  This study addresses how the incidence rate of strong O VI absorbers in a
galaxy's circumgalactic medium (CGM) depends on galaxy mass and, independently,
on the amount of star formation in the galaxy. We use HST/COS absorption
spectroscopy of quasars to measure O VI absorption within 400 projected kpc and
300 km s$^{-1}$ of 52 $M_{*}\sim 10^{10}$ $M_\odot$ galaxies. The galaxies have
redshifts $0.12<z<0.6$, stellar masses $10^{10.1} < M_* < 10^{10.9}$ $M_\odot$,
and spectroscopic classifications as star-forming or passive. We compare the
incidence rates of high column density O VI absorption ($N_{\rm O\, VI} \geq
10^{14.3}$ cm$^{-2}$) near star-forming and passive galaxies in two narrow
stellar mass ranges and, separately, in a matched halo mass range. In all three
mass ranges, the O VI covering fraction within 150 kpc is higher around
star-forming galaxies than around passive galaxies with greater than
$3\sigma$-equivalent statistical significance. On average, the CGM of $M_*\sim
10^{10}$ $M_\odot$ star-forming galaxies contains more O VI than the CGM of
passive galaxies with the same mass. This difference is evidence for a CGM
transformation that happens together with galaxy quenching and is not driven
primarily by halo mass.
