Pulsational velocity fields in the atmospheres of two roAp stars HR1217 and γ Equ

We discuss spectroscopic observations of pulsations in the roAp stars γ Equ and HR 1217. In both stars we observe strong variations of rare-earth lines and detect running magneto-acoustic waves, but do not find evidence for a standing pulsational wave. In γ Equ we find strong pulsational variations across line profiles, characteristic of l ≥ 2 modes.

Radial Velocity Variations of the Rapidly Oscillating Ap Star 33 Lib

We 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.

Turbulence Variations in Cepheids

From radial velocity measurements obtained with a cross-correlation technique, the variation of turbulence during the pulsation cycle is studied for a sample of 40 Cepheids. We will propose a new way to separate classical and s-Cepheids. More complete results will appear in a forthcoming paper (Bersier & Burki 1995)The radial velocities have been measured with the spectrometer CORAVEL (Baranne et al. 1979), whose cross-correlation function (CCF) is fitted with a Gaussian, giving the radial velocity Vr, the width σobs the depth H and the continuum, normalised to 1. The pulsation broadens the lines and thus also the CCF. In the Gaussian approximation one can writewhere σobs is the observed width, σinst is the instrumental width, σpuls is the additional width caused by the pulsational velocity field and σres contains all the other effects (turbulence, rotation, magnetic field, etc.). To be less affected by the noise in the data, a Fourier series has been fitted to each curve of σobs. With numerical simulations, one is able to synthesise the additional Doppler width due to pulsation, with a high accuracy. The instrumental width being well known for CORAVEL, the computation of σres is then straightforward. One then has a curve in phase for σres. From this curve, we determined the maximum residual broadening σmax (observed at or very close to minimum radius), and the width σo that the star would have if it did not pulsate. As shown by Bersier & Burki (1995), σo is slightly higher than the mean value of σres.

The Period-Radius Relation from 101 Cepheid Radii

Surface brightness solutions using the (V-R) color index have been carried out for 52 southern Cepheids and 63 northern Cepheids, with 14 stars in common. For the southern stars the data came from the study by Gieren (1986, M.N.R.A.S, 222, 251), with new observations, and for the northern stars, from Moffett and Barnes (1987, Ap.J., 323, 280). All stars were reduced using the same surface brightness relation and the same transformation from radial velocity to pulsational velocity. The 14 stars in common show that there is only a small systematic difference between the southern and northern data sets and reductions. The combined solution for the 101 Cepheids in the period range 3 to 45 days is log R = 1.108 + 0.743 log P with uncertainties of ±0.023 in the zero point and ±0.023 in the slope. This result is consistent with the individual results of the above references but has much smaller uncertainty.