I think that the current observers of Z Tau, visual and CCD, must read this article:
http://www.aavso.org/files/webpublications/ejaavso/v37n2/101.pdf
It's clear that they all are estimating the close companion of Z Tau.
See current lightcurve:
regards, Hubert
Links:
[1] http://www.aavso.org/lcg/plot?auid=000-BBK-328&starname=Z%20TAU&lastdays=700&start=&stop=2456184.222967685&obscode=&obscode_symbol=2&obstotals=yes&calendar=calendar&forcetics=&grid=on&visual=on&uband=on&bband=on&v=on&pointsize=1&width=800&height=450&mag1=&mag2=&mean=&vmean=
[2] http://www.aavso.org/forums/variable-stars/long-period-variables-lpvs