| Presentation Title: | Bisector velocities of the photospheric line near the limb observed with Hinode SOT/SP |
| Author(s): | Akie Moritsuka, Yukio Katsukawa, Ryohtaroh T. Ishikawa
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Abstract:
Bisector velocities of photospheric lines show significant center-to-limb variation: they have a C-shape with a blueshift at the line core while they become a \-shape with a redshift at the line core toward the limb. Although the bisector velocities are known to reflect the corrugated 3-dimensional structure of the granular convection, it is poorly known how the bisector velocities change very close to the limb because it has been difficult to achieve high spectral resolution with spatial resolution enough to resolve the granular convection. The purpose of this study is to improve our understanding of the 3-dimensional structure of the granular convection based on bisector analysis of high-resolution spectroscopic data obtained with Hinode SOT/SP. We analyzed the bisector velocities of the Fe I 630.15 nm line very close to the limb in the polar regions and found that the bisector velocities of granules show changes from a \-shape with a blueshift to an I-shape with a redshift from 60 degrees to 89 degrees in the heliocentric angles. On the other hand, the bisector velocities of intergranules remained an I-shape with a redshift at the line core. The \-shape of the granules can be interpreted as a large velocity gradient in a thicker line formation height, while the I-shape of the intergranules is due to a thinner formation height. Because bright areas in the photosphere were considered as the granules in our analysis, the decrease of the blueshift in the granules toward the limb may be caused by the redshifts of the horizontal flow appearing brighter.