Investigation of the binary fraction among candidate A-F type hybrid stars detected by Kepler

¹ Koninklijke Sterrenwacht van België, Brussel, Belgium
² Konkoly Observatory, MTA CSFK, Budapest, Hungary
³ Instituut voor Sterrenkunde, K.U. Leuven, Leuven, Belgium

^a e-mail: patricia.lampens@oma.be Based on data gathered with NASA’s Discovery mission Kepler. Also based on data gathered with the HERMES spectrograph, installed at the Mercator Telescope, operated by the Institute of Astronomy, K.U.Leuven, Leuven, on the island of La Palma at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

Published online: 23 September 2015

Abstract

We are currently monitoring up to 40 Kepler candidate δ Scuti-γ Doradus (resp. γ Doradus-δ Scuti) hybrid stars in radial velocity in order to identify the physical cause behind the low frequencies observed in the periodograms based on the ultra-high accuracy Kepler space photometry. The presence of low frequency variability in unevolved or slightly evolved oscillating A/F-type stars can generally be explained in three ways: either 1) the star is an (un)detected binary or multiple system, or 2) the star is a g-mode pulsator (i.e. a genuine hybrid), or 3) the star’s atmosphere displays an asymmetric intensity distribution (caused by spots, i.e. chemical anomalies, or by (very) high rotation), which is detected through rotational modulation. Our targets were selected from the globally characterized variable A/F-type stars of the Kepler mission [7]. We observe each star at least 4 times unevenly spread over a time lapse up to 2 months with the HERMES spectrograph [6]. In the case of composite, multiple-lined spectra, these observations also provide the atmospheric properties of each component. Our principal goal is to estimate the fraction of short-period, spectroscopic systems in the sample.