Abstract The subgiant eta Boo (G5 IV) has been reported to show p-mode pulsations, as evidenced by variations in the equivalent width of its hydrogen Balmer lines (Kjeldsen et al. 1995}. In an attempt to confirm this report, we observed eta Boo's radial velocity with the AFOE spectrograph for a total of 22 hours spread over 7 successive nights in March 1995. We find no evidence for the presence of excess power at the frequencies reported by Kjeldsen et al.; our upper limit corresponds to typical mode amplitudes of 0.5 m/s, about 3 times smaller than the velocity amplitudes they inferred. Signals with amplitudes larger than 0.5 m/s may be present at other frequencies within the 0 to 1000 uHz range, but evidence for such signals is scanty, and typical mode amplitudes greater than 1.5 m/s are clearly inconsistent with our observations.
(Top panel) A portion of the power spectrum of the radial velocity of eta Boo, plotted to show only the range 700 to 1000 uHz. The frequencies identified as p-modes by Kjeldsen et al. are indicated with vertical dashed lines.
(Bottom panel) The same spectrum, with Kjeldsen et al.'s frequencies, after application of a CLEAN algorithm in an attempt to remove the effects of the window function of the observations.