ISSN 1783-3426
|
Nomenclature of Galactic Wolf-Rayet
stars
Leonid Georgiev (1961 - 2012)
A spectroscopic investigation of the
O-type star population in four Cygnus OB associations. I.
Determination of the binary fraction
Massive
star evolution: Luminous Blue Variables as unexpected Supernova
progenitors
Discovery of X-ray
emission from young suns in the Small Magellanic Cloud
A
detailed X-ray investigation of ζ Puppis III. A spectral analysis of
the whole RGS spectrum
Variability
in Optical Spectra of epsilon Orionis
Exploring
the origin of magnetic fields in massive stars: II.~New magnetic
field measurements in cluster and field stars.
Variable
dust formation by the colliding-wind Wolf-Rayet system HD 36402 in
the Large Magellanic Cloud
The
Rotation Rates of Massive Stars: The Role of Binary Interaction
through Tides, Mass Transfer, and Mergers
Far-Ultraviolet
Detection of the Suspected Subdwarf Companion to the Be Star 59
Cygni
The temperatures of Red
Supergiants
Phase-resolved
ultraviolet spectroscopy of the magnetic Of?p star HD
191612
Polarimetric observations of
$sigma$ Orionis E
2 PhD studentships on the theory of convection and evolution of stars
Putting A Stars into Context:
Evolution, Environment, and Related Stars
Massive
Stars: From α to Ω
The nomenclature of Galactic
Wolf-Rayet stars has been fixed since the 6th Catalogue (van der
Hucht 1981), e.g. WR20. Subsequently discovered stars have been
inserted via alphabetical identifications ordered by RA, as
implemented for the 7th Catalogue and Annex (van der Hucht 2001,
2006), such as WR20a between WR20 and WR21.
Since the advent
of efficient IR detectors the number of Galactic WR stars has greatly
increased, necessitating a new scheme. A subset of the IAU Working
Group for Massive Stars has been charged with new recommendations for
the nomenclature for Milky Way WR stars, as follows:
1. All
WR identifications up to 7th Catalogue/Annex remain unchanged since
many are in widespread usage in the literature (e.g. WR20, WR20a).
2. All subsequent discoveries are switched from alphabetical
(WRXXa, b) to numerical (WRXX-1, -2) identification, sorted by
year/month of discovery, in RA order if multiple discoveries arise
from a single source.
3. Multiple WR stars identified within
a single source are indicated with CAPITAL letters (e.g. WR43a, b, c
-> WR43A, B, C).
By way of example, three WR stars have
been discovered since 2006 whose RA's are intermediate between WR20
and WR21. The first (discovered by Mauerhan et al. 2011) is assigned
WR20-1, while two subsequent discoveries (from Roman-Lopez et al.
2011) are assigned WR20-2 and -3 (RA ordered). Since a few journal
papers have referred to recently discovered stars using the former
[alphabetical] scheme it is intended to retain such aliases, albeit
solely for discoveries up to the end of Dec 2012 (WR20aa for WR20-2,
WR20c for WR20-3).
Identifications for all known Galactic WR
stars listed at the weblink have been updated to take into account
these changes. Please contact Paul Crowther for advice on new
additions.
Paul Crowther, Wolf-Rainer Hamann, Ian Howarth,
Karel van der Hucht, Gregor Rauw
Dec 2012
Weblink:
http://pacrowther.staff.shef.ac.uk/WRcat
Email:
Paul.Crowther@sheffield.ac.uk
Back to
contents
Leonid Georgiev, mexican
astrophysicist and member of the Instituto de Astronomia of the
Universidad Nacional Autonoma de Mexico, passed away on December 26,
2012. Born in 1961 in Lom, Bulgaria Leonid earned a PhD degree in
Astronomy from the Faculty of Physics of Sofia University in 1992
with the thesis entitled: The spectral variability of 11 single
Wolf-Rayet stars and its nature and connection to their evolution.
This investigation was the prelude to what would become the central
topic of his work throughout the rest of his life, and one which
would lead him to become an expert in the observations and
theoretical modeling of the spectroscopic characteristics of stars
possessing stellar winds.
After graduation, Leonid Georgiev
occupied a permanent position in the Department of Astronomy of Sofia
University and then, in 1995, he traveled to Mexico for a 2-year
postdoctoral visit at the Instituto de Astronomia. In 1998 he was
offered a research position at this same Institute, where he remained
for the rest of his life, becoming fully committed with teaching,
observatory development and other institutional activities in
addition to his research activities.
Most recently, he was
tackling the problem of theoretically determining the observational
properties of non-isotropic stellar wind configurations, such as
occur in close binary systems where the interactions due to stellar
winds and irradiation can lead to significantly asymmetric wind
structures. He was also developing methods for the self-consistent
analysis of circumstellar nebulae and the stellar atmosphere and wind
of the associated central star, and, in addition, he was part of the
team working on the robotization of the Observatorio Astronomico
Nacional de San Pedro Martir 1.5m telescope and its use for detecting
Gamma-ray burst optical counterparts.
Besides being an
extremely skilled observational astronomer, Leonid was a wonderful
colleague, always forthcoming with help, advice and insight on topics
ranging from fundamental astronomy to galactic cluster evolution, on
astronomical instrumentation and computational techniques. His warm
and direct approach to treating people gained him the respect and
admiration of students, colleagues and friends.
Leonid was a
resourceful and tenacious researcher, admired teacher, and devoted to
his family and friends. He will be missed greatly by us
all.
Weblink:
Email:
gloria@astro.unam.mx
Back to contents
L. Mahy(1), G. Rauw(1), M. De
Becker(1), P. Eenens(2), C. A. Flores(2)
(1) Institut
d'Astrophysique et de Géophysique, University of Liège, Belgium
(2)Departamento de Astronomia, Universidad de Guanajuato,
Mexico
Context. Establishing the multiplicity of O-type stars
is the first step towards accurately determining their stellar
parameters. Moreover, the distribution of the orbital parameters
provides observational clues to the way that O-type stars form and to
the interactions
during their evolution.
Aims. Our objective
is to constrain the multiplicity of a sample of O-type stars
belonging to poorly investigated OB associations in the Cygnus
complex and for the first time to provide orbital parameters for
binaries identified in our sample. Such information is relevant to
addressing the issue of the binarity in the context of O-type star
formation scenarios.
Methods. We performed a long-term
spectroscopic survey of nineteen O-type stars. We searched for radial
velocity variations to unveil binaries on timescales from a few days
up to a few years, on the basis of a large set of optical spectra.
Results. We confirm the binarity for four objects: HD193443,
HD228989, HD229234 and HD194649. We derive for the first time the
orbital solutions of three systems, and we confirm the values of the
fourth, showing that these four systems all have orbital periods
shorter than 10 days. Besides these results, we also detect several
objects that show non-periodic line profile variations in some of
their spectral lines. These variations mainly occur in the spectral
lines, that are generally affected by the stellar wind and are not
likely to be related to binarity.
Conclusions. The minimal binary
fraction in our sample is estimated to be 21%, but it varies from one
OB association to the next. Indeed, 3 O stars of our sample out of 9
(33%) belonging to CygOB1 are binary systems, 0% (0 out of 4) in
CygOB3, 0% (0 out of 3) in CygOB8, and 33% (1 out of 3) in CygOB9.
Our spectroscopic investigation also stresses the absence of
long-period systems among the stars in our sample. This result
contrasts with the case of the O-type stellar population in NGC 2244
among which no object showed radial velocity variations on short
timescales. However, we show that it is probably an effect of the
sample and that this difference does not a priori suggest a somewhat
different star forming process in these two environments.
Reference:
arXiv:1301.0500
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1301.0500
Comments:
22 pages, 26 figures, 5 tables (Table 2 only available on
CDS)
Email: mahy@astro.ulg.ac.be
Back
to contents
Jose H. Groh, Georges Meynet,
Sylvia Ekstrom
Geneva Observatory, Switzerland
Stars
more massive than about 8 Msun end their lives as a Supernova (SN),
an event of fundamental importance Universe-wide. Theoretically,
these stars have been expected to be either at the red supergiant,
blue supergiant, or Wolf-Rayet stage before the explosion. We
performed coupled stellar evolution and atmospheric modeling of stars
with initial masses between 20 Msun and 120 Msun. We found that the
20 Msun and 25 Msun rotating models, before exploding as SN, have
spectra that do not resemble any of the aforementioned classes of
massive stars. Rather, they have remarkable similarities with rare,
unstable massive stars known as Luminous Blue Variables (LBV). While
observations show that some SNe seem to have had LBVs as progenitors,
no theoretical model had yet predicted that a star could explode at
this stage. Our models provide theoretical support for relatively
low-luminosity LBVs exploding as SN in the framework of single
stellar evolution. This is a significant shift in paradigm, meaning
that a fraction of LBVs could be the end stage of massive star
evolution, rather than a transitory evolutionary phase. We suggest
that type IIb SN could have LBV as progenitors, and a prime example
could be SN 2008ax.
Reference: A&A, in
press
Status: Manuscript has been accepted
Weblink:
Comments:
Email:
jose.groh@unige.ch
Back to contents
L. M. Oskinova, W. Sun, C. J.
Evans, V. Hénault-Brunet, Y.-H. Chu, J. S. Gallagher III, M. A.
Guerrero, R. A. Gruendl, M. Güdel, S. Silich, Y. Chen, Y. Nazé, R.
Hainich, J. Reyes-Iturbide
(1) University of Potsdam,
Germany
We report the discovery of extended X-ray emission
within the young star cluster NGC 602 in the Wing of the Small
Magellanic Cloud (SMC) based on observations obtained with the
Chandra X-ray Observatory. X-ray emission is detected from the
cluster core area with the highest stellar density and from a dusty
ridge surrounding the HII region. We use a census of massive stars in
the cluster to demonstrate that a cluster wind or wind-blown bubble
is unlikely to provide a significant contribution to the X-ray
emission detected from the central area of the cluster. We therefore
suggest that X-ray emission at the cluster core originates from an
ensemble of low- and solar-mass pre-main-sequence (PMS) stars, each
of which would be too weak in X-rays to be detected individually. We
attribute the X-ray emission from the dusty ridge to the embedded
tight cluster of the new-born stars known in this area from infrared
studies. Assuming that the levels of X-ray activity in young stars in
the low-metallicity environment of NGC 602a are comparable to their
Galactic counterparts, then the detected spatial distribution,
spectral properties, and level of X-ray emission are largely
consistent with those expected from low- and solar-mass PMS stars and
young stellar objects (YSOs). This is the first discovery of X-ray
emission attributable to PMS stars and YSOs in the SMC, which
suggests that the accretion and dynamo processes in young, low-mass
objects in the SMC resemble those in the Galaxy.
Reference:
ApJ
Status: Manuscript has been accepted
Weblink:
arXiv:1301.3500
Comments:
Section 3: X-ray emission from massive stars in NGC602
Email:
lida@astro.physik.uni-potsdam.de
Back
to contents
A. Hervé, G. Rauw, Y.
Nazé
University of Liège
Context. Zeta Pup is the
X-ray brightest O-type star of the sky. This object was regularly
observed with the RGS instrument aboard XMM-Newton for calibration
purposes, leading to an unprecedented set of high-quality spectra.
Aims. We have previously reduced and extracted this data set and
combined it into the most detailed high-resolution X-ray spectrum of
any early-type star so far. Here we present the analysis of this
spectrum accounting for the presence of structures in the stellar
wind. Methods. For this purpose, we use our new modeling tool that
allows fitting the entire spectrum with a multi-temperature plasma.
We illustrate the impact of a proper treatment of the radial
dependence of the X-ray opacity of the cool wind on the best-fit
radial distribution of the temperature of the X-ray plasma. Results.
The best fit of the RGS spectrum of Zeta Pup is obtained assuming no
porosity. Four plasma components at temperatures between 0.10 and
0.69 keV are needed to adequately represent the observed spectrum.
Whilst the hardest emission is concentrated between ~3 and 4 R*, the
softer emission starts already at 1.5 R* and extends to the outer
regions of the wind. Conclusions. The inferred radial distribution of
the plasma temperatures agrees rather well with theoretical
expectations. The mass- loss rate and CNO abundances corresponding to
our best-fit model also agree quite well with the results of recent
studies of Zeta Pup in the UV and optical domain.
Reference:
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1301.5090
Comments:
Email: anthony.herve@univ-montp2.fr
Back
to contents
Gregory B. Thompson (1),
Nancy D. Morrison (2)
(1) Department of Physics, Adrian
College
(2) Ritter Astrophysical Research Center, Department of
Physics and Astronomy, University of Toledo
We present the
results of a time-series analysis of 130 echelle spectra of epsilon
Ori (B0 Ia), acquired over seven observing seasons between 1998 and
2006 at Ritter Observatory. The equivalent widths of Halpha (net) and
He I 5876 were measured and radial velocities were obtained from the
central absorption of He I 5876. Temporal variance spectra (TVS)
revealed significant wind variability in both Halpha and He I 5876.
The He I TVS have a double-peaked profile consistent with radial
velocity oscillations. A periodicity search was carried out on the
equivalent width and radial velocity data, as well as on
wavelength-binned spectra. This analysis has revealed several periods
in the variability with time scales of 2-7 d. Many of these periods
exhibit sinusoidal modulation in the associated phase diagrams.
Several of these periods were present in both Halpha and He I,
indicating a possible connection between the wind and the
photosphere. Due to the harmonic nature of these periods, stellar
pulsations may be the origin of some of the observed variability.
Periods on the order of the rotational period were also detected in
the He I line in the 98-99 season and in both lines during the 04-05
season. These periods may indicate rotational modulation due to
structure in the wind.
Reference: Accepted for
publication in The Astronomical Journal
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1301.5368
Comments:
Email: gthompson@adrian.edu
Back
to contents
S.~Hubrig$^1$,
M.~Sch"oller$^2$,
I.~Ilyin$^1$,
N.~V.~Kharchenko$^3$,
L.~M.~Oskinova$^4$,
J.~F.~Gonz'alez$^5$,
N.~Langer$^6$,
A.~F.~Kholtygin$^7$, and
the MAGORI collaboration
1
- Leibniz-Institut f"ur Astrophysik Potsdam (AIP), An der
Sternwarte~16, 14482~Potsdam, Germany;
2 - European Southern
Observatory, Karl-Schwarzschild-Str.~2, 85748~Garching, Germany;
3
- Main Astronomical Observatory, 27~Academica Zabolotnogo Str.,
03680~Kiev, Ukraine;
4 - Universit"at Potsdam, Institut f"ur
Physik und Astronomie, 14476~Potsdam, Germany;
5 - Instituto de
Ciencias Astronomicas, de la Tierra, y del Espacio (ICATE),
5400~San~Juan, Argentina;
6 - Argelander-Institut f"ur
Astronomie, Universit"at Bonn, Auf dem H"ugel~71,
53121~Bonn, Germany;
7 - Astronomical Institute, Saint-Petersburg
State University, Saint-Petersburg, Russia
heories on the
origin of magnetic fields in massive stars remain poorly developed,
because the properties of their magnetic field as function of stellar
parameters could not yet be investigated. Additional observations are
of utmost importance to constrain the conditions that are conducive
to magnetic fields and to determine first trends about their
occurrence rate and field strength distribution.
To investigate
whether magnetic fields in massive stars are ubiquitous or appear
only in stars with a specific spectral classification, certain ages,
or in a special environment, we acquired 67 new spectropolarimetric
observations for 30 massive stars. Among the observed sample, roughly
one third of the stars are probable members of star clusters at
different ages, whereas the remaining stars are field stars not known
to belong to any cluster or association.
Spectropolarimetric
observations were obtained during four different nights using the
low-resolution spectropolarimetric mode of FORS,2 (FOcal Reducer low
dispersion Spectrograph) mounted on the 8-m Antu telescope of the
VLT. Furthermore, we present a number of follow-up observations
carried out with the high-resolution spectropolarimeters SOFIN
mounted at the Nordic Optical Telescope (NOT) and HARPS mounted at
the ESO 3.6,m between 2008 and 2011. To assess the membership in open
clusters and associations, we used astrometric catalogues with the
highest quality kinematic and photometric data currently available.
The presence of a magnetic field is confirmed in nine stars
previously observed with FORS,1/2: HD,36879, HD,47839, CPD$-$28,2561,
CPD$-$47,2963, HD,93843, HD,148937, HD,149757, HD,328856, and
HD,164794. New magnetic field detections at a significance level of
at least 3$sigma$ were achieved in five stars: HD,92206c, HD,93521,
HD,93632, CPD$-$46,8221, and HD,157857. Among the stars with a
detected magnetic field, five stars belong to open clusters at high
membership probability. According to previous kinematic studies, five
magnetic O-type stars in our sample are candidate runaway
stars.
Reference: A&A, accepted
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1301.4376
Comments:
Email: mschoell@eso.org
Back
to contents
P. M. Williams (1), Y.-H. Chu
(2), R. A. Gruendl (2), M. A. Guerrero (3)
(1) Institute
for Astronomy, Royal Observatory, Edinburgh, (2) Department of
Astronomy, University of Illinois at Urbana-Champaign, (3) Instituto
de Astrofisica de Andalucia, Granada
Infrared photometry of
the probable triple WC4(+O?)+O8I: Wolf-Rayet system HD 36402 (=
BAT99-38) in the Large Magellanic Cloud (LMC) shows emission
characteristic of heated dust. The dust emission is variable on a
time-scale of years, with a period near 4.7 yr, possibly associated
with orbital motion of the O8 supergiant and the inner P ~ 3.03-d
WC4+O binary. The phase of maximum dust emission is close to that of
the X-ray minimum, consistent with both processes being tied to
colliding wind effects in an elliptical binary orbit. It is evident
that Wolf-Rayet dust formation occurs also in metal-poor
environments.
Reference: arXiv:1302.2002
[astro-ph.SR]
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1302.2002
Comments:
Email: pmw@roe.ac.uk
Back
to contents
de Mink, S. E.; Langer, N.;
Izzard, R. G.; Sana, H.; de Koter, A.
AA(Space Telescope
Science Institute, Baltimore, MD, USA ; Department of Physics and
Astronomy, Johns Hopkins University, Baltimore, MD, USA),
AB(Argelander-Institut für Astronomie der Universität Bonn, D-53121
Bonn, Germany), AC(Argelander-Institut für Astronomie der
Universität Bonn, D-53121 Bonn, Germany), AD(Astronomical Institute
Anton Pannekoek, University of Amsterdam, 1098 XH Amsterdam, The
Netherlands), AE(Astronomical Institute Anton Pannekoek, University
of Amsterdam, 1098 XH Amsterdam, The Netherlands; Astronomical
Institute, Utrecht University, 3508 TA Utrecht, The Netherlands ;
Institute of Astronomy, KU Leuven, B-3001 Leuven, Belgium)
Rotation
is thought to be a major factor in the evolution of massive
stars—especially at low metallicity—with consequences for their
chemical yields, ionizing flux, and final fate. Deriving the birth
spin distribution is of high priority given its importance as a
constraint on theories of massive star formation and as input for
models of stellar populations in the local universe and at high
redshift. Recently, it has become clear that the majority of massive
stars interact with a binary companion before they die. We
investigate how this affects the distribution of rotation rates,
through stellar winds, expansion, tides, mass transfer, and mergers.
For this purpose, we simulate a massive binary-star
population typical for our Galaxy assuming continuous star formation.
We find that, because of binary interaction, 20(+5 -10)% of all
massive main-sequence stars have projected rotational velocities in
excess of 200 km/s. We evaluate the effect of uncertain input
distributions and physical processes and conclude that the main
uncertainties are the mass transfer efficiency and the possible
effect of magnetic braking, especially if magnetic fields are
generated or amplified during mass accretion and stellar mergers. The
fraction of rapid rotators we derive is similar to that observed.
If indeed mass transfer and mergers are the main cause for
rapid rotation in massive stars, little room remains for rapidly
rotating stars that are born single. This implies that spin-down
during star formation is even more efficient than previously thought.
In addition, this raises questions about the interpretation of the
surface abundances of rapidly rotating stars as evidence for
rotational mixing. Furthermore, our results allow for the possibility
that all early-type Be stars result from binary interactions and
suggest that evidence for rotation in explosions, such as long
gamma-ray bursts, points to a binary origin.
Reference: The
Astrophysical Journal, Volume 764, Issue 2, article id. 166, 17 pp.
(2013)
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2013ApJ...764..166D
Comments:
Published: February 4, 2013; Accepted: December 19, 2012
Email:
sedemink@gmail.com
Back to contents
Geraldine J. Peters (1),
Tiffany D. Pewett (2), Douglas R. Gies (2), Yamina N. Touhami (2),
and Erika D. Grundstrom (3)
(1) Space Sciences Center and
Department of Physics and Astronomy, University of Southern
California, Los Angeles, CA
90089-1341, USA
(2) Center for
High Angular Resolution Astronomy and Department of Physics and
Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA
30302-4106, USA
(3) Physics and Astronomy Department, Vanderbilt
University, 6301 Stevenson Center, Nashville, TN 37235, USA
We
report on the detection of a hot subdwarf component in the Be binary
system, 59 Cygni. The spectral signature is found in
cross-correlation functions of photospheric model spectra with
far-ultraviolet spectra obtained by the International Ultraviolet
Explorer Satellite, and we used radial velocities from the
cross-correlation functions to determine a double-lined spectroscopic
orbit. The individual spectra of the binary components were extracted
using a Doppler tomography algorithm. The flux of the system is
dominated by the rapidly rotating Be star. However, the subdwarf
contributes approximately 4% of the UV flux, and its spectrum bears a
strong resemblance to that of the hot sdO star BD +75°325. Based on
the appearance of the UV spectrum and the orbital elements, we
present estimates for the stellar masses, radii, and temperatures.
The presence of the hot companion causes excess emission from the
outer part of the Be disk facing the companion. We present a set of
red spectra that show the orbital phase variations of the He I λ6678
emission formed in the heated region of the disk, which probably
occurs near the disk outer boundary. 59 Cygni, FY Canis Majoris, and
phi Persei comprise the known set of Be binaries with detected hot
evolved companions, which are the stripped down remains of mass
transfer. Their properties demonstrate that some fraction of Be stars
were spun up through angular momentum transfer by Roche lobe
overflow.
Reference: ApJ, 765, 2, 2013 (March
1)
Status: Manuscript has been accepted
Weblink: at
http://stacks.iop.org/0004-637X/765/2
Comments:
Email: gjpeters@mucen.usc.edu
Back
to contents
Ben Davies (Liverpool JMU),
Rolf-Peter Kudritzki (Hawaii), Bertrand Plez (Montpellier), Scott
Trager (Groningen), Ariane Lancon (Strasbourg), Zach Gazak (Hawaii),
Maria Bergemann (MPA), Chris Evans (UKATC), Andrea Chiavassa
(Nice)
Liverpool John Moores University
We present
a re-appraisal of the temperatures of Red Supergiants (RSGs) using
their optical and near-infrared spectral energy distributions (SEDs).
We have obtained data of a sample of RSGs in the Magellanic Clouds
using VLT+XSHOOTER, and we fit MARCS model atmospheres to different
regions of the spectra, deriving effective temperatures for each star
from (a) the TiO bands, (b) line-free continuum regions of the
spectral energy distributions (SEDs), and (c) the integrated fluxes.
We show that the temperatures derived from fits to the TiO bands are
systematically {it lower} than the other two methods by several
hundred Kelvin. The TiO fits also dramatically over-predict the flux
in the near-IR, and imply extinctions which are anomalously low
compared to neighbouring stars. In contrast, the SED temperatures
provide good fits to the fluxes at all wavelengths other than the TiO
bands, are in agreement with the temperatures from the flux
integration method, and imply extinctions consistent with nearby
stars. After considering a number of ways to reconcile this
discrepancy, we conclude that 3-D effects (i.e. granulation) are the
most likely cause, as they affect the temperature structure in the
upper layers where the TiO lines form. The continuum, however, which
forms at much deeper layers, is apparently more robust to such
effects. We therefore conclude that RSG temperatures are much warmer
than previously thought. We discuss the implications of this result
for stellar evolution and supernova progenitors, and provide
relations to determine the bolometric luminosities of RSGs from
single-band photometry.
Reference: Accepted for
publication in ApJ
Status: Manuscript has been accepted
Weblink:
http://xxx.lanl.gov/abs/1302.2674
Comments:
Email: b.davies@ljmu.ac.uk
Back
to contents
W. L. F. Marcolino, J. -C.
Bouret, J. O. Sundqvist, N. R. Walborn, A. W. Fullerton, I. D.
Howarth, G. A. Wade, A. ud-Doula
-
We present for
the first time phase-resolved UV spectroscopy of an Of?p star,
namely, HD 191612. The observations were acquired with the Space
Telescope Imaging Spectrograph (STIS) on-board the Hubble Space
Telescope (HST). We report the variability observed in the main
photospheric and wind features and compare the results with previous
findings for the Of?p star HD 108. We show that UV line strengths,
H(alpha), and longitudinal magnetic field, vary coherently according
to the rotational period (P = 537.6d), providing additional support
for the magnetic oblique rotator scenario. The stellar and wind
parameters of HD 191612 are obtained based on NLTE expanding
atmosphere models. The peculiar wind line profile variations revealed
by the new STIS data - not reproduced by 1D atmosphere models - are
addressed through non-spherical MHD simulations coupled with
radiative transfer. The basic aspects of the UV variability observed
are explained and the structure of the dynamical magnetosphere of HD
191612 is discussed.
Reference: MNRAS
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1302.4708
Comments:
Email: wagner@astro.ufrj.br
Back
to contents
Alex C. Carciofi, Daniel M.
Faes, Richard H. D. Townsend, Jon E. Bjorkman
Instituto de
Astronomia, Geof'isica e Ci^encias Atmosf'ericas, Universidade de
S~ao Paulo, Rua do Mat~ao 1226, Cidade Universit'aria, 05508-900,
S~ao Paulo, SP, BRAZIL
Department of Astronomy, University of
Wisconsin-Madison, Sterling Hall, 475 N. Charter Street, Madison, WI
53706, USA
Ritter Observatory, Department of Physics &
Astronomy, University of Toledo,Toledo, OH 43606, USA
Some
massive stars possess strong magnetic fields that confine plasma in
the
circumstellar environment. These textit{magnetospheres} have
been studied
spectroscopically, photometrically and, more
recently, interferometrically.
Here we report on the first firm
detection of a magnetosphere in continuum linear polarization, as a
result of monitoring of $sigma$,Ori,E at the Pico dos Dias
Observatory. {The non-zero intrinsic polarization indicates an
asymmetric structure, whose minor elongation axis is oriented
$150fdg0$ east of the celestial north.}
A modulation of the
polarization was observed, with a period of half of the rotation
period, which supports the theoretical prediction of the presence of
two diametrally opposed, co-rotating blobs of gas.
A phase lag of
$-0.085$ was detected between the polarization minimum and the
primary minimum of the light curve, suggestive of a complex shape of
the plasma clouds.
We present a preliminary analysis of the data
with the Rigidly Rotating Magnetosphere model, which could not
reproduce simultaneously the photometric and polarimetric data. A toy
model comprising two spherical co-rotating blobs {joined by a thin
disk} proved more successful in reproducing the polarization
modulation.
{With this model we were able to determine that the
total scattering mass of the thin disk is similar to the mass of the
blobs ($2M_{rm b}/M_{rm d}=1.2$) and that the blobs are rotating
counterclockwise on the plane of the sky.}
This result shows that
polarimetry can provide a diagnostic of the geometry of clouds, which
will serve as an important constraint for {improving} the Rigidly
Rotating Magnetosphere model.
Reference: Accepted by
The Astrophysical Journal Letters
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1302.4684
Comments:
Email: carciofi@usp.br
Back
to contents
Raphael Hirschi
Keele
University
Lennard-Jones Laboratories 2.09
Keele
ST5
5BG
Dr Raphael Hirschi has been awarded a European Research
Council starting grant, that will fund a 5-year multi-disciplinary
project entitled SHYNE (Stellar HYdrodynamics, Nucleosynthesis and
Evolution). The grant will enable Dr Hirschi to build a team of two
post-doctoral researchers and two PhD students, and to acquire a
dedicated 1000-CPU computer cluster. The SHYNE team will collaborate
with the Norwegian company Numascale, adding an inter-sectoral
component to the project. More details on the SHYNE project are given
here: http://www.astro.keele.ac.uk/shyne/.
1) Convection in
stars: developing synergy between 1D and 3D models:
This PhD
project will focus on convection and rotation in stars. The
successful candidate will analyse results of 3D simulations using
both numerical and theoretical frameworks in order to establish new
prescriptions for convective boundary mixing to be used in 1D models.
2) Life and death of stars:
This PhD project will focus
on calculating grids of stellar evolution models in order to
determine the properties and fate of massive and intermediate-mass
stars. The successful candidate will model the evolution of massive
stars from birth till death using state-of-the-art 1D stellar
evolution codes while studying the effects of rotation, magnetic
fields and improved treatment of convective boundary mixing. In
particular, the candidate will calculate progenitor models of
core-collapse supernovae and more exotic explosions (gamma-ray
bursts, electron-capture supernovae and pair-creation supernovae).
The successful candidates will learn key computing skills and
be exposed to the industry, which will give them a strong skills set
for both an academic and an industrial career.
These 4-year
studentships are available to UK/EU students only (only partial
funding available for non-EU students). Candidates must hold at least
a first-class Bachelors degree or an appropriate Masters
qualification in a physics related subject or its equivalent. In
order to be considered for a studentship you must complete an
application form for PhD study, please indicate ERC-SHYNE studentship
ref EPSAM 2012-2 or 2012-3.
Details of the application
procedure for study are on the Keele website
http://www.keele.ac.uk/pgresearch/howtoapply/ .
Attention/Comments:
For informal enquiries, contact Dr Hirschi by email:
r.hirschi@epsam.keele.ac.uk.
Weblink:
http://www.keele.ac.uk/pgresearch/choosingaresearchdegree/studentships/
Email:
r.hirschi@epsam.keele.ac.uk
Deadline: 28 February
2013
Back to contents
June 3-7, 2013
Venue:
Moscow, Russia
This is the third announcement for the
upcoming conference:
Putting A Stars into Context: Evolution,
Environment, and Related Stars,
June 3-7, 2013
Moscow,
Russia
We remind all potential participants that the deadline
for registration and submission of abstracts is April 1, 2013.
Registration
To register for the meeting and submit
your abstract, please, point your browser to
http://agora.guru.ru/astars2013/ and follow the instructions
The
registration fee covers all regular meeting costs including abstract
book, welcome party, coffee breaks, conference banquet, Moskva-river
cruise tour, and classical music concert. Full conference
registration costs 280 Euros (11 300 Rubles). Participants who pay
the registration fee before April 1, 2013, benefit from a discount of
30 Euros. Payments can be made via credit card.
Program:
Overview introductory talk (John D. Landstreet)
Session
1: A-star formation
1a. Big clouds to open clusters
Invited
talks:
1.1. Chemically peculiar tepid stars in the Milky Way and
beyond (Martin Netopil)
1.2. Elemental abundances in open cluster
A-type and related stars (Luca Fossati)
1b. Small clouds to
stars
Invited talks:
1.3. Discs around A-type and related
stars (Helmut Abt)
1.4. Accretion discs around magnetic stars
(Caroline D'Angelo)
1.5. Planets around A stars (David
Mkrtichian)
1.6. Distant sub-stellar companions of A-type and
related stars
1.7. Multiplicity of A-type and related stars
(Pierre North)
1c. Magnetic field generation
Invited
talks:
1.8. Magnetic fields in Herbig Ae/Be stars (Evelyne
Alecian)
1.9. Generation and evolution of stable stellar magnetic
fields (Rainer Arlt)
1.10. The protostar merger scenario of Ap
star magnetic field generation (Lilia Ferrario)
Session 2:
Properties of A-type stars
Invited talks:
2.1. Determinations
of fundamental parameters of (chemically peculiar) A stars through
optical interferometry (Karine Perraut)
2.2. Recent results and
current challenges in normal and chemically peculiar A-star model
atmospheres (Denis Shulyak)
2.3. Simultaneous mapping of chemical
abundances and magnetic field structure in Ap stars (Theresa
Lueftinger)
2.4. Element spots in HgMn stars (Heidi Korhonen)
2.5. The origin of light variability in Ap stars (Jiri Krticka)
2.6. Vertical abundance gradients in Ap-star atmospheres (Tatyana
Ryabchikova)
Session 3: Rotation and hydrodynamics of A-type
and related stars
Invited talks:
3.1. Time-dependent
diffusion and abundance stratification in A- and B-type stars(with
and without mass-loss)
3.2. A-star rotation (Frederic Royer)
3.3. Ap stars with variable rotation periods (Zdenek Mikulasek)
3.4. Rotation and hydrodynamical processes in upper main-sequence
stars (Stephane Mathis)
Session 4: Pulsation of A-type and
related stars
Invited talks:
4.1. A- and B-type star
pulsations in the Kepler and CoRoT era: observational results
(Katrien Uytterhoeven)
4.2. A- and B-type star pulsations in the
Kepler and CoRoT era: theoretical considerations (Hideyuki Saio)
4.3. Observational studies of roAp stars (Mikhail Sachkov)
4.4.
Stochastic oscillations in A-type and related stars (Victoria Antoci)
Session 5: Magnetic fields from O to early F stars
Invited
talks:
5.1. Magnetic fields in O stars
5.2. Magnetic fields
in beta Cep, SPB and Be stars
5.3. Recent results and current
challenges in observations of Ap/Bp star magnetic fields (Iosif
Romanyuk)
5.4. Magnetic fields in A stars besides Ap stars (Oleg
Kochukhov)
5.5. Non-pulsational variability of A- and B-type
stars as observed by Kepler (Luis Balona)
5.6. X-ray emission of
Ap stars and of other A stars (Jan Robrade)
5.7. Bp star
magnetospheres (Asif ud-Doula)
Session 6: A-stars at
post-main-sequence stages
Invited talks:
6.1. Descendants of
magnetic and non-magnetic A-type and related stars
6.2. White
dwarf magnetic fields (Gennady Valyavin)
6.3. A-type blue
stragglers
6.4. Horizontal-Branch A stars
6.5. Non-LTE
studies of A supergiants (Maria-Fernanda Nieva)
6.6. A
supergiants in the Local Group of galaxies and beyond (Miguel
Urbaneja)
Summary talk and closing discussion (Charles
Cowley)
Invited Speakers (confirmed):
Helmut Abt,
Evelyne Alecian, Victoria Antoci, Rainer Arlt, Luis Balona, Charles
Cowley, Caroline D'Angelo, Lilia Ferrario, Luca Fossati, Oleg
Kochukhov, Heidi Korhonen, Jiri Krticka, John D. Landstreet, Theresa
Lueftinger, Stephane Mathis, Zdenek Mikulasek, David Mkrtichian,
Martin Netopil, Maria-Fernanda Nieva, Pierre North, Karine Perraut,
Jan Robrade, Iosif Romanyuk, Frederic Royer, Tatyana Ryabchikova,
Mikhail Sachkov, Hideyuki Saio, Denis Shulyak, Asif ud-Doula, Miguel
Urbaneja, Katrien Uytterhoeven, Gennady Valyavin
Abstract
submission
Contributed talks will be selected from the
submitted abstracts, and there will also be a poster session.
Scientific Organizing Committee:
Gautier Mathys
(chair), Maryline Briquet, Margarida Cunha, Oleg Kochukhov, Friedrich
Kupka, Francis LeBlanc, Lyudmila Mashonkina, Richard Monier, Olga
Pintado, Hiromoto Shibahashi, Kazimierz Stepien, Glenn
Wahlgren
Weblink: http://agora.guru.ru/astars2013/
Email:
astars2013@inasan.ru
Back to contents
June 10-14, 2013
Venue: Rhodes,
Greece
The 'Massive Stars' meetings have enjoyed more than 40
years of startling success since the first meeting in Argentina in
1971. Held every 4 to 5 years, these meetings aim to encapsulate the
current state-of-the-art of our understanding of the physics of
Massive Stars and their role in the Universe. For this 10th meeting
in the Massive Stars series the Institute of Astronomy, Astrophysics,
Space Applications and Remote Sensing of the National Observatory of
Athens, invites you to the island of Rhodes, once home to one of the
greatest astronomers of antiquity, Hipparchos, who is generally
acknowledged as the founder of trigonometry, discoverer of precession
and publisher of the first modern star catalog around 135 BC.
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. 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.
Looking forward to seeing you in
Rhodes!
Weblink: http://a2omega-conference.net
Email:
a2omega@astro.noa.gr
DEADLINE FOR ABSTRACT SUBMISSION OF ORAL CONTRIBUTIONS: March
13!!
DEADLINE FOR EARLY REGISTRATION: April 20!!