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New URL for the Galactic O-Star Catalog
Observational properties of massive
black hole binary progenitors
The
Structure of the Young Star Cluster NGC 6231. II. Structure,
Formation, and Fate
The Evolution
of Supermassive Population III Stars
Coupling
hydrodynamics with comoving frame radiative transfer: II. Stellar
wind stratification in the high-mass X-ray binary Vela X-1
The
IACOB project. V. Spectroscopic parameters of the O-type stars in the
modern grid of standards for spectral classification
New
massive members of Cygnus OB2
A
search for the presence of magnetic fields in the two Supergiant Fast
X-ray Transients
Low-frequency
photospheric and wind variability in the early-B supergiant HD
2905
Detection of magnetic field
in the B2 star ρ Oph A with ESO FORS2
Global
hot-star wind models for stars from Magellanic Clouds
A
changing wind collision
Detection
of a centrifugal magnetosphere in one of the most massive stars in
the rho Oph star-forming cloud
Astrophysics
of Red Supergiants
Optical-NIR
dust extinction towards Galactic O stars
Accretion from a clumpy massive-star wind in Supergiant X-ray binaries
The VLT-FLAMES Tarantula
Survey
Multiple, short-lived
"stellar prominences" on the O giant xi Persei: a magnetic
star?
The impact and evolution of
magnetic confinement in hot stars
POSTDOC POSITION in the field of
Theoretical Physics and Astrophysics
PDRA
in massive star populations and the host environments of supernovae
IAU Symp. 346
"High Mass X-ray Binaries: illuminating the passage from massive
binaries to merging compact objects"
Massive
stars and Supernovae:
The Galactic O-Star Catalog
(GOSC) has been updated with the latest results of Maíz Apellániz &
Barbá (2018). More importantly, the main URL has been finally
changed to http://gosc.cab.inta-csic.es and is now sited at the
institution where I moved three years ago. For the time being, the
old URL (http://gosc.iaa.es) will be left as a mirror. Merry
Christmas to all.
Weblink:
http://gosc.cab.inta-csic.es
Email:
jmaiz@cab.inta-csic.es
Back to
contents
R. Hainich (1), L. M. Oskinova (1), T. Shenar (1), P.
Marchant (2,3), J. J. Eldridge (4), A. A. C. Sander (1), W.-R. Hamann
(1), N. Langer (2), and H. Todt (1)
(1) Institut für
Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str.
24/25, D-14476 Potsdam, Germany
(2) Argelander-Institut für
Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
(3) Center for Interdisciplinary Exploration and Research in
Astrophysics (CIERA) and Department of Physics and Astronomy,
Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA
(4) Department of Physics, University of Auckland, Private Bag
92019, Auckland, New Zealand
The first directly detected
gravitational waves (GW 150914) were emitted by two coalescing black
holes (BHs) with masses of ~36Msun and ~29Msun. Several scenarios
have been proposed to put this detection into an astrophysical
context. The evolution of an isolated massive binary system is among
commonly considered models. Various groups have performed detailed
binary-evolution calculations that lead to BH merger events. However,
the question remains open as to whether binary systems with the
predicted properties really exist. The aim of this paper is to help
observers to close this gap by providing spectral characteristics of
massive binary BH progenitors during a phase where at least one of
the companions is still non-degenerate. Stellar evolution models
predict fundamental stellar parameters. Using these as input for our
stellar atmosphere code (PoWR), we compute a set of models for
selected evolutionary stages of massive merging BH progenitors at
different metallicities. The synthetic spectra obtained from our
atmosphere calculations reveal that progenitors of massive BH merger
events start their lives as O2-3V stars that evolve to early-type
blue supergiants before they undergo core-collapse during the
Wolf-Rayet phase. When the primary has collapsed, the remaining
system will appear as a wind-fed high-mass X-ray binary. Based on our
atmosphere models, we provide feedback parameters, broad band
magnitudes, and spectral templates that should help to identify such
binaries in the future. While the predicted parameter space for
massive BH binary progenitors is partly realized in nature, none of
the known massive binaries match our synthetic spectra of massive BH
binary progenitors exactly. Comparisons of empirically determined
mass-loss rates with those assumed by evolution calculations reveal
significant differences. The consideration of the empirical mass-loss
rates in evolution calculations will possibly entail a shift of the
maximum in the predicted binary-BH merger rate to higher
metallicities, that is, more candidates should be expected in our
cosmic neighborhood than previously assumed.
Reference:
Astronomy & Astrophysics (arXiv:1707.01912)
Status:
Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1707.01912
Comments:
Email: rhainich@astro.physik.uni-potsdam.de
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Michael A. Kuhn (1,2), Konstantin V. Getman (3), Eric D.
Feigelson (3,1), Alison Sills (4), Mariusz Gromadzki (5,1,2), Nicolas
Medina (1,2), Jordanka Borissova (1,2), Radostin Kurtev (1,2)
(1)
Millennium Institute of Astrophysics; (2) Universidad de Valparaiso;
(3) Pennsylvania State University; (4) McMaster University; (5)
Warsaw University Astronomical Observatory
The young
cluster NGC 6231 (stellar ages ~2-7 Myr) is observed shortly after
star-formation activity has ceased. Using the catalog of 2148
probable cluster members obtained from Chandra, VVV, and optical
surveys (Paper I), we examine the cluster's spatial structure and
dynamical state. The spatial distribution of stars is remarkably well
fit by an isothermal sphere with moderate elongation, while other
commonly used models like Plummer spheres, multivariate normal
distributions, or power-law models are poor fits. The cluster has a
core radius of $1.2\pm0.1$ pc and a central density of ~200 stars
pc$^{-3}$. The distribution of stars is mildly mass segregated.
However, there is no radial stratification of the stars by age.
Although most of the stars belong to a single cluster, a small
subcluster of stars is found superimposed on the main cluster, and
there are clumpy non-isotropic distributions of stars outside ~4 core
radii. When the size, mass, and age of NGC 6231 are compared to other
young star clusters and subclusters in nearby active star-forming
regions, it lies at the high-mass end of the distribution but along
the same trend line. This could result from similar formation
processes, possibly hierarchical cluster assembly. We argue that NGC
6231 has expanded from its initial size but that it remains
gravitationally bound.
Reference: AJ, 154,
214
Status: Manuscript has been accepted
Weblink:
http://iopscience.iop.org/article/10.3847/1538-3881/aa9177
Comments:
2 tables and 14 figures
Email:
mkuhn1@gmail.com
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Lionel Haemmerlé $^1$,
Tyrone. E. Woods $^2$,
Ralf S. Klessen $^1,3$,
Alexander Heger $^2$, and
Daniel
J. Whalen $^4$
1 - Universität Heidelberg, Zentrum
für Astronomie, Institut für Theoretische Astrophysik,
Albert-Ueberle-Str. 2,
D-69120 Heidelberg, Germany;
2 -
Monash Centre for Astrophysics, School of Physics and Astronomy,
Monash University, VIC 3800, Australia;
3 - Interdisziplinäres
Zentrum für wissenschaftliches Rechnen der Universität Heidelberg,
Im Neuenheimer Feld 205, D-69120 Heidelberg, Germany;
4 -
Institute of Cosmology and Gravitation, University of Portsmouth,
Dennis Sciama Building, Portsmouth PO1 3FX, UK
Supermassive
primordial stars forming in atomically-cooled halos at z~15-20 are
currently thought to be the progenitors of the earliest quasars in
the Universe. In this picture, the star evolves under accretion rates
of 0.1-1 Msun/yr until the general relativistic instability triggers
its collapse to a black hole at masses of ~10^5 Msun. However, the
ability of the accretion flow to sustain such high rates depends
crucially on the photospheric properties of the accreting star,
because its ionising radiation could reduce or even halt accretion.
Here we present new models of supermassive Population III protostars
accreting at rates 0.001-10 Msun/yr, computed with the GENEVA stellar
evolution code including general relativistic corrections to the
internal structure. We compute for the first time evolutionary tracks
in the mass range M > 10^5 Msun. We use the polytropic stability
criterion to estimate the mass at which the collapse occurs, which
has been shown to give a lower limit of the actual mass at collapse
in recent hydrodynamic simulations. We find that at accretion rates
higher than 0.01 Msun/yr the stars evolve as red, cool supergiants
with surface temperatures below 10^4 K towards masses >10^5 Msun.
Moreover, even with the lower rates 0.001 Msun/yr < dM/dt <
0.01 Msun/yr, the surface temperature is substantially reduced from
10^5 K to 10^4 K for M > 600 Msun. Compared to previous studies,
our results extend the range of masses and accretion rates at which
the ionising feedback remains weak, reinforcing the case for direct
collapse as the origin of the first quasars. We provide numerical
tables for the surface properties of our models.
Reference:
MN-17-1478-MJ (in press)
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/pdf/1705.09301.pdf
Comments:
Email: lionel.haemmerle@unige.ch
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Andreas A.C. Sander$^1$, Felix Fürst$^2$, Peter
Kretschmar$^2$, Lidia M. Oskinova$^1$, Helge Todt$^1$, Rainer
Hainich$^1$, Tomer Shenar$^1$, Wolf-Rainer Hamann$^1$
1
- Institut für Physik und Astronomie, Universität Potsdam, Germany
2 - European Space Astronomy Centre (ESA/ESAC), Villanueva de
la Cañada (Madrid), Spain
CONTEXT: Vela X-1, a
prototypical high mass X-ray binary (HMXB), hosts a neutron star (NS)
in a close orbit around an early-B supergiant donor star. Accretion
of the donor star's wind onto the NS powers its strong X-ray
luminosity. To understand the physics of HMXBs, detailed knowledge
about the donor star winds is required.
AIMS: To gain a
realistic picture of the donor star in Vela X-1, we constructed a
hydrodynamically consistent atmosphere model describing the wind
stratification while properly reproducing the observed donor
spectrum. To investigate how X-ray illumination affects the stellar
wind, we calculated additional models for different X-ray luminosity
regimes.
METHODS: We use the recently updated version of the
PoWR code to consistently solve the hydrodynamic equation together
with the statistical equations and the radiative transfer.
RESULTS:
The wind flow in Vela X-1 is driven by ions from various elements
with Fe III and S III leading in the outer wind. The model-predicted
mass-loss rate is in line with earlier empirical studies. The
mass-loss rate is almost unaffected by the presence of the accreting
NS in the wind. The terminal wind velocity is confirmed at v_inf ≈
600 km/s. On the other hand, the wind velocity in the inner region
where the NS is located is only ≈100 km/s, which is not expected on
the basis of a standard β-velocity law. In models with an enhanced
level of X-rays, the velocity field in the outer wind can be altered.
If the X-ray flux is too high, the acceleration breaks down because
the ionization increases.
CONCLUSIONS: Accounting for radiation
hydrodynamics, our Vela X-1 donor atmosphere model reveals a low wind
speed at the NS location, and it provides quantitative information on
wind driving in this important HMXB.
Reference: A&A,
forthcoming article in press
Status: Manuscript has been
accepted
Weblink:
https://arxiv.org/abs/1708.02947
Comments:
19 pages, 10 figures
Email:
ansander@astro.physik.uni-potsdam.de
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G. Holgado (1 and 2), S. Simón-Díaz (1 and 2),
R.H.Barbá (3), J. Puls (4), A. Herrero (1 and 2), N. Castro (5), M.
Garcia (6), J. Maíz Apellániz (7), I. Negueruela (8), C.
Sabín-Sanjulián (3)
1-Instituto de Astrofísica de
Canarias, E-38200 La Laguna, Tenerife,Spain.
2-Departamento de
Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife,
Spain.
3-Departamento de Física y Astronomía, Universidad de
la Serena, Av.Juan Cisternas 1200 Norte, La Serena, Chile.
4-Universitätssternwarte, Scheinerstr. 1, D-81679 München,
Germany.
5-Department of Astronomy, University of Michigan,
1085 S. University Avenue, Ann Arbor, MI 48109-1107, USA.
6-Centro
de Astrobiología (INTA-CSIC), Departamento de Astrofísica.Ctra.
Torrejón a Ajalvir km.4, E-28850 Torrejón de Ardoz (Madrid),Spain.
7-Centro de Astrobiología, CSIC-INTA, campus ESAC, camino bajo
del castillo s/n, E-28692 Madrid, Spain.
8-Departamento de
Física, Ingeniería de Sistemas y Teoría de la Señal,Escuela
Politécnica Superior, Universidad de Alicante, Carretera deSan
Vicente del Raspeig s/n, 03690 San Vicente del Raspeig, Alicante,
Spain.
The IACOB and OWN surveys are two ambitious
complementary observational projects which have made available a
large multi-epoch spectroscopic database of optical high resolution
spectra of Galactic massive O-type stars. As a first step in the
study of the full sample of (more than 350) O stars surveyed by the
IACOB/OWN projects, we have performed the quantitative spectroscopic
analysis of a subsample of 128 stars included in the modern grid of
O-type standards for spectral classification. We use semi-automatized
tools to determine the set of spectroscopic parameters that can be
obtained from the optical spectrum of O-type stars. We also benefit
from the multi-epoch character of the surveys to perform a
spectroscopic variability study of the sample, accounting for
spectroscopic binarity and variability of the main wind diagnostic
lines. We provide a general overview of the stellar and wind
parameters of this reference sample, and updated recipes for the
SpT-Teff/log g calibrations for Galactic O-type stars. We evaluate
our semi-automatized analysis strategy with ~40 stars from the
literature, and find a good agreement. The agreement between the
synthetic spectra associated with fastwind best fitting models and
the observed spectra is good for most targets, but 46 stars present a
particular behavior of the wind diagnostic lines that cannot be
reproduced by our grid of spherically symmetric unclumped models.
These are potential targets of interest for more detailed
investigations of clumpy winds and/or the existence of additional
circumstellar components. Last, our variability study has led to the
detection of signatures of spectroscopic binarity in 27% of the stars
and small amplitude radial velocity variations in the photospheric
lines of another 30%. Additionally, 31% of the investigated stars
show variability in the wind diagnostic lines.
Reference:
accepted for publication in A&A
Status: Manuscript has
been accepted
Weblink:
https://arxiv.org/abs/1711.10043
Comments:
20 pages, 18 figures
Email: gholgado@iac.es
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S. R. Berlanas (1,2), A. Herrero (1,2), F. Comerón (3),
A. Pasquali (4), C. Bertelli Motta (4), A. Sota (5)
1-
Instituto de Astrofísica de Canarias, E-38200 La Laguna,
Tenerife,Spain.
2- Departamento de Astrofísica, Universidad de
La Laguna, E-38205 La Laguna, Tenerife, Spain.
3- ESO,
Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany.
4- Astronomisches Rechen-Institut, Zentrum für Astronomie der
Universität Heidelberg, Mönchhofstr 12–14, 69120 Heidelberg,
Germany.
5- Instituto de Astrofísica de Andalucía-CSIC, 18008
Granada, Spain.
The Cygnus complex is one of the most
powerful star forming regions at a close distance from the Sun (~1.4
kpc). Its richest OB association Cygnus OB2 is known to harbor many
tens of O-type stars and hundreds of B-type stars, providing a large
homogeneous population of OB stars that can be analyzed. Many studies
of its massive population have been developed in the last decades,
although the total number of OB stars is still incomplete. Our aim is
to increase the sample of O and B members of Cygnus OB2 and its
surroundings by spectroscopically classifying 61 candidates as
possible OB-type members of Cygnus OB2. We have obtained new blue
intermediate-resolution spectra suitable for spectral classification
of the 61 candidates in Cygnus OB2 and surroundings. We thus
performed a spectral classification of the sample using He I-II and
metal lines rates, as well as the Marxist Ghost Buster (MGB) software
for O-type stars and the IACOB standards catalog for B-type stars.
Out of the 61 candidates, we have classified 42 stars as new massive
OB-type stars, earlier than B3, in Cygnus OB2 and surroundings,
including 11 O-type stars. The other candidates are discarded as they
display later spectral types inconsistent with membership in the
association. However, the magnitude cutoff and dust extinction
introduce an incompleteness. Many O and early B stars at B > 16
mag are still undiscovered in the region. Finally, we have studied
the age and extinction distribution of our sample within the region,
placing them in the Hertzsprung-Russell Diagram using different
stellar models in order to assess age uncertainties. Massive star
formation in Cygnus OB2 seems to have proceeded from lower to higher
Galactic longitudes, regardless of the details of the models used.
The correlation between age and Galactic longitude previously found
in the region is now confirmed.
Reference: Accepted
for publication in A&A
Status: Manuscript has been
accepted
Weblink:
http://arxiv.org/abs/1711.06945
Comments:
20 pages, 12 figures
Email: srberlan@iac.es
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S. Hubrig$^1$, L. Sidoli$^2$, K. Postnov$^3$, M.
Sch\"oller$^4$, A.F. Kholtygin$^5$, S.P. J\"arvinen$^1$, P.
Steinbrunner$^6$
$^1$ AIP, $^2$ INAF Milano, $^3$
Sternberg Institute, $^4$ ESO, $^5$ Saint-Petersburg State
University, $^6$ Freie Universit\"at Berlin
A
significant fraction of high-mass X-ray binaries are supergiant fast
X-ray transients (SFXTs). The prime model
for the physics
governing their X-ray behaviour suggests
that the winds of
donor OB supergiants are magnetized. To investigate if magnetic
fields are indeed present in
the optical counterparts of such
systems, we acquired low-resolution spectropolarimetric
observations
of the two optically brightest SFXTs, IGR\,J08408$-$4503 and
IGR\,J11215$-$5952 with the ESO FORS\,2 instrument
during two
different observing runs. No field detection at a significance level
of 3$\sigma$ was achieved
for IGR\,J08408$-$4503. For
IGR\,J11215$-$5952, we obtain 3.2$\sigma$ and 3.8$\sigma$ detections
($\left< B_{\rm z}\right>_{\rm hydr}=-978\pm308$\,G and
$\left< B_{\rm z}\right>_{\rm hydr}=416\pm110$\,G) on
two
different nights in 2016. These results indicate that the
model
involving the interaction of a magnetized stellar wind with the
neutron star magnetosphere can
indeed be considered to
characterize the behaviour of SFXTs.
We detected long-term
spectral variability in IGR\,J11215$-$5952, while for
IGR\,J08408$-$4503 we find
an indication of the presence of
short-term variability on a time scale of minutes.
Reference:
MNRAS
Status: Manuscript has been accepted
Weblink:
arxiv.org/abs/1712.00345
Comments:
Email: shubrig@aip.de
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S. Simón-Díaz, C. Aerts, M.A. Urbaneja, I. Camacho, V.
Antoci, M. Fredslund Andersen, F. Grundahl, P.L. Pallé
IAC,
ULL, KULeuven, U. Innsbruck, SAC-Aarhus
Despite the
important advances in space asteroseismology during the last decade,
the early phases of evolution of stars with masses above $\sim$15
M$_{\odot}$ have been only vaguely explored up to now. Our goal is to
detect, analyze and interpret variability in the early-B type
supergiant HD 2905 using long-term, ground based, high resolution
spectroscopy. We gather a total of 1141 high-resolution spectra
covering some 2900 days. We complement these observations with the
Hipparcos light curve, which includes 160 data points obtained during
a time span of $\sim$1200 days. We investigate spectroscopic
variability of up to 12 diagnostic lines by using the zero and first
moments of the line profiles. We perform a frequency analysis of both
the spectroscopic and photometric dataset. HD 2905 is a spectroscopic
variable with peak-to-peak amplitudes in the zero and first moments
of the photospheric lines of up to 15\% and 30 \kms, respectively.
The amplitude of the line-profile variability is correlated with the
line formation depth in the photosphere and wind. All investigated
lines present complex temporal behavior indicative of multi-periodic
variability with timescales of a few days to several weeks. The
Scargle periodograms of the Hipparcos light curve and the first
moment of purely photospheric lines reveal a low-frequency amplitude
excess and a clear dominant frequency at $\sim$0.37 d$^{-1}$. In the
spectroscopy, several additional frequencies are present in the range
0.1 - 0.4 d$^{-1}$. These may be associated with heat-driven gravity
modes, convectively-driven gravity
waves, or sub-surface
convective motions. Additional frequencies are detected below 0.1
d$^{-1}$. In the particular case of H$\alpha$, these are produced by
rotational modulation of a non-spherically symmetric stellar
wind.
Reference: A&A
Status: Manuscript
has been accepted
Weblink:
https://arxiv.org/abs/1711.08994
Comments:
Email: ssimon@iac.es
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I. Pillitteri (1,2), L. Fossati (3), N. Castro Rodriguez (4),
L. Oskinova (5), S. J. Wolk (2)
1- INAF - Osservatorio
Astronomico di Palermo G.S. Vaiana, Palermo, Italy,
2-
Harvard-Smithsonian Center for Astrophysics, Cambridge (MA), USA,
3-
Space Research Institute, Austrian Academy of Sciences, Graz,
Austria,
4- Department of Astronomy, University of Michigan,
Ann Arbor, MI, USA,
5- Institut für Physik und Astronomie,
Universität Potsdam, Potsdam-Golm, Germany
Circumstantial
evidence suggests that magnetism and enhanced X-ray emission are
likely correlated in early B-type stars: similar fractions of them (∼
10 %) are strong and hard X-ray sources and possess strong magnetic
fields. It is also known that some B-type stars have spots on their
surface. Yet up to now no X-ray activity associated with spots on
early-type stars was detected. In this Letter we report the detection
of a magnetic field on the B2V star ρ Oph A. Previously, we assessed
that the X-ray activity of this star is associated with a surface
spot, herewith we establish its magnetic origin. We analyzed FORS2
ESO VLT spectra of ρ Oph A taken at two epochs and detected a
longitudinal component of the magnetic field of order of ∼500 G in
one of the datasets. The detection of the magnetic field only at one
epoch can be explained by stellar rotation which is also invoked to
explain observed periodic X-ray activity. From archival HARPS ESO VLT
high resolution spectra we derived the fundamental stellar parameters
of ρ Oph A and further constrained its age. We conclude that ρ Oph
A provides strong evidence for the presence of active X-ray emitting
regions on young magnetized early type stars.
Reference:
A&A Letter in press, arxiv:1712.00728
Status: Manuscript
has been accepted
Weblink:
Comments:
Email: ignazio.pillitteri@gmail.com
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J. Krticka, J. Kubat
Masaryk University,
Brno, Czech Republic
Astronomical Institute, Ondrejov, Czech
Republic
We provide mass-loss rate predictions for O stars
from Large and Small Magellanic Clouds. We calculate global (unified,
hydrodynamic) model atmospheres of main sequence, giant, and
supergiant stars for chemical composition corresponding to Magellanic
Clouds. The models solve radiative transfer equation in comoving
frame, kinetic equilibrium equations (also known as NLTE equations),
and hydrodynamical equations from (quasi-)hydrostatic atmosphere to
expanding stellar wind. The models allow us to predict wind density,
velocity, and temperature (consequently also the terminal wind
velocity and the mass-loss rate) just from basic global stellar
parameters. As a result of their lower metallicity, the line
radiative driving is weaker leading to lower wind mass-loss rates
with respect to the Galactic stars. We provide a formula that fits
the mass-loss rate predicted by our models as a function of stellar
luminosity and metallicity. On average, the mass-loss rate scales
with metallicity as Z^0.59. The predicted mass-loss rates are lower
than mass-loss rates derived from Halpha diagnostics and can be
reconciled with observational results assuming clumping factor Cc=9.
On the other hand, the predicted mass-loss rates either agree or are
slightly higher than the mass-loss rates derived from ultraviolet
wind line profiles. The calculated PV ionization fractions also agree
with values derived from observations for LMC stars with Teff<40
000 K. Taken together, our theoretical predictions provide reasonable
models with consistent mass-loss rate determination, which can be
used for quantitative study of stars from Magellanic
Clouds.
Reference: Astronomy & Astrophysics, in
press
Status: Manuscript has been accepted
Weblink:
http://adsabs.harvard.edu/abs/2017arXiv171203321K
Comments:
Email: krticka@physics.muni.cz
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Yael Naze (1), Gloria Koenigsberger (2), Julian M.
Pittard (3), Elliot Ross Parkin, Gregor Rauw (1), Michael F. Corcoran
(4), D. John Hillier (5)
((1) ULg, (2) UNAM, (3) Univ.
of Leeds, (4) GSFC, (5) PITT PACC)
We report on the first
detection of a global change in the X-ray emitting properties of a
wind-wind collision, thanks to XMM-Newton observations of the massive
SMC system HD5980. While its lightcurve had remained unchanged
between 2000 and 2005, the X-ray flux has now increased by a factor
of ~2.5, and slightly hardened. The new observations also extend the
observational coverage over the entire orbit, pinpointing the
lightcurve shape. It has not varied much despite the large overall
brightening, and a tight correlation of fluxes with orbital
separation is found, without any hysteresis effect. Moreover, the
absence of eclipses and of absorption effects related to orientation
suggests a large size for the X-ray emitting region. Simple
analytical models of the wind-wind collision, considering the varying
wind properties of the eruptive component in HD5980, are able to
reproduce the recent hardening and the flux-separation relationship,
at least qualitatively, but they predict a hardening at apastron and
little change in mean flux, contrary to observations. The brightness
change could then possibly be related to a recently theorized
phenomenon linked to the varying strength of thin-shell instabilities
in shocked wind regions.
Reference: Accepted by
ApJ
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1712.05625
Comments:
Email: naze@astro.ulg.ac.be
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S. Hubrig (1), M. Schoeller (2), S.P. Jarvinen (1), M.
Kueker (1), A.F. Kholtygin (3), P. Steinbrunner (4)
(1)
AIP, (2) ESO, (3) Saint-Petersburg State University, (4) FU
Berlin
Recent XMM-Newton observations of the B2 type star
rho Oph A indicated a periodicity of 1.205d, which was ascribed to
rotational modulation. Since variability of X-ray emission in massive
stars is frequently the signature of a magnetic field, we
investigated whether the presence of a magnetic field can indeed be
invoked to explain the observed X-ray peculiarity. Two FORS2
spectropolarimetric observations in different rotation phases
revealed the presence of a negative (B_z_all=-419+-101G) and positive
(B_z_all=538+-69G) longitudinal magnetic field, respectively. We
estimate a lower limit for the dipole strength as B_d = 1.9+-0.2kG.
Our calculations of the Kepler and Alfven radii imply the presence of
a centrifugally supported, magnetically confined plasma around rho
Oph A. The study of the spectral variability indicates a behaviour
similar to that observed in typical magnetic early-type Bp
stars.
Reference: AN
Status: Manuscript has
been accepted
Weblink:
https://arxiv.org/abs/1712.05939
Comments:
Email: shubrig@aip.de
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Emily M. Levesque
University of
Washington
'Astrophysics of Red Supergiants' is the first
book of its kind devoted to our current knowledge of red supergiant
stars, a key evolutionary phase that is critical to our larger
understanding of massive stars. It provides a comprehensive overview
of the fundamental physical properties of red supergiants, their
evolution, and their extragalactic and cosmological applications. It
serves as a reference for researchers from a broad range of fields
(including stellar astrophysics, supernovae, and high-redshift
galaxies) who are interested in red supergiants as extreme stages of
stellar evolution, dust producers, supernova progenitors,
extragalactic metallicity indicators, members of massive binaries and
mergers, or simply as compelling objects in their own right. The book
is accessible to a range of experience levels, from graduate students
up to senior researchers.
Reference: AAS-IOP eBook
series
Status: Manuscript has been accepted
Weblink:
http://iopscience.iop.org/book/978-0-7503-1329-2
Comments:
Email: emsque@uw.edu
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J. Maíz Apellániz (1) and R. H.
Barbá (2)
(1) CAB, CSIC-INTA, (2) ULS
Context.
O stars are excellent tracers of the intervening ISM because of their
high luminosity, blue intrinsic SED, and relatively featureless
spectra. We are currently conducting the Galactic O-Star
Spectroscopic Survey (GOSSS), which is generating a large sample of O
stars with accurate spectral types within several kpc of the Sun.
Aims. To obtain a global picture of the properties of dust
extinction in the solar neighborhood based on optical-NIR photometry
of O stars with accurate spectral types.
Methods. We have
processed a carefully selected photometric set with the CHORIZOS code
to measure the amount [E(4405-5495)] and type [R_5495] of extinction
towards 562 O-type stellar systems. We have tested three different
families of extinction laws and analyzed our results with the help of
additional archival data.
Results. The Maíz Apellániz et al.
(2014, A&A 564, A63) family of extinction laws provides a better
description of Galactic dust that either the Cardelli et al. (1989,
ApJ 345, 245) or Fitzpatrick (1999, PASP 111, 63) families, so it
should be preferentially used when analyzing samples similar to the
one in this paper. In many cases O stars and late-type stars
experience similar amounts of extinction at similar distances but
some O stars are located close to the molecular clouds left over from
their births and have larger extinctions than the average for nearby
late-type populations. In qualitative terms, O stars experience a
more diverse extinction than late-type stars, as some are affected by
the small-grain-size, low-R_5495 effect of molecular clouds and
others by the large-grain-size, high-R_5495 effect of H II regions.
Late-type stars experience a narrower range of grain sizes or R_5495,
as their extinction is predominantly caused by the average, diffuse
ISM. We propose that the reason for the existence of
large-grain-size, high-R_5495 regions in the ISM in the form of H II
regions and hot-gas bubbles is the selective destruction of small
dust grains by EUV photons and possibly by thermal sputtering by
atoms or ions.
Reference: Accepted for publication
in A&A
Status: Manuscript has been accepted
Weblink:
https://arxiv.org/abs/1712.09228
Comments:
Email: jmaiz@cab.inta-csic.es
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I. El Mellah$^1$, J. O.
Sundqvist$^2$, R. Keppens$^1$
1 - Center for
mathematical Plasma Astrophysics, KU Leuven
2 - Institute of
Astronomy, KU Leuven
Supergiant X-ray Binaries (SgXB) host
a compact object, often a neutron star (NS), orbiting an evolved O/B
star. Mass transfer proceeds through the intense line-driven wind of
the stellar donor, a fraction of which is captured by the
gravitational field of the NS. The subsequent accretion process onto
the NS is responsible for the abundant X-ray emission from SgXB. They
also display peak-to-peak variability of the X-ray flux by a factor
of a few 10 to 100, along with changes in the hardness ratios
possibly due to varying absorption along the line-of-sight. We use
recent radiation-hydrodynamic simulations of inhomogeneities (aka
clumps) in the non-stationary wind of massive hot stars to evaluate
their impact on the time-variable accretion process. For this, we run
3D hydrodynamic simulations of the wind in the vicinity of the
accretor to investigate the formation of the bow shock and follow the
inhomogeneous flow over several spatial orders of magnitude, down to
the NS magnetosphere. In particular, we show that the impact of the
wind clumps on the time-variability of the intrinsic mass accretion
rate is severely tempered by the crossing of the shock, compared to
the purely ballistic Bondi-Hoyle-Lyttleton estimation. We also
account for the variable absorption due to clumps passing by the
line-of-sight and estimate the final effective variability of the
column density and mass accretion rate for different orbital
separations. Finally, we compare our results to the most recent
analysis of the X-ray flux and the hardness ratio in Vela
X-1.
Reference: arXiv:1711.08709
Status:
Manuscript has been submitted
Weblink:
https://arxiv.org/abs/1711.08709
Comments:
Email: ileyk.elmellah@kuleuven.be
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Vink, Jorick S.; Evans, C. J.;
Bestenlehner, J.; McEvoy, C.; Ramirez-Agudelo, O.;
Sana, H.; Schneider, F.; VFTS
Armagh
Observatory
We present a number of notable results from
the VLT-FLAMES Tarantula Survey (VFTS), an ESO Large Program during
which we obtained multi-epoch medium-resolution optical spectroscopy
of a very large sample of over 800 massive stars in the 30 Doradus
region of the Large Magellanic Cloud (LMC). This unprecedented
data-set has enabled us to address some key questions regarding
atmospheres and winds, as well as the evolution of (very) massive
stars. Here we focus on O-type runaways, the width of the main
sequence, and the mass-loss rates for (very) massive stars. We also
provide indications for the presence of a top-heavy initial mass
function (IMF) in 30 Dor.
Reference: 2017, IAUS
329: "The Lives and Death-Throes of Massive Stars", eds.
Eldridge, J.J.,Bray, J.C., McClelland, L.A.S.,
Xiao, L.
Status: Conference proceedings
Weblink:
http://adsabs.harvard.edu/abs/2017arXiv171011220V
Comments:
7 Figures, 8 pages. Invited talk.
Email:
jsv@arm.ac.uk
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N. Sudnik(1) and H.F. Henrichs(2)
(1)
Belarussian State Pedagogical University, 220050, Sovetskaya 18,
Minsk, Belarus
(2) Anton Pannekoek Institute for Astronomy,
University of Amsterdam, Science Park 904, 1098 XH Amsterdam,
Netherlands
We present strong evidence for a rotation
period of 2.0406 d of the O giant xi Persei, derived from the N IV
1718 wind line in 12 yr of IUE data. We predict that xi Per has a
magnetic dipole field, with superposed variable magnetic prominences.
Favorable dates for future magnetic measurements can be predicted. We
also analysed time-resolved He II 4686 spectra from a campaign in
1989 by using the same simplified model as before for lambda Cephei,
in terms of multiple spherical blobs attached to the surface, called
stellar prominences (Sudnik & Henrichs 2016). These represent
transient multiple magnetic loops on the surface, for which we find
lifetimes of mostly less than 5 h.
Reference: Contrib.
Astron. Obs. Skalnat´e Pleso 48, 1 – 2, (2018)
Status:
Conference proceedings
Weblink:
https://arxiv.org/abs/1711.02531
Comments:
Proceedings "Stars with a stable magnetic field: from
pre-main sequence to compact remnants", Brno, Czech Republic,
August 28 - September 01, 2017
Email:
h.f.henrichs@uva.nl
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Zsolt Keszthelyi [1,2], Gregg
A. Wade [1], Veronique Petit [3], Georges Meynet [4], Cyril Georgy
[4]
1 - Royal Military College of Canada
2 -
Queen's University
3 - University of Delaware
4 - Geneva
Observatory
Magnetic confinement of the winds of hot,
massive stars has far-reaching consequences on timescales ranging
from hours to Myr. Understanding the long-term effects of this
interplay has already led to the identification of two new
evolutionary pathways to form `heavy' stellar mass black holes and
pair-instability supernova even at galactic metallicity. We are
performing 1D stellar evolution model calculations that, for the
first time, account for the surface effects and the time evolution of
fossil magnetic fields. These models will be thoroughly confronted
with observations and will potentially lead to a significant revision
of the derived parameters of observed magnetic massive
stars.
Reference: to appear in proceedings of
'Stars with a stable magnetic field: from pre-main sequence to
compact remnants' conference, held in Brno, Czech Republic, 28 Aug -
1 Sep, 2017, Contributions of the Astronomical Observatory Skalnate
Pleso, 2017
Status: Conference proceedings
Weblink:
https://arxiv.org/abs/1711.06886
Comments:
Email: zsolt.keszthelyi@rmc.ca
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Prof. Rikard von Unge unge@physics.muni.cz
Institute
for Theoretical Physics and Astrophysics
Masaryk University
Kotlarska 2
Brno, Czech Republic
The Institute
for Theoretical Physics and Astrophysics conducts research on a wide
range of topics. In Astrophysics we focus on the physics of massive
stars, star clusters and the intergalactic medium using spectroscopic
data and theoretical modelling where satellite data is an
increasingly important source of information. In string theory we are
active in the fields of supersymmetry, D-branes, integrability and
formal aspects of BRST-BV quantisation. In optics we investigate and
design new optical devices based on transformation optics and on the
analogy between optics and mechanics.
The successful
candidate should:
-be a researcher who has received a PhD or
its equivalent within the last 7 years
-be a researcher who has
worked at least two whole years in the last three outside the
territory of the Czech Republic in the field of research with a
working time of at least 0.5 full-time equivalent, or who has been
PhD student (or equivalent) abroad
-have a publishing record –
in the last three years at least two publication outputs registered
in the Thomson Reuters Web of Science, Scopus or ERIH PLUS databases
and at the same time publications such as “articles”, “books”,
“book chapters”, “letters” and “reviews”. The applicant
must be the principal author of at least one publication (according
to the subject specificity it may be as the first author, the
corresponding/reprint author, or the role of the individual authors
stated in the article).
-have experience in the field of either
Astrophysics – Experience with ESO instrumentation (VLA,
ALMA) or space observatories is a strong advantage.
String
theory – with a specialisation in the AdS/CFT correspondence.
Transformation optics – with specialisation in applications
of metamaterials and constructing new optical instruments.
-have
experience with research projects (an advantage)
-have
excellent communication skills and an ability to collaborate with
multiple teams
The application should include:
-a
CV including a summary of work experience, -publication activity,
involvement in research grants, etc.
-a Cover Letter
-contact
information for at least three referees
MU offers
the opportunity to gain:
-an interesting job in a dynamically
expanding university area
-diverse and challenging work in an
excellent research environment
-possible tenure track with an
initial appointment for two years
-a professional team and a
pleasant working environment
-interaction with leading
scientists in an inspiring, internationalised environment
-a
Welcome Service for the successful candidate and his/her family
have
excellent communication skills and an ability to collaborate with
multiple teams
Attention/Comments:
Weblink:
http://postdoc.muni.cz
Email:
krticka@physics.muni.cz
Deadline: 28 January
2018
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Justyn Maund
Department
of Physics & Astronomy, University of Sheffield, Hounsfield Road,
Sheffield S3 7RH, UK
Applications are invited for a 3-year
PDRA position in observational astronomy within the Astronomy Group
based at The University of Sheffield, UK. The successful applicant
will work with Justyn Maund and Paul Crowther on investigating the
connections between populations of massive stars and stripped
envelope core-collapse supernovae in nearby star-forming galaxies.
This research will involve the reduction, analysis and
interpretation of high quality HST WFC3 observations of massive star
regions in other galaxies, associated with recent stripped-envelope
supernova explosions. Further information on the activities of the
astronomy group can be found at: http://www.astro.group.shef.ac.uk
The PDRA will be expected to hold a PhD in astrophysics
at the start of the appointment, and to have experience of the
analysis and interpretation of observations of massive star
populations. A good general knowledge of the astrophysics of massive
star evolution and core-collapse supernovae is desirable. As part of
your application, please upload a copy of your CV, including a list
of publications, and a cover letter briefly explaining why you are
applying for the role and how your experience is suited to the
project.
Attention/Comments: Justyn Maund
j.maund@sheffield.ac.uk or Paul Crowther
paul.crowther@sheffield.ac.uk
Weblink:
https://jobregister.aas.org/ad/25be982e
Email:
paul.crowther@sheffield.ac.uk
Deadline: 12 Jan
2018
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27-31 August 2018
Venue: Austria
Center Vienna
The IAUS 346 will be the first IAU symposium
devoted to high-mass X-ray binaries (HMXBs). The Symposium will
build a bridge between mature field of massive binary astrophysics
and nascent field of gravitational wave astronomy. This large
international meeting will consolidate our knowledge on massive
stars, binary evolution, accretion physics, compact objects and
gravitational wave sources to give us a new perspective on the cosmos
illuminated by HMXBs.
Please help us to spread the news
and share this announcement.
We are looking forward to
seeing you in Vienna in 2018!
The SOC
Weblink:
http://www.astro.physik.uni-potsdam.de/IAUS346
Email:
lida@astro.physik.uni-potsdam.de
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5-9 November 2018
Venue: Bariloche,
Argentina
Massive stars definitely play the leading role
among the cast that dictates the evolution of the Universe as we know
it. Outnumbered and outlived by all their less massive support
players they still manage to impose their character by dramatically
transforming the stage at early times via their powerful stellar
winds through an outstanding finale in core-collapse supernova
explosions. Since early age, massive stars violently disrupt the
interstellar medium where they were born. They erode and compress the
molecular material and ionize atoms of different species, allowing to
derive properties of galaxies at cosmological distances. On top of
that, massive stars explode as core-collapse supernovae, and along
with their thermonuclear counterparts (type Ia supernovae), are the
main source of chemical enrichment as they yield the materials
produced in its core and further process elements during their final
blast. The connection between supernovae of different types and their
stellar progenitors is currently under debate.
Multiplicity
rate for these stars is detected at a rate high enough to make it a
factor that has to be included when elaborating models and/or
scenarios to account for any parameter derivation from observations.
The implications that close binarity has in the evolution of massive
stars since formation through post-main-sequence stages need further
refinements of statistics in the distribution of orbital parameters
and evolution models including stellar-wind interactions and mass
transfer. The advent of unprecedented volumes of data on massive
stars from upcoming surveys set up an excellent opportunity for
intense and fruitful discussions to devise the best strategies to
identify and tackle pressing issues. Throughout her active career,
Nidia Morrell has dedicated to improve our knowledge on most of the
topics recently outlined. Either as a passionate observer, a
dedicated teacher and supervisor or an enthralling collaborator,
Nidia definitely makes a difference for all of us who have the
pleasure of working with her.
In this conference, we aim
to review and discuss all present knowledge about massive stars and
supernovae, with a view toward the coordination of efforts to advance
our understanding of this important subject in years to
come.
Weblink:
http://nidiafest.fcaglp.unlp.edu.ar/
Email:
nidiafest2018@gmail.com
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