ISSN 1783-3426
|
Letter of Intent to become an IAU
Commission -- announcement
Proposed
IAU Commission on Stellar Magnetism
voting
for the new Commission on Massive Stars
UV
astronomy commission proposal
Massive stars in the giant molecular
cloud G23.3-0.3 and W41.
Interacting
supernovae from photoionization-confined shells around red supergiant
stars
X-ray emission from magnetic
massive stars
The modulated X-ray
emission of the magnetic O8.5V-star Tr16-22
Gas
physical conditions and kinematic of the giant outflow Ou4
A
multi-wavelength view on the dusty Wolf-Rayet star WR 48a
Eclipses
and dust formation by WC9 type Wolf-Rayet stars
Measuring
the shock-heating rate in the winds of O stars using X-ray line
spectra
Investigating the inner
discs of Herbig Ae/Be stars with CO bandhead and Br Gamma
emission
Radial dependence of line
profile variability in seven O9--B0.5 stars
Time-series
photometry of the O4 I(n)fp star zeta Puppis
A
Blue Point Source at the Location of Supernova 2011dh
iPTF13bvn:
The First Evidence of a Binary Progenitor for a Type Ib
Supernova
Southern Massive Stars at
High Angular Resolution: Observational Campaign and Companion
Detection
Evidence of the Evolved
Nature of the B[e] Star MWC 137
The
IACOB project: II. On the scatter of O-dwarf spectral type -
effective temperature calibrations
The
Multiplicity of Massive Stars: A High Angular Resolution Survey with
the HST Fine Guidance Sensor
Radio
emission variability and proper motions of WR 112
The
properties of ten O-type stars in the low-metallicity galaxies IC
1613, WLM and NGC 3109
Short-term
spectroscopic variability of Plaskett's star
Near-infrared
spectroscopy of candidate red supergiant stars in clusters.
The
Cocoon Nebula and its ionizing star: do stellar and nebular
abundances agree?
The spectroscopic
Hertzsprung-Russell diagram of Galactic massive stars
High-Energy
Properties of the Enigmatic Be Star gamma Cassiopeiae
Suzaku
Monitoring of Hard X-ray Emission from Eta Carinae over a Single
Binary Orbital Cycle
MY
Camelopardalis, a very massive merger progenitor
Enhancement
of Surface Helium Abundance in Intermediate-Mass Main-Sequence
Stars
Magnetorotational instability
in decretion disks of critically rotating stars and the outer
structure of Be and Be/X-ray disks
Gas
physical conditions and kinematics of the giant outflow
Ou4
Analytical Solutions for
Radiation-Driven Winds in Massive Stars. I: The Fast Regime
Constraining general massive-star
physics by exploring the unique properties of magnetic O-stars:
Rotation, macroturbulence and sub-surface convection
Massive
star population synthesis
Physics
of Mass Loss in Massive Stars
Deriving
extinction laws with O stars: from the IR to the UV
A
photometric variability study of massive stars in Cygnus OB2
The
Hourglass as seen with HST/WFPC2
MGB
and the new Galactic O-Star Spectroscopic Survey spectral
classification standard grid
Asteroseismology
of OB stars with hundreds of single snapshot spectra (and a few
time-series of selected targets)
Closed (original deadline passed):
Tenure-track faculty position
Tenure
Track Position in Astrophysics at Instituto de Astronomía, UNAM, at
Ensenada, Baja California, México
Tenure
Track Position in Astrophysics at Instituto de Astronomía, UNAM,
México
Research Position in NLTE
stellar atmosphere modelling
Open:
Research Fellow - Nuclear Astrophysics
1 Postdoc and 2 PhD Positions at the
University of Tübingen
The physics
of evolved star:A conference dedicated to the memory of Olivier
Chesneau
Stellar Physics in
Galaxies throughout the Universe
dear friends of the MSWG,
the Organizing Committee has submitted a Letter of Intent to
the IAU to turn our Working Group into an IAU Commission. You find
the LoI text at the end of this message. The final decission will be
taken by the IAU Executive Committee in April 2015. If you are
interested in the details, visit:
http://www.iau.org/news/announcements/detail/ann14014/
http://iau.org/news/announcements/detail/ann14008/
http://www.iau.org/news/announcements/detail/ann14029/
In
the next days the IAU will open an electronic poll on the proposed
Commissions as part of the whole decission process. The results of
the poll will be taken into account by the IAU for the final
decission. All IAU members can vote for up to three of the proposed
Commissions.
The Massive Stars Working Group encourages all
IAU members of the group to vote in the electronic poll before its
deadline (foreseen November 30), to show our interest in becoming a
Commission after 20 years of uninterrupted operation of the Working
Group. The IAU will announce shortly the votation procedure.
The
full proposal is due in January, 31, 2015 and will be based on the
LoI. If you have comments or suggestions to improve the proposal,
please send them to me or to any of the members of the MSWG
Organizing Committe. You find the names and addresses in the Working
Group web page
http://www.astroscu.unam.mx/massive_stars
with
best regards,
Artemio Herrero
chair, on behalf of the
Organizing Committee of the Massive Stars Working Group
==================================================
Submission
details
==================
Name of the Commission:
Massive Stars Commission
Inter-Division Commission
Primary
Division: Division G Stars and Stellar Physics
Parent Division 1:
Division H Interstellar Matter and Local Universe
Parent Division
2: Division J Galaxies and Cosmology
First Co-Proposer:
First name: Gregor
Last name: Rauw
Institute: Institute
d'Astrophysique
City: Liège
Country: Belgium
Email:
rauw@astro.ulg.ac.be
Second Co-Proposer:
First name:
Nicole
Last name: St.-Louis
Institute: Université de
Montreal
City: Montreal
Country: Canada
Email:
stlouis@ASTRO.UMontreal.CA
Third Co-Proposer:
First name:
Jorick
Last name: Vink
Institute: Armagh Observatory
City:
Armagh
Country: United Kingdom
Email: jsv@arm.ac.uk
Commission based one existing Working Group: Division G WG
Massive Stars
Rationale:
The massive stars community
organized itself and created the Massive Stars Working Group (MSWG)
in 1995, nearly 20 years ago. Since then, it has been in operation
without interruption, being re-appointed after each General Assembly.
The MSWG contains over 400 members, with more than 100 senior IAU
members. These facts already indicate that their activities and
interests go beyond the goals and limits of a Working Group.
The
MSWG is very active in organizing, focussing and promoting massive
star research. Every two months it publishes the Massive Stars
Newsletter, which includes the latest accepted papers, PhD theses,
upcoming meetings and workshops and job offers, as well as any
information of interest for the community. Up to now, 142 Newsletters
have been issued. For even faster information dissemination within
the community, the MSWG maintains a 24-hours announcement service.
New submissions in the last 24 hours are distributed to interested
members upon subscription to this service.
One of the most
important activities of the MSWG is the organization of regular
meetings of broad interest to the whole massive star community, most
of them IAU Symposia, with an approximate frequency of 4-5 years. In
addition, numerous IAU Symposia directly related to massive stars
have been organized in the intervening years. As recent examples, we
may cite the IAUS 307 ("New windows on massive stars",
Geneva, June 2013), IAUS 279 ("Death of Massive Stars:
Supernovae and GRBs", Nikko, 2012) or IAUS 272 ("Active OB
stars- structure, evolution, mass-loss and critical limits",
Paris, 2010).
The activities of the MSWG are coordinated by the
MSWG Organizing Committee (OC), elected by all members of the MSWG
following the IAU rules and by-laws of the WG. The OC reports on the
group activities to the IAU every three years at the General
Assembly. All information concerning the MSWG (including by-laws,
membership and Newsletter issues) can be found on the web page of the
group
http://www.astroscu.unam.mx/massive_stars
The MSWG
started an internal discussion to become an IAU Commission some time
ago. As a result, it was decided at the General Assembly in Beijing
that the MSWG would apply to become a Commission once the
corresponding call for Commissions Reform would have been issued by
the IAU Executive Committee.
The MSWG activity fits smoothly into
the expectations for new Commissions. In the announcements for
Commissions Reform it is claimed that new "Commissions are thus
expected to be more focussed, in areas where IAU members voluntarily
choose to work usefully and effectively together to achieve specific
goals, perform significant roles, or for some other particular
purpose of interest to the community or to society". We are
convinced that this is the case of our MSWG.
Massive star
research is centred on the stars themselves, but it offers a large
number of links to other areas of Astrophysics. Massive stars are
very luminous and thus they can be studied individually at relatively
large distances, even with the detail of high resolution
spectroscopy, spectropolarimetry or interferometry. When the spatial
resolution becomes insufficient, they are the key agents behind
starbursts or giant HII regions.
Massive stars span a wide range
of physical parameters (masses, temperatures, energies...) and a
large diversity of physical states, strongly impacting on other
fields such as star formation, stellar population synthesis, galactic
chemical and dynamical evolution at different redshifts or the
re-ionization of the Universe, for which they have been proposed to
be an active agent. From their birth to their death, massive stars go
through phases of luminous OB stars, Luminous Blue Variables and
hypergiants, Red Supergiants, Wolf-Rayets, Supernovae, Gamma Ray
Bursts, neutron stars and black holes. The physics of these stars is
complex, and thus stellar evolution and atmosphere models provide
strong links between observations and analyses of individual objects.
In recent times, the roles of multiplicity and magnetic fields have
been added to those of rotation and stellar winds, thanks to modern
spectroscopic, large scale surveys, that allow us to homogeneously
study large samples
of massive stars and set constraints on their
initial conditions and evolution.
With the new instrumental
facilities and the developments for the immediate future, like the
30-40m telescopes and their associated instrumentation, the role of
massive stars as tools to understand the nearby and far Universe will
only increase, as will their role as central objects at the
crossroads of different astrophysical disciplines. Because of these
broad topics, we feel that the proposed Commission should be an
Inter-Division Commission, hosted by Division G, but affiliated to
Divisions H and J.
Turning the IAU MSWG into a Commission will
benefit the whole astronomical community. It will offer a stable
environment for discussion of all areas in which massive stars are
involved within the IAU. The recent developments in the field still
require strong research efforts for at least a decade, and the new
avenues that will be opened by new telescopes and instruments will
become a reality at the end of that decade. This guarantees that
massive stars will remain one of the main research focuses of the
astronomical community for at least the next two decades.
An IAU
Commission would promote the development of the field and provide a
well-defined forum for discussion and results dissemination. As an
IAU Commission we will also expand our present activities. Thus, for
the next years following a possible Commission status we will
concentrate on the following tasks:
(a) Maintain the Massive
Stars Newsletter and the 24-hours service and promote its
dissemination.
(b) Continue promoting international conferences
and workshops. At least 3 IAU Symposia or similar level meetings
should be held between 2015 and 2025.
(c) Increase our efforts to
strengthen our links with other research communities and make our
results easily accessible to them. To this aim we will promote the
Massive Stars Newsletter among those communities, look for common
meetings and develop web tools.
(d) Foster new ways of active
participation in our community, particularly for young researchers,
by regular consultation and web tools. We expect also a large number
of "Associates" for which these ways of participating will
be of first importance.
(e) We will reinforce public outreach by
means of open web pages and public talks and seminars. To this aim we
will seek links with and advices from the IAU Office for Astronomy
Outreach and the National Outreach Contacts.
We think that our
proposal will be beneficial for the massive star researchers, the IAU
and the astronomical community as a whole.
=====================================================
Weblink:
Email: ahd@iac.es
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In the context of the IAU
Commission renewal process, a new Commission on Stellar Magnetism has
been proposed.
To quote from the Letter of Intent:
"Considering the diverse and universal impact of stellar
magnetism on the physics of stars, the clear scientific and societal
importance of major unsolved problems in the field (e.g. the solar
dynamo, space weather), and the large, broad international community
engaged in this field, we propose the organization of a
Commission on Stellar Magnetism with the aim of facilitating
progress in understanding all aspects of stellar magnetism
and activity, and in particular to coordinate international
efforts in this regard. We welcome all individuals interested in
pursuing the goals of the Commission."
Over 50 new
Commissions have been proposed, including 8 in Division G ("Stars
and Stellar Physics").
Members of the IAU should have
recently received an email invitation to vote for up to 3 of the
proposed commissions as part of an "Expression of Interest"
activity.
We invite Massive Stars WG members to review the
proposed Stellar Magnetism Commission LOI.
Weblink:
http://www.iau.org/submissions/commissionproposal/list
Email:
wade-g@rmc.ca
Back to contents
dear Massive Stars Working
Group members,
the IAU has started the voting procedure for the
new Commissions.
As we announced a few weeks ago, the Organizing
Committee of the
Massive Stars Working Group has submitted a
Letter of Interest to turn our
Working Group into an IAU
Commission, following previous WG decissions.
The OC
encourages all WG members that are also IAU members to vote for the
new Commission on Massive Stars following the instructions given
in the email
sent by the IAU General Secretary (to IAU members).
The OC also encourages all WG members to send comments and
suggestions
on the LoI for the final proposal. Please send them
before December 31 to
me (ahd@iac.es) or any OC member.
with
best regards,
Artemio Herrero,
chair, on behalf of the
Massive Stars Working Group Organizing Committee
Email:
ahd@iac.es
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Dear colleagues and aficionados
of ultraviolet astronomy:
Those of you who are members of the
IAU will have received yesterday or today an Email from the General
Secretary Thierry Montmerle announcing the start of the “indicative
voting” for the new Commissions that were proposed earlier. This,
because all existing Commissions will cease to exist at the coming
General Assembly (GA) in August 2015 and the new ones will be
established.
If you browsed through the list of commissions
visible at http://www.iau.org/submissions/commissionproposal/list/,
you probably noticed NC-19, which is our proposal to establish a
Commission to deal with UV astronomy. The need for this Commission
became evident at the last GA in Beijing, since the parent Division
(XI) morphed into Division D that deals only with high energy
astrophysics.
We believe that a dedicated Commission will
play a major role in promoting the UV domain to a place of prominence
among the different spectral domains, perhaps as much (or more) that
the X-ray and IR, both in securing space missions and in educating a
new generation of UV astronomers.
In order to secure these
goals, we urge you to vote for NC-19 and to convince your colleagues
to do the same. Please spread the word and make sure you finalize
your vote before 31 December. If you are NOT a member of the IAU and
have not received the GS Email, you can still help by convincing your
colleagues who ARE members to vote for NC-19.
Thank you for
your help, and hoping to revitalize UV astronomy,
Ana Ines
Gomez de Castro, Jayant Murthy, Noah Brosch (proposers)
Weblink:
Email: Noah@wise.tau.ac.il
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Maria Messineo (1), Karl M. Menten (1), Donald F. Figer
(2), Ben Davies (3),
J. Simon Clark (4), Valentin D. Ivanov (5),
Rolf-Peter Kudritzki (6), R. Michael Rich (7), John W. MacKenty (8),
Christine Trombley (2)
Max Planck for Radioastronomy (1),
Rochester Institute of Technology (2), Liverpool John Moores
University (3), The Open University (4), European Southern
Observatory (5),
University of Hawaii (6), University of
California (7), Space Telescope Science Institute (8)
Young
massive stars and stellar clusters continuously form in the Galactic
disk, generating new HII regions within their natal giant molecular
clouds and subsequently enriching the interstellar medium via their
winds and supernovae.
Massive stars are among the brightest
infrared stars in such regions; their identification permits the
characterization of the star formation history of the associated
cloud as well as constraining the location of stellar aggregates and
hence their occurrence as a function of global environment.
We
present a stellar spectroscopic survey in the direction of the giant
molecular cloud G23.3-0.3. This complex is located at a distance of ~
4-5 kpc, and consists of several HII regions and supernova remnants.
We discovered 11 OfK+ stars, one candidate Luminous Blue Variable,
several OB stars, and candidate red supergiants. Stars with K-band
extinction from ~1.3 - 1.9 mag appear to be associated with the GMC
G23.3-0.3; O and B-types satisfying this criterion have
spectro-photometric distances consistent with that of the giant
molecular cloud.
Combining near-IR spectroscopic and photometric
data allowed us to characterize the multiple sites of star formation
within it. The O-type stars have masses from 25 - 45 Msun, and ages
of 5-8 Myr. Two new red supergiants were detected with interstellar
extinction typical of the cloud; along with the two RSGs within the
cluster GLIMPSE9, they trace an older burst with an age of 20--30
Myr. Massive stars were also detected in the core of three supernova
remnants - W41, G22.7-0.2, and G22.7583-0.4917.
A large
population of massive stars appears associated with the GMC
G23.3-0.3, with the properties inferred for them indicative of an
extended history of stars formation.
Reference: A&A
Journal
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1408.3558
Comments:
Email: messineo@mpifr-bonn.mpg.de
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Jonathan Mackey (1), Shazrene Mohamed (2), Vasilii V.
Gvaramadze (3,4,5), Rubina Kotak(6), Norbert Langer (1), Dominique
M.-A. Meyer(1), Takashi J. Moriya (1), Hilding R. Neilson (7)
(1)
Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn,
Germany
(2) South African Astronomical Observatory, PO Box 9,
7935 Observatory, South Africa
(3) Sternberg Astronomical
Institute, Lomonosov Moscow State University, Universitetskij
Prospect 13, Moscow 119992, Russia
(4) Isaac Newton Institute of
Chile, Moscow Branch, Universitetskij Prospect 13, Moscow 119992,
Russia
(5) Space Research Institute, Russian Academy of Sciences,
Profsoyuznaya 84/32, Moscow 117997, Russia
(6) Astrophysics
Research Centre, School of Mathematics and Physics, Queen’s
University Belfast, Belfast BT7 1NN, UK
(7) Department of Physics
and Astronomy, East Tennessee State University, Box 70652, Johnson
City, Tennessee 37614, USA
Betelgeuse, a nearby red
supergiant, is a fast-moving star with a powerful stellar wind that
drives a bow shock into its surroundings. This picture has been
challenged by the discovery of a dense and almost static shell that
is three times closer to the star than the bow shock and has been
decelerated by some external force. The two physically distinct
structures cannot both be formed by the hydrodynamic interaction of
the wind with the interstellar medium. Here we report that a model in
which Betelgeuse’s wind is photoionized by radiation from external
sources can explain the static shell without requiring a new
understanding of the bow shock. Pressure from the photoionized wind
generates a standing shock in the neutral part of the wind and forms
an almost static, photoionization-confined shell. Other red
supergiants should have much more massive shells than Betelgeuse,
because the photoionization-confined shell traps up to 35 per cent of
all mass lost during the red supergiant phase, confining this gas
close to the star until it explodes. After the supernova explosion,
massive shells dramatically affect the supernova light curve,
providing a natural explanation for the many supernovae that have
signatures of circumstellar interaction.
Reference: 2014,
Nature, 512, 282-285
Status: Manuscript has been
accepted
Weblink:
http://dx.doi.org/10.1038/nature13522
Comments:
Email: jmackey@astro.uni-bonn.de
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Yael Naze (1), Veronique Petit (2), Melanie Rinbrand (3),
David Cohen (4), Stan Owocki (3), Asif ud-Doula (5), Gregg A Wade
(6)
(1) ULg, (2) FIT, (3) Udel, (4) Swarthm. Col., (5)
Penn State Wor. Sc., (6) RMC
Magnetically confined winds of
early-type stars are expected to be sources of bright and hard
X-rays. To clarify the systematics of the observed X-ray properties,
we have analyzed a large series of Chandra and XMM observations,
corresponding to all available exposures of known massive magnetic
stars (over 100 exposures covering ~60% of stars compiled in the
catalog of Petit et al. 2013). We show that the X-ray luminosity is
strongly correlated with the stellar wind mass-loss-rate, with a
power-law form that is slightly steeper than linear for the majority
of the less luminous, lower-Mdot B stars and flattens for the more
luminous, higher-Mdot O stars. As the winds are radiatively driven,
these scalings can be equivalently written as relations with the
bolometric luminosity. The observed X-ray luminosities, and their
trend with mass-loss rates, are well reproduced by new MHD models,
although a few overluminous stars (mostly rapidly rotating objects)
exist. No relation is found between other X-ray properties (plasma
temperature, absorption) and stellar or magnetic parameters, contrary
to expectations (e.g. higher temperature for stronger mass-loss
rate). This suggests that the main driver for the plasma properties
is different from the main determinant of the X-ray luminosity.
Finally, variations of the X-ray hardnesses and luminosities, in
phase with the stellar rotation period, are detected for some objects
and they suggest some temperature stratification to exist in massive
stars' magnetospheres.
Reference: accepted by
ApJ
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1409.1690
Email:
naze@astro.ulg.ac.be
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Yael Naze (1), Gregg A Wade (2), Veronique Petit (3)
(1)
ULg, (2) RMC, (3) FIT - UDel
Using an extensive X-ray dataset,
we analyze the X-ray emission of the massive O-star Tr16-22, which
was recently found to be magnetic. Its bright X-ray emission is found
to be modulated with a ~54d period. This timescale should represent
the rotational timescale of the star, as for other magnetic massive
stars. In parallel, new spectropolarimetric data confirm the
published magnetic detection.
Reference: accepted by
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1408.6098
Comments:
Email: naze@astro.ulg.ac.be
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Romano L.M. Corradi (1,2), Nicolas Grosso (3), Agnes
Acker(3), Robert Greimel (4), Patrick Guillout (3)
(1)
Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife,
Spain
(2) Departamento de Astrofisica, Universidad de La Laguna,
E-38206 La Laguna, Tenerife, Spain
(3) Observatoire Astronomique
de Strasbourg, Universite de Strasbourg, CNRS, UMR 7550, 11 rue de
l'Universite, 67000 Strasbourg, France
(4) IGAM, Institut fur
Physik, Universitat Graz, Universitatsplatz 5/II, A-8010 Graz,
Austria
Ou4 is a recently discovered bipolar outflow with a
projected size of more than one degree in the plane of the sky. It is
apparently centred on the young stellar cluster -whose most massive
representative is the triple system HR8119- inside the HII region Sh
2-129. The driving source, the nature, and the distance of Ou4 are
not known. Deep narrow-band imagery of the whole nebula at arcsec
resolution was obtained to study its morphology. Long-slit
spectroscopy of the tips of the bipolar lobes was secured to
determine the gas ionization mechanism, physical conditions, and
line-of-sight velocities. An estimate of the proper motions at the
tip of the south lobe using archival images is attempted. The
existing multi-wavelength data for Sh 2-129 and HR 8119 are also
comprehensively reviewed. The morphology of Ou4, its emission-line
spatial distribution, line flux ratios, and the kinematic modelling
adopting a bow-shock parabolic geometry, illustrate the expansion of
a shock-excited fast collimated outflow. The radial velocities and
reddening are consistent with those of Sh 2-129 and HR 8119. The
improved determination of the distance to HR8119 (composed of two B0
V and one B0.5 V stars) and Sh 2-129 is 712 pc. We identify in WISE
images a 5 arcmin-radius (1 pc at the distance above) bubble of
emission at 22 micron emitted by hot (107 K) dust, located inside the
central part of Ou4 and corresponding to several [O III] emission
features of Ou4. The apparent position of Ou4 and the properties
studied in this work are consistent with the hypothesis that Ou4 is
located inside the Sh 2-129 HII region, suggesting that it was
launched some 90 000 yrs ago by HR8119. The outflow total kinetic
energy is estimated to be ~4e47~ergs. However, the alternate
possibility that Ou4 is a bipolar planetary nebula, or the result of
an eruptive event on a massive AGB or post-AGB star not yet
identified, cannot be ruled out.
Reference: Astronomy
and Astrophysics, in press
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1407.4617,
http://hal.archives-ouvertes.fr/hal-01022286
Comments:
Email: rcorradi@iac.es
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Svetozar A. Zhekov (1), Toma Tomov (2), Marcin P. Gawronski
(2), Leonid N. Georgiev (3), Jura Borissova (4), Radostin Kurtev (4),
Marc Gagne (5) and Marcin Hajduk (6)
(1) Space Research
and Technology Institute, Sofia, Bulgaria; (2) Centre for Astronomy,
Nicolaus Copernicus University, Torun, Poland; (3) Instituto de
Astronomía, Universidad Nacional Autónoma de Mexico, Mexico; (4)
Instituto de Fisica y Astronomia, Universidad de Valparaiso, Chile;
(5) Department of Geology and Astronomy, West Chester University,
West Chester, PA, USA; (6) Nicolaus Copernicus Astronomical Center,
Torun, Poland
We present results from the first attempts to
derive various physical
characteristics of the dusty Wolf-Rayet
star WR 48a based on a
multi-wavelength view of its observational
properties. This is done on
the basis of new optical and
near-infrared spectral observations and
on data from various
archives in the optical, radio and X-rays. The
optical spectrum
of WR 48a is acceptably well represented by a sum of
two spectra:
of a WR star of the WC8 type and of a WR star of the WN8h
type.
The strength of the interstellar absorption features in the
optical
spectra of WR 48a and the near-by stars D2-3 and D2-7 (both
members
of the open cluster Danks 2) indicates that WR 48a is located
at
a distance of ~4 kpc from us. WR 48a is very likely a thermal
radio
source and for such a case and smooth (no clumps) wind its radio
emission suggests a relatively high mass-loss rate of this dusty
WR
star (dM/dt = a few x 10^(-4) solar masses per year). Long
timescale
(years) variability of WR 48a is established in the
optical, radio and
X-rays. Colliding stellar winds likely play a
very important role in
the physics of this object. However, some
LBV-like (luminous blue
variable) activity could not be excluded
as well.
Reference: Monthly Notices of the Royal
Astronomical Society
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1409.2684
Email:
szhekov@space.bas.bg
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P. M. Williams
Institute for Astronomy, Royal
Observatory, Edinburgh, United Kingdom
Visual photometry of 16
WC8-9 dust-making Wolf-Rayet (WR) stars during 2001--2009 was
extracted from the All Sky Automated Survey All Star Catalogue
(ASAS-3) to search for eclipses attributable to extinction by dust
formed in clumps in our line of sight. Data for a comparable number
of dust-free WC6-9 stars were also examined to help characterise the
dataset. Frequent eclipses were observed from WR 104, and several
from WR 106, extending the 1994-2001 studies by Kato et al.
(2002a,b), but not supporting their phasing the variations in WR 104
with its `pinwheel' rotation period. Only four other stars showed
eclipses, WR 50 (one of the dust-free stars), WR 69, WR 95 and WR
117, and there may have been an eclipse by WR 121, which had shown
two eclipses in the past. No dust eclipses were shown by the
`historic' eclipsers WR 103 and WR 113. The atmospheric eclipses of
the latter were observed but the suggestion by David-Uraz et al.
(2012) that dust may be partly responsible for these is not
supported. Despite its frequent eclipses, there is no evidence in the
infrared images of WR 104 for dust made in its eclipses,
demonstrating that any dust formed in this process is not a
significant contributor to its circumstellar dust cloud and
suggesting that the same applies to the other stars showing fewer
eclipses.
Reference: MNRAS (in Press)
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1408.6759
Comments:
Email: pmw@roe.ac.uk
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David H. Cohen (1), Zequn Li (1), Kenneth G. Gayley (2),
Stanley P. Owocki (3), Jon O. Sundqvist (3,4), Veronique Petit (3,5),
Maurice A. Leutenegger (6,7)
(1) Swarthmore College
(2)
Univ. Iowa
(3) Univ. Delaware
(4) Univ. Munich
(5)
Florida Tech
(6) NASA/GSFC
(7) CRESST and UMBC
We
present a new method for measuring the shock-heating rate in O star
winds directly from wind-absorption-corrected X-ray emission line
luminosities. This analysis method, applied to an ensemble of lines
each with different temperature sensitivity, naturally generates a
cumulative probability distribution of the wind shock-heating rate.
We apply this new technique to the analysis of the Chandra grating
spectra of five O stars and find similar results for all the sample
stars: (1) roughly a tenth of the wind mass passes through a shock of
2 million K or more; (2) the distribution of shock temperatures is a
strongly declining function, consistent with a power-law of index n =
-3; and (3) there are indications of a cut-off or faster fall-off in
the heating rate for shock temperatures above about 10 million K.
These results provide direct constraints for hydrodynamic simulations
of X-ray production in O star winds.
Reference: MNRAS
in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1409.0856
Comments:
Email: dcohen1@swarthmore.edu
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John D. Ilee (1), John Fairlamb (2), Rene D. Oudmaijer (2),
Ignacio Mendigutia (2), Mario van den Ancker (3), Stefan Kraus (4),
Hugh E. Wheelwright (5)
(1) University of St Andrews, UK;
(2) University of Leeds, UK;
(3) ESO, Garching; (4) University of
Exeter; (5) MPIfR, Bonn
Herbig Ae/Be stars lie in the mass
range between low and high mass young stars, and therefore offer a
unique opportunity to observe any changes in the formation processes
that may occur across this boundary. This paper presents medium
resolution VLT/X-Shooter spectra of six Herbig Ae/Be stars, drawn
from a sample of 91 targets, and high resolution VLT/CRIRES spectra
of five Herbig Ae/Be stars, chosen based on the presence of CO first
overtone bandhead emission in their spectra. The X-Shooter survey
reveals a low detection rate of CO first overtone emission (7 per
cent), consisting of objects mainly of spectral type B. A positive
correlation is found between the strength of the CO v=2-0 and Br
gamma emission lines, despite their intrinsic linewidths suggesting a
separate kinematic origin. The high resolution CRIRES spectra are
modelled, and are well fitted under the assumption that the emission
originates from small scale Keplerian discs, interior to the dust
sublimation radius, but outside the co-rotation radius of the central
stars. In addition, our findings are in very good agreement for the
one object where spatially resolved near-infrared interferometric
studies have also been performed. These results suggest that the
Herbig Ae/Be stars in question are in the process of gaining mass via
disc accretion, and that modelling of high spectral resolution
spectra is able to provide a reliable probe into the process of
stellar accretion in young stars of intermediate to high
masses.
Reference: MNRAS, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1409.4897
Comments:
Email: john.ilee@st-andrews.ac.uk
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F. Martins $^1$, W. Marcolino $^2$, D.J. Hillier $^3$,
J.-F. Donati $^4$, J.-C. Bouret $^5$
1- LUPM, CNRS &
Montpellier University; 2- Universidade do Rio de Janeiro; 3-
University of Pittsburgh; 4- IRAP, CNRS & Toulouse University; 5-
LAM, CNRS & Aix-Marseille University
Massive stars show a
variety of spectral variability: presence of discrete absorption
components in UV P-Cygni profiles, optical line profile variability,
X-ray variability, radial velocity modulations. Our goal is to study
the spectral variability of single OB stars to better understand the
relation between photospheric and wind variability. For that, we rely
on high spectral resolution, high signal-to-noise ratio optical
spectra collected with the spectrograph NARVAL on the Telescope
Bernard Lyot at Pic du Midi. We investigate the variability of twelve
spectral lines by means of the Temporal Variance Spectrum (TVS). The
selected lines probe the radial structure of the atmosphere, from the
photosphere to the outer wind. We also perform a spectroscopic
analysis with atmosphere models to derive the stellar and wind
properties, and to constrain the formation region of the selected
lines. We show that variability is observed in the wind lines of all
bright giants and supergiants, on a daily timescale. Lines formed in
the photosphere are sometimes variable, sometimes not. The dwarf
stars do not show any sign of variability. If variability is observed
on a daily timescale, it can also (but not always) be observed on
hourly timescales, albeit with lower amplitude. There is a very clear
correlation between amplitude of the variability and fraction of the
line formed in the wind. Strong anti-correlations between the
different part of the temporal variance spectrum are observed. Our
results indicate that variability is stronger in lines formed in the
wind. A link between photospheric and wind variability is not obvious
from our study, since wind variability is observed whatever the level
of photospheric variability. Different photospheric lines also show
different degrees of variability.
Reference: A&A
accepted
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1409.5057
Comments:
Email: fabrice.martins@univ-montp2.fr
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Ian D. Howarth (1)
Ian R. Stevens (2)
(1)
Department of Physics and Astronomy, University College London, Gower
St., London WC1E 6BT, UK
(2) School of Physics and Astronomy,
University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
We
report a time-series analysis of the O4I(n)fp star zeta Pup, based on
optical photometry obtained with the SMEI instrument on the Coriolis
satellite, 2003--2006. A single astrophysical signal is found, with P
= (1.780938 pm 0.000093) d and a mean semi-amplitude of (6.9 pm 0.3)
mmag. There is no evidence for persistent coherent signals with
semi-amplitudes in excess of ca. 2~mmag on any of the timescales
previously reported in the literature. In particular, there is no
evidence for a signature of the proposed rotation period, ca.
5.1~days; zeta Pup is therefore probably not an oblique magnetic
rotator. The 1.8-day signal varies in amplitude by a factor ca. 2 on
timescales of 10-100d (and probably by more on longer timescales),
and exhibits modest excursions in phase, but there is no evidence for
systematic changes in period over the 1000-d span of our
observations. Rotational modulation and stellar-wind variability
appear to be unlikely candidates for the underlying mechanism; we
suggest that the physical origin of the signal may be pulsation
associated with low-l oscillatory convection modes.
Reference:
Accepted in MNRAS
Status: Manuscript has been
accepted
Weblink:
http://adsabs.harvard.edu/abs/2014arXiv1409.5258H
Comments:
Email: idh@star.ucl.ac.uk
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Folatelli, Gastón(1); Bersten, Melina C.(1); Benvenuto,
Omar G.(2); Van Dyk,
Schuyler D.(3); Kuncarayakti, Hanindyo(4,5);
Maeda, Keiichi(6);
Nozawa, Takaya(7); Nomoto, Ken'ichi(1); Hamuy,
Mario(4,5); and Quimby,
Robert M.(1)
1 - Kavli
Institute for the Physics and Mathematics of the Universe
(WPI),
The University of Tokyo, Kashiwa, Chiba 277-8583, Japan;
2 -
Facultad de Ciencias Astronómicas y Geofísicas, Universidad
Nacional de La Plata, Paseo del Bosque S/N, B1900FWA La Plata,
Argentina;
3 - Spitzer Science Center/Caltech, Mailcode
220-6, Pasadena, CA
91125, USA;
4 - Millennium Institute of
Astrophysics (MAS), Casilla 36-D,
Santiago, Chile;
5 -
Departamento de Astronomía, Universidad de Chile, Casilla 36-D,
Santiago, Chile;
6 - Department of Astronomy, Kyoto
University,
Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502,
Japan;
7 - National Astronomical Observatory of Japan, Mitaka,
Tokyo
181-8588, Japan
We present Hubble Space Telescope
(HST) observations of the field of the Type IIb supernova (SN) 2011dh
in M51 performed at ≈1161 rest-frame days after explosion using the
Wide Field Camera 3 and near-UV filters F225W and F336W. A star-like
object is detected in both bands and the photometry indicates it has
negative (F225W - F336W) color. The observed object is compatible
with the companion of the now-vanished yellow supergiant progenitor
predicted in interacting binary models. We consider it unlikely that
the SN is undergoing strong interaction and thus estimate that it
makes a small contribution to the observed flux. The possibilities of
having detected an unresolved light echo or an unrelated object are
briefly discussed and judged unlikely. Adopting a possible range of
extinction by dust, we constrain parameters of the proposed binary
system. In particular, the efficiency of mass accretion onto the
binary companion must be below 50%, if no significant extinction is
produced by newly formed dust. Further multiband observations are
required in order to confirm the identification of the object as the
companion star. If confirmed, the companion star would already be
dominant in the UV-optical regime, so it would readily provide a
unique opportunity to perform a detailed study of its
properties.
Reference: ApJ 793, L22
Status:
Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2014ApJ...793L..22F
Comments:
6 pages, 3 figures
Email: melina.bersten@ipmu.jp
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Bersten, Melina C.(1); Benvenuto, Omar G.(2); Folatelli,
Gastón(1); Nomoto, Ken'ichi(1); Kuncarayakti, Hanindyo(3,4);
Srivastav, Shubham(5); Anupama, G. C.(5); Quimby, Robert(1); Sahu,
Devendra K.(5)
1 - Kavli Institute for the Physics and
Mathematics of the Universe
(WPI), The University of Tokyo,
Kashiwa, Chiba 277-8583, Japan;
2 - Facultad de Ciencias
Astronómicas y Geofísicas, Universidad
Nacional de La Plata,
Paseo del Bosque S/N, B1900FWA La Plata,
Argentina;
3 -
Millennium Institute of Astrophysics (MAS), Casilla 36-D,
Santiago,
Chile;
4 - Departamento de Astronomía, Universidad de Chile,
Casilla 36-D,
Santiago, Chile;
5 - Indian Institute of
Astrophysics, Koramangala, Bangalore 560034, India
The recent
detection in archival Hubble Space Telescope images of an object at
the location of supernova (SN) iPTF13bvn may represent the first
direct evidence of the progenitor of a Type Ib SN. The object's
photometry was found to be compatible with a Wolf-Rayet pre-SN star
mass of ≈11 M &sun;. However, based on hydrodynamical models,
we show that the progenitor had a pre-SN mass of ≈3.5 Msun; and
that it could not be larger than ≈ 8 Msun;. We propose an
interacting binary system as the SN progenitor and perform
evolutionary calculations that are able to self-consistently explain
the light curve shape, the absence of hydrogen, and the pre-SN
photometry. We further discuss the range of allowed binary systems
and predict that the remaining companion is a luminous O-type star of
significantly lower flux in the optical than the pre-SN object. A
future detection of such a star may be possible and would provide the
first robust identification of a progenitor system for a Type Ib
SN.
Reference: AJ, 148, 68
Status: Manuscript has
been accepted
Weblink:
http://adsabs.harvard.edu/abs/2014AJ....148...68B
Comments:
7 pages, 5 figures
Email: melina.bersten@ipmu.jp
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H. Sana [1,2], J.-B. Le Bouquin [3,4], S. Lacour [5], J.-P.
Berger [6], G. Duvert [3,4], L. Gauchet [5], B. Norris [7], J.
Olofsson [8], D. Pickel [5], G. Zins [3,4], O. Absil [9], A. de Koter
[10,11], K. Kratter [12,13], O. Schnurr [14], H. Zinnecker [15]
1.
European Space Agency / Space Telescope Science Institute, 3700 San
Martin Drive, Baltimore, MD 21218, United States
2. E-mail:
hsana@stsci.edu
3. Univ. Grenoble Alpes, IPAG, F-38000 Grenoble,
France
4. CNRS, IPAG, F-38000 Grenoble, France
5. LESIA,
Observatoire de Paris, CNRS, UPMC, Universit'e Paris-Diderot, Paris
Sciences et Lettres, 5 Place Jules Janssen, 92195 Meudon, France
6.
European Southern Observatory, Schwarzschild-Str. 2, 85748 Garching
bei M"unchen, Germany
7. Sydney Institute for Astronomy,
Institute for Photonics and Optical Science, School of Physics,
University of Sydney, NSW 2006, Australia
8. Max-Planck-Institut
f"ur Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany
9.
D'epartement d'Astrophysique, G'eophysique et Oc'eanographie,
Universit'e de Li`ege, 17 All'ee du Six Ao^ut, 4000 Li`ege, Belgium
10. Astrophysical Institute Anton Pannekoek, Universiteit van
Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands
11.
Instituut voor Sterrenkunde, Universiteit Leuven, Celestijnenlaan 200
D, 3001, Leuven, Belgium}
12. Hubble Fellow, JILA, 440 UCB,
University of Colorado, Boulder, CO 80309-0440, United States
13.
Steward Observatory / Dept. of Astronomy, University of Arizona, 933
N Cherry Ave, Tucson, AZ, 85721
14. Leibniz-Institut f"ur
Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
15. Deutsches SOFIA Institute, SOFIA Science Center, NASA Ames
Research Center, M.S, N232-12, Moffett Field CA 94035, United
States
Multiplicity is one of the most fundamental observable
properties of massive O-type stars and offers a promising way to
discriminate between massive star formation theories.
Nevertheless,
companions at separations between
1 and 100 milli-arcsec (mas)
remain mostly unknown due to intrinsic observational limitations. At
a typical distance of 2~kpc, this corresponds to projected physical
separations of 2-200~AU.
The Southern MAssive Stars at High
angular resolution survey (smash) was designed to fill this gap by
providing the first systematic interferometric survey of Galactic
massive stars. We observed 117 O-type stars with VLTI/PIONIER and 162
O-type stars with NACO/SAM, respectively probing the separation
ranges 1-45 and 30-250~mas and brightness contrasts of $Delta H <
4$ and $Delta H < 5$. Taking advantage of NACO's field-of-view, we
further uniformly searched for visual companions in an 8arcsec-radius
down to $Delta H = 8$.
This paper describes the observations and
data analysis, reports the discovery of almost 200 new companions in
the separation range from 1~mas to 8arcsec and presents the catalog
of detections, including the first resolved measurements of over a
dozen known long-period spectroscopic binaries.
Excluding
known runaway stars for which no companions are detected, 96 objects
in our main sample ($delta < 0$degr; $H<7.5$) were observed
both with PIONIER and NACO/SAM. The fraction of these stars with at
least one resolved companion within 200~mas is 0.53. Accounting for
known but unresolved spectroscopic or eclipsing companions, the
multiplicity fraction at separation $rho < 8$arcsec increases to
$f_mathrm{m}=0.91pm0.03$. The fraction of luminosity class V stars
that have a bound companion reaches 100% at 30~mas while their
average number of physically connected companions within 8arcsec is
$f_mathrm{c}=2.2pm0.3$.
This demonstrates that massive stars form
nearly exclusively in multiple systems. The nine non-thermal radio
emitters observed by smash are all resolved, including the newly
discovered pairs HD,168112 and CPD$-$47degr2963. This lends strong
support to the universality of the wind-wind collision scenario to
explain the non-thermal emission from O-type stars.
Reference:
ApJS, in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1409.6304
Comments:
Email: hsana@stsci.edu
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M. F. Muratore (1), M. Kraus (2), M. E. Oksala (2), M. L.
Arias (1), L. Cidale (1), M. Borges Fernandes (3), A. Liermann (4)
1
- Departamento de Espectroscopía Estelar, Facultad de Ciencias
Astronómicas y Geofísicas, Universidad Nacional de La Plata, and
Instituto de Astrofísica de La Plata, CCT La Plata, CONICET-UNLP,
Paseo del Bosque S/N, B1900FWA, La Plata, Argentina
2 -
Astronomický ústav, Akademie věd České Republiky, Fričova 298,
251 65 Ondřejov, Czech Republic
3 - Observatório Nacional, Rua
General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro,
Brazil
4 - Leibniz-Institut für Astrophysik Potsdam (AIP), An
der Sternwarte 16, 14482 Potsdam, Germany
The evolutionary
phase of B[e] stars is difficult to establish due to the
uncertainties in their fundamental parameters. For instance, possible
classifications for the Galactic B[e] star MWC 137 include
pre-main-sequence and post-main-sequence phases, with a large range
in luminosity. Our goal is to clarify the evolutionary stage of this
peculiar object, and to study the CO molecular component of its
circumstellar medium. To this purpose, we modeled the CO molecular
bands using high-resolution K-band spectra. We find that MWC 137 is
surrounded by a detached cool (T = 1900 +-100 K) and dense (N = (3 +-
1) x 10^{21} cm^{-2}) ring of CO gas orbiting the star with a
rotational velocity, projected to the line of sight, of 84 +- 2 km/s.
We also find that the molecular gas is enriched in the isotope 13C,
excluding the classification of the star as a Herbig Be. The observed
isotopic abundance ratio (12C / 13C = 25 +- 2) derived from our
modeling is compatible with a proto-PN, main-sequence or supergiant
evolutionary phase. However, based on some observable characteristics
of MWC 137, we propose that the supergiant scenario seems to be the
most plausible. Hence, we suggest that MWC 137 could be in an
extremely short-lived phase, evolving from a B[e] supergiant to a
blue supergiant with a bipolar ring nebula.
Reference: The
Astronomical Journal
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1409.7550
Comments:
Email: fmuratore@carina.fcaglp.unlp.edu.ar
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Simón-Díaz, S.; Herrero, A.; Sabín-Sanjulián, C.;
Najarro, F.; Garcia, M.; Puls, J.; Castro, N.; Evans, C. J.
IAC,
ULS, CAB/CSIC, USM, UBonn, ROE
We are now in an era of large
spectroscopic surveys of OB-type stars. Quantitative spectroscopic
analysis of these modern datasets is enabling us to review the
physical properties of blue massive stars with robust samples, not
only revisiting mean properties and general trends, but also
incorporating information about the effects of second-order
parameters. We investigate the spectral type -- effective temperature
(SpT - Teff) calibration for O-type dwarfs, and its claimed
dependence on metallicity, using statistically-meaningful samples of
stars extracted from the IACOB and VFTS surveys. We perform a
homogeneous differential spectroscopic analysis of 33 Galactic and 53
LMC O~dwarfs (spanning spectral types of O4 -- O9.7) using the
IACOB-GBAT package, a $chi^2$-fitting algorithm based on a large
pre-computed grid of FASTWIND models, and standard techniques for the
hydrogen/helium analysis of O-type stars. We compare the estimated
effective temperatures and gravities as a function of (internally
consistent) spectral classifications. While the general trend is that
the temperature of a star increases with earlier spectral types and
decreasing metallicity, we show that the large range of gravities
found for O-type dwarfs -- spaning up to 0.45-0.50 dex in some
spectral bins -- plays a critical role on the dependence of the
effective temperature calibrations as a function of spectral type and
metallicity. This result warns us about the use of SpT - Teff
calibrations for O-dwarfs which ignore the effects of gravity, and
highlights the risks of employing calibrations based on small
samples. The effects of this scatter in gravities (evolutionary
status) for O-type dwarfs should be included in future recipes which
employ SpT - Teff calibrations.
Reference:
http://arxiv.org/abs/1409.6653
Status: Manuscript has been
accepted
Weblink:
Comments: Accepted for
publication in A&A letters
Email: ssimon@iac.es
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E. J. Aldoretta (1,2), S. M. Caballero-Nieves (3), D. R.
Gies (1), E. P. Nelan (4), D. J. Wallace (5,6), W. I. Hartkopf (7),
T. J. Henry (1), W.-C. Jao (1), J. Maíz Apellániz (8), B. D. Mason
(7), A. F. J. Moffat (2), R. P. Norris (1), N. D. Richardson (2), S.
J. Williams (9)
(1) Center for High Angular Resolution
Astronomy, Department of Physics and Astronomy, Georgia State
University, Atlanta, GA, USA
(2) Departement de physique and
Centre de Recherche en Astrophy
sique du Quebec (CRAQ),
Universite de Montreal, Montreal, Qc, Canada
(3) Department of
Physics and Astronomy, University of Sheffield, Sheffield, United
Kingdom
(4) Space Telescope Science Institute, Baltimore, MD, USA
(5) Department of Natural Science, University of South Carolina,
Beaufort, SC, USA
(6) NASA, Astrophysics Division, Washington,
DC, USA
(7) US Naval Observatory, Astronomy Department,
Washington, DC, USA
(8) Instituto de Astrofısica de Andalucı,
Granada, Spain
(9) Institute for Astronomy, Astrophysics, Space
Applications and Remote Sensing (IAASARS), National Observatory of
Athens, Athens, Greece
We present the results of an all-sky
survey made with the Fine Guidance Sensor on Hubble Space Telescope
to search for angularly resolved binary systems among the massive
stars. The sample of 224 stars is comprised mainly of Galactic O- and
B-type stars and Luminous Blue Variables, plus a few luminous stars
in the Large Magellanic Cloud. The FGS TRANS mode observations are
sensitive to detection of companions with an angular separation
between 0."01 and 1."0 and brighter than △m=5. The FGS
observations resolved 52 binary and 6 triple star systems and
detected partially resolved binaries in 7 additional targets (43 of
these are new detections). These numbers yield a companion detection
frequency of 29% for the FGS survey. We also gathered literature
results on the numbers of close spectroscopic binaries and wider
astrometric binaries among the sample, and we present estimates of
the frequency of multiple systems and the companion frequency for
subsets of stars residing in clusters and associations, field stars,
and runaway stars. These results confirm the high multiplicity
fraction, especially among massive stars in clusters and
associations. We show that the period distribution is approximately
flat in increments of log P. We identify a number of systems of
potential interest for long term orbital determinations, and we note
the importance of some of these companions for the interpretation of
the radial velocities and light curves of close binaries that have
third companions.
Reference: The Astronomical
Journal
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1410.0021
Comments:
Email: emily@astro.umontreal.ca
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J. O. Yam (1), S. A. Dzib (2), L. F. Rodríguez (3,4) and
V. Rodríguez-Gomez (5)
1 - Departamento de Ciencias,
Universidad de Quintana Roo, Mexico.
2 - Max-Planck-Institut fuer
Radioastronomie, Bonn, Germany.
3 - Centro de Radioastronomia y
Astrofisica, UNAM, Mexico.
4 - Astronomy Department, Faculty of
Science, King Abdulaziz University, Jeddah, Saudi Arabia
5 -
Harvard-Smithsonian Center for Astrophysics, USA.
We analyzed
64 radio observations at the frequency of 8.4 GHz of the Wolf-Rayet
star WR 112, taken from the Very Large Array archive. These
observations cover a time baseline of 13 years, from June 2000 to
July 2013. The radio structure of WR 112 is consistent with it being
a point source in all the epochs and with its flux density varying
from 0.6 mJy to 2.1 mJy. We tried to search for periodicities in
these variations but our results were not conclusive. We also looked
for extended emission from the infrared nebula that surrounds WR 112,
setting upper limits of 50 μJy. Finally, we used the highest angular
resolution images to measure the proper motions of WR 112, obtaining
μ_{α}cos(δ)=−2.6±1.1 mas/yr, and μ_{δ}=−5.4±1.4 mas/yr.
These proper motions are smaller than those previously reported, but
still suggest significant peculiar motions for WR 112.
Reference:
Revista Mexicana de Astronomía y Astrofísica
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1409.6484
Comments:
Email: sdzib@mpifr-bonn.mpg.de
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F. Tramper (1), H. Sana (2), A. de Koter (1,3), L. Kaper
(1), and O. H. Ramirez-Agudelo (1)
(1) - Anton Pannekoek
Institute for Astronomy, University of Amsterdam
(2) - ESA -
Space Telescope Science Institute
(3) - Instituut voor
Sterrenkunde, University of Leuven
Massive stars likely played
an important role in the reionization of the Universe, and the
formation of the first black holes. They are potential progenitors of
long-duration gamma-ray bursts, seen up to redshifts of about ten.
Massive stars in low-metallicity environments in the local Universe
are reminiscent of their high redshift counterparts, emphasizing the
importance of the study of their properties and evolution. In a
previous paper, we reported on indications that the stellar winds of
low-metallicity O stars may be stronger than predicted, which would
challenge the current paradigm of massive star evolution.
In this
paper, we aim to extend our initial sample of six O stars in
low-metallicity environments by four. The total sample of ten stars
consists of the optically brightest sources in IC1613, WLM, and
NGC3109. We aim to derive their stellar and wind parameters, and
compare these to radiation-driven wind theory and stellar evolution
models.
We have obtained intermediate-resolution VLT/X-Shooter
spectra of our sample of stars. We derive the stellar parameters by
fitting synthetic Fastwind line profiles to the VLT/X-Shooter spectra
using a genetic fitting algorithm. We compare our parameters to
evolutionary tracks and obtain evolutionary masses and ages. We also
investigate the effective temperature versus spectral type
calibration for SMC and lower metallicities. Finally, we reassess the
wind momentum versus luminosity diagram.
The derived parameters
of our target stars indicate stellar masses that reach values of up
to 50 Msun. The wind strengths of our stars are, on average, stronger
than predicted from radiation-driven wind theory and reminiscent of
stars with an LMC metallicity. We discuss indications that the iron
content of the host galaxies is higher than originally thought and is
instead SMC-like. We find that the discrepancy with theory is
reduced, but remains significant for this higher metallicity. This
may imply that our current understanding of the wind properties of
massive stars, both in the local universe as well as at cosmic
distances, remains incomplete.
Reference: Astronomy &
Astrophysiscs
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1410.0934
Comments:
Email: F.Tramper@uva.nl
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Matthieu Palate, Gregor Rauw
Institut
d'Astrophysique & Geophysique, Liège University
Plaskett's
star (HD47129) is a very massive O-star binary in a post Roche-lobe
overflow stage. CoRoT observations of this system revealed
photometric variability with a number of frequencies. The aim of this
paper is to characterize the variations in spectroscopy and
investigate their origin. To sample its short-term variability,
HD47129 was intensively monitored during two spectroscopic campaigns
of six nights each. The spectra were disentangled and Fourier
analyses were performed to determine possible periodicities and to
investigate the wavelength dependence of the phase constant and the
amplitude of the periodicities. Complex line profile variations are
observed. Frequencies near 1.65, 0.82, and 0.37 d^-1 are detected
consistently in the He I 4471, He II 4542, and N III 4510-4518 lines.
These frequencies are consistent with those of the strongest signals
detected in photometry. The possibilities that these variations stem
from pulsations, a recently detected magnetic field or tidal
interactions are discussed. Whilst all three scenarios have their
strengths, none of them can currently account for all the observed
properties of the line profile variations.
Reference: A&A
in press
Status: Manuscript has been accepted
Weblink:
arXiv:1410.1801
Comments:
Email: palate@astro.ulg.ac.be
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Messineo M. (1,2,3), Qingfeng Z. (4), Ivanov V. D. (5),
Figer D. F. (3), Davies B. (6), Menten K. M. (1), Kudritzki R. P.
(7), Chen C.-H. R. (1)
MPIfR(1), ESA(2), RIT(3),
University of Science and Technology of China(4), ESO(5), Liverpool
John Moores University(6), University of Hawaii(7)
Clear
identifications of Galactic young stellar clusters farther than a few
kpc from the Sun are rare, despite the large number of candidate
clusters.
We aim to improve the selection of candidate clusters
rich in massive stars with a multiwavelength analysis of photometric
Galactic data that range from optical to mid-infrared wavelengths.
We present a photometric and spectroscopic analysis of five
candidate stellar clusters,
which were selected as overdensities
with bright stars (Ks <7 mag) in GLIMPSE and 2MASS images. A total
of 48 infrared spectra were obtained. The combination of photometry
and spectroscopy yielded six new red supergiant stars with masses
from 10 Msun to 15 Msun. Two red supergiants are located at Galactic
coordinates (l,b) (16.7 deg, -0.63 deg) and at a distance of about
3.9 kpc; four other red supergiants are members of a cluster at
Galactic coordinates (l,b)=(49.3 deg,+0.72 deg) and at a distance of
~7.0 kpc.
Spectroscopic analysis of the brightest stars of
detected overdensities and studies of interstellar extinction along
their line of sights are fundamental to distinguish regions of low
extinction from actual stellar clusters. The census of young star
clusters containing red supergiants is incomplete; in the existing
all-sky near-infrared surveys, they can be identified as
overdensities of bright stars with infrared color-magnitude diagrams
characterized by gaps.
Reference: A&A
Status:
Manuscript has been accepted
Weblink:
http://cdsads.u-strasbg.fr/abs/2014arXiv1409.7906M
Comments:
Email: messineo@mpifr-bonn.mpg.de
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J. Garcia-Rojas, S. Simon-Diaz, C. Esteban
(1)
IAC, Tenerife, Spain, (2) Dep. Astrofísica, ULL, tenerife,
Spain
Main sequence massive stars embedded in an Hii region
should have the same chemical abundances as the surrounding nebular
gas+dust. The Cocoon nebula (IC5146), a close-by Galactic Hii region
ionized by a narrow line B0.5 V single star (BD+46 3474), is an ideal
target to perform a detailed comparison of nebular and stellar
abundances in the same Galactic Hii region.
We investigate
the chemical content of oxygen and other elements in the Cocoon
nebula from two different points of view: an empirical analysis of
the nebular spectrum and a detailed spectroscopic analysis of the
associated early B-type star using state-of-the-art stellar
atmosphere modeling. By comparing the stellar and nebular abundances,
we aim to indirectly address the long-standing problem of the
discrepancy found between abundances obtained from collisionally
excited lines and optical recombination lines in photoionized
nebulae.
We collect long-slit spatially resolved spectroscopy
of the Cocoon nebula and a high resolution optical spectrum of the
ionizing star. Standard nebular techniques along with updated atomic
data are used to compute the physical conditions and gaseous
abundances of O, N and S in 8 apertures extracted across a
semidiameter of the nebula. We perform a self-consistent
spectroscopic abundance analysis of BD+46 3474 based on the
atmosphere code FASTWIND to determine the stellar parameters and Si,
O, and N abundances.
The Cocoon nebula and its ionizing star,
located at a distance of 800±80 pc, have a very similar chemical
composition as the Orion nebula and other B-type stars in the solar
vicinity. This result agrees with the high degree of homogeneity of
the present-day composition of the solar neighbourhood (up to 1.5 Kpc
from the Sun) as derived from the study of the local cold-gas ISM.
The comparison of stellar and nebular collisionally excited line
abundances in the Cocoon nebula indicates that O and N gas+dust
nebular values are in better agreement with stellar ones assuming
small temperature fluctuations, of the order of those found in the
Orion nebula (t^2 = 0.022). For S, the behaviour is somewhat
puzzling, reaching to different conclusions depending on the atomic
data set used.
Reference: A&A (in press)
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1410.0119
Comments:
Email: ssimon@iac.es
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N. Castro, L. Fossati, N. Langer, S. Simón-Díaz, F. R. N.
Schneider, R. G. Izzard
(1) Argelander-Institut für
Astronomie der Universität Bonn (2) Instituto de Astrofisica de
Canarias (3) Universidad de La Laguna
The distribution of
stars in the Hertzsprung-Russell diagram narrates their evolutionary
history and directly assesses their properties. Placing stars in this
diagram however requires the knowledge of their distances and
interstellar extinctions, which are often poorly known for Galactic
stars. The spectroscopic Hertzsprung-Russell diagram (sHRD) tells
similar evolutionary tales, but is independent of distance and
extinction measurements. Based on spectroscopically derived effective
temperatures and gravities of almost 600 stars, we derive for the
first time the observational distribution of Galactic massive stars
in the sHRD. While biases and statistical limitations in the data
prevent detailed quantitative conclusions at this time, we see
several clear qualitative trends. By comparing the observational sHRD
with different state-of-the-art stellar evolutionary predictions, we
conclude that convective core overshooting may be mass-dependent and,
at high mass ($geq 15,M_odot$), stronger than previously thought.
Furthermore, we find evidence for an empirical upper limit in the
sHRD for stars with $T_{rm{eff}}$ between 10000 and 32000 K and, a
strikingly large number of objects below this line. This over-density
may be due to inflation expanding envelopes in massive main-sequence
stars near the Eddington limit.
Reference: A&A
Letters
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1410.3499
Comments:
Email: norberto@astro.uni-bonn.de
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C. R. Shrader, K. Hamaguchi, S. J. Sturner, L.M. Oskinova,
T. Almeyda, R.Petre
Astrophysics Science Division,
NASA/GSFC, Greenbelt, MD 20771, et al.
We present the results
of a broad-band X-ray study of the enigmatic Be star Gamma
Cassiopeiae (herein gamma Cas) based on observations made with both
the Suzaku and INTEGRAL observatories. gamma Cas has long been
recognized as the prototypical example of a small subclass of Be
stars with moderately strong X-ray emission dominated by a hot
thermal component in the 0.5-12 keV energy range Lx ~ 10^32 - 10^33
erg s^-1. This places them at the high end of the known luminosity
distribution for stellar emission, but several orders of magnitude
below typical accretion powered Be X-ray binaries. The INTEGRAL
observations spanned an 8 year baseline and represent the deepest
measurement to date at energies above ~50 keV. We find that the
INTEGRAL data are consistent within statistics to a constant
intensity source above 20 keV, with emission extending up to ~100 keV
and that searches for all of the previously reported periodicities of
the system at lower energies led to null results. We further find
that our combined Suzaku and INTEGRAL spectrum, which we suggest is
the most accurate broad-band X-ray measurement of gamma Cas to date,
is fitted extremely well with a thermal plasma emission model with a
single absorption component. We found no compelling need for an
additional non-thermal high-energy component. We discuss these
results in the context of a currently favored models for gamma Cas
and its analogs.
Reference: accepted for publication in
ApJ
Status: Manuscript has been accepted
Weblink:
arXiv:1410.4050
Email:
Chris.R.Shrader@nasa.gov
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Kenji Hamaguchi, Michael F. Corcoran, Hiromitsu Takahashi,
Takayuki Yuasa, Manabu Ishida, Theodore R. Gull, Julian M. Pittard,
Christopher M. P. Russell, Thomas I. Madura
NASA/GSFC,
UMBC, USRA, Hiroshima University, RIKEN, ISAS/JAXA, The University of
Leeds, University of Delaware, NPP
The Suzaku X-ray
observatory monitored the supermassive binary system Eta Carinae 10
times during the whole 5.5 year orbital cycle between 2005-2011. This
series of observations presents the first long-term monitoring of
this enigmatic system in the extremely hard X-ray band between 15-40
keV. During most of the orbit, the 15-25 keV emission varied
similarly to the 2-10 keV emission, indicating an origin in the hard
energy tail of the kT ~4 keV wind-wind collision (WWC) plasma.
However, the 15-25 keV emission declined only by a factor of 3 around
periastron when the 2-10 keV emission dropped by two orders of
magnitude due probably to an eclipse of the WWC plasma. The observed
minimum in the 15-25 keV emission occurred after the 2-10 keV flux
had already recovered by a factor of ~3. This may mean that the WWC
activity was strong, but hidden behind the thick primary stellar wind
during the eclipse. The 25-40 keV flux was rather constant through
the orbital cycle, at the level measured with INTEGRAL in 2004. This
result may suggest a connection of this flux component to the
gamma-ray source detected in this field. The Helium-like Fe Kalpha
line complex at ~6.7 keV became strongly distorted toward periastron
as seen in the previous cycle. The 5-9 keV spectra can be reproduced
well with a two-component spectral model, which includes plasma in
collision equilibrium (CE) and a plasma in non-equilibrium ionization
(NEI) with tau ~1e11 cm-3 s-1. The NEI plasma increases in importance
toward periastron.
Reference: Astrophysical Journal,
2014, 795, 119 (arXiv1410.6171)
Status: Manuscript has been
accepted
Email: Kenji.Hamaguchi@nasa.gov
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J. Lorenzo (1), I. Negueruela (1), A.K.F. Val Baker (2), M.
García (3), S. Simón-Díaz (4), P. Pastor (1), and M. Méndez
Majuelos (5)
1-Universidad Alicante;2-University Malaya;
3-CSIC-INTA; 4-IAC; 5-IES Arroyo Hondo
Context. The early-type
binary MY Cam belongs to the young open cluster Alicante 1, embedded
in Cam OB3.
Aims. MY Cam consists of two early-O type
main-sequence stars and shows a photometric modulation suggesting an
orbital period slightly above one day. We intend to confirm this
orbital period and derive orbital and stellar parameters.
Methods.
Timing analysis of a very exhaustive (4607 points) light curve
indicates a period of 1.1754514 ± 0.0000015 d. High-resolution
spectra and the cross-correlation technique implemented in the TODCOR
program were used to derive radial velocities and obtain
the
corresponding radial velocity curves for MY Cam. Modelling with the
stellar atmosphere code FASTWIND was used to obtain stellar
parameters and create templates for cross-correlation. Stellar and
orbital parameters were derived using the Wilson-Devinney code, such
that a complete solution to the binary system could be described.
Results. The determined masses of the primary and secondary stars
in MY Cam are 37.7 ± 1.6 and 31.6 ± 1.4 Msol , respectively. The
corresponding temperatures, derived from the model atmosphere fit,
are 42 000 and 39 000 K, with the more massive component being
hotter. Both stars are overfilling their Roche lobes, sharing a
common envelope.
Conclusions. MY Cam contains the most massive
dwarf O-type stars found so far in an eclipsing binary. Both
components are still on the main sequence, and probably not far from
the zero-age main sequence. The system is a likely merger progenitor,
owing to its very short period.
Reference: DOI:
10.1051/0004-6361/201424345
Status: Manuscript has been
accepted
Weblink:
http://esoads.eso.org/abs/2014arXiv1410.5575L
Comments:
Email: fjle3@alu.ua.es
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Staritsin E.
Astronomical Observatory, Ural
Federal University, Yekaterinburg
The evolution of rapidly
rotating 8, 4, and 2 solar masses main-sequence stars is considered
together with hydrodynamical transfer in their interiors. The
conditions under which turbulent erosion, semiconvection, and shear
turbulence lead to partial mixing of the matter in the radiative
envelope and central regions of the stars are determined. The
enhancement of the surface helium abundance with time depends on both
the intensity of partial mixing in their interiors and mass loss by
the stellar wind. The ratio of the number densities of helium and
hydrogen at the surface can rise by the end of main-sequence stage by
~30% for a 8 solar mass star and ~10-20% for a 4 solar mass star,
depending on the mass-loss rate. Partial mixing of the matter in the
radiative envelope and in the central region of the star can provide
an explanation for the observed enhancement of the atmospheric helium
abundances of early B stars toward the end of their main-sequence
evolution. The enhancement of the surface helium abundance in a 2
solar mass star is so small that it cannot be detected, and is
appreciably lower than the enhancement beneath the
surface.
Reference: Astronomy Reports
Status:
Manuscript has been accepted
Weblink:
Comments:
Email: Evgeny.Staritsin@urfu.ru
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Jiri Krticka, Petr Kurfurst, Iva Krtickova
Masaryk
University, Brno, Czech Republic
Evolutionary models of
fast-rotating stars show that the stellar rotational velocity may
approach the critical speed. Critically rotating stars cannot spin up
more, therefore they lose their excess angular momentum through an
equatorial outflowing disk. The radial extension of such disks is
unknown, partly because we lack information about the radial
variations of the viscosity. We study the magnetorotational
instability, which is considered to be the origin of anomalous
viscosity in outflowing disks. We used analytic calculations to study
the stability of outflowing disks submerged in the magnetic field.
The magnetorotational instability develops close to the star if the
plasma parameter is large enough. At large radii the instability
disappears in the region where the disk orbital velocity is roughly
equal to the sound speed. The magnetorotational instability is a
plausible source of anomalous viscosity in outflowing disks. This is
also true in the region where the disk radial velocity approaches the
sound speed. The disk sonic radius can therefore be roughly
considered as an effective outer disk radius, although disk material
may escape from the star to the insterstellar medium. The radial
profile of the angular momentum-loss rate already flattens there,
consequently, the disk mass-loss rate can be calculated with the
sonic radius as the effective disk outer radius. We discuss a
possible observation determination of the outer disk radius by using
Be and Be/X-ray binaries.
Reference: Astronomy &
Astrophysics, in press
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1410.7831
Comments:
Email: krticka@physics.muni.cz
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Romano L. M. Corradi (1,2), Nicolas Grosso (3), Agnès
Acker (3), Robert Greimel (4) and Patrick Guillout (3)
1 -
Instituto de Astrofísica de Canarias, 38200, La Laguna, Tenerife,
Spain
2 - Departamento de Astrofísica, Universidad de La Laguna,
38206, La Laguna, Tenerife, Spain
3 - Observatoire Astronomique
de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de
l’Université, 67000 Strasbourg, France
4 - IGAM, Institut für
Physik, Universität Graz, Universitätsplatz 5/II, 8010 Graz,
Austria
Context. The recently discovered bipolar outflow Ou4
has a projected size of more than one degree in the plane of the sky.
It is apparently centred on the young stellar cluster – whose most
massive representative is the triple system HR 8119 – inside the
H II region Sh 2-129. The driving source, the nature, and the
distance of Ou4 are not known.
Aims. The basic properties of
Ou4 and its environment are investigated to shed light on the origin
of this remarkable outflow.
Methods. Deep narrow-band imagery
of the whole nebula at arcsecond resolution was obtained to study the
details of its morphology. Long-slit spectroscopy of the bipolar lobe
tips was secured to determine the gas ionisation mechanism, physical
conditions, and line-of-sight velocities. An estimate of the proper
motions at the tip of the south lobe using archival plate images was
attempted. The existing multi-wavelength data for Sh 2-129 and HR
8119 were also comprehensively reviewed.
Results. The
observed morphology of Ou4, its emission-line spatial distribution,
line flux ratios, and the kinematic modelling developed adopting a
bow-shock parabolic geometry, illustrate the expansion of a
shock-excited fast collimated outflow. The observed radial velocities
of Ou4 and its reddening are consistent with those of Sh 2-129 and HR
8119. The improved determination of the distance to HR 8119 (composed
of two B0 V and one B0.5 V stars) and Sh 2-129 is 712 pc. We identify
in WISE images at 22 μm an emission bubble of 5 arcmin radius (1 pc
at the distance above) emitted by hot (107 K) dust grains, located
inside the central part of Ou4 and corresponding to several [O III]
emission features of Ou4.
Conclusions. The apparent position
of Ou4 and the properties studied in this work are consistent with
the hypothesis that Ou4 is located inside the Sh 2-129 H ii region,
suggesting that it was launched some 90 000 yr ago by HR 8119. The
outflow total kinetic energy is estimated to be
~4e47 ergs.
However, we cannot rule out the alternative possibility that Ou4 is a
bipolar planetary nebula or the result of an eruptive event on a
massive AGB or post–AGB star not yet identified.
Reference:
A&A 570, A105 (2014)
Status: Other
Weblink:
http://www.aanda.org/articles/aa/abs/2014/10/aa22718-13/aa22718-13.html
Comments:
Email: rcorradi@iac.es
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Ignacio Araya(1), Michel Cure(1)
and Lydia S. Cidale(2)
(1) Instituto de Fisica y
Astronomia, Universidad de Valparaıso, Chile;
(2) Departamento
de Espectroscopıa, Facultad de Ciencias Astronomicas y Geofısicas,
Universidad Nacional de La Plata and Instituto de Astrofısica La
Plata, CCT La Plata, CONICET-UNLP,
Accurate mass-loss rate
estimates are crucial keys in the study of wind properties of massive
stars and for testing different evolutionary scenarios. From a
theoretical point of view, this implies solving a complex set of
differential equations in which the radiation field and the
hydrodynamics are strongly coupled. The use of an analytical
expression to represent the radiation force and the solution of the
equation of motion has many advantages over numerical integrations.
Therefore, in this work, we present an analytical expression as a
solution of the equation of motion for radiation-driven winds in
terms of the force multiplier parameters. This analytical expression
is obtained by employing the line acceleration expression given by
Villata and the methodology proposed by Müller & Vink. On the
other hand, we find useful relationships to determine the parameters
for the line acceleration given by Müller & Vink in terms of the
force multiplier parameters.
Reference: ApJ, 795 81
(2014)
Status: Other
Weblink:
http://arxiv.org/abs/1411.0751
Comments:
Email: michel.cure@uv.cl
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Jon O. Sundqvist(1)
1. University Observatory of
Munich
A quite remarkable aspect of non-interacting O-stars
with detected surface magnetic fields is that they all are very slow
rotators. This paper uses this unique property to first demonstrate
that the projected rotational speeds of massive, hot stars, as
derived using current standard spectroscopic techniques, can be
severely overestimated when significant ``macroturbulent''
line-broadening is present. This may, for example, have consequences
for deriving the statistical distribution of rotation rates in
massive-star populations, and for the use of these rates in stellar
evolution models. It is next shown how such macroturbulence
(seemingly a universal feature of hot, massive stars) is present in
all but one of the magnetic O-stars, namely NGC 1624-2. Assuming then
a simple model in which NGC 1624-2's exceptionally strong,
large-scale magnetic field suppresses atmospheric motions down to
layers where the magnetic and gas pressures are comparable, first
empirical constraints on the formation depth of this enigmatic
hot-star macroturbulence are derived. The results suggest an origin
in the thin sub-surface convection zone of massive stars, consistent
with a physical origin due to, e.g., stellar pulsations excited by
the convective motions.
Reference: 6 pages, 2 figures,
to appear in Proc. IAU307: New windows on massive stars:
asteroseismology, interferometry, and spectropolarimetry, Editors: G.
Meynet, C. Georgy, J.H. Groh & Ph. Stee
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1409.0028
Comments:
Email: mail@jonsundqvist.com
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D. Vanbeveren
Astronomy and Astrophysics
Research Group
Vrije Universiteit Brussels
We review
massive star population synthesis with a realistic population of
binaries, research that started in the late sixties, early seventies.
We focus on the comparison between observed star numbers (as a
function of metallicity) and theoretically predicted numbers of
stellar populations in regions of continuous star formation and in
starburst regions. Special attention is given to the O-type star/WR
star/red supergiant star populations, the population of blue
supergiants, the supernova rates. Finally, we consider massive double
compact star mergers and the link with gravitational wave sources
(the advanced LIGO II).
Reference: ppt presentation of
a review paper presented at the conference 'Binary systems, their
evolution and environments' that was held in UlaanBaatar, Mongolia,
1-5 September 2014
Status: Conference proceedings
Weblink:
http://mongolia.csp.escience.cn/dct/page/65580
Comments:
Email: dvbevere@vub.ac.be
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J. Puls(1), J.O. Sundqvist(1), N. Markova(2)
1 -
University Observatory Munich, Germany
2 - Institute of Astronomy
with NAO Smolyan, Bulgaria
We review potential mass-loss
mechanisms in the various evolutionary stages of massive stars, from
the well-known line-driven winds of O-stars and BA supergiants to the
less-understood winds from Red Supergiants. We discuss optically
thick winds from Wolf-Rayet stars and Very Massive Stars, and the
hypothesis of porosity-moderated, continuum-driven mass loss from
stars formally exceeding the Eddington limit, which might explain the
giant outbursts from Luminous Blue Variables. We finish this review
with a glance on the impact of rapid rotation, magnetic fields and
small-scale inhomogeneities in line-driven winds.
Reference:
Invited review to appear in: New windows on massive stars:
asteroseismology, interferometry, and spectropolarimetry. G. Meynet,
C. Georgy, J.H. Groh & Ph. Stee, eds.
Status: Conference
proceedings
Weblink: http://arxiv.org/abs/1409.3582
Email:
uh101aw@usm.uni-muenchen.de
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J. Maíz Apellániz
Centro de Astrobiología
(INTA-CSIC)
We have recently derived a family of extinction
laws for 30 Doradus that provides better fits to the optical
photometry of obscured stars in the Galaxy and the LMC.
Simultaneously, we are extending our Galactic O-Star Spectroscopic
Survey (GOSSS) to fainter, more extinguished stars to obtain accurate
spectral types for massive stars with more than 6 magnitudes of
V-band extinction. I have combined both lines of research with 2MASS,
WISE, and Spitzer photometry to obtain the 1-10 micron extinction law
for O stars in the solar neighborhood. I present these results and
compare them with the extinction laws in the same wavelength range
derived from late-type stars and H II regions. I also discuss plans
to extend the newly derived optical-IR extinction laws to the
UV.
Reference: To appear in Highlights of Spanish
Astrophysics VIII, Proceedings of the XI Scientific Meeting of the
Spanish Astronomical Society held on September 8-12, 2014, in Teruel,
Spain.
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1410.5184
Email:
jmaiz@cab.inta-csic.es
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contents
J. Salas, J. Maíz Apellániz, and R. H. Barbá
Agrupación
Astronómica de Huesca, Centro de Astrobiología, Universidad de La
Serena
We have conducted a 1.5 year-long variability study of
the stars in the Cygnus OB2 association, the region in the northern
hemisphere with the highest density of optically visible massive
stars. The survey was conducted using four pointings in the Johnson R
and I bands with a 35 cm Meade LX200-ACF telescope equipped with a
3.2 Mpixel SBIG ST10-XME CCD camera and includes 300+ epochs in each
filter. A total of 1425 objects were observed with limiting
magnitudes of 15 in R and 14 in I. The photometry was calibrated
using reference stars with existing UBVJHK photometry. Bright stars
have precisions better than 0.01 magnitudes, allowing us to detect 52
confirmed and 19 candidate variables, many of them massive stars
without previous detections as variables. Variables are classified as
eclipsing, pulsating, irregular/long period, and Be. We derive the
phased light curves for the eclipsing binaries, with periods ranging
from 1.3 to 8.5 days.
Reference: To appear in
Highlights of Spanish Astrophysics VIII, Proceedings of the XI
Scientific Meeting of the Spanish Astronomical Society held on
September 8-12, 2014, in Teruel, Spain.
Status: Conference
proceedings
Weblink: http://arxiv.org/abs/1410.6767
Email:
jmaiz@cab.inta-csic.es
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contents
J. Maíz Apellániz, L. Úbeda, R. H. Barbá, J. W.
MacKenty, J. I. Arias, and A. I. Gómez de Castro
CAB,
STScI, ULS, STScI, ULS, UCM
We present a multi-filter
HST/WFPC2 UV-optical study of the Hourglass region in M8. We have
extracted the stellar photometry of the sources in the area and
obtained the separations and position angles of the Herschel 36
multiple system: for Herschel 36 D we detect a possible orbital
motion between 1995 and 2009. We have combined our data with archival
IUE spectroscopy and measured the Herschel 36 extinction law,
obtaining a different result from that of Cardelli et al. (1989) due
to the improvement in the quality of the optical-NIR data, in
agreement with the results of Maíz Apellániz et al. (2014). A large
fraction of the UV flux around Herschel 36 arises from the Hourglass
and not directly from the star itself. In the UV the Hourglass
appears to act as a reflection nebula located behind Herschel 36
along the line of sight. Finally, we also detect three new
Herbig-Haro objects and the possible anisotropic expansion of the
Hourglass Nebula.
Reference: To appear in Highlights of
Spanish Astrophysics VIII, Proceedings of the XI Scientific Meeting
of the Spanish Astronomical Society held on September 8-12, 2014, in
Teruel, Spain.
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1410.6766
Email:
jmaiz@cab.inta-csic.es
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contents
J. Maíz Apellániz, E. J. Alfaro, J.
I. Arias, R. H. Barbá, R. C. Gamen, A. Herrero, J. R. S. Leão, A.
Marco, I. Negueruela, S. Simón-Díaz, A. Sota, and N. R.
Walborn
CAB, IAA, ULS, ULS, IALP, IAC+ULL, UFRG, UA, UA,
IAC+ULL, IAA, and STScI
In this poster we present three
developments related to the Galactic O-Star Spectroscopic Survey
(GOSSS). First, we are making public the first version of MGB, an IDL
code that allows the user to compare oberved spectra to a grid of
spectroscopic standards to measure spectral types, luminosity
classes, rotation indexes, and spectral qualifiers. Second, we
present the associated grid of standard stars for the spectral types
O2 to O9.7, with several improvements over the original GOSSS grid of
Sota et al. (2011). Third, we present a list of egregious
classification errors in SIMBAD: stars that are or have been listed
there as being of O type but that in reality are late-type
stars.
Reference: To appear in Highlights of Spanish
Astrophysics VIII, Proceedings of the XI Scientific Meeting of the
Spanish Astronomical Society held on September 8-12, 2014, in Teruel,
Spain.
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1410.7615
Comments:
Email: jmaiz@cab.inta-csic.es
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S. Simón-Díaz
Instituto de Astrofísica de
Canarias
Imagine we could do asteroseismology of large samples
of OB-type stars by using just one spectrum per target. That would be
great! But this is probably a crazy and stupid idea. Or maybe not.
Maybe we have the possibility to open a new window to investigate
stellar oscillations in massive stars that has been in front of us
for many years, but has not attracted very much our attention: the
characterization and understanding of the so-called macroturbulent
broadening in OB-type stars.
Reference: Proceedings
IAUS307: New windows on massive stars: asteroseismology,
interferometry, and spectropolarimetry. G. Meynet, C. Georgy, J.H.
Groh & Ph. Stee, eds
Status: Other
Weblink:
http://arxiv.org/abs/1409.2416
Comments:
Email: ssimon@iac.es
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Closed Job Offers (original deadline passed)
Jim Kneller
Department of Physics
North
Carolina State University
421 Riddick Hall
Campus Box 8202
Raleigh, NC 27695-8202
(919) 515-2521
Join Our
Faculty!
The Department of Physics at NC State University is
seeking exceptionally qualified candidates for a tenure-track
position to begin Fall 2015. We are looking for faculty who will
establish a highly competitive research program and will have a
strong commitment to excellence in teaching and mentoring.
Astrophysics (Position Number: 00104147):
Emphasis on
astrophysics or space-based astronomy that compliments the
department's current strengths in computational astrophysics,
supernovae and supernova remnants, stellar astrophysics, and
theoretical nuclear / neutrino astrophysics.
Our Vision:
We envision North Carolina State University's Department of Physics
as performing creative, highly visible research in fundamental and
applied science. Our vision blends fundamental physics and
applications, theory and experiment, and integrates research and
innovative teaching to create a vibrant intellectual atmosphere
within a welcoming and collegial environment.
While these
searches are broadly defined, we seek candidates who share our vision
and who are open to collaborations in areas of current research
strengths in our department.
Attention/Comments:
Weblink:
http://physics.ncsu.edu/facultypositions/
Email:
physicsjobs@ncsu.edu
Deadline: 1 November
2014
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Dr. Barbara Pichardo
Instituto de Astronomía of
the Universidad Nacional Autónoma de México (IA-UNAM) at
Ensenada,
Baja California,
Mexico.
The Instituto de Astronomía of
the Universidad Nacional Autónoma de México (IA-UNAM) has openings
for junior faculty level, tenure track positions in astrophysics, at
its branch in Ensenada, Baja California, Mexico. Applicants should
hold a Ph.D. degree in astronomy or physics, and have at least two
years of postdoctoral experience. Mexican citizens are particularly
encouraged to apply.
Selection criteria include research
accomplishments and promise of future achievement as well as
opportunities to collaborate with other faculty members in Ensenada.
Faculty members are expected to carry out original research and must
teach astronomy and/or physics courses at the graduate and/or
undergraduate level, as well as mentor students.
Institute
members have access to Observatorio Astronómico Nacional in San
Pedro Mártir (OAN-SPM), Baja California. Astronomers at Mexican
institutions can compete for the Mexican share of observing time on
the 10.4-m Gran Telescopio Canarias (GTC), the Large Millimeter
Telescope (LMT), and also have competitive access to the EVLA, the
VLBA, and to ALMA, via collaboration with the USA National Radio
Astronomy Observatory. The Institute is a member of the
Transneptunian Automated Occultation Survey-II (TAOS-II), which is
being installed at OAN-SPM, the HAWC (High Altitude Water Cerenkov)
Observatory and the Cerenkov Telescope Array collaboration, as well
as a funding partner of the Sloan Digital Sky Survey, which will
execute the SDSS-IV. The Institute has extensive computing facilities
of its own and members have access to general UNAM supercomputers.
Members of the Institute conduct research in most major
astronomical and astrophysical fields. Candidates are encouraged to
contact individual faculty members to explore potential
collaborations as well as review the facilities and instrumentation
at the OAN-SPM to identify research opportunities at the site.
Inquiries can be made by email to barbara@astro.unam.mx
Additional information can be found at:
bufadora.astrosen.unam.mx/
www.astroscu.unam.mx
www.astroscu.unam.mx/job_ia
INCLUDED BENEFITS:
Health insurance is provided by UNAM.
Attention/Comments:
Weblink:
http://www.astroscu.unam.mx/IA/index.php?option=com_content&view=article&id=846&Itemid=248〈=es
Email:
barbara@astro.unam.mx
Deadline: 7 October
2014
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A conference
dedicated to the memory of Olivier Chesneau
Dr. Barbara Pichardo
The Instituto de Astronomía
of the Universidad Nacional Autónoma de México (IA-UNAM) at
Ciudad
Universitaria, UNAM
C.P. 04510
Mexico, City
The
Instituto de Astronomía of the Universidad Nacional Autónoma de
México (IA-UNAM) has openings for junior faculty level, tenure track
positions in astrophysics, at its branch in Mexico City, Mexico.
Applicants should hold a Ph.D. degree in astronomy or
physics, and have at least two years of postdoctoral experience.
Preference will be given to candidates less than 40 years old, by the
start date. Mexican citizens are particularly encouraged to apply.
The main selection criteria will be outstanding research
accomplishments and promise of future achievement. Faculty members
are expected to carry out original research, collaborate with faculty
members and must teach astronomy and/or physics courses at the
graduate and/or undergraduate level, as well as mentor students.
Candidates must send a complete curriculum vitae including a
full list of publications, as well as a statement of previous
experience and current and future professional interests, and arrange
for three letters of recommendation to be sent to Dr. Barbara
Pichardo at the IA-UNAM (barbara@astro.unam.mx) by 7 October 2014.
Unsigned material can be sent by e-mail; letters can be sent
by e-mail (scanned) or by courier. Please do not use regular post
mail.
Inquiries can be made by email to barbara@astro.unam.mx
Additional information can be found at:
www.astroscu.unam.mx
www.astroscu.unam.mx/job_ia
INCLUDED BENEFITS:
Health insurance is provided by UNAM.
Attention/Comments:
Weblink:
http://www.astroscu.unam.mx/IA/index.php?option=com_content&view=article&id=846&Itemid=248〈=es
Email:
barbara@astro.unam.mx
Deadline: 7 October
2014
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Jiří Kubát
Astronomical Institute Ondřejov
Fričova 298
251 65 Ondřejov
Czech Republic
The
Astronomical Institute of the Academy of Sciences of the Czech
Republic (www.asu.cas.cz) opens one temporary position in its Stellar
department in the field of NLTE radiative transfer and atmosphere
modelling. The applicant is expected to have basic experience in this
field and to have a university degree at the time of arrival.
The
Stellar Department of the Astronomical Institute
(http://www.asu.cas.cz) is located on the observatory campus in
Ondrejov, which is situated approximately 30 km south-east of Prague.
The stellar department (http://stelweb.asu.cas.cz) operates a 2m
telescope with a coudé spectrograph. Czech Republic is a member
state of both ESO, and has access to ESO facilities. The department
includes about a dozen active researchers, with a total of about 60
scientists working at the Astronomical Institute. The department
offers excellent computing facilities, running under Linux.
Researchers of the stellar department also have free access to the
computer cluster (http://wave.asu.cas.cz/ocas/).
The salary
will be based on the standard domestic scale. The starting date is as
soon as possible and the appointment is initially for 1 year. Further
extension will be possible upon satisfactory scientific results,
publication output, and availability of funding.
The
candidates should send their applications (list of publications,
curriculum vitae, and summary of their research work) and arrange two
letters of recommendation to be sent directly to Dr. J. Kubát,
Astronomical Institute, Fričova 298, 251 65 Ondřejov, Czech
Republic; (phone +420 323620328, fax +420 323620250), preferrably via
e-mail kubat@sunstel.asu.cas.cz. Applications should be received
before 30th October 2014. The selection process will continue until a
suitable candidate is found.
Attention/Comments:
Weblink:
http://www.asu.cas.cz/~kubat/granty/14-02385S/job.html
Email:
kubat@sunstel.asu.cas.cz
Deadline: 30 October 2014
or until a suitable candidate found
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Open JOB offers
Alexander Heger
Monash
Centre for Astrophysics
School of Mathematical Sciences
Building
28, M401
Monash University, VIC 3800
Australia
Applications
are invited for a full time research fellow (Level A/B) in the wider
field of stellar evolution and nuclear astrophysics with Prof.
Alexander Heger at the Monash Centre for Astrophysics (MoCA) at
Monash University, Melbourne, Australia.
The successful
candidate must hold, or be about to obtain, a Ph.D. degree in a
relevant discipline and should have experience in theoretical or
numerical modelling in nuclear astrophysics in one or several of the
following fields: formation and evolution of massive or very massive
stars, supernovae, binary stars, stellar rotation and magnetic
fields, gamma-ray burst and other transients and outbursts, galactic
chemical evolution, formation and evolution first stars, and Type I
X-ray burst and superbursts.
MoCA has very active research
groups in Stellar Interiors and Nucleosynthesis (SINs - Lattanzio,
Heger, Campbell, Mueller), High-energy Astrophysics (Galloway, Levin,
Donea, Heger, Price, Mueller, Lazendic-Galloway, Thrane),
Astrophysical Fluid Dynamics and MHD (Monaghan; Price - star
formation), Galaxy Evolution (Bown), Numerical General Relativity,
and solar physics, amongst others. The initial appointment is for two
years, at level A or B depending on experience. Extension for a third
year contingent upon funding, satisfactory performance, and managment
approval. Commencement date should be on or before Oct. 1, 2015.
To
apply for this post, follow the link provided to the job listing at
Monash. Please arrange for three letters of reference to be sent to
alexander.heger@monash.edu by the closing date.
Attention/Comments:
For full application, please visit Monash web site at
http://jobs.monash.edu.au/jobDetails.asp?sJobIDs=528279
The
application needs to be submitted through the online web
form.
Weblink:
http://jobregister.aas.org/job_view?JobID=49604
Email:
alexander.heger@monash.edu
Deadline: Monday, 1
December 2014, 11:55pm Australian Eastern Daylight Saving Time (early
morning hours in US).
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Rolf Kuiper
Computational Physics^M
Institute
of Astronomy and Astrophysics Tübingen^M
University of
Tübingen^M
Auf der Morgenstelle 10^M
D-72076
Tübingen^M
Germany
The Institute of Astronomy and
Astrophysics at the University of Tübingen (IAAT) has an opening for
a Postdoc and two PhD positions within the Emmy Noether Research
Group „Accretion flows and feedback in realistic models of massive
star formation“.
The successful applicants will carry out original research in the field of Massive Star Formation working in the Emmy Noether group of Dr. Rolf Kuiper. Emphasis lies on the (radiation-/magneto-)hydrodynamical and chemical evolution of jets, outflows, and accretion disk around massive protostars. Applicants with previous experience in numerical modeling will be favored.
The research activities of the IAAT
(http://www.tat.physik.uni-tuebingen.de) include Astronomy,
Instrumental Design/ High Energy Physics, Computational Astrophysics
and Relativistic Astrophysics. The focus of research of the Emmy
Noether group lies in the field of massive star formation and the
physics/chemistry of jets, outflows, and accretion disks.
The
appointments are funded by the German Research Foundation (DFG) and
paid according to German public service scale. Starting dates are
negotiable. Applicants should check for details of the application
procedure at links below.
The University of Tübingen seeks to increase the fraction of female scientists in research and teaching and particularly encourages applications from women. Disabled candidates are given preference if equally qualified.
For further enquires about the positions, please contact Rolf
Kuiper (rolf.kuiper@uni-tuebingen.de).
Attention/Comments:
Weblink: http://www.mpia-hd.mpg.de/~kuiper
Email:
rolf.kuiper@uni-tuebingen.de
Deadline: December,
15th for PhDs and January, 19th for Postdoc
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June 8-12, 2015
Venue: Nice
(France)
First announcement
As a talented scientist,
animated with a constant passion for astronomy, Olivier Chesneau led
pioneering works using visible and infrared long-baseline
interferometry. Olivier used this technique to study disk formation
around varied astrophysical objects, such as evolved massive stars,
planetary nebulae, and novae. His foremost results include the study
of the close environment of Eta Carinae and other massive stars, the
first direct detection of disks in planetary nebulae, finding
evidences of dust bipolar ejections by novae shortly after eruption,
and the discovery of the largest yellow hypergiant star in the Milky
Way. His results were often widely publicized through press releases
from ESO and CNRS-INSU. The 2012 Michelson Prize of the International
Astronomical Union and of Mount Wilson Institute was awarded to
Olivier Chesneau for major contributions in stellar astrophysics made
with long-baseline interferometry.
After his untimely
departure several months ago, his friends and colleagues in Nice have
decided to organize a conference that brings together experts in
different fields to study the physics of evolved stars: this was
Olivier’s approach to tackle outstanding questions about these
stars. The conference will concentrate on four different processes in
evolved stars: mass loss, binarity, rotation, and astrochemistry
(dust formation). Contributions are invited along these themes, from
theory and numerical simulations to all observational approaches.
Only two invited talks are planned to leave as much room as possible
to individual contributions (oral and posters) and discussions.
The
conference will be held on June 8-12, 2015, in Nice, France.
Pre-registration is open (see instructions at
olivier-chesneau.oca.eu) and please submit an abstract (even
tentative) during registration. We expect the registration fee to be
around 150 euros, and it could be waived for some students. Based on
the proposed contributions received by 2014 December 15, a
preliminary program will be established by the SOC and announced in
early January 2015 with detailed information for
registration.
Weblink:
http://poe2015.sciencesconf.org/
Email:
eric.lagadec@oca.eu
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12 - 14 August 2015
Venue: Honolulu,
Hawaii
A 3-day Focus Meeting entitled "Stellar Physics in
Galaxies throughout the Universe" will be held during the IAU
XXIX General Assembly. The meeting will bring together astronomers
from the stellar physics, extragalactic astrophysics and cosmology
communities to discuss how current and future results can foster
progress in these disjoint science areas. Areas covered include
stellar evolution of single and binary stars from the zero-age
main-sequence to the terminal stage, the feedback of stars to the
interstellar medium via radiation, dust production and chemical
enrichment, and the properties of the most massive stars and of
cosmologically significant stellar phases such as AGB and Wolf-Rayet
stars. We will evaluate the limitations of our understanding of the
physics of local stars and their effects on, e.g., ages, chemical
composition and the initial mass function of galaxies at low to high
redshift. The meeting is timely because of new results from recently
commissioned telescopes and because of the prospects from future 30-m
class telescopes.
Weblink: http://iau-fm7.stsci.edu
Email:
leitherer@stsci.edu
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