Periodic variations of the Ba II 4554 Å and Ca II 8542 Å line profiles in coronal holes

详细

The oscillations of the half-width of the Ba II 4554 Ǻ and Ca II 8542 Ǻ spectral lines have been analyzed using observations at the base of solar coronal holes (CHs). The observed variations (~50 m Ǻ for Ca II and ~4 m Ǻ for Ba II) exceed considerably the thermal broadenings of these lines calculated from the measured intensity oscillations, suggesting their nonthermal nature. We point out a number of observational facts that hamper an unambiguous interpretation of the periodic Ba II and Ca II profile variations solely by the manifestation of torsional Alfve´ n waves in the lower solar atmosphere.