Frequency, splitting, linewidth and amplitude estimates of low-l p modes of α Cen A: analysis of WIRE photometry

We present results of fitting the 50-d time series of photometry of alpha Cen A taken by the Wide-Field Infrared Explorer (WIRE) satellite in 1999. Both power spectrum and autocovariance function (ACF) fitting techniques were used in an attempt to determine mode frequencies, rotational splittings, lifetimes and amplitudes of low-l p modes. In all, using both techniques, we managed to fit 18 modes (seven l = 0, eight l= 1 and three l = 2) with frequencies determined to within 1-2 mu Hz. These estimates are shown to be 0.6 +/- 0.3 mu Hz lower, on average, than the frequencies determined from two other more recent studies, which used data gathered about 19 months after the WIRE observations. This could be indicative of an activity cycle, although due to the large uncertainty, more data would be needed to confirm this. Over a range of 1700-2650 mu Hz, we were also able to use the ACF fitting to determine an average lifetime of 3.9 +/- 1.4 d, and an average rotational splitting of 0.54 +/- 0.22 mu Hz, which is the first ever reliable estimate of this parameter. In contrast to the ACF, the power spectrum fitting was shown to return significantly biased results for these parameters.