  Using the Parker Solar Probe FIELDS bandpass filter data and SWEAP electron
data from Encounters 1 through 9, we show statistical properties of narrowband
whistlers from ~16 Rs to ~130 Rs, and compare wave occurrence to electron
properties including beta, temperature anisotropy and heat flux. Whistlers are
very rarely observed inside ~28 Rs (~0.13 au). Outside 28 Rs, they occur within
a narrow range of parallel electron beta from ~1 to 10, and with a beta-heat
flux occurrence consistent with the whistler heat flux fan instability. Because
electron distributions inside ~30 Rs display signatures of the ambipolar
electric field, the lack of whistlers suggests that the modification of the
electron distribution function associated with the ambipolar electric field or
changes in other plasma properties must result in lower instability limits for
the other modes (including solitary waves, ion acoustic waves) that are
observed close to the Sun. The lack of narrowband whistler-mode waves close to
the Sun and in regions of either low (<.1) or high (>10) beta is also
significant for the understanding and modeling of the evolution of
flare-accelerated electrons, and the regulation of heat flux in astrophysical
settings including other stellar winds, the interstellar medium, accretion
disks, and the intra-galaxy cluster medium
