Frequency Separation Variations of the Solar Low-Degree p-Modes

Abstract

Abstract Variations of frequency separations of low-degree p-modes have been studied over the solar-activity cycle. The studied separations were obtained from the frequencies of low-degree p-modes of the Global Oscillation Network Group (GONG). The 10.7 cm radio flux was used as an index of solar activity. Small separations of the p-mode frequencies are considered to be mainly dependent on the conditions in stellar interiors. Thus, they could be applied to a diagnosis of the changes in the stellar interior. Our calculation results show that the magnitudes of the variations of the mean large separations are less than 1$ \sigma$ over the solar-activity cycle. Small separations show different behaviors in the ascending and descending phases of activity. In the ascending phase, variations of the small separations are less than 1$ \sigma$. However, the small separations had systematic shifts during the period from 2004 to 2007. These shifts were roughly 1$ \sigma$ or more. The variations in the ratios of the small-to-large separations with time were similar to the changes of the small separations. The effects of the changes in the large separations on the ratios were negligible. The variations of the separations may be a consequence of influence from the surface activity, or systematic errors in measurements, or some processes taking place in the solar interior.