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

TL;DR

This study confirms HD 183986 as a binary system with a long orbital period, revealing a pulsating primary and a faster-rotating secondary, using spectroscopic and photometric data to analyze its properties.

Contribution

The paper provides the first detailed spectroscopic and photometric analysis of HD 183986, establishing its binary nature and characterizing its orbital and stellar parameters.

Findings

HD 183986 is a binary star with a 1268-day orbit.

The primary is a slowly rotating star, secondary rotates faster.

Photometric variability includes δ Sct pulsations and rotational modulation.

Abstract

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.