Radial velocity variations in pulsating Ap stars

Abstract

We have used precise stellar radial velocities to study the pulsational motion of the rapidly oscillating Ap star 10 Aql. Observations were made on three separate nights using the high resolution spectrograph of the Harlan J. Smith 2.7 m telescope at McDonald Observatory. A high radial velocity precision was achieved by using an iodine gas absorption cell. The integrated radial velocity measurements using the full wavelength region covered by iodine absorption lines (5000–6300 Å) failed to detect any coherent pulsational velocity variations to a level of 2.5–5 m s-1. An analysis over a much narrower wavelength range revealed that pulsational radial velocity variations are indeed present in 10 Aql, but only in 5 spectral lines. The amplitude of these variations ranged from about 100 m s-1 to as high as 398 m s-1 for an unidentified feature at λ5471.40 Å. Other spectral features showing pulsational radial velocity variations are tentatively identified as Sm II and Tm II.