CY Aquarii: A Triple System with Twin Companions

Abstract

In this study, we conducted a comprehensive analysis of the SX Phoenicis (SX Phe) type star CY Aquarii (CY Aqr). Our investigation included a detailed $O-C$ analysis based on a 90-year observational dataset, augmented by 1,367 newly determined times of maximum light. The $O-C$ diagram reveals that (i) the primary star of CY Aqr exhibits a linear period variation rate of $(1/P_0)(\mathrm{d}P/\mathrm{d}t)=(2.132\pm 0.002)\times 10^{-8}{\mathrm{yr}}^{-1}$ for its dominant pulsation mode; (ii) the primary star is disturbed by two companions and part of a triple system; (iii) Companion A has an orbital period of approximately 60.2 years and Companion B has an orbital period of approximately 50.8 years. It is highly probable that both Companion A and B are white dwarfs, with Companion A's elliptical orbit displaying an eccentricity of $e=0.139\pm 0.002$, which is the lowest confirmed value in similar binary and triple systems to date. Most notably, Companion A and B have masses that are identical within the uncertainties, with a mass ratio exceeding 0.99. Whether this is considered a coincidental event or the result of an underlying mechanism, CY Aqr is an exceptionally rare case that broadens our understanding of multiple star systems and offers a unique opportunity to delve into the enigmatic evolutionary histories of such configurations. Further intriguing characteristics of this system warrant investigation in future studies, based on additional observational data.

29 pages, 7 figures, 7 tables. ApJ Accepted

References in corpus (19)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates
• Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
• KIC5950759: a high-amplitude $\delta$ Sct star with amplitude and frequency modulation near the terminal age main sequence
• Binarity and multiperiodicity in high-amplitude delta Scuti stars
• The Period Changes of the Cepheid RT Aurigae
• A rapidly evolving high-amplitude $\delta$ Scuti star crossing the Hertzsprung Gap
• Pulsation Analysis of High-Amplitude $\delta$ Scuti Stars with TESS
• Precise Evolutionary Asteroseismology of High-Amplitude δ Scuti Star AE Ursae Majoris
• Pulsations of the SX Phe Star BL Camelopardalis
• Hybrid origins of the cosmic-ray nuclei spectral hardening at a few hundred GV
• TESS search for substellar companions through pulsation timing of $\delta$ Scuti stars. I. Discovery of companions around Chang 134 and V393 Car
• Pulsations and Period Variations of the $\delta$ Scuti Star AN Lyncis in a possible three-body system
• Uncorrelated Amplitude and Frequency Variations of the Harmonics in SX Phoenicis Star XX Cygni
• Two Different Weak Modulations in ab-type RR Lyrae Variable V838 Cyg, and Potential Influence of Metal Abundance on Blazhko Modulation
• Asteroseismology of double-mode radial $\delta$ Scuti stars: AE Ursae Majoris and RV Arietis

Cited by in corpus (1)

• BE Lyncis: A Pulsating Star in the Most Eccentric Binary with a Massive Unseen Companion