1,839 research outputs found
Comparisons for Esta-Task3: Cles and Cesam
We present the results of comparing three different implementations of the
microscopic diffusion process in the stellar evolution codes CESAM and CLES.
For each of these implementations we computed models of 1.0, 1.2 and 1.3
M. We analyse the differences in their internal structure at three
selected evolutionary stages, as well as the variations of helium abundance and
depth of the stellar convective envelope. The origin of these differences and
their effects on the seismic properties of the models are also considered.Comment: 10 pages, 8 figures, Joint HELAS and CoRoT/ESTA Workshop on
Solar/Stellar Models and Seismic Analysis Tools, Novembre, Porto 2007 To be
published in EAS Publications Serie
Mode stability in delta Scuti stars: linear analysis versus observations in open clusters
A comparison between linear stability analysis and observations of pulsation
modes in five delta Scuti stars, belonging to the same cluster, is presented.
The study is based on the work by Michel et al. (1999), in which such a
comparison was performed for a representative set of model solutions obtained
independently for each individual star considered. In this paper we revisit the
work by Michel et al. (1999) following, however, a new approach which consists
in the search for a single, complete, and coherent solution for all the
selected stars, in order to constrain and test the assumed physics describing
these objects. To do so, refined descriptions for the effects of rotation on
the determination of the global stellar parameters and on the adiabatic
oscillation frequency computations are used. In addition, a crude attempt is
made to study the role of rotation on the prediction of mode instabilities.The
present results are found to be comparable with those reported by Michel et al.
(1999). Within the temperature range log T_eff = 3.87-3.88 agreement between
observations and model computations of unstable modes is restricted to values
for the mixing-length parameter alpha_nl less or equal to 1.50. This indicates
that for these stars a smaller value for alpha_nl is required than suggested
from a calibrated solar model. We stress the point that the linear stability
analysis used in this work still assumes stellar models without rotation and
that further developments are required for a proper description of the
interaction between rotation and pulsation dynamics.Comment: 8 pages, 4 figures, 3 tables. (MNRAS, in press
Asteroseismology of delta Scuti stars in open clusters: Praesepe
The present paper provides a general overview of the asteroseismic potential
of delta Scuti stars in clusters, in particular focusing on convection
diagnostics. We give a summarise of the last results obtained by the authors
for the Praesepe cluster of which five delta Scuti stars are analysed. In that
work, linear analysis is confronted with observations, using refined
descriptions for the effects of rotation on the determination of the global
stellar parameters and on the adiabatic oscillation frequency computations. A
single, complete, and coherent solution for all the selected stars is found,
which lead the authors to find important restrictions to the convection
description for a certain range of effective temperatures. Furthermore, the
method used allowed to give an estimate of the global parameters of the
selected stars and constrain the cluster.Comment: 6 pages, 1 figure. Accepted for publication in Communications in
Asteroseismolog
Radiation-hydrodynamics simulations of surface convection in low-mass stars: connections to stellar structure and asteroseismology
Radiation-hydrodynamical simulations of surface convection in low-mass stars
can be exploited to derive estimates of i) the efficiency of the convective
energy transport in the stellar surface layers; ii) the convection-related
photometric micro-variability. We comment on the universality of the
mixing-length parameter, and point out potential pitfalls in the process of its
calibration which may be in part responsible for the contradictory findings
about its variability across the Hertzsprung-Russell digramme. We further
comment on the modelling of the photometric micro-variability in HD49933 - one
of the first main COROT targets.Comment: 6 pages, 5 figures, Proceedings paper of IAU Symposium 25
Modelos poblacionales del gran ánsar nival: comparación entre distintos enfoques empleados para evaluar los impactos potenciales de la cosecha
Demographic models, which are a natural extension of capture–recapture (CR) methodology, are a powerful tool to guide decisions when managing wildlife populations. We compare three different modelling approaches to evaluate the effect of increased harvest on the population growth of Greater Snow Geese (Chen caerulescens atlantica). Our first approach is a traditional matrix model where survival was reduced to simulate increased harvest. We included environmental stochasticity in the matrix projection model by simulating good, average, and bad years to account for the large inter–annual variation in fecundity and first–year survival, a common feature of birds nesting in the Arctic. Our second approach is based on the elasticity (or relative sensitivity) of population growth rate (lambda) to changes in survival as simple functions of generation time. Generation time was obtained from the mean transition matrix based on the observed proportion of good, average and bad years between 1985 and 1998. If we assume that hunting mortality is additive to natural mortality, then a simple formula predicts changes in lambda as a function of changes in harvest rate. This second approach can be viewed as a simplification of the matrix model because it uses formal sensitivity results derived from population projection. Our third, and potentially more powerful approach, uses the Kalman Filter to combine information on demographic parameters, i.e. the population mechanisms summarized in a transition matrix model, and the census information (i.e. annual survey) within an overall Gaussian likelihood. The advantage of this approach is that it minimizes process and measured uncertainties associated with both the census and demographic parameters based on the variance of each estimate. This third approach, in contrast to the second, can be viewed as an extension of the matrix model, by combining its results with the independent census information.Los modelos demográficos, que son una ampliación natural de la metodología de captura–recaptura (CR), constituyen un excelente instrumento orientativo a la hora de decidir cómo gestionar las poblaciones de flora y fauna. Comparamos tres enfoques de modelos distintos para evaluar los efectos de una mayor cosecha en el crecimiento poblacional del ánsar nival (Chen caerulescens atlantica). Nuestro primer enfoque consiste en un modelo de matrices tradicional en el que se redujo la supervivencia a efectos de simular una mayor cosecha. Incluimos estocasticidad medioambiental en el modelo de proyección matricial simulando años buenos, medios y malos a efectos justificar la significativa variación interanual en la fecundidad y en la supervivencia durante el primer año, dado que constituyen una característica común de las aves que nidifican en el Ártico. Nuestro segundo enfoque se basa en la elasticidad (o sensibilidad relativa) de la tasa de crecimiento poblacional (lambda) con respecto a los cambios en la supervivencia como funciones simples del tiempo generacional. El tiempo generacional se obtuvo a partir de la matriz de transición media basada en la proporción observada de años buenos, medios y malos entre 1985 y 1998. Si suponemos que la mortalidad por caza se suma a la mortalidad natural, una fórmula simple predice cambios en la lambda como una función de cambios en la tasa de cosechas. El segundo enfoque puede considerarse como una simplificación del modelo de matrices, puesto que emplea resultados de sensibilidad formal derivados de la proyección poblacional. Nuestro tercer enfoque, de mayor alcance potencial, utiliza el filtro de Kalman para combinar información sobre parámetros demográficos; es decir, los mecanismos poblacionales resumidos en un modelo de matrices de transición, y la información censal (es decir, la inspección anual) en una probabilidad gaussiana general. La ventaja de este enfoque es que minimiza los procesos y las incertidumbres medidas que se asocian, tanto con el censo como con los parámetros demográficos basados en la varianza de cada estimación. El tercer enfoque, a diferencia del segundo, puede considerarse como una ampliación del modelo de matrices, combinando sus resultados con la información censal independiente
Hierarchical clustering based on the combination of chlorophyll fluorescence parameters for the discrimination of biotic stresses displaying similar phenotypes on leaves
Dietary glucose regulates yeast consumption in adult Drosophila males
The adjustment of feeding behavior in response to hunger and satiety contributes to homeostatic regulation in animals. The fruit fly Drosophila melanogaster feeds on yeasts growing on overripe fruit, providing nutrients required for adult survival, reproduction and larval growth. Here, we present data on how the nutritional value of food affects subsequent yeast consumption in Drosophila adult males. After a period of starvation, flies showed intensive yeast consumption. In comparison, flies stopped feeding after having access to a nutritive cornmeal diet. Interestingly, dietary glucose was equally efficient as the complex cornmeal diet. In contrast, flies fed with sucralose, a non-metabolizable sweetener, behaved as if they were starved. The adipokinetic hormone and insulin-like peptides regulate metabolic processes in insects. We did not find any effect of the adipokinetic hormone pathway on this modulation. Instead, the insulin pathway was involved in these changes. Flies lacking the insulin receptor (InR) did not respond to nutrient deprivation by increasing yeast consumption. Together these results show the importance of insulin in the regulation of yeast consumption in response to starvation in adult D. melanogaster males
Mass-luminosity relation for FGK main sequence stars: metallicity and age contributions
The stellar mass-luminosity relation (MLR) is one of the most famous
empirical "laws", discovered in the beginning of the 20th century. MLR is still
used to estimate stellar masses for nearby stars, particularly for those that
are not binary systems, hence the mass cannot be derived directly from the
observations. It's well known that the MLR has a statistical dispersion which
cannot be explained exclusively due to the observational errors in luminosity
(or mass). It is an intrinsic dispersion caused by the differences in age and
chemical composition from star to star. In this work we discuss the impact of
age and metallicity on the MLR. Using the recent data on mass, luminosity,
metallicity, and age for 26 FGK stars (all members of binary systems, with
observational mass-errors <= 3%), including the Sun, we derive the MLR taking
into account, separately, mass-luminosity, mass-luminosity-metallicity, and
mass-luminosity-metallicity-age. Our results show that the inclusion of age and
metallicity in the MLR, for FGK stars, improves the individual mass estimation
by 5% to 15%.Comment: 7 pages, 4 figures, 1 table, accepted in Astrophysics and Space
Scienc
Use of Chlorophyll Fluorescence Imaging to phenotype type 3 effectors impacts of Xanthosmonas on leaves
- …