| 1. |
- Ahrer, E., et al.
(författare)
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Atmospheric characterization and tighter constraints on the orbital misalignment of WASP-94 A b with HARPS
- 2024
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 530:3, s. 2749-2759
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Tidskriftsartikel (refereegranskat)abstract
- We present high spectral resolution observations of the hot Jupiter WASP-94 A b using the HARPS instrument on ESO’s 3.6-m telescope in La Silla, Chile. We probed for Na absorption in its atmosphere as well as constrained the previously reported misaligned retrograde orbit using the Rossiter–McLaughlin effect. Additionally, we undertook a combined atmospheric retrieval analysis with previously published low-resolution data. We confirm the retrograde orbit as well as constrain the orbital misalignment with our measurement of a projected spin-orbit obliquity of λ = 123.0 ± 3.0°. We find a tentative detection of Na absorption in the atmosphere of WASP-94 A b, independent of the treatment of the Rossiter–McLaughlin effect in our analysis (3.6σ and 4.4σ). We combine our HARPS high-resolution data with low-resolution data from the literature and find that while the posterior distribution of the Na abundance results in a tighter constraint than using a single data set, the detection significance does not improve (3.2σ), which we attribute to degeneracies between the low- and high-resolution data.
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| 2. |
- Cunningham, Tim, et al.
(författare)
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Horizontal spreading of planetary debris accreted by white dwarfs
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 503:2, s. 1646-1667
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Tidskriftsartikel (refereegranskat)abstract
- White dwarfs with metal-polluted atmospheres have been studied widely in the context of the accretion of rocky debris from evolved planetary systems. One open question is the geometry of accretion and how material arrives and mixes in the white dwarf surface layers. Using the three-dimensional (3D) radiation hydrodynamics code (COBOLD)-B-5, we present the first transport coefficients in degenerate star atmospheres that describe the advection-diffusion of a passive scalar across the surface plane. We couple newly derived horizontal diffusion coefficients with previously published vertical diffusion coefficients to provide theoretical constraints on surface spreading of metals in white dwarfs. Our grid of 3D simulations probes the vast majority of the parameter space of convective white dwarfs, with pure-hydrogen atmospheres in the effective temperature range of 6000-18 000K and pure-helium atmospheres in the range of 12 000-34 000 K. Our results suggest that warm hydrogen-rich atmospheres (DA; greater than or similar to 13 000 K) and helium-rich atmospheres (DB and DBA; greater than or similar to 30 000 K) are unable to efficiently spread the accreted metals across their surface, regardless of the time dependence of accretion. This result may be at odds with the current non-detection of surface abundance variations in white dwarfs with debris discs. For cooler hydrogen- and helium-rich atmospheres, we predict a largely homogeneous distribution of metals across the surface within a vertical diffusion time-scale. This is typically less than 0.1 per cent of disc lifetime estimates, a quantity that is revisited in this paper using the overshoot results. These results have relevance for studies of the bulk composition of evolved planetary systems and models of accretion disc physics.
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| 3. |
- Hon, Marc, et al.
(författare)
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A close-in giant planet escapes engulfment by its star
- 2023
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 618:7967, s. 917-920
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Tidskriftsartikel (refereegranskat)abstract
- When main-sequence stars expand into red giants, they are expected to engulf close-in planets(1-5). Until now, the absence of planets with short orbital periods around post-expansion, core-helium-burning red giants(6-8) has been interpreted as evidence that short-period planets around Sun-like stars do not survive the giant expansion phase of their host stars(9). Here we present the discovery that the giant planet 8 Ursae Minoris b(10) orbits a core-helium-burning red giant. At a distance of only 0.5 au from its host star, the planet would have been engulfed by its host star, which is predicted by standard single-star evolution to have previously expanded to a radius of 0.7 au. Given the brief lifetime of helium-burning giants, the nearly circular orbit of the planet is challenging to reconcile with scenarios in which the planet survives by having a distant orbit initially. Instead, the planet may have avoided engulfment through a stellar merger that either altered the evolution of the host star or produced 8 Ursae Minoris b as a second-generation planet(11). This system shows that core-helium-burning red giants can harbour close planets and provides evidence for the role of non-canonical stellar evolution in the extended survival of late-stage exoplanetary systems.
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| 4. |
- Izquierdo, Paula, et al.
(författare)
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Fast spectrophotometry of WD 1145+017
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 481:1, s. 703-714
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Tidskriftsartikel (refereegranskat)abstract
- WD 1145+017 is currently the only white dwarf known to exhibit periodic transits of planetary debris as well as absorption lines from circumstellar gas. We present the first simultaneous fast optical spectrophotometry and broad-band photometry of the system, obtained with the Gran Telescopio Canarias (GTC) and the Liverpool Telescope, respectively. The observations spanned 5.5 h, somewhat longer than the 4.5-h orbital period of the debris. Dividing the GTC spectrophotometry into five wavelength bands reveals no significant colour differences, confirming grey transits in the optical. We argue that absorption by an optically thick structure is a plausible alternative explanation for the achromatic nature of the transits that can allow the presence of small-sized (~µm) particles. The longest (87 min) and deepest (50 per cent attenuation) transit recorded in our data exhibits a complex structure around minimum light that can be well modelled by multiple overlapping dust clouds. The strongest circumstellar absorption line, Fe II λ5169, significantly weakens during this transit, with its equivalent width reducing from a mean out-of-transit value of 2 to 1 Å in-transit, supporting spatial correlation between the circumstellar gas and dust. Finally, we made use of the Gaia Data Release 2 and archival photometry to determine the white dwarf parameters. Adopting a helium-dominated atmosphere containing traces of hydrogen and metals, and a reddening E(B - V) = 0.01 we find T_eff=15 020 ± 520 K, log g = 8.07 ± 0.07, corresponding to M_WD=0.63± 0.05 M☉ and a cooling age of 224 ± 30 Myr.
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| 5. |
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| 6. |
- Manser, Christopher J., et al.
(författare)
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A planetesimal orbiting within the debris disc around a white dwarf star
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 364:6435, s. 66-69
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Tidskriftsartikel (refereegranskat)abstract
- Many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through emission lines. We report a stable 123.4-minute periodic variation in the strength and shape of the Ca II emission line profiles originating from the debris disc around the white dwarf SDSS J122859.93+104032.9. We interpret this short-period signal as the signature of a solid-body planetesimal held together by its internal strength.
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| 7. |
- Mustill, Alexander J., et al.
(författare)
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Unstable low-mass planetary systems as drivers of white dwarf pollution
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 476, s. 3939-3955
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Tidskriftsartikel (refereegranskat)abstract
- At least 25 percent of white dwarfs show atmospheric pollution by metals, sometimes accompanied by detectable circumstellar dust/gas discs or (in the case of WD 1145+017) transiting disintegrating asteroids. Delivery of planetesimals to the white dwarf by orbiting planets is a leading candidate to explain these phenomena. Here, we study systems of planets and planetesimals undergoing planet–planet scattering triggered by the star's post-main-sequence mass loss, and test whether this can maintain high rates of delivery over the several Gyr that they are observed. We find that low-mass planets (Earth to Neptune mass) are efficient deliverers of material and can maintain the delivery for Gyr. Unstable low-mass planetary systems reproduce the observed delayed onset of significant accretion, as well as the slow decay in accretion rates at late times. Higher-mass planets are less efficient, and the delivery only lasts a relatively brief time before the planetesimal populations are cleared. The orbital inclinations of bodies as they cross the white dwarf's Roche limit are roughly isotropic, implying that significant collisional interactions of asteroids, debris streams and discs can be expected. If planet–planet scattering is indeed responsible for the pollution of white dwarfs, many such objects, and their main-sequence progenitors, can be expected to host (currently undetectable) super-Earth planets on orbits of several au and beyond.
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| 8. |
- Veras, Dimitri, et al.
(författare)
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Linking the formation and fate of exo-Kuiper belts within Solar system analogues
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 493:4, s. 5062-5078
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Tidskriftsartikel (refereegranskat)abstract
- Escalating observations of exo-minor planets and their destroyed remnants both passing through the Solar system and within white dwarf planetary systems motivate an understanding of the orbital history and fate of exo-Kuiper belts and planetesimal discs. Here, we explore how the structure of a 40–1000 au annulus of planetesimals orbiting inside of a Solar system analogue that is itself initially embedded within a stellar cluster environment varies as the star evolves through all of its stellar phases. We attempt this computationally challenging link in four parts: (1) by performing stellar cluster simulations lasting 100 Myr, (2) by making assumptions about the subsequent quiescent 11 Gyr main-sequence evolution, (3) by performing simulations throughout the giant branch phases of evolution, and (4) by making assumptions about the belt’s evolution during the white dwarf phase. Throughout these stages, we estimate the planetesimals’ gravitational responses to analogues of the four Solar system giant planets, as well as to collisional grinding, Galactic tides, stellar flybys, and stellar radiation. We find that the imprint of stellar cluster dynamics on the architecture of ≳100 km-sized exo-Kuiper belt planetesimals is retained throughout all phases of stellar evolution unless violent gravitational instabilities are triggered either (1) amongst the giant planets, or (2) due to a close (≪103 au) stellar flyby. In the absence of these instabilities, these minor planets simply double their semimajor axis while retaining their primordial post-cluster eccentricity and inclination distributions, with implications for the free-floating planetesimal population and metal-polluted white dwarfs.
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| 9. |
- Veras, Dimitri, et al.
(författare)
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Prospects for detecting decreasing exoplanet frequency with main-sequence age using PLATO
- 2015
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 453:1, s. 67-72
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Tidskriftsartikel (refereegranskat)abstract
- The space mission PLATO will usher in a new era of exoplanetary science by expanding our current inventory of transiting systems and constraining host star ages, which are currently highly uncertain. This capability might allow PLATO to detect changes in planetary system architecture with time, particularly because planetary scattering due to Lagrange instability may be triggered long after the system was formed. Here, we utilize previously published instability time-scale prescriptions to determine PLATO's capability to detect a trend of decreasing planet frequency with age for systems with equal-mass planets. For two-planet systems, our results demonstrate that PLATO may detect a trend for planet masses which are at least as massive as super-Earths. For systems with three or more planets, we link their initial compactness to potentially detectable frequency trends in order to aid future investigations when these populations will be better characterized.
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| 10. |
- Veras, Dimitri, et al.
(författare)
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The entry geometry and velocity of planetary debris into the Roche sphere of a white dwarf
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 506:1, s. 1148-1164
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Tidskriftsartikel (refereegranskat)abstract
- Our knowledge of white dwarf planetary systems predominately arises from the region within a few Solar radii of the white dwarfs, where minor planets breakup, form rings and discs, and accrete on to the star. The entry location, angle, and speed into this Roche sphere has rarely been explored but crucially determines the initial geometry of the debris, accretion rates on to the photosphere, and ultimately the composition of the minor planet. Here, we evolve a total of over 105 asteroids with single-planet N-body simulations across the giant branch and white dwarf stellar evolution phases to quantify the geometry of asteroid injection into the white dwarf Roche sphere as a function of planetary mass and eccentricity. We find that lower planetary masses increase the extent of anisotropic injection and decrease the probability of head-on (normal to the Roche sphere) encounters. Our results suggest that one can use dynamical activity within the Roche sphere to make inferences about the hidden architectures of these planetary systems.
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| 11. |
- Veras, Dimitri, et al.
(författare)
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The unstable fate of the planet orbiting the A star in the HD 131399 triple stellar system
- 2017
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 465, s. 1499-1504
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Tidskriftsartikel (refereegranskat)abstract
- Validated planet candidates need not lie on long-term stable orbits, and instability triggered by post-main-sequence stellar evolution can generate architectures which transport rocky material to white dwarfs, hence polluting them. The giant planet HD 131399Ab orbits its parent A star at a projected separation of about 50-100 au. The host star, HD 131399A, is part of a hierarchical triple with HD 131399BC being a close binary separated by a few hundred au from the A star. Here, we determine the fate of this system, and find the following: (i) Stability along the main sequence is achieved only for a favourable choice of parameters within the errors. (ii) Even for this choice, in almost every instance, the planet is ejected during the transition between the giant branch and white dwarf phases of HD 131399A. This result provides an example of both how the free-floating planet population may be enhanced by similar systems and how instability can manifest in the polluted white dwarf progenitor population.
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