ISSN 1783-3426
|
Special Issue on "Evolved Massive Stars in Transition Phases"
Herschel imaging and spectroscopy of
the nebula around the luminous blue variable star WRAY
15-751
DETECTION OF THE COMPRESSED
PRIMARY STELLAR WIND IN ETA CARINAE
Low-amplitude
rotational modulation rather than pulsations in the CoRoT B-type
supergiant HD 46769
The XMM-Newton
EPIC X-ray Light Curve Analysis of WR 6
Probing
the ejecta of evolved massive stars in transition: A VLT/SINFONI
K-band survey
Grids of stellar
models with rotation - III. Models from 0.8 to 120 M⊙ at a
metallicity Z = 0.002
GYRE: An
open-source stellar oscillation code based on a new Magnus Multiple
Shooting Scheme
Wind Bubbles, Astrospheres and the Heliosphere: Environments and Cosmic Ray Accelerators
We would like to draw the
attention of the massive star community to the call for papers for a
Special Issue on "Evolved Massive Stars in Transition Phases".
This issue is aimed at providing a platform for recent results and
new ideas in the field.
The post-main sequence evolution of
massive stars is one of the big open issues in modern astronomy. On
their evolutionary paths, crossing the region of the classical blue
supergiants, all the way up to the final supernova explosion, massive
stars pass through several transition phases (B[e] supergiants, red
supergiants, yellow hypergiants, luminous blue variables, and
Wolf-Rayet stars), in which they often undergo strong mass loss. The
physical mechanisms behind it and the amount of material ejected,
both in form of asymmetric, steady winds or violent episodic
eruptions, are currently unknown but crucial to understand stellar
evolution. Recent advances in both numerical modeling techniques and
high-quality observations will provide the key physical ingredients
for the next generation of evolutionary and wind models. We invite
investigators to contribute to original research articles as well as
review articles that will stimulate the continuing effort to
understand both the classical blue supergiants and massive stars in
transition phases. We are interested in articles that explore aspects
of evolutionary connections, the mass-loss behavior, the triggering
mechanisms for variability and mass eruptions, the interaction of the
ejected material with the environment, and dust production from both
observational and modeling perspectives. Potential topics include,
but are not limited to:
1. Origin of the variability seen in
classical blue supergiants and evolved massive stars in transition
phases, focusing in particular on the role of the high luminosity and
proximity to the Eddington limit, pulsations, rotation, and magnetic
fields
2. Insights from high-quality spectroscopic,
photometric, polarimetric, and interferometric data into reliable
timescales of the variabilities and their influence throughout the
evolution of massive stars
3. The shape of the circumstellar
environment and the feedback of the interstellar medium to the
variable mass loss and eruptions, and how studies on the stellar
environments improve our knowledge about the history of the gas and
the evolution of these stars
4. Evidences of evolutionary
connections (progenitors, fates) between different transition phases
5. Role of binarity in the evolution of massive stars, and
the consequences of binary interactions for the surroundings
All
submissions will be refereed. More details on the schedule, and
information on the submission process can be found at the web-address
below.
On behalf of the editors
Michaela Kraus, Lydia
Cidale and Jose Groh
Weblink:
http://www.hindawi.com/journals/aa/si/839059/cfp/
Email:
kraus@sunstel.asu.cas.cz
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C. Vamvatira-Nakou, D. Hutsemekers, P. Royer, Y. Naze, P.
Magain, K. Exter, C. Waelkens, M. A. T. Groenewegen
ULg,
ULg, KUL, ULg, ULg, KUL, KUL, ROB
We have obtained
far-infrared Herschel PACS imaging and spectroscopic observations of
the nebular environment of the luminous blue variable WRAY 15-751.
These images clearly show that the main, dusty nebula is a shell of
radius 0.5 pc and width 0.35 pc extending outside the H-alpha nebula.
They also reveal a second, bigger and fainter dust nebula, observed
for the first time. Both nebulae lie in an empty cavity, likely the
remnant of the O-star wind bubble formed when the star was on the
main sequence. The kinematic ages of the nebulae are about 20000 and
80000 years and each nebula contains about 0.05 Msun of dust.
Modeling of the inner nebula indicates a Fe-rich dust. The
far-infrared spectrum of the main nebula revealed forbidden emission
lines coming from ionized and neutral gas. Our study shows that the
main nebula consists of a shell of ionized gas surrounded by a thin
photodissociation region illuminated by an "average"
early-B star. The derived abundance ratios N/O=1.0+/-0.4 and
C/O=0.4+/-0.2 indicate a mild N/O enrichment. We estimate that the
inner shell contains 1.7+/-0.6 Msun of gas. Assuming a similar
dust-to-gas ratio for the outer nebula, the total mass ejected by
WRAY 15-751 amounts to 4+/-2 Msun. The measured abundances, masses
and kinematic ages of the nebulae were used to constrain the
evolution of the star and the epoch at which the nebulae were
ejected. Our results point to an ejection of the nebulae during the
RSG evolutionary phase of an ~ 40 Msun star. The presence of multiple
shells around the star suggests that the mass-loss was not a
continuous ejection but rather a series of episodes of extreme
mass-loss. Our measurements are compatible with the recent
evolutionary tracks computed for an 40 Msun star with little
rotation. They support the O-BSG-RSG-YSG-LBV filiation and the idea
that high-luminosity and low-luminosity LBVs follow different
evolutionary paths.
Reference: accepted for publication
in A&A
Status: Manuscript has been accepted
Weblink:
http://fr.arxiv.org/abs/1307.0759
Comments:
Email: chloevn@astro.ulg.ac.be
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M. Teodoro (1,2), T. I.
Madura (1,3), T. R. Gull (1), M. F. Corcoran (4,5), and K. Hamaguchi
(4,6)
1 - Astrophysics Science Division, Code 667, NASA
Goddard Space Flight Center, Greenbelt, MD 20771, USA; 2 -
CNPq/Science without Borders Fellow; 3 - NASA Postdoctoral Program
Fellow; 4 - CRESST and Xray Astrophysics Laboratory, Code 662, NASA
Goddard Space Flight Center, Greenbelt, MD 20771, USA; 5 -
Universities Space Research Association, 10211 Wincopin Circle, Suite
500 Columbia, MD 21044, USA; 6 - Department of Physics, University of
Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250,
USA
A series of three HST/STIS spectroscopic mappings, spaced
approximately one year apart, reveal three partial arcs in [Fe II]
and [Ni II] emissions moving outward from eta Carinae. We identify
these arcs with the shell-like structures, seen in the 3D
hydrodynamical simulations, formed by compression of the primary wind
by the secondary wind during periastron passages.
Reference:
To appear in ApJ Letters
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1307.3244
Comments:
Email: mairan.teodoro@nasa.gov
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C. Aerts, S. Simon-Diaz, C.
Catala, C. Neiner, M. Briquet, N. Castro, V.S. Schmid, M. Scardia, M.
Rainer, E. Poretti, P.I. Papics, P. Degroote, S. Bloemen, R.H.
Oestensen, M. Auvergne, A. Baglin, F. Baudin, E. Michel, R.
Samadi
Instituut voor Sterrenkunde, KU Leuven,
Celestijnenlaan 200D, B-3001 Leuven, Belgium
and
Department
of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010,
6500 GL Nijmegen, The Netherlands
and
Instituto de
Astrof'{i}sica de Canarias, 38200, La Laguna, Tenerife, Spain
and
Departamento de Astrof'{i}sica, Universidad de La Laguna, 38205,
La Laguna,
Tenerife, Spain
and
LESIA, CNRS UMR8109,
Universit'e Pierre et Marie Curie, Universit'e Denis
Diderot,
Observatoire de Paris, 92195 Meudon Cedex, France
and
Institut
d'Astrophysique et de G'eophysique, Universit'e de Li`ege, All'ee
du
6 Ao^ut 17 B-4000 Li`ege, Belgium
and
Argelander-Institut
f"ur Astronomie der Universit"at Bonn,
D-53121 Bonn,
Germany
and
INAF - Osservatorio Astronomico di Brera, via E.
Bianchi 46, 23807, Merate, LC,
Italy
and
Institut
d'Astrophysique Spatiale, CNRS/Universit'e Paris XI UMR 8617,
F-091405
Orsay, France
{We aim to detect and interpret
photometric and spectroscopic variability of the bright CoRoT B-type
supergiant target HD,46769 ($V=5.79$). We also attempt to detect a
magnetic field in the target.} {We analyse a 23-day oversampled CoRoT
light curve after detrending, as well as spectroscopic follow-up
data, by using standard Fourier analysis and Phase Dispersion
Minimization methods. We determine the fundamental parameters of the
star, as well as its abundances from the most prominent spectral
lines. We perform a Monte Carlo analysis of spectropolarimetric data
to obtain an upper limit of the polar magnetic field, assumping a
dipole field.} {In the CoRoT data, we detect a dominant period of
4.84,d with an amplitude of 87,ppm, and some of its (sub-)multiples.
Given the shape of the phase-folded light curve and the absence of
binary motion, we interpret the dominant variability in terms of
rotational modulation, with a rotation period of 9.69,d. Subtraction
of the rotational modulation signal does not reveal any sign of
pulsations. Our results are consistent with the absence of
variability in the Hipparcos light curve. The spectroscopy leads to a
projected rotational velocity of 72$pm 2$,km,s$^{-1}$ and does not
reveal periodic variability nor the need to invoke macroturbulent
line broadening. No signature of a magnetic field is detected in our
data. A field stronger than $sim 500$,G at the poles can be excluded,
unless the possible non-detected field were more complex than
dipolar.} {The absence of pulsations and of macroturbulence of this
evolved B-type supergiant is placed into context of instability
computations and of observed variability of evolved B-type
stars.}
Reference: Accepted for publication in
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1307.5791
Comments:
Email: conny.aerts@ster.kuleuven.be
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R. Ignace, K.G. Gayley, W. R.
Hamann, D. P. Huenemoerder, L. M. Oskinova, A. M. T. Pollock, M.
McFall
ETSU, U of Iowa, U of Potsdam, MIT, U of Potsdam,
ESA, Ohio State U
We obtained four pointings of over 100 ks
each of the well-studied Wolf-Rayet star WR 6 with the XMM-Newton
satellite. With a first paper emphasizing the results of spectral
analysis, this follow-up highlights the X-ray variability clearly
detected in all four pointings. However, phased light curves fail to
confirm obvious cyclic behavior on the well-established 3.766 d
period widely found at longer wavelengths. The data are of such
quality that we were able to conduct a search for "event
clustering" in the arrival times of X-ray photons. However, we
fail to detect any such clustering. One possibility is that X-rays
are generated in a stationary shock structure. In this context we
favor a co-rotating interaction region (CIR) and present a
phenomenological model for X-rays from a CIR structure. We show that
a CIR has the potential to account simultaneously for the X-ray
variability and constraints provided by the spectral analysis.
Ultimately, the viability of the CIR model will require both
intermittent long-term X-ray monitoring of WR 6 and better physical
models of CIR X-ray production at large radii in stellar
winds.
Reference: to appear in ApJ
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1307.7074
Comments:
Email: ignace@etsu.edu
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M.E. Oksala(1), M. Kraus(1),
L.S. Cidale(2,3), M.F. Muratore(2,3), M. Borges Fernandes(4)
(1)
Astronomical Institute, ASCR; (2) Universidad Nacional de La Plata
(UNLP); (3) Instituto de Astrofisica La Plata, CONICET; (4)
Observatorio Nacional
Massive evolved stars in transition
phases, such as Luminous Blue Variables (LBVs), B[e] Supergiants
(B[e]SGs), and Yellow Hypergiants (YHGs), are not well understood,
and yet crucial steps in determining accurate stellar and galactic
evolution models. The circumstellar environments of these stars
reveal their mass-loss history, identifying clues to both their
individual evolutionary status and the connection between objects of
different phases. Here we present a survey of 25 such evolved massive
stars (16 B[e]SGs, 6 LBVs, 2 YHGs, and 1 Peculiar Oe star), observed
in the K-band with the Spectrograph for INtegral Field Observation in
the Near-Infrared (SINFONI; R = 4500) on the ESO VLT UT4 8 m
telescope. The sample can be split into two categories based on
spectral morphology: one group includes all of the B[e]SGs, the
Peculiar Oe star, and two of the LBVs, while the other includes the
YHGs and the rest of the LBVs. The difference in LBV spectral
appearance is due to some objects being in a quiescent phase and some
objects being in an active or outburst phase. CO emission features
are found in 13 of our targets, with first time detections for MWC
137, LHA 120-S 35, and LHA 115-S 65. From model fits to the CO band
heads, the emitting regions appear to be detached from the stellar
surface. Each star with ^12CO features also shows ^13CO emission,
signaling an evolved nature. Based on the level of ^13C enrichment,
we conclude that many of the B[e]SGs are likely in a pre-Red
Supergiant phase of their evolution. There appears to be a lower
luminosity limit of log L/L_solar = 5.0 below which CO is not
detected. The lack of CO features in several high luminosity B[e]SGs
and variability in others suggests that they may in fact be LBV
candidates, strengthening the connection between these two very
similar transition phases.
Reference: To appear in
A&A.
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1308.2103
Comments:
Email: meo@udel.edu
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C. Georgy$^{1,2}$, S.
Ekström$^3$, P. Eggenberger$^3$, G. Meynet$^3$, L. Haemmerlé$^3$,
A. Maeder$^3$, A. Granada$^3$, J. H. Groh$^3$, R. Hirschi$^{1,4}$, N.
Mowlavi$^3$, N. Yusof$^{6,7}$, C. Charbonnel$^{3,5}$, T.
Decressin$^3$, and F. Barblan$^3$
1 - Astrophysics group,
EPSAM, Keele University, Lennard-Jones Labs, Keele, ST5 5BG, UK
2
- Centre de recherche astrophysique, Ecole Normale Supérieure de
Lyon, 46, allée d’Italie, F-69384 Lyon cedex 07, France
3 -
Geneva Observatory, University of Geneva, Maillettes 51, CH-1290
Sauverny, Switzerland
4 - Institute for the Physics and
Mathematics of the Universe (WPI), University of Tokyo, 5-1-5
Kashiwanoha, Kashiwa, 277-8583,
Japan
5 - IRAP, UMR 5277 CNRS
and Université de Toulouse, 14, Av. E.Belin, 31400 Toulouse, France
6 - Department of Physics, Faculty of Science, University of
Malaya, 50603 Kuala Lumpur, Malaysia
7 - Quantum Science Center,
Faculty of Science, University of Malaya, 50603 Kuala Lumpur,
Malaysia
Aims. We study the impact of a subsolar metallicity
on various properties of non-rotating and rotating stars, such as
surface velocities and abundances, lifetimes, evolutionary tracks and
evolutionary scenarios.
Methods. We provide a grid of single star
models covering a mass range from 0.8 to 120 M⊙ with an initial
metallicity Z = 0.002 with and without rotation. We discuss the
impact of a change in the metallicity by comparing the current tracks
with models computed with exactly the same physical ingredients but
with a metallicity Z = 0.014 (solar).
Results. We show that the
width of the main-sequence (MS) band in the upper part of the
Hertzsprung-Russell diagram (HRD), for luminosity above log(L/L⊙) >
5.5, is very sensitive to rotational mixing. Strong mixing
significantly reduces the MS width. We confirm, but here for the
first time on the whole mass range, that surface enrichments are
stronger at low metallicity provided that comparisons are made for
equivalent initial mass, rotation and evolutionary stage. We show
that the enhancement factor due to a lowering of the metallicity (all
other factors kept constant) increases when the initial mass
decreases. Present models predict an upper luminosity for the red
supergiants (RSG) of log (L/L⊙) around 5.5 at Z = 0.002 in
agreement with the observed upper limit of RSG in the Small
Magellanic Cloud. We show that models using shear diffusion
coefficient calibrated to reproduce the surface enrichments observed
for MS B-type stars at Z = 0.014 can also reproduce the stronger
enrichments observed at low metallicity. In the framework of the
present models, we discuss the factors governing the timescale of the
first crossing of the Hertzsprung gap after the MS phase. We show
that any process favouring a deep localisation of the H-burning shell
(steep gradient at the border of the H-burning convective core, low
CNO content) and/or the low opacity of the H-rich envelope favour a
blue position in the HRD for the whole or at least a significant
fraction of the core He-burning phase.
Reference: Astronomy
and Astrophysics
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1308.2914
Comments:
Email: c.georgy@keele.ac.uk
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R. H. D. Townsend, S. A.
Teitler
University of Wisconsin-Madison, Department of
Astronomy, Madison, WI 53706, USA
We present a new oscillation
code, GYRE, which solves the stellar pulsation equations (both
adiabatic and non-adiabatic) using a novel Magnus Multiple Shooting
numerical scheme devised to overcome certain weaknesses of the usual
relaxation and shooting schemes appearing in the literature. The code
is accurate (up to 6th order in the number of grid points), robust,
efficiently makes use of multiple processor cores and/or nodes, and
is freely available in source form for use and distribution. We
verify the code against analytic solutions and results from other
oscillation codes, in all cases finding good agreement. Then, we use
the code to explore how the asteroseismic observables of a 1.5 Msun
star change as it evolves through the red-giant bump.
Reference:
MNRAS, in press
Status: Manuscript has been accepted
Weblink:
http://www.astro.wisc.edu/~townsend/gyre/
Comments:
Website includes preprint, source code, &
documentation
Email: townsend@astro.wisc.edu
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Y. Naze
ULg
Over
the last decade, large-scale, organized (generally dipolar) magnetic
fields with a strength between 0.1 and 20 kG were detected in dozens
of OB stars. This contribution reviews the impact of such magnetic
fields on the stellar winds of O-stars, with emphasis on variability
and X-ray emission.
Reference: Invited review at
"Putting A-stars into context" (June 2013 ; Moscow,
Russia)
Status: Conference proceedings
Weblink:
http://fr.arxiv.org/abs/1306.6753
Comments:
Email: naze@astro.ulg.ac.be
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4 - 8 November 2013
Venue: Ruhr-University
Bochum, Bochum, Germany
The interdisciplinary workshop will
give a synoptic overview of the commonality and differences between
astrospheres (or stellar wind bubbles) and the heliosphere, as well
as the production and leakage of cosmic rays in such 'Spheres'.
The
heliophysical research has reached a state of unprecedented
theoretical knowledge, a very detailed modeling and rich high
resolution in-situ and remote sensing observations. The astronomical
remote sensing and modeling approach also reached a sophisticated
level. Because the large-scale modeling in both fields is based on a
similar set of (magneto-)hydrodynamic equations, one aim of this
workshop is to identify the commonalities and discuss the underlying
physics like the influence of neutrals or plasma cooling on the
large-scale structure. In addition, the transport of energetic
particles, which are naturally involved in the dynamics of the
heliosphere, and its extension to astrospheres will be a major topic
of the workshop. This workshop is important because it allows to
explore and compare physical processes that are fundamental for
astrophysical and heliophysical as well as for laboratory plasmas.
The workshop is very timely, because with the present and
especially the upcoming observational possibilities to detect the
details of astrospherical structures, an understanding and
quantitative modeling of the underlying fundamental physical
properties is required. Moreover, astrospheres of hot stars can
contribute the flux of (sub-)TeV cosmic rays, which is observed by
large-area cosmic ray telescopes. Beside the modeling and observation
of large-scale astrospherical structures, one of the main topics.
Thus the workshop will cover many aspects regarding the large-scale
structure of the heliosphere and astrospheres, its observational
aspects, as well as the role of the latter as sources of cosmic rays
and other energetic particles. This is manifest by the five major
workshop topics, namely
* The heliosphere as a special
example of an astrosphere
* Astrospheres
* Magnetic fields in
and around astrospheres
* Acceleration and leakage of energetic
particles from astrospheres
* Latest developments in
astrospherical physics (including the heliosphere)
Weblink:
http://helio_cr.tp4.rub.de/Astrosphere/home.php
Email:
kweis@astro.rub.de
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