Evidence for Binarity and Possible Disk Obscuration in Kepler Observations of the Pulsating RV Tau Variable DF Cygni

Abstract

The Kepler light curve of DF Cyg is unparalleled in precision and cadence for any RV Tau star to date spanning a baseline of $\sim$4 years and clearly displaying the signature pulsating behavior of alternating deep and shallow minima as well as the long-term trend indicative of an RVb-type variable. We measured DF Cyg's formal period (the time interval between two successive deep minima) to be $49.84\pm 0.02$days. The trend in the arrival times emulates that of the long-term period. There appears to be precisely 16 deep+shallow minima cycles in one long-term cycle, suggesting a long-term cycle period of $\approx$ $795\pm 5$days. We argue that binarity may naturally explain the long-term periodicity in DF Cyg. The spectral energy distribution of DF Cyg features an infrared excess indicative of a disk possibly linked to a binary companion. From a recent Gaia parallax measurement for DF Cyg, we calculated that it has a distance of $990\pm 372$pc and a physical radius of $R_{\star }=10.3\pm 3.8$ R${}_{\odot }$. From kinematics and geometric arguments, we argue that the most likely interpretation for the decrease in flux from the long-period maximum to the long-period minimum, as well as the reduction of short-term pulsation amplitude, is caused by an occulting body such as a disk surrounding DF Cyg and its binary companion.

12 pages, 7 figures, and 2 tables in aastex6 format. Accepted to ApJ. Corrected Figure 6 Caption and other smaller typos. The content/results are unchanged

References in corpus (10)

• The Gaia mission
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• A Three-Dimensional Map of Milky-Way Dust
• Keplerian discs around post-AGB stars: a common phenomenon?
• The WISE View of RV Tauri Stars
• Establishing binarity amongst Galactic RV Tauri stars with a disc
• The evolved circumbinary disk of AC Her: a radiative transfer, interferometric and mineralogical study
• An interferometric study of the post-AGB binary 89 Herculis. II Radiative transfer models of the circumbinary disk
• Periodicities of the RV Tau-type pulsating star DF Cygni: a combination of Kepler data with ground-based observations
• Kepler and the Long Period Variables

Cited by in corpus (11)

• TESS observations of Cepheid stars: first light results
• TESS Data for Asteroseismology (T'DA) Stellar Variability Classification Pipeline: Set-Up and Application to the Kepler Q9 Data
• Amplitude variations of modulated RV Tauri stars support the dust obscuration model of the RVb phenomenon
• The spectroscopic binaries RV Tauri and DF Cygni
• Chaotic dynamics in the pulsation of DF Cygni, as observed by Kepler
• Gaia Data Release 2: Validation of the classification of RR Lyrae and Cepheid variables with the Kepler and K2 missions
• Second-generation protoplanetary discs around evolved binaries: a high-resolution polarimetric view with SPHERE/IRDIS
• Multiwavelength Observations of the RV Tauri Variable System U Monocerotis: Long-Term Variability Phenomena That Can Be Explained by Binary Interactions with a Circumbinary Disk
• Type II and anomalous Cepheids in the Kepler K2 mission
• SPHERE/ZIMPOL insights into discs around evolved stars: arcs, asymmetries and dust properties
• Decoding the RVb Enigma of DF Cyg: Pulsations, Circumstellar Disks, and Post-RGB Evolution Revealed by Multi-Wavelength Observations