EDP Sciences
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Volume 479, Number 1, February III 2008
Page(s) 207 - 212
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20077622

A&A 479, 207-212 (2008)
DOI: 10.1051/0004-6361:20077622

Influence of temperature fluctuations on the shape of the spectral continuum

N. A. Silant'ev1 and G. A. Alexeeva2

1  Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51 y 216, CP 7200, Puebla, Pue., México
    e-mail: silant@inaoep.mx
2  Main Astronomical observatory of Russian Academy of Sciences, Pulkovskoe shosse 65, S.-Petersburg 196140, Russia

(Received 9 April 2007 / Accepted 1 November 2007)

We investigate the influence of stochastic temperature fluctuations on the observed spectra in continuum. Temperature fluctuations exist in the photospheres and atmospheres of stars, in interstellar media, and in the vicinity of AGN and quasars. In these cases we observe the mean values of intensities from the objects. The particular calculations were made for the frequently used model of semi-infinite turbulent homogeneous atmosphere with the Planck source function. We show that temperature fluctuations T' change the spectral distribution of observed radiation in all regions of spectra, especially in the ultraviolet region, where they increase the mean intensity compared with the Planck intensity $B_{\nu}(T^{(0)})$ at the mean temperature T(0). In the maximum of Planck's spectrum, the difference between the Planck intensity $B_{\nu}(T^{(0)})$ and the observed mean intensity $I^{(0)}_{\nu}$ can also be large (about 5-30%). This difference can be negative or positive depending on the particular form of the absorption coefficient. Our results demonstrate that the turbulence-related small-scale temperature fluctuations contribute to the overall deviations from the Planck intensity. The temperature fluctuations change the observed U-B, B-V, etc. colour indices. Our simple technique can also be used to analyze of the radiation spectra from all sources, not only for the thermal Planck radiation.

Key words: radiative transfer -- turbulence -- line: formation -- line: profiles

© ESO 2008