ISSN 1783-3426
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Result of the MSWG-OC election
An
international campaign for monitoring the next periastron passage of
eta Carinae in 2014
A Magnetic Confinement vs. Rotation
Classification of Massive-Star Magnetospheres
Massive
open star clusters using the VVV survey II. Discovery of six clusters
with Wolf-Rayet stars
A Report on
the X-ray Properties of the tau Sco Like Stars
Long-term
semi-regular dust formation by the WC9+B0I system WR 70
The
young stellar population of IC 1613. III. New O-type stars unveiled
by GTC-OSIRIS
Molecular emission
from GG Car's circumbinary disk
On
the effects of optically thick gas (disks) around massive
stars
Origin of Two Types of X-Ray
Outbursts in Be/X-Ray Binaries. I. Accretion Scenarios
CO
bandhead emission of massive young stellar objects: determining disc
properties
A detailed X-ray
investigation of zeta Puppis - The variability on short and long
timescales
The Initial Mass
Function of Field OB Stars in the Small Magellanic Cloud
The
2.35 year itch of Cyg OB2#9. II. Radio monitoring
Thin-shell
mixing in radiative wind-shocks and the Lx-Lbol scaling of O-star
X-rays
WR 120bb and WR 120bc: a
pair of WN9h stars with possibly interacting circumstellar shells
The Peculiar Balmer Decrement of SN 2009ip: Constraints on Circumstellar Geometry
POSTDOC POSITION
Post-doc
position in stellar astrophysics
Putting A
Stars into Context: Evolution, Environment, and Related Stars
What
asteroseismology has to offer to astrophysics?
Dear members of the MSWG,
The deadline for the OC election of the Working Group on
Massive Stars (MSWG) passed last week, and I am pleased to report
that there was a healthy turnout (74 voters) with the following
elected to the OC, or re-elected in the case of NSL (in alphabetical
order)
Chris Evans
John Hillier
Lida Oskinova
Nicole
St. Louis
Jorick Vink
The composition of the new OC from
Jan 2013 is as follows (* newbies):
*Chris Evans, Margaret
Hanson, Artemio Herrero, *John Hillier, Norbert Langer, *Lida
Oskinova, Gregor Rauw, Nicole St Louis, Rich Townsend, *Jorick Vink
The new OC will vote for a new Chair (in Jan 2013), and we
will keep you informed about the result.
With best regards,
Jo Puls (old Chair) and the (old) OC of the MSWG
Weblink:
Email: uh101aw@usm.uni-muenchen.de
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We are calling for
collaborators to join us in the monitoring of the next periastron
passage of eta Carinae, which will occur on July 26th 2014. We are
planning on an international, co-ordinated campaign to observe eta
Car using as many southern telescopes as possible in order to obtain
a dense, multispectral monitoring, especially around periastron
passage.
We welcome the collaborations of both amateur and
professional observers, as occurred during the ProAm ConVento
campaign, which included a workshop after the campaign.
A
document containing a detailed description of the proposed campaign
can be downloaded from this link: tinyurl.com/cys65ub
A web
page is currently being developed to host all the relevant
informations about the campaign.
People who are interested in
participating should send an e-mail to mairan.teodoro@nasa.gov. The
subject must be 'etaCar2014', and the body message should contain
your full name and affiliation.
Weblink:
www.etacar2014.wikidot.com
Email:
mairan.teodoro@nasa.gov
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contents
V. Petit (1), S. P. Owocki
(2), G. A. Wade (3), D. H. Cohen (4), J. O. Sundqvist (2), M. Gagné
(1), J. Maíz Apellániz (5), M. E. Oksala (6), D. A. Bohlender (7),
Th. Rivinius (8), H. F. Henrichs (9), E. Alecian (10), R. H. D.
Townsend (11), A. ud-Doula (12), the MiMeS Collaboration (13)
(1)
Dept. of Geology & Astronomy, West Chester University
(2)
Dept. of Physics & Astronomy, University of Delaware
(3)
Dept. of Physics, Royal Military College of Canada
(4) Dept. of
Physics & Astronomy, Swarthmore College
(5) Instituto de
Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía
(6)
Astronomick'y ústav, Akademie vv{e}d v{C}eské republiky
(7)
National Research Council of Canada, Herzberg Institute of
Astrophysics
(8) ESO - European Organisation for Astronomical
Research in the Southern Hemisphere
(9) Astronomical Institute
Anton Pannekoek, University of Amsterdam
(10) LESIA, Observatoire
de Paris
(11) Department of Astronomy, University of
Wisconsin-Madison
(12) Penn State Worthington Scranton
(13)
http://www.physics.queensu.ca/~wade/mimes/
Building on results
from the Magnetism in Massive Stars (MiMeS) project, this paper shows
how a two-parameter classification of massive-star magnetospheres in
terms of the magnetic wind confinement (which sets the Alfv'en radius
RA) and stellar rotation (which sets the Kepler co-rotation radius
RK) provides a useful organisation of both observational signatures
and theoretical predictions. We compile the first comprehensive study
of inferred and observed values for relevant stellar and magnetic
parameters of 64 confirmed magnetic OB stars with Teff > 16 kK.
Using these parameters, we locate the stars in the magnetic
confinement-rotation diagram, a log-log plot of RK vs. RA. This
diagram can be subdivided into regimes of centrifugal magnetospheres
(CM), with RA > RK, vs. dynamical magnetospheres (DM), with RK >
RA. We show how key observational diagnostics, like the presence and
characteristics of Halpha emission, depend on a star's position
within the diagram, as well as other parameters, especially the
expected wind mass-loss rates. In particular, we identify two
distinct populations of magnetic stars with Halpha emission: namely,
slowly rotating O-type stars with narrow emission consistent with a
DM, and more rapidly rotating B-type stars with broader emission
associated with a CM. For O-type stars, the high mass-loss rates are
sufficient to accumulate enough material for line emission even
within the relatively short free-fall timescale associated with a DM:
this high mass-loss rate also leads to a rapid magnetic spindown of
the stellar rotation. For the B-type stars, the longer confinement of
a CM is required to accumulate sufficient emitting material from
their relatively weak winds, which also lead to much longer spindown
timescales. Finally, we discuss how other observational diagnostics,
e.g. variability of UV wind lines or X-ray emission, relate to the
inferred magnetic properties of these stars, and prospects for future
developments in our understanding of massive-star
magnetospheres.
Reference: Accepted for publication in
MNRAS
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1211.0282
Comments:
Email: vpetit@wcupa.edu
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A.-N. Chené(1,2), J.
Borissova(2,3), C. Bonatto(4), D. J. Majaess(5), G. Baume(6), J. R.
A. Clarke(2,7), R. Kurtev(2), O. Schnurr(8), J.-C. Bouret(9), M.
Catelan(10), J. P. Emerson(11), C. Feinstein(6), D. Geisler(1), R. de
Grijs(12), A. Hervé(13), V. D. Ivanov (14), M. S. N. Kumar (15), P.
Lucas(7), L. Mahy(13), F. Martins(16), F. Mauro(1), D.
Minniti(3,10,17,18), C. Moni Bidin(2,3)
(1) U. de
Concepción
(2) U. de Valparaíso
(3) The Milky Way
Millennium Nucleus
(4) U. Federal do Rio Grande do Sul
(5)
Saint Mary's University
(6) IALP
(7) U. of Hertfordshire
(8)
AIP
(9) LAM
(10) PUC de Chile
(11) Queen Mary University
of London
(12) Kavli Institute for Astronomy and Astrophysics
(13) U. de Liège
(14) ESO
(15) Centro de Astrofisica da
Universidade do Porto
(16) U. Montpellier II
(17) Vatican
Observatory
(18) Princeton University
Context: The ESO
Public Survey "VISTA Variables in the V'ia L'actea" (VVV)
provides deep multi-epoch infrared observations for an unprecedented
562 sq. degrees of the Galactic bulge, and adjacent regions of the
disk. In this survey nearly 150 new open clusters and cluster
candidates have been discovered. Aims: This is the second in a series
of papers about young, massive open clusters observed using the VVV
survey. We present the first study of six recently discovered
clusters. These clusters contain at least one newly discovered
Wolf-Rayet (WR) star. Methods: Following the methodology presented in
the first paper of the series, wide-field, deep JHKs VVV
observations, combined with new infrared spectroscopy, are employed
to constrain fundamental parameters for a subset of clusters.
Results: We affirm that the six studied stellar groups are real young
(2-7 Myr) and massive (between 0.8 and 2.2 10^3 Msol) clusters. They
are highly obscured (Av ~ 5-24 mag) and compact (1-2 pc). In addition
to WR stars, two of the six clusters also contain at least one red
supergiant star. We claim the discovery of 8 new WR stars, and 3
stars showing WR-like emission lines which could be classified WR or
OIf. Preliminary analysis provides initial masses of ~30-50 Msol for
the WR stars. Finally,we discuss the spiral structure of the Galaxy
using as tracers the six new clusters together with the previously
studied VVV clusters.
Reference: accepted in
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1211.2801
Comments:
17 pages, 8 figures
Email:
andrenicolas.chene@gmail.com
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Ignace^1, R, Oskinova^2, L,
Massa^3, D
^1 Physics & Astronomy, East Tennessee
State University
^2 Institute for Physics and Astronomy,
University of Potsdam
^3 Space Telescope Science Institute
An
increasing number of OB stars have been shown to possess magnetic
fields. Although the sample remains small, it is surprising that
the magnetic and X-ray properties of these stars appear to be far
less correlated than expected. This contradicts model
predictions,
which generally indicate that the X-rays from
magnetic stars are harder
and more luminous than their
non-magnetic counterparts. Instead,
the X-ray properties of
magnetic OB stars are quite diverse.
$tau$~Sco is one example
where the expectations are better met.
This bright main sequence,
early B star has been studied extensively
in a variety of
wavebands. It has a surface magnetic field of
around 500~G, and
Zeeman Doppler tomography has revealed an unusual
field
configuration. Furthermore, $tau$~Sco displays an unusually
hard
X-ray spectrum, much harder than similar, non-magnetic OB
stars.
In addition, the profiles of its UV P~Cygni wind lines have
long
been known to possess a peculiar morphology.
Recently, two
stars, HD~66665 and HD~63425, whose spectral types
and UV wind
line profiles are similar to those of $tau$~Sco, have
also been
determined to be magnetic. In the hope of establishing
a magnetic
field -- X-ray connection for at least a sub-set of the
magnetic
stars, we obtained XMM-Newton EPIC spectra of these two
objects.
Our results for HD~66665 are somewhat inconclusive. No
especially
strong hard component is detected; however, the number
of source
counts is insufficient to {em rule out} hard emission.
longer
exposure is needed to assess the nature of the X-rays from
this
star. On the other hand, we do find that HD~63425 has a
substantial
hard X-ray component, thereby bolstering its close
similarity to
$tau$~Sco.
Reference: to appear in MNRAS
Status:
Manuscript has been accepted
Weblink:
http://lanl.arxiv.org/abs/1211.0861
Comments:
Email: ignace@etsu.edu
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Peredur M. Williams (1), Karel A. van der Hucht (2,3),
Francois van Wyk (4), Fred Marang (4), Patricia A. Whitelock (4,5),
Patrice Bouchet (6) and Diah Y. A. Setia Gunawan (7)
1 -
Institute for Astronomy, University of Edinburgh, Royal Observatory,
Edinburgh EH9 3HJ;
2 - Space Research Organization Netherlands,
Sorbonnelaan 2,
NL-3584 CA Utrecht, The Netherlands;
3 -
Astronomical Institute `Anton Pannekoek', University of
Amsterdam,
Science Park 904, NL-1098 XH Amsterdam, The Netherlands;
4 -
South African Astronomical Observatory, P.O. Box 9, 7935 Observatory,
South Africa;
5 - Astronomy, Cosmology and Gravitation
Centre, Astronomy Department,
University of Cape Town, 7700
Rondebosch, South Africa;
6 - Service d'Astrophysique
DSM/IRFU/SAp CEA - Saclay, L'Orme des Merisiers, b^atiment 709,
F-91191 Gif-sur-Yvette France;
7 - Atacama Large
Millimetre/submillimetre Array (ALMA), Alonso de Cordova 3107,
Vitacura, Santiago 763 0355, Chile
We present infrared photometry
of the WC9+B0I Wolf-Rayet binary system WR 70 (HD 137603) observed
with telescopes at ESO, the SAAO and the AAT between 1983 and 2010
which shows persistent but variable circumstellar dust emission.
Optical spectroscopy confirms the classification of the companion as
a B0 supergiant and suggests that the Balmer lines in its spectrum
suffer in-fill from wind emission. Re-examination of the reddening
suggests a revised distance of 3.5~kpc. In the near-IR, the amplitude
of variation increases with wavelength, with no significant variation
in J (nor is there in the visible), implying that it is the amount of
dust in the wind of WR 70 that is varying. Period searches show a
period near 2.82~y. (1030~d.) but the variations are not strictly
regular and there are other factors affecting the dust formation and
repeatability of the light curves. There may be a secondary period
near 5.88 yr. but there is no evidence for periods less than a year.
A model of the spectral energy distribution in 1991 gives a dust
formation rate of 5.9 x 10^7 M_Sun y^-1, around one-third of the
available carbon from the WC9 wind going into the wind-collision
region, estimating its size from average WC9 and B0Ia wind
properties. The fraction of carbon going into dust varied between ~
11 and 46 percent during our campaign, possibly as a consequence of
the stars moving in an elliptical orbit.
Reference: MNRAS
in Press
Status: Manuscript has been accepted
Weblink:
ftp://ftp.roe.ac.uk:/pub/pmw/WR70rv.psf
Comments:
...a system crying out for an orbit
Email:
pmw@roe.ac.uk
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Miriam Garcia$^{1,2}$ and
Artemio Herrero$^{1,2}$
1- Instituto de Astrofisica de
Canarias (Spain)
2- Departamento de Astrofisica, Universidad de
La Laguna (Spain)
Recent findings hint that the winds of
massive stars with poorer metallicity than the SMC may be stronger
than predicted by theory. Besides calling the paradigm of radiation
driven winds into question, this result would impact the predicted
evolutionary paths of massive stars, their calculated ionizing
radiation and mechanical feedback and the role these objects play at
different stages of the Universe. The field needs a systematic study
of the winds of a large set of very metal poor massive stars, but the
sampling of spectral types is particularly poor in the very early
types. This paper's goal is to increase the list of known O-type
stars in the dwarf irregular galaxy IC1613, whose metallicity is
smaller than the SMC's by roughly a factor 2.
Using the
reddening-free Q-parameter, evolutionary masses and GALEX photometry,
we built a list of very likely O-type stars. We obtained
low-resolution R~1000 GTC-OSIRIS spectra for a fraction of them and
performed spectral classification, the only way to unequivocally
confirm candidate OB-stars. We have discovered 8 new O-type stars in
IC1613, increasing the list of 7 known O-type stars in this galaxy by
a factor of 2. The best quality spectra were analyzed with the model
atmosphere code FASTWIND to derive stellar parameters. We present the
first spectral type -- effective temperature scale for O-stars beyond
the SMC. The derived effective temperature calibration for IC1613 is
about 1000K hotter than the scale at the SMC. The analysis of an
increased list of O-type stars will be crucial for the studies of the
winds and feedback of massive stars at all ages of the
Universe.
Reference: A&A
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1211.4582
Comments:
Email: mgg@iac.es
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Michaela Kraus$^1$, Mary
Oksala$^1$, Dieter Nickeler$^1$, Florencia Muratore$^2$, Marcelo
Borges Fernandes$^3$, Anna Aret$^4$, Lydia Cidale$^2$, Willem-Jan de
Wit$^5$
$^1$Astronomick'y 'ustav, Akademie vv{e}d
v{C}esk'e republiky, Friv{c}ova 298, 251,65 Ondv{r}ejov, Czech
Republic;
$^2$Departamento de Espectroscop'ia Estelar, Facultad
de Ciencias Astron'omicas y Geof'isicas, Universidad Nacional de La
Plata, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina;
$^3$
Observat'orio Nacional, Rua General Jos'e Cristino 77, 20921-400 S~ao
Cristov~ao, Rio de Janeiro, Brazil;
$^4$ Tartu Observatory,
61602, T~oravere, Tartumaa, Estonia;
$^5$ European Southern
Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
The
appearance of the B[e] phenomenon in evolved massive stars such as
B[e] supergiants is still a mystery. While these stars are generally
found to have disks that are cool and dense enough for efficient
molecule and dust condensation, the origin of the disk material is
still unclear. We aim at studying the kinematics and origin of the
disk in the eccentric binary system GG,Car, whose primary component
is proposed to be a B[e] supergiant. Based on medium- and
high-resolution near-infrared spectra we analyzed the CO-band
emission detected from GG,Car. The complete CO-band structure
delivers information on the density and temperature of the emitting
region, and the detectable element[][13]{CO} bands allow us to
constrain the evolutionary phase. In addition, the kinematics of the
CO gas can be extracted from the shape of the first element[][12]{CO}
band head. We find that the CO gas is located in a ring surrounding
the eccentric binary system, and its kinematics agrees with Keplerian
rotation with a velocity, projected to the line of sight, of $80pm
1$,km,s$^{-1}$. The CO ring has a column density of $(5pm 3)times
10^{21}$,cm$^{-2}$ and a temperature of $3200pm 500$,K. In addition,
the material is chemically enriched in element[][13]{C}, which agrees
with the primary component being slightly evolved off the main
sequence. We discuss two possible scenarios for the origin of the
circumbinary disk: (i) non-conservative Roche lobe overflow, and (ii)
the possibility that the progenitor of the primary component could
have been a classical Be star. Neither can be firmly excluded, but
for Roche lobe overflow to occur, a combination of stellar and
orbital parameter extrema would be required.
Reference:
Astronomy and Astrophysics
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1211.5149
Comments:
Email: kraus@sunstel.asu.cas.cz
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Rolf Kuiper, Harold W.
Yorke
Jet Propulsion Laboratory, California Institute of
Technology, 4800 Oak Grive Drive, Pasadena, CA 91109, USA
Numerical
simulations have shown that the often cited radiation pressure
barrier to accretion onto massive stars can be circumvented, when the
radiation field is highly anisotropic in the presence of a
circumstellar accretion disk with high optical depth. Here, these
studies of the so-called flashlight effect are expanded by including
the opacity of the innermost dust-free but potentially optically
thick gas regions around forming massive stars. In addition to
frequency-dependent opacities for the dust grains, we use
temperature- and density-dependent Planck- and Rosseland mean
opacities for the gas. The simulations show that the innermost
dust-free parts of the accretion disks are optically thick to the
stellar radiation over a substantial fraction of the solid angle
above and below the disk's midplane. The temperature in the shielded
disk region decreases faster with radius than in a comparison
simulation with a lower constant gas opacity, and the dust
sublimation front is shifted to smaller radii. The shielding by the
dust-free gas in the inner disk thus contributes to an enhanced
flashlight effect, which ultimately results in a smaller opening
angle of the radiation pressure driven outflow and in a much longer
timescale of sustained feeding of the circumstellar disk by the
molecular cloud core. We conclude that it is necessary to properly
account for the opacity of the inner dust-free disk regions around
forming massive stars in order to correctly assess the effectiveness
of the flashlight effect, the opening angle of radiation pressure
driven outflows, and the lifetime and morphological evolution of the
accretion disk.
Reference: ApJ
Status: Manuscript
has been accepted
Weblink:
http://arxiv.org/abs/1211.6432
Comments:
Email: Rolf.Kuiper@jpl.nasa.gov
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Atsuo T. Okazaki (1),
Kimitake Hayasaki (2,3) and Yuki Moritani (2,4)
1 -
Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku,
Sapporo 062-8605, Japan
2 - Department of Astronomy, Kyoto
University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502,
Japan
3 - Korea Astronomy and Space Science Institute,
Daedeokdaero 776, Yuseong, Daejeon 305-348, Korea
4 - Hiroshima
Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama
Higashi-Hiroshima City 739-8511, Japan
We propose the new
scenario for X-ray outbursts in Be/X-ray binaries that normal and
giant outbursts are respectively caused by radiatively inefficient
accretion flows (RIAFs) and Bondi-Hoyle-Lyttleton (BHL) accretion of
the material transferred from the outermost part of a Be disk
misaligned with the binary orbital plane. Based on simulated
mass-transfer rates from misaligned Be disks, together with
simplified accretion flow models, we show that mass-accretion rates
estimated from the luminosity of the normal X-ray outbursts are
consistent with those obtained with advection-dominated accretion
flows, not with the standard, radiative-cooling dominated, accretion.
Our RIAF scenario for normal X-ray outbursts resolves problems that
have challenged the standard disk picture for these outbursts. When a
misaligned Be disk crosses the orbit of the neutron star, e.g., by
warping, the neutron star can capture a large amount of mass via
BHL-type accretion during the disk transit event. We numerically show
that such a process can reproduce the X-ray luminosity of giant X-ray
outbursts. In the case of very high Be disk density, the accretion
flow associated with the disk transit becomes supercritical, giving
rise to the luminosity higher than the Eddington
luminosity.
Reference: to appear in PASJ, Vol.65, No.3
(2013)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1211.5225
Comments:
Email: okazaki@lst.hokkai-s-u.ac.jp
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J. D. Ilee (1), H. E.
Wheelwright (2), R. D. Oudmaijer (1), W. J. de Wit (3), L. T. Maud
(1), M. G. Hoare (1), S. L. Lumsden (1), T. J. T. Moore (4), J. S.
Urquhart (2) and J. C. Mottram (5).
1 - School of Physics
and Astronomy, EC Stoner Building, University of Leeds, Leeds, LS2
9JT, UK
2 - Max-Planck-Institut fur Radioastronomie, Auf dem
Hugel 69, 53121, Bonn, Germany
3 - European Southern Observatory,
Alonso de Cordova 3107, Vitacura, Santiago, Chile
4 -
Astrophysics Research Institute, Liverpool John Moores University,
Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD
5 - Leiden
Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the
Netherlands
Massive stars play an important role in many areas
of astrophysics, but numerous details regarding their formation
remain unclear. In this paper we present and analyse high resolution
(R ~ 30,000) near-infrared 2.3 micron spectra of 20 massive young
stellar objects from the RMS database, in the largest such study of
CO first overtone bandhead emission to date. We fit the emission
under the assumption it originates from a circumstellar disc in
Keplerian rotation. We explore three approaches to modelling the
physical conditions within the disc - a disc heated mainly via
irradiation from the central star, a disc heated mainly via
viscosity, and a disc in which the temperature and density are
described analytically. We find that the models described by heating
mechanisms are inappropriate because they do not provide good fits to
the CO emission spectra. We therefore restrict our analysis to the
analytic model, and obtain good fits to all objects that possess
sufficiently strong CO emission, suggesting circumstellar discs are
the source of this emission. On average, the temperature and density
structure of the discs correspond to geometrically thin discs, spread
across a wide range of inclinations. Essentially all the discs are
located within the dust sublimation radius, providing strong evidence
that the CO emission originates close to the central protostar, on
astronomical unit scales. In addition, we show that the objects in
our sample appear no different to the general population of MYSOs in
the RMS database, based on their near- and mid-infrared colours. The
combination of observations of a large sample of MYSOs with CO
bandhead emission and our detailed modelling provide compelling
evidence of the presence of small scale gaseous discs around such
objects, supporting the scenario in which massive stars form via disc
accretion.
Reference: To appear in MNRAS
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1212.0554
Comments:
Email: pyjdi@leeds.ac.uk
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Yael Naze, Lidia M. Oskinova,
Eric Gosset
FNRS/ULg, Uni. Potsdam, FNRS/ULg
Stellar
winds are a crucial component of massive stars, but their exact
properties still remain uncertain. To shed some light on this
subject, we have analyzed an exceptional set of X-ray observations of
zeya Pup, one of the closest and brightest massive stars. The
sensitive lightcurves that were derived reveal two major results. On
the one hand, a slow modulation of the X-ray flux (with a relative
amplitude of up to 15% over 16h in the 0.3--4.0keV band) is detected.
Its characteristic timescale cannot be determined with precision, but
amounts from one to several days. It could be related to corotating
interaction regions, known to exist in zeta Pup from UV observations.
Hour-long changes, linked to flares or to the pulsation activity, are
not observed in the last decade covered by the XMM observations; the
17h tentative period, previously reported in a ROSAT analysis, is not
confirmed either and is thus transient, at best. On the other hand,
short-term changes are surprisingly small (<1% relative amplitude
for the total energy band). In fact, they are compatible solely with
the presence of Poisson noise in the data. This surprisingly low
level of short-term variability, in view of the embedded wind-shock
origin, requires a very high fragmentation of the stellar wind, for
both absorbing and emitting features (>10^5 parcels, comparing
with a 2D wind model). This is the first time that constraints have
been placed on the number of clumps in an O-type star wind and from
X-ray observations.
Reference: ApJ, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1212.1554
Comments:
Email: naze@astro.ulg.ac.be
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Lamb, J. B.
Oey, M. S.
Graus, A. S.
Adams, F. C.
Segura-Cox, D. M.
University
of Michigan
Some theories of star formation suggest massive
stars may only form in clustered environments, which would create a
deficit of massive stars in low density environments.
Observationally, Massey (2002) finds such a deficit in samples of the
field population in the Small and Large Magellanic Clouds, with an
IMF slope of {Gamma} ~ 4. These IMF measurements represent some of
the largest known deviations from the standard Salpeter IMF slope of
{Gamma}=1.35. Here, we carry out a comprehensive investigation of the
mass function above 20 solar masses for the entire field population
of the Small Magellanic Cloud, based on data from the Runaways and
Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). This
is a spatially complete census of the entire field OB star population
of the SMC obtained with the IMACS multi-object spectrograph and MIKE
echelle spectrograph on the Magellan telescopes. Based on Monte-Carlo
simulations of the evolved present-day mass function, we find the
slope of the field IMF above 20 solar masses is {Gamma}=2.3+/-0.4. We
extend our IMF measurement to lower masses using BV photometry from
the OGLE II survey. We use a statistical approach to generate a
probability distribution for the mass of each star from the OGLE
photometry, and we again find {Gamma}=2.3+/-0.6 for stellar masses
from 7-20 solar masses. The discovery and removal of ten runaways in
our RIOTS4 sample steepens the field IMF slope to {Gamma}=2.8+/-0.5.
We discuss the possible effects of binarity and star-formation
history on our results, and conclude that the steep field massive
star IMF is most likely a real effect.
Reference: Accepted
for publication in ApJ
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1212.1205
Comments:
Email: joellamb@umich.edu
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R. Blomme (1), Y. Naze (2),
D. Volpi (1), M. De Becker (2), R.K. Prinja (3), J.M. Pittard (4),
E.R. Parkin (5), O. Absil (2)
1 - Royal Observatory of
Belgium, Ringlaan 3, 1180 Brussel, Belgium
2 - Departement AGO,
Universite de Liege, Allee du 6 Aout 17, Bat. B5C, B-4000 Liege,
Belgium
3 - Department of Physics & Astronomy, University
College London, Gower Street, London WC1E 6BT, UK
4 - School of
Physics and Astronomy, The University of Leeds, Woodhouse Lane, Leeds
LS2 9JT, UK
5 - Research School of Astronomy and Astrophysics,
The Australian National University, Australia
Cyg OB2 #9 is
one of a small set of non-thermal radio emitting massive O-star
binaries. The non-thermal radiation is due to synchrotron emission in
the colliding-wind region. Cyg OB2 #9 was only recently discovered to
be a binary system and a multi-wavelength campaign was organized to
study its 2011 periastron passage. We report here on the results of
the radio observations obtained in this monitoring campaign. We used
the Expanded Very Large Array (EVLA) radio interferometer to obtain 6
and 20 cm continuum fluxes. The observed radio light curve shows a
steep drop in flux sometime before periastron. The fluxes drop to a
level that is comparable to the expected free-free emission from the
stellar winds, suggesting that the non-thermal emitting region is
completely hidden at that time. After periastron passage, the fluxes
slowly increase. We introduce a simple model to solve the radiative
transfer in the stellar winds and the colliding-wind region, and thus
determine the expected behaviour of the radio light curve. From the
asymmetry of the light curve, we show that the primary has the
stronger wind. This is somewhat unexpected if we use the
astrophysical parameters based on theoretical calibrations. But it
becomes entirely feasible if we take into account that a given
spectral type - luminosity class combination covers a range of
astrophysical parameters. The colliding-wind region also contributes
to the free-free emission, which can help to explain the high values
of the spectral index seen after periastron passage. Combining our
data with older Very Large Array (VLA) data allows us to derive a
period P = 860.0 +- 3.7 days for this system. With this period, we
update the orbital parameters that were derived in the first paper of
this series.
Reference: To appear in A&A
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1212.2381
Comments:
Email: Ronny.Blomme@oma.be
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Stanley P. Owocki^1, Jon O.
Sundqvist^1, David H. Cohen^2, and Kenneth G. Gayley^3
1-University
of Delaware, Newark,DE 19716 USA
2-Swarthmore College,
Swarthmore, PA 19081 USA
3-University of Iowa, Iowa City, IA
52242 USA
X-ray satellites since Einstein have empirically
established that the X-ray luminosity from single O-stars scales
linearly with bolometric luminosity, Lx ~ 10^{-7} Lbol. But
straightforward forms of the most favored model, in which X-rays
arise from instability-generated shocks embedded in the stellar wind,
predict a steeper scaling, either with mass loss rate Lx ~ Mdot ~
Lbol^{1.7} if the shocks are radiative, or with Lx ~ Mdot^{2} ~
Lbol^{3.4} if they are adiabatic. This paper presents a generalized
formalism that bridges these radiative vs. adiabatic limits in terms
of the ratio of the shock cooling length to the local radius. Noting
that the thin-shell instability of radiative shocks should lead to
extensive mixing of hot and cool material, we propose that the
associated softening and weakening of the X-ray emission can be
parametrized as scaling with the cooling length ratio raised to a
power m$, the "mixing exponent". For physically reasonable
values m ~= 0.4, this leads to an X-ray luminosity Lx ~ Mdot^{0.6} ~
Lbol that matches the empirical scaling. To fit observed X-ray line
profiles, we find such radiative-shock-mixing models require the
number of shocks to drop sharply above the initial shock onset
radius. This in turn implies that the X-ray luminosity should
saturate and even decrease for optically thick winds with very high
mass-loss rates. In the opposite limit of adiabatic shocks in
low-density winds (e.g., from B-stars), the X-ray luminosity should
drop steeply with Mdot^2. Future numerical simulation studies will be
needed to test the general thin-shell mixing ansatz for X-ray
emission.
Reference: MNRAS, in press
Status:
Manuscript has been accepted
Weblink:
http://www.bartol.udel.edu/~owocki/preprints/LxLbol-MNRAS-Dec12.pdf
Email:
owocki@bartol.udel.edu
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Sonja Burgemeister (1), Vasilii V.
Gvaramadze, Guy S. Stringfellow, Alexei Y. Kniazev, Helge Todt,
Wolf-Rainer Hamann
(1) Universitaet Potsdam, Germany
Two
optically obscured Wolf-Rayet (WR) stars have been recently
discovered by means of their infrared (IR) circumstellar shells,
which show signatures of interaction with each other. Following the
systematics of the WR star catalogues, these stars obtain the names
WR,120bb and WR,120bc. In this paper, we present and analyse new
near-IR, $J$, $H$, and $K$-band, spectra using the Potsdam Wolf-Rayet
(PoWR) model atmosphere code. For that purpose, the atomic data base
of the code has been extended in order to include all significant
lines in the near-IR bands.
The spectra of both stars are
classified as WN9h. As their spectra are very similar the parameters
that we obtained by the spectral analyses hardly differ. Despite
their late spectral subtype, we found relatively high stellar
temperatures of 63 kK. The wind composition is dominated by helium,
while hydrogen is depleted to 25 per cent by mass.
Because of
their location in the Scutum-Centaurus arm, WR,120bb and WR,120bc
appear highly reddened, $A_{K_{rm s}} approx 2$ mag. We adopt a
common distance of 5.8,kpc to both stars, which complies with the
typical absolute $K$-band magnitude for the WN9h subtype of -6.5 mag,
is consistent with their observed extinction based on comparison with
other massive stars in the region, and allows for the possibility
that their shells are interacting with each other. This leads to
luminosities of $log(L/L_odot) = 5.66$ and 5.54 for WR,120bb and
WR,120bc, with large uncertainties due to the adopted distance.
The
values of the luminosities of WR,120bb and WR,120bc imply that the
immediate precursors of both stars were red supergiants (RSG). This
implies in turn that the circumstellar shells associated with
WR,120bb and WR,120bc were formed by interaction between the WR wind
and the dense material shed during the preceding RSG
phase.
Reference: 2012, MNRAS (astro-ph
1212.3727)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1212.3727
Comments:
Email: wrh@astro.physik.uni-potsdam.de
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Emily M. Levesque, Guy S.
Stringfellow, Adam G. Ginsburg, John Bally, Brian A.
Keeney
University of Colorado at Boulder
We present
optical and near-IR spectroscopic observations of the luminous blue
variable SN 2009ip during its remarkable photometric evolution of
2012. The spectra sample three key points in the SN 2009ip
lightcurve, corresponding to its initial brightening in August
(2012-A) and its dramatic rebrightening in early October (2012-B).
Based on line fluxes and velocities measured in our spectra, we find
a surprisingly low I(H-alpha)/I(H-beta) ratio (~1.5) in the 2012-B
spectra. Such a ratio implies either a rare Case B recombination
scenario where H-alpha, but not H-beta, is optically thick, or an
extremely high density for the circumstellar material of n_e >
10^(13) cm^(-3). The H-alpha line intensity yields a minimum
radiating surface area of >~20,000 AU^2 in H-alpha at the peak of
SN 2009ip's photometric evolution. Combined with the nature of this
object's spectral evolution in 2012, a high circumstellar density and
large radiating surface area imply the presence of a thin disk
geometry around the central star (and, consequently, a possible
binary companion), suggesting that the observed 2012-B rebrightening
of SN 2009ip can be attributed to the illumination of the disk's
inner rim by fast-moving ejecta produced by the underlying events of
2012-A.
Reference: submitted to ApJ
Status:
Manuscript has been submitted
Weblink:
http://arxiv.org/abs/1211.4577
Comments:
Email: Emily.Levesque@colorado.edu
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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:
March 31st
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Norbert Przybilla
Institute
for Astro- and Particle Physics
University of Innsbruck
Technikerstrasse 25/8
A-6020 Innsbruck
Austria
The
Institute for Astro- and Particle Physics at the University of
Innsbruck invites applications for a post doc position in stellar
astrophysics. The successful candidate will work on observational
aspects in order to exploit the possibilities provided by the recent
accession of Austria to ESO, quantitative analyses and/or modelling
of stellar atmospheres, with a focus on massive, luminous stars.
Participation in teaching is expected.
The appointment may
start as early as March 1, 2013 and will be for four years.
Applicants should have a PhD in astronomy, physics or a related
field. They should send by email curriculum vitae, publication list,
a brief statement of research interests, and arrange for three
letters of recommendation to be sent.
Attention/Comments:
job applications shall be sent
attn. Theresia Freiseisen
theresia.freiseisen@uibk.ac.at
Weblink:
http://jobregister.aas.org/job_view?JobID=43992
Email:
norbert.przybilla@fau.de
Deadline: January 9,
2013
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June 3-7, 2013
Venue:
Moscow M.V. Lomonosov State University in Moscow, Russia
Main
Topics:
- A-star formation: abundances and chemical
peculiarities of A-type and related stars in open clusters
-
A-star formation: formation and evolution of discs and planetary
systems around A-type and related stars; A-star multiplicity
-
A-star formation: magnetic field generation
- Fundamental
parameters, chemical abundances and inhomogeneities in A-type and
related stars
- Magnetic fields in Main-Sequence A-type and
related stars
- Pulsation in Main-Sequence A-type and
related stars
- Rotation and hydrodynamical processes in
Main-Sequence A-type and related stars
- Evolution of A
stars off the Main Sequence: generic aspects, magnetism and
dissipation of chemical peculiarities
- Evolved A-type
stars in the Galaxy and beyond
Scientific Organizing
Committee:
Gautier Mathys, JAO/ESO, Chile, chair
Maryline
Briquet, Universite de Liege, Belgium
Margarida Cunha,
Universidade do Porto, Portugal
Oleg Kochukhov, University of
Uppsala, Sweden
Friedrich Kupka, University of Vienna, Austria
Francis LeBlanc, Universite de Moncton, Canada
Lyudmila
Mashonkina, Russian Academy of Sciences, Russia
Richard Monier,
Universite de Nice, France
Olga Pintado, INSUGEO, Tucuman,
Argentina
Hiromoto Shibahashi, University of Tokyo, Japan
Kazimierz Stepien, Warsaw University, Poland
Glenn Wahlgren,
Catholic University of America, USA
Russian institutions
organizing the conference:
Sternberg Astronomical Institute
of Moscow M.V. Lomonosov State University,
Institute of Astronomy
of the Russian Academy of Sciences,
Eurasian Astronomical
Society.
Invited Speakers (confirmed):
Evelyne
Alecian, Observatoire de Paris, France
Victoria Antoci,
University of Vienna, Austria
Rainer Arlt, Leibniz-Institut fuer
Astrophysik Potsdam, Germany
Luca Fossati, University of Bonn,
Germany
Swetlana Hubrig, Leibniz-Institut fuer Astrophysik
Potsdam, Germany
Heidi Korhonen, University of Copenhagen,
Denmark
Jiri Krticka, Masaryk University Brno, Czech Republic
Rolf Kudritzki, University of Hawaii, USA
John D. Landstreet,
University of Western Ontario, Canada
Theresa Lueftinger,
University of Vienna, Austria
Stephane Mathis, Observatoire de
Paris, France
Zdenek Mikulasek, Masaryk University Brno, Czech
Republic
Martin Netopil, University of Vienna, Austria
Pierre
North, Ecole Polytechnique Federale de Lausanne, Switzerland
Jan
Robrade, Hamburg Observatory, Germany
Iosif Romanyuk, Special
Astrophysical Observatory, RAS, Russia
Frederic Royer,
Observatoire de Paris, France
Tatyana Ryabchikova, Institute of
Astronomy, RAS, Russia
Mikhail Sachkov, Institute of Astronomy,
RAS, Russia
Hideyuki Saio, Tohoku University Sendai, Japan
Denis
Shulyak, Georg-August University Goettingen, Germany
Asif
ud-Doula, Penn State Worthington Scranton, USA
Registration
Registration is now open and ends on April 1st 2013. Please
register at your earliest convenience. Please note that timely
registration is essential to ensure that visa formalities can be
completed in due time. The registration fee covers all regular
meeting costs including abstract materials, welcome party, coffee
breaks, conference banquet, Moskva-river cruise tour, and classical
music concert. Full conference registration costs 280 Euro (11 300
Rubles). A discount of 30 Euros is provided for the participants, who
pay the registration fee before April 1st 2013.
To register,
point your browser to http://agora.guru.ru/astars2013/ and follow the
instructions; payments can be made via credit card.
Visa
The LOC will provide a letter of invitation for a visa
application should you require one. Please see
http://agora.guru.ru/astars2013/ for details, and contact us through
astars2013@inasan.ru for questions or requests.
Abstract
submission
Contributed talks will be selected from the
submitted abstracts, and there will also be a poster session. All
contributions will be included in the proceedings.
More
information can be found on the conference website:
http://agora.guru.ru/astars2013/
Key Dates
1
April 2013: Deadline abstract submissions
1 April 2013: Early
registration closes
2 June 2013: Welcome party/Conference Begins
3-7 June 2013: Conference
1 August 2013: Deadline for
submission of proceedings contributions.
Weblink:
http://agora.guru.ru/astars2013/
Email:
astars2013@inasan.ru
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2-4 December 2013
Venue: University
Foundation, Brussels, Belgium
Symposium Scope and Objective:
Stellar astrophysics is the foundation of our understanding
of the nature of the Universe. The luminous energy emitted from the
surfaces of stars has given astrophysicists the clues to deduce the
nature of stellar structure and to map the physical changes stars
undergo over their lifetimes, from birth out of the interstellar
medium to death as white dwarfs, neutron stars or black holes. We
have now reached the long-awaited stage where we can test and improve
our understanding of stellar structure and evolution theory, with
important implications for all research fields that build on this
foundation. For the first time we can peer into the interiors of
stars to see their structures using asteroseismology. This
revolutionary new view is the result of uninterrupted space
photometry, precise to parts per million, delivered for thousands of
stars by the Kepler and CoRoT Space Telescopes. The primary aim of
these space missions is to detect exoplanet systems, with an ultimate
goal of finding Earth-like planets in the habitable zone. The
ultra-high precision continuous observations obtained have produced
tremendous benefits for asteroseismology. Asteroseismic inference of
the exoplanet host star provides crucial input to characterise the
planetary system. We can now peer into the interiors of stars in all
stages of evolution, including their red giant and compact stages -
for both binary and single stars - probing extreme physical
conditions with unprecedented confidence. We can even perform
asteroseismic galactic studies of clusters and populations in the
Milky Way.
The goal of this three-day symposium is to present
recent progress in asteroseismology to the broader astrophysics
community and to discuss what this field may offer to other research
domains in astrophysics. Keynote invited speakers will cover broad
areas of importance for astrophysics; their review talks will be
followed by dedicated talks on how asteroseismology has brought, or
will bring improvements in that topic. In addition to these invited
presentations, shorter contributed talks in this same spirit will be
solicited from the community. The list of invited talks, as well as
the programme, can be found on the conference website:
http://fys.kuleuven.be/ster/meetings/francqui/francqui
The
purpose of this 1st announcement is to make the community aware of
the symposium and to present the list of invited talks. A call for
participation, registration and abstract submission for a contributed
talk will be sent out in January 2013 to all those who pre-registered
through the weblink below.
Weblink:
http://fys.kuleuven.be/ster/meetings/francqui/francqui
Email:
katrijn@ster.kuleuven.be
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