2. Data analysis
The Cepheids with available data for a reliable analysis are reported in Table 1, where the subscript `L ' refers to the light curve data and the subscript `RV ' to the radial velocity data. The stars are identified with the Harvard Variable number, while the letters L and S indicate Large and Small Magellanic Cloud, respectively. The other columns give the period, the number of data points, the sources of the data, the order of Fourier fit and the standard deviation of the fit for both light and radial velocity curves. The time interval of all the photometric (V magnitude) data is quite long for each star, usually about 22 years, and during this interval the period change (probably related to evolution) is significant, therefore it was not always possible to use all of the available data for the Fourier decomposition. In particular, for HV 5497 and HV 2447 only the observations in the time interval between JD 2442300 and 2442900 were used. The best photometric period was derived for each star, while for the radial velocity data the adopted period was essentially the same as reported in the literature. The photometric and radial velocity periods are usually different, because of the different observing dates. See e.g. van Genderen (1983) for a discussion of period changes in Magellanic Cloud Cepheids. The adopted formula for the Fourier decomposition was
for both light and radial velocity curves ; in some data sets few deviating points were discarded. The Tables 2 and 3 with the Fourier parameters, that is phase differences and amplitude ratios , are available at CDS. For some stars with period between 30 and 50 d, such as HV2195, the fitted curve shows unphysical `wiggles', a defect which is typical of curves with steep rising branch (Antonello & Morelli 1996). The criteria adopted for determining the best fit were similar to those of previous works; usually these criteria yield different orders of best fit for different stars. However, for stars with good phase coverage as in the present case, the lower order Fourier parameters do not change significantly when the fit is truncated at different higher orders (see Antonello et al. 1990).
Table 1. List of the analyzed long-period Cepheids in Magellanic Clouds.
© European Southern Observatory (ESO) 1998
Online publication: April 20, 1998