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A new interpretation of the redshift observed in optically thin transition region lines
Hansteen, Viggo
AA(Oslo Univ., Norway)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 402, no. 2, p. 741-755. (ApJ Homepage)
Publication Date:
Solar Physics
NASA/STI Keywords:
Coronal Loops, Optical Thickness, Red Shift, Solar Spectra, Sound Waves, Spectral Bands, Dynamic Response, Emission Spectra, Hydrodynamic Equations, Line Spectra, Stellar Models, Wave Propagation
Bibliographic Code:


It is proposed that the pervasive redshift observed in transition region spectral lines is caused by downward propagating acoustic waves. The dynamic response of a coronal loop to energy released as heat near the loop apex is examined by solving the hydrodynamic equations numerically, consistently including the effects of nonequilibrium ionization on the radiative losses and on the internal energy. It is found that the radiative loss curve may change by a factor of 2 during the loop evolution as a result of flows and waves. A simple analytical analysis is performed to isolate the physical effects relevant to the line formation process. The amplitude of the line shift is found to depend on the characteristic time scale for ionization of the radiating ion as well as the global loop parameters, the time scales for loop cooling, the maximum temperature, and the base pressure.

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Database: Astronomy
arXiv e-prints