Complexity in the light curve of Delta Scuti stars

We apply horizontal visibility graphs (HVG) to study the complex network behavior for the delta Sct stars’ light curves observed by TESS. The delta Sct stars are pulsating stars with spectral types A0-F5 and intermediate masses between low-mass stars (≤ 1 Msun) and high-mass stars (≥ 2 Msun). They pulsate in low-order pressure modes and have dominant pulsation frequencies in the 5-80 d⁻¹ range. The high amplitude delta Sct stars (called HADS), are classified in population I of delta Sct stars with V band amplitude ≥ 0.3 mag and low-amplitude delta Sct stars (called LADS) pulsate in several modes with V band amplitudes ≤ 0.1 mag. The lower clustering for high amplitude delta Sct than low amplitude delta Sct indicates a more straightforward light curve (containing one or two independent modes) than a more complex light curve. The average shortest path length of the HVG network of delta Sct light curves is a linear function of the network sizes (logarithm), indicating the small-world and non-random properties. By considering the degree distributions of stellar networks, both lognormal and power-law behaviors of nodes’ degrees are likely not to be rejected, and deviation from the analytical expression of uncorrelated random series is evidence for non-random processes.