156 research outputs found
Intermediate Mass Stars <--> Massive Stars. A workshop around causes and consequences of differing evolutionary paths
The post-main sequence evolution of stars of intermediate or large masses is
notoriously complex. In the recent past, a number of workshops and meetings
have focused on either the Asymptotic Giant Branch of intermediate mass stars,
or the evolution of massive stars. But how well defined is the boundary between
these categories of objects defined? How would an observer proceed to classify
stars into one or the other category? How do objects near the boundary evolve,
die, and contribute to the chemical evolution of their environment? During this
3-day international workshop, 26 high quality presentations were given by
specialists in the relevant fields of astrophysics, and stimulating discussions
followed. It is technically impossible to provide an exhaustive census of the
results and ideas that emerged. In this brief article, we choose to point to
key elements of the workshop, some of which are now the topic of new
collaborations and will lead to publications elsewhere. For the sake of
brevity, we deliberately cite only the contributors to the workshop and no
external references. Many bibliographic references can be found in the original
presentations, which can be retrieved through:
http://astro.u-strasbg.fr/observatoire/obs/stars2009/stars2009.html The
programme workshop, which includes the titles of the individual contributions,
is provided as an appendix.Comment: 8 pages, 4 figure
A new nonlocal thermodynamical equilibrium radiative transfer method for cool stars
Context: The solution of the nonlocal thermodynamical equilibrium (non-LTE)
radiative transfer equation usually relies on stationary iterative methods,
which may falsely converge in some cases. Furthermore, these methods are often
unable to handle large-scale systems, such as molecular spectra emerging from,
for example, cool stellar atmospheres.
Aims: Our objective is to develop a new method, which aims to circumvent
these problems, using nonstationary numerical techniques and taking advantage
of parallel computers.
Methods: The technique we develop may be seen as a generalization of the
coupled escape probability method. It solves the statistical equilibrium
equations in all layers of a discretized model simultaneously. The numerical
scheme adopted is based on the generalized minimum residual method.
Result:. The code has already been applied to the special case of the water
spectrum in a red supergiant stellar atmosphere. This demonstrates the fast
convergence of this method, and opens the way to a wide variety of
astrophysical problems.Comment: 13 pages, 9 figure
The low wind expansion velocity of metal-poor carbon stars in the Halo and the Sagittarius stream
We report the detection, from observations using the James Clerk Maxwell
Telescope, of CO J 3 2 transition lines in six carbon stars, selected
as members of the Galactic Halo and having similar infrared colors. Just one
Halo star had been detected in CO before this work. Infrared observations show
that these stars are red (J-K 3), due to the presence of large dusty
circumstellar envelopes. Radiative transfer models indicates that these stars
are losing mass with rather large dust mass-loss rates in the range 1--3.3
Myr, similar to what can be observed in the
Galactic disc. We show that two of these stars are effectively in the Halo, one
is likely linked to the stream of the Sagittarius Dwarf Spheroidal galaxy (Sgr
dSph), and the other three stars certainly belong to the thick disc. The wind
expansion velocities of the observed stars are low compared to carbon stars in
the thin disc and are lower for the stars in the Halo and the Sgr dSph stream
than in the thick disc. We discuss the possibility that the low expansion
velocities result from the low metallicity of the Halo carbon stars. This
implies that metal-poor carbon stars lose mass at a rate similar to metal-rich
carbon stars, but with lower expansion velocities, as predicted by recent
theoretical models. This result implies that the current estimates of mass-loss
rates from carbon stars in Local Group galaxies will have to be reconsidered.Comment: 10 pages, 7 figures, accepted for publication in MNRA
NLTE water lines in Betelgeuse-like atmospheres
The interpretation of water lines in red supergiant stellar atmospheres has
been much debated over the past decade. The introduction of the so-called
MOLspheres to account for near-infrared "extra" absorption has been
controversial. We propose that non-LTE effects should be taken into account
before considering any extra-photospheric contribution.
After a brief introduction on the radiative transfer treatment and the
inadequacy of classical treatments in the case of large-scale systems such as
molecules, we present a new code, based on preconditioned Krylov subspace
methods. Preliminary results suggest that NLTE effects lead to deeper water
bands, as well as extra cooling.Comment: 9 pages, 5 figures, Proceedings of the Betelgeuse Workshop, Paris,
201
Populations of the Beet Cyst Nematode Heterodera schachtii Exhibit Strong Differences in Their Life-History Traits Across Changing Thermal Conditions
It is widely accepted that climate has an essential influence on the distribution of species and that temperature is the major abiotic factor that affects their life-history traits. Species with very restricted active dispersal abilities and a wide geographical distribution are thus expected to encompass distinct populations adapted to contrasted local conditions. The beet cyst nematode Heterodera schachtii is a good biological model to study temperature adaptation in populations collected from different environments. Here, we tested the effect of temperature on H. schachtii life-history traits using seven field populations from Morocco, Spain, France, Germany, Austria, Poland and Ukraine. We tested hatching and multiplication rates of each population at different temperatures, as well as hatching rates of each population after storage at different temperatures – simulating survival conditions during the inter-cropping period. Results showed a strong temperature effect on the life-history traits explored. Temperature impact on hatching (at different temperatures and after storage at different temperatures) depended on the origin of populations, separating southern from northern ones. Surprisingly, low temperatures influenced hatching less in southern populations. However, for these populations, a storage period at low temperatures strongly reduce subsequent hatching. Conversely, nematode multiplication was not differentially affected by temperatures, as favorable conditions for the host are also favorable for the parasite. Finally, a significant correlation between the genetic diversity and the level of specialization showed that the less diverse populations were more specialized than the more diverse ones
The Effective Temperature Scale of Galactic Red Supergiants: Cool, But Not As Cool As We Thought
We use moderate-resolution optical spectrophotometry and the new MARCS
stellar atmosphere models to determine the effective temperatures of 74
Galactic red supergiants. From these we find a new effective temperature scale
that is significantly warmer than those in the literature. We show that this
temperature scale, along with the newly derived bolometric corrections, gives
much better agreement between our red supergiants and stellar evolutionary
tracks. This agreement provides an independent verification of our new
temperature scale. The combination of effective temperature and bolometric
luminosities allows us to calculate stellar radii; the coolest and most
luminous stars have radii of roughly 1500 solar radii (7 AU), in excellent
accordance with the largest stellar radii predicted from current evolutionary
theory. We find that similar results are obtained for the effective
temperatures and bolometric luminosities using only the de-reddened V-K colors,
providing a powerful demonstration of the self-consistency of the MARCS models.Comment: 32 pages, 16 figures; Accepted by the Astrophysical Journa
Synthetic Stellar libraries and SSP simulations in the Gaia Era
AbstractThe Gaia mission will obtain accurate positions, parallaxes and proper motions for 109object all over the sky. In addition, it will collect low resolution spectroscopy in the optical range for ~109objects, stars, galaxies, and QSOs. Parameters of those objects are expected to be part of the final Catalog. Complete and up-to-date libraries of synthetic stellar spectra are needed to train the algorithms to classify this huge amount of data. Here we focus on the use of the synthetic libraries of spectra calculated by the Gaia community to derive grids of Single Stellar Populations as building blocks of population synthesis models
The genome of the yellow potato cyst nematode, Globodera rostochiensis, reveals insights into the basis of parasitism and virulence
BACKGROUND: The yellow potato cyst nematode, Globodera rostochiensis, is a devastating plant pathogen of global economic importance. This biotrophic parasite secretes effectors from pharyngeal glands, some of which were acquired by horizontal gene transfer, to manipulate host processes and promote parasitism. G. rostochiensis is classified into pathotypes with different plant resistance-breaking phenotypes. RESULTS: We generate a high quality genome assembly for G. rostochiensis pathotype Ro1, identify putative effectors and horizontal gene transfer events, map gene expression through the life cycle focusing on key parasitic transitions and sequence the genomes of eight populations including four additional pathotypes to identify variation. Horizontal gene transfer contributes 3.5 % of the predicted genes, of which approximately 8.5 % are deployed as effectors. Over one-third of all effector genes are clustered in 21 putative ‘effector islands’ in the genome. We identify a dorsal gland promoter element motif (termed DOG Box) present upstream in representatives from 26 out of 28 dorsal gland effector families, and predict a putative effector superset associated with this motif. We validate gland cell expression in two novel genes by in situ hybridisation and catalogue dorsal gland promoter element-containing effectors from available cyst nematode genomes. Comparison of effector diversity between pathotypes highlights correlation with plant resistance-breaking. CONCLUSIONS: These G. rostochiensis genome resources will facilitate major advances in understanding nematode plant-parasitism. Dorsal gland promoter element-containing effectors are at the front line of the evolutionary arms race between plant and parasite and the ability to predict gland cell expression a priori promises rapid advances in understanding their roles and mechanisms of action.SE-vdA is supported by BBSRC grant BB/M014207/1. Sequencing was funded by BBSRC grant BB/F000642/1 to the University of Leeds and grant BB/F00334X/1 to the Wellcome Trust Sanger Institute). DRL was supported by a fellowship from The James Hutton Institute and the School of Biological Sciences, University of Edinburgh. GK was supported by a BBSRC PhD studentship. The James Hutton Institute receives funding from the Scottish Government. JAC and NEH are supported by the Wellcome Trust through its core funding of the Wellcome Trust Sanger Institute (grant 098051). This work was also supported by funding from the Canadian Safety and Security Program, project number CRTI09_462RD
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