Orbits Of Post-AGB Binaries With Dusty Discs

Details Orbits Of Post-AGB Binaries With Dusty Discs Orbits Of Post-AGB Binaries With Dusty Discs

Aug 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007iaus..240..391l&link_type=abstract

Binary Stars as Critical Tools and Tests in Contemporary Astrophysics, International Astronomical Union. Symposium no. 240, he

Astronomy and Astrophysics

Astrophysics

Scientific paper

Introduction. Post-AGB stars with RV Tauri-like spectral energy distributions have been studied to establish a connection between binarity and this type of SED. Methods. Stars were selected from those with the appropriate IRAS colours by their F-type optical spectra and the existence of an infrared excess at K and L. These stars are hotter than classical RV Tauri stars and have pulsations of smaller amplitude, making it simpler to disentangle orbital from pulsational radial velocity variations. Radial velocity measurements were made with CORALIE on the Swiss telescope on La Silla, and spectroscopic orbits were obtained for all six stars. Optical photometry from SAAO, the Flemish Mercator Telescope and the ASAS-3 data bank enabled the determination of pulsation periods for these stars. Results. These six stars have orbits with periods of several hundred days; several have significantly non-zero eccentricities. The dust may be contained in a circum-binary disc, which in the past has acted as the site where refractory elements have been sequestered in dust grains, leaving depleted gas, which has been returned to the star and has modified the elemental abundances in the photosphere. Discussion. These observations confirm the close relation between binarity and the presence of a Keplerian dusty disc. The mode of formation of the disc is still poorly understood: dust is commonly observed in the form of an expanding shell about AGB stars, but the presence of a companion provides the possibility of it forming a disk. The non-zero eccentricities of several of the orbits are surprising, as circularising interactions might have been expected when the primary star was on the AGB and may have filled its Roche lobe.

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