Stars stripped in binaries -- the living gravitational wave sources
  Binary interaction can cause stellar envelopes to be stripped, which
significantly reduces the radius of the star. The orbit of a binary composed of
a stripped star and a compact object can therefore be so tight that the
gravitational radiation the system produces reaches frequencies accessible to
the Laser Interferometer Space Antenna (LISA). Two such stripped stars in tight
orbits with white dwarfs are known so far (ZTF J2130+4420 and CD-30 11223), but
many more are expected to exist. These binaries provide important constraints
for binary evolution models and may be used as LISA verification sources. We
develop a Monte Carlo code that uses detailed evolutionary models to simulate
the Galactic population of stripped stars in tight orbits with either neutron
star or white dwarf companions. We predict 0-100 stripped star + white dwarf
binaries and 0-4 stripped star + neutron star binaries with SNR>5 after 10
years of observations with LISA. More than 90% of these binaries are expected
to show large radial velocity shifts of $\gtrsim 200$ km/s, which are
spectroscopically detectable. Photometric variability due to tidal deformation
of the stripped star is also expected and has been observed in ZTF J2130+4420
and CD-30 11223. In addition, the stripped star + neutron star binaries are
expected to be X-ray bright with $L_X \gtrsim 10^{33} - 10^{36}$ erg/s. Our
results show that stripped star binaries are promising multi-messenger sources
for the upcoming electromagnetic and gravitational wave facilities.
