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Astron. Astrophys. 347, 583-589 (1999) 3. Several variabililty states?Fig. 4 presents the skewness calculated for the line NIV
The photometric variability of EZ CMa has a behavior similar to that of the skewness in that the light curve is variable in shape and amplitude (Duijsens et al., 1996). However, here also one can identify patterns in the shape of the light curves which recur, and one can thus extend the concept of different variability "states" to the photometric behavior. For example, the data of Cherepashchuk(1981) and Robert et al.(1992), obtained respectively in 1980 and 1990 have almost identical phase-dependent behaviors, as can be seen in Fig. 5a. These light curves have a maximum near phase 0.5 and a trend towards a maximum at phase 0.0 which is broken by a minimum. The other two light curves plotted in Fig. 5b and 5c (data obtained in 1988 (Robert et al., 1992) and 1987 (Drissen et al., 1989), respectively) have maxima near phase 0.0, with only a hint of a maximum near phase 0.5 A similar story is illustrated in Fig. 6: the data of Balona et al.(1989a), obtained in 1986, and Lamontagne et al.(1986), obtained in 1985, have almost identical shapes as illustrated in Fig. 6c, with a prominent maximum near phase 0.65 and a hint of a maximum near phase 0.2. The other light curves in this figure, corresponding to data obtained in 1993 (Antokhin et al., 1995) (Fig. 6a) and 1990/91 (Duijsens et al., 1996) (Fig. 6b) also have maxima near these same phases, although the maximum near phase 0.2 is much more pronounced. We emphasize that the phases computed for the data plotted in Figs. 5 and 6 have the same initial epoch and period as all the rest of the data in this paper, and no artificial phase shift has been introduced to match up the data. Hence, once again, it is remarkable that when the light curves are very similar, they display coherent variations (as in Figs. 5a and 6c), despite being separated by numerous cycles. Furthermore, it is interesting to note that there are two sets of phase intervals within which a maximum can occur: (0.2, 0.65), "state" A; and (0.0, 0.5), "state" B. The photometric data used are described in Table 2.
Table 2. List of the photometric data.
What is responsible for the maxima in the light curves? What physical process can switch the system from one state to another one, and yet retain coherent variability within each of the two different states? It is beyond the scope of this paper to even attempt providing aswers to these questions. All we are able to conclude at this time is that the phase coherence of the data, separated by many years, points to a common underlying periodic process with a stable ephemeris. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1999 Online publication: June 30, 1999 ![]() |