The Kepler view of magnetic chemically peculiar stars

¹ Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne e.V. (BAV), 12169 Berlin, Germany
e-mail: ernham@rz-online.de
² American Association of Variable Star Observers (AAVSO), 49 Bay State Rd, Cambridge, MA, 02138 USA
³ Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
⁴ Special astrophysical observatory of the RAS, Nizhnii Arkhyz, 369167 Karachai-Cherkessian Republic, Russia
⁵ Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica, Slovakia

Received: 2 March 2018
Accepted: 1 July 2018

Abstract

Context. Magnetic chemically peculiar (mCP) stars exhibit complex atmospheres that allow the investigation of such diverse phenomena as atomic diffusion, magnetic fields, and stellar rotation. The advent of space-based photometry provides the opportunity for the first precise characterizations of the photometric variability properties of these stars, which might advance our understanding of the processes involved and the atmospheric structures of mCP stars.

Aims. We carried out a search for new mCP stars in the Kepler field with the ultimate aim of investigating their photometric variability properties using Kepler data. As an aside, we describe criteria for selecting mCP star candidates based on light curve properties, and assess the accuracy of the spectral classifications provided by the MKCLASS code.

Methods. As only very few known mCP stars are situated in the Kepler field, we had to depend largely on alternative (non-spectroscopic) means of identifying suitable candidates that rely mostly on light curve properties; in particular we relied on monoperiodic variability and light curve stability. Newly acquired and archival spectra were used to confirm most of our mCP star candidates. Linear ephemeris parameters and effective amplitudes were derived from detrended Kepler data.

Results. Our final sample consists of 41 spectroscopically confirmed mCP stars of which 39 are new discoveries, 5 candidate mCP stars, and 7 stars in which no chemical peculiarities could be established. Our targets populate the whole age range from zero-age main sequence to terminal-age main sequence and are distributed in the mass interval from 1.5 M_⊙ to 4 M_⊙. About 25% of the mCP stars show a hitherto unobserved wealth of detail in their light curves indicative of complex surface structures. We identified light curve stability as a primary criterion for identifying mCP star candidates among early-type stars in large photometric surveys, and prove the reliability of the spectral classifications provided by the MKCLASS code.