ISSN 1783-3426
|
VLTI Observatory survey at High Angular
resolution of Active OB stars
The IACOB project: I. Rotational
velocities in Northern Galactic O and early B-type stars revisited.
The impact of other sources of line-broadening
HI
Lyman-alpha equivalent widths of stellar populations
Modeling
Tracers of Young Stellar Population Age in Star-Forming Galaxies
The
Dynamics of Ultracompact HII Regions
Optical
spectra of 5 new Be/X-ray Binaries in the Small Magellanic Cloud and
the link of the supergiant B[e] star LHA 115-S 18 with an X-ray
source
On the origin of variable
structures in the winds of hot luminous stars
Wind
collisions in three massive stars of Cyg OB2
Discovery
of the first B[e] supergiants in M 31
Constraints
on Massive Star Formation: Cygnus OB2 was always an Association
The
feedback of massive stars on interstellar astrochemical processes
The
VLT-FLAMES Tarantula Survey. XIII: On the nature of O Vz stars in 30
Doradus
The eccentric massive
binary V380 Cyg: revised orbital elements and interpretation of the
intrinsic variability of the primary component
The
incidence of stellar mergers and mass gainers among massive stars
The
surface nitrogen abundance of a massive star in relation to its
oscillations, rotation, and magnetic field
The
Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern
Stars
Can the magnetic field in the
Orion arm inhibit the growth of instabilities in the bow shock of
Betelgeuse?
A Rare Encounter with
Very Massive Stars in NGC 3125-A1
Stellar Spectral Signatures in High-Redshift Galaxies
Two Ph.D. positions
Research
Fellow
NEW WINDOWS
ON MASSIVE STARS: Asteroseismology, interferometry, and
spectropolarimetry
X-ray
Astrophysics of Hot Massive Stars
Magnetism
and Variability in O stars
Dear colleagues of the massive star
community,
you might have heard already that Dimitri Mihalas
has passed away, after serious illness. This is very sad news for us
all. According to Ivan Hubeny, just one day before his death Dimitri
saw the more or less final manuscript of their new book on Stellar
Atmospheres. This and all his other books, as well as our memories,
will make him immortal to us.
Please find enclosed the
official obituary from Los Alamos, and a more personal obituary by
Ivan Hubeny, who was in close contact with Dimitri until his last
hours.
-------------------------------------
Obituary (from Los Alamos)
World-renowned astrophysicist
Dimitri Mihalas passed away in his sleep at his home on November 21,
2013 in Santa Fe, New Mexico. Dr. Mihalas retired from the University
of Illinois at Urbana-Champaign in 1999 and from the Los Alamos
National Laboratory in 2011. Dimitri, to his friends and family, has
donated his body to the University of New Mexico Medical School and
his library to New Mexico Tech.
Dimitri was born on March 20,
1939 in Los Angeles, California where he grew up. He received his B.
A., with Highest Honors, in three majors: Physics, Mathematics, and
Astronomy from the University of California at Los Angeles at age 20.
Four years later he received his Ph. D in Astronomy and Physics from
the California Institute of Technology. He then joined the faculty
of the Department of Astrophysical Sciences at Princeton
University. In the following three decades, he was a professor in the
Department of Astronomy at the University of Chicago, the University
of Colorado at Boulder, and the University of Illinois at
Urbana-Champaign. He was also a pioneer in astrophysics and
computational physics and remained a world leader in the fields of
radiation transport, radiation hydrodynamics, and astrophysical
quantitative
spectroscopy for most of his career. His broad
knowledge and immense contributions earned him election to the U.S.
National Academy of Sciences in 1981 (at age 42, fifteen years
earlier than the usual age of entry) and many other distinguished
awards. He was a laboratory fellow at the Los Alamos National
Laboratory.
Dimitri had an exceptional record of both
quantity and quality of work, and developed new and far-reaching
methodologies yielding results of great importance. He made
outstanding contributions to the field of Astronomy and Astrophysics.
Besides many high-quality papers, he authored or co-authored seven
books and co-edited three others. Among them, three of his books have
been used as textbooks for both undergraduate and graduate students
worldwide and translated into other languages such as Russian and
Chinese. His book Foundations of Radiation
Hydrodynamics has
become the “bible” of the radiation hydrodynamics community,
especially at Los Alamos and Lawrence Livermore National Laboratories
and the Naval Research Laboratory.
Dimitri’s colleagues and
graduate students held him in high appreciation and expressed their
admiration for him at the International Conference in Honor of
Dimitri Mihalas for his Lifetime Scientific Contributions on the
Occasion of his 70th Birthday held at Boulder in late March 2009.
A
symposium was published following the conference.
Throughout
his long career, Dimitri gave generously of himself to all with whom
he interacted. As an advisor, role model, confidant, and friend, he
saw each person as an individual, acknowledging strengths, helping
overcome weaknesses, giving encouragement, and enthusiastically
praising their success. He touched the lives and careers of many
students and colleagues and has left a lasting legacy to be cherished
by those who knew him.
-------------------------------------
Obituary (from Ivan Hubeny)
By now most of us have heard the sad news that Dimitri Mihalas passed away on November 21, 2013.
Dimitri was a leading figure in stellar atmospheres theory over the past more than four decades. He was enormously productive. In his early carrier he worked intensively with Larry Auer, and together they developed several crucial numerical schemes that spurred rapid progress in the computation of model stellar atmospheres. Among them, a momentous achievement was their Complete Linearization Method, which revolutionized the field. Dimitri was author of numerous books, including the classic "Galactic Astronomy" with James Binney, but his famous monograph "Stellar Atmospheres," published in 1970 with a major 2nd edition in 1978, immediately became for most of us the true bible of the field.
In the 1970's and early 1980's Dimitri worked at the High Altitude Observatory of the National Center of Atmospheric Research in Boulder, CO. Surrounded by solar observers there, Dimitri was constantly exposed to detailed pictures of the Sun's atmosphere, graphically showing severe departures from the then computational paradigm of a plane-parallel, horizontally-homogeneous hydrostatic structure. This confrontation led Dimitri to became deeply interested in radiation hydrodynamics, a field which would address these issues. Quite typically of him, in a few years he had produced the classic monograph "Foundations of Radiation Hydrodynamics," in collaboration with his then wife Barbara. Needless to say, this book quickly became a second bible of the field.
These texts are well known to the astronomical community. What is less well known is that Dimitri also published several collections of his poetry and other writings. From an early age, he suffered from bipolar syndrome and transient severe depression. Characteristically for him, he found a way to turn this difficult problem into help for others in a similar situation by writing several books, including "Depression and Spiritual Growth" and "Friendly Primer on Depression." I leaned that people suffering from these conditions have profited from Dimitri's books as much as, if not more than, we have benefited from his professional textbooks and articles.
All this demonstrates that Dimitri not only was a brilliant scientist, but also a truly great and exceptional human being. For many of us he was a teacher, role model, and good friend. He always offered personal, gentle, and yet very strong encouragement to his students and colleagues. He profoundly touched the lives of all who came in contact with him. This was clearly seen during a conference in Boulder in 2009, to honor Dimitri's lifetime work on the occasion of his 70th birthday. There, his many colleagues expressed their profound gratitude to him and shared many stories about how their work and life had been influenced by him.
As to me personally, I feel very privileged that I could collaborate with him on what sadly turned out to be his last major work: a project that first was conceived as a third edition of "Stellar Atmospheres," but in time grew into a completely new book, with a new title, "Theory of Stellar Atmospheres: An Introduction to Astrophysical Non-equilibrium Quantitative Spectroscopic Analysis." As a sad coincidence, Dimitri passed away just days after the final manuscript was submitted to press.
Dimitri will be missed dearly. But as with all great scientists, great minds, and great human beings, his legacy will continue for a long time to come.
Ivan Hubeny
-------------------------------------
Dear colleagues,
we
would like to announce a public, interferometric survey of the
gaseous circumstellar environments of hot stars. The survey is a bad
weather/filler program currently carried out by the VLTI group at the
Paranal observatory. The targets are selected from three classes: Be
stars, supergiants and LBVs, and interacting binaries. The data are
taken with the AMBER instrument in high spectral resolution setting
(R=12000). The data are available immediately through the ESO
archive. Quick-look reductions are published soon after and can be
obtained from a dedicated forum:
http://activebstars.iag.usp.br/index.php/forum/ohana
Read
more, including the proposal, at
http://activebstars.iag.usp.br/index.php/34-ohana
We hope the
data will be useful.
Best regards,
Willem-Jan de Wit,
Thomas Rivinius, and the Paranal VLTI group
Weblink:
http://activebstars.iag.usp.br/index.php/34-ohana
Email:
triviniu@eso.org
Back to contents
S. Simón-Díaz & A.
Herrero
Instituto de Astrofísica de Canarias
Stellar
rotation is an important parameter in the evolution of massive stars.
Accurate and reliable measurements of projected rotational velocities
in large samples of OB stars are crucial to confront the predictions
of stellar evolutionary models with observational constraints.
We
reassess previous determinations of projected rotational velocities
(vsini) in Galactic OB stars using a large, high quality
spectroscopic dataset, and a strategy which account for other sources
of broadening appart from rotation affecting the diagnostic lines.
We present a versatile and user friendly IDL tool --- based
on a combined Fourier Transform (FT) + goodness of fit (GOF)
methodology --- for the line-broadening characterization in OB-type
stars. We use this tool to (a) investigate the impact of
macroturbulent and microturbulent broadenings on vsini measurements,
and (b) determine vsini in a sample of ~200 Galactic OB-type stars,
also characterizing the amount of macroturbulent broadening (vmacro)
affecting the line profiles.
We present observational
evidence illustrating the strengths and limitations of the proposed
FT+GOF methodology for the case of OB stars. We confirm previous
statements (based on indirect arguments or smaller samples) that the
macroturbulent broadening is ubiquitous in the massive star domain.
We compare the newly derived vsini in the case of O stars and early-B
Supergiants and Giants (where the effect of the macroturbulent
broadening is found to be larger) with previous determinations not
accounting for this extra line-broadening contribution, and show that
those cases with vsini < 120 km/s need to be systematically
revised downwards by ~25 (+/-20) km/s. We suggest that
microturbulence may impose an upper limit below which vsini and
vmacro could be incorrectly derived by means of the proposed
methodology as presently used, and discuss the implications of this
statement on the study of relatively narrow line massive stars.
An
investigation of impact of the revised vsini distributions on the
predictions by massive star evolutionary models is now warranted.
Also, the reliability of vsini measurements in the low vsini regime,
using a more precise description of the intrinsic profiles used for
the line-broadening analysis, needs to be further
investigated.
Reference: A&A
Status: Manuscript
has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2013arXiv1311.3360S
Comments:
Accepted for publication in A&A (19 pages, 15 figures, 6
tables). Tables A1-A5 will be make available in the final edited
version of the paper (or under request to SS-D)
Email:
ssimon@iac.es
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Maria A. Peña-Guerrero &
Claus Leitherer
Space Telescope Science Institute
We
have compiled a library of stellar lya equivalent widths in O and B
stars using the model atmosphere codes cgen and tlus, respectively.
The equivalent widths range from about 0 to 30 AA in absorption for
early-O to mid-B stars. The purpose of this library is the prediction
of the underlying stellar lya absorption in stellar populations of
star-forming galaxies with nebular lya emission. We implemented the
grid of individual equivalent widths into the Starburst99 population
synthesis code to generate synthetic lya equivalent widths for
representative star-formation histories. A starburst observed after
10 Myr will produce a stellar lya line with an equivalent width of ~
-10$pm$4 AA in absorption for a Salpeter initial mass function. The
lower value (deeper absorption) results for an instantaneous burst,
and the higher value (shallower line) for continuous star formation.
Depending on the escape fraction of nebular lya photons, the effect
of stellar lya on the total profile ranges from negligible to
dominant. If the nebular escape fraction is 10%, the stellar
absorption and nebular emission equivalent widths become comparable
for continuous star formation at ages of 10 to 20 Myr.
Reference:
AJ, 146, 158
Status: Manuscript has been accepted
Weblink:
http://stacks.iop.org/1538-3881/146/158
Comments:
Email: pena@stsci.edu
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Emily M. Levesque, Claus
Leitherer
University of Colorado at Boulder; STScI
The
young stellar population of a star-forming galaxy is the primary
engine driving its radiative properties. As a result, the age of a
galaxy's youngest generation of stars is critical for a detailed
understanding of its star formation history, stellar content, and
evolutionary state. Here we present predicted equivalent widths for
the H-beta, H-alpha, and Br-gamma recombination lines as a function
of stellar population age. The equivalent widths are produced by the
latest generations of stellar evolutionary tracks and the Starburst99
stellar population synthesis code, and are the first to fully account
for the combined effects of both nebular emission and continuum
absorption produced by the synthetic stellar population. Our grid of
model stellar populations spans six metallicities (0.001 < Z <
0.04), two treatments of star formation history (a 10^6 Mo
instantaneous burst and a continuous star formation rate of 1 Mo per
year), and two different treatments of initial rotation rate (v_rot =
0.0v_crit and v_rot = 0.4v_crit). We also investigate the effects of
varying the initial mass function. Given constraints on galaxy
metallicity, our predicted equivalent widths can be applied to
observations of star-forming galaxies to approximate the age of their
young stellar populations.
Reference: ApJ, Vol. 779, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1311.1202
Comments:
Email: emily.levesque@colorado.edu
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Nathaniel Roth
Steven W.
Stahler
Eric Keto
Dept. of Physics, U. of California,
Berkeley CA 94720 USA
Dept. of Astronomy, U. of California,
Berkeley, CA 94720 USA
Harvard-Smithsonian Center for
Astrophysics, Cambridge, MA 02138 USA
Many ultracompact HII
regions exhibit a cometary morphology in radio continuum emission. In
such regions, a young massive star is probably ablating, through its
ultraviolet radiation, the molecular cloud that spawned it. On one
side of the star, the radiation drives an ionization front that
stalls in dense molecular gas. On the other side, ionized gas streams
outward into the more rarefied environment. This wind is
underpressured with respect to the neutral gas. The difference in
pressure draws in more cloud material, feeding the wind until the
densest molecular gas is dissipated.
Recent, time-dependent
simulations of massive stars turning on within molecular gas show the
system evolving in a direction similar to that just described. Here,
we explore a semi-analytic model in which the wind is axisymmetric
and has already achieved a steady state. Adoption of this simplified
picture allows us to study the dependence of both the wind and its
bounding ionization front on the stellar luminosity, the peak
molecular density, and the displacement of the star from the center
of the clump. For typical parameter values, the wind accelerates
transonically to a speed of about 15 km/s, and transports mass
outward at a rate of 10^{-4} msun/yr. Stellar radiation pressure acts
to steepen the density gradient of the wind.
Reference:
MNRAS
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1311.5912
Comments:
Email: nathaniel.roth@berkeley.edu
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G. Maravelias (1)
A.
Zezas (1,2,3)
V. Antoniou (3,4)
D. Hatzidimitriou
(5)
(1)University of Crete, Physics Department &
Institute of Theoretical & Computational Physics, GR-710 03
Heraklion, Crete, Greece
(2)Foundation for Research and
Technology-Hellas, Institute of Electronic Structure & Laser,
GR-711 10 Heraklion, Crete, Greece
(3)Harvard-Smithsonian Center
for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
(4)Iowa
State University, Department of Physics & Astronomy, Ames, IA
50011, USA
(5)University of Athens, Department of Physics,
Section of Astrophysics, Astronomy, and Mechanics, GR-157 84
Zografou, Athens, Greece
The Small Magellanic Cloud (SMC) is
well known to harbor a large number of High-Mass X-ray Binaries
(HMXBs). The identification of their optical counterparts provides
information on the nature of the donor stars and can help to
constrain the parameters of these systems and their evolution. We
obtained optical spectra for a number of HMXBs identified in previous
textit{Chandra} and textit{XMM-Newton} surveys of the SMC using the
AAOmega/2dF fiber-fed spectrograph at the Anglo-Australian Telescope.
We find 5 new Be/X-ray binaries (BeXRBs; including a tentative one),
by identifying the spectral type of their optical counterparts, and
we confirm the spectral classification of an additional 15 known
BeXRBs. We compared the spectral types, orbital periods, and
eccentricities of the BeXRB populations in the SMC and the Milky Way
and we find marginal evidence for difference between the spectral
type distributions, but no statistically significant differences for
the orbital periods and the eccentricities. Moreover, our search
revealed that the well known supergiant B[e] star LHA 115-S 18 (or
AzV 154) is associated with the weak X-ray source CXOU
J005409.57-724143.5. We provide evidence that the supergiant star LHA
115-S 18 is the optical counterpart of the X-ray source, and we
discuss different possibilities of the origin of its low X-ray
luminosity (Lx~4x10^33 erg/s).
Reference: MNRAS
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1312.0593
Comments:
Email: gmaravel@physics.uoc.gr
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Yannick J. L. Michaux ^{1,
2},
Anthony F. G. Moffat ^{1},
André-Nicolas Chené ^{3, 4,
5},
Nicole Saint-Louis ^{1}.
{1} : Département de
physique, Université de Montréal & Centre de Recherche en
Astrophysique du Québec
{2} École Normale Supérieure de Lyon &
Centre de Recherche en Astrophysique de Lyon
{3} Departamento de
Fisica y Astronomia, Universidad de Valparaiso
{4} Departamento
de Astronomia, Universidad de Concepcion
{5} Gemini Observatory,
Northern Operations Center
Examination of the temporal
variability properties of several strong optical recombination lines
in a large sample of Galactic Wolf–Rayet (WR) stars reveals
possible trends, especially in the more homogeneous WC than the
diverse WN subtypes, of increasing wind variability with cooler
subtypes. This could imply that a serious contender for the driver of
the variations
is stochastic, magnetic subsurface convection
associated with the 170 kK partial-ionization zone of iron, which
should occupy a deeper and larger zone of greater mass in cooler WR
subtypes. This empirical evidence suggests that the heretofore
proposed ubiquitous driver of
wind variability, radiative
instabilities, may not be the only mechanism playing a role in the
stochastic multiple small-scaled structures seen in the winds of hot
luminous stars. In addition to small-scale stochastic behaviour,
subsurface convection guided by a global magnetic field with
localized emerging loops may also be at the origin of the large-scale
corotating interaction
regions as seen frequently in O stars and
occasionally in the winds of their descendant WR
stars.
Reference:
On the origin of variable structures in the winds of hot luminous
stars
Yannick J. L. Michaux; Anthony F. J. Moffat; Andre-Nicolas
Chene; Nicole St-Louis
Monthly Notices of the Royal
Astronomical Society 2013; doi: 10.1093/mnras/stt2102
Status:
Manuscript has been accepted
Weblink:
Comments:
Email: michaux@astro.umontreal.ca
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Constantin Cazorla, Yael
Naze, Gregor Rauw
University of Liege
Aims: We wish
to study the origin of the X-ray emission of three massive
stars
in the Cyg OB2 association: Cyg OB2 #5, #8A, #12. Methods: To this
aim,
dedicated X-ray observations from XMM and Swift are used, as
well as archival
ROSAT and Suzaku data. Results: Our results on
Cyg OB2 #8A improve the phase
coverage of the orbit and confirm
previous studies: the signature of a
wind-wind collision is
conspicuous. In addition, signatures of a wind-wind
collision are
also detected in Cyg OB2 #5, but the X-ray emission appears to be
associated with the collision between the inner binary and the
tertiary
component orbiting it with a 6.7yr period, without a
putative collision inside
the binary. The X-ray properties
strongly constrain the orbital parameters,
notably allowing us to
discard some proposed orbital solutions. To improve the
knowledge
of the orbit, we revisit the light curves and radial velocity of the
inner binary, looking for reflex motion induced by the third
star. Finally, the
X-ray emission of Cyg OB2 #12 is also
analyzed. It shows a marked decrease in
recent years, compatible
with either a wind-wind collision in a wide binary or
the
aftermath of a recent eruption.
Reference: Accepted by
A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1312.1871
Comments:
Email: cazorla@astro.ulg.ac.be
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Michaela Kraus$^1$, Lydia S.
Cidale$^{2,3}$, Maria Laura Arias$^{2,3}$, Mary E. Oksala$^1$,
Marcelo Borges Fernandes$^4$
$^1$Astronomick'y 'ustav,
Akademie vv{e}d v{C}esk'e republiky, Friv{c}ova 298, 251,65
Ondv{r}ejov, Czech Republic
$^2$Departamento de Espectroscop'ia
Estelar, Facultad de Ciencias Astron'omicas y Geof'isicas,
Universidad Nacional de La Plata, B1900FWA, La Plata, Argentina
$^3$Instituto de Astrof'isica de La Plata, CCT La Plata,
CONICET-UNLP, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina
$^4$Observat'orio Nacional, Rua General Jos'e Cristino 77,
20921-400 S~ao Cristov~ao, Rio de Janeiro, Brazil
B[e]
supergiants (B[e]SGs) are transitional objects in the post-main
sequence evolution of massive stars. The small number of B[e]SGs
known so far in the Galaxy and the Magellanic Clouds indicates that
this evolutionary phase is short. Nevertheless, the strong aspherical
mass loss occurring during this phase, which leads to the formation
of rings or disk-like structures, and the similarity to possible
progenitors of SN1987A emphasize the importance of B[e]SGs for the
dynamics of the interstellar medium as well as stellar and galactic
chemical evolution. The number of objects and their mass loss
behavior at different metallicities are essential ingredients for
accurate predictions from stellar and galactic evolution
calculations. However, B[e]SGs are not easily identified, as they
share many characteristics with luminous blue variables (LBVs) in
their quiescent (hot) phase. We present medium-resolution
near-infrared K-band spectra for four stars in M 31, which have been
assigned a hot LBV (candidate) status. Applying diagnostics that were
recently developed to distinguish B[e]SGs from hot LBVs, we classify
two of the objects as bonafide LBVs; one of them currently in
outburst. In addition, we firmly classify the two stars 2MASS
J00441709+4119273 and 2MASS J00452257+4150346 as the first B[e]SGs in
M 31 based on strong CO band emission detected in their spectra, and
infrared colors typical for this class of stars.
Reference:
ApJ Letters (in press)
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1312.1836
Comments:
Email: kraus@sunstel.asu.cas.cz
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Nicholas J. Wright (1),
Richard J. Parker (2), Simon P. Goodwin (3), Jeremy J. Drake (3)
1.
University of Hertfordshire
2. ETH Zurich
3. University of
Sheffield
4. Smithsonian Astrophysical Observatory
We
examine substructure and mass segregation in the massive OB
association Cygnus OB2 to better understand its initial conditions.
Using a well understood Chandra X-ray selected sample of young stars
we find that Cyg OB2 exhibits considerable physical substructure and
has no evidence for mass segregation, both indications that the
association is not dynamically evolved. Combined with previous
kinematical studies we conclude that Cyg OB2 is dynamically very
young, and what we observe now is very close to its initial
conditions: Cyg OB2 formed as a highly substructured, unbound
association with a low volume density (< 100 stars/pc^3). This is
inconsistent with the idea that all stars form in dense, compact
clusters. The massive stars in Cyg OB2 show no evidence for having
formed particularly close to one another, nor in regions of higher
than average density. Since Cyg OB2 contains stars as massive as ~100
Mo this result suggests that very massive stars can be born in
relatively low-density environments. This would imply that the
massive stars in Cyg OB2 did not form by competitive accretion, or by
mergers.
Reference: 9 pages, 3 figures, accepted for
publication in MNRAS
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1311.4537
Email:
nick.nwright@gmail.com
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contents
M. De Becker
Department
of Astrophysics, Geophysics and Oceanography, University of Liège,
Belgium
Astrochemistry is a discipline that studies
physico-chemical processes in astrophysical environments. Such
environments are characterized by conditions that are substantially
different from those existing in usual chemical laboratories. Models
which aim to explain the formation of molecular species in
interstellar environments must take into account various factors,
including many that are directly, or indirectly related to the
populations of massive stars in galaxies. The aim of this paper is to
review the influence of massive stars, whatever their evolution
stage, on the physico-chemical processes at work in interstellar
environments. These influences include the ultraviolet radiation
field, the production of high energy particles, the synthesis of
radionuclides and the formation of shocks that permeate the
interstellar medium.
Reference: Accepted for
publication in Astrophysics and Space Science
Status: Manuscript
has been accepted
Weblink:
http://hdl.handle.net/2268/159499
Comments:
arXiv link: http://arxiv.org/abs/1312.2453
Email:
debecker@astro.ulg.ac.be
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C. Sab'in-Sanjuli'an(1,2), S.
Sim'on-D'iaz(1,2), A. Herrero(1,2), N. R. Walborn(3), J. Puls(4), J.
Ma'iz Apell'aniz(5), C. J. Evans(6), I. Brott(7), A. de
Koter(8,9), M. Garcia(10), N. Markova(11), F. Najarro(10), O. H.
Ram'irez-Agudelo(8), H. Sana(3), W. D. Taylor(6) and J. S.
Vink(12)
1- Instituto de Astrof'isica de Canarias, E-38200
La Laguna, Tenerife, Spain
2- Departamento de Astrof'isica,
Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain
3-
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore,
MD 21218, USA
4- Universit"ats-Sternwarte, Scheinerstrasse
1, 81679 Munchen, Germany
5- Instituto de Astrof'isica de
Andaluc'ia-CSIC, Glorieta de la Astronom'ia s/n, E-18008
Granada, Spain
6- UK Astronomy Technology Centre, Royal
Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK
7-
University of Vienna, Department of Astrophysics, Turkenschanzstr.
17, 1180, Vienna, Austria
8- Astronomical Institute Anton
Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ,
Amsterdam, The etherlands
9- Instituut voor Sterrenkunde,
Universiteit Leuven, Celestijnenlaan 200 D, 3001, Leuven, Belgium
10- Centro de Astrobiolog'ia (CSIC-INTA), Ctra. de Torrej'on a
Ajalvir km-4, E-28850 Torrej'on de Ardoz, Madrid, Spain
11-
Institute of Astronomy with NAO, Bulgarian Academy of Sciences, PO
Box 136, 4700 Smoljan, Bulgaria
12- Armagh Observatory, College
Hill, Armagh, BT61 9DG, Northern Ireland, UK
AIMS. We test the
hypothesis of O Vz stars (characterized by having HeII4686 stronger
in absorption than other He lines in their blue-violet spectra) being
at a younger evolutionary stage than are normal O-type dwarfs.
METHODS. We have performed a quantitative spectroscopic analysis
of a sample of 38 O Vz and 46 O V stars, identified by the VLT-FLAMES
Tarantula Survey in the 30 Doradus region of the Large Magellanic
Cloud (LMC). We obtained the stellar and wind parameters of both
samples using the FASTWIND stellar atmosphere code and the IACOB-GBAT
grid-based automatic tool. In the framework of a differential study,
we compared the physical and evolutionary properties of both samples,
regarding Teff, logg, logQ and logL. We also investigated the
predictions of the FASTWIND code about the O Vz phenomenon.
RESULTS.
We find a differential distribution of objects in terms of effective
temperature, with O Vz stars dominant at intermediate values. The O
Vz stars in 30 Doradus tend to be younger and less luminous, and they
have weaker winds than the O V stars, but we also find examples with
ages of 2-4 Myr and with luminosities and winds that are similar to
those of normal O dwarfs. Moreover, the O Vz stars do not appear to
have higher gravities than the O V stars. In addition to effective
temperature and wind strength, our FASTWIND predictions indicate how
important it is to take other stellar parameters (gravity and
projected rotational velocity) into account for correctly
interpreting the O Vz phenomenon.
CONCLUSIONS. In general, the O
Vz stars appear to be on or very close to the ZAMS, but there are
some examples where the Vz classification does not necessarily imply
extreme youth. In particular, the presence of O Vz stars in our
sample at more evolved phases than expected is likely a consequence
of modest O-star winds owing to the low-metallicity environment of
the LMC.
Reference: arXiv:1312.3278
Status:
Manuscript has been accepted
Weblink:
Comments:
Email: cssj_ext@iac.es
Back
to contents
A. Tkachenko, P. Degroote, C.
Aerts, K. Pavlovski, J. Southworth, P. I. Papics, E. Moravveji, V.
Kolbas, V. Tsymbal, J. Debosscher, and K. Clemer
Institute
of Astronomy, KU Leuven, Belgium
We present a detailed
analysis and interpretation of the high-mass binary V380 Cyg, based
on high-precision space photometry gathered with the Kepler space
mission as well as high-resolution ground-based spectroscopy obtained
with the HERMES spectrograph attached to the 1.2m Mercator telescope.
We derive a precise orbital solution and the full physical properties
of the system, including dynamical component mass estimates of
11.43+/-0.19 and 7.00+/-0.14 solar masses for the primary and
secondary, respectively. Our frequency analysis reveals the rotation
frequency of the primary in both the photometric and spectroscopic
data and additional low amplitude stochastic variability at low
frequency in the space photometry with characteristics that are
compatible with recent theoretical predictions for gravity mode
oscillations excited either by the convective core or by sub-surface
convective layers. Doppler Imaging analysis of the silicon lines of
the primary suggests the presence of two high-contrast stellar
surface abundance spots which are located either at the same latitude
or longitude. Comparison of the observed properties of the binary
with present-day single-star evolutionary models shows that the
latter are inadequate and lack a serious amount of near-core
mixing.
Reference: Monthly Notices of the Royal
Astronomical Society (MNRAS)
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1312.3601
Comments:
Email: andrew@ster.kuleuven.be
Back
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S.E. de Mink, H. Sana, N.
Langer, R.G. Izzard, F.R.N. Schneider
Carnegie
Observatories / Caltech, Space Telescope Science Institute,
Argelander Institute Bonn
Because the majority of massive
stars are born as members of close binary systems, populations of
massive main-sequence stars contain stellar mergers and products of
binary mass transfer. We simulate populations of massive stars
accounting for all major binary evolution effects based on the most
recent binary parameter statistics and extensively evaluate the
effect of model uncertainties.
Assuming constant star
formation, we find that 8+9−4% of a sample of early type stars to
be the product of a merger resulting from a close binary system. In
total we find that 30+10−15% of massive main-sequence stars are the
product of binary interaction.
We show that the commonly
adapted approach to minimize the effects of binaries on an observed
sample by excluding systems detected as binaries through radial
velocity campaigns can be counterproductive. Systems with significant
radial velocity variations are mostly pre-interaction systems.
Excluding them substantially enhances the relative incidence of
mergers and binary products in the non radial velocity variable
sample.
This poses a challenge for testing single stellar
evolutionary models. It also raises the question of whether certain
peculiar classes of stars, such as magnetic O-stars, are the result
of binary interaction and it emphasizes the need to further study the
effect of binarity on the diagnostics that are used to derive the
fundamental properties (star-formation history, initial mass
function, mass to light ratio) of stellar populations nearby and at
high redshift.
Reference: Tentatively scheduled for the
February 1, 2014, V781 - 2 issue of ApJ.
Status: Manuscript has
been accepted
Weblink:
http://arxiv.org/abs/1312.3650
Comments:
8 pages, 3 figures, accepted for publ. in ApJ
Email:
demink@obs.carnegiescience.edu
Back to
contents
Conny Aerts, Geert
Molenberghs, Michael G. Kenward, Coralie Neiner
Institute
of Astronomy, KULeuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium;
Department of Astrophysics, IMAPP, Radboud University Nijmegen,
P.O. Box 9010, 6500 GL Nijmegen, The Netherlands;
Faculty of
Science, Hasselt University, Martelarenlaan 42,
B-3500 Hasselt,
Belgium;
I-BioStat, KULeuven, Kapucijnenvoer 35,
B-3000
Leuven, Belgium;
Department of Medical Statistics, London School
of Hygiene and
Tropical Medicine, Keppel Street,
London
WC1E7HT, United Kingdom;
LESIA, UMR 8109 du CNRS, Observatoire de
Paris, UPMC, Paris
Diderot, 5 Place Jules Janssen 92195 Meudon
Cedex, France
We have composed a sample of 68 massive stars in
our galaxy whose projected
rotational velocity, effective
temperature and gravity are available from
high-precision
spectroscopic measurements. The additional seven observed
variables
considered here are their surface nitrogen abundance, rotational
frequency, magnetic field strength, and the amplitude and
frequency of their
dominant acoustic and gravity mode of
oscillation. Multiple linear regression
to estimate the nitrogen
abundance combined with principal components analysis,
after
addressing the incomplete and truncated nature of the data, reveals
that
the effective temperature and the frequency of the dominant
acoustic oscillation
mode are the only two significant predictors
for the nitrogen abundance,
while the projected rotational
velocity and the rotational frequency have no
predictive power.
The dominant gravity mode and the magnetic field strength
are
correlated with the effective temperature but have no predictive
power for
the nitrogen abundance.
Our findings are completely
based on observations and their proper
statistical treatment and
call for a new strategy in evaluating the
outcome of stellar
evolution computations.
Reference: Accepted for
publication in The Astrophysical Journal
Status: Manuscript has
been accepted
Weblink:
http://adsabs.harvard.edu/abs/2013arXiv1312.4144A
Comments:
Table 3 in electronic format available upon request.
Email:
conny@ster.kuleuven.be
Back to
contents
A. Sota, J. Maíz Apellániz,
N. I. Morrell, R. H. Barbá, N. R.
Walborn, R. C. Gamen, J. I.
Arias, and E. J. Alfaro
IAA-CSIC, LCO, ULS, STScI,
IALP
We present the second installment of GOSSS, a massive
spectroscopic survey of Galactic O stars, based on new homogeneous,
high signal-to-noise ratio, R ~ 2500 digital observations from both
hemispheres selected from the Galactic O-Star Catalog (GOSC). In this
paper we include bright stars and other objects drawn mostly from the
first version of GOSC, all of them south of delta = -20 degrees, for
a total number of 258 O stars. We also revise the northern sample of
paper I to provide the full list of spectroscopically classified
Galactic O stars complete to B = 8, bringing the total number of
published GOSSS stars to 448. Extensive sequences of exceptional
objects are given, including the early Of/WN, O Iafpe, Ofc, ON/OC,
Onfp, Of?p, and Oe types, as well as double/triple-lined
spectroscopic binaries. The new spectral subtype O9.2 is
also
discussed. The magnitude and spatial distributions of the observed
sample are analyzed. We also present new results from OWN, a
multi-epoch high-resolution spectroscopic survey coordinated with
GOSSS that is assembling the largest sample of Galactic spectroscopic
massive binaries ever attained. The OWN data combined with additional
information on spectroscopic and visual binaries from the literature
indicate that only a very small fraction (if any) of the stars with
masses above 15-20 M_Sol are born as single systems. In the future we
will publish the rest of the GOSSS survey, which is expected to
include over 1000 Galactic O stars.
Reference: To
appear in ApJS
Status: Manuscript has been accepted
Weblink:
http://jmaiz.iaa.es/files/Sotaetal14.pdf
Comments:
Email: jmaiz@iaa.es
Back
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Allard Jan van Marle$^1$
Leen Decin$^1$
Zakaria Meliani$^2$
$^1$Institute
of Astronomy, KU Leuven
$^2$Observatoire de Paris, Meudon
Many
evolved stars travel through space at supersonic velocities, which
leads to the formation of bow shocks ahead of the star where the
stellar wind collides with the interstellar medium (ISM). Herschel
observations of the bow shock of α-Orionis show that the shock is
almost free of instabilities, despite being, at least in theory,
subject to both Kelvin-Helmholtz and Rayleigh-Taylor instabilities. A
possible explanation for the lack of instabilities lies in the
presence of an interstellar magnetic field. We wish to investigate
whether the magnetic field of the interstellar medium (ISM) in the
Orion arm can inhibit the growth of instabilities in the bow shock of
α-Orionis. We used the code MPI-AMRVAC to make magneto-hydrodynamic
simulations of a circumstellar bow shock, using the wind parameters
derived for α-Orionis and interstellar magnetic field strengths of
B=1.4,3.0, and 5.0μG, which fall within the boundaries of the
observed magnetic field strength in the Orion arm of the Milky Way.
Our results show that even a relatively weak magnetic field in the
interstellar medium can suppress the growth of Rayleigh-Taylor and
Kelvin-Helmholtz instabilities, which occur along the contact
discontinuity between the shocked wind and the shocked ISM. The
presence of even a weak magnetic field in the ISM effectively
inhibits the growth of instabilities in the bow shock. This may
explain the absence of such instabilities in the Herschel
observations of α-Orionis.
Reference: A&A,
accepted
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1312.5877
Comments:
Email: allardjan@ster.kuleuven.be
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Aida Wofford (1), Claus Leitherer
(2), Rupali Chandar (3), and Jean-Claude Bouret (4)
1
-UPMC-CNRS, UMR7095, Institut d’Astrophysique de Paris, F-75014,
Paris, France
2- Space Telescope Science Institute, 3700 San
Martin Drive, Baltimore, MD 21218, USA
3- University of Toledo,
Department of Physics and Astronomy, Toledo, OH 43606, USA
4- Aix
Marseille Universite, CNRS, LAM (Laboratoire d’Astrophysique de
Marseille) UMR 7326, 13388, Marseille, France
Super star
cluster A1 in the nearby starburst galaxy NGC 3125 is characterized
by broad He II 1640 emission (full width at half maximum, FWHM∼1200
km s−1) of unprecedented strength (equivalent width, EW=7.1±0.4
AA). Previous attempts to characterize the massive star content in
NGC 3125-A1 were hampered by the low resolution of the UV spectrum
and the lack of co-spatial panchromatic data. We obtained far-UV to
near-IR spectroscopy of the two principal emitting regions in the
galaxy with the Space Telescope Imaging Spectrograph (STIS) and the
Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope
(HST). We use these data to study three clusters in the galaxy, A1,
B1, and B2. We derive cluster ages of 3-4 Myr, intrinsic reddenings
of E(B−V)=0.13, 0.15, and 0.13, and cluster masses of 1.7×10^5,
1.4×10^5, and 1.1×10^5 M⊙, respectively. A1 and B2 show O V 1371
absorption from massive stars, which is rarely seen in star-forming
galaxies, and have Wolf-Rayet (WR) to O star ratios of
N(WN5−6)/N(O)=0.23 and 0.10, respectively. The high N(WN5−6)/N(O)
ratio of A1 cannot be reproduced by models that use a normal IMF and
generic WR star line luminosities. We rule out that the extraordinary
He II 1640 emission and O V 1371 absorption of A1 are due to an
extremely flat upper IMF exponent, and suggest that they originate in
the winds of very massive (>120M⊙) stars. In order to reproduce
the properties of peculiar clusters such as A1, the present grid of
stellar evolution tracks implemented in Starburst99 needs to be
extended to masses >120M⊙.
Reference: Tentatively
scheduled for the ApJ, February 10, 2014, V782 -
1 issue
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1312.5982
Email:
wofford@iap.fr
Back to contents
N. Markova, J. Puls, S.
Simon-Diaz, A. Herrero, H.Markov, N. Langer
Rotation is
of key importance for the evolution of massive stars, including their
fate as supernovae or Gamma-ray bursts. However, the rotational
velocities of OB stars are difficult to determine. Based on our own
data for 31 Galactic O stars and incorporating similar data for 86 OB
supergiants from the literature, we investigated the properties of
rotational and extra line-broadening as a function of stellar
parameters and put constrains on model predictions about the
evolution of stellar rotation. Fundamental stellar parameters were
determined by means of the
code FASTWIND. Projected rotational
and extra broadening velocities, originate from a combined Fourier
transform + Goodness-of- fit method. Model calculations published
previously were used to estimate the initial evolutionary masses.
Our analysis shows that the sample O stars with initial masses
larger than 50~Msun rotate with less that 26% of their break-up
velocity, and they also lack slow rotators (vsini < 50~kms). For
the more massive stars (Minit > 35 Msun) on the hotter side of the
bi-stability jump, the observed and predicted rotational rates agree
quite well; for those on the cooler side of the jump, the measured
velocities are systematically higher than the predicted ones. In
general, the derived extra-broadening velocities decrease toward
cooler Teff, whilst for later evolutionary phases they appear, at the
same vsini, higher for high-mass stars than for low-mass ones. None
of the sample stars shows extra broadening velocities larger than
110~kms. For the majority of the more massive stars, extra broadening
either dominates or is in strong competition with rotation. The main
implications of our results are at least twofold: i) when appearing
at or close to the zero-age main sequence, most of the single and
more massive stars may rotate slower than previously thought; (ii)
model predictions for the evolution of rotation in hot massive stars
may need to be updated.
Reference: A&A
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/2013arXiv1310.8546M
Email:
nmarkova@astro.bas.bg
Back to contents
Claus Leitherer
STScI
Stellar emission and
absorption lines are routinely observed in galaxies at redshifts up
to 5 with spectrographs on 8-10m class telescopes. While the overall
spectra are well understood and have been successfully modeled using
empirical and theoretical libraries, some challenges remain. Three
issues are discussed: determining abundances using stellar and
interstellar spectral lines, understanding the origin of the strong,
stellar He II 1640 line, and gauging the influence of stellar
Lyman-alpha on the combined stellar+nebular profile. All three issues
can be tackled with recently created theoretical stellar libraries
for hot stars which take into account the radiation-hydrodynamics of
stellar winds.
Reference: International Workshop on
Stellar Spectral Libraries, Lyon (France), October 14 - 17, 2013. To
be published in ASI Conference Series, 2014, Vol. 10, editors: H. P.
Singh & P. Prugniel
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1312.2464
Email:
leitherer@stsci.edu
Back to contents
Georges Meynet
Astronomical
Observatory of Geneva University
The Geneva Observatory
invites applications for two PhD positions in the stellar evolution
group led by Prof. Georges Meynet.
The themes of the research
in the group are stellar physics, non standard mixing processes in
stars, massive star evolution, first stars, population of stars in
galaxies, nucleosynthesis, progenitors of core-collapse supernovae
and Gamma Ray Bursts, and asteroseismology. The group uses stellar
evolution codes, population synthesis codes, modeling of stellar
spectra, and predictions of asteroseismic observables to address
topical questions in the above themes.
The group would like
to take the opportunity of these two Ph.D positions to expand its
research activities along the two directions below:
1) The
modeling of close binary massive stars in order to study the
formation of systems containing compact objects such as neutron stars
and particularly black holes. The goal of the project is to
investigate the origin of compact object spin, and how it is
connected to the different physical processes taking place in the
evolution of close binary massive stars, progenitors of compact
object binaries.
2) The development of new models for the
first stellar generations in the Universe, in particular studying the
impact of rotation and magnetic fields on the expected
nucleosynthesis of these objects and obtaining better diagnostics for
identifying the presence of these first stellar generations in high
redshift galaxies.
The starting date of both positions is as
early as April 1st 2014, but later starting dates are possible. The
salary scale is attractive (starting at CHF 50 000) and funding is
available for up to 4 years.
The interested candidates are
invited to send to Georges Meynet (georges.meynet@unige.ch) the
following documents:
1) A motivation letter
2) A brief (1-2
pages) CV
3) At least two recommendation letters (one from the
master’s thesis advisor)
Deadline : January 31rst
2014.
Attention/Comments:
Weblink:
http://obswww.unige.ch/Recherche/evol/?lang=en
Email:
georges.meynet@unige.ch
Deadline: January 31st
2014.
Back to contents
Alexander Heger
Monash
Centre for Astrophysics
School of Mathematical Sciences
Monash
University, VIC 3800
Australia
We invite applications for
a Research Fellowship 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 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, first stars (formation and evolution),
or Type I X-ray burst and superbursts.
MoCA has very active
research groups in Stellar Interiors and Nucleosynthesis (SINs -
Lattanzio, Lugaro, Heger, Campbell, Mueller), High-energy
Astrophysics (Galloway, Levin, Donea, Heger, Price, Mueller,
Lazendic-Galloway), Astrophysical Fluid Dynamics and MHD (Monaghan;
Price - star formation), Galaxy Evolution (Bown), Numerical General
Relativity, and solar physics, amongst others (see
http://moca.monash.edu/research). The initial appointment is for two
years, with the possibility of extension for a third year contingent
upon satisfactory performance, at level A or B depending on
experience (A$64.175 - A$108.788 pa including 9.25% employer
superannuation). Commencement date should be on or before Oct. 1,
2014
The application needs to be submitted online at by Jan
31, 2013 (AEDT). For the full job ad and application instructions
please visit
http://jobs.monash.edu.au/jobDetails.asp?sJobIDs=518885
Attention/Comments:
Weblink:
http://jobs.monash.edu.au/jobDetails.asp?sJobIDs=518885
Email:
alexander.heger@monash.edu
Deadline: Jan 31, 2014
(COB AEDT)
Back to contents
June 23-27, 2014
Venue:
Geneva
(Switzerland)
=============================================================================================
FIRST ANNOUNCEMENT
IAU symposium 307
"NEW WINDOWS ON
MASSIVE STARS:
Asteroseismology, interferometry, and
spectropolarimetry"
Geneva (Switzerland)
June 23-27,
2014
=============================================================================================
* CONTACT:
email: iau307@unige.ch
webpage:
http://obswww.unige.ch/Conferences/IAU307/
* IMPORTANT DATES:
Deadline for grant request: January 31, 2014
Deadline for
abstract submission: April 30, 2014
Deadline for early fees (250
CHF): May 15, 2014
Conference: June 23-27, 2014
*
SCIENTIFIC RATIONALE:
The important outputs of mass, momentum and
energy of massive stars strongly modify their environment and make
them key agents in the evolution of galaxies during the whole of
cosmic history. Their high luminosities make them objects detectable
at far distances in the Universe. Massive stars are thus important
probes for studying star formation at high redshifts. As the
progenitors of core collapse supernovae, of the long soft Gamma Ray
Bursts, and of neutron stars and black holes, they are connected with
the most intriguing objects in the Universe.
Their physics is,
however, not yet very well known and such basic understanding as the
origin of the various massive star populations (Be-type stars, red
and blue supergiants, Luminous Blue Variables, Wolf- Rayet stars) are
still matters of debate, as well as the nature of the progenitors of
the various types of core-collapse supernovae (type IIP, IIL, IIb,
IIn, Ibc).
Among the great challenges faced nowadays in our
understanding of massive star evolution, we can cite the following
two points :
• Hydrodynamical processes: turbulent flow,
rotation, magnetic fields, as well as mass loss, are all basically
fluid dynamics of plasmas. These processes, by governing the quantity
of fuel available for a given nuclear burning stage, by modifying the
chemical structure of the stars, and by allowing the total mass to
strongly decline with time have a dramatic impact on the evolution of
massive stars. This also has strong consequences on the chemical
evolution of galaxies and on the evolution of their spectral energy
distribution.
• Role of multiplicity in massive star evolution
: in addition to the complex physics involved in single stars,
multiplicity adds new types of interactions through tidal forces,
mass transfer and/or stellar mergers, opening the path to a variety
of different evolutionary pathways populating various parts of the HR
diagram and leading to specific final structures and thus particular
supernova events.
Nowadays, asteroseismology, interferometry and
spectropolarimetry allow a view into what could have been thought
once as unreachable characteristics of stars in general and of
massive stars in particular, and thus can provide new clues on how
massive stars are evolving:
• Asteroseismology (MOST, CoRoT,
Kepler, BRITE) allows to probe what happens into the interior of
stars, to identify the zones where steep gradients of chemical
composition and of angular velocity occur. This provides essential
clues on transport processes inside stars. These transport processes,
together with the change of composition due to nuclear reactions and
mass loss by stellar winds and/or through mass transfer in close
binaries drive the evolution of stars.
• Interferometry (e.g.
VLTI, CHARA) explores the shape of stars, the structure and the
kinematics of their circumstellar environments. This allows us to
probe the deformation of stars resulting from fast rotation and/or
tidal forces, to explore the physics of disk formation around
early-type stars, to obtain diagnostics of possible anisotropies in
the stellar winds and probably in the future to determine if
latitudinal differential rotation occurs at the surface of massive
stars.
• Spectropolarimetry (Narval, Espadons, HARPSpol) gives
information on the amplitudes and topologies of surface magnetic
fields. Magnetic fields represent one of the great issues in massive
star physics. Fields impact the way angular momentum is distributed
in the interior and it may also couple the wind with the surface of
the star. These two characteristics probably play a key role in the
angular momentum content of the core at the time of the core-collapse
event and thus have an important impact on the way stars explode and
on the physical properties of the stellar remnants (neutron stars and
black holes).
All these three techniques have already obtained
fascinating results on massive stars and the time is ripe for
organising an international conference focusing on the achievements
reached so far. The main aims of the conference will be to:
•
allow astronomers interested in massive stars to understand the
basics of these three techniques, to what extent the results obtained
depend on the theoretical models used for the interpretation of the
observed features, to understand the potential of these techniques as
well as their present limitations and future developments;
•
explore the potential benefits and synergies of these techniques used
together and also with more classical approaches such as photometry
and spectroscopy to address topical questions in massive star
evolution;
• allow observers to learn about the most recent
challenges in massive star modeling.
* TOPICS:
The
conference will cover the following topics in 6 sessions:
Session
1: CHALLENGES IN MASSIVE STAR EVOLUTION
• Hydrodynamic
processes in massive stars and consequences for understanding the
main observed characteristics of massive stars
• Massive star
populations in galaxies
• Starbursts in distant galaxies
•
Chemical evolution of galaxies
Session 2: ASTEROSEISMOLOGY
•
How are the interesting astrophysical quantities extracted from the
data ? To what extent do these values depend on models ?
• What
can be said about the size of the convective core during main
sequence evolution ?
• What can be said about the way massive
stars rotate internally ? (solid body or not ?)
Session 3:
INTERFEROMETRY
• How are the interesting astrophysical
quantities extracted from the data ? To what extent do these values
depend on models ?
• The shape of stars and testing of the von
Zeipel theorem
• Stars with disks.
• Stars with polar
winds
• Surfaces of massive stars (differential rotation ?)
•
Sizes of the convective cells at the surface of red supergiants ?
Session 4: SPECTROPOLARIMETRY
• How are the interesting
astrophysical quantities extracted from the data ? To what extent do
these values depend on models ?
• Results of large surveys
•
Fossil or dynamo fields ?
• Is there any correlation of the
strength of the surface magnetic field with other observed quantities
as surface abundances and rotation ?
Session 5: SYNERGY
BETWEEN DIFFERENT TECHNIQUES
• Can we see how a star having a
strong surface magnetic field rotates internally ?
• Have the
slow rotators with strong surface nitrogen enhancement a detectable
surface magnetic field ?
Session 6: TOWARDS A SYNTHETIC VIEW
OF MASSIVE STAR EVOLUTION
• What are the perspectives for
studying stars in stellar clusters with these techniques ?
•
What can be expected from future observational facilities ?
• A
summary of the conference will be presented by invited speakers.
*
LIST OF CONFIRMED INVITED SPEAKERS (provisional):
C. Aerts
D.
Arnett
A. Chieffi
J. Grunhut
J. Landstreet
N. Langer
A. Maeder
C. Meakin
A. Meilland
A. Miglio
A.
Noels
N. Przybilla
J. Puls
P. Stee
A. Ud Doula
G.
van Belle
G. Wade
* SCIENTIFIC ORGANISING COMMITTEE:
Georges Meynet (Switzerland) -- Chair
Philippe Stee (France)
-- Co-chair
David Arnett (USA)
Lydia Cidale (Argentina)
Raphael Hirschi (UK)
Emily Levesque (USA)
Marco Limongi
(Italy)
André Maeder (Switzerland)
Philip Massey (USA)
Coralie Neiner (France)
Arlette Noels (Belgium)
Stanley
Owocki (USA)
Thomas Rivinius (Chile)
Hideyuki Saio (Japan)
Rich Townsend (USA)
Gregg Wade (Canada)
* LOCAL
ORGANISING COMMITTEE:
Georges Meynet -- Chair
Patrick
Eggenberger
Sylvia Ekström
Anahí Granada
José Groh
Lionel Haemmerlé
Giovanni Privitera
Gilles Simond
Chantal Taçoy
Weblink:
http://obswww.unige.ch/Conferences/IAU307/
Email:
r.hirschi@keele.ac.uk
Back to contents
02 Aug - 10 Aug 2014
Venue:
Moscow, Russia
New generation of X-ray telescopes allowed
important development in the astrophysics of hot massive stars. While
some questions about X-ray emission from massive stars have been
answered, there are unexpected findings pointing out that our picture
of stellar winds is not yet complete. High-resolution spectroscopy,
time monitoring, and detailed imaging in X-rays allow to probe
stellar atmospheres, magnetospheres, and stellar winds and their
impact on interstellar medium and galactic ecology. The most
important progress made from the X-ray studies of Wolf-Rayet, O, B,
and A-type stars and massive star clusters will be reviewed and the
opportunities presented by new facilities will be discussed during
this 2 day Scientific event E.3, which will be part of the 40th
COSPAR Scientific assembly.
The abstract submission,
registration, and visa support is via main COSPAR web-site.
Please
contact E3 event organizers in case of questions regarding this
event.
Weblink: https://www.cospar-assembly.org/
Email:
lida@astro.physik.uni-potsdam.de
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17-19 September 2014
Venue: De Rode Hoed,
Amsterdam, The Netherlands
For more than 30 years,
spectroscopic observations from space have shown that wind
variability in massive OB stars is a widespread phenomenon. This
variability is not strictly periodic, but cyclic (like sunspots) with
a dominant quasi period that scales with the estimated rotation
period. The underlying cause or trigger of this variability is not
known. The major time-variable wind features likely find their origin
close to, or at the surface and have been suggested to be connected
to non-radial pulsations or bright magnetic star spots.
The
past few years have shown very promising new developments, both
observationally and theoretically. High-precision space-based
photometry reveals rapid variations, incompatible with pulsations,
but consistent with the continuous presence of a multitude of
co-rotating bright spots that live at most a few days. These spots
are suggested to be of magnetic origin and could trigger large-scale
wind variability. Theoretical studies show that magnetic fields can
be generated with a short estimated turnover time in sub-surface
convective layers in massive stars. These may lead to magnetic spots.
Understanding the role of magnetic fields and variability in
O and early B stars is a major challenge in massive star research.
This is the focus of a 3-day conference to be held in Amsterdam,
organized to mark the formal retirement of Huib Henrichs, who has
worked in this field throughout his scientific life.
This
conference will be organized in a somewhat different way. Rather than
having a skeleton with specific names of invited speakers, the
community is invited to come forward on their own accord, thus giving
more people a chance to provide their input. From this, a list of
speakers and topics will be drawn up, with ample time for discussion.
The aim is 25 and 15 min talks (each including discussion) and
posters.
Note that an evening welcome reception will preceed
the conference, and that the social programme continues on the
Saturday afterwards.
Please apply for a talk/poster and
pre-register at your earliest convenience on the conference website:
http://www.astro.uva.nl/ostars/
Registration and payment will be
open on February 15th, 2014.
First announcement and
pre-registration: December 20th, 2013
Second announcement and
registration: February 15th, 2014
Early payment fee (275 €):
before May 1st, 2014
Regular payment fee (325 €)
Registration
closed: June 15th, 2014
SOC:
Huib Henrichs, Ed van den
Heuvel, Lex Kaper (chair), Alex de Koter, Tony Moffat (Montreal,
Canada), Stan Owocki (Delaware, USA), Gregg Wade (Kingston, Canada)
LOC:
Susan Franzen, Olga Hartoog, Martin Heemskerk,
Milena Hoekstra, Lex Kaper (chair), Bertrand Lemasle
Weblink:
http://www.astro.uva.nl/ostars/
Email:
ostarsws@list.uva.nl
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