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August 18, 2025Open Access

Binary Analysis and Period Study of the Long-period, High-mass-ratio Contact Binary KIC 7766185

Key Points

KIC 7766185 exhibits a shallow contact state with a fillout factor of 0.029 ± 0.002, demonstrating unique characteristics among W UMa systems.
Radial velocity measurements were derived from spectroscopic observations at the Mayall 4 m telescope and used alongside photometry for comprehensive analysis.
Binary analysis was performed in PHOEBE, allowing for the determination of crucial orbital and stellar parameters for KIC 7766185.
Eclipse timing variations suggest further underlying cyclic behaviors, hinting at interesting dynamics within this system.

Abstract

Abstract We present an in-depth photometric and spectroscopic study of the contact binary KIC 7766185. Spectroscopic observations were conducted on the Mayall 4 m telescope at Kitt Peak National Observatory and used to extract radial velocities. Using the radial velocity measurements, Kepler photometry, and Gaia multicolor photometry, binary analysis was performed in PHOEBE to determine orbital and stellar parameters. The results classify KIC 7766185 as an A-type W UMa system and reveal one of the largest and most massive secondary stars in the sample of well studied W UMa systems. The two stars are in a shallow contact state, with a small fillout factor of 0.029 ± 0.002. Along with the binary analysis, we conduct a period study that reveals evidence for a cyclic variation in the eclipse timings.

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