99 research outputs found
An interferometric study of the post-AGB binary 89 Herculis I Spatially resolving the continuum circumstellar environment at optical and near-IR wavelengths with the VLTI, NPOI, IOTA, PTI, and the CHARA Array
Binary post-AGB stars are interesting laboratories to study both the
evolution of binaries as well as the structure of circumstellar disks. A
multiwavelength high angular resolution study of the prototypical object 89
Herculis is performed with the aim of identifying and locating the different
emission components seen in the SED. A large interferometric data set,
collected over the past decade and covering optical and near-IR wavelengths, is
analyzed with simple geometric models. Combining the interferometric
constraints with the photometry and the optical spectra, we reassess the energy
budget of the post-AGB star and its circumstellar environment. We report the
first (direct) detection of a large (35-40%) optical circumstellar flux
contribution and spatially resolve its emission region. Given this large amount
of reprocessed and/or redistributed optical light, the fitted size of the
emission region is rather compact and fits with(in) the inner rim of the
circumbinary dust disk. This rim dominates our K band data through thermal
emission and is rather compact, emitting significantly already at a radius of
twice the orbital separation. We interpret the circumstellar optical flux as
due to a scattering process, with the scatterers located in the extremely
puffed-up inner rim of the disk and possibly also in a bipolar outflow seen
pole-on. A non-LTE gaseous origin in an inner disk cannot be excluded but is
considered highly unlikely. This direct detection of a significant amount of
circumbinary light at optical wavelengths poses several significant questions
regarding our understanding of both post-AGB binaries and the physics in their
circumbinary disks. Although the identification of the source of
emission/scattering remains inconclusive without further study on this and
similar objects, the implications are manifold.Comment: Accepted for publication in A&A, 16 pages, 15 figure
- …