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Session 102 - Pulsating Stars.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
Kjeldsen et al. 1994 (Astron. J 109, 1313 ) have reported the presence of p-mode pulsations in Balmer line equivalent widths measured in the spectrum of \eta Boo (G5 IV); they give accurate frequencies for 13 modes of oscillation, and estimate velocity amplitudes for these modes of typically 1.6 m/s.
We report here time-series observations of the radial velocity of \eta Boo obtained with the Advanced Fiber Optic Echelle (AFOE) spectrograph. In March 1995 we obtained 555 spectra of \eta Boo for a total of 21.6 hours of observing time spread over 7 consecutive nights. The radial velocity time series clearly shows the night-to-night orbital motion of \eta Boo; the residual velocities after removing this motion are typically 10 m/s for single spectra, a value that is roughly consistent with shot noise limits. The power spectrum of the time series shows no evidence for Kjeldsen et al.'s frequencies. With 95 % confidence, we can rule out the presence of these 13 frequencies with typical amplitudes of 0.5 m/s or more. The spectrum is consistent with pure photon noise, but also with the presence of pulsations having other frequencies (not those given by Kjeldsen et al.) and with typical amplitudes as large as about 1.5 m/s. Possible explanations for the discrepancy between the two results are (a) an incorrect conversion between the amplitudes of equivalent width and Doppler pulsations, and (b) a fluke in the noise behavior of one or both observations.
Program listing for Thursday