Radial velocity monitoring of (candidate) hybrid A- and F-type stars from the Kepler mission P. Lampens 1,*, L. Vermeylen 1, P. De Cat 1, Á. Sódor 2, Zs. Bognár 2, Y. Frémat 1, M. Skarka 3,4 and H. Lehmann 5 1Royal Observatory of Belgium (ROB), Ringlaan 3, 1180 Brussels - Belgium 2 Konkoly Observatory, Konkoly Thege M. u. 15-17 H-1121 Budapest - Hungary 3 Astronomical Institute of the Czech Academy of Sciences, Fričova 1, CZ-25165 Ondřejov - Czech Republic 4 Department of Theoretical Physics and Astrophysics, Masaryk Univerzity, Kotlářská 2, CZ-61137 Brno - Czech Republic 5Thüringer Landessternwarte Tautenburg (TLS) , Sternwarte 5, 07778 Tautenburg - Germany *e-mail: Patricia.Lampens@oma.be Instruments and spectroscopic observations Previous and new targets Acknowledgements Abstract We monitored an ensemble of 50 candidate hybrid A/F-type stars from the Kepler mission with the HERMES spectrograph attached to the Mercator telescope over a period of four years. For each target, we obtained radial velocities, improved or new atmospheric properties (Teff, log g, v sin i), and a classification in terms of multiplicity, pulsation and/or fast rotation (LA18). Recently, a sample of 40 additional candidate hybrid A- and F-type stars from the Kepler mission has been identified as an extension of the first survey. High- resolution spectra of the hybrid candidate stars are systematically collected with small and medium-sized telescopes. Furthermore, by combining the radial velocities with the time delays obtained via the study of the pulsation frequencies during the four years of Kepler photometry, we obtained accurate orbits for a number of new stellar systems with good radial velocity coverage. Astrophysical rationale Fig. 1. The mechanisms of stellar formation explain why a vast majority of stars belongs to double and multiple star systems (Tobin, Univ. Oklahoma/Leiden et al.) B. Saxton, ALMA (ESO/NAOJ/NRAO), NRAO/AUI/NSF Physics of Oscillating STars, 03 - 07 Sept. 2018, Banyuls-sur-mer (France) Fig.2. The Mercator telescope is located at the observatory Roque de los Muchachos, La Palma (Canary Islands, Spain). Equipped with HERMES, it offers high-efficiency and high-resolution spectroscopy to all the partners of the HERMES Consortium. References Balona et al. 2015, MNRAS 452, 3073 (BA15) Balona 2018, MNRAS 476, 4840 (BA18) Derekas et al. 2017, MNRAS 464, 1553 (DE17) Grigahcène et al. 2010, ApJ 713, L192 (GR10) Lampens et al. 2018, A&A 610, A17 (LA18) Nemec et al. 2017, MNRAS 466, 1290 (NE17) Raskin et al. 2011, A&A 526, A69 (RA11) Reyniers & Smeyers 2003, A&A 404, 1051 (RS03) Uytterhoeven et al. 2011, A&A 534, A125 (UY11) Fig3. The [0-4] d-1 region of the periodogram of KIC 6381306 (based on Kepler data) Fig. 4. A powerful combination: photometric time delays and radial velocities (KIC 4480321). The time delays (in pink) and the radial velocities (comp. C in red; comp. A & B in blue) are overlaid with the orbital solution (solid lines). The first survey Objectives & Summary - 1. The goal is to characterize the spectroscopic variability of a large sample of Kepler hybrid (Dor - Sct/Sct - Dor) pulsators. We need 4-5 observations at least (Fig. 5) to be able to detect binarity/multiplicity at very different orbital periods, up to a few years, and to establish a meaningful classification/interpretation. We also aim to determine the orbital periods and solutions for the new binary and multiple systems with sufficient and good phase coverage. In the first survey, we performed a multi-epoch spectroscopic study of 49 A/F-type candidate hybrid stars and one target classified as Scuti star from the Kepler mission (cf. Table 3 in UY11). We classified our targets on the basis of their (constant vs variable) behaviour in radial velocity and the shape of the cross correlation functions over a period of four years. Both short- and long-period systems were found, i.e. 4 single-lined (SB1), 4 double-lined (SB2) and 3 triple-lined (SB3) systems.