  We present a search for continuous gravitational waves from five radio
pulsars, comprising three recycled pulsars (PSR J0437-4715, PSR J0711-6830, and
PSR J0737-3039A) and two young pulsars: the Crab pulsar (J0534+2200) and the
Vela pulsar (J0835-4510). We use data from the third observing run of Advanced
LIGO and Virgo combined with data from their first and second observing runs.
For the first time we are able to match (for PSR J0437-4715) or surpass (for
PSR J0711-6830) the indirect limits on gravitational-wave emission from
recycled pulsars inferred from their observed spin-downs, and constrain their
equatorial ellipticities to be less than $10^{-8}$. For each of the five
pulsars, we perform targeted searches that assume a tight coupling between the
gravitational-wave and electromagnetic signal phase evolution. We also present
constraints on PSR J0711-6830, the Crab pulsar and the Vela pulsar from a
search that relaxes this assumption, allowing the gravitational-wave signal to
vary from the electromagnetic expectation within a narrow band of frequencies
and frequency derivatives.
