Issue |
A&A
Volume 620, December 2018
|
|
---|---|---|
Article Number | A85 | |
Number of page(s) | 21 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/201833816 | |
Published online | 04 December 2018 |
Orbital properties of binary post-AGB stars⋆
1 Instituut voor Sterrenkunde (IvS), KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
e-mail: glennmichael.oomen@kuleuven.be
2 Department of Astrophysics/IMAPP, Radboud University, PO Box 9010 6500 GL Nijmegen, The Netherlands
3 Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, ULB, Campus Plaine C.P. 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium
4 Department of Physics & Astronomy, Macquarie University, Sydney, NSW, 2109
Australia
5 Astronomy, Astrophysics and Astrophotonics Research Centre, Macquarie University, Sydney, NSW, 2109
Australia
Received:
10
July
2018
Accepted:
3
October
2018
Binary post-asymptotic giant branch (post-AGB) stars are thought to be the products of a strong but poorly understood interaction during the AGB phase. The aim of this contribution is to update the orbital elements of a sample of galactic post-AGB binaries observed in a long-term radial-velocity monitoring campaign by analysing these systems in a homogeneous way. Radial velocities are computed from high signal-to-noise spectra via a cross-correlation method. The radial-velocity curves are fitted by using both a least-squares algorithm and a Nelder–Mead simplex algorithm. We use a Monte Carlo method to compute uncertainties on the orbital elements. The resulting mass functions are used to derive a companion mass distribution by optimising the predicted to the observed cumulative mass-function distributions, after correcting for observational bias. As a result, we derive and update orbital elements for 33 galactic post-AGB binaries, among which 3 are new orbits. The orbital periods of the systems range from 100 to about 3000 days. Over 70% (23 out of 33) of our binaries have significant non-zero eccentricities ranging over all periods. Their orbits are non-circular even though the Roche-lobe radii are smaller than the maximum size of a typical AGB star and tidal circularisation should have been strong when the objects were on the AGB. We derive a distribution of companion masses that is peaked around 1.09 M⊙ with a standard deviation of 0.62 M⊙. The large spread in companion masses highlights the diversity of post-AGB binary systems. Post-AGB binaries are often chemically peculiar, showing in their photospheres the result of an accretion process of circumstellar gas devoid of refractory elements. We find that only post-AGB stars with high effective temperatures (> 5500 K) in wide orbits are depleted in refractory elements, suggesting that re-accretion of material from a circumbinary disc is an ongoing process. It appears, however, that depletion is inefficient for the closest orbits irrespective of the actual surface temperature.
Key words: stars: AGB and post-AGB / binaries: spectroscopic / circumstellar matter
Radial velocity data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A85
© ESO 2018
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.