## 3. Time series analysisWe performed the time series analysis of V 368 Cep photometry with the TSPA method from Jetsu & Pelt (1999: Paper I), where four detailed application examples are also given. A prolonged time series of V1794 Cyg photometry was recently analysed with this method in Jetsu et al. (1999: Paper II). The parameters of our second order () light curve model were the mean (
The observing window in photometry is usually one sidereal day
(i.e. ). If the real period is
where and (Tanner 1948). Combining with predicts , , and . These five alternatives explain the whole period finding history of V 368 Cep in our Table 1. The most recent study presented "unambiguous indications" for , and also mentioned some spurious periodicities (Bossi & La Franceschina 1995). Unfortunately, Eq. 1 connecting the real and spurious periodicities does not identify the correct one, i.e. the probability of mistaking a spurious periodicity for a real one should never be underestimated, as reminded by Table 1 in Paper I. Thus we decided to perform the TSPA method analysis between and , i.e. the above five alternative periodicities were tested against each other. The window periods within each subset were determined with the Deeming (1975) method. The for -
: *If*the distribution of the model residuals or that of the*M*,*P*,*A*, or bootstrap estimates is not gaussian,*then*the*P*, and estimates are rejected. -
: *P*, and of subsets are rejected. -
: Those not present in 95% of the bootstrap models are "unreal".
Comparison between Tables 3 and 4 confirmed that the rejections occur for low amplitude light curves (SET=2, 5 and 6). The rejection in SET=8 only implies that this secondary minimum may be "unreal", but the model itself is reliable. In conclusion, reliable periodicity detection in V 368 Cep succeeded for with a subset length of about one month, and .
© European Southern Observatory (ESO) 1999 Online publication: October 4, 1999 |