Orbital properties of binary post-AGB stars

Glenn Michael Oomen, Hans Van Winckel, Onno Pols, Gijs Nelemans, Ana Escorza, Rajeev Manick, Devika Kamath, Christoffel Waelkens

Research output: Contribution to journalArticleResearchpeer-review

Abstract

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 Mâ with a standard deviation of 0.62 Mâ. 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.

LanguageEnglish
Article numberA85
Pages1-21
Number of pages21
JournalAstronomy and Astrophysics
Volume620
DOIs
Publication statusPublished - 4 Dec 2018

Fingerprint

asymptotic giant branch stars
orbital elements
radial velocity
orbits
orbitals
refractories
accretion
noise spectra
photosphere
mass distribution
eccentricity
lobes
cross correlation
surface temperature
Monte Carlo method
standard deviation
depletion
distribution functions
radii
curves

Keywords

  • Binaries: spectroscopic
  • Circumstellar matter
  • Stars: AGB and post-AGB

Cite this

Oomen, G. M., Van Winckel, H., Pols, O., Nelemans, G., Escorza, A., Manick, R., ... Waelkens, C. (2018). Orbital properties of binary post-AGB stars. Astronomy and Astrophysics, 620, 1-21. [A85]. https://doi.org/10.1051/0004-6361/201833816
Oomen, Glenn Michael ; Van Winckel, Hans ; Pols, Onno ; Nelemans, Gijs ; Escorza, Ana ; Manick, Rajeev ; Kamath, Devika ; Waelkens, Christoffel. / Orbital properties of binary post-AGB stars. In: Astronomy and Astrophysics. 2018 ; Vol. 620. pp. 1-21.
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Oomen, GM, Van Winckel, H, Pols, O, Nelemans, G, Escorza, A, Manick, R, Kamath, D & Waelkens, C 2018, 'Orbital properties of binary post-AGB stars', Astronomy and Astrophysics, vol. 620, A85, pp. 1-21. https://doi.org/10.1051/0004-6361/201833816

Orbital properties of binary post-AGB stars. / Oomen, Glenn Michael; Van Winckel, Hans; Pols, Onno; Nelemans, Gijs; Escorza, Ana; Manick, Rajeev; Kamath, Devika; Waelkens, Christoffel.

In: Astronomy and Astrophysics, Vol. 620, A85, 04.12.2018, p. 1-21.

Research output: Contribution to journalArticleResearchpeer-review

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AU - Oomen, Glenn Michael

AU - Van Winckel, Hans

AU - Pols, Onno

AU - Nelemans, Gijs

AU - Escorza, Ana

AU - Manick, Rajeev

AU - Kamath, Devika

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AB - 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 Mâ with a standard deviation of 0.62 Mâ. 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.

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Oomen GM, Van Winckel H, Pols O, Nelemans G, Escorza A, Manick R et al. Orbital properties of binary post-AGB stars. Astronomy and Astrophysics. 2018 Dec 4;620:1-21. A85. https://doi.org/10.1051/0004-6361/201833816