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 (vsini=27
km.s−1) while the cooler and less massive secondary rotates much faster
(vsini∼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 δ 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