Panel a: detection rates of CO gas in debris disks as a function of host star luminosity. Within the 52-member sample, four subgroups (L1–L4) were defined according to luminosities, with 13 disks in each subgroup. Panel b: detection rates of CO-rich debris disks as a function of host star luminosity. Panel c: detection rates of debris disks with low CO content as a function of host star luminosity.