surface magnetic disturbance. Finally, to a limit of 5
mmag, we find no evidence for any photometric variation corresponding
to the gamma Cas binary period, 203.55 days, or to the first few
harmonics.
Reference: Astrophysical Journal
Status:
Manuscript has been accepted
Weblink:
Comments:
To be published in the Astrophysical Journal, Nov. or Dec.
2012
Email: msmith@stsci.edu
Back
to contents
B. Vaidya (1), C. Goddi (2,3)
1
- School of Physics and Astronomy, University of Leeds, Leeds LS29JT
2 - European Southern Observatory, Garching, Germany
3 -
Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The
Netherlands
Very long baseline interferometry (VLBI)
observations of SiO masers in
Orion Source I has enabled for the
first time to resolve the outflow from a high-mass protostar in the
launch and collimation region. Therefore, Source I provides a unique
laboratory to study mass-loss
and mass-accretion in a high-mass
protostar.
We numerically simulate the dynamics of the disk-wind
inside 100
AU from Source I.
This enables us to investigate
the balance of different forces
(gravitational, magnetic,
thermal) regulating gas dynamics in massive star formation. In this
work, we adopt magnetohydrodynamic (MHD) disk-wind models to explain
the
observed properties of the disk-wind from Orion Source I.
The central source is assumed to be a binary composed of two
10,$rm M_{odot}$ stars
in a circular orbit with an orbital
separation of 7 AU. High resolution ideal MHD wind
launching
simulations (which prescribe disk as a boundary) are performed using
the PLUTO code. The simulations are allowed to run until a steady
state is obtained. MHD driven disk-wind provides a consistent
model for the wide-angle
flow from Source I probed by SiO masers,
reproducing the bipolar
morphology, the velocity amplitude and
rotational profile, the
physical conditions, and the magnetic
field strength.
Reference: MNRAS Letters
Status:
Manuscript has been accepted
Weblink:
www.arxiv.org/abs/1210.7775
Comments:
Email: B.Vaidya@leeds.ac.uk
Back
to contents
Jon C. Mauerhan, Nathan
Smith, Alexei Filippenko, Kyle Blanchard, Peter Blanchard, Chadwick
F. E. Casper, S. Bradley Cenko, Kelsey I. Clubb, Daniel Cohen, Gary
Li, and Jeffrey M. Silverman
University of Arizona,
Steward Observatory;
UC Berkeley.
Some reports of
supernova (SN) discoveries turn out not to be true core-collapse
explosions. One such case was SN 2009ip, which was recognized to be a
luminous blue variable (LBV) eruption. This source had a massive
(50-80 Msun) hot progenitor star identified in pre-explosion data, it
had documented evidence of pre-outburst variability, and it was
subsequently discovered to have a 2nd outburst in 2010. This same
source rebrightened again in 2012, and early spectra showed the same
narrow-line profiles as before, suggesting another LBV-like eruption.
We present new photometry and spectroscopy of SN 2009ip, indicating
that its 3rd observed outburst in under 4 years appears to have
transitioned into a genuine SN. The most striking discovery in these
data is that unlike previous reports, the spectrum exhibited Balmer
lines with very broad P-Cygni profiles characteristic of normal Type
II supernovae (SNe II), in addition to narrow emission lines seen in
SNe IIn and LBVs. Emission components have FWHM~8000 km/s, while the
P-Cygni absorption component has blue wings extending to about
-13,000 km/s. These features are typical of Type II SNe, but have
never been seen in a nonterminal LBV-like eruption. Initially, the
peak absolute magnitude of M_V~ -14.5 seemed fainter than that of
normal SNe and faded much more rapidly. However, the source quickly
brightened again to M_R=-17.6 mag, indicating that it is indeed a
true SN. In this bright phase, the broad lines mostly disappeared,
and the spectrum became dominated by broad-winged Lorentzian profiles
of H-alpha and HeI that are characteristic of the early optically
thick phases of luminous SNe IIn. We conclude that the most recent
2012 outburst of SN 2009ip is most likely a true core-collapse SN IIn
that was initially faint, but then rapidly achieved high
luminosities, as a result of interaction with circumstellar material
(abridged).
Reference: Mauerhan et al. 2012,
arXiv:1209.6320
Status: Manuscript has been submitted
Weblink:
http://arxiv.org/abs/1209.6320
Comments:
Submitted to MNRAS on 2012 September 27
8 pages, 5
figures
Email: mauerhan@as.arizona.edu
Back
to contents
J. Puls, Chair IAU WG on Massive
Stars
University Observatory Munich
We report on
the business meeting of the IAU WG on Massive Stars held during the
IAU General Assembly 2012 in Beijing. Major topics were (i) the
re-structuring of the IAU Divisions and consequences for our Working
Group, and (ii) a potential conversion of our WG into a
Commission.
Reference: Transactions IAU, Volume
XXVIIIB, Proc. XXVIII IAU General Assembly, August 2012, ed. T.
Montmerle
Status: Manuscript has been submitted
Weblink:
http://www.usm.uni-muenchen.de/people/puls/papers/TrB_WG_massive_stars.pdf
Comments:
Email: uh101aw@usm.uni-muenchen.de
Back
to contents
edited by Y. Naze
Univ.
Liege
At the recent IAU GA, there was a session entitled "IR
view of massive stars". Three main subjects were discussed :
I.
Obscured and distant clusters ;
II. Stellar and Wind Parameters ;
III. Matter ejection and feedback.
Three 10p summaries will
be published in Highlights of Astronomy, and they are available in
arxiv. PDF files of the contributions are also available on the
session website.
Reference: http://arxiv.org/abs/1210.3985
http://arxiv.org/abs/1210.4280
http://arxiv.org/abs/1210.3986
Status: Conference
proceedings
Weblink:
http://www.gaphe.ulg.ac.be/IAU_XXVIII/prg.html
Comments:
proceedings of SpS5 which took place at IAU-GA
Email:
naze@astro.ulg.ac.be
Back to contents
vacancy@astro.iag.usp.br
Instituto
de Astronomia, Geofísica e Ciências Atmosféricas
IAG/USP
Several
groups at the Astronomy Department of IAG/University of Sao Paulo,
Brazil, invite applications for various 2-yr postdoctoral
fellowships,
renewable for an additional year.
The
Astronomy department of IAG consists of 35 faculty members who work
in
many areas, including: the dynamics of exoplanets and solar
systems,
astrobiology, astrometry, stellar astronomy, the
interstellar medium, Galactic
and extragalactic astronomy and
cosmology, both theoretical and observational.
Applicants with
strong background in radio astronomy, high energy astrophysics
or
instrumentation are also encouraged to apply. IAG/USP astronomers
enjoy
access to international facilities including SOAR, Gemini
and CFHT
Observatories, as well as a 2300-core supercomputer.
Requirements are an outstanding publication list (for the
career stage) and an
exciting plan of work. The candidate must
have interests that overlap with
those of the IAG staff members
(access the list of faculty members at
http://www.astro.iag.usp.br/index.php?dir=inst/pessoal&file=pessoal.php?cod=docentes).
The interested candidates should send a CV, that includes a
publication list,
a research statement (including past work and
future plans), with a maximum of
five pages, and two letters of
recommendation to Claudia Mendes de Oliveira at
email
vacancy@astro.iag.usp.br by March 31st, or until suitable candidates
are
found.
The successful candidate will have a
fellowship reviewed and awarded by the
Sao Paulo State funding
agency FAPESP. Time for research is typically 80-90%
with a small
requirement for dedication to institute activities. The current,
tax
exempt monthly stipend is R$ 5,578.80 (about 2,200EUR or US$2,700 in
Oct
2012). An additional Research Contingency fund (e.g., for
travel, computers,
etc.) of US$4,500 per year is also available.
For further details, contact
vacancy@astro.iag.usp.br.
Attention/Comments:
Weblink:
Email: vacancy@astro.iag.usp.br
Deadline:
Back to contents
2013, August 26-30
Venue:
Biarritz, France
http://iaus302.sciencesconf.org
Dear
colleagues,
This is the first announcement for the Symposium
302 of the International Astronomical Union, entitled "Magnetic
fields throughout stellar evolution". The conference will be
held in Biarritz (France), 26-30 August 2013. Preregistration is now
open!
*Topics include:*
* Stellar structure and
evolution
* Magnetized accretion and outflows in young stellar
objects
* Magnetic braking of PMS stars
* Solar and stellar
activity in photospheres, chromospheres and
coronae, and stellar
cycles
* Magnetism in very low-mass stars and brown dwarfs
*
Star-planet interaction
* Stellar dynamos across the HR diagram
* Magnetic field origin and stability in massive stars
*
Magnetically-confined winds of massive stars
* Small-scale dynamo
and mass-loss in giant and supergiant stars
* Final phases of
stellar evolution : magnetism in compact objects
*Confirmed
speakers:*
Evelyne Alecian - Jonathan Braithwaite -
Jean-François Donati - Rim Fares - Oleg Kochukhov - François
Lignières - Stuart Littlefair - Nanda Rea - Andreas Reisenegger -
Marina Romanova - Saku Tsuneta - Aline Vidotto
*Important
dates:*
* Early registration opens: 07 Jan 2013
*
Deadline for IAU grant application: 15 Feb 2013
* Decision for
IAU financial support: 08 Mar 2013
* Deadline for early
registration: 01 Apr 2013
* Abstract deadline for contributed
talks: 03 May 2013
* Abstract deadline for posters: 21 Jun 2013
* Deadline for proceedings submission: 30 Sep 2013
We
invite you to express your interest by filling out the
preregistration form on the conference webpage
(http://iaus302.sciencesconf.org ). You can also join us on facebook
(http://www.facebook.com/events/100425383448793/).
We hope to
see as many of you as possible in Biarritz next year!
Best
regards,
Pascal Petit (on behalf of the SOC and LOC)
--
Pascal Petit
IRAP (Univ. Toulouse & CNRS)
14 avenue
Edouard Belin
31400 Toulouse, France
web :
http://sites.google.com/site/pascalpetit08
email :
ppetit@irap.omp.eu
tel : +33 5 61 33 28 28
Weblink:
http://iaus302.sciencesconf.org
Email:
ppetit@irap.omp.eu
Back to contents
June 10-14, 2013
Venue: Rhodes,
Greece
The conference will build on results from ongoing
large-scale multi-wavelength surveys of massive stars which are being
coupled with new theoretical advances dealing with stellar evolution
and the processes which effect that evolution: mass-loss, rotation,
convection, magnetic fields, multiplicity and environment. It will
tackle important problems from birth, through main sequence evolution
and until core collapse. There will be a strong focus on relating the
major theoretical uncertainties afflicting stellar evolution through
these phases to the current observational picture.
The
impetus for this focus is derived from the realization that our
understanding of massive star evolution is severely challenged by new
observations powered largely by technological advances in telescopes
and instrumentation. This has enabled new ways of looking at old
long-standing problems enabling large-scale high-quality surveys of
resolved stellar populations (e.g the FLAMES and MiMeS Surveys). As
theoretical approaches try to keep pace with this increase in
information the cracks in our assumptions concerning stellar
evolution have become more apparent, even glaring. Whereas before it
might have been possible to understand some of the stars some of the
time it is now clear that understanding stellar populations is a
considerable challenge and will require substantial efforts to
resolve.
This is an exciting time as observations have
revealed large gaps in understanding of the formation and evolution
of massive stars. The huge impact that massive stars have on their
immediate environment, parent galaxies, and through the Universe,
demands better understanding of massive star evolution from alpha to
Omega.
Scientific Program Topics:
· New observational &
theoretical results from large-scale surveys (FLAMES, MiMeS,
PanSTARRS, PTF), techniques (astrometry) and computation.
·
Consequences of zero-age conditions on stellar evolution
·
Massive star environments, massive clusters, dynamical evolution,
runaway stars and mergers
· The importance of binaries for
populations of massive stars
· The upper end of the IMF and the
role of mergers
· Massive-star magnetism and pulsation,
evolutionary consequences
· The role and evolution of stellar
rotation across the H-R diagram
· Mass-loss across the H-R
diagram and episodic mass-loss from LBVs and other transients
·
Constraints from endpoints
· Massive stars at very low
metallicity
SOC: D. Lennon (co-chair), A. Bonanos
(co-chair), C. Evans, M. Hanson, R. Hirschi, E. Levesque, S. de Mink,
N. Morrell, J. Puls, S. Smartt, N. Smith, G. Wade
Weblink:
http://a2omega.astro.noa.gr
Email:
a2omega@astro.noa.gr
Back to contents