HD 183648: a Kepler eclipsing binary with anomalous ellipsoidal variations and a pulsating component

Abstract

KIC 8560861 (HD 183648) is a marginally eccentric (e = 0.05) eclipsing binary with an orbital period of P orb = 31.973 d, exhibiting mmag amplitude pulsations on time scales of a few days. We present the results of the complex analysis of high and medium-resolution spectroscopic data and Kepler Q0 -Q16 long cadence photometry. The iterative combination of spectral disentangling, atmospheric analysis, radial velocity and eclipse timing variation studies, separation of pulsational features of the light curve, and binary light curve analysis led to the accurate determination of the fundamental stellar parameters. We found that the binary is composed of two main sequence stars with an age of 0.9 ± 0.2 Gyr, having masses, radii and temperatures of M 1 = 1.93 ± 0.12 M ⊙ , R 1 = 3.30 ± 0.07 R ⊙ , T eff1 = 7650 ± 100 K for the primary, and M 2 = 1.06 ± 0.08 M ⊙ , R 2 = 1.11 ± 0.03 R ⊙ , T eff2 = 6450 ± 100 K for the secondary. After subtracting the binary model, we found three independent frequencies, two of which are separated by twice the orbital frequency. We also found an enigmatic half orbital period sinusoidal variation that we attribute to an anomalous ellipsoidal effect. Both of these observations indicate that tidal effects are strongly influencing the luminosity variations of HD 183648. The analysis of the eclipse timing variations revealed both a parabolic trend, and apsidal motion with a period of P obs apse = 10 400 ± 3 000 y, which is three times faster than what is theoretically expected. These findings might indicate the presence of a distant, unseen companion.

A comprehensive study of theKeplertriples via eclipse timing

“…An additional example of the oscillating EB system KIC 08560861 can be found in Fig. 1 of Borkovits et al (2014). Local smoothing was found to be effective mainly for detached systems with definite and sharp eclipses, but we could also use it even for some semi-detached binaries.…”

“…Finally, when a light curve is distorted by the effects of, e.g., stellar spots or pulsations, the measurement process tends to yield spurious ETVs that may include periodic or quasiperiodic components (see e.g Kalimeris et al 2002;Tran et al 2013;Balaji et al 2015, for spots andBorkovits et al 2014, for stellar oscillations).…”

The age and interior rotation of stars from asteroseismology

“…The subject of tidal asteroseismology, i.e., stellar modelling based on tidally excited or tidally affected pulsations, only turned into a practical science since the availability of the uninterrupted CoRoT and Kepler lightcurves of either eclipsing binaries with tidally excited g-modes (e.g., Maceroni et al 2009;Welsh et al 2011;Hambleton et al 2013;Debosscher et al 2013;Borkovits et al 2014) or pulsating stars that were initially thought to be single stars but turned out to be a member of a spectroscopic binary from follow-up data (e.g., Pápics et al 2013). In all of those studies, clear evidence was found that some or all of the g-modes are tidally triggered, after iterative light curve modelling schemes in the cases where the binary and pulsational variability are of the same order of magnitude.…”

A COORDINATED X-RAY AND OPTICAL CAMPAIGN OF THE NEAREST MASSIVE ECLIPSING BINARY,δORIONIS Aa. III. ANALYSIS OF OPTICAL PHOTOMETRIC (MOST) AND SPECTROSCOPIC (GROUND-BASED) VARIATIONS

“…However, frequency spacing at multiples of the orbital frequency has been seen in several other close binary stars Borkovits et al 2014;Maceroni et al 2014), and indicates that the pulsations are tidally "influenced." Similar to the papers cited above, we speculate that the frequency spacing at multiples of the orbital frequency may arise from nonlinear interactions between stellar oscillation modes and tidally excited oscillations.…”