One month convection timescale on the surface of a giant evolved star

The transport of energy through convection is important during many stages of stellar evolution^1,2, and is best studied in our Sun³ or giant evolved stars⁴. Features that are attributed to convection are found on the surface of massive red supergiant stars^5-8. Also for lower-mass evolved stars, indications of convection are found^9-13, but convective timescales and sizes remain poorly constrained. Models indicate that convective motions are crucial to produce strong winds that return the products of stellar nucleosynthesis into the interstellar medium¹⁴. Here we report a series of reconstructed interferometric images of the surface of the evolved giant star R Doradus. The images reveal a stellar disk with prominent small-scale features that provide the structure and motions of convection on the stellar surface. We find that the dominant structure size of the features on the stellar disk is 0.72 ± 0.05 astronomical units. We measure the velocity of the surface motions to vary between -18 and +20 km s^-1, which means that the convective timescale is approximately one month. This indicates a possible difference between the convection properties of low-mass and high-mass evolved stars.