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Synthetic Spectra (synthetic + spectrum)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Hydrogen Balmer Spectrum from a High-Pressure Arc Discharge: Revisited

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 4-5 2007
B. Omar
Abstract The interpretation of hydrogen Balmer spectra emitted from a high-pressure arc discharge (Radtke and Günther, Contrib. Plasma Phys. 26, 143 (1986)) is re-examined. Assuming local thermodynamic equilibrium, synthetic Balmer spectra are calculated for given temperature and density conditions. Radiation transport is accounted for using a one-dimensional plasma layer model. The lineshape of bound-bound transitions is determined using a microscopic quantum-statistical approach. Free-free and free-bound contributions are added by taking expressions from literature. Comparing the synthetic spectra with experimental ones, plasma temperature and density conditions are inferred. The plasma parameters are confronted with theoretical results for the compositions of dense plasma. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A semi-empirical model of the infrared emission from galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008
D. C. Ford
ABSTRACT We present a semi-empirical model for the infrared emission of dust around star-forming sites in galaxies. Our approach combines a simple model of radiative transfer in dust clouds with a state-of-the-art model of the microscopic optical properties of dust grains pioneered by Draine & Li. In combination with the starburst99 stellar spectral synthesis package, this framework is able to produce synthetic spectra for galaxies which extend from the Lyman limit through to the far-infrared. We use it to probe how model galaxy spectra depend on the physical characteristics of their dust grain populations, and on the energy sources which heat that dust. We compare the predictions of our model with the 8- and 24-,m luminosities of sources in the Spitzer First Look Survey, and conclude by using the models to analyse the relative merits of various colour diagnostics in distinguishing systems out to a redshift of 2 with ongoing star formation from those with only old stellar populations. [source]

Evolutionary population synthesis for binary stellar population at high spectral resolution: integrated spectral energy distributions and absorption-feature indices

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005
Fenghui Zhang
ABSTRACT Using evolutionary population synthesis, we present high-resolution (0.3 Å) integrated spectral energy distributions from 3000 to 7000 Å and absorption-line indices defined by the Lick Observatory Image Dissector Scanner (Lick/IDS) system, for an extensive set of instantaneous-burst binary stellar populations with binary interactions. The ages of the populations are in the range 1,15 Gyr and the metallicities are in the range 0.004,0.03. These high-resolution synthesis results can satisfy the needs of modern spectroscopic galaxy surveys, and are available on request. By comparing the synthetic continuum of populations at high and low resolution, we show that there is good agreement for solar metallicity and tolerable disagreement for non-solar metallicity. The strength of the Balmer lines at high spectral resolution is greater than that at low resolution for all metallicities. The comparison of Lick/IDS absorption-line indices at low and high resolution, both of which are obtained by the fitting functions, shows that the discrepancies in all indices except for TiO1 and TiO2 are insignificant for populations with Z= 0.004 and 0.02. The high-resolution Ca4227, Fe5015 and Mgb indices are redder than the corresponding low-resolution ones for populations with Z= 0.01 and 0.03; this effect lowers the derived age and metallicity of the population. The high-resolution Mg1, Fe5709 and Fe5782 indices are bluer than those at low resolution; this effect raises the age and metallicity. The discrepancy in these six indices is greater for populations with Z= 0.03 in comparison to Z= 0.01. At high resolution we compare the Lick/IDS spectral absorption indices obtained by using the fitting functions with those measured directly from the synthetic spectra. We find that the Ca4455, Fe4668, Mgb and Na D indices obtained by the use of the fitting functions are redder for all metallicities, Fe5709 is redder at Z= 0.03 and becomes bluer at Z= 0.01 and 0.004, and the other indices are bluer for all metallicities than the corresponding values measured directly from the synthetic spectra. [source]

Search for narrow energy-shifted lines in AGN spectra in the XMMNewton archive,

ASTRONOMISCHE NACHRICHTEN, Issue 10 2006
A. L. Longinotti
Abstract Thanks to the large effective area and the spectral resolution of current X-ray satellites, the detection of X-ray narrow spectral features in the 5,7 keV band is becoming commonplace in many AGN observations. Such lines, both in emission and in absorption, are mostly interpreted as arising from Iron atoms. When observed with some displacement from their rest frame position, these lines carry the potential to study the motion of circumnuclear gas in AGN, providing a diagnostic of the effects of the gravitational field of the central black hole. These narrow features have been often found with marginal statistical significance. A systematic search for narrow features in type1 AGN is being performed on all spectra available in the XMM-Newton archive with the aim to estimate the significance of the features with Monte Carlo simulations of synthetic spectra. The project and preliminary results are presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]