post-AGB Stars Research Articles

Elasticity of a Sintered Contact between Dust Grains

Abstract The collisional growth of dust grains in a protoplanetary nebula is impacted by sintering because this increases the elasticity of the neck between dust grains. The high elasticity of a neck can lead to bouncing and not sticking of dust aggregates. This hinders the formation of planetesimals, and dust aggregates accumulate at a particular location in a protoplanetary nebula. Following sintering, the key parameter is the elasticity of a neck between dust grains. This study determined elasticity using numerical simulation and laboratory experiments. Elasticity was substantially smaller than that of a previous model, in which it was assumed that only the neck between grains was deformed. However, the results of this study demonstrated a change is negligible in the sticking efficiency of sintered dust aggregates compared to the results in a previous study.

Keplerian disks and outflows in post-AGB stars: AC Herculis, 89 Herculis, IRAS 19125+0343, and R Scuti

Context. There is a class of binary post-AGB stars with a remarkable near-infrared excess that are surrounded by Keplerian or quasi-Keplerian disks and extended outflows composed of gas escaping from the disk. The Keplerian dynamics had been well identified in four cases, namely the Red Rectangle, AC Her, IW Car, and IRAS 08544−4431. In these objects, the mass of the outflow represents ~10% of the nebular mass, the disk being the dominant component of the nebula. Aims. We aim to study the presence of rotating disks in sources of the same class in which the outflow seems to be the dominant component. Methods. We present interferometric NOEMA maps of 12CO and 13CO J = 2–1 in 89 Her and 12CO J = 2–1 in AC Her, IRAS 19125+0343, and R Sct. Several properties of the nebula are obtained from the data and model fitting, including the structure, density, and temperature distributions, as well as the dynamics. We also discuss the uncertainties on the derived values. Results. The presence of an expanding component in AC Her is doubtful, but thanks to new maps and models, we estimate an upper limit to the mass of this outflow of ≲3 × 10−5 M⊙, that is, the mass of the outflow is ≲5% of the total nebular mass. For 89 Her, we find a total nebular mass of 1.4 × 10−2 M⊙, of which ~50% comes from an hourglass-shaped extended outflow. In the case of IRAS 19125+0343, the nebular mass is 1.1 × 10−2 M⊙, where the outflow contributes ~70% of the total mass. The nebular mass of R Sct is 3.2 × 10−2 M⊙, of which ~75% corresponds to a very extended outflow that surrounds the disk. Conclusions. Our results for IRAS 19125+0343 and R Sct lead us to introduce a new subclass of binary post-AGB stars, for which the outflow is the dominant component of the nebula. Moreover, the outflow mass fraction found in AC Her is smaller than those found in other disk-dominated binary post-AGB stars. 89 Her would represent an intermediate case between both subclasses.

Astrometric Membership Tests for the Zinn–Newell–Gibson UV-bright Stars in Galactic Globular Clusters

Abstract In 1972, Zinn, Newell, & Gibson (ZNG) published a list of 156 candidate UV-bright stars they had found in 27 Galactic globular clusters (GCs), based on photographs in the U and V bands. UV-bright stars lie above the horizontal branch (HB) and blueward of the asymptotic giant branch (AGB) and red giant branch in the clusters’ color–magnitude diagrams. They are in rapid evolutionary phases—if they are members and not unrelated bright foreground stars. The ZNG list has inspired numerous follow-up studies, aimed at understanding late stages of stellar evolution. However, the ZNG candidates were presented only in finding charts, and celestial coordinates were not given. Using my own collection of CCD frames in u and V, I have identified all of the ZNG objects, and have assembled their coordinates, parallaxes, and proper motions from the recent Gaia Early Data Release 3 (EDR3). Based on the Gaia astrometry, I have determined which objects are probable cluster members (45% of the sample). For the members, using photometry from EDR3, I have assigned the stars to various evolutionary stages, including luminous post-AGB stars, and stars above the HB. I point out several ZNG stars of special interest that have still, to my knowledge, never been studied in detail. This study is an adjunct to a forthcoming survey of the Galactic GCs in the uBVI photometric system, designed for detection of low-gravity stars with large Balmer discontinuities.

Multiwavelength Observations of the RV Tauri Variable System U Monocerotis: Long-term Variability Phenomena That Can Be Explained by Binary Interactions with a Circumbinary Disk

Abstract We present an X-ray through submillimeter observations of the classical RV Tauri (RVb-type) variable U Mon, a post-asymptotic giant branch (AGB) binary with a circumbinary disk (CBD). Our SMA observations indicate a CBD diameter of ≲550 au. Our XMM-Newton observations make U Mon the first RV Tauri variable detected in X-rays. The X-ray emission is characteristic of a hot plasma (∼10 MK), with L X =5 × 1030 erg s−1, and we consider its possible origin from U Mon, its companion, and/or binary system interactions. Combining DASCH and AAVSO data, we extend the time-series photometric baseline back to the late 1880s and find evidence that U Mon has secular changes that appear to recur on a timescale of ∼60 yr, possibly caused by a feature in the CBD. From literature radial velocities we find that the binary companion is a ∼2 M ⊙ A-type main-sequence star. The orientation of the binary’s orbit lies along our line of sight (ω = 95°), such that apastron corresponds to photometric RVb minima, consistent with the post-AGB star becoming obscured by the near side of the CBD. In addition, we find the size of the inner-CBD hole (∼4.5–9 au) to be comparable to the binary separation, implying that one or both stars may interact with the CBD at apastron. The obscuration of the post-AGB star implicates the companion as the likely source of the enhanced Hα observed at RVb minima and of the X-ray emission that may arise from accreted material.

Molecular remnant of Nova 1670 (CK Vulpeculae)

CK Vul is the remnant of an energetic eruption known as Nova 1670 that is thought to be caused by a stellar merger. The remnant is composed of (1) a large hourglass nebula of recombining gas (of 71′′ in size), very similar to some classical planetary and pre-planetary nebulae (PPNe), and (2) a much smaller and cooler inner remnant that is prominent in millimeter-wave emission from molecules. We investigate the three-dimensional spatio-kinematic structure of both components. Our analysis of the hourglass structure yields a revised distance to the object of >2.6 kpc, at least 3.7 times greater than previously assumed. At this distance, the stellar remnant has a bolometric luminosity >12 L⊙ and is surrounded by molecular material with a total mass >0.8 M⊙ (the latter value has a large systematic uncertainty). We also analyzed the architecture of the inner molecular nebula using ALMA observations of rotational emission lines obtained at subarcsecond resolution. We find that the distribution of neutral and ionized gas in the lobes can be reproduced by several nested and incomplete shells or jets with different velocity fields and varying orientations. The analysis indicates that the molecular remnant was created in several ejection episodes, possibly involving an interacting binary system. We calculated the linear momentum (≈1040 g cm s−1) and kinetic energy (≈1047 erg) of the CK Vul outflows and find values that are within the limits typical for classical PPNe. Given the similarities of the CK Vul outflows to PPNe, we suggest there may be CK Vul analogs among wrongly classified PPNe with low intrinsic luminosities, especially among PPNe with post-red-giant-branch central stars.

Jet parameters for a diverse sample of jet-launching post-AGB binaries

ABSTRACT Jets are a commonly observed phenomenon in post-asymptotic giant branch (post-AGB) binaries. Due to the orbital motion of the binary, the jet causes variable absorption in the Balmer profiles. In previous work, we have developed spatio-kinematic and radiative transfer models to reproduce the observed Balmer line variability and derive the spatio-kinematic structure of the jet and its mass-loss rate. Here, we apply our jet model to five post-AGB binaries with distinct H α line variability and diverse orbital properties. Our models fit the H α line variations very well. We estimate jet mass-loss rates between $10^{-8}\,$M$_\odot \, \text{yr}^{-1}$ and $10^{-4}\,$ M$_\odot \, \text{yr}^{-1}$, from which we deduce accretion rates on to the companion between $10^{-7}\,$ M$_\odot \, \text{yr}^{-1}$ and $10^{-3}\,$ M$_\odot \, \text{yr}^{-1}$. These accretion rates are somewhat higher than can be comfortably explained with reasonable sources of accretion, but we argue that the circumbinary disc in these systems is most likely the source feeding the accretion, although accretion from the post-AGB star cannot be ruled out. The diversity of the variability in the five objects is due to their wide ejection cones combined with a range of viewing angles, rather than inherent differences between the objects. The nature of the observations does not let us easily distinguish which jet launching model (stellar jet, disc wind, or X-wind) should be favoured. In conclusion, we show that our jet model includes the physical parameters to successfully reproduce the H α line variations and retrieve the structure and mass-loss rates of the jet for all five objects that are representative of the diverse sample of Galactic post-AGB binaries.

MACROCHONDRULES IN SOME CHONDRITES: 2. GENETIC ASPECTS

An electron microscopic and microprobe study of the macrochondrules from the chondrites Allende CV3, Krymka LL3.1, Saratov L4, "Velyka Balka" L4-5 and Château-Renard L6 allow to clear some aspects of their formation. The main of them are following: 1) The texture and mineral composition of the majority of the macrochondrules does not differ from those of ordinary chondrules, thus indicating a similarity in formation conditions, 2) It is shown for the first time that the SiO2/MgO and FeO/(FeO+MgO) ratios of the fine-grained rims of the macrochondrules and one`s of chondrules in the Krymka meteorite are well correlated. This indicates to their coexistence in the same dusty environment of the protoplanetary nebula, 3) The unique characteristics of the two firstly found macrochondrules allowed us to detail conditions of their formation and existence in the protoplanetary nebula. A polyzonal graphite-bearing macrochondrule from the Krymka meteorite formed by accretional growth in a mineralogically variable dusty environment. Its complex evolutional history involved remelting and selective evaporation of the macrochondrule surface layer, accretion of an environmental dust, late formation of a fine-grained rim and migratory intrusion of an organic protomaterial and finally a metamorphic event that produced graphite. The melted surface of a macrochondrule from the Allende chondrite was notably affected by high-energy processes and instantaneous cooling in the protoplanetary nebula, 4) The rarity of macrochondrules in chondrites compared to typical chondrules is probably related to their priority destruction. This was caused by permanent movement and collision between them and other solid objects in the pre-agglomeration period of meteorite development.

Macrochondrules in Some Chondrites: 1. Structural-Mineralogical Characteristics

The results of structural, mineralogical and chemical study of rare structural units of chondrites, macrochondrules and their fragments, found in five chondrites of different chemical groups and petrological types (Allende CV3, Krymka LL3.1, Saratov L4, "Velyka Balka" L4-5, Château-Renard L6), are given. Most of them are generally similar to ordinary chondrules and previously studied macrochondrules. They have a radial and porphyritic texture, consist of olivine and pyroxene, and are covered by a silicate rim, which is fine-grained in the macrochondrules of unequilibrated chondrites and coarse-grained in equilibrated ones. Only two macrochondrules among studied one’s are extraordinary and indicate specific conditions for their formation in the protoplanetary nebula. The first one, separated directly from the Allende chondrite, is characterized by the presence of a thin amorphous shell with a porous structure and with unambiguous sculpture features of instantaneous melting and solidification of its surface silicate layer. The second one, studied in a polished section of the Krymka meteorite, is characterized by a zonal structure and the presence of graphite grains and possibly bitumen inclusions. According to the SiO2/MgO ratio, its fine-grained silicate rim with rare graphite crystals and possibly bitumen inclusions corresponds to the fine-grained rims of ordinary chondrules, but is different from the carbonaceous material of meteorites.

The Nature and Origins of Sub-Neptune Size Planets.

Planets intermediate in size between the Earth and Neptune, and orbiting closer to their host stars than Mercury does the Sun, are the most common type of planet revealed by exoplanet surveys over the last quarter century. Results from NASA's Kepler mission have revealed a bimodality in the radius distribution of these objects, with a relative underabundance of planets between 1.5 and 2.0 R⊕. This bimodality suggests that sub‐Neptunes are mostly rocky planets that were born with primary atmospheres a few percent by mass accreted from the protoplanetary nebula. Planets above the radius gap were able to retain their atmospheres (“gas‐rich super‐Earths”), while planets below the radius gap lost their atmospheres and are stripped cores (“true super‐Earths”). The mechanism that drives atmospheric loss for these planets remains an outstanding question, with photoevaporation and core‐powered mass loss being the prime candidates. As with the mass‐loss mechanism, there are two contenders for the origins of the solids in sub‐Neptune planets: the migration model involves the growth and migration of embryos from beyond the ice line, while the drift model involves inward‐drifting pebbles that coagulate to form planets close‐in. Atmospheric studies have the potential to break degeneracies in interior structure models and place additional constraints on the origins of these planets. However, most atmospheric characterization efforts have been confounded by aerosols. Observations with upcoming facilities are expected to finally reveal the atmospheric compositions of these worlds, which are arguably the first fundamentally new type of planetary object identified from the study of exoplanets.

Post-AGB stars as tracers of the origin of elements in the universe

The chemical evolution of galaxies is governed by the chemical yields from stars, especially from Asymptotic Giant Branch (AGB) stars. This underlines the importance of understanding how AGB stars produce their elements by obtaining accurate stellar nucleosynthetic yields. Although AGB nucleosynthesis has general validity, critical uncertainties (such as the treatment of convective-driven mixing processes and mass loss) exist in current stellar models. Observations from post-Asymptotic Giant Branch (post-AGB) stars serve as excellent tools to quantify the strongest discrepancies, and eliminate crucial uncertainties that hamper stellar modelling. Our recent studies of post-AGB stars have shown an intriguing chemical diversity that ranges from stars that are extremely enriched in carbon and s-process elements to the discovery of the first post-AGB star with no traces of carbon nor s-process elements. Additionally, AGB nucleosynthesis is significantly affected by a binary companion. These results reflect the complexity that surrounds the element production in AGB stars. In this review, I will briefly present the intriguing chemical diversity observed in post-AGB stars and its implications on element/isotope production in AGB stars and stellar nucleosynthetic yields.

Recent advances in RV Tauri stars

The availability of multi-wavelength observations and parallaxes from the space missions and very comprehensive models of AGB evolution that include the accretion of matter from the circumbinary disc have strongly impacted our understanding of these enigmatic objects. The important developments made in the recent times are summarized here. The revised estimates of luminosities (derived from better-defined Spectral Energy Distributions (SEDs) and new distances from Gaia DR2) further support the opinion that RV Tauri stars contain a mixture of post-AGB stars and post-RGB stars. Their locations in HR diagram also indicate that the instability strip (IS) of RV Tauri stars have a broader extension in the cooler edge than that of classical Cepheids. A new P−L relation has been calibrated for the galactic Cepheids which have a steeper slope than that derived for the Population II Cepheids and RV Tauri stars in Magellanic clouds . The most significant chemical peculiarity exhibited by RV Tauri stars and other post-AGB stars is the selective depletion of refractory elements that correlates with their condensation temperatures. A large range in the size of depletion as well as in the shapes of the depletion curves has been observed. Earlier models to explain this effect were mostly qualitative. Recent investigators model these depletions using evolutionary codes (e.g. MESA) to evolve stars in the post-AGB phase, while including accretion of metal-poor gas from circumbinary disc. These authors model the accretion rate onto a the binary post-AGB star from a viscously evolving disc for a range of initial accretion rates and disc masses. It is reported that large initial accretion rates and disc masses are required to explain the large depletion and saturated depletion curve that could extend the evolution time of post-AGB star. It is also proposed that the unsaturated depletion curve (with a plateau) are likely to be caused by post-RGB stars.

Evolutionary and pulsation properties of Type II Cepheids

We discuss the observed pulsation properties of Type II Cepheids (TIICs) in the Galaxy and in the Magellanic Clouds. We found that period (P) distributions, luminosity amplitudes, and population ratios of the three different sub-groups (BL Herculis [BLH, P < 5 days], W Virginis [WV, 5 ≤ P < 20 days], RV Tauri [RVT, P > 20 days]) are quite similar in different stellar systems, suggesting a common evolutionary channel and a mild dependence on both metallicity and environment. We present a homogeneous theoretical framework based on horizontal branch (HB) evolutionary models, showing that TIICs are mainly old (t ≥ 10 Gyr) low-mass stars. The BLH stars (BLHs) are predicted to be post-early asymptotic giant branch (PEAGB) stars (double shell burning) on the verge of reaching their AGB track (first crossing of the instability strip), while WV stars (WVs) are a mix of PEAGB and post-AGB stars (hydrogen shell burning) moving from the cool to the hot side (second crossing) of the Hertzsprung-Russell Diagram. This suggests that they are a single group of variable stars. The RVT stars (RVTs) are predicted to be a mix of post-AGB stars along their second crossing (short-period tail) and thermally pulsing AGB stars (long-period tail) evolving towards their white dwarf cooling sequence. We also present several sets of synthetic HB models by assuming a bi-modal mass distribution along the HB. Theory suggests, in agreement with observations, that TIIC pulsation properties marginally depend on metallicity. Predicted period distributions and population ratios for BLHs agree quite well with observations, while those for WVs and RVTs are almost a factor of two smaller and higher than observed, respectively. Moreover, the predicted period distributions for WVs peak at periods shorter than observed, while those for RVTs display a long-period tail not supported by observations. We investigate several avenues to explain these differences, but more detailed calculations are required to address these discrepancies.

Molecular remnant of Nova 1670 (CK Vulpeculae)

CK Vul erupted in 1670 and is considered a Galactic stellar-merger candidate. Its remnant, observed 350 yr after the eruption, contains a molecular component of surprisingly rich composition, including polyatomic molecules as complex as methylamine (CH3NH2). We present interferometric line surveys with subarcsec resolution with ALMA and SMA. The observations provide interferometric maps of molecular line emission at frequencies between 88 and 243 GHz that allow imaging spectroscopy of more than 180 transitions of 26 species. We present, classify, and analyze the different morphologies of the emission regions displayed by the molecules. We also perform a non-LTE radiative-transfer analysis of emission of most of the observed species, deriving the kinetic temperatures and column densities in five parts of the molecular nebula. Non-LTE effects are clearly seen in complex species including methanol absorption against the cosmic microwave background. The temperatures are about 17 K in the inner remnant and 14 K in the extended lobes, both higher than excitation temperatures estimated earlier in an LTE approach and based on single-dish spectra. We find total (hydrogen plus helium) densities in the range of 104 − 106 cm−3. The column densities provide rough relative abundance patterns in the remnant which currently are not understood. Attempts to derive elemental abundances within the assumption of a chemical equilibrium give only loose constraints on the CNO elements. That the formation of many of the observed molecules requires a major involvement of circumstellar shocks remains the preferred possibility. The molecular gas could have formed 350 yr ago or more recently. The molecules are well shielded from the interstellar radiation field by the circumstellar dust. Their presence alone indicates that the unobservable central star cannot be a hot object such as a white dwarf. This excludes some of the proposed scenarios on the nature of CK Vul. The general characteristics of the molecular environment of CK Vul derived in this study resemble quite well those of some pre-planetary nebulae and asymptotic giant branch stars, most notably that of OH231.8+4.2.

THE EMISSION-LINE DUSTY OBJECT IRAS 07080+0605, A LESS-EVOLVED EXAMPLE OF THE RED RECTANGLE

The all-sky survey conducted bythe InfraRed Astronomical Satellite (IRAS) in the1980’s discovered many objects with infrared excesseswhose nature has not been explored until recently.IRAS07080+0605 is one of those identified in thevisual spectral range with an early-type star, whichshows the B[e] phenomenon. The object is puzzling,because it exhibits one of the strongest infraredexcesses associated with a star of one of the lowestsurface temperatures (∼8500 K) among objects withthe B[e] phenomenon, an apparent combination ofspectral features of dwarfs and supergiants, andthe absence of a surrounding optical nebula. Ourphotometric and spectroscopic study shows that theobject’s properties are similar to those of the famousRed Rectangle proto-planetary nebula. In this paperwe describe our findings and hypotheses about thenature and evolutionary status of IRAS07080+0605

Nondetection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets

Abstract We present a search for helium in the upper atmospheres of three sub-Neptune-sized planets to investigate the origins of these ubiquitous objects. The detection of helium for a low-density planet would be strong evidence for the presence of a primary atmosphere accreted from the protoplanetary nebula because large amounts of helium are not expected in the secondary atmospheres of rocky planets. We used Keck+NIRSPEC to obtain high-resolution transit spectroscopy of the planets GJ 1214b, GJ 9827d, and HD 97658b around the 10833 Å He triplet feature. We did not detect helium absorption for any of the planets despite achieving a high level of sensitivity. We used the nondetections to set limits on the planets’ thermosphere temperatures and atmospheric loss rates by comparing grids of 1D models to the data. We also performed coupled interior structure and atmospheric loss calculations, which suggest that the bulk atmospheres (winds) of the planets would be at most modestly enhanced (depleted) in helium relative to their primordial composition. Our lack of detections of the helium triplet for GJ 1214b and GJ 9827d is highly inconsistent with the predictions of models for the present-day mass loss on these planets. Higher signal-to-noise data would be needed to detect the helium feature predicted for HD 97658b. We identify uncertainties in the extreme-ultraviolet fluxes of the host stars and the lack of detailed mass-loss models specifically for cool and metal-enhanced atmospheres as the main limitations to the interpretation of our results. Ultimately, our results suggest that the upper atmospheres of sub-Neptune planets are fundamentally different from those of gas giant planets.

Pre-planetary nebulae: a context for principles, progress, and questions on how binaries and magnetic fields produce jets

AbstractAstrophysical outflows treated initially as spherically symmetric often show evidence for asymmetry once seen at higher resolution. The preponderance of aspherical and multipolar planetary nebulae (PN) and pre-planetary nebulae (PPN) was evident after many observations from the Hubble Space Telescope. Binary interactions have long been thought to be essential for shaping asymmetric PN/PPN, but how? PPN are the more kinematically demanding of the two, and warrant particular focus. I address how progress from observation and theory suggests two broad classes of accretion driven PPN jets: one for wider binaries (PPN-W) where the companion is outside the outer radius of the giant and accretes via Roche lobe overflow, and the other which occurs in the later stages of CE for close binaries (PPN-C). The physics within these scenarios connects to progress and open questions about the role and origin of magnetic fields in the engines and in astrophysical jets more generally.

3D hydrodynamical survey of the impact of a companion on the morphology and dynamics of AGB outflows

AbstractWith the use of high-resolution ALMA observations, complex structures that resemble those observed in post-AGB stars and planetary nebulae are detected in the circumstellar envelopes of low-mass evolved stars. These deviations from spherical symmetry are believed to be caused primarily by the interaction with a companion star or planet. With the use of three-dimensional hydrodynamic simulations, we study the impact of a binary companion on the wind morphology and dynamics of an AGB outflow. We classifiy the wind structures and morphology that form in these simulations with the use of a classification parameter, constructed with characteristic parameters of the binary configuration. Finally we conclude that the companion alters the wind expansion velocity through the slingshot mechanism, if it is massive enough.

Tracing the role of AGB stars in the Galactic Fluorine budget

AbstractThe cosmic origin of fluorine is still under debate. Asymptotic giant branch (AGB) stars are among the few suggested candidates to efficiently synthesis F in our Galaxy, however their relative contribution is not clear. In this paper, we briefly review the theoretical studies from stellar yield models of the F synthesis and chemical equilibrium models of the F-containing molecules in the outflow around AGB stars. Previous detections of the F-bearing species towards AGB and post-AGB stars are also highlighted. We suggest that high-resolution ALMA observations of the AlF, one of the two main carriers of F in the outflow of AGB stars, can provide a reliable tracer of the F-budget in AGB stars. This will be helpful to quantify the role of AGB stars in the Galactic F budget.

Gaia DR2 data and the evolutionary status of eight high-velocity hot post-AGB candidates

Abstract From Gaia DR2 data of eight high-velocity hot post-AGB candidates, LS 3593, LSE 148, LS 5107, HD 172324, HD 214539, LS IV −12 111, LS III +52 24, and LS 3099, we found that six of them have accurate parallaxes which made it possible to derive their distances, absolute visual magnitudes (MV) and luminosity (log L/L⊙). All the stars except LS 5107 have an accurate effective temperature (Teff) in the literature. Some of these stars are metal poor, and some of them do not have circumstellar dust shells. In the past, the distances of some stars were estimated to be 6 kpc, which we find to be incorrect. The accurate Gaia DR2 parallaxes show that they are relatively nearby, post-AGB stars. When compared with post-AGB evolutionary tracks we find their initial masses to be in the range 1 M⊙ to 2 M⊙. We find the luminosity of LSE 148 to be significantly lower than that of post-AGB stars, suggesting that this is a post-horizontal-branch star or post-early-AGB star. LS 3593 and LS 5107 are new high-velocity hot post-AGB stars from Gaia DR2.

Disc-binary interactions in depleted post-AGB binaries

Binary post-asymptotic giant branch (post-AGB) stars have orbital periods in the range of 100−2500 days in eccentric orbits. They are surrounded by circumbinary dusty discs. They are the immediate result of unconstrained binary interaction processes. Their observed orbital properties do not correspond to model predictions: Neither the periods nor the high eccentricities are expected. Indeed, many orbits are eccentric despite the strong tidal interaction when the primary had giant dimensions on the red giant branch and AGB. Our goal is to investigate if interactions between a binary and its circumbinary disc during the post-AGB phase can result in their eccentric orbits, while simultaneously explaining the chemical anomaly known as depletion. For this paper, we selected three binaries (EP Lyr, RU Cen, HD 46703) with well-constrained orbits, luminosities, and chemical abundances. We used theMESAcode to evolve post-AGB models, while including the accretion of metal-poor gas. This allows us to constrain the evolution of the stars and study the impact of circumbinary discs on the orbital properties of the models. We investigate the effect of torques produced by gas inside the binary cavity and the effect of Lindblad resonances on the orbit, while also including the tidal interaction following the equilibrium tide model. We find that none of our models are able to explain the high orbital eccentricities of the binaries in our sample. The accretion torque does not significantly impact the binary orbit, while Lindblad resonances can pump the eccentricity up to onlye ≈ 0.2. At higher eccentricities, the tidal interaction becomes too strong, so the high observed eccentricities cannot be reproduced. However, even if we assume tides to be ineffective, the eccentricities in our models do not exceed ≈0.25. Finally, the orbit of RU Cen is too wide to reproduce with disc-binary interactions by starting from a circular orbit. We conclude that either our knowledge of disc-binary interactions is still incomplete, or the binaries must have left their phase of strong interaction in an eccentric orbit.