  We extend our previous demonstration of the first on-sky primary mirror
segment closed-loop control on Keck using a vector-Zernike wavefront sensor
(vZWFS), which improved the Strehl ratio on the NIRC2 science camera by up to
10 percentage points. Segment co-phasing errors contribute to Keck contrast
limits and will be necessary to correct for the segmented Extremely Large
Telescopes and future space missions. The goal of the post-AO vZWFS on Keck is
to monitor and correct segment co-phasing errors in parallel with science
observations. The ZWFS is ideal for measuring phase discontinuities and is one
of the most sensitive WFSs, but has limited dynamic range. The Keck vZWFS
consists of a metasurface mask imposing two different phase shifts to
orthogonal polarizations, split into two pupil images, extending its dynamic
range. We report on the vZWFS closed-loop co-phasing performance and early work
towards understanding the interactions between the AO system and segment
phasing. We discuss a comparison of the AO performance when co-phasing by
aligning segment edges, as is currently done at Keck, compared with aligning to
the average phase over the segments, as is done by the vZWFS.
