Do we see the simultaneous occurrence of stellar rotational effects and short-period pulsations in some A-type Kepler stars?


  • Based on observations obtained with the HERMES spectrograph and the Mercator Telescope, operated by the Flemish Community on the island of La Palma, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, and with the 2-m Alfred-Jensch telescope of the Thüringer Landessternwarte Tautenburg.


We used high-quality Kepler photometry and recent spectroscopic data to investigate the Kepler target KIC 005988140 considering three possible scenario’s: (1) binarity, (2) co-existence of δ Scuti- and γ Doradus-type oscillations, and (3) rotational modulation with spots over the stellar surface. Using spectrum synthesis, we derived improved atmospheric parameters from high-resolution, high signal-to-noise spectra. The star is of spectral type A7.5 IV–III with a metallicity slightly lower than that of the Sun. The Fourier analyses of both the photometric and the spectroscopic data reveal two dominant frequencies – with an integer ratio equal to two – in the low frequency regime. Nine more frequencies located in the typical δ Scuti range were also detected. The mean light and radial velocity curves which are not exactly in antiphase, show a similar double-wave shape. We therefore suggest on a preliminary basis that the physical cause of the observed light and radial velocity variations is the simultaneous occurrence of (δ Sct-type) pressure modes and stellar rotation coupled to inhomogeneities on the surface of this late A-type star (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)