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

## TL;DR

This study uses Kepler data to investigate DF Cyg, revealing evidence for binarity and a possible circumstellar disk causing long-term variability and flux obscuration in this pulsating RV Tau star.

## Contribution

It provides the first detailed analysis linking long-term periodicity and flux variations in DF Cyg to binarity and disk obscuration, supported by precise Kepler observations and Gaia data.

## Key findings

- Identified a long-term cycle of approximately 795 days.
- Detected infrared excess indicating a circumstellar disk.
- Suggested flux variations are caused by disk occultation.

## 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.