4 Conclusions

The main results presented in this paper can be summarized as follows:

1.

New Strömgren by photometric observations of the semiregular variable AI Aurigae are presented and discussed. The period analysis of the whole light curve confirms the early period determination of 63.9 days. However, the light curve shows typical semiregular behaviour with changing amplitude and cycle length;

2.

The b-y colour measurements revealed highly paralel light and colour variations. Since the b-y colour is considerably good temperature indicator (rather than molecule indicator, as is the B-V colour), the phase dependent light and temperature changes resemble classical radially pulsating stars. The observations imply radial oscillation with dominant thermal effects as the main reason for light variability;

3.

We estimated the basic stellar parameters, such as the effective temperature ( $3520\pm100$ K), mean radius ( $123\pm34~R_\odot$), mass ( $2.0\pm0.8~M_\odot$). The spectral type-mass and spectral type-radius values give a pulsational constant of 0.065^+0.06_-0.03. The results are consistent with radial pulsation in the fundamental or (more likely) first overtone mode. The period-gravity relation of Fernie (1995) also supports this conclusion.

Acknowledgements

This research was supported by the "Bolyai János'' Research Scholarship of LLK from the Hungarian Academy of Sciences, Hungarian OTKA Grant #T032258 and Szeged Observatory Foundation. The NASA ADS Abstract Service was used to access data and references. This research has made use of the SIMBAD database, operated at CDS-Strasbourg, France.