Capability of detecting UV and optical emission from RSGs and BSGs with ULTRASAT and the ZTF. (a) Maximum redshift from which RSGs and BSGs would have UV and optical emissions detectable by ULTRASAT and the ZTF as a function of the emission time t. (b) Rate of SNe II per year from RSGs and BSGs detectable with ULTRASAT and the ZTF and a function of the emission time t. In both panels, the following fiducial parameters are adopted: for RSGs R_* = 722 R_⊙, E = 10⁵¹ erg, M_ej = 2.8 M_⊙, and f_ρ = 1.455; for BSGs R_* = 50 R_⊙, M_ej = 10 M_⊙, f_ρ = 0.0465, and E = 10⁵¹ erg. The emission time corresponds to the time elapsed since the SBO. Results for RSGs and BSGs are shown in red and blue, respectively. The solid and dashed lines show ULTRASAT and ZTF, respectively.