| Abstract
| - We present the first results from a high-precision radial velocity study of the K2 III giant star α Ari . Observations were acquired over 6 nights in 2004 using the new high-resolution spectrograph BOES ( Bohyunsan Observatory Echelle Spectrograph) of the 1.8-m telescope. A high radial-velocity precision was achieved by using the high-resolution ( $R=90\,000$) mode of BOES and an iodine gas absorption cell. The radial velocity measurements made during $\rm JD = 2\,452\,948{-}2\,452\,950$ show coherent, low-amplitude variations with a period of $P_{1}=0.571$ days (or aliases at 0.445 or 0.821 days), and an amplitude of 18.9 m s -1. Observations of τ Cet over this same interval are constant to within 3 m s -1. After subtracting the contribution of the 0.57-day period, we find evidence for a second period, $P_{2} = 0.190$ days. Observations made on a second run during $\rm JD = 2\,452\,975{-}2\,452\,981$ show that the radial velocity variations are indeed present, but on shorter time-scales and with a lower amplitude. Two probable periods fit the radial velocity measurements from the second run reasonably well: 0.185 days or an alias of 0.256 days. The shorter period coincides with the secondary one found in the earlier measurements. We conclude that, similar to other K-giant pulsating stars, α Ari shows unstable acoustic pulsations or mode switching on time scales of tens of days. The calculated pulsation constants for the dominant 0.571-day period is consistent with third-overtone pulsations, while the secondary periodicity found in both data runs corresponds to a high overtone ( $n\geq 12$).
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