Interferometric and seismic constraints on the roAp star alpha Cir
Invited comunication

I. M. Brandão, H. Bruntt, M. S. Cunha, D. W. Kurtz

Abstract
We present new constraints on the rapidly oscillating Ap star  alpha Cir, derived from a combination of interferometric and  photometric data obtained with the Sydney University Stellar  Interferometer (SUSI) and the WIRE satellite. The highlights of our  study are:

• the determination, for the first time, of the angular diameter of a  rapidly oscillating Ap star;
• an independent determination of the effective temperature of  alpha Cir, which is found to be lower than the values previously  estimated;
• two additional oscillation frequencies, which provide a new  determination of the large separation of the star.

Based on this new information, we have computed non-magnetic and  magnetic models for alpha Cir. We show that the value of the large  separation derived from the new data agrees well with that derived from theoretical models. Moreover, we also show how the magnetic field may  explain the two main anomalies seen in the oscillation spectrum, and how those provide constraints on the magnetic field topology and magnitude.

XVIII Encontro Nacional de Astronomia e Astrofísica
Évora, Portugal
2008 September

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