  A periodogram analysis of 47 stars noted in GCVS as RV-type stars was carried
out. The research methods applied here to RV-type stars have previously been
applied to long-period variables Mira-type stars and semi-variables.
Periodograms are previously classified by their shape, or rather the presence
or absence of certain structures: two peaks in a 2:1 ratio, the presence of
satellites at these peaks indicating the result of beats. Table 1 shows the
classification groups. Examples of periodograms of stars of all three groups
are shown. The study identified stars that most likely do not belong to the RV
Taurus type. The star SU Gem has been studied in detail, which shows rather the
variability characteristic of the Mira-type or semi-regular. A summary of the
results is given in table 2. The elements was calculated on databases AAVSO,
AFOEV and ASAS. The period of 50 days specified in GCVS was not revealed
according to our researches. According to the observations of different
databases, the period of 684 days is specified in the range from 682 to 715
days.
