Orbital solutions derived from radial velocities and time delays for four {\it Kepler} systems with A/F-type (candidate) hybrid pulsators

Abstract

The presence of A/F-type {\it Kepler} hybrid stars extending across the entire $\delta$ Sct-$\gamma$ Dor instability strips and beyond remains largely unexplained. In order to better understand these particular stars, we performed a multi-epoch spectroscopic study of 49 candidate A/F-type hybrid stars and one cool(er) hybrid object detected by the {\it Kepler} mission. We determined a lower limit of 27 % for the multiplicity fraction. For six spectroscopic systems, we also reported long-term variations of the time delays. For four systems, the time delay variations are fully coherent with those of the radial velocities and can be attributed to orbital motion. We aim to improve the orbital solutions for those systems with long orbital periods (order of 4-6 years) among the {\it Kepler} hybrid stars. The orbits are computed based on a simultaneous modelling of the RVs obtained with high-resolution spectrographs and the photometric time delays derived from time-dependent frequency analyses of the {\it Kepler} light curves. We refined the orbital solutions of four spectroscopic systems with A/F-type {\it Kepler} hybrid component stars: KIC 4480321, 5219533, 8975515 and KIC 9775454. Simultaneous modelling of both data types analysed together enabled us to improve the orbital solutions, obtain more robust and accurate information on the mass ratio, and identify the component with the short-period $\delta$ Sct-type pulsations. In several cases, we were also able to derive new constraints for the minimum component masses. From a search for regular frequency patterns in the high-frequency regime of the Fourier transforms of each system, we found no evidence of tidal splitting among the triple systems with close (inner) companions. However, some systems exhibit frequency spacings which can be explained by the mechanism of rotational splitting.

arXiv comment11 pages, 15 figures and 5 tables. Accepted for publication in A&A

References in corpus (21)

• HERMES: a high-resolution fibre-fed spectrograph for the Mercator telescope
• The Kepler characterization of the variability among A- and F-type stars. I. General overview
• Rotation periods of 12 000 main-sequence Kepler stars: Dependence on stellar spectral type and comparison with v sin i observations
• Hybrid gamma Doradus - delta Scuti pulsators: New insights into the physics of the oscillations from Kepler observations
• The interior rotation of a sample of gamma Doradus stars from ensemble modelling of their gravity mode period spacings
• General Cosmography Model with Spatial Curvature
• FM stars: A Fourier view of pulsating binary stars, a new technique for measuring radial velocities photometrically
• Pulsation frequency distribution in Delta Scuti stars
• Finding binaries from phase modulation of pulsating stars with Kepler: V. Orbital parameters, with eccentricity and mass-ratio distributions of 341 new binaries
• Finding binaries among Kepler pulsating stars from phase modulation of their pulsations
• Gravity-mode period spacings and near-core rotation rates of 611 $\gamma$ Doradus stars with \textit{Kepler}
• Period spacings of $\gamma$ Doradus pulsators in the Kepler field: detection methods and application to 22 slow rotators
• MOBSTER - II. Identification of rotationally variable A stars observed with \emph{TESS} in Sectors 1 to 4
• Discovery of tidally-perturbed pulsations in the eclipsing binary U Gru: a pioneering system for tidal asteroseismology
• KIC 4142768: An Evolved Gamma Doradus/Delta Scuti Hybrid Pulsating Eclipsing Binary with Tidally Excited Oscillations
• The effect of tides on near-core rotation: analysis of 35 Kepler $\gamma$ Doradus stars in eclipsing and spectroscopic binaries
• Deriving the orbital properties of pulsators in binary systems through their light arrival time delays
• Finding binaries from phase modulation of pulsating stars with Kepler. IV. Detection limits and radial velocity verification
• Multi-technique investigation of the binary fraction among A-F type candidate hybrid variable stars discovered by Kepler
• The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign. II. Evidence of a binary - possibly triple - system
• KIC~8975515: a fast-rotating ($\gamma$ Dor - $\delta$ Sct) hybrid star with Rossby modes and a slower $\delta$ Sct companion in a long-period orbit

Cited by in corpus (1)

• Pulsation in TESS Objects of Interest