Optical Follow-up of Planck Cluster Candidates with Small Instruments
  We report on the search for optical counterparts of Planck Sunyaev-Zel'dovich
(SZ) cluster candidates using a 0.6 meter non-professional telescope. Among the
observed sources, an unconfirmed candidate, PSZ2 G156.24+22.32, is found to be
associated with a region of more than 100 galaxies within a 3 arcminutes radius
around the Sunyaev-Zel'dovich maximum signal coordinates. Using 14 hours of
cumulated exposure over the Sloan color filters g', r', i', and, z', we
estimate the photometric redshift of these galaxies at zphot=0.29 +- 0.08.
Using the red-sequence galaxy method gives a photometric redshift of 0.30 +0.03
-0.05. Combined with the Planck SZ proxy mass function, this would favor a
cluster of 4.4 x 10^{14} solar masses. This result suggests that a dedicated
pool of observatories equipped with such instruments could collectively
contribute to optical follow-up programs of massive cluster candidates at
moderate redshifts.
