Periods have been determined for seven of the eight variables in and around the globular cluster M19. Four of these are Population II Cepheids with periods from 2.4 to 16.9 days and three are RR Lyrae variables. All of the Cepheids and two of the RR Lyrae stars may be members. The only galactic globular clusters known to have more Cepheids within their boundaries are Omega Centauri and Messier 14.
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Clement et al. (1978) studied this question.