  Due to their computational limitations, searches for continuous gravitational
waves (GW) are significantly more sensitive when informed by observational
photon astronomy and theoretical astrophysics. Indirect upper limits on GW
emission inferred from photon astronomy indicate which objects are more
interesting for GW searches, and also set sensitivity milestones which GW
searches need to beat to be considered GW astronomy. How GW results are
interpreted depends on previous indirect limits and the theory of astrophysical
GW emission mechanisms. I describe the interplay between these issues for the
four types of continuous GW search, and show how photon astronomers can help
the growing field of GW astronomy now and in the near future.
