arXiv subjects

Toon De Prins

Publications and source records attributed to Toon De Prins.

5 recordsLinked to original sources

arXiv2026

VLTI/PIONIER imaging of post-AGB binaries. An INSPIRING hunt for inner rim substructures in circumbinary discs

We image the detailed inner rim morphology for a sample of post-AGB circumbinary discs observed using NIR interferometry. At resolutions down to ~1-2 mas (corresponding to ~1-10 AU), we aim to reveal potential substructures that may trace perturbations from the binary or embedded substellar companions, or that arise from hydrodynamical instabilities. We developed an image reconstruction workflow using the SPARCO approach together with the ORGANIC reconstruction algorithm. This was applied to VLTI/PIONIER data of eight diverse post-AGB binaries, providing high-fidelity images of dust continuum emission at the inner rim. Extensive tests were applied to assess the robustness of the recovered image features. The dusty disc rim is well-resolved for all targets. Only one of the images can be fully accounted for by simple radiative transfer effects due to disc inclination, while in several others indications of potential substructures are detected. Strikingly, four exhibit robust azimuthal brightness enhancements at locations not expected from inclination effects alone. These can indicate strong radiative or dynamical responses to the binary, or vortices formed via hydrodynamical instabilities. One target displays an even more puzzling morphology, showing a single large-scale outer flux arc and several small-scale arcs closer to the binary, possibly revealing accretion streams onto the binary, a misaligned innermost disc, or a spiral feature located in the disc or in an outflow. This work presents the first homogeneous interferometric imaging survey of the inner regions of post-AGB circumbinary discs, enabling direct comparison of inner rim morphologies across a representative sample. The inner disc regions are highly diverse and dynamic, harbouring a significant amount of substructure candidates. Multi-wavelength and time-series imaging will be essential in uncovering their physical origins.

astro-ph.SR↗

arXiv2026

Bridging stellar evolution and planet formation: from birth, to survivors of the fittest, to the second generation of planets

Stars and planets form, live, and evolve in unison. Throughout the life of a star, dusty circumstellar discs and stellar outflows influence the further evolution of both the star(s) and their orbiting planet(s). Planet-forming discs, winds of red giant branch (RGB) or asymptotic giant branch (AGB) stars, and post-RGB/post-AGB discs are examples of such host environments where dust physics plays a key role. The physical processes that occur during each of these stages establishes how the Solar System as well as exoplanetary systems were formed, are evolving, and will eventually die. This White Paper aims to bridge the fields of stellar evolution and planet formation by peering into the dust kinematics and macrostructure formation, and its effect on planet-host interaction, in dusty environments from stellar birth to death. Near-future advancements in the 2030s will enable the detection, orbital monitoring and atmospheric/mineralogical characterisation of close-in (proto)planets across diverse stages of stellar evolution. To take full advantage of these developments by the 2040s, we should develop the capabilities required to image the varied dusty environments in which planets are entrained over their lifetime. This will enable extensive testing of current theoretical understandings - from the micro-scales of dust assembly to the deeply interlinked macro-scales of planet-host interactions - across diverse settings often too small, distant, and faint to be resolved in the next decade, simultaneously providing valuable constraints on the two-way interplay of dusty host environments and planetary formation/evolution.

astro-ph.IM↗

arXiv2025

SPHERE/ZIMPOL insights into discs around evolved stars: arcs, asymmetries and dust properties

Second-generation circumbinary discs around evolved binary stars, such as post-Asymptotic Giant Branch (post-AGB) binaries, provide insights into poorly understood mechanisms of dust processing and disc evolution across diverse stellar environments. We present a multi-wavelength polarimetric survey of five evolved binary systems - AR Pup, HR 4049, HR 4226, U Mon, and V709 Car - using the Very Large Telescope SPHERE/ZIMPOL instrument. Post-AGB discs show significant polarimetric brightness at optical and near-IR wavelengths, often exceeding 1% of the system's total intensity. We also measured a maximum fractional polarisation of the scattered light for AR Pup of ~0.7 in the V-band and ~0.55 in the I-band. To investigate wavelength-dependent polarisation, we combine the SPHERE/ZIMPOL dataset with results from previous SPHERE/IRDIS studies. This analysis reveals that post-AGB discs exhibit a grey to blue polarimetric colour in the optical and near-IR. Along with high fractional polarisation of the scattered light and polarised intensity distribution, these findings are consistent with a surface dust composition dominated by porous aggregates, reinforcing independent observational evidence for such grains in post-AGB circumbinary discs. We also find evidence of diverse disc geometries within the post-AGB sample, including arcs, asymmetries and significant variations in disc size across optical and near-IR wavelengths for some systems (U Mon, V709 Car). On comparing post-AGB discs to circumstellar environments around AGB stars and YSOs, we found that post-AGB systems exhibit a higher degree of polarisation than single AGB stars and are comparable to the brightest protoplanetary discs around YSOs.

astro-ph.SR↗

arXiv2024

Jet formation in post-AGB binaries: Confronting cold magnetohydrodynamic disc wind wind models with observations

Aims: We consider cold self-similar magnetohydrodynamic (MHD) disc wind solutions to describe jets that are launched from the circumcompanion accretion discs in post-AGB binaries. Resulting predictions are matched to observations for five different post-AGB binaries. This both tests the physical validity of the MHD disc wind paradigm and reveals the accretion disc properties. Results: Many of the time-series' properties are reproduced well by the models, though systematic mismatches, such as overestimated rotation, remain. Four targets imply accretion discs that reach close to the secondary's stellar surface, while one is fitted with an unrealistically large inner radius of about 20 stellar radii. Some fits imply inner disc temperatures over 10 000 K, seemingly discrepant with a previous observational estimate from H band interferometry. This estimate is, however, shown to be biased. Fitted mass-accretion rates range from about 10^-6 to 10^-3 solar masses per year. Relative to the jets launched from young stellar objects (YSOs), all targets prefer winds with higher ejection efficiencies, lower magnetizations and thicker discs. Conclusions: Our models show that current cold MHD disc wind solutions can explain many of the jet-related Balmer alpha features seen in post-AGB binaries, though systematic discrepancies remain. This includes, but is not limited to, overestimated rotation and underestimated post-AGB circumbinary disc lifetimes. The consideration of thicker discs and the inclusion of irradiation from the post-AGB primary, leading to warm magnetothermal wind launching, might alleviate these.

astro-ph.SR↗

arXiv2024

Magnetically driven winds from accretion disks in post-asymptotic giant branch binaries

Context. Jets are commonly detected in post-asymptotic giant branch (post-AGB) binaries and originate from an accretion process onto the companion of the post-AGB primary. These jets are revealed by high-resolution spectral time series. Aims. This paper is part of a series. In this work, we move away from our previous parametric modelling and include a self-similar wind model that allows the physical properties of post-AGB binaries to be characterised. This model describes magnetically driven jets from a thin accretion disk threaded by a large-scale, near equipartition vertical field. Methods. We expanded our methodology in order to simulate the high-resolution dynamic spectra coming from the obscuration of the primary by the jets launched by the companion. We present the framework to exploit the self-similar jet models for post-AGB binaries. We performed a parameter study to investigate the impact of different parameters (inclination, accretion rate, inner and outer launching radius) on the synthetic spectra. Results. We successfully included the physical jet models into our framework. The synthetic spectra have a very similar orbital phase coverage and absorption strengths as the observational data. The magnetohydrodynamic (MHD) jet models provide a good representation of the actual jet creation process in these evolved binaries. Challenges remain, however, as the needed high-accretion rate would induce accretion disks that are too hot in comparison to the data. Moreover, the rotational signature of the models is not detected in the observations. In future research, we will explore models with a higher disk ejection efficiency and even lower magnetisation in order to solve some of the remaining discrepancies between the observed and synthetic dynamic spectra.

astro-ph.SR↗