Using Polar Faculae to Determine the Sun’s High-latitude Rotation Rate. I. Techniques and Initial Measurements

• Published in: The Astrophysical Journal
• Main Author: Neil R. Sheeley Jr.
• Format: Article in Journal/Newspaper
• Language: English
• Published: IOP Publishing 2024
• Subjects: Solar faculae; Solar rotation; Solar cycle; Solar magnetic fields; Astrophysics; QB460-466; Lambda; South Pole; South pole
• Online Access: https://doi.org/10.3847/1538-4357/ad85d0; https://doaj.org/article/b75dc6c9ddb744ec98da268b35d84df9

This paper describes a new way of determining the high-latitude solar rotation rate statistically from simultaneous observations of many polar faculae. In this experiment, I extracted frames from a movie made previously from flat-fielded images obtained in the 6767 Å continuum during 1997–1998 February and used those frames to construct spacetime maps from high-latitude slices of the favorably oriented south polar cap. These maps show an array of slanted tracks whose average slope indicates the east–west speed of faculae at that latitude, λ _s . When the slopes are measured and plotted as a function of latitude, they show relatively little scatter ∼ 0.01–02 km s ^−1 from a straight line whose zero-speed extension passes through the Sun’s south pole. This means that the speed, v ( λ _s ), and the latitudinal radius, ${{R}}_{\odot }\cos {\lambda }_{s}$ , approach 0 at the same rate, so that their ratio gives a nearly constant synodic rotation rate ∼8.°6 day ^−1 surrounding the Sun’s south pole. A few measurements of the unfavorably oriented north polar cap are consistent with these measurements near the south pole.