Spectroscopic Studies of Steady Coronal Structures ?Line Width Variations with Height of Fe X朮IV Emission Lines

摘要

We have obtained spectrographic observations of several steady coronal structures at the limb overlying the sunspot regions on several days in Fe X-XIV emission lines. The line-width measurements indicate that in steady coronal structures the FWHM of the 6374 ? line increases with height above the limb with an average value of 1.02 m? per arcsec. Whereas the FWHM of the 5303 ? line decreases with an average value of ?0.66 m? per arcsec. The FWHM of the 7892 ? and 10747 ? lines increases with values of 0.55 and 0.29 m? per arcsec, respectively. We find that FWHM of emission lines in coronal structures increases with height if the associated ionization temperature is less than 1.6 MK, with gradient depending upon the ionization temperature of the line, while the FWHM decreases with height for lines whose ionization temperature is greater than 1.6 MK. It implies that it may not always be possible to interpret the observed increase in FWHM with height in terms of an increase in the non-thermal velocity. To investigate further, we propose simultaneous observations in number of EUV lines with EIS onboard Solar-B and in Fe X-XIV in the visible wavelengths with the 25-cm coronagraph at Norikura.