Impressive! You take this quite seriously Mauro.
This is actually a lot more complicated than it seems at first glance. Probably because the 11 year cycle is not really exact, but the statistical arguments are hard for me to follow. You have to wonder how accurate older data is as well. Is this your hobby only? As I recall, your profession (like so many who turn up on vortex for some reason) is software development, no? From: Mauro Lacy I'll perform a power spectral density analysis of sunspot number/solar activity data. If there's a 5.52 year cycle in solar activity, it'll show up, along with the main 11 year cycle. I don't think something that big can be easily overlooked, but nevertheless... it bodes well with my modest attempts at statistical signal processing :-) More about this later, probably. Well, here are the graphs: http://maurol.com.ar/solar_cycle The data was obtained from http://solarscience.msfc.nasa.gov/greenwch. I used the daily sunspot area as an indicator of solar activity. The method used is an estimate of power spectral density by the Welch (1967) periodogram/FFT method, which is readily available, by example in octave or Matlab. I had to do some manual preprocessing of the data, and after fiddling for a relatively long time with the scales, I finally began to obtain some meaningful values. As can be seen in http://maurol.com.ar/solar_cycle/daily_area-PSD3.png, there are two peaks near Eta Carinae's period (5.539 years) of dimming X-ray activity , at 5.51 and 5.3 years. They are both much less significant than the main period of the solar cycle (which by the way, seems to be actually near 10.6 years, not 11.04 years as usually stated), and there's is not a period of exactly 5.539 years, but they are close nevertheless. That is, there are (secondary) periods of the solar system not in, but closer, to 5.539. I obtained 5.539 years from the literature. This site in particular was very helpful: http://etacar.umn.edu/ Regarding these results, I suppose you take it or leave it. I mean, they really aren't that significant. But if you take it, there are some interesting things to try: 1) smooth/consolidate the periodograms, to try to obtain less noise, and higher peaks. 2) look for north hemisphere vs. south hemisphere cycles. As Eta Car is south, maybe the periods in the south hemisphere are closer to Eta Car's period. I'll do this next. 3) look for phase, not only frequency, correlations. I have yet to learn how to do statistical phase analysis. I hope you enjoy the pictures! If there are some people interested, I can publish the scripts and techniques I used to obtain the graphs. It really wasn't that difficult. Best regards, Mauro
