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Red giants are unstable to radial pulsation. About a third of them also showa long secondary period, 5 to 10 times the pulsation period. The long secondaryperiods were recently ascribed to eclipses of the red giant by a low-massdust-enshrouded companion. Long secondary periods have been known for over acentury. In this paper, I use primarily American Association of Variable StarObservers visual and photoelectric observations to look for evidence of longsecondary periods in 103 red giant stars listed by Nancy Houk in 1963 as havinglong secondary periods, based mostly on photographic photometry. I havedetermined long secondary periods in 37 stars, and upper limits (some of themnot very stringent) in 25. In the former, the ratio of long secondary period topulsation period peaks strongly at 10, which suggests that most of the starsare pulsating in the first overtone. The loong secondary periods are consistentwith those o0f Houk in 33 of the 37 stars. I have identified 16 stars asbimodal pulsaters;their period ratios are consistent with previousobservational and theoretical results. For 14 stars,the periods in the GeneralCatalogue of Variable Stars are incorrect or absent.

Long Secondary Periods in Pulsating Red Giants: A Century of Investigation