Radial Velocity Variations of the Rapidly Oscillating Ap Star 33 Lib

Abstract

AbstractWe present precise stellar radial velocity (RV) measurements of the rapidly oscillating Ap (roAp) star 33 Lib taken in rapid succession over a 3-hr time span. A Fourier analysis of the data clearly shows the 8.2 min. pulsation period found previously by photometric investigations and gives a peak-to-peak (2K) amplitude of about 80 ms−1. We find, like in other roAp stars we have studied, that the RV amplitude depends on the spectral region used for measuring the pulsational RV amplitude and is as high as 57 ± 4.7 ms−1 in the region 5411–5500 Å and as low as 7 ± 3 ms−1 in the 5877–5976 Å region. An analysis of individual spectral lines show considerable scatter in the RV amplitude, ranging as high as 320 ms−1 and as low as 7 m−1. There is an overall trend of increasing RV amplitude with decreasing line strength. We also found that spectral lines due to nickel have a higher mean RV amplitude than chromium lines. We believe that the line strength variations result from the vertical atmospheric structure of the pulsations and that the elemental differences are related to the inhomogeneous distribution of elements known to occur on Ap stars. Precise stellar radial velocity studies of roAp stars may be a powerful tool for studying both the spatial (surface) and vertical structure to the pulsational velocity field.