Temperature of activity regions versus S/N and flux enhancement in the TESS observation band for active regions. The solid blue, red, and black lines represent the S/N of planet single with different active regions radii of 1, 3, and 10 R_⊕ , respectively. The dashed blue, red, and black lines indicate the flux enhancement due to stellar activity in the TESS observation band for active regions with the same radii. The left and right panels show the results on G and M dwarfs, respectively. The vertical lines represent the temperature of 1000 (spots) and 10 000 K (flares), as well as the stellar effective temperature.