Abstract
We present the first near-IR milli-arcsecond-scale image of a post-AGB binary that is surrounded by hot circumbinary dust. A very rich interferometric data set in six spectral channels was acquired of IRAS08544-4431 with the new RAPID camera on the PIONIER beam combiner at the Very Large Telescope Interferometer (VLTI). A broadband image in the \textit{H} band was reconstructed by combining the data of all spectral channels using the SPARCO method. We spatially separate all the building blocks of the IRAS08544-4431 system in our milliarcsecond-resolution image. Our dissection reveals a dust sublimation front that is strikingly similar to that expected in early-stage protoplanetary disks, as well as an unexpected flux signal of $\sim$4\% from the secondary star. The energy output from this companion indicates the presence of a compact circum-companion accretion disk, which is likely the origin of the fast outflow detected in H$\alpha$. Our image provides the most detailed view into the heart of a dusty circumstellar disk to date. Our results demonstrate that binary evolution processes and circumstellar disk evolution can be studied in detail in space and over time.
Highlights
Binary interactions play a fundamental role in many poorly understood stellar phenomena
The energy output from this companion indicates the presence of a compact circum-companion accretion disk, which is likely the origin of the fast outflow detected in Hα
Our results provide the first direct view into the central region of an evolved binary surrounded by a circumbinary disk
Summary
Binary interactions play a fundamental role in many poorly understood stellar phenomena. One peculiar class of objects concerns the post-asymptotic giant branch (post-AGB) stars in SB1 binary systems, which have hot as well as cold circumstellar dust and gas (van Winckel 2003). The presence of a near-IR excess in the spectral energy distribution (SED) of a post-AGB star correlates well with the central star being part of a ∼1−2 au-wide binary system (e.g. van Winckel et al 2009). Such evolved binaries are common in the Galaxy (de Ruyter et al 2006) and recent studies show that about 30% of all optically bright postAGB stars have this typical SED (Kamath et al 2015). We present the first near-IR milliarcsecond-scale image that fully dissects the inner object into its constituent components
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