Helioseismology and Asteroseismology: Looking for Gravitational Waves in
  acoustic oscillations
  Current helioseismology observations allow the determination of the
frequencies and surface velocity amplitudes of solar acoustic modes with
exceptionally high precision. In some cases, the frequency accuracy is better
than one part in a million. We show that there is a distinct possibility that
the quadrupole acoustic modes of low order could be excited by gravitational
waves (GWs), if the GWs have a strain amplitude in the range $10^{-20}h_{-20}$
with $h_{-20}\sim 1$ or $h_{-20}\sim 10^{3}$, as predicted by several types of
GW sources, such as galactic ultracompact binaries or extreme mass ratio
inspirals and coalescence of black holes. If the damping rate at low order is $
10^{-3}\eta_N$ $\mu{\rm Hz}$, with $\eta_N\sim 10^{-3} $ - $1,$ as inferred
from the theory of stellar pulsations, then GW radiation will lead to a maximum
rms surface velocity amplitude of quadrupole modes of the order of
$h_{-20}\eta_N^{-1}\sim$ $10^{-9}$ - $10^{-3}$ ${\rm cm\; s^{-1}}$, on the
verge of what is currently detectable via helioseismology. The frequency and
sensitivity range probed by helioseismological acoustic modes overlap with, and
complement, the capabilities of eLISA for the brightest resolved ultracompact
galactic binaries.
