Amplitude variations of modulated RV Tauri stars support the dust obscuration model of the RVb phenomenon

Abstract

Context. RV Tauri-type variables are pulsating post-AGB stars that evolve rapidly through the instability strip after leaving the Asymptotic Giant Branch. Their light variability is dominated by radial pulsations. Members of the RVb subclass show an additional variability in form of a long-term modulation of the mean brightness, for which the most popular theories all assume binarity and some kind of circumstellar dust. Here we address if the amplitude modulations are consistent with the dust obscuration model. Aims. We measure and interpret the overall changes of the mean amplitude of the pulsations along the RVb variability. Methods. We compiled long-term photometric data for RVb-type stars, including visual observations of the American Association of Variable Star Observers, ground-based CCD photometry from the OGLE and ASAS projects and ultra-precise space photometry of one star, DF Cygni, from the Kepler space telescope. After converting all the observations to flux units, we measure the cycle-to-cycle variations of the pulsation amplitude and correlate them to the actual mean fluxes. Results. We find a surprisingly uniform correlation between the pulsation amplitude and the mean flux: they scale linearly with each other for a wide range of fluxes and amplitudes. It means that the pulsation amplitude actually remains constant when measured relative to the system flux level. The apparent amplitude decrease in the faint states has long been noted in the literature but it was always claimed to be difficult to explain with the actual models of the RVb phenomenon. Here we show that when fluxes are used instead of magnitudes, the amplitude attenuation is naturally explained by periodic obscuration from a large opaque screen, one most likely corresponding to a circumbinary dusty disk that surrounds the whole system.

arXiv comment8 pages, 6 figures, accepted for publication in A&A

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• TESS Data for Asteroseismology (T'DA) Stellar Variability Classification Pipeline: Set-Up and Application to the Kepler Q9 Data
• The spectroscopic binaries RV Tauri and DF Cygni
• Resolved imaging of the AR Puppis circumbinary disk
• Diversity of dynamical phenomena in type II Cepheids of the OGLE collection
• Physical properties of galactic RV Tauri stars from Gaia DR2 data
• Chaotic dynamics in the pulsation of DF Cygni, as observed by Kepler
• 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
• SPHERE/ZIMPOL insights into discs around evolved stars: arcs, asymmetries and dust properties
• Circumbinary disc interactions and stochastic dust obscuration in the post-asymptotic-giant-branch binary HD 213985
• Decoding the RVb Enigma of DF Cyg: Pulsations, Circumstellar Disks, and Post-RGB Evolution Revealed by Multi-Wavelength Observations