arXiv subjects

R. F. Maldonado

Publications and source records attributed to R. F. Maldonado.

9 recordsLinked to original sources

arXiv2026

Wind accretion onto planets orbiting an evolving Solar-like star and their detectability

As stars evolve, they undergo significant changes in their physical properties, which can have a profound impact on the planets orbiting them. In particular, the mass lost through stellar wind may be partially accreted by orbiting planets. We present the results of 18 simulations of one-planet systems with planetary masses of 0.5, 1, 2.5, 5, 10, and 13~$\mathrm{M}_\mathrm{J}$, each at initial orbital distances of 5, 10, and 20~AU, orbiting a 2~M$_\odot$ star through its red giant branch and thermally pulsating asymptotic giant branch phases. Our results show that planets with smaller orbits and higher masses accrete more stellar wind material than their wider-orbit and lower-mass counterparts, although the total mass accreted across all simulations remains small compared to their initial planetary mass. Even for the most massive planet, 13 $\mathrm{M}_\mathrm{J}$ at 5 AU, the total mass accreted was $\sim0.56$\% of the planet's initial mass; nevertheless, we find that the accretion luminosities of the simulated planets, with the exception of one planet, exceed their expected equilibrium luminosities, suggesting that such emission could be potentially detected. This result is key for the detection of planets around AGB stars, which have no confirmed detections as of yet. We also estimated the accretion and luminosities of two detected two-planet systems over a few orbits, obtaining results consistent with the one-planet simulated systems. Additional tests without wind accretion and with stellar wind drag force showed that, while both have a negligible effect on the orbital evolution, wind accretion remains relevant for the planetary luminosity.

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arXiv2025

Entering the Wind Roche Lobe Overflow realm in Symbiotic Systems

We present a suite of dynamical simulations designed to explore the orbital and accretion properties of compact (2$-$7 AU) symbiotic systems, focusing on wind accretion, drag forces, and tidal interactions. Using three levels of physical complexity, we model systems of accreting white dwarfs (WDs) with masses of 0.7, 1.0, and 1.2 M$_\odot$ orbiting evolving Solar-like stars with 1, 2, and 3 M$_\odot$. We show that systems alternate between standard wind accretion and Wind Roche Lobe Overflow (WRLO) regimes during periods of high mass-loss rate experienced by the donor star (the peak of red giant phase and/or thermal pulses). For some configurations, the standard wind accretion has mass accretion efficiencies similar to those obtained by WRLO regime. Tidal forces play a key role in compact systems, leading to orbital shrinkage and enhanced accretion efficiency. We find that systems with high-mass WDs ($\geq 1$ M$_\odot$) and massive donors (2$-$3 M$_\odot$) are the only ones to reach the Chandrasekhar limit. Interestingly, the majority of our simulations reach the Roche lobe overflow condition that is not further simulated given the need of more complex hydrodynamical simulations. Our analysis shows that increasing physical realism, by including drag and tides, systematically leads to more compact final orbital configurations. Comparison with compact known symbiotic systems seems to suggest that they are very likely experiencing orbital decay produced by tidal forces.

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arXiv2025

The impact of wind accretion in Evolving Symbiotic Systems

We investigate the impact of geometric corrections to the Bondi-Hoyle-Lyttleton (BHL) accretion scheme applied to evolving symbiotic systems. We model systems where 0.7 and 1 M$_\odot$ white dwarfs accrete material from Solar-like stars with initial masses of 1, 2, and 3 M$_\odot$. The primary star is evolved using the MESA stellar evolution code, while the orbital dynamics of the system are calculated using REBOUND. The analysis focuses on systems evolving through the red giant branch and the thermally-pulsating asymptotic giant branch phases that do not experience a Wind Roche Lobe Overflow phase. We compare three scenarios: no accretion, standard BHL accretion, and the improved wind accretion. The choice of accretion prescription critically influences the evolution of symbiotic systems. Simulations using the modified model did not reach the Chandrasekhar limit, suggesting that type Ia supernova progenitors require accretors originating from ultra-massive WDs. In contrast, the standard BHL model predicts WD growth to this limit in compact systems. This discrepancy suggests that population synthesis studies adopting the traditional BHL approach may yield inaccurate results. The revised model successfully reproduces the accretion properties of observed symbiotic systems and predicts transitions between different accretion regimes driven by donor mass-loss variability. These results emphasize the need for updated wind accretion models to accurately describe the evolution of symbiotic binaries.

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arXiv2024

Accretion onto WD 2226$-$210, the central star of the Helix Nebula

The central star of the Helix Nebula, WD 2226$-$210 presents enigmatic hard X-ray emission and mid-IR excess. The latter has been attributed to a dusty disk or a cloud-like structure around WD 2226$-$210 formed from material of Kuiper Belt-like or comet-like objects in highly eccentric orbits. We present here a detailed analysis of multi-epoch Chandra and XMM-Newton X-ray observations of WD 2226$-$210, comparing these to previous Einstein and ROSAT data. The luminosity of the hard X-ray component of WD 2226$-$210 has remained basically constant in the decade from 1992 to 2002, with very subtle evidence for variability in timescales of hours. Under the assumption that the X-ray emission from WD 2226$-$210 is due to accretion of material, an accretion rate of $\dot{M}\approx10^{-10}$ M$_\odot$ yr$^{-1}$ is estimated. The origin of the material accreted by WD 2226$-$210 is uncertain, and can be attributed to the disk-like structure around it or to a sub-stellar donor companion. The accretion rate proposed for the continuous replenishment by bombardment of the mid-IR-emitting structure around WD 2226$-$210 cannot match that required by the X-ray emission.

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arXiv2023

Synthetic X-ray emission from white dwarf accreting planetary material

The emission of hard X-rays associated with white dwarfs (WD) can be generated by the presence of a stellar companion either by the companion's coronal emission or by an accretion disk formed by material stripped from the companion. Recent studies have suggested that a Jupiter-like planet can also be donor of material whose accretion onto the WD can generate hard X-rays. We use the {\sc guacho} code to reproduce the conditions of this WD-planet scenario. With the example of the hard X-ray WD KPD\,0005+5106, we explore different terminal wind velocities and mass-loss rates of a donor planet for a future network of simulations to investigate the luminosity and the spectral and temporal properties of the hard X-ray emission in WD-planet systems. Our simulations show that the material stripped from the planet forms a disk and accretes onto the WD to reach temperatures high enough to generate hard X-rays as usually seen in X-ray binaries with low-mass companions. For high terminal wind velocities, the planet material does not form a disk, but it rather accretes directly onto the WD surface. The simulations reproduce the X-ray luminosity of another X-ray accreting WD (G\,29$-$38), and only for some times reaches the hard X-ray luminosity of KPD\,0005+5106. The X-ray variability is stochastic and does not reproduce the period of KPD\,0005+5106, suggesting that additional physical processes (e.g., hot spots resulting from magnetic channelling of the accreting material) need to be explored.

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arXiv2022

Disentangling the parameter space: The role of planet multiplicity in triggering dynamical instabilities on planetary systems around white dwarfs

Planets orbiting intermediate and low-mass stars are in jeopardy as their stellar hosts evolve to white dwarfs (WDs) because the dynamics of the planetary system changes due to the increase of the planet:star mass ratio after stellar mass-loss. In order to understand how the planet multiplicity affects the dynamical stability of post-main sequence (MS) systems, we perform thousands of N-body simulations involving planetary multiplicity as the variable and with a controlled physical and orbital parameter space: equal-mass planets; the same orbital spacing between adjacent planet's pairs; and orbits with small eccentricities and inclinations. We evolve the host star from the MS to the WD phase following the system dynamics for 10 Gyr. We find that the fraction of dynamically active simulations on the WD phase for two-planet systems is $10.2^{+1.2}_{-1.0}$-$25.2^{+2.5}_{-2.2}$ $\%$ and increases to $33.6^{+2.3}_{-2.2}$-$74.1^{+3.7}_{-4.6}$ $\%$ for the six-planet systems, where the ranges cover different ranges of initial orbital separations. Our simulations show that the more planets the system has, the more systems become unstable when the star becomes a WD, regardless of the planet masses and range of separations. Additional results evince that simulations with low-mass planets (1, 10 $\mathrm{M_\oplus}$) lose at most two planets, have a large fraction of systems undergoing orbit crossing without planet losses, and are dynamically active for Gyr time-scales on the WD's cooling track. On the other hand, systems with high-mass planets (100, 1000 $\mathrm{M_\oplus}$) lose up to five planets, preferably by ejections, and become unstable in the first few hundred Myr after the formation of the WD.

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arXiv2020

Do instabilities in high-multiplicity systems explain the existence of close-in white dwarf planets?

We investigate the origin of close-in planets and related phenomena orbiting white dwarfs (WDs), which are thought to originate from orbits more distant from the star. We use the planetary architectures of the 75 multiple-planet systems (four, five and six planets) detected orbiting main-sequence stars to build 750 dynamically analogous templates that we evolve to the WD phase. Our exploration of parameter space, although not exhaustive, is guided and restricted by observations and we find that the higher the multiplicity of the planetary system, the more likely it is to have a dynamical instability (losing planets, orbit crossing and scattering), that eventually will send a planet (or small object) through a close periastron passage. Indeed, the fraction of unstable four- to six-planet simulations is comparable to the 25-50$\%$ fraction of WDs having atmospheric pollution. Additionally, the onset of instability in the four- to six-planet configurations peaks in the first Gyr of the WD cooling time, decreasing thereafter. Planetary multiplicity is a natural condition to explain the presence of close-in planets to WDs, without having to invoke the specific architectures of the system or their migration through the von Zeipel-Lidov-Kozai (ZLK) effects from binary companions or their survival through the common envelope phase.

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arXiv2020

Understanding the origin of white dwarf atmospheric pollution by dynamical simulations based on detected three-planet systems

Between 25-50 % of white dwarfs (WD) present atmospheric pollution by metals, mainly by rocky material, which has been detected as gas/dust discs, or in the form of photometric transits in some WDs. Planets might be responsible for scattering minor bodies that can reach stargazing orbits, where the tidal forces of the WD can disrupt them and enhance the chances of debris to fall onto the WD surface. The planet-planet scattering process can be triggered by the stellar mass-loss during the post main-sequence evolution of planetary systems. In this work, we continue the exploration of the dynamical instabilities that can lead to WD pollution. In a previous work we explored two-planet systems found around main-sequence (MS) stars and here we extend the study to three-planet system architectures. We evolved 135 detected three-planet systems orbiting MS stars to the WD phase by scaling their orbital architectures in a way that their dynamical properties are preserved by using the $N$-body integrator package Mercury. We find that 100 simulations (8.6 %) are dynamically active (having planet losses, orbit crossing and scattering) on the WD phase, where low mass planets (1-100 $\mathrm{M}_\oplus$) tend to have instabilities in Gyr timescales while high mass planets ($>100~\mathrm{M}_\oplus$) decrease the dynamical events more rapidly as the WD ages. Besides, 19 simulations (1.6 %) were found to have planets crossing the Roche radius of the WD, where 9 of them had planet-star collisions. Our three-planet simulations have an slight increase percentage of simulations that may contribute to the WD pollution than the previous study involving two-planet systems and have shown that planet-planet scattering is responsible of sending planets close to the WD, where they may collide directly to the WD, become tidally disrupted or circularize their orbits, hence producing pollution on the WD atmosphere.

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arXiv2020

Dynamical evolution of two-planet systems and its connection with white dwarf atmospheric pollution

Asteroid material is detected in white dwarfs (WDs) as atmospheric pollution by metals, in the form of gas/dust discs, or in photometric transits. Within the current paradigm, minor bodies need to be scattered, most likely by planets, into highly eccentric orbits where the material gets disrupted by tidal forces and then accreted onto the star. This can occur through a planet-planet scattering process triggered by the stellar mass loss during the post main-sequence evolution of planetary systems. So far, studies of the $N$-body dynamics of this process have used artificial planetary system architectures built ad hoc. In this work, we attempt to go a step further and study the dynamical instability provided by more restrictive systems, that, at the same time allow us an exploration of a wider parameter space: the hundreds of multiple planetary systems found around main-sequence (MS) stars. We find that most of our simulated systems remain stable during the MS, Red and Asymptotic Giant Branch and for several Gyr into the WD phases of the host star. Overall, only $\approx$ 2.3$\%$ of the simulated systems lose a planet on the WD as a result of dynamical instability. If the instabilities take place during the WD phase most of them result in planet ejections with just 5 planetary configurations ending as a collision of a planet with the WD. Finally 3.2$\%$ of the simulated systems experience some form of orbital scattering or orbit crossing that could contribute to the pollution at a sustained rate if planetesimals are present in the same system.

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