  Observations with the Karl G. Jansky Very Large Array at 46 GHz (7 mm) have
been used to measure the size and shape of the radio photospheres of four
long-period variable stars: R Leonis (R Leo), IRC+10216 (CW Leo), chi Cygni
(chi Cyg), and W Hydrae (W Hya). The shapes of the stars range from nearly
round to ellipticities of ~0.15. Comparisons with observations taken several
years earlier show that the photospheric parameters (mean diameter, shape,
and/or flux density) of each of the stars have changed over time. Evidence for
brightness asymmetries and non-uniformities across the radio surfaces are also
seen in the visibility domain and in images obtained using a sparse modeling
image reconstruction technique. These trends may be explained as manifestations
of large-scale irregular convective flows on the stellar surface, although
effects from non-radial pulsations cannot be excluded. Our data also allow a
new evaluation of the proper motion of IRC+10216. Our measurement is in
agreement with previous values obtained from radio wavelength measurements, and
we find no evidence of statistically significant astrometric perturbations from
a binary companion.
