Name/Affiliation: Mark Giampapa (National Solar Observatory)
The Variability of Photospheric Line Bisectors in the Sun-as-a-Star
We utilize spectra obtained with the SOLIS Integrated Sunlight Spectrometer (ISS) to examine the variability of line asymmetries in selected solar photospheric lines since 2007. The intrinsic asymmetry that characterizes the photospheric lines in the Sun and late-type stars arises from the velocity-brightness correlation between hotter and brighter upward (blue shifted) moving granules and downward (redshifted) flowing plasma in the intergranular lanes. Thus, the intrinsic line asymmetries present in the ISS spectra are a diagnostic of the nature of global velocity fields in the solar or stellar atmosphere. We adopt the line bisector as a measure of the intrinsic asymmetry and calculate various measures of the velocity span, or amplitude, in the Mn I line at 539.5 nm and the nearby Fe I feature at 539.3 nm, respectively. We examine the correlation of the time series of velocity spans in these features with the solar cycle as manifested in the Ca II K line. The National Solar Observatory is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation.