ISSN 1783-3426
|
New IAU Commission on Massive Stars (Commission
C.G2)
ASR Special Issue "X-rays
from hot stars"
Fizeau
exchange visitors program - call for applications
UV and X-ray monitoring of CPD -28
2561
A Consistent Spectral Model of
WR 136 and its Associated Bubble NGC 6888
Massive
stars on the verge of exploding: The properties of oxygen-sequence
Wolf-Rayet stars
Spectral
Variations of Of?p Oblique Magnetic Rotator Candidates in the
Magellanic Clouds
Kepler's first
view of O-star variability: K2 data of five O stars in Campaign 0 as
a proof-of-concept for O-star asteroseismology
B
fields in OB stars (BOB): Detection of a strong magnetic field in the
O9.7 V star HD54879
The internal
rotation profile of the B-type star KIC 10526294 from frequency
inversion of its dipole gravity modes and statistical model
comparison
OBSERVATIONAL
CONSEQUENCES OF TURBULENT PRESSURE IN THE ENVELOPES OF MASSIVE
STARS
Wolf-Rayet stars in the Small
Magellanic Cloud: I. Analysis of the single WN stars
The
VLT-FLAMES Tarantula Survey XXI. Stellar spin rates of O-type
spectroscopic binaries
A
Coordinated X-ray and Optical Campaign of the Nearest Massive
Eclipsing Binary,
$delta$ Orionis Aa: III. Analysis of Optical
Photometric MOST and Spectroscopic (Ground Based) Variations
A
Coordinated X-ray and Optical Campaign on the Nearest Massive
Eclipsing Binary, Delta Ori Aa: I. Overview of the X-ray Spectrum
A
Coordinated X-ray and Optical Campaign of the Nearby Massive Binary
Delta Orionis Aa: II. X-ray Variability
X-ray
emission from the giant magnetosphere of the magnetic O-type star NGC
1624-2
Effect of scattering on the
transonic solution topology and intrinsic variability of line-driven
stellar winds
Fe xxv line profiles
in colliding wind binaries
Massive
star evolution in close binaries:conditions for homogeneous chemical
evolution
Finding Wolf-Rayet Stars in the Local
Group
The Discovery and Physical
Parameterization of a New Type of Wolf-Rayet Star
The
Importance of Wolf-Rayet Ionization and Feedback on Super Star
Cluster Evolution
Postdoctoral Fellow: Massive stars and binaries
IAUS 329: The lives and death-throes of massive stars
dear friends and colleagues,
welcome to our first Massive Star Newsletter as the new IAU Commission on Massive Stars (Commission C.G2). I would like to thank you all for your support during the process of becoming a Commission and congratulate us all for the success of our proposal.
The web page and the Massive Star Newsletter will continue hosted in the UNAM (thanks to Gloria Koenigsberger and the UNAM people) edited by Raphael Hirschi and Philippe Eenens (thanks to them as well). Therefore you can continue submitting your abstracts, job offers, news and announcements in the same way as before. In the near future, of course, the web page will experience some updates and changes.
The Organizing Committee will be formed by Artemio Herrero (President), Jorick Vink (Vice-president and future president), Nicole St.-Louis and Gregor Rauw (Commission proponents) and Jose Groh, You-Hua Chu and Asif ud-Doula (elected members).
The old Working Group has disappeared, and those of you who are not IAU members cannot be part of the new Commission. The IAU has lowered the requirements to become a member. Please, check whether you can become an IAU member (if you are not) and join our Commission. Nevertheless, the services on our web page will continue for all people registered in the web page, and new registrations are open. We hope that the change will be transparent to most of you.
Becoming a Commission is a recognition of the work done by the members of the Massive Stars Working Group and will give our community more weight in the IAU structure. We shall see this new status as an opportunity to promote the role of Massive Stars in Astrophysics and their links to other fields.
with best regards,
Artemio Herrero
President, on behalf of the Organizing Committee of the IAU Commission on Massive Stars
Email: ahd@iac.es
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Original contributions and reviews of X-ray emission from
hot stars and their winds, are solicited for a special topical issue
of
Advances in Space Research. Given large interest and in
response to multiple requests the deadline for submission is extended
to 1st September 2015.
This special issue is aimed to
summarize our current knowledge of X-ray emission from hot stars as
well as open new avenues and perspectives in anticipation of the next
generation of X-ray telescopes.
The manuscript submission
site is at http://ees.elsevier.com/jasr/ (Advances in
Space
Research). Please select "X-ray Emission: Hot Stars" in the
special issue
drop-down for article type. Submitted papers must
be written in English. Only
full-length papers will be considered
for publication, subject to peer review by
two reviewers. There
are no page limits although the length of the paper should be
appropriate for the material being presented. The deadline for
submissions is
1 September 2015. Papers will be published
electronically as soon as they are accepted. The printed issue will
be assembled within a reasonable time.
We are looking forward
to receiving your manuscript.
Weblink:
Email:
lida@astro.physik.uni-potsdam.de
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J. Hron & L.
Misoni
European Interferometry Initiative
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.
The deadline for applications is
September 15. Fellowships can be awarded for missions starting in
November.
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)
Reference:
www.european-interferometry.eu
Status: Other
Weblink:
www.european-interferometry.eu
Comments:
Email: fizeau@european-interferometry.eu
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Naze, Yael (1); Sundqvist, Jon O. (2,3); Fullerton, Alex W.
(4); ud-Doula, Asif (5); Wade, Gregg A. (6); Rauw, Gregor (1);
Walborn, Nolan R. (4)
1 - ULg; 2 - Univ. Munchen ; 3 -
Univ. Delaware ; 4 - STScI ; 5 - Penn State Worth. Scr. ; 6 -
RMC
The Of?p star CPD -28 2561 was monitored at high energies
with XMM-Newton and HST. In X-rays, this magnetic oblique rotator
displays bright and hard emission that varies by ~55% with rotational
phase. These changes occur in phase with optical variations, as
expected for magnetically confined winds; there are two maxima and
two minima in X-rays during the 73d rotational period of CPD -28
2561. However, contrary to previously studied cases, no significant
hardness variation is detected between minima and maxima, with the
exception of the second minimum which is slightly distinct from the
first one. In the UV domain, broad-band fluxes remain stable while
line profiles display large variations. Stronger absorptions at low
velocities are observed when the magnetic equator is seen edge-on,
which can be reproduced by a detailed 3D model. However, a difference
in absorption at high velocities in the CIV and NV lines is also
detected for the two phases where the confined wind is seen nearly
pole-on. This suggests the presence of strong asymmetries about the
magnetic equator, mostly in the free-flowing wind (rather than in the
confined dynamical magnetosphere).
Reference: accepted
by MNRAS
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1506.08572
Comments:
Email: naze@astro.ulg.ac.be
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J. Reyes-Pérez(1), C. Morisset(1), M. Peña(1), A.
Mesa-Delgado(2)
(1)Instituto de Astronomía, Universidad
Nacional Autónoma de México; (2)Instituto de Astrofísica,
Facultad de Física, Ponticia Universidad Católica de Chile
We
analyse whether a stellar atmosphere model computed with the code
CMFGEN
provides an optimal description of the stellar
observations of WR 136 and
simultaneously reproduces the nebular
observations of NGC 6888, such as the
ionization degree, which is
modelled with the pyCloudy code. All the
observational material
available (far and near UV and optical spectra) were
used to
constrain such models. We found that even when the stellar luminosity
and the mass-loss rate were well constrained, the stellar
temperature T_* at
tau = 20, can be in a range between 70 000 and
110 000 K. When using the nebula
as an additional restriction we
found that the stellar models with T_* sim 70
000 K represent the
best solution for both, the star and the nebula. Results
from the
photoionization model show that if we consider a chemically
homogeneous nebula, the observed N+/O+ ratios found in different
nebular
zones can be reproduced, therefore it is not necessary to
assume a chemical
inhomogeneous nebula. Our work shows the
importance of calculating coherent
models including stellar and
nebular constraints. This allowed us to determine,
in a
consistent way, all the physical parameters of both the star and its
associated nebula. The chemical abundances derived are 12 +
log(N/H) = 9.95, 12
+ log(C/H) = 7.84 and 12 + log(O/H) = 8.76
for the star and 12 + log(N/H) =
8.40, 12 + log(C/H) = 8.86 and
12 + log(O/H) = 8.20. Thus the star and the
nebula are largely N-
and C- enriched and O-depleted.
Reference: accepted by
MNRAS
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1507.00051
Comments:
Email: jperez@astro.unam.mx
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Tramper, F.(1); Straal, S. M.(1,2); Sanyal, D(3).; Sana,
H.(4); de Koter, A.(1,5); Gräfener, G.(6); Langer, N.(3); Vink, J.
S.(6); de Mink, S. E.(1); Kaper, L.(1)
(1) Anton Pannekoek
Institute for Astronomy, University of Amsterdam; (2) ASTRON; (3)
Argelander Institut fur Astronomie, University of Bonn; (4)
ESA/STScI; (5) Insituut voor Sterrenkunde, KU Leuven; (6) Armagh
Observatory
Context. Oxygen sequence Wolf-Rayet (WO) stars
represent a very rare stage in the evolution of massive stars. Their
spectra show strong emission lines of helium-burning products, in
particular highly ionized carbon and oxygen. The properties of WO
stars can be used to provide unique constraints on the (post-)helium
burning evolution of massive stars, as well as their remaining
lifetimes and the expected properties of their supernovae. Aims. We
aim to homogeneously analyze the currently known presumed-single WO
stars to obtain the key stellar and outflow properties and to
constrain their evolutionary state. Methods. We use the
line-blanketed non-local thermal equilibrium atmosphere code cmfgen
to model the X-Shooter spectra of the WO stars and deduce their
atmospheric parameters. We calculate dedicated evolutionary models to
determine the evolutionary state of the stars. Results. The WO stars
have extremely high temperatures that range from 150 kK to 210 kK,
and have very low surface helium mass fractions that range from 44%
down to 14%. Their properties can be reproduced by evolutionary
models with helium zero-age main sequence masses of M(He,ini) =
15-25M sun that exhibit fairly strong (a few times 10?^5 Msun/yr?),
homogeneous (fc > 0.3) stellar winds. Conclusions. WO stars
represent the final evolutionary stage of stars with estimated
initial masses of Mini = 40-?60Msun. They are post core-helium
burning and predicted to explode as type Ic supernovae within a few
thousand years.
Reference: Accepted by A&A
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1507.00839
Comments:
Email: F.Tramper@uva.nl
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Nolan R. Walborn (1), Nidia I. Morrell (2), Yael Naze (3),
Gregg A. Wade (4), Stefano Bagnulo (5), Rodolfo H. Barba (6), Jesus
Maiz Apellaniz (7), Ian D. Howarth (8), Christopher J. Evans (9),
Alfredo Sota (10)
1 - STScI, 2 - LCO, 3 - ULg, 4 - RMC, 5
- Armagh Obs, 6 - Univ. La Serena, 7 - CSIC-INTA, 8 - UCL, 9 - ROE,
10 - CSIC
Optical spectroscopic monitoring has been conducted
of two O stars in the Small and one in the Large Magellanic Cloud,
the spectral characteristics of which place them in the Of?p
category, which has been established in the Galaxy to consist of
oblique magnetic rotators. All of these Magellanic stars show
systematic spectral variations typical of the Of?p class, further
strengthening their magnetic candidacy to the point of virtual
certainty. The spectral variations are related to photometric
variations derived from OGLE data by Naze et al. (2015) in a parallel
study, which yields rotational periods for two of them. Now circular
spectropolarimetry is required to measure their fields, and
ultraviolet spectroscopy to further characterize their
low-metallicity, magnetically confined winds, in support of
hydrodynamical analyses.
Reference: accepted by
AJ
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1507.02434
Comments:
Email: naze@astro.ulg.ac.be
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Buysschaert, B.; Aerts, C.; Bloemen, S.; Debosscher, J.;
Neiner, C.; Briquet, M.; Vos, J.; Papics, P.; Manick, R.; Schmid, V.;
Van Winkel, H.; Tkachenko, A.
1 LESIA, Observatoire de
Paris, PSL Research University, CNRS, Sorbonne Universite´s, UPMC
Univ. Paris 06, Univ. Paris Diderot, Sorbonne PariskCite´, France
2Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D,
3001 Leuven, Belgium
3Department of Astrophysics/IMAPP, Radboud
University Nijmegen, 6500 GL Nijmegen, The Netherlands
4 Institut
d’Astrophysique et de G´eophysique, Universit´e de Li`ege,
Quartier Agora, Alle du 6 aoˆut 19C, B-4000 Li`ege, Belgium
We
present high-precision photometric light curves of five O-type stars
observed with the refurbished {it Kepler/} satellite during its
Campaign 0. For one of the stars, we also assembled high-resolution
ground-based spectroscopy with the {sc hermes} spectrograph attached
to the 1.2-m Mercator telescope. The stars EPIC202060097 (O9.5V) and
EPIC202060098 (O7V) exhibit monoperiodic variability due to
rotational modulation with an amplitude of 5.6 mmag and 9.3 mmag and
a rotation period of 2.63 d and 5.03 d, respectively. EPIC202060091
(O9V) and EPIC202060093 (O9V:pe) reveal variability at low frequency
but the cause is unclear. EPIC202060092 (O9V:p) is discovered to be a
spectroscopic binary with at least one multiperiodic βCep-type
pulsator whose detected mode frequencies occur in the range
[0.11,6.99] d−1 and have amplitudes between 0.8 and 2.0 mmag. Its
pulsation spectrum is shown to be fully compatible with the ones
predicted by core-hydrogen burning O-star models. Despite the short
duration of some 33,d and the limited data quality with a precision
near 100 μmag of these first K2 data, the diversity of possible
causes for O-star variability already revealed from campaigns of
similar duration by the MOST and CoRoT satellites is confirmed with
{it Kepler}. We provide an overview of O-star space photometry and
give arguments why future K2 monitoring during Campaigns 11 and 13 at
short cadence, accompanied by time-resolved high-precision
high-resolution spectroscopy opens up the possibility of in-depth
O-star seismology.
Reference: Accepted for publication
in MNRAS
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2015arXiv150703091B
Email:
conny.aerts@ster.kuleuven.be
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N. Castro(1), L. Fossati(1), S. Hubrig(2), S.
Simon-Diaz(3), M. Scholler(4), I. Ilyin(2), T. A. Carrol(2), N.
Langer(1), T. Morel(5), F. R. N. Schneider(1,6), N. Przybilla(7), A.
Herrero(3), A. de Koter(8), L. M. Oskinova(9), A. Reisenegger(10), H.
Sana(11) and the BOB collaboration
1 - AIfA, 2 - AIP, 3 -
IAC-ULL, 4 - ESO, 5 - AGO-ULG, 6 - OXF, 7 - UIBK, 8 - UVA-KU, 9 -
Univ. Potsdam, 10 - PUC, 11 - STScI
The number of magnetic
stars detected among massive stars is small;
nevertheless, the
role played by the magnetic field in stellar evolution cannot
be
disregarded. Links between line profile variability,
enhancements/depletions
of surface chemical abundances, and
magnetic fields have been identified for
low-mass B-stars, but
for the O-type domain this is almost unexplored. Based on
FORS2
and HARPS spectropolarimetric data, we present the first detection of
a
magnetic field in HD54879, a single slowly rotating O9.7 V
star. Using two
independent and different techniques we obtained
the firm detection of a
surface average longitudinal magnetic
field with a maximum amplitude of about
600 G, in modulus. A
quantitative spectroscopic analysis of the star with the
stellar
atmosphere code FASTWIND results in an effective temperature and a
surface gravity of 33000 K and 4.0 dex. The abundances of
carbon, nitrogen, oxygen, silicon, and magnesium are found to be
slightly lower
than solar, but compatible within the errors. We
investigate line-profile
variability in HD54879 by complementing
our spectra with spectroscopic data
from other recent OB-star
surveys. The photospheric lines remain constant in
shape between
2009 and 2014, although Ha shows a variable emission. The
Ha
emission is too strong for a standard O9.7 V and is probably linked
to the magnetic field and the presence of circumstellar material.
Its normal
chemical composition and the absence of photospheric
line profile variations
make HD54879 the most strongly magnetic,
non-variable single O-star detected to
date.
Reference:
http://arxiv.org/abs/1507.03591
Status: Manuscript has been
accepted
Weblink:
Comments:
Email:
norberto@astro.uni-bonn.de
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Santiago Andrés Triana, Ehsan Moravveji, Péter Pápics,
Conny Aerts, Steven D. Kawaler, Joergen Christensen-Dalsgaard
Leuven
University, B; Radboud University Nijmegen, NL; Iowa State
University, USA; Aarhus University, D
The internal angular
momentum distribution of a star is key to determine its evolution.
Fortunately, the stellar internal rotation can be probed through
studies of rotationally-split non-radial oscillation modes. In
particular, detection of non-radial gravity modes (g modes) in
massive young stars has become feasible recently thanks to the Kepler
space mission. Our aim is to derive the internal rotation profile of
the Kepler B8V star KIC 10526294 through asteroseismology. We
interpret the observed rotational splittings of its dipole g modes
using four different approaches based on the best seismic models of
the star and their rotational kernels. We show that these kernels can
resolve differential rotation the radiative envelope if a smooth
rotational profile is assumed and the observational errors are small.
Based on Kepler data, we find that the rotation rate near the
core-envelope boundary is well constrained to $163pm89$ nHz. The
seismic data are consistent with rigid rotation but a profile with
counter-rotation within the envelope has a statistical advantage over
constant rotation. Our study should be repeated for other massive
stars with a variety of stellar parameters in order to deduce the
physical conditions that determine the internal rotation profile of
young massive stars, with the aim to improve the input physics of
their models.
Reference: Accepted for publication in
ApJ
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2015arXiv150704574A
Comments:
Email: conny.aerts@ster.kuleuven.be
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Luca Grassitelli(1), Luca Fossati(1),Sergio
Simon-Diaz(2,3), Norbert Langer(1),Norberto Castro(1),Debashis
Sanyal(1)
(1) Argelander Institute for Astronomy,
University of Bonn
(2) Instituto de Astrofısica de Canarias,
Tenerife
(3) Departamento de Astrofisica, Universidad de La
Laguna
The major mass fraction of the envelope of hot luminous
stars is radiatively stable. However, the partial ionisation of
hydrogen, helium and iron gives rise to extended sub-surface
convection zones in all of them. In this work, we investigate the
effect of the pressure induced by the turbulent motion in these zones
based on the mixing length theory, and search for observable
consequences. We find that the turbulent pressure fraction can amount
up to 5% in OB supergiants, and to 30% in cooler supergiants. The
resulting structural changes are, however, not significantly
affecting the evolutionary tracks compared to previous calculations.
Instead, a comparison of macroturbulent velocities derived from
high quality spectra of OB stars with the turbulent pressure fraction
obtained in corresponding stellar models reveals a strong correlation
of these two quantities. We discuss a possible physical connection,
and conclude that turbulent pressure fluctuations may drive
high-order oscillations, which — as conjectured earlier —
manifest themselves as macroturbulence in the photospheres of hot
luminous stars.
Reference: ApJ Letters
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/pdf/1507.03988.pdf
Comments:
Email: luca@astro.uni-bonn.de
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R. Hainich(1), D. Pasemann(1,2), H. Todt(1), T. Shenar(1),
A. Sander(1), and W.-R. Hamann(1)
1 -Institut fuer Physik
und Astronomie, Universitaet Potsdam, Karl-Liebknecht-Str. 24/25,
D-14476 Potsdam, Germany; 2 - Charité, Humboldt-Universitaet zu
Berlin, Charitéplatz 1, D-10117 Berlin, Germany
Wolf-Rayet
(WR) stars have a severe impact on their environments owing to their
strong ionizing radiation fields and powerful stellar winds. Since
these winds are considered to be driven by radiation pressure, it is
theoretically expected that the degree of the wind mass-loss depends
on the initial metallicity of WR stars. Following our comprehensive
studies of WR stars in the Milky Way, M31, and the LMC, we derive
stellar parameters and mass-loss rates for all seven putatively
single WN stars known in the SMC. Based on these data, we discuss the
impact of a low-metallicity environment on the mass loss and
evolution of WR stars. The quantitative analysis of the WN stars is
performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code.
The physical properties of our program stars are obtained from
fitting synthetic spectra to multi-band observations. In all SMC WN
stars, a considerable surface hydrogen abundance is detectable. The
majority of these objects have stellar temperatures exceeding 75 kK,
while their luminosities range from 10^5.5 to 10^6.1 Lsun. The WN
stars in the SMC exhibit on average lower mass-loss rates and weaker
winds than their counterparts in the Milky Way, M31, and the LMC. By
comparing the mass-loss rates derived for WN stars in different Local
Group galaxies, we conclude that a clear dependence of the wind
mass-loss on the initial metallicity is evident, supporting the
current paradigm that WR winds are driven by radiation. A metallicity
effect on the evolution of massive stars is obvious from the HRD
positions of the SMC WN stars at high temperatures and high
luminosities. Standard evolution tracks are not able to reproduce
these parameters and the observed surface hydrogen abundances.
Homogeneous evolution might provide a better explanation for their
evolutionary past.
Reference: Accepted for publication
in A&A
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1507.04000
Comments:
Email: rhainich@astro.physik.uni-potsdam.de
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O.H. Ramírez-Agudelo$^{1}$, H. Sana$^{2}$, S.E. de
Mink$^{1}$, V. Hénault-Brunet$^{3}$, A. de Koter $^{1,4}$, N.
Langer$^{5}$, F. Tramper$^{1}$, G. Gr"afener$^{6}$, C.J.
Evans$^{7}$, J.S. Vink$^{6}$, P.L. Dufton$^{8}$, and W.D.
Taylor$^{7}$
1- Anton Pannekoek Institute for Astronomy,
University of Amsterdam; 2- ESA/Space Telescope Science Institute; 3-
Department of Physics, University of Surrey; 4- Instituut voor
Sterrenkunde, Universiteit Leuven; 5- Argelander-Institut f"ur
Astronomie, Universit"at Bonn; 6- Armagh Observatory, UK; 7- UK
Astronomy Technology Centre; 8- Astrophysics Research Centre, Queen's
University of Belfast, UK
The initial distribution of spin
rates of massive stars is a fingerprint of their elusive formation
process. It also sets a key initial condition for stellar evolution
and is thus an important ingredient in stellar population synthesis.
So far, most studies have focused on single stars. Most O stars are,
however, found in multiple systems. By establishing the spin-rate
distribution of a sizeable sample of O-type spectroscopic binaries
and by comparing the distributions of binary subpopulations with one
another and with that of presumed-single stars in the same region, we
aim to constrain the initial spin distribution of O stars in
binaries, and to identify signatures of the physical mechanisms that
affect the evolution of the spin rates of massive stars spin. We use
ground-based optical spectroscopy obtained in the framework of the
VLT-FLAMES Tarantula Survey (VFTS) to establish the projected
equatorial rotational velocities (vrot) for components of 114
spectroscopic binaries in 30 Doradus. The vrot values are derived
from the full width at half maximum (FWHM) of a set of spectral
lines, using a FWHM vs. vrot calibration that we derive based on
previous line analysis methods applied to single O-type stars in the
VFTS sample. The overall vrot distribution of the primary stars
resembles that of single O-type stars in the VFTS, featuring a
low-velocity peak (at $vrot < 200$,kms) and a shoulder at
intermediate velocities ($200 < vrot < 300$,kms). The
distributions of binaries and single stars, however, differ in two
ways. First, the main peak at $vrot sim$100~kms is broader and
slightly shifted towards higher spin rates in the binary distribution
than that of the presumed-single stars. This shift is mostly due to
short-period binaries ($P_mathrm{orb} lesssim 10$~d). Second, the
vrot distribution of primaries lacks a significant population of
stars spinning faster than 300 kms, while such a population is
clearly present in the single-star sample. The vrot distribution of
binaries with amplitudes of radial velocity variation in the range of
20 to 200~kms (mostly binaries with $P_mathrm{orb} sim 10-1000$,d
and/or with $q < 0.5$) is similar to that of single O stars below
$vrot lesssim 170$~kms. Our results are compatible with the
assumption that binary components formed with the same spin
distribution as single stars, and that this distribution contains few
or no fast-spinning stars. The higher average spin rate of stars in
short-period binaries may either be explained by spin-up through
tides in such tight binary systems, or by spin-down of a fraction of
the presumed-single stars and long-period binaries through magnetic
braking (or by a combination of both mechanisms). Most primaries and
secondaries of SB2 systems with $P_mathrm{orb} lesssim 10,$d appear
to have similar rotational velocities. This is in agreement with
tidal locking in close binaries where the components have similar
radii. The lack of very rapidly spinning stars among binary systems
supports the idea that most stars with $vrot gtrsim 300$~kms in the
single-star sample are actually spun-up post-binary interaction
products. Finally, the overall similarities (low-velocity peak and
intermediate-velocity shoulder) of the spin distribution of binary
and single stars argue for a massive star formation process in which
the initial spin is set independently of whether stars are formed as
single stars or as components of a binary system.
Reference:
Astronomy & Astrophysics (in press)
Status: Manuscript has
been accepted
Weblink:
http://adsabs.harvard.edu/abs/2015arXiv150702286R
Comments:
None
Email: o.h.ramirezagudelo@uva.nl
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Herbert Pabloaltaffilmark{1},
Noel D.
Richardsonaltaffilmark{1},
Anthony F. J. Moffataltaffilmark{1},
Michael Corcoranaltaffilmark{2,3},
Tomer
Shenaraltaffilmark{4},
Omar Benvenutoaltaffilmark{5,6},
Jim
Fulleraltaffilmark{7,8},
Ya"el Naz'ealtaffilmark{9},
Jennifer L. Hoffmanaltaffilmark{10},
Anatoly
Miroshnichenkoaltaffilmark{11},
Jes{'us} Ma'iz
Apell'anizaltaffilmark{12},
Nancy Evansaltaffilmark{13},
Thomas
Eversbergaltaffilmark{14},
Ken Gayleyaltaffilmark{15},
Ted
Gullaltaffilmark{16},
Kenji Hamaguchialtaffilmark{2},
Wolf-Rainer Hamannaltaffilmark{4},
Huib
Henrichsaltaffilmark{17},
Tabetha Holealtaffilmark{18},
Richard
Ignacealtaffilmark{18},
Rosina Ipingaltaffilmark{3},
Jennifer
Laueraltaffilmark{13},
Maurice Leuteneggeraltaffilmark{8},
Jamie
Lomaxaltaffilmark{19},
Joy Nicholsaltaffilmark{13},
Lida
Oskinovaaltaffilmark{4},
Stan Owockialtaffilmark{20},
Andy
Pollockaltaffilmark{21},
Christopher M. P.
Russellaltaffilmark{22,23},
Wayne Waldronaltaffilmark{24},
Christian Builaltaffilmark{25},
Thierry
Garrelaltaffilmark{26},
Keith Grahamaltaffilmark{27},
Bernard
Heathcotealtaffilmark{28},
Thierry Lemoultaltaffilmark{29},
Dong
Lialtaffilmark{30},
Benjamin Mauclairealtaffilmark{31},
Mike
Potteraltaffilmark{32},
Jose Ribeiroaltaffilmark{33},
Jaymie
Matthewsaltaffilmark{34},
Chris Cameronaltaffilmark{35},
David
Guentheraltaffilmark{36},
Rainer Kuschnigaltaffilmark{34,37},
Jason Rowealtaffilmark{38},
Slavek Rucinskialtaffilmark{39},
Dimitar Sasselovaltaffilmark{40}, and
Werner
Weissaltaffilmark{37}
"1-D'epartement de physique and
Centre de Recherche en Astrophysique du Qu'ebec (CRAQ), Universit'e
de Montr'eal, C.P. 6128, Succ.~Centre-Ville, Montr'eal, Qu'ebec, H3C
3J7, Canada;
2-CRESST and X-ray Astrophysics Laboratory,
NASA/GSFC, Greenbelt, MD 20771, USA;
3-Universities Space
Research Association, 7178 Columbia Gateway Drive, Columbia, MD
21046, USA;
4-Institut f"{u}r Physik und Astronomie,
Universit"{a}t Potsdam, Karl-Liebknecht-Str. 24/25, 14476,
Potsdam, Germany;
5-Facultad de Ciencias Astron'{o}micas y
Geof'{i}sicas, Universidad Nacional de La Plata, 1900 La Plata,
Buenos Aires, Argentina;
6-Instituto de Astrofs'{i}ica de La
Plata (IALP), CCT-CONICET-UNLP. Paseo del Bosque S/N (B1900FWA), La
Plata, Argentina;
7-TAPIR, Walter Burke Institute for Theoretical
Physics, Mailcode 350-17, California Institute of Technology,
Pasadena, CA 91125, USA;
8-Kavli Institute for Theoretical
Physics, Kohn Hall, University of California, Santa Barbara, CA
93106, USA;
9-FNRS D'epartement AGO, Universit'e de Li`ege,
All'ee du 6 Aout 17, Bat. B5C, 4000, Li`ege, Belgium;
10-Department
of Physics & Astronomy, University of Denver, 2112 East Wesley
Avenue, Denver, CO 80208, USA;
11-Department of Physics and
Astronomy, University of North Carolina at Greensboro, Greensboro, NC
27402-6170, USA;
12-Centro de Astrobiolog{'i}a (CSIC-INTA), ESAC
Campus, P.O. Box 78, 28691 Villanueva de la Cañada, Madrid, Spain;
13-Smithsonian Astrophysical Observatory, 60 Garden St.,
Cambridge, MA 02138, USA;
14-Schn"{o}rringen Telescope
Science Institute, Waldbr"{o}l, Germany;
15-Department of
Physics and Astronomy, University of Iowa, Iowa City, IA 52242;
16-Astrophysics Science Division, NASA Goddard Space Flight
Center, Greenbelt, MD 20771, USA;
17-Astronomical Institute
"Anton Pannekoek", University of Amsterdam, Science Park
904, 1098 XH Amsterdam, The Netherlands;
18-Department of Physics
& Astronomy, East Tennessee State University, Box 70652, Johnson
City, TN 37614, USA;
19-HL Dodge Department of Physics and
Astronomy, University of Oklahoma, Norman, OK, USA;
20-Bartol
Research Institute, University of Delaware, Newark, DE 19716, USA;
21-European Space Agency, Apartado 78, Villanueva de la Canada,
E-28691 Madrid, Spain;
22-X-ray Astrophysics Lab, Code 662, NASA
Goddard Space Flight Center, Greenbelt, MD
20771 USA;
23-Oak
Ridge Associated Universities (ORAU), Oak Ridge, TN 37831 USA;
24-Eureka Scientific Inc., 2452 Dellmer Street, Suite 100,
Oakland, CA 94602, USA;
25-Castanet Tolosan Observatory, 6 place
Cl'emence Isaure, 31320, Castanet Tolosan, France;
26-Observatoire
de Juvignac, 19 avenue du Hameau du Golf, 34990 Juvignac, France;
27-The ConVento Group;
28-Barfold Observatory, Glenhope,
Victoria 3444, Australia;
29-Chelles Observatory, 23 avenue
H{'e}nin, 77500 Chelles, France;
30-Jade Observatory, Jin Jiang
Nan Li, He Bei District, 300251 Tianjin, China;
31-Observatoire
du Val de lÕArc, route de Peynier, 13530 Trets, France;
32-3206
Overland Ave, Baltimore, MD 21214 USA;
33-Observatorio do
Instituto Geografico do Exercito, Lisboa, Portugal;
34-Department
of Physics and Astronomy, University of British Columbia, 6224
Agricultural Road, Vancouver, BC V6T 1Z1, Canada;
35-Department
of Mathematics, Physics & Geology, Cape Breton University, 1250
Grand Lake Road, Sydney, Nova Scotia, Canada, B1P 6L2;
36-Institute
for Computational Astrophysics, Dept. of Astronomy and Physics, St
Mary's University Halifax, NS B3H 3C3, Canada;
37-University of
Vienna, Institute for Astronomy, T"urkenschanzstrasse 17, A-1180
Vienna, Austria;
38-NASA Ames Research Center, Moffett Field, CA
94035, USA;
39-Dept. of Astronomy and Astrophysics, University of
Toronto, 50 St George Street, Toronto, ON M5S 3H4, Canada;
40-Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,
Cambridge, MA 02138, USA;
We report on both high-precision
photometry from the textit{MOST} space telescope and ground-based
spectroscopy of the triple system $delta$ Ori A consisting of a
binary O9.5II+early-B (Aa1 and Aa2) with $P=$ 5.7d, and a more
distant tertiary (O9 IV $P >400$ yrs). This data was collected in
concert with X-ray spectroscopy from the Chandra X-ray Observatory.
Thanks to continuous coverage for 3 weeks, the textit{MOST} light
curve reveals clear eclipses between Aa1 and Aa2 for the first time
in non-phased data. From the spectroscopy we have a well constrained
radial velocity curve of Aa1. While we are unable to recover radial
velocity variations of the secondary star, we are able to constrain
several fundamental parameters of this system and determine an
approximate mass of the primary using apsidal motion. We also
detected second order modulations at 12 separate frequencies with
spacings indicative of tidally influenced oscillations. These
spacings have never been seen in a massive binary, making this system
one of only a handful of such binaries which show evidence for
tidally induced pulsations.
Reference: apj516687
Status:
Manuscript has been accepted
Weblink:
Comments:
Email: hpablo@astro.umontreal.ca
Back
to contents
M. F. Corcoran$^{1,2}$, J. S. Nichols$^{3}$, H.
Pablo$^{4}$, T. Shenar$^{5}$, A. M. T. Pollock$^{6}$, W. L.
Waldron$^{7}$, A. F. J. Moffat$^{4}$, N. D. Richardson$^{4}$, C. M.
P. Russell$^{8}$, K. Hamaguchi$^{1,9}$, D. P. Huenemoerder$^{10}$, L.
Oskinova$^{5}$, W.-R. Hamann$^{5}$, Y. Naz'e$^{11, 23}$, R.
Ignace$^{12}$, N. R. Evans$^{13}$, J. R. Lomax$^{14}$, J. L.
Hoffman$^{15}$, K. Gayley$^{16}$, S. P. Owocki$^{17}$, M.
Leutenegger$^{1,9}$, T. R. Gull$^{18}$, K. T. Hole$^{19}$, J.
Lauer$^{3}$, & R. C. Iping$^{20,21}$
1 - CRESST and
X-ray Astrophysics Laboratory, NASA/Goddard Space Flight Center,
Greenbelt, MD 20771, USA; 2 - Universities Space Research
Association, 7178 Columbia Gateway Dr. Columbia, MD 21046, USA; 3 -
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 34,
Cambridge, MA 02138, USA; 4 - D'epartement de physique and Centre de
Recherche en Astrophysique du Qu'ebec (CRAQ), Universit'e de
Montr'eal, C.P. 6128, Succ.~Centre-Ville, Montr'eal, Qu'ebec, H3C
3J7, Canada; 5 - Institut f"ur Physik und Astronomie,
Universit"at Potsdam, Karl-Liebknecht-Str. 24/25, D-14476
Potsdam, Germany; 6 - European Space Agency, textit{XMM-Newton};
Science Operations Centre, European Space Astronomy Centre, Apartado
78, E-28691 Villanueva de la Ca~{n}; ada, Spain; 7 - Eureka
Scientific, Inc., 2452 Delmer St., Oakland, CA 94602, USA; 8 -
NASA-GSFC, Code 662, Goddard Space Flight Center, Greenbelt, MD,
20771 USA; 9 - Department of Physics, University of Maryland,
Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA; 10 -
Massachusetts Institute of Technology, Kavli Institute for
Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge,
MA 02139 USA; 11 - Groupe d'Astrophysique des Hautes Energies,
Institut d'Astrophysique et de G'eophysique, Universit'e de Li'ege,
17, All'{e}e du 6 Ao^{u}t, B5c, B-4000 Sart Tilman, Belgium; 12 -
Physics and Astronomy, East Tennessee State University, Johnson City,
TN 37614, USA.; 13 - Harvard-Smithsonian Center for Astrophysics, 60
Garden Street, MS 4, Cambridge, MA 02138, USA; 14 - Homer L. Dodge
Department of Physics and Astronomy, University of Oklahoma, 440 W
Brooks Street, Norman, OK, 73019, USA; 15 - Department of Physics and
Astronomy, University of Denver, 2112 E. Wesley Avenue, Denver, CO,
80208, USA; 16 - Department of Physics and Astronomy, University of
Iowa, Iowa City, IA 52242, USA; 17 - University of Delaware, Bartol
Research Institute, Newark, DE 19716, USA; 18 - Laboratory for
Extraterrestrial Planets and Stellar Astrophysics, Code 667,
NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA; 19 -
Department of Physics, Weber State University, 2508 University
Circle, Ogden, UT 84408, USA; 20 - CRESST and Observational Cosmology
Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD 20771,
USA; 21 - Department of Astronomy, University of Maryland, 1113
Physical Sciences Complex, College Park, MD 20742-2421, USA; 22 -
FNRS Research Associate.
We present an overview of four deep
phase-constrained Chandra HETGS X-ray observations of Delta Ori A.
Delta Ori A is actually a triple system which includes the nearest
massive eclipsing spectroscopic binary, Delta Ori Aa, the only such
object that can be observed with little phase-smearing with the
Chandra gratings. Since the fainter star, Delta Ori Aa2, has a much
lower X-ray luminosity than the brighter primary (Delta Ori Aa1),
Delta Ori Aa provides a unique system with which to test the spatial
distribution of the X-ray emitting gas around Delta Ori Aa1 via
occultation by the photosphere of, and wind cavity around, the X-ray
dark secondary. Here we discuss the X-ray spectrum and X-ray line
profiles for the combined observation, having an exposure time of
nearly 500 ks and covering nearly the entire binary orbit. The
companion papers discuss the X-ray variability seen in the Chandra
spectra, present new space-based photometry and ground-based radial
velocities obtained simultaneous with the X-ray data to better
constrain the system parameters, and model the effects of X-rays on
the optical and UV spectra. We find that the X-ray emission is
dominated by embedded wind shock emission from star Aa1, with little
contribution from the tertiary star Ab or the shocked gas produced by
the collision of the wind of Aa1 against the surface of Aa2. We find
a similar temperature distribution to previous X-ray spectrum
analyses. We also show that the line half-widths are about 0.3-0.5
times the terminal velocity of the wind of star Aa1. We find a strong
anti-correlation between line widths and the line excitation energy,
which suggests that longer-wavelength, lower-temperature lines form
farther out in the wind. Our analysis also indicates that the ratio
of the intensities of the strong and weak lines of Fe XVII and Ne X
are inconsistent with model predictions, which may be an effect of
resonance scattering.
Reference: ApJ (in press)
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1507.05101
Comments:
Other papers in the series are:
II. X-ray Variability,
Nichols et al., 2015, ApJ, in press ( arXiv:1507.04972)
III.
Analysis of Optical Photometric MOST and Spectroscopic (Ground Based)
Variations, Pablo et al., 2015, ApJ, in press ( arXiv:1504.08002)
IV. A multiwavelength, non-LTE spectroscopic analysis, Shenar
et al,, 2015, ApJ, in press ( arXiv:1503.03476)
Email:
michael.f.corcoran@nasa.gov
Back to
contents
J. Nichols$^{1}$, D. P. Huenemoerder$^{2}$, M. F.
Corcoran$^{3}$, W. Waldron$^{4}$, Y. Naz'e$^{5}$, A. M. T.
Pollock$^{6}$, A. F. J. Moffat$^{7}$, J. Lauer$^{1}$, T.
Shenar$^{8}$, C. M. P. Russell$^{15,16}$, N. D. Richardson$^{7}$, H.
Pablo$^{7}$, N. R. Evans$^{1}$, K. Hamaguchi$^{3,9}$,T. Gull$^{10}$,
W.-R. Hamann $^{8}$, L. Oskinova$^{8}$, R. Ignace $^{11}$, Jennifer
L. Hoffman$^{12}$, K. T. Hole$^{13}$, and J. R. Lomax$^{14}$
1
- Harvard-SmithsonianCenter for Astrophysics, Cambridge, MA, USA; 2 -
Kavli Institute for Astrophysics and Space Research, MIT, Cambridge,
MA, USA; 3 - USRA CRESST, Universities Space Research Association,
GSFC; 4 - Eureka Scientific, Inc, 2452 Delmer St., Oakland, CA 94602;
5 - FNRS/Dept AGO, Univ. of Li`ege, All'ee du 6 Ao^ut 19c B5C,
4000-Li`ege, Belgium; 6 - European Space Agency, textit{XMM-Newton}
Science Operations Centre, European Space Astronomy Centre, Apartado
78, 28691 Villanueva de la Ca {n; ada, Spain; 7 - D'epartement de
physique, Universit'e de Montr'eal,C.P. 6128, Succ. C.-V., QC, H3C
3J7, Canada; 8 - Institut f"ur Physik und Astronomie,
Universit"at Potsdam, Karl-Liebknecht-Str. 24/25, D-14476
Potsdam, Germany; 9 - Department of Physics, University of Maryland,
Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA; 10 -
Code 667, NASA/GSFC, Greenbelt, MD 20771 USA; 11 - Physics &
Astronomy, East Tennessee State University, Johnson City, TN 37614
USA; 12 - Department of Physics and Astronomy, University of Denver,
2112 E. Wesley Ave., Denver, CO, 80208 USA; 13 - Department of
Physics, Weber State University, 2508 University Circle, Ogden, UT
84408; 14 - Homer L. Dodge Department of Physics and Astronomy,
University of Oklahoma, 440 W Brooks St, Norman, OK, 73019 USA
We
present time-resolved and phase-resolved variability studies of an
extensive X-ray high-resolution spectral dataset of the Delta Ori Aa
binary system. The four observations, obtained with Chandra ACIS
HETGS, have a total exposure time of $approx$479 ks and provide
nearly complete binary phase coverage. Variability of the total X-ray
flux in the range 5-25 Ang. is confirmed, with maximum amplitude of
about $pm$15% within a single $approx$125 ks observation. Periods of
4.76d and 2.04d are found in the total X-ray flux, as well as an
apparent overall increase in flux level throughout the 9-day
observational campaign. Using 40 ks contiguous spectra derived from
the original observations, we investigate variability of emission
line parameters and ratios. Several emission lines are shown to be
variable, including S, Si, and Ne. For the first time,variations of
the X-ray emission line widths as a function of the binary phase are
found in a binary system, with the smallest widths at phase 0.0 when
the secondary Delta Ori Aa2 is at inferior conjunction. Using 3D
hydrodynamic modeling of the interacting winds, we relate the
emission line width variability to the presence of a wind cavity
created by a wind-wind collision, which is effectively void of
embedded wind shocks and is carved out of the X-ray-producing primary
wind, thus producing phase locked X-ray variability.
Reference:
ApJ (in press)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1507.04972
Comments:
Email: michael.f.corcoran@nasa.gov
Back
to contents
V. Petit (1), D. H. Cohen (2), G. A. Wade (3), Y. Nazé
(4), S. P. Owocki (5), J. O. Sundqvist (5), A. ud-Doula (6), A.
Fullerton (7), M. Leutenegger (8,9), M. Gagné (10)
1-
Dept. of Physics & Space Sciences, Florida Institute of
Technology, Melbourne, FL 32904, USA
2 - Dept. of Physics &
Astronomy, Swarthmore College, Swarthmore, PA 19081, USA
3 -
Dept. of Physics, Royal Military College of Canada, PO Box 17000, Stn
Forces, Kingston, Ontario K7K 7B4, Canada
4 - GAPHE, Université
de Liège, Quartier Agora, Allée du 6 Août 19c, Bat. B5C, B-4000
Liège, Belgium
5 - Dept. of Physics & Astronomy, University
of Delaware, Bartol Research Institute, Newark, Delaware 19716, USA
6 - Penn State Worthington Scranton, Dunmore, PA 18512, USA
7
- Space Telescope Science Institute, 3700 San Martin Dr., Baltimore,
MD 21218, USA
8 - NASA/Goddard Space Flight Center, Code 662,
Greenbelt, MD 20771, USA
9 - CRESST and University of Maryland,
Baltimore County, Baltimore, MD 21250, USA
10 - Department of
Geology & Astronomy, West Chester University, West Chester, PA
19383, USA
We observed NGC 1624-2, the O-type star with the
largest known magnetic field Bp~20 kG), in X-rays with the ACIS-S
camera onboard the Chandra X-ray Observatory. Our two observations
were obtained at the minimum and maximum of the periodic Halpha
emission cycle, corresponding to the rotational phases where the
magnetic field is the closest to equator-on and pole-on,
respectively. With these observations, we aim to characterise the
star's magnetosphere via the X-ray emission produced by magnetically
confined wind shocks. Our main findings are:
(i) The observed
spectrum of NGC 1624-2 is hard, similar to the magnetic O-type star
Theta 1 Ori C, with only a few photons detected below 0.8 keV. The
emergent X-ray flux is 30% lower at the Halpha minimum phase.
(ii)
Our modelling indicated that this seemingly hard spectrum is in fact
a consequence of relatively soft intrinsic emission, similar to other
magnetic Of?p stars, combined with a large amount of local absorption
(~1-3 x 10^22 cm^-2). This combination is necessary to reproduce both
the prominent Mg and Si spectral features, and the lack of flux at
low energies. NGC 1624-2 is intrinsically luminous in X-rays (log LX
emission ~ 33.4) but 70-95% of the X-ray emission produced by
magnetically confined wind shocks is absorbed before it escapes the
magnetosphere (log LX ISM corrected ~ 32.5).
(iii) The high
X-ray luminosity, its variation with stellar rotation, and its large
attenuation are all consistent with a large dynamical magnetosphere
with magnetically confined wind shocks.
Reference: MNRAS,
in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1507.08621
Comments:
13 pages
Email: vpetit@fit.edu
Back
to contents
Jon O. Sundqvist(1,2), Stanley P. Owocki(1)
1 -
University of Delaware, USA; 2 - Centro de Astrobiologia (CSIC-INTA),
Madrid, Spain
For line-driven winds from hot, luminous OB
stars, we examine the subtle but important role of diffuse, scattered
radiation in determining both the topology of steady-state solutions
and intrinsic variability in the transonic wind base. We use a smooth
source function formalism to obtain nonlocal, integral expressions
for the direct and diffuse components of the line-force that account
for deviations from the usual localized, Sobolev forms. As the
scattering source function is reduced, we find the solution topology
in the transonic region transitions from X-type, with a unique wind
solution, to a nodal type, characterized by a degenerate family of
solutions.
Specifically, in the idealized case of an
optically thin source function and a uniformly bright stellar disk,
the unique X-type solution proves to be a stable attractor to which
time-dependent numerical radiation-hydrodynamical simulations relax.
But in models where the scattering strength is only modestly reduced,
the topology instead turns nodal, with the associated solution
degeneracy now manifest by intrinsic structure and variability that
persist down to the photospheric wind base. This highlights the
potentially crucial role of diffuse radiation for the dynamics and
variability of line driven winds, and seriously challenges the use of
Sobolev theory in the transonic wind region. Since such Sobolev-based
models are commonly used in broad applications like stellar evolution
and feedback, this prompts development of new wind models, not only
for further quantifying the intrinsic variability found here, but
also for computing new theoretical predictions of global properties
like velocity laws and mass-loss rates.
Reference: 10
pages, 6 figures (incl. 1 Appendix), accepted for publication in
MNRAS
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1508.02955
Comments:
Email: mail@jonsundqvist.com
Back
to contents
Gregor Rauw (1), Enmanuelle Mossoux (2), Yael Naze (1)
(1)
Liege University, Belgium
(2) Strasbourg Observatory,
France
Strong wind-wind collisions in massive binaries
generate a very hot plasma that frequently produces a moderately
strong iron line. The morphology of this line depends upon the
properties of the wind interaction zone and its orientation with
respect to the line of sight. As the binary components revolve around
their common centre of mass, the line profiles are thus expected to
vary. With the advent of the next generation of X-ray observatories
(Astro-H, Athena) that will offer high-resolution spectroscopy above
6 keV, it will become possible to exploit these changes as the most
sensitive probe of the inner parts of the colliding wind interaction.
Using a simple prescription of the wind-wind interaction in an
early-type binary, we have generated synthetic line profiles for a
number of configurations and orbital phases. These profiles can help
constrain the properties of the stellar winds in such binary
systems.
Reference: New Astronomy, in press
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1508.04965
Comments:
Email: rauw@astro.ulg.ac.be
Back
to contents
H.F. Song (1,3), G. Meynet(2), A.
Maeder(2), S. Ekstrom(2), P. Eggenberger(2)
(1) College of
Science, Guizhou University, Guiyang, Guizhou Province, 550025, P.R.
China
(2) Geneva Observatory, Geneva University, CH-1290
Sauverny, Switzerland
(3) Key Laboratory for the Structure and
Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming
650011
We investigate the impact of tidal interactions, before
any mass transfer, on various properties of the stellar models. We
study the conditions for obtaining homogeneous evolution triggered by
tidal interactions, and for avoiding any Roche lobe overflow during
the Main-Sequence phase. By homogeneous evolution, we mean stars
evolving with a nearly uniform chemical composition from the center
to the surface. We consider the case of rotating stars computed with
a strong coupling mediated by an interior magnetic field. Models with
initial masses between 15 and 60 M$_\odot$, for metallicities between
0.002 and 0.014, with initial rotation equal to 30\% and 66\% the
critical rotation on the ZAMS are computed for single stars and for
stars in close binary systems. Close binary systems with initial
orbital periods equal to 1.4, 1.6 and 1.8 days and a mass ratio equal
to 3/2 are considered. In models without any tidal interaction
(single stars and wide binaries), homogeneous evolution in solid body
rotating models is obtained when two conditions are realized: the
initial rotation must be high enough, the loss of angular momentum by
stellar winds should be modest. This last point favors metal-poor
fast rotating stars. In models with tidal interactions, homogeneous
evolution is obtained when rotation imposed by synchronization is
high enough (typically a time-averaged surface velocities during the
Main-Sequence phase above 250 km s$^{-1}$), whatever the mass losses.
We give plots indicating for which masses of the primary and for
which initial periods, the conditions for the homogenous evolution
and for the avoidance of the Roche lobe overflow are met, this for
different initial metallicities and rotations. In close binaries,
mixing is stronger at higher than at lower metallicities. Homogeneous
evolution is thus favored at higher metallicities. Roche lobe
overflow avoidance is favored at lower metallicities due to the fact
that stars with less metals remain more compact. We study also the
impact of different processes for the angular momentum transport on
the surface abundances and velocities in single and close binaries.
In models where strong internal coupling is assumed, strong surface
enrichments are always associated to high surface velocities in
binary or single star models. In contrast, models computed with mild
coupling may produce strong surface enrichments associated to low
surface velocities. This observable difference can be used to probe
different models for the transport of the angular momentum in stars.
Homogeneous evolution is more easily obtained in models (with or
without tidal interactions) with solid body rotation. Close binary
models may be of interest for explaining homogeneous massive stars,
fast rotating Wolf-Rayet stars, and progenitors of long soft gamma
ray bursts, even at high metallicities.
Reference: in
press for Astronomy and Astrophysics
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1508.06094
Comments:
21 pages, 13 figures, 3 tables
Email:
georges.meynet@unige.ch
Back to
contents
Philip Massey (1), Kathryn F. Neugent (1), and Nidia
Morrell (2)
(1) Lowell Observatory, Flagstaff, AZ 86001;
(2) Las Campanas Observatory La Serena, Chile
We summarize
past and current surveys for Wolf-Rayet stars among the Local Group
galaxies, emphasizing both the how and the why. Such studies are
invaluable for helping us learn about massive star evolution, and for
providing sensitive tests of the stellar evolution models. But for
such surveys to be useful, the completeness limits must be well
understood. We illustrate that point in this review by following the
``evolution" of the observed WC/WN ratio in nearby galaxies. We
end by examining our new survey for WR stars in the Magellanic
Clouds, which has revealed a new type of WN star, never before
seen.
Reference: To appear in the proceedings of the
Potsdam Wolf-Rayet Workshop, ed. W.-R. Hamann, A. Sander, & H.
Todt
Status: Conference proceedings
Weblink:
http://arxiv.org/abs/1507.07297
Comments:
Email: phil.massey@lowell.edu
Back
to contents
K. F. Neugent (1), P. Massey (1), D. J. Hillier (2), and N.
I. Morrell (3)
(1) Lowell Observatory, (2) University of
Pittsburgh, (3) Las Campanas Observatory
As part of our
ongoing Wolf-Rayet (WR) Magellanic Cloud survey, we have discovered
13 new WRs. However, the most exciting outcome of our survey is not
the number of new WRs, but their unique characteristics. Eight of our
discoveries appear to belong to an entirely new class of WRs. While
one might naively classify these stars as WN3+O3V binaries, such a
pairing is unlikely. Preliminary CMFGEN modeling suggests physical
parameters similar to early-type WNs in the Large Magellanic Cloud
except with mass-loss rates three to five times lower and slightly
higher temperatures. The evolution status of these stars remains an
open question.
Reference: To appear in the proceedings
of the Potsdam Wolf-Rayet workshop
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1507.07154
Comments:
Email: phil.massey@lowell.edu
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Kimberly R. Sokal (1), Kelsey E.
Johnson (1), Philip Massey (2), Remy Indebetouw (1,3)
1 -
University of Virginia, 2 - Lowell Observatory, 3 - NRAO
The
feedback from massive stars is important to super star cluster (SSC)
evolution and the timescales on which it occurs. SSCs form embedded
in thick material, and eventually, the cluster is cleared out and
revealed at optical wavelengths -- however, this transition is not
well understood. We are investigating this critical SSC evolutionary
transition with a multi-wavelength observational campaign. Although
previously thought to appear after the cluster has fully removed
embedding natal material, we have found that SSCs may host large
populations of Wolf-Rayet stars. These evolved stars provide
ionization and mechanical feedback that we hypothesize is the tipping
point in the combined feedback processes that drive a SSC to emerge.
Utilizing optical spectra obtained with the 4m Mayall Telescope at
Kitt Peak National Observatory and the 6.5m MMT, we have compiled a
sample of embedded SSCs that are likely undergoing this short-lived
evolutionary phase and in which we confirm the presence of Wolf-Rayet
stars. Early results suggest that WRs may accelerate the cluster
emergence.
Reference: To appear in the conference
proceedings of the June 2015 Potsdam Wolf-Rayet workshop, edited by
W.-R. Hamann, A. Sander, and H. Todt.
Status: Conference
proceedings
Weblink:
http://arxiv.org/abs/1508.00572
Comments:
Email: krs9tb@virginia.edu
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Sally Oey
University
of Michigan
Astronomy Department
311 West Hall
1085 South
University Ave.
Ann Arbor, MI 48109-1107
USA
Applications
are invited for a postdoctoral fellow at the University of Michigan
to work with Prof. Sally Oey on topics related to massive star
populations. This may include massive binaries, runaway stars, or
Oe/Be stars. The successful candidate will have access to the
University of Michigan telescope facilities, including the twin 6.5-m
Magellan Telescopes at Las Campanas, the MDM 2.4-m and 1.3-m
telescopes at Kitt Peak, and the Swift X-ray satellite. The
department has a vibrant environment with several journal clubs and
discussion groups. This position is initially available for one year,
with likely extension to three years, pending satisfactory
performance. The start date is flexible, to begin as soon as
possible. The ideal candidate will have experience with multi-object
spectroscopic data reduction and analysis for hot stars and/or
analysis of binary systems.
To apply, please submit a CV,
statement of research interests, and contact details for three
references to msoey@umich.edu. Applications should be in PDF format.
Please also include your available start date. The position will
remain open until filled, but applications received by 30 September
2015 will receive first consideration. The University of Michigan is
an Equal Opportunity/Affirmative Action Employer. Women and
minorities are encouraged to apply.
Attention/Comments:
Weblink: http://www.lsa.umich.edu/astro/
Email:
msoey@umich.edu
Deadline: 30 September 2015
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November 28 to December 2, 2016
Venue:
Auckland, New Zealand
Topics
- new results from
large-scale surveys at different wavelengths and techniques for
massive stars and supernovae
- new observational techniques and
instrumentation for massive stars and supernovae
- the link
between massive stars and their deaths (core-collapse and other SNe)
- short-lived phases of massive stars (LBVs, WRs and RSGs) and
their characteristics as supernova progenitors
- constraints on
the nucleosynthesis production in supernovae and the production of
dust
- explosion mechanisms of supernovae and the parameters
required for a successful explosion
- well established facts and
open problems in our knowledge of massive stars
- challenges to
present theoretical models: 2D and 3D models of interior and
atmospheres
- massive stars as astrophysical tools: tracing the
Milky Way and other galaxies structure; limits to our interpretation
of the high-z Universe
Dear colleagues,
Research on
Massive Stars is undergoing a period of rapid progress. While these
stars are relatively few in number they are the main driver of
chemical and dynamical evolution in galaxies via their stellar winds
and explosive deaths in core-collapse supernovae. Our understanding
of massive stars is going through a remarkable time of change with
long held convictions being shown to be incomplete. This evidence
arises from new research concerning the formation and evolution of
massive stars and linking this to their deaths in core-collapse
supernovae. Now is a fortuitous time to make significant advances in
massive star research. We propose a meeting with the central
rationale to bring together the two communities that study massive
stars and their supernovae.
The impact of massive stars is
widely recognized in many areas. They are often used as tools to
interpret the conditions and processes arising in different
environments (studies of Galactic structure, chemical and dynamical
feedback, population synthesis, Starbursts, high-z galaxies and
cosmic reionization). In parallel, the development of new
instrumentation, analysis techniques and dedicated surveys across all
possible wavelengths have delivered large amounts of exquisite new
data. This data is now providing a harsh test for the current
state-of-the-art theoretical calculations of massive star birth,
evolution and death.
We are beginning to gain some measure of
success understanding how complex phenomena such as magnetic fields,
pulsations, rotation, mergers and multiplicity act within massive
stars. This enables us to revolutionize our understanding of
short-lived and enigmatic phases such as seen in Wolf-Rayet stars,
Red Supergiants, the Luminous Blue Variables and B-Supergiants. But
at the same time, mysteries persist surrounding these phases and the
supernovae produced by these stars. For example there is growing
evidence that all these stars, except the Wolf-Rayet stars, give rise
to supernovae.
Finally, while we know individual stars are
important, the impact of massive star populations via their evolution
and death, including the influence of X-ray and gamma-ray binaries,
is of high interest to those studying the high-z Universe. Locating
the source of photons needed to reionize the early Universe remains
unsolved. Uncertainties in our understanding of massive star
populations impacts our interpretation of galaxies at the edge of the
observable Universe and how the Universe became transparent.
In
view of recent developments and the significant impact massive stars
have in the broader community, a new IAU Symposium in late 2016 was
proposed and supported by the IAU. The meeting will summarize recent
progress and establish stronger links between the massive star
community and closely-linked fields, particularly those studying end
stages of massive star evolution and massive star cosmic
implications.
In particular we plan to address the following
topics:
- new results from large-scale surveys at different
wavelengths and techniques for massive stars (e.g. influence of
rotation, multiplicity fractions, asteroseismology, magnetic fields,
high-energy detections, polarization, interferometry) and supernovae
(e.g. relative rates of different types, peculiar new classes of
events, most energetic and least luminous events)
- new
observational techniques and instrumentation for massive stars (e.g.
interferometry, astereoseismology) and supernovae (e.g. polarization
and light echos)
- the link between massive stars and their
deaths (core-collapse and other SNe and GRBs; progenitors of black
holes, neutron stars and magnetars)
- short-lived phases of
massive stars (LBVs, WRs and RSGs) and their characteristics as
supernova progenitors
- constraints on the nucleosynthesis
production in supernovae and the production of dust
- explosion
mechanisms of supernovae and the parameters required for a successful
explosion
- well established facts and open problems in our
knowledge of massive stars, particularly in the so-thought well
understood phases
- challenges to present theoretical models of
interior and atmospheres; connecting interior and atmospheres; wind
structure; episodic mass-loss mechanisms; binaries in interaction;
gamma-ray production
- massive stars as astrophysical tools:
tracing galaxies' structure; tracers of star formation; feedback from
massive stars; population synthesis; limits to our interpretation of
the high-z Universe; cosmic reionization; first stars and galaxies.
Dr J.J. Eldridge (University of Auckland), Prof Margaret
Hanson (University of Cincinnati) and Dr Artemio Herrero (Instituto
de Astrofisica) will act as co-chairs of the SOC. The MSWG will
assist in the preparation of the final proposal and will pay special
attention to guarantee scientific, geographical and gender diversity
balance in the SOC following the IAU rules for universality in
science. This aim for diversity and balance will be carried through
to selection of invited speakers and session chairs. We will also
consider the particular importance to early career astronomers of
presenting their work at this significant large scale meeting.
The
massive star community has traditionally held IAU Symposia with a
frequency of 4-5 years (Argentina, 1971; Canada, 1978; Mexico, 1981;
Greece, 1985; Indonesia, 1990; Italy, 1994; Mexico, 1998; Spain,
2002; USA, 2007). More recently, a last meeting was held in Greece in
June 2013, without IAU sponsorship, but with great success (225
participants from 27 countries). Seeking for a long-term geographical
balance, the IAU MSWG selected New Zealand as location for this
meeting among a total of seven proposals. We hope that the selection
of this venue will allow greater participation by countries in the
Asia and Pacific area.
Weblink:
http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/meetings/getMeetings.html?number=4716
Email:
j.eldridge@auckland.ac.nz
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