HD 183986: a high-contrast SB2 system with a pulsating component

There is a small group of peculiar early-type stars on the main sequence that show different rotation velocities from different spectral lines. This inconsistency might be due to the binary nature of these objects. We aim to verify this hypothesis by a more detailed spectroscopic and photometric investigation of one such object: HD 183986. We obtained 151 high and medium resolution spectra that covered an anticipated long orbital period. There is clear evidence of theorbital motion of the primary component. We uncovered a very faint and broad spectrum of the secondary component. The corresponding SB2 orbital parameters, and the component spectra, were obtained by Fourier disentangling using the KOREL code. The component spectra were further modeled by iSpec code to arrive at the atmospheric quantities and the projected rotational velocities. We have proven that this object is a binary star with the period $P$ = 1268.2(11) d, eccentricity $e$ = 0.5728(20), and mass ratio $q$ = 0.655. The primary component is a slowly rotating star ($v \sin i = 27$ km.s$^{-1}$) while the cooler and less massive secondary rotates much faster ($v \sin i \sim 120$ km.s$^{-1}$). Photometric observations obtained by the TESS satellite were also investigated to shed more light on this object. A multi-period photometric variability was detected in the TESS data ranging from hours (the $\delta$ Sct-type variability) to a few days (spots/rotational variability). The physical parameters of the components and the origin of the photometric variability are discussed in more detail.Comment: Accepted to AJ. arXiv admin note: text overlap with arXiv:1307.2553 by other authors. text overlap with arXiv:1307.2553 by other author

Rapidly rotating stars and their transiting planets: KELT-17b, KELT-19Ab, and KELT-21b in the CHEOPS and TESS era

Rapidly rotating early-type main-sequence stars with transiting planets are interesting in many aspects. Unfortunately, several astrophysical effects in such systems are not well understood yet. Therefore, we performed a photometric mini-survey of three rapidly rotating stars with transiting planets, namely KELT-17b, KELT-19Ab, and KELT-21b, using the Characterising Exoplanets Satellite (CHEOPS), complemented with Transiting Exoplanet Survey Satellite (TESS) data, and spectroscopic data. We aimed at investigating the spin-orbit misalignment and its photometrical signs, therefore the high-quality light curves of the selected objects were tested for transit asymmetry, transit duration variations, and orbital precession. In addition, we performed transit time variation analyses, obtained new stellar parameters, and refined the system parameters. For KELT-17b and KELT-19Ab we obtained significantly smaller planet radius as found before. The gravity-darkening effect is very small compared to the precision of CHEOPS data. We can report only on a tentative detection of the stellar inclination of KELT-21, which is about 60 deg. In KELT-17b and KELT-19Ab we were able to exclude long-term transit duration variations causing orbital precession. The shorter transit duration of KELT-19Ab compared to the discovery paper is probably a consequence of a smaller planet radius. KELT-21b is promising from this viewpoint, but further precise observations are needed. We did not find any convincing evidence for additional objects in the systems.Comment: Accepted for publication in MNRA