Studies of the Long Secondary Periods in Pulsating Red Giants

摘要

We have used systematic, sustained visual observations from the AAVSO International Database and the AAVSO timeseries analysis package vstar to study the unexplained "long secondary periods" (LSPs) in 27 pulsating red giants. In our sample, the LSPs range from 479 to 2,967 days, and are on average 8.1 ± 1.3 times the excited pulsation period. There is no evidence for more than one LSP in each star. In stars with both the fundamental and first overtone radial period present, LSP is more often about 5 times the former and 10 times the latter. The visual amplitudes of the LSPs are typically 0.1 magnitude and do not correlate with the LSP. The phase curves tend to be sinusoidal, but at least two are sawtooth. The LSPs are stable, within their errors, over the timespan of our data, which is typically 25,000 days. The amplitudes, however, vary by up to a factor of two or more on a time scale of roughly 20-30 LSPs. There is no obvious difference between the behavior of the carbon (C) stars and the normal oxygen (M) stars. Previous multicolor photoelectric observations showed that the LSP color variations are similar to those of the pulsation period, and of the LSPs in the Magellanic Clouds, and not like those of eclipsing stars. Although our results are suggestive of rotational variability, there are several arguments against this. So the cause of the LSPs remains unknown.