Precise radial velocities with BOES. Detection of low-amplitude pulsations in the K-giant α Arietis

Details Precise radial velocities with BOES. Detection of low-amplitude pulsations in the K-giant α Arietis Precise radial velocities with BOES. Detection of low-amplitude pulsations in the K-giant α Arietis

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006a%26a...454..839k&link_type=abstract

Astronomy and Astrophysics, Volume 454, Issue 3, August II 2006, pp.839-844

Astronomy and Astrophysics

Astrophysics

5

Stars: Late-Type, Stars: Oscillations

Scientific paper

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 JD = 2 452 948{-}2 452 950 show coherent, low-amplitude variations with a period of P1=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, P2 = 0.190 days. Observations made on a second run during 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≥ 12).

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