Publication details
Multi-technique investigation of the binary fraction of A-F type candidate hybrid variable stars discovered by Kepler
| Authors | |
|---|---|
| Year of publication | 2018 |
| Type | Article in Periodical |
| Magazine / Source | Astronomy and Astrophysics |
| Citation | |
| Web | ADS link |
| Doi | http://dx.doi.org/10.1051/0004-6361/201730694 |
| Keywords | Techniques: spectroscopic; Stars: binaries: spectroscopic; Techniques: photometric ; Stars: oscillations (including pulsations); Stars: rotation; Stars: variables: delta Scuti |
| Description | Hundreds of candidate hybrid pulsators of intermediate type A–F were revealed by the recent space missions. Hybrid pulsators allow to study the full stellar interiors, where both low-order p- and high-order g-modes are simultaneously excited. The true hybrid stars must be identified since other processes, related to stellar multiplicity or rotation, might explain the presence of (some) low frequencies observed in their periodograms. We measured the radial velocities of 50 candidates dtla Scuti - gamma Doradus hybrid stars from the Kepler mission with the Hermes and Ace spectrographs over a time span of months to years. We aim to derive the fraction of binary and multiple systems and to provide an independent and homogeneous determination of the atmospheric properties and vsini for all targets. The long(er)-term objective is to identify the (probable) physical cause of the low frequencies. We computed 1-D cross-correlation functions (CCFs) in order to find the best set of parameters in terms of the number of components, spectral type(s) and vsini for each target. Radial velocities were measured from spectrum synthesis and by using a 2-D cross-correlation technique in the case of double- and triple-lined systems. Fundamental parameters were determined by fitting (composite) synthetic spectra to the normalised median spectra corrected for the appropriate Doppler shifts. We report on the analysis of 478 high-resolution Hermes and 41 Ace spectra of A/F-type candidate hybrid pulsators from the Kepler field. We determined their radial velocities, projected rotational velocities, atmospheric properties and classified our targets based on the shape of the CCFs and the temporal behaviour of the radial velocities. We derived orbital solutions for seven new systems. Three long-period preliminary orbital solutions are confirmed by a photometric time-delay analysis. Finally, we determined a global multiplicity fraction of 27 % in our sample of candidate hybrid stars. |