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Evolutionary Tracks (evolutionary + tracks)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Spectral models for solar-scaled and ,-enhanced stellar populations

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
P. Coelho
ABSTRACT We present the first models allowing one to explore in a consistent way the influence of changes in the ,-element-to-iron abundance ratio on the high-resolution spectral properties of evolving stellar populations. The models cover the wavelength range from 3000 Å to 1.34 ,m at a constant resolution of full width at half-maximum (FWHM) = 1 Å and a sampling of 0.2 Å, for overall metallicities in the range 0.005 ,Z, 0.048 and for stellar population ages between 3 and 14 Gyr. These models are based on a recent library of synthetic stellar spectra and a new library of stellar evolutionary tracks, both computed for three different iron abundances ([Fe/H]=,0.5, 0.0 and 0.2) and two different ,-element-to-iron abundance ratios ([,/Fe]= 0.0 and 0.4). We expect our fully synthetic models to be primarily useful for evaluating the differential effect of changes in the ,/Fe ratio on spectral properties such as broad-band colours and narrow spectral features. In addition, we assess the accuracy of absolute model predictions in two ways: first, by comparing the predictions of models for scaled-solar metal abundances ([,/Fe]= 0.0) to those of existing models based on libraries of observed stellar spectra; and secondly, by comparing the predictions of models for ,-enhanced metal abundances ([,/Fe]= 0.4) to observed spectra of massive early-type galaxies in the Sloan Digital Sky Survey Data Release 4. We find that our models predict accurate strengths for those spectral indices that are strongly sensitive to the abundances of Fe and , elements. The predictions are less reliable for the strengths of other spectral features, such as those dominated by the abundances of C and N, as expected from the fact that the models do not yet allow one to explore the influence of these elements in an independent way. We conclude that our models are a powerful tool for extracting new information about the chemical properties of galaxies for which high-quality spectra have been gathered by modern surveys. [source]

From observations to physics: Cosmological evolution of radio galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
A.D. Kapi
Abstract Recent theoretical progress has allowed us to determine the influence of the intrinsic properties of radio galaxies and their environments on their luminosity and size evolution. There are still, however, considerable uncertainties regarding our understanding of radio source evolution, in particular the relationship between CSS and GPS sources and larger radio galaxies. Here, we present our preliminary results on the cosmological evolution of the entire radio galaxy population. We use recent analytical models for the dynamical and luminosity evolution of FR II radio galaxies to convert observational data into distributions of source properties such as pressure of the source lobes. As input parameters we use the observed P - D (radio power,linear size) diagrams built up from flux-limited radio samples with complete redshift information. This allows us to examine the environments of evolving radio sources, and to shed more light on the (early) evolutionary tracks of radio galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The chromospherically active binary star EI Eridani: I. Absolute dimensions

ASTRONOMISCHE NACHRICHTEN, Issue 1 2009
A. Washuettl
Abstract We present a detailed determination of the astrophysical parameters of the chromospherically active binary star EI Eridani. Our new radial velocities allow to improve the set of orbital elements and reveal long-term variations of the barycentric velocity. A possible third-body orbit with a period of ,19 years is presented. Absolute parameters are determined in combination with the Hipparcos parallax. EI Eri's inclination angle of the rotational axis is confined to 56°.0 ± 4°.5, ist luminosity class IV is confirmed by its radius of 2.37 ± 0.12 R,. A comparison to theoretical stellar evolutionary tracks suggests a mass of 1.09 ± 0.05 M, and an age of , 6.15 Gyr. The present investigation is the basis of our long-term Doppler imaging study of its stellar surface (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Local group dwarf galaxies in the ,CDM paradigm

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2008
J. Peñarrubia
Abstract We report the results of two theoretical studies that examine the dynamics of stellar systems embedded within cold dark matter (CDM) halos in order to assess observational constraints on the dark matter content of Local Group dwarf spheroidals (dSphs). (i) Firstly, approximating the stellar and dark components by King and NFW models, respectively, we calculate the parameters of dark halos consistent with the kinematics and spatial distribution of stars in dSphs as well as with cosmological N-body simulations. (ii) Subsequently, N-body realization of these models are constructed to study the evolution of dwarf spheroidal galaxies (dSphs) driven by galactic tides. The analytical estimates highlight the poor correspondence between luminosity and halo mass. In systems where data exist, the stellar velocity dispersion profiles remains flat almost to the nominal "tidal" radius, implying that stars are deeply embedded within the dwarf halos and are therefore quite resilient to tidal disruption. This is confirmed by our N-body experiments: halos need to lose more than 90% of their original mass before stars can be stripped. As tidal mass loss proceeds, the stellar luminosity, L, velocity dispersion, ,0, central surface brightness, ,0, and core radius, Rc, decrease monotonically. Remarkably, the evolution of these parameters is solely controlled by the total amount of mass lost from within the luminous radius, which permit us to derive a tidal evolutionary track for each of them. This information is used to examine whether the newly-discovered ultra-faintMilkyWay dwarfs are tidally-stripped versions of the "classical", bright dwarfs. Although dSph tidal evolutionary tracks parallel the observed scaling relations in the luminosity-radius plane, they predict too steep a change in velocity dispersion compared with the observational estimates. The ultra-faint dwarfs are thus unlikely to be the tidal remnants of systems like Fornax, Draco, or Sagittarius. Despite spanning four decades in luminosity, dSphs appear to inhabit halos of comparable peak circular velocity, lending support to scenarios that envision dwarf spheroidals as able to form only in halos above a certain mass threshold. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]