Continued Photometric Monitoring Supports Long-Term Dynamical Evolution in the Young Binary Star-Disk System KH 15D

TL;DR

This study uses multi-year photometric data to analyze the evolving eclipsing behavior of the binary star KH 15D, supporting models of a precessing circumbinary disk causing complex lightcurve variations.

Contribution

It provides long-term observational evidence confirming the precession and structural changes of the circumbinary disk in KH 15D, advancing understanding of disk dynamics in young binary systems.

Findings

Verification of disk precession through eclipse timing analysis

Observation of increasing amplitude of central re-brightening

Color variation analysis supporting clumping in the disk

Abstract

We present photometric time series data spanning 2018-2024 that show the effects of temporal dynamics in the binary system KH 15D, a member of the NGC 2264 star forming region. This source exhibits complex eclipsing behavior due to a precessing circumbinary disk or ring that is slightly inclined relative to the orbital plane of the binary. Using g-band and r-band observations from the Zwicky Transient Facility (ZTF) over seven observing seasons, we follow the evolution of the KH 15D lightcurve as it continues to emerge from its deepest observed photometric minimum about 15 years ago. Our observations are consistent with previous models that propose a precessing, warped circumbinary disk orbiting KH 15D. We verify the gradual precession of the disk by quantifying the times of eclipse ingresses and egresses. We also examine the central re-brightening within the minima of the phased lightcurve. This feature has increased in amplitude over our observing seasons, and we measure its evolution in both amplitude and phase from year to year. Finally, we assess color as a function of phase and brightness. Our findings support the assertion that line-of-sight variations in disk density and structure, possibly due to clumping, coupled with a precessing circumbinary disk are responsible for the central re-brightening event.