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Astron. Astrophys. 364, 543-551 (2000)

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4. Discussion and conclusions

Both presentations of our results obtained in the analysis of AB And light curves between 1968 and 1995 (Table 1 and the corresponding figures) show that the Roche model with single spotted areas on both components provides a satisfying fit of the observations. The solutions obtained by solving the inverse problem do not show any significant variations of the system's basic parameters among different curves during the analysed period. Consequently, the main variations in the light curves can be explained by the change of the temperature contrast, the position and the size of spotted areas on the system's components. All these results indicate that the complex nature of the light-curve variations may be attributed to variable starspot activity.

Moreover, several attempts were made to fit the observations by assuming a double spot model on the cooler primary component. In that case, the obtained fit was similar in quality, but the system's basic parameters derived by analysing the individual light curves showed stronger variations around a mean value. We consider that case as less reliable, to the point of being possibly excluded.

The present analysis shows that the changes in the light curves can be interpreted relatively well by the development and migration of spotted regions on the components. Still, we cannot exclude other possibilities. Namely, in this analysis we have not examined all possible working hypotheses that determine the parameters' evaluation. So far we do not have a satisfactory explanation for the difference in the B and V light curve shape during 1990.

Although a rough approximation of the possible real processes in the AB And system was applied in this analysis, the model could successfully simulate the observed light curves, covering an interval of 27 years.

The solutions presented here show that AB And is in the overcontact configuration [FORMULA], with a small temperature difference between the components ([FORMULA]) proving a good thermal contact between the components. The mass ratio estimated to [FORMULA] ([FORMULA]) suggests a significant energy transfer between the components.

Having in mind the large changes in the shape of the light curves, the future photometric observations of this interesting system are of great importance. The application of different working hypotheses in the analysis of the light curves could offer more reliable information on the nature of the system's activity.

The problem of the uniqueness of obtained solutions remains open to some degree. To solve the problem of the surface brightness distribution, the photometry must be coupled with other data. The use of an independent method is necessary to test the validity of the spot parameters obtained through the analysis of the light curves. Doppler stellar tomography based on spectroscopic observations is a promising way to solve this problem. Such spectroscopic observations require the use of large telescopes (high spectral resolution and high signal to noise ratio). Because of that, high resolution spectroscopic observations of the system will be very important. The eclipse mapping method (Spruit 1994) is also in use for solving of the light-curve inversion problem.

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001