Relationship between TIGRE solar S-index and USET Ca II K full disk images

• DOI: 10.48550/arxiv.2407.04475
• Publication Date: 2024-07-05
• Authors: G. Vanden Broeck; Sabrina Bechet; F. Clette; G. Rauw; K.‐P. Schröder; M. Mittag
• Keywords: Astrophysics - Solar and Stellar Astrophysics; 0103 physical sciences; FOS: Physical sciences; 01 natural sciences; Solar and Stellar Astrophysics (astro-ph.SR)

Full disk observations of the solar chromosphere in Ca II K line represent a valuable dataset for studies magnetic activity. The S-index is widely used to investigate activity stars, however, its connection coverage stellar structure still poorly understood. We use archives full images taken by Royal Observatory Belgium with USET derive area fraction brightest chromospheric structures over last decade. These data allowed us study end cycle 24 and beginning 25. regions surface were then segmented using an algorithm based on intensity threshold. computed compared it from TIGRE. For detection periodic modulations, we applied discrete Fourier power spectrum method both datasets. A tight linear relationship was found between TIGRE S-index, improved correlation obtained low-activity regime considering enhanced network. In time series, detected modulation caused rotation bright disk. However, this constrained case due observation strategy. studied variability overlapping period ten years. concluded that index good proxy will be useful future solar-type stars. most appropriate evaluating works analyze impact inclination axis detectability such modulations