NY Bootes: An Active Deep and Low-mass-ratio Contact Binary with a Cool Companion in a Hierarchical Triple System

Abstract

The first detailed photometric and spectroscopic study of G-type short-period binary NY Boo is presented. The radial velocity curve was obtained by the cross-correlation function (CCF) method based on LAMOST and SDSS spectra, which derived its mass ratio as q = 0.139(1/7.2). The CCF profiles of the SDSS spectra clearly show the existence of a cool third component, which is supported by the results of the orbital period investigation. The period study based on the O-C analysis indicates that besides a long-term decrease, the orbital period has a periodic oscillation due to the light-travel time effect caused by a third body. When the third light contribution is consistent with the CCF results, the orbit of the third body and the inner pair are non-coplanar with m 3 = 0.31 M ⊙. Combining with the TESS light curves, it is found that the target is a deep and low-mass-ratio contact binary (DLMRCB) with a fill-out factor of f = 73%. The notable asymmetry in light curves was detected and explained by the spot model very well. The spectroscopic profiles, the cyclic variation in the O-C diagram, and the radial velocity curve and light-curve solutions all suggest that NY Boo is a hierarchical triple system with a cool tertiary component orbiting around an active DLMRCB. With the orbital period shrinking, the binary may eventually merge. The period of NY Boo decreases faster than other shrinking DLMRCB, together with active inner pair and non-coplanar tertiary component, making NY Boo an important target for studying the late evolution of binaries.

V0405 Dra: A New Deep and Low Mass Ratio Contact Binary with Extremely Fast Decrease in the Orbital Period

“…the rate of mass transfer for V0405 Dra is determined to be dM 2 /dt = −6.27(±0.06) × 10 −7 M e year −1 . This rate is significantly higher compared to other DLMRCBs (Li et al 2022;Meng et al 2023), suggesting that the fast decreases in the orbital period might result from a combination of mass transfer and angular momentum loss due to the tertiary body. Given the accelerated period decrease, V0405 Dra is likely to evolve toward a more closely contracted configuration, potentially culminating as an FK Com-type star.…”

“…They could offer an excellent opportunity to study scenarios of stellar mergers (Stepien 2006). By examining the long-term period changes in DLMRCBs, Qian et al (2006) proposed two potential evolutionary scenarios by which DLMRCBs can evolve into Blue Straggler/FK Com-type stars: systems with a decreasing period will experience a contraction of the inner and outer critical Roche lobes, and this contraction would enhance the degree of contact configuration; once the photospheric surface reaches the outer critical lobe, these systems will merge rapidly due to dynamic instability (Meng et al 2023). While systems with an increasing period are undergoing the mass transfer from the less massive component to the more massive one, such a process could result in the decrease of mass ratio and the increase of J spin /J orb .…”

OO Leo: An Active Contact Binary with Possible Solar-like Differential Rotation

“…In order to clearly define the two possible causes, one should search for additional evidence of magnetic activity (e.g., periodic effects in some emission lines as activity indicators or cyclic effects in long-term photometry) or third-body effects (e.g., a third spectrum in high-resolution spectroscopy or periodic changes of the γ velocity). For instance, using infrared spectra, Meng et al (2023) confirmed a cool tertiary component for the NY Boo system. From the longterm photometry, Hu et al (2020) provided strong evidence of cyclic magnetic activity for the near-contact binary V0599 Aur.…”

“…Because the component stars of contact binaries undergo rapid rotation with deep convective zones, the O'Connell effect is, in general, associated with stellar activity (Sriram et al 2017). For some contact binaries, the O'Connell effect is almost stable, while in other systems, it follows an irregular (Balaji et al 2015;Sriram et al 2017) or quasiperiodic variation (Meng et al 2023;Yılmaz et al 2023), even accompanied by an anticorrelation variation between the primary and secondary eclipse times (Tran et al 2013). Usually, the quasi-periodic and anticorrelated variations, which are often dominated by a period of 50-200 days in short-period eclipsing binaries, can be attributed to the surface differential rotation, leading to longitudinal spot migration (Kalimeris et al 2002;Tran et al 2013).…”