Three dimensional resolution of the strongly magnetic photospheres and upper atmospheres of the rapidly oscillating peculiar A stars
Lead Research Organisation:
University of Central Lancashire
Department Name: Centre for Astrophysics
Abstract
Asteroseismology uses sounds in stars to probe their interiors. Just as ultrasound is used to see the face of a foetus before it is born, astronomers can 'see' inside the stars by studying their light variations caused by pulsations within them. This research will provide unprecedent 3D views of the pulsation modes and abundance distributions in the rapidly oscillating peculiar A stars.
| Description | We mapped the 3D pulsation and abundance patterns in roAp stars in more detail than is possible for any other star but the Sun. We had simultaneous nights of observations on the Subaruy 8-m telescope in Hawaii and the 8-m VLT in Chile, both costed at £50000 per night for use. Our most spectacular success was for the roAp star HD99653: We have used high-speed spectroscopy of the rapidly oscillating Ap (roAp) star HD99563 to study the pulsation amplitude and phase behaviour of elements in its stratified atmosphere over one 2.91-d rotation cycle. We identify spectral features related to patches in the surface distribution of chemical elements and study the pulsation amplitudes and phases as the patches move across the stellar disc. The variations are consistent with a distorted non-radial dipole pulsation mode. We measure a 1.6kms-1 rotational variation in the mean radial velocities of Ha and argue that this is the first observation of Ha abundance spots caused by He settling through suppression of convection by the magnetic field on an oblique rotator, in support of a prime theory for the excitation mechanism of roAp star pulsation. We demonstrate that HD99563 is the second roAp star to show aspect dependence of blue-to-red running wave line profile variations in NdIII spots. |
| Exploitation Route | Similar studies of other stars are planned. New surveys with the upcoming TESS and PLATO space missions are planned that will then lead to more 3D studies of new targets. |
| Sectors | Education |