  Continuous gravitational waves are nearly monochromatic signals emitted by
asymmetries in rotating neutron stars. These signals have not yet been
detected. Deep all-sky searches for continuous gravitational waves from
isolated neutron stars require significant computational expense. Deep searches
for neutron stars in binary systems are even more expensive, but potentially
these targets are more promising emitters, especially in the hundreds-Hz
region, where ground-based gravitational wave detectors are most sensitive. We
present here an all-sky search for continuous signals with frequency between
300 and 500 Hz, from neutron stars in binary systems with orbital period
between 15 and 60 days, and projected semi-major axis between 10 and 40
light-seconds. This is the only binary search on Advanced-LIGO data that probes
this frequency range. Compared to previous results, our search is over an order
of magnitude more sensitive. We do not detect any signals, but our results
exclude plausible and unexplored neutron star configurations, for example,
neutron stars with relative deformations greater than 3e-6 within 1 kpc from
Earth and r-mode emission at the level of alpha ~ few 1e-4 within the same
distance.
