The Doradus-type variable 9 Aurigae: results from a multi-site campaign
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We present the results of a multi-longitude coordinated photometric campaign on the Dor variable 9 Aur. Three frequencies can be determined from the data (f1 = 0.7948,f3 = 0.7679, f5 = 0.3429 d-1); two of them have already been recognized in past seasons while the third frequency is reported for the first time. Analysis shows that the third was 'turned off' or present with an amplitude below the limits of detection during previous observing seasons. This evidence, together with consistent amplitude changes in the two previously recognized signals, suggests that the stellar structure responsible for 9 Aur's variability is extremely dynamic. Intermediate-resolution spectra and CORAVEL radial velocities collected simultaneously show variability on time-scales commensurable with the photometry. The only sensible explanation appears to be a non-radial pulsation (NRP) model. However, results obtained reveal a number of features that deviate from classical NRP behaviour. Such features are emphasized in this paper in support of the future development of a specific NRP model - a model which has yet to be elucidated for Dor-type variables. 1997 RAS.
