4. Parameters of the light curves

4.1. Mean parameters

Mean parameters have been calculated for the light curve of each star of our sample using 75 years of AAVSO data. Their average values and standard deviations are given in Table 2. The information in the columns is as follows:

• Column (1): The name of the star.
• Columns (2) to (5): The available number of entries for the periods, maxima, minima, and visual amplitudes, respectively.
• Column (6): The mean period.
• Column (7): The mean asymmetry factor.
• Column (8): The mean magnitude at maximum brightness.
• Column (9): The mean magnitude at minimum brightness. We note that the average magnitude at minimum for some stars may have low reliability due to the observationnal limit that can be reached at this phase. The minima of these stars should be treated with caution; the standard deviations can give a confidence level.
• Column (10): The mean visual amplitude. On average, the estimation of the amplitude from either maximum to the following minimum or else from minimum to the following maximum, lead to the same value. Note, however, that low reliability of the minima causes a low confidence of the corresponding amplitude value. Hence, some mean amplitudes should be treated with caution.
• Columns (11) to (15): The standard deviations of, respectively, period, asymmetry factor, magnitudes at maximum and minimum, and amplitude.
• Columns (16) to (17). Variability type and spectral type taken from the GCVS.

4.2. Properties of some standard deviations

Figure 1 (click here) shows that, except the semiregular variables of M spectral type, the other LPVs roughly obey constant for days and a relation /P constant for longer periods. This could be related to the fact that longer-period stars generally exhibit more complex pulsation, inducing more important mass-loss.

  
Figure 1: The standard deviation of the period as a function of the period length for the 355 LPVs. Dots are for M Miras, triangles for S Miras, filled triangles for C Miras, cross for MC Miras, asterisks for CS or SC Miras, plus for SM or MS Miras, filled circles for M SRa's or SRb's, filled squares for C SR's, diamonds for SRd's

4.3. Period-amplitude-asymmetry relations

Reviews about the importance of these parameters are given by Whitelock et al. (1991) and by Jura & Kleinmann (1992a). We have summarized our results in Fig. 2 (click here). We distinguish between Miras and SRs, and the various spectral types.

As is well-known, we find in general that carbon-rich Miras have large periods with small amplitudes, and that only a third of them show significant asymmetry in their light curves. S-Miras have large periods and amplitudes. Only S-Miras show a clear tendency of increasing amplitude with period. The "continuity'' between SR's and C-stars is to be noted.

  
Figure 2: Amplitude-period-asymmetry relations for the 355 LPVs discriminating by variability and spectral types. The symbols are the same as in Fig. 1 (click here)