Granulations are structures characterized by convection cells reaching the stellar surface and are well-known through observations of the Sun. However, similar granulation structures may also be present on the surfaces of the largest and brightest cool stars in the Universe—the red supergiants (RSGs)—potentially serving as the primary mechanism of their irregular light variations. As predicted by basic physical processes, there is a correlation between the granulation parameters of RSGs and the stellar parameters (i.e., the scaling relation), which provides a new method for inferring the stellar parameters of RSGs. In this talk, I will present our recent findings on granulations with the complete and pure RSG samples in the Magellanic Clouds and long-term light curves from the Optical Gravitational Lensing Experiment (OGLE) and the All-Sky Automated Survey for Supernovae (ASAS-SN). The granulation amplitude and timescale are found to have well-defined scaling relations with stellar parameters, which coincide with previous results. Comparison of the results from the LMC and SMC indicates that metallicity affects the properties of granulation, with larger amplitude and longer timescale of granulation in metal-rich environments. Different modeling approaches for light curves—Continuous-time AutoRegressive Moving Average, Gaussian Process regression, and direct fitting of the PSD—are discussed, and the advantages of each are compared.
https://ui.adsabs.harvard.edu/abs/2020ApJ...898...24R/abstract
https://arxiv.org/abs/2405.01405
BIO
Zehao Zhang is currently a first-year graduate student at Beijing Normal University, under the supervision of Prof. Biwei Jiang. He obtained his Bachelor's degree in Astronomy from Beijing Normal University in 2023. His research interests focus on samples and light variations of red supergiants.
