Electron optical depths and temepratures of symbiotic nebulae from Thomson scattering
Authors:
M. Sekeras, A. Skopal
Image & caption:
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Image caption::
The top right panel shows the modeled and observed wings of the OVI 1032, 1038 Å lines and the top left panel displays the spectral energy distribution during quiescent and active phase of the symbiotic star AG Dra. The bottom panel depicts the relationship between electron optical depth and the magnitude in the U filter (the thick grey line at the top left), where the nebular radiation dominates the spectrum (the dotted line).
Description:
Circumstellar environment of symbiotic stars is appropriate for investigation of different effects of scattering processes. In our work we applied a model of the light scattering on free electrons with the aim to explain the very broad and shallow wings of strong emission lines OVI 1032, 1038 Å and HeII 1640 Å, observed in the spectra of symbiotic stars Z And, AG Dra and V1016 Cyg during different phases of activity. Modeling these wings we determined mean values of electron optical depth and electron temperature of symbiotic nebulae, where these lines are formed. Our electron temperatures are in agreement with those determined independently from modeling the spectral energy distribution. The values of electron optical depth in quiescent phases are significantly smaller than during active phases. We interpreted the higher values of electron optical depth during active phases as a result of an increased production of the ionized stellar wind from the hot star. The relationship between the electron optical depth and the level of the activity can be used to determine more precisely mass loss rate from the hot star, which is very important in understanding the nature of the outbursts of symbiotic stars.
Reference:
Monthly Notices of the Royal Astronomical Society 427, 979-987 (2012)
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