Astron. Astrophys. 483, L43−L46, 2008
Oscillations in β Ursae Minoris: Observations with SMEI
N.J. Tarrant, W. J. Chaplin, Y. Elsworth, S. A. Spreckley and I. R. Stevens
School of Physics and Astronomy, Univ. of Birmingham, Birmingham, UK
Aims. From observations of the K4III star β UMi we attempt to determine whether
oscillations or any other form of variability is present.
Methods. A high-quality photometric time series of ~1000 days in length obtained
from the SMEI instrument on the Coriolis satellite is analysed. Various statistical
tests were performed to determine the significance of features seen in the power
density spectrum of the light curve.
Results. Two oscillations with frequencies 2.44 and 2.92 μHz have been identified.
We interpret these oscillations as consecutive overtones of an acoustic spectrum,
implying a large frequency spacing of 0.48 μHz. Using derived asteroseismic parameters in
combination with known astrophysical parameters, we estimate the mass of β UMi to be
1.3±0.3 MSun. Peaks of the oscillations in the power density spectrum
show width, implying that modes are stochastically excited and damped by convection.
The mode lifetime is estimated at 18±9 days.