ISSN 1783-3426
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The Yellow and Red Supergiants of M33
A
dynamical magnetosphere model for periodic Halpha emission from the
slowly rotating magnetic O star HD191612
The
Quintuplet Cluster III.
Modeling
high-energy light curves of the PSR B1259-63/LS 2883 binary based on
3-D SPH simulations
Discovery of a
young and massive stellar cluster: Spectrophotometric near-infrared
study of Masgomas-1
Clumped stellar
winds in supergiant high-mass X-ray binaries: X-ray variability and
photoionization
The Effects of
Stellar Rotation. I. Impact on the Ionizing Spectra and Integrated
Properties of Stellar Populations
Grids
of stellar models with rotation
Radiation-driven
winds of hot luminous stars
A
hydrodynamical model of the circumstellar bubble created by two
massive stars
The long period
eccentric orbit of the particle accelerator HD167971 revealed by long
baseline interferometry
Magnetometry
of a sample of massive stars in Carina
Spectral
Types of Red Supergiants in NGC 6822 and the Wolf-Lundmark-Melotte
Galaxy
A Workshop on Outstanding Problems in Massive Star Research --- the final stages
Maria R. Drout (1, 2), Philip
Massey (2), and Georges Meynet (3)
1 -- Center for
Astrophysics, Harvard University; 2--Lowell Observatory; 3--Geneva
University
Yellow and red supergiants are evolved massive
stars whose numbers and lo- cations on the HR diagram can provide a
stringent test for models of massive star evolution. Previous studies
have found large discrepancies between the rel- ative number of
yellow supergiants observed as a function of mass and those predicted
by evolutionary models, while a disagreement between the predicted
and observed locations of red supergiants on the HR diagram was only
recently resolved. Here we extend these studies by examining the
yellow and red super- giant populations of M33. Unfortunately,
identifying these stars is difficult as this portion of the
color-magnitude diagram is heavily contaminated by foreground dwarfs.
We identify the red supergiants through a combination of radial
velocities and a two-color surface gravity discriminant and, after
re-characterizing the rotation curve of M33 with our newly selected
red supergiants, we identify the yellow supergiants through a
combination of radial velocities and the strength of the OI 7774
triplet. We examine about 1300 spectra in total and identify 121
yellow supergiants (a sample which is unbiased in luminosity above
log(L/Lsun) = 4.8) and 189 red supergiants. After placing these
objects on the HR diagram, we find that the latest generation of
Geneva evolutionary tracks show excellent agree- ment with the
observed locations of our red and yellow supergiants, the observed
relative number of yellow supergiants with mass and the observed red
supergiant upper mass limit. These models therefore represent a
drastic improvement over previous generations.
Reference:
ApJ, in press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/pdf/1203.0247v1.pdf
Comments:
Email: phil.massey@lowell.edu
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Jon O. Sundqvist(1), Asif
ud-Doula(2), Stanley P. Owocki(1), Richard H. D. Townsend(3), Ian D.
Howarth(4), Gregg A. Wade(5), and the MiMeS Collaboration
1
- University of Delaware, Bartol Research Institute, USA; 2 -Penn
State Worthington Scranton, USA; 3 University of Wisconsin,
Department of Astronomy, USA; 4 - University College London,
Department of Physics and Astronomy, United Kingdom; 5 - Royal
Military College of Canada, Department of Physics, Kingston,
Canada
The magnetic O-star HD191612 exhibits strongly
variable, cyclic Balmer line emission on a 538-day period. We show
here that its variable Halpha emission can be well reproduced by the
rotational phase variation of synthetic spectra computed directly
from full radiation magneto-hydrodynamical simulations of a
magnetically confined wind. In slow rotators such as hd, wind
material on closed magnetic field loops falls back to the star, but
the transient suspension of material within the loops leads to a
statistically overdense, low velocity region around the magnetic
equator, causing the spectral variations. We contrast such
``dynamical magnetospheres'' (DMs) with the more steady-state
``centrifugal magnetospheres'' of stars with rapid rotation, and
discuss the prospects of using this DM paradigm to explain periodic
line emission from also other non-rapidly rotating
magnetic
massive stars.
Reference: MNRAS letters, in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1203.1050
Comments:
Email: jon@bartol.udel.edu
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A. Liermann (1), W.-R. Hamann
(2), L. M. Oskinova (2)
1 - Max-Planck-Institute for
Radioastronomy, Bonn;
2 - University of Potsdam
The
Quintuplet, one of three massive stellar clusters in the Galactic
center, is located about 30pc in projection from Sagittarius A*.
Based on near-infrared K-band spectra we determine temperatures and
luminosities for all stars in our sample and construct the
Herztsprung-Russell diagram. We find two distinct groups:
early-type OB stars and late-type KM stars, well separated from each
other. By comparison with Geneva stellar evolution models we derive
initial masses exceeding 8 solar masses for the OB stars, that are
located along an isochrone corresponding to a cluster age of about 4
million years. In addition, we derive number ratios (e. g. N_WR/N_O$)
and compare them with predictions of population synthesis models. We
find that an instantaneous burst of star formation at about 3.3 to
3.6 Myr ago is the most likely scenario to form the Quintuplet
cluster. The late-type stars in the sample are red giant branch (RGB)
stars or red supergiants (RSGs) according to their spectral
signatures. It is discussed if they could physically belong to the
Quintuplet cluster. Furthermore, we apply a mass-luminosity relation
to construct the initial mass function (IMF) of the cluster. We find
indications for a slightly top-heavy IMF.
Reference: A&A
in press; arXiv:1203.2435
Status: Manuscript has been
accepted
Weblink:
Comments:
Email:
liermann@mpifr-bonn.mpg.de
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J. Takata^1, A.T. Okazaki^2, S. Nagataki^3, T. Naito^4, A.
kawachi^5, S.-H. Lee^^3, M. Mori^6, K. Hayasaki^7, M.S. Yamaguchi^8,
S.P. Owocki^9
1-Department of Physics, The University of
Hong-Kong, Hong Kong
2-Faculty of Engineering, Hokkai-Gakuen
University, Toyohira-ku, Sapporo 062-8605, Japan
3-Yukawa
Institute for Theoretical Physics, Oiwake-cho, Kitashirakawa,
Sakyo-ku, Kyoto 606-8502, Japan
4-Faculty of Management
Information, Yamanashi Gakuin University, Kofu, Yamanashi 400-8575,
Japan
5-Department of Physics, Tokai University, Hiratsuka,
Kanagawa 259-1292, Japan
6-Department of Physical Sciences,
Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga 525-8577,
Japan
7-Department of Astronomy, Kyoto University, Oiwake-cho,
Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
8-Department of
Earth and Space Science, Graduate School of Science, Osaka
University, Toyonaka, Osaka 560-0043, Japan
9-Bartol Research
Institute, University of Delaware, Newark, DE 19716, USA
Temporal
changes of X-ray to very-high-energy gamma-ray emissions from the
pulsar-Be star binary PSR~B1259-63/LS~2883 are studied based on 3-D
SPH simulations of pulsar wind interaction with Be-disk and wind. We
focus on the periastron passage of the binary and calculate the
variation of the synchrotron and inverse-Compton emissions using the
simulated shock geometry and pressure distribution of the pulsar
wind. The characteristic double-peaked X-ray light curve from
observations is reproduced by our simulation under a dense Be disk
condition (base density ~10^{-9} g~cm^{-3}). We interpret the pre-
and post-periastron peaks as being due to a significant increase in
the conversion efficiency from pulsar spin down power to the
shock-accelerated particle energy at orbital phases when the pulsar
crosses the disk before periastron passage, and when the pulsar wind
creates a cavity in the disk gas after periastron passage,
respectively. On the contrary, in the model TeV light curve, which
also shows a double peak feature, the first peak appears around the
periastron phase. The possible effects of cooling processes on the
TeV light curve are briefly discussed.
Reference: Accepted
for publication in ApJ.
Status: Manuscript has been
accepted
Weblink: http://arXiv.org/abs/1203.2179
Comments:
Email: takata@hku.hk
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S. Ramírez Alegría (1,2),
A. Marín-Franch (3,4) & A. Herrero (1,2)
(1)
Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife,
Spain. sramirez@iac.es, ahd
(2) Departamento de Astrofísica,
Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain.
(3)
Centro de Estudios de Física del Cosmos de Aragón (CEFCA), E-44001,
Teruel, Spain. amarin@cefca.es
(4) Departamento de Astrofísica,
Universidad Complutense de Madrid, E-38040, Madrid, Spain.
Context:
Recent near-infrared data have contributed to the discovery of new
(obscured) massive stellar clusters and massive stellar populations
in previously known clusters in our Galaxy. These discoveries lead us
to view the Milky Way as an active star-forming machine.
Aims:
The main purpose of this work is to determine physically the main
parameters (distance, size, total mass and age) of Masgomas-1, the
first massive cluster discovered by our systematic search programme.
Methods: Using near-infrared (J, H, and K_S) photometry we
selected 23 OB-type and five red supergiant candidates for
multi-object H- and K-spectroscopy and spectral classification.
Results: Of the 28 spectroscopically observed stars, 17 were
classified as OB-type, four as supergiants, one as an A-type dwarf
star, and six as late-type giant stars. The presence of a supergiant
population implies a massive nature of Masgomas-1, supported by our
estimate of the cluster initial total mass of (1.94pm0.28)cdot10^4
M_{Sun}, obtained after integrating the cluster mass function. The
distance estimate of 3.53 kpc locates the cluster closer than the
Scutum-Centaurus base but still within that Galactic arm. The
presence of an O9V star and red supergiants in the same population
indicates that the cluster age is in the range of 8 to 10
Myr.
Reference: 2012, A&A, accepted
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1203.4174
Comments:
Email: sramirez@iac.es
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L. M. Oskinova, A. Feldmeier,
P. Kretschmar
University of Potsdam; ESA
The
clumping of massive star winds is an established paradigm, which is
confirmed by multiple lines of evidence and is supported by stellar
wind theory. The purpose of this paper is to bridge the gap between
detailed models of inhomogeneous stellar winds in single stars and
the phenomenological description of donor winds in supergiant
high-mass X-ray binaries (HMXBs). We use the results from
time-dependent hydrodynamical models of the instability in the
line-driven wind of a massive supergiant star to derive the
time-dependent accretion rate on to a compact object in the
Bondi–Hoyle–Lyttleton approximation. The strong density and
velocity fluctuations in the wind result in strong variability of the
synthetic X-ray light curves. The model predicts a large-scale X-ray
variability, up to eight orders of magnitude, on relatively short
time-scales. The apparent lack of evidence for such strong
variability in the observed HMXBs indicates that the details of the
accretion process act to reduce the variability resulting from the
stellar wind velocity and density jumps.
We study the
absorption of X-rays in the clumped stellar wind by means of a
two-dimensional stochastic wind model. The monochromatic absorption
in the cool stellar wind, depending on the orbital phase, is computed
for realistic stellar wind opacity. We find that the absorption of
X-rays changes strongly at different orbital phases. The degree of
the variability resulting from the absorption in the wind depends on
the shape of the wind clumps, and this is stronger for oblate clumps.
We address the photoionization in the clumped wind, and we
show that the degree of ionization is affected by the wind clumping.
We derive a correction factor for the photoionization parameter, and
we show that the photoionization parameter is reduced by a factor
inline image compared to the smooth wind models with the same
mass-loss rate, where inline image is the wind inhomogeneity
parameter. We conclude that wind clumping must also be taken into
account when comparing the observed and model spectra of the
photoionized stellar wind.
Reference: 2012, MNRAS, 5
March
Status: Manuscript has been accepted
Weblink:
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2966.2012.20507.x/full
Comments:
Supporting Information: Synthetic X-ray light curves for
Bondi-Hoyle accretion of a non-stationary stellar wind on to a NS is
provided in the on-lne version of the paper or on demand from
authors
Email: lida@astro.physik.uni-potsdam.de
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Emily M. Levesque (1), Claus
Leitherer (2), Sylvia Ekstrom (3), Georges Meynet (3), Daniel
Schaerer (3)
(1) University of Colorado at Boulder
(2)
Space Telescope Science Institute
(3) Geneva Observatory
We
present a sample of synthetic massive stellar populations created
using the Starburst99 evolutionary synthesis code and new sets of
stellar evolutionary tracks, including one set that adopts a detailed
treatment of rotation. Using the outputs of the Starburst99 code, we
compare the populations' integrated properties, including ionizing
radiation fields, bolometric luminosities, and colors. With these
comparisons we are able to probe the specific effects of rotation on
the properties of a stellar population. We find that a population of
rotating stars produces a much harder ionizing radiation field and a
higher bolometric luminosity, changes that are primarily attributable
to the effects of rotational mixing on the lifetimes, luminosities,
effective temperatures, and mass loss rates of massive stars. We
consider the implications of the profound effects that rotation can
have on a stellar population, and discuss the importance of refining
stellar evolutionary models for future work in the study of
extragalactic, and particularly high-redshift, stellar
populations.
Reference: ApJ, in press
Status:
Manuscript has been accepted
Weblink:
http://xxx.lanl.gov/abs/1203.5109
Comments:
Email: Emily.Levesque@colorado.edu
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Cyril Georgy$^1$, Sylvia
Ekström$^2$, Georges Meynet$^2$, Philip Massey$^3$, Emily M.
Levesque$^4$, Raphael Hirschi$^{5,6}$, Patrick Eggenberger$^2$, André
Maeder$^2$
1 - Centre de Recherche Astrophysique de Lyon,
Ecole Normale Supérieure de Lyon, 46, allée d’Italie, F-69384
Lyon cedex 07, France
2 - Geneva Observatory, University of
Geneva, Maillettes 51, CH-1290 Sauverny, Switzerland
3 - Lowell
Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001, USA
4 -
CASA, Department of Astrophysical and Planetary Sciences, University
of Colorado 389-UCB, Boulder, CO 80309, USA
5 - Astrophysics
group, EPSAM, Keele University, Lennard-Jones Labs, Keele, ST5 5BG,
UK
6 - Institute for the Physics and Mathematics of the Universe,
University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8583,
Japan
Context: In recent years, many very interesting
observations have appeared concerning the positions of Wolf-Rayet
(WR) stars in the Hertzsprung-Russell diagram (HRD), the number
ratios of WR stars, the nature of type Ibc supernova (SN)
progenitors, long and soft gamma ray bursts (LGRB), and the frequency
of these various types of explosive events. These observations
represent key constraints on massive star evolution.
Aims: We
study, in the framework of the single-star evolutionary scenario, how
rotation modifies the evolution of a given initial mass star towards
the WR phase and how it impacts the rates of type Ibc SNe. We also
discuss the initial conditions required to obtain collapsars and
LGRB.
Methods: We used a recent grid of stellar models computed
with and without rotation to make predictions concerning the WR
populations and the frequency of different types of core-collapse
SNe. Current rotating models were checked to provide good fits to the
following features: solar luminosity and radius at the solar age,
main-sequence width, red-giant and red-supergiant (RSG) positions in
the HRD, surface abundances, and rotational velocities.
Results:
Rotating stellar models predict that about half of the observed WR
stars and at least half of the type Ibc SNe may be produced through
the single-star evolution channel. Rotation increases the duration of
the WNL and WNC phases, while reducing those of the WNE and WC
phases, as was already shown in previous works. Rotation increases
the frequency of type Ic SNe. The upper mass limit for type II-P SNe
is ∼ 24.9 M⊙ for the non rotating models and ∼ 19.9 M⊙ for
the rotating ones. This last value agrees better with observations.
Moreover, present rotating models provide a very good fit to the
progenitor of SN 2008ax. We discuss future directions of research for
further improving the agreement between the models and the
observations. We conclude that the mass-loss rates in the WNL and RSG
phases are probably underestimated at present. We show that up to an
initial mass of 40 M⊙, a surface magnetic field inferior to about
200 G may be sufficient to produce some braking. Much lower values
are needed at the red supergiant stage. We suggest that the
presence/absence of any magnetic braking effect may play a key role
in questions regarding rotation rates of young pulsars and the
evolution leading to LGRBs.
Reference: A&A in
press
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1203.5243
Comments:
Email: Cyril.Georgy@ens-lyon.fr
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C. B. Kaschinski, A.W.A.
Pauldrach, T. L. Hoffmann
Institut für Astronomie und
Astrophysik der Universitaet Muenchen, Scheinerstrasse 1, 81679
Muenchen, Germany
Context: The commonly accepted
mass-luminosity relation of central stars of planetary nebulae
(CSPNs) might not be universally valid. While earlier optical
analyses could not derive masses and luminosities independently
(instead taking them from theoretical evolutionary models)
hydrodynamically consistent modelling of the stellar winds allows
using fits to the UV spectra to consistently determine also stellar
radii, masses, and luminosities without assuming a mass-luminosity
relation. Recent application to a sample of CSPNs raised questions
regarding the validity of the theoretical mass-luminosity relation of
CSPNs.
Aims: The results of the earlier UV analysis are
reassessed by means of a simultaneous comparison of observed optical
and UV spectra with corresponding synthetic spectra.
Methods:
Using published stellar parameters (a) from a consistent UV analysis
and (b) from fits to optical H and He lines, we calculate
simultaneous optical and UV spectra with our model atmosphere code,
which has been improved by implementing Stark broadening for H and He
lines.
Results: Spectra computed with the parameter sets from the
UV analysis yield good agreement to the observations, but spectra
computed with the stellar parameters from the published optical
analysis and using corresponding consistent wind parameters show
large discrepancies to both the observed optical and UV spectra. The
published optical analyses give good fits to the observed spectrum
only because the wind parameters assumed in these analyses are
inconsistent with their stellar parameters. By enforcing consistency
between stellar and wind parameters, stellar parameters are obtained
which disagree with the core-mass-luminosity relation for the objects
analyzed. This disagreement is also evident from a completely
different approach: an investigation of the dynamical wind
parameters.
Reference: Publication in A&A
Pre-print available on astro-ph
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1204.1200
Comments:
22 pages, 18 fugres
Email:
uh10107@usm.uni-muenchen.de
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Allard Jan van Marle$^{1,2}$
Zakaria Meliani$^3$
Alexandre Marcowith$^4$
1-Institute of Astronomy, KU
Leuven,
2-Centre for Plasma Astrophysics, KU Leuven
3-Observatoire de Paris (Meudon)
4- Laboratoire Univers et
Particules (LUPM) Universit{'e} Montpellier
Numerical models
of the wind-blown bubble of massive stars usually account only for
the wind of a single star. However, since massive stars are usually
formed in clusters, it would be more realistic to follow the
evolution of a bubble created by several stars. We make a 2D model of
the circumstellar bubble created by two massive stars: a 40 solar
mass star and a 25 solar mass star and follow its evolution. The
stars have a separation of approx. 16 pc and surrounded by a cold
medium with a density of 20 particles per cubic cm. We use the
MPI-AMRVAC hydrodynamics code to solve the conservation equations of
hydrodynamics on a 2D cylindrical grid using time-dependent models
for the parameters of the wind of the two stars. At the end of the
stellar evolution (4.5 and 7.0 million years for the 40 and 25 solar
mass stars respectively) we simulate the supernova explosion of each
star. Initially, each star creates its own bubble. However, as the
bubbles expand they merge, creating a combined, a-spherical bubble.
The combined bubble evolves over time, influenced by the stellar
winds and supernova explosions. The evolution of a wind-blown bubble,
created by two stars deviates from that of the bubbles around single
stars. In particular, once one of the stars has exploded, the bubble
is too large to maintain for the wind of the remaining star and the
outer shell starts to fall apart. The lack of thermal pressure inside
the bubble also changes the behavior of circumstellar features close
to the remaining star. The supernovae are contained inside the
bubble, which reflects part of the energy back into the circumstellar
medium.
Reference: Accepted for publication in
Astronomy & Astrophysics
Status: Manuscript has been
accepted
Weblink: http://arxiv.org/abs/1204.2078
Comments:
additional data to be published online
Email:
AllardJan.vanMarle@ster.kuleuven.be
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M. De Becker (1), H. Sana
(2), O. Absil (1), J.-B. Le Bouquin (3), R. Blomme (4)
1.
University of Liège, Belgium
2. University of Amsterdam,
Netherlands
3. UJF-Grenoble, France
4. Royal Observatory of
Belgium, Belgium
Using optical long baseline interferometry,
we resolved for the first time the two wide components of HD167971, a
candidate hierarchical triple system known to efficiently accelerate
particles. Our multi-epoch VLTI observations provide direct evidence
for a gravitational link between the O8 supergiant and the close
eclipsing O + O binary. The separation varies from 8 to 15 mas over
the three-year baseline of our observations, suggesting that the
components evolve on a wide and very eccentric orbit (most probably
e>0.5). These results provide evidence that the wide orbit
revealed by our study is not coplanar with the orbit of the inner
eclipsing binary. From our measurements of the near-infrared
luminosity ratio, we constrain the spectral classification of the
components in the close binary to be O6-O7, and confirm that these
stars are likely main-sequence objects. Our results are discussed in
the context of the bright non-thermal radio emission already reported
for this system, and we provide arguments in favour of a maximum
radio emission coincident with periastron passage. HD167971 turns out
to be an efficient O-type particle accelerator that constitutes a
valuable target for future high angular resolution radio imaging
using VLBI facilities.
Reference: MNRAS (in
press)
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1204.3537
Comments:
Email: debecker@astro.ulg.ac.be
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Y. Naze (1), S. Bagnulo (2),
V. Petit (3), T. Rivinius (4), G. Wade (5), G. Rauw (1), M. Gagne
(3)
1-ULg, 2-Armagh Obs., 3-West Chester Un., 4-ESO,
5-RMC
X-ray surveys of the Carina nebula have revealed a few
hard and luminous sources associated with early-type stars. Such
unusual characteristics for the high-energy emission may be related
to magnetically-confined winds. To search for the presence of
magnetic fields in these objects, we performed a limited
spectropolarimetric survey using the FORS instrument. The
multi-object mode was used, so that a total of 21 OB stars could be
investigated during a one-night-long run. A magnetic field was
detected in two objects of the sample, with a 6 sigma significance;
Tr16-22 and 13. Such a detection was expected for Tr16-22, as its
X-ray emission is too bright, variable and hard, compared to other
late-type O or O+OB systems. It is more surprising for Tr16-13, a
poorly known star which so far has never shown any peculiar
characteristics. Subsequent monitoring is now needed to ascertain the
physical properties of these objects and enable a full modelling of
their magnetic atmospheres and winds.
Reference: accepted
by MNRAS
Status: Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1204.4267
Comments:
Email: naze@astro.ulg.ac.be
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Emily M. Levesque, Philip
Massey
University of Colorado at Boulder; Lowell
Observatory
We present moderate-resolution spectroscopic
observations of red supergiants (RSGs) in the low-metallicity Local
Group galaxies NGC 6822 (Z = 0.4Zsun) and Wolf-Lundmark-Melotte (WLM;
Z = 0.1Zsun). By combining these observations with reduction
techniques for multislit data reduction and flux calibration, we are
able to analyze spectroscopic data of 16 RSGs in NGC 6822 and
spectrophotometric data of 11 RSGs in WLM. Using these observations
we determine spectral types for these massive stars, comparing them
to Milky Way and Magellanic Clouds RSGs and thus extending
observational evidence of the abundance-dependent shift of RSG
spectral types to lower metallicities. In addition, we have uncovered
two RSGs with unusually late spectral types (J000158.14-152332.2 in
WLM, with a spectral type of M3 I, and J194453.46-144552.6 in NGC
6822, with a spectral type of M4.5 I) and a third RSG
(J194449.96-144333.5 in NGC 6822) whose spectral type has varied from
a M2.5 in 1997 to a K5 in 2008. All three of these stars could
potentially be members of a recently-discovered class of extreme RSG
variables.
Reference: Astronomical Journal
Status:
Manuscript has been accepted
Weblink:
http://arxiv.org/abs/1204.4450
Comments:
Email: Emily.Levesque@colorado.edu
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Richard Ignace
East
Tennessee State University
Box 70652
Johnson City, TN 37614
USA
A postdoctoral research position in theoretical
modeling of spectropolarimetry of massive stars is available. The
research will involve radiative transfer in polarization with
applications to massive stars and their circumstellar environments.
The work is primarily theoretical modeling, but can include
observational components. The position starts no earlier than August
1st. The individual filling the position must hold a PhD in astronomy
or physics by the time the appointment begins. Consideration of
applications will begin May 15th and will continue until the position
is filled.
Applications, including a cover letter, CV,
contact information for references, and an ETSU application form,
must be submitted through an institutional website. Please see the
link below. Questions can be directed to Richard Ignace at
ignace@etsu.edu.
Attention/Comments:
Weblink:
https://jobs.etsu.edu/applicants/jsp/shared/position/JobDetails_css.jsp?postingId=151138
Email:
ignace@etsu.edu
Deadline:
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September 30 to October 3, 2012
Venue: St.
Paul, Minnesota, USA (on the banks of the Mississippi)
Current
transient surveys are finding SN-like events which are not true
supernovae. Some of the "supernova impostors" are suspected
to be giant eruptions resembling eta Carinae, possibly related to the
Luminous Blue Variables. Meanwhile, the most luminous true
supernovae are believed to be explosions into debris formed by
previous mass ejections, and two SNae were observed to have outbursts
prior to their final events. All these developments emphasize the
importance of instabilities and episodic mass loss in the most
massive stars, but
the mechanisms remain mysterious. Do they
involve the outer layers, or the core regions, or both? How do stars
above 50 solar masses end their lives? Do they just collapse to black
holes? Recent studies confirm that classical Type II SN progenitors
have much lower initial masses. Many of the outstanding questions
about final stages of very massive stars are primarily theoretical,
but observations are scarce, especially of the progenitor class.
The meeting will be a three day topical workshop to bring
together theorists and observers studying very massive stars, their
instabilities, SNe and their progenitors, and the outcomes of the
final eruptions. The emphasis of the workshop will be on the final
stages of massive star evolution and the unsolved theoretical and
observational questions.
SOC members:
Dave Arnett
Kris
Davidson
Alexander Heger - co-chair
Roberta Humphreys-
co-chair
Norbert Langer
Vuk Mandic
Peter Meszaros
Yong
Qian
Stephen Smartt
Stan Woosley
Weblink:
http://www.astro.umn.edu/massive
Email:
massive@astro.umn.edu
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