The secular period behavior of 23 field RR Lyrae stars is studied in order to determine if the observed period changes could be attributed. at least in the mean. to stellar evolution. The sample of stars is subdivided into two Oosterhoff groups based on the metallicity and period-shift. https://afjlrgdbhs90ei.timeblog.net/70682665/reliability-and-safety-of-elevators-and-escalators-travelators-past-present-and-future