Letter to the Editor

The discovery of high-amplitude, 10.9-minute oscillations in the cool magnetic Ap star HD 115226 ^*

¹ Department of Astronomy and Space Physics, Uppsala University, 75120 Uppsala, Sweden e-mail: oleg@astro.uu.se
² Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia
³ Department of Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
⁴ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
⁵ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Casilla 19001 Santiago 19, Chile

Received: 3 December 2007
Accepted: 19 December 2007

Abstract

We present the discovery of pulsational variations in the cool magnetic Ap star HD 115226 – the first high-amplitude rapidly oscillating Ap (roAp) star discovered with time-series spectroscopy. Using high-resolution spectra obtained with the HARPS instrument at the European Southern Observatory 3.6-m telescope, we detect radial velocity variations with a period of 10.86 min in , , lines, and in the narrow cores of hydrogen lines. Pulsational amplitudes exceed 1 km s^-1 in individual lines of . The presence of running waves in the stellar atmosphere is inferred from a phase shift between the radial velocity maxima of rare-earth and hydrogen lines. Our abundance analysis demonstrates that HD 115226 exhibits a typical roAp spectroscopic signature, notably ionization anomaly of Pr, Nd, and Dy. We discuss the discovery of pulsations in HD 115226 in the context of recent spectroscopic studies of roAp stars and point to the existence of a correlation between spectroscopic pulsational amplitude and the stellar rotation rate.