Analysis of the Petersen Diagram of Double-Mode High-Amplitude {\delta}   Scuti Stars
  I created the Petersen diagram relative to all the Double Mode High Amplitude {\delta} Scuti stars listed in the AAVSO's International Variable Star Index up to date December 29, 2015. For the first time I noticed that the ratio between the two periods P1/P0 seems in evident linear relation with the duration of the period P0, a finding never explicitly described in literature regarding this topic. 
Riccardo Furgoni
astro-ph.SR