ISSN 1783-3426
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Candidacies for the Organizing Committee of the
Massive Stars Commission (from May 16th to June 1st)
Massive
Stars Commission approved by IAU Executive Committee
Fizeau
exchange visitors program - special call for applications
The Massive Star Population of Cygnus
OB2
2.5D global-disk oscillation
models of the Be shell star ζ Tauri I. Spectroscopic and
polarimetric analysis
3D Printing
Meets Computational Astrophysics: Deciphering the Structure of Eta
Carinae's Inner Colliding Winds
On
the consistent treatment of the quasi-hydrostatic layers in hot star
atmospheres
A New Luminous Blue
Variable in M31
Eta Carinae's
2014.6 Spectroscopic Event: The Extraordinary He II and N II
Features
The Massive Star Population in M101.
III. Spectra and Photometry of the Luminous and Variable Stars
A
coordinated X-ray and Optical Campaign of the Nearest Massive
Eclipsing Binary, delta Orionis Aa: IV. A multiwavelength, non-LTE
spectroscopic analysis
On X-ray
pulsations in beta Cephei-type variables
Photometric
identification of the periods of the first candidate extragalactic
magnetic stars
A spectroscopic
investigation of the O-type star population in four Cygnus OB
associations. II. Determination of the fundamental parameters
The
origin of the puzzling hard X-ray emission of gamma Cassiopeiae
The
Herschel view of the nebula around the luminous blue variable star AG
Carinae
A Survey of Extended H2
Emission from Massive YSOs
Surface
abundances of ON stars
The
little-studied cluster Berkeley 90. I. LS III +46 11: a very massive
O3.5 If* + O3.5 If* binary.
The IACOB spectroscopic database: recent updates and first data release
Very Massive Stars in the Local
Universe
Mass-loss rates of Very
Massive Stars
(original deadline passed):
XXIX IAU
General Assembly - Focus Meeting 10: "Stellar explosions in an
ever-changing environment"
Radiation
mechanisms of astrophysical objects: classics today
dear members of the MSWG,
now that the Massive Stars
Commission has been approved by the IAU, we have to elect the
Organizing Committee (OC) and the Vice-president. To be a candidate
and vote for the OC you must be registered as a member of the
Commission. Registration is open until May 15. To register you have
to follow the instructions in the email sent by the General Secretary
on April 29, 2015 using the "My vote" system. If you have
not received an email, contact the IAU: iauinfos@iap.fr
.
According to IAU rules, the OC shall consist of 4-8 members.
The proponents of the new Commission (4 in our case) will be
ex-officio members of the OC, and the first proponent will be
president of the Commission. Thus our new OC Commission already has
four members: Artemio Herrero (president), Gregor Rauw, Nicole
St.-Louis and Jorick Vink.
Depending on the final number of
members of our Commission, 1-4 new OC members will be elected by the
Commission members. IAU regulations for the process indicate that
candidates for the OC shall propose themselves.
Candidacies
can be sent to the (future) Commission president (ahd-at-iac.es) from
** May, 16th to June, 1st **. Interested people shall send a brief CV
and motivation, with a photo inserted. The four present OC members
will be in charge of presenting a balanced slate of candidate for
election by the Commission members. The dates for the votation will
be announced later.
The Vice-president candidate will be
proposed by the Commission president.
Please note that there
has been a call for candidacies to the Division Steering Committees.
Candidates shall be different.
with best regards,
Artemio
Herrero
chair, Massive Stars Working Group
Email:
ahd@iac.es
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dear friends,
as you have probably seen by the email
distributed by the IAU General Secretary, the proposal for a new IAU
Commision on Massive Stars has been approved. This is great news for
our group.
Thanks to all of you who supported the proposal,
and particular thanks to those that helped to prepare it.
IAU
members please note that you will have from **April 30th until May
15th** to sign-up in up to three IAU Commissions. This will be
required for the subsequent election processes of the Organizing
Committes.
Again, congratulations to all members of the
former IAU Working Group on Massive Stars.
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!
The Fizeau
exchange visitors program in optical interferometry funds (travel and
accommodation) visits of researchers to an institute of his/her
choice (within the European Community) to perform collaborative work
and training on one of the active topics of the European
Interferometry Initiative. The visits will typically last for one
month, and strengthen the network of astronomers engaged in
technical, scientific and training work on optical/infrared
interferometry. The program is open for all levels of astronomers
(Ph.D. students to tenured staff), non-EU based missions will only be
funded if considered essential by the Fizeau Committee. Applicants
are strongly encouraged to seek also partial support from their home
or host institutions.
IMPORTANT NOTE:
This is a special
call to support attendance of the 8th VLTI summer school:
http://www.astro.uni-koeln.de/vltischool2015.
Therefore no
research plan and invitation letter from the host institution are
required.
The deadline for applications is May 30.
Further
informations and application forms can be found at
www.european-interferometry.eu
The program is funded by
OPTICON/FP7.
Please distribute this message also to
potentially interested colleagues outside of your community!
Looking forward to your applications,
Josef Hron &
Laszlo Mosoni
(for the European Interferometry
Initiative)
Weblink: www.european-interferometry.eu
Email:
fizeau@european-interferometry.eu
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Nicholas J. Wright, Janet E. Drew, Michael
Mohr-Smith
Centre for Astrophysics Research, University of
Hertfordshire
We have compiled a significantly updated and
comprehensive census of massive stars in the nearby Cygnus OB2
association by gathering and homogenising data from across the
literature. The census contains 169 primary OB stars, including 52
O-type stars and 3 Wolf-Rayet stars. Spectral types and photometry
are used to place the stars in a Hertzprung-Russell diagram, which is
compared to both non-rotating and rotating stellar evolution models,
from which stellar masses and ages are calculated. The star formation
history and mass function of the association are assessed, and both
are found to be heavily influenced by the evolution of the most
massive stars to their end states. We find that the mass function of
the most massive stars is consistent with a `universal' power-law
slope of $Gamma = 1.3$. The age distribution inferred from stellar
evolutionary models with rotation and the mass function suggest the
majority of star formation occurred more or less continuously between
1 and 7~Myr ago, in agreement with studies of low- and intermediate
mass stars in the association. We identify a nearby young pulsar and
runaway O-type star that may have originated in Cyg~OB2 and suggest
that the association has already seen its first supernova. Finally we
use the census and mass function to calculate the total mass of the
association of $16500^{+3800}_{-2800}$~M$_odot$, at the low end, but
consistent with, previous estimates of the total mass of Cyg~OB2.
Despite this Cyg~OB2 is still one of the most massive groups of young
stars known in our Galaxy making it a prime target for studies of
star formation on the largest scales.
Reference: MNRAS,
accepted
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1502.05718
Email:
nick.nwright@gmail.com
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contents
C. Escolano (1), A. C. Carciofi (1), A. T. Okazaki (2), T. Rivinius (3), D. Baade (4), and S. Stefl (5)
(1) - Instituto de- Astronomia, Geofisica e Ciencias
AtmosfeÌricas (Sao Paulo, Brazil); (2) - Hokkai-Gakuen University
(Sapporo, ESO (Santiago, Japan); (3) - ESO (Santiago, Chile); (4) -
ESO (Garching, Germany); (5) - ALMA (Santiago, Chile)
Context.
A large number of Be stars exhibit intensity variations of their
violet and red emission peaks in their HI lines observed in emission.
This is the so-called V/R phenomenon, usually explained by the
precession of a one-armed spiral density perturbation in the
circumstellar disk. That global-disk oscillation scenario was
confirmed, both observationally and theoretically, in the previous
series of two papers analyzing the Be shell star ζ Tauri. The
vertically averaged (2D) global-disk oscillation model used at the
time was able to reproduce the V/R variations observed in Hα, as
well as the spatially resolved interferometric data from AMBER/VLTI.
Unfortunately, that model failed to reproduce the V/R phase of Br15
and the amplitude of the polarization variation, suggesting that the
inner disk structure predicted by the model was incorrect.
Aims.
The first aim of the present paper is to quantify the temporal
variations of the shell-line characteristics of ζ Tauri. The second
aim is to better understand the physics underlying the V/R phenomenon
by modeling the shell-line variations together with the V/R and
polarimetric variations. The third aim is to test a new 2.5D disk
oscillation model, which solves the set of equations that describe
the 3D perturbed disk structure but keeps only the equatorial (i.e.,
2D) component of the solution. This approximation was adopted to
allow comparisons with the previous 2D model, and as a first step
toward a future 3D model.
Methods. We carried out an
extensive analysis of ζ Tauri’s spectroscopic variations by
measuring various quantities characterizing its Balmer line profiles:
red and violet emission peak intensities (for Hα, Hβ, and Br15),
depth and asymmetry of the shell absorption (for Hβ, Hγ, and Hδ),
and the respective position (i.e., radial velocity) of each
component. We attempted to model the observed variations by
implementing in the radiative transfer code HDUST the perturbed disk
structure computed with a recently developed 2.5D global-disk
oscillation model.
Results. The observational analysis
indicates that the peak separation and the position of the shell
absorption both exhibit variations following the V/R variations and,
thus, may provide good diagnostic tools of the global-disk
oscillation phenomenon. The shell absorption seems to become slightly
shallower close to the V/R maximum, but the scarcity of the data does
not allow the exact pattern to be identified. The asymmetry of the
shell absorption does not seem to correlate with the V/R cycle; no
significant variations of this parameter are observed, except during
certain periods where Hα and Hβ exhibit perturbed emission
profiles. The origin of these so-called triple-peak phases remains
unknown. On the theoretical side, the new 2.5D formalism appears to
improve the agreement with the observed V/R variations of Hα and
Br15, under the proviso that a large value of the viscosity
parameter, α = 0.8, be adopted. It remains challenging for the
models to reproduce consistently the amplitude and the average level
of the polarization data. The 2D formalism provides a better match to
the peak separation, although the variation amplitude predicted by
both the 2D and 2.5D models is smaller than the observed value.
Shell-line variations are difficult for the models to reproduce,
whatever formalism is adopted.
Reference: A&A
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1503.00590
Email:
cyril.escolano@gmail.com
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contents
Thomas I. Madura(1), Nicola Clementel(2), Theodore R.
Gull(1), Chael J.H. Kruip(2), and Jan-Pieter Paardekooper(3,4)
1
- NASA Goddard Space Flight Center; 2 - Leiden Observatory; 3 -
Universitat Heidelberg; 4 - Max Planck Institute for Extraterrestrial
Physics
We present the first 3D prints of output from a
supercomputer simulation of a complex astrophysical system, the
colliding stellar winds in the massive (>120 M_Sun), highly
eccentric (e~0.9) binary star system Eta Carinae. We demonstrate the
methodology used to incorporate 3D interactive figures into a PDF
journal publication and the benefits of using 3D visualization and 3D
printing as tools to analyze data from multidimensional numerical
simulations. Using a consumer-grade 3D printer (MakerBot Replicator
2X), we successfully printed 3D smoothed particle hydrodynamics (SPH)
simulations of Eta Carinae's inner (r ~ 110 au) wind-wind collision
interface at multiple orbital phases. The 3D prints and
visualizations reveal important, previously unknown 'finger-like'
structures at orbital phases shortly after periastron (phi~1.045)
that protrude radially outward from the spiral wind-wind collision
region. We speculate that these fingers are related to instabilities
(e.g. thin-shell, Rayleigh-Taylor) that arise at the interface
between the radiatively-cooled layer of dense post-shock primary-star
wind and the fast (3000 km/s), adiabatic post-shock companion-star
wind. The success of our work and easy identification of previously
unrecognized physical features highlight the important role 3D
printing and interactive graphics can play in the visualization and
understanding of complex 3D time-dependent numerical simulations of
astrophysical phenomena.
Reference: For publication in
MNRAS
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1503.00716
Comments:
To view 3D interactive figures and movie, use Adobe PDF
viewer.
Email: thomas.i.madura@nasa.gov
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Andreas Sander (1), Tomer Shenar (1), Rainer Hainich (1),
Angel Gímenez-García (2), Helge Todt (1), Wolf-Rainer Hamann
(1)
(1) - Institut for Physics and Astronomy, University
of Potsdam, Germany;
(2) - Departamento de Física, Ingeniería
de Sistemas y Teoría de la Señal, Universidad de Alicante,
Spain
CONTEXT: Spectroscopic analysis remains the most common
method to derive masses of massive stars, the most fundamental
stellar parameter. While binary orbits and stellar pulsations can
provide much sharper constraints on the stellar mass, these methods
are only rarely applicable to massive stars. Unfortunately,
spectroscopic masses of massive stars heavily depend on the detailed
physics of model atmospheres.
AIMS: We demonstrate the impact
of a consistent treatment of the radiative pressure on inferred
gravities and spectroscopic masses of massive stars. Specifically, we
investigate the contribution of line and continuum transitions to the
photospheric radiative pressure. We further explore the effect of
model parameters, e.g., abundances, on the deduced spectroscopic
mass. Lastly, we compare our results with the plane-parallel TLUSTY
code, commonly used for the analysis of massive stars with
photospheric spectra.
METHODS: We calculate a small set of
O-star models with the Potsdam Wolf-Rayet (PoWR) code using different
approaches for the quasi-hydrostatic part. These models allow us to
quantify the effect of accounting for the radiative pressure
consistently. We further use PoWR models to show how the Doppler
widths of line profiles and abundances of elements such as iron
affect the radiative pressure, and, as a consequence, the derived
spectroscopic masses.
RESULTS: Our study implies that errors
on the order of a factor of two in the inferred spectroscopic mass
are to be expected when neglecting the contribution of line and
continuum transitions to the radiative acceleration in the
photosphere. Usage of implausible microturbulent velocities, or the
neglect of important opacity sources such as Fe, may result in errors
of approximately 50% in the spectroscopic mass. A comparison with
TLUSTY model atmospheres reveals a very good agreement with PoWR at
the limit of low mass-loss rates.
Reference: A&A,
in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1503.01338
Email:
ansander@astro.physik.uni-potsdam.de
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Roberta M. Humphreys (1), John C. Martin (2) and Michael S.
Gordon (1)
(1) University of Minnesota, (2) University of
Illinois - Springfield
We report the fifth confirmed Luminous
Blue Variable/S Doradus variable in M31. In 2006, J004526.62+415006.3
had the spectrum of hot Fe II emission line star with strong P Cygni
profiles in the Balmer lines. In 2010, its absorption line spectrum
resembled an early A-type supergiant with H and Fe II emission lines
with strong P Cygni profiles, and in 2013 the spectrum had fully
transitioned to an F-type supergiant due to the formation of the
optically thick, cool wind which characterizes LBVs at maximum light.
The photometric record supports the LBV/S Dor nature of the
variability. Its bolometric luminosity ~ -9.65 mag places it on the
HR Diagram near the known LBVs, AE And, Var C in M33 and S
Dor.
Reference: To appear in the Publications of the
Astronomical Society of the Pacific
Status: Manuscript has been
accepted
Email: roberta@umn.edu
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Kris Davidson(1), Andrea Mehner(2), Roberta M. Humphreys
(1), John C. Martin (3), and Kazunori Ishibashi (4)
(1)
University of Minnesota, (2) ESO, (3) University of Illinois -
Springfield, (4) Nagoya Univ., Japan
Eta Carinae's
spectroscopic events (periastron passages) in 2003, 2009, and 2014
differed progressively. He ii lambda4687 and nearby N ii multiplet 5
have special significance because they respond to very soft X-rays
and the ionizing UV radiation field (EUV). Hubble Space Telescope
(HST)/STIS observations in 2014 show dramatic increases in both
features compared to the previous 2009.1 event. These results appear
very consistent with a progressive decline in the primary wind
density, proposed years ago on other grounds. If material falls onto
the companion star near periastron, the accretion rate may now have
become too low to suppress the EUV.
Reference: ApJ
Letters, 801L, 15D
Status: Manuscript has been accepted
Email:
roberta@umn.edu
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Skyler H. Grammer and Roberta M. Humphreys
University
of Minnesota
We discuss moderate resolution spectra,
multicolor photometry, and light curves of thirty-one of the most
luminous stars and variables in the giant spiral M101. The majority
are intermediate A to F-type supergiants. We present new photometry
and light curves for three known "irregular blue variables"
V2, V4 and V9) and identify a new candidate. Their spectra and
variability confirm that they are LBV candidates and V9 may be in an
LBV-like maximum light state or eruption.
Reference: To
appear in the Astronomical Journal
Status: Manuscript has been
accepted
Weblink:
http://etacar.umn.edu/LuminousStars/M101/
Email:
roberta@umn.edu
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T. Shenar, L. Oskinova, W.-R. Hamann, M. F. Corcoran, A. F.
J. Moffat, H. Pablo, N. D. Richardson, W. L. Waldron, D. P.
Huenemoerder, J. Maíz Apellániz, J. S. Nichols, H. Todt, Y. Nazé,
J. L. Hoffman, A. M. T. Pollock, I. Negueruela
University
of Potsdam, Germany
Eclipsing systems of massive stars allow
one to explore the properties of their components in great detail. We
perform a multi-wavelength, non-LTE analysis of the three components
of the massive multiple system delta Ori A, focusing on the
fundamental stellar properties, stellar winds, and X-ray
characteristics of the system.
The primary’s
distance-independent parameters turn out to be characteristic for its
spectral type (O9.5 II), but usage of the Hipparcos parallax yields
surprisingly low values for the mass, radius, and luminosity.
Consistent values follow only if delta Ori lies at about twice the
Hipparcos distance, in the vicinity of the sigma-Orionis cluster. The
primary and tertiary dominate the spectrum and leave the secondary
only marginally detectable. We estimate the V-band magnitude
difference between primary and secondary to be 2.8 mag. The inferred
parameters suggest the secondary is an early B-type dwarf (~B1 V),
while the tertiary is an early B-type subgiant (~B0 IV). We find
evidence for rapid turbulent velocities (∼200 km/s) and wind
inhomogeneities, partially optically thick, in the primary’s wind.
The bulk of the X-ray emission likely emerges from the primary’s
stellar wind (log LX/LBol~ −6.85), initiating close to the stellar
surface at R0∼1.1R∗. Accounting for clumping, the mass-loss rate
of the primary is found to be log Mdot ~ 6.4 [Msun/yr], which agrees
with hydrodynamic predictions, and provides a consistent picture
along the X-ray, UV, optical and radio spectral domains.
Reference:
To appear in the Astronomical Journal
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1503.03476
Email:
shtomer@astro.physik.uni-potsdam.de
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Oskinova, L. M.; Todt, H.; Huenemoerder, D. P.; Hubrig, S.;
Ignace, R.; Hamann, W.-R.; Balona, L.
University of
Potsdam, etc.
Beta Cephei-type variables are early B-type
stars that are characterized by oscillations observable in their
optical light curves. At least one Beta Cep-variable also shows
periodic variability in X-rays. Here we study the X-ray light curves
in a sample of beta Cep-variables to investigate how common X-ray
pulsations are for this type of stars. We searched the Chandra and
XMM-Newton X-ray archives and selected stars that were observed by
these telescopes for at least three optical pulsational periods. We
retrieved and analyzed the X-ray data for kappa Sco, beta Cru, and
alpha Vir. The X-ray light curves of these objects were studied to
test for their variability and periodicity. While there is a weak
indication for X-ray variability in beta Cru, we find no
statistically significant evidence of X-ray pulsations in any of our
sample stars. This might be due either to the insufficient data
quality or to the physical lack of modulations. New, more sensitive
observations should settle this question.
Reference:
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1503.05749
Email:
lida@astro.physik.uni-potsdam.de
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Yael Naze (1), Nolan R. Walborn (2), Nidia Morrell (3),
Gregg A. Wade (4), Michal K. Szymanski (5)
1 - ULg, 2 -
STScI, 3 - Las Campanas, 4 - RMC, 5 - Warsaw University
Galactic
stars belonging to the Of?p category are all strongly magnetic
objects exhibiting rotationally modulated spectral and photometric
changes on timescales of weeks to years. Five candidate Of?p stars in
the Magellanic Clouds have been discovered, notably in the context of
ongoing surveys of their massive star populations. Here we describe
an investigation of their photometric behaviour, revealing
significant variability in all studied objects on timescales of one
week to more than four years, including clearly periodic variations
for three of them. Their spectral characteristics along with these
photometric changes provide further support for the hypothesis that
these are strongly magnetized O stars, analogous to the Of?p stars in
the Galaxy.
Reference: accepted by A&A
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1503.07654
Email:
naze@astro.ulg.ac.be
Back to contents
L.Mahy(1), G.Rauw(1), M. De Becker (1), P. Eenens (2), and
C. A. Flores(2)
(1): Institut d’Astrophysique et de
Géophysique, Université de Liège, Bât. B5C, Allée du 6 Août 17,
B-4000, Liège, Belgium
(2): Departamento de Astronomía,
Universidad de Guanajuato, Apartado 144, 36000 Guanajuato, GTO,
Mexico
Aims. Having established the binary status of nineteen
O-type stars located in four Cygnus OB associations, we now determine
their fundamental parameters to constrain their properties and their
evolutionary status. We also investigate their surface nitrogen
abundances, which we compare with other results from the literature
obtained for galactic O-type stars.
Methods. Using optical
spectra collected for each object in our sample and some UV data from
the archives, we apply the CMFGEN atmosphere code to determine their
main properties. For the binary systems, we have disentangled the
components to obtain their individual spectra and investigate them as
if they were single stars.
Results. We find that the distances of
several presumably single O-type stars seem poorly constrained
because their luminosities are not in agreement with the "standard"
luminosities of stars with similar spectral types. The ages of these
O-type stars are all less than 7 Myrs. Therefore, the ages of these
stars agree with those, quoted in the literature, of the four
associations, except for Cyg OB8 for which the stars seem older than
the association itself. However, we point out that the distance of
certain stars is debatable relative to values found in the
literature. The N content of these stars put in perspective with N
contents of several other galactic O-type stars seems to draw the
same five groups as found in the "Hunter" diagram for the O
and B-type stars in the LMC even though their locations are obviously
different. We determine mass-loss rates for several objects from the
Hα line and UV spectra. Finally, we confirm the "mass
discrepancy" especially for O stars with masses smaller than
30Msun.
Reference: A&A in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1504.03107
Comments:
11 pages, 26 pages of Appendix
Email:
mahy@astro.ulg.ac.be
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Christian Motch (1), Raimundo Lopes de Oliveira (2,3), and
Myron A. Smith (4)
(1) Observatoire Astronomique,
Université de Strasbourg, France;
(2) Universidade Federal de
Sergipe, Brazil;
(3) Observatório Nacional, Brazil;
(4)
National Optical Astronomy Observatory, USA.
Massive B and Be
stars produce X-rays from shocks in high velocity winds with
temperatures of a few million degrees and maximum X-ray luminosities
of ~10^(31) erg/s. Surprisingly, a sub-group of early Be stars
exhibits > 20 times hotter X-ray temperatures and > 10 times
higher X-ray luminosities than normal. This group of Be stars, dubbed
Gamma-Cas analogs, contains about 10 known objects. The origin of
this bizarre behavior has been extensively debated in the past
decades. Two mechanisms have been put forward, accretion of
circumstellar disk matter onto an orbiting white dwarf, or magnetic
field interaction between the star and the circumstellar disk (Smith
& Robinson 1999). We show here that the X-ray and optical
emissions of the prototype of the class, Gamma-Cas, are very well
correlated on year time scales with no significant time delay. Since
the expected migration time from internal disk regions that emit most
of the optical flux to the orbit of the companion star is of several
years, the simultaneity of the high energy and optical fluxes
variations indicates that X-ray emission arises from close to the
star. The systematic lack of magnetic field detection reported in
recent spectro-polarimetric surveys of Be stars is consistent with
the absence of strong magnetic wind braking in these fast spinning
stars but put strong constraints on the possible origin of the
magnetic field. We propose that in Gamma-Cas the magnetic field
emerges from equatorially condensed subsurface convecting layers the
thickness of which steeply increases with rotation rate and that
Gamma-Cas and its analogs are the most massive and closest to
critical rotation Be stars.
Reference: ApJ in
press.
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1504.01105
Email:
christian.motch@unistra.fr
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contents
C. Vamvatira-Nakou(1), D. Hutsemekers(1), P. Royer(2), N.
L. J. Cox(2), Y. Naze(1), G. Rauw(1), C. Waelkens(2), M. A. T.
Groenewegen(3)
1 - Institut d'Astrophysique et de
Geophysique, Universite de Liege, Allee du 6 aout, 17 - Bat. B5c,
B-4000 Liege, Belgium;
2 - Instituut voor Sterrenkunde, KU
Leuven, Celestijnenlaan 200D, Bus 2401, B-3001 Leuven, Belgium;
3
- Koninklijke Sterrenwacht van Belgie, Ringlaan 3, B-1180 Brussels,
Belgium
Far-infrared Herschel PACS imaging and spectroscopic
observations of the nebula around the luminous blue variable (LBV)
star AG Car have been obtained along with optical imaging in the
Halpha+[NII] filter. In the infrared light, the nebula appears as a
clumpy ring shell that extends up to 1.2 pc with an inner radius of
0.4 pc. It coincides with the Halpha nebula, but extends further out.
Dust modeling of the nebula was performed and indicates the presence
of large grains. The dust mass is estimated to be ~ 0.2 Msun. The
infrared spectrum of the nebula consists of forbidden emission lines
over a dust continuum. Apart from ionized gas, these lines also
indicate the existence of neutral gas in a photodissociation region
that surrounds the ionized region. The abundance ratios point towards
enrichment by processed material. The total mass of the nebula
ejected from the central star amounts to ~ 15 Msun, assuming a
dust-to-gas ratio typical of LBVs. The abundances and the mass-loss
rate were used to constrain the evolutionary path of the central star
and the epoch at which the nebula was ejected, with the help of
available evolutionary models. This suggests an ejection during a
cool LBV phase for a star of ~ 55 Msun with little
rotation.
Reference: A&A in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1504.03204
Email:
chloevn@astro.ulg.ac.be
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Felipe Navarete(1), Augusto Damineli(1), Cassio L.
Barbosa(2), Robert D. Blum(3)
(1) Instituto de Astronomia,
Geofisica e Ciencias Atmosfericas - University of Sao Paulo (IAG-USP)
(2) MCTI/Laboratorio Nacional de Astrofisica
(3) National
Optical Astronomy Observatory (NOAO)
We present the results
from a survey, designed to investigate the accretion process of
massive young stellar objects (MYSOs) through near infrared narrow
band imaging using the H2 ν=1-0 S(1) transition filter. A sample of
353 Massive Young Stellar Object (MYSO) candidates was selected from
the Red MSX Source survey using photometric criteria at longer
wavelengths (infrared and submillimeter) and chosen with positions
throughout the Galactic Plane. Our survey was carried out at the SOAR
Telescope in Chile and CFHT in Hawaii covering both hemispheres. The
data reveal that extended H2 emission is a good tracer of outflow
activity, which is a signpost of accretion process on young massive
stars. Almost half of the sample exhibit extended H2 emission and 74
sources (21%) have polar morphology, suggesting collimated outflows.
The polar-like structures are more likely to appear on radio-quiet
sources, indicating these structures occur during the pre-UCHII
phase. We also found an important fraction of sources associated with
fluorescent H2 diffuse emission that could be due to a more evolved
phase. The images also indicate only ∼23% (80) of the sample is
associated with extant (young) stellar clusters. These results
support the scenario in which massive stars are formed by accretion
disks, since the merging of low mass stars would not produce outflow
structures.
Reference: To appear in the MNRAS
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1504.06174
Comments:
Email: navarete@usp.br
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F. Martins$^1$, S. Simon-Diaz$^2$$^3$, A. Palacios$^1$, I.
Howarth$^4$, C. Georgy$^5$, N.R. Walborn$^6$, J.-C. Bouret$^7$, R.
Barba$^8$
1 - LUPM, CNRS & Montpellier University; 2 -
IAC; 3 - La Laguna University; 4 - University College London; 5 -
Keele University; 6 - Space Telescope Science Institute; 7 - LAM,
CNRS & Aix-Marseille University; 8 - La Serena
University
Massive stars burn hydrogen through the CNO cycle
during most of their evolution. When mixing is efficient, or when
mass transfer in binary systems happens, chemically processed
material is observed at the surface of O and B stars. ON stars show
stronger lines of nitrogen than morphologically normal counterparts.
Whether this corresponds to the presence of material processed
through the CNO cycle or not is not known. Our goal is to answer this
question. We perform a spectroscopic analysis of a sample of ON stars
with atmosphere models. We determine the fundamental parameters as
well as the He, C, N, and O surface abundances. We also measure the
projected rotational velocities. We compare the properties of the ON
stars to those of normal O stars. We show that ON stars are usually
helium-rich. Their CNO surface abundances are fully consistent with
predictions of nucleosynthesis. ON stars are more chemically evolved
and rotate - on average - faster than normal O stars. Evolutionary
models including rotation cannot account for the extreme enrichment
observed among ON main sequence stars. Some ON stars are members of
binary systems, but others are single stars as indicated by stable
radial velocities. Hence, mass transfer is not a simple explanation
for the observed chemical properties. We conclude that ON stars show
extreme chemical enrichment at their surface, consistent with
nucleosynthesis through the CNO cycle. Its origin is not clear at
present.
Reference: A&A accepted
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1504.06194
Email:
fabrice.martins@univ-montp2.fr
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J. Maíz Apellániz, I.
Negueruela, R. H. Barbá, N. R. Walborn, A. Pellerin, S. Simón-Díaz,
A. Sota, A. Marco, J. Alonso-Santiago, J. Sanchez Bermudez, R. C.
Gamen, and J. Lorenzo
CAB, UA, ULS, STScI, SUNY, IAC, ULL,
IAA, and IALP.
CONTEXT. It appears that most (if not all)
massive stars are born in multiple systems. At the same time, the
most massive binaries are hard to find due to their low numbers
throughout the Galaxy and the implied large distances and
extinctions.
AIMS. We want to study: [a] LS III +46 11,
identified in this paper as a very massive binary; [b] another nearby
massive system, LS III +46 12; and [c] the surrounding stellar
cluster, Berkeley 90.
METHODS. Most of the data used in this
paper are multi-epoch high-S/N optical spectra though we also use
Lucky Imaging and archival photometry. The spectra are reduced with
devoted
pipelines and processed with our own software, such as a
spectroscopic-orbit code, CHORIZOS, and MGB.
RESULTS LS III
+46 11 is identified as a new very-early-O-type spectroscopic binary
[O3.5 If* + O3.5 If*] and LS III +46 12 as another early O-type
system [O4.5 V((f))]. We measure a 97.2-day period for LS III +46 12
and derive minimum masses of 38.80±0.83 M_Sol and 35.60±0.77 M_Sol
for its two stars. We measure the extinction to both stars, estimate
the distance, search for optical companions, and study the
surrounding cluster. In doing so, a variable extinction is found as
well as discrepant results for the distance. We discuss possible
explanations and suggest that LS III +46 12 may be a hidden binary
system, where the companion
is currently undetected.
Reference:
Accepted for publication in A&A.
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1504.06977
Email:
jmaiz@cab.inta-csic.es
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S. Simón-Díaz (1,2), I. Negueruela,
J. Maíz Apellániz, N. Castro, A. Herrero, M. Garcia, J. A.
Pérez-Prieto, N. Caon, J. M. Alacid, I. Camacho, R. Dorda, M.
Godart, C. González-Fernández, G. Holgado, K. Rübke
(1)
Instituto de Astrofísica de Canarias
(2) Universidad de La
Laguna
The IACOB project is an ambitious long-term project
which is contributing to step forward in our knowledge about the
physical properties and evolution of Galactic massive stars. The
project aims at building a large database of high-resolution,
multi-epoch, spectra of Galactic OB stars, and the scientific
exploitation of the database using state-of-the-art models and
techniques. In this proceeding, we summarize the latest updates of
the IACOB spectroscopic database and highlight some of the first
scientific results from the IACOB project; we also announce the first
data release and the first public version of the iacob-broad tool for
the line-broadening characterization of OB-type spectra.
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/1504.04257
Email:
ssimon@iac.es
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Jorick S. Vink (Ed.)
Armagh Observatory,
Northern Ireland
Recent studies suggest the existence of very
massive stars (VMS) up to 300 solar masses in the local Universe. As
this finding may represent a paradigm shift for the canonical stellar
upper-mass limit of 150 solar masses, it is timely to evaluate the
physics specific to VMS, which is currently missing. For this reason,
we decided to construct a book entailing both a discussion of the
accuracy of VMS masses (Martins), as well as the physics of VMS
formation (Krumholz), mass loss (Vink), instabilities (Owocki),
evolution (Hirschi), and fate (theory -- Woosley & Heger;
observations -- Smith).
Reference: Very Massive Stars
in the Local Universe: , Astrophysics and Space Science Library,
Volume 412. Springer 2015
Status: Other
Weblink:
http://www.springer.com/astronomy/astrophysics+and+astroparticles/book/978-3-319-09595-0
Comments:
Book (Springer). 8 Chapters.
Email: jsv@arm.ac.uk
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Jorick S. Vink
Armagh
Observatory
We discuss the basic physics of hot-star winds and
we provide mass-loss rates for (very) massive stars. Whilst the
emphasis is on theoretical concepts and line-force modelling, we also
discuss the current state of observations and empirical modelling,
and we address the issue of wind clumping.
Reference: Vink,
J.S., 2015, ASSL 412, 77
Status: Other
Weblink:
http://adsabs.harvard.edu/abs/2015ASSL..412...77V
Comments:
Chapter in VMS Book
Email: jsv@arm.ac.uk
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Closed Job Offers (original deadline passed)
Leen Decin
Institute
of Astronomy, Leuven University
Celestijnenlaan 200D
B-3001
Heverlee (Leuven)
Belgium
Interdisciplinary project on the
stellar winds around evolved stars at the Leuven University in
Belgium funded by the ERC-CoG 2014 grant AEROSOL (PI. L. Decin).
The project
At the Leuven University (Belgium), we
seek candidates for two post-doctoral and two PhD research positions,
ready to play a key role in a new interdisciplinary project focusing
on stellar winds around evolved (low-mass) stars. The candidates will
interact closely with a team consisting of astrophysicists, chemists,
and computational mathematicians, as the goal of the project is to
boost our understanding of the physics and chemistry characterizing
these stellar winds. The project builds upon novel data (including
ALMA, Herschel, etc.), detailed theoretical wind models, and targeted
laboratory experiments (see
http://fys.kuleuven.be/ster/Projects/aerosol/aerosol).
Institute
of Astronomy
The Institute of Astronomy of the Leuven
University is a young and active research group of some 50
scientists, engineers and administrative staff
(http://www.ster.kuleuven.be). The institute is involved in several
international networks and research projects, involving telescopes at
international observatories and space missions. The institute is also
responsible for the organisation of the Master in Astronomy &
Astrophysics of the Faculty of Science at the Leuven University. The
institute has a long tradition in the observational and theoretical
studies of the late stages of evolution of low and intermediate mass
stars.
For the ERC-CoG AEROSOL project of Prof. L. Decin, we
seek one post-doc and one PhD candidate to work on the reduction,
analysis and (radiative transfer) modeling of a whole suit of
observations ranging from the UV to mm wavelength regime with the aim
to retrieve the geometrical, thermodynamical and chemical structures
of stellar winds. The post-doc preferentially has experience with
infrared and (sub)millimeter observations and has in any case
sufficient experience in implementing and exploiting radiative
transfer models. The post-doc will also be allowed to carry out
(part-time) his/her own research in collaboration with affiliated
group members. The successful candidates will have access to recently
obtained and granted observational data, advanced radiative transfer
and forward chemistry modeling tools and will have the possibility to
develop their own (hydro)simulations.
Physical Chemistry
As
part of this project, one post-doc and one PhD position is open in
the research group of Prof. S. Carl in the field of experimental
gas-phase reaction kinetics in the Department of Chemistry, division
of Quantum and Physical chemistry, beginning preferably on 1st
October 2015. The experimental work will be carried out in the modern
and fully-equipped new research laboratories of the Department of
Chemistry, opening in mid 2015. The experimental research concerns
the determination of rate coefficients and product distributions of
elementary gas-phase reactions involving key reactive species (Si-
and S-bearing species and HCCO radicals) in stellar winds for which
data is currently lacking. Specifically, several advanced
laser-spectroscopic and chemiluminescence techniques will be employed
by the PhD student to follow photolytically-generated reactive
species in real time in a novel temperature-graded reaction vessel
(200−900 K) coupled with cavity-ringdown/Fourier-transform infrared
spectroscopy to elucidate reaction product channels. The post-doc
will concentrate on the construction and exploitation of a novel
low-temperature Laval-nozzle apparatus with the aim to obtain the
rates of the same gas-phase reactions at temperatures below 200 K.
Candidates should have an interest in physical chemistry,
high-resolution laser spectroscopy, and technical experimentation.
The group currently enjoys and encourages further close collaboration
with researches in the department employing high-level quantum
chemical calculations on species related to this project.
The
position
At the Leuven University, the candidates will join
the Institute for Astronomy (Prof. L. Decin) or the Physical
Chemistry section (Prof. S. Carl). The interdisciplinary project is
carried out in collaboration with Prof. T. Millar (Belfast
University) and Prof. J. Nuth (NASA, Greenbelt). The four candidates
will interact closely with the other team members at the Institute of
Astronomy and Department of Chemistry. At the Leuven University, we
have access to parallel computing facilities, to be exploited
extensively in this project.
Contract
The PhD candidates
will be employed for a 2+2 (after positive evaluation) period at the
Institute of Astronomy or a 2+1 period at the Department of
Chemistry. The initial contract for the post-doc positions runs over
2 years and could be prolonged with another year after positive
evaluation. The salary will be commensurate to the standard scale for
PhD and post-doctoral researchers at the Leuven University. The
preferred starting date is between 1 October 2015 and 1 December
2015, but will be adapted to the selected candidate’s availability.
Candidates are thus requested to indicate their preferred starting
date in the application.
Interested?
The successful
post-doc candidates must have a PhD degree in astrophysics or
chemistry, while the PhD candidates must have obtained a master
degree in (astro)physics, mathematics or chemistry. The application
must include
• A Curriculum Vitae (including publication list).
• A statement of research interests and future plans (maximum 3
pages).
• A letter detailing your specific qualifications for
the position and your career/educational goals (maximum 1 page).
•
Two letters of recommendation from professors well acquainted with
your academic achievements. The letters are to be submitted
separately to the address mentioned below.
DEADLINE for the
application: 1 May 2015
More information can be obtained by
contacting
Prof. L. Decin
Institute for Astronomy
Department
of Physics and Astronomy, KU Leuven
Celestijnenlaan 200D, 3001
Heverlee, Belgium
Leen.Decin@ster.kuleuven.be
++32-16-32 70
41
http://fys.kuleuven.be/ster/staff/senior-staff/leen
See
also: http://www.fys.kuleuven.be/ster/
Prof. S. Carl
Physical Chemistry Section
Department of Chemistry, KU Leuven
Celestijnenlaan 200F, 3001 Heverlee, Belgium
Shaun.Carl@chem.kuleuven.be
++32-16-32 76
13
Attention/Comments:
Weblink:
http://fys.kuleuven.be/ster/vacancies
Email:
Leen.Decin@ster.kuleuven.be
Deadline: 01/05/2015
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August 11-13, 2015
Venue: XXIX IAU
General Assembly (Honolulu, HI)
Dear colleagues,
We
want to draw your attention to Focus Meeting 10 "Stellar
explosions in an ever-changing environment", which takes place
during the XXIX IAU General Assembly this August in Hawai'i. The
meeting itself is scheduled from August 11-13.
In this
meeting we want to foster the interaction between the communities
working on massive stellar explosions (GRBs, SNe, SLSNe) and those
working on star-forming galaxies and galaxy evolution, to study their
mutual influences. Both observational and theoretical contributions
are welcome.
The key topics to be covered are the following:
-Host galaxies of GRBs, SNe and massive stars
-Starburst
galaxies as potential host of massive stellar explosions
-Diversity
of GRBs, SNe and their progenitors
-Dependence of stellar
evolution on the properties of their progenitors and environments
-Resolved observations of the explosion environments
-Influence
of stellar explosions on their environments
-Chemical evolution
of galaxies due to massive stellar explosions
-Probing the first
galaxies with GRBs
-Future facilities and techniques
Invited
speakers (confirmed) are:
Chris Fryer, Nancy Elias de la Rosa,
Selma de Mink, Giorgos Leloudas, Lisa Kewley, Janice Lee, Michal
Michalowski, Sebastian Sánchez, Paul Vreeswijk, Emily Levesque and
Chiaki Kobayashi
More information can be found on our meeting
webpage:
www.iaa.es/iau2015_fm10
We would be happy to
receive your contribution. Registration and abstract submission is
done through the IAU GA pages, with a deadline of March 18:
http://astronomy2015.org/
Students, postdocs and participants
from countries in difficult economic situations can apply for some
small funding for the meeting (deadline April 1). Participants
applying for funding have to submit an abstract.
Christina
Thöne and Lise Christensen
on behalf of the FM 10 SOC
Weblink:
www.iaa.es/iau2015_fm10
Email:
Emily.Levesque@colorado.edu
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September 21-25, 2015
Venue:
St.Petersburg
Studies of radiation mechanisms and
processes of spectra formation in astrophysical objects are among the
fundamental tasks of modern astrophysics. A powerful tool for the
solution of these problems is provided by the theory of radiative
transfer, which has been substantially contributed to and developed
by the full member of the Soviet (Russian) Academy of Sciences Victor
Victorovich Sobolev. The Sobolev method to solve the radiative
transfer equations, among his numerous results in the field of
radiative transfer, became classical nowadays. In 1947-1998 V.V.
Sobolev was the head of the Chair of Astrophysics of the
Leningrad/St. Petersburg State University and a leader of the
Leningrad/St. Petersburg astrophysical school, which had won
international recognition for many valuable results.
The
100th birthday anniversary of V.V. Sobolev will be celebrated on
September 2, 2015. On this occasion the Saint-Petersburg State
University organizes an international conference “Radiation
mechanisms of astrophysical objects: classics today”, which will be
held in St. Petersburg from September, 21 to September, 25, 2015. The
conference will highlight recent advances in the field of interests
of V.V. Sobolev. The conference will include plenary sessions with
review talks by internationally recognized Russian and foreign
scientists and a memorial session.
Weblink:
http://www.astro.spbu.ru/Sobolev100/?q=en
Email:
lida@astro.physik.uni-potsdam.de
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