142 research outputs found
Capture and evolution of dust in planetary mean-motion resonances: A fast, semi-analytic method for generating resonantly trapped disc images
Dust grains migrating under Poynting-Robertson drag may be trapped in mean-motion resonances with planets. Such resonantly trapped grains are observed in the solar system. In extrasolar systems, the exozodiacal light produced by dust grains is expected to be a major obstacle to future missions attempting to directly image terrestrial planets. The patterns made by resonantly trapped dust, however, can be used to infer the presence of planets, and the properties of those planets, if the capture and evolution of the grains can be modelled. This has been done with N-body methods, but such methods are computationally expensive, limiting their usefulness when considering large, slowly evolving grains, and for extrasolar systems with unknown planets and parent bodies, where the possible parameter space for investigation is large. In this work, we present a semi-analytic method for calculating the capture and evolution of dust grains in resonance, which can be orders of magnitude faster than N-body methods. We calibrate the model against N-body simulations, finding excellent agreement for Earth to Neptune mass planets, for a variety of grain sizes, initial eccentricities, and initial semimajor axes. We then apply the model to observations of dust resonantly trapped by the Earth. We find that resonantly trapped, asteroidally produced grains naturally produce the ‘trailing blob’ structure in the zodiacal cloud, while to match the intensity of the blob, most of the cloud must be composed of cometary grains, which owing to their high eccentricity are not captured, but produce a smooth disk.We thank James Harrod for assistance in setting up the project, Grant Kennedy for useful discussions, and the anonymous referee for useful suggestions. AS and MW are supported by the European Union through ERC grant number 279973. AJM acknowledges support from Spanish grant AYA 2010/20630, grant number KAW 2012.0150 from the Knut and Alice Wallenberg foundation, and the Swedish Research Council (grant 2011-3991).This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv04
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
-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 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.Comment: 18 pages, 14 figure
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.Comment: 5 pages, 4 figures, 1 table, accepted to MNRAS Letter
Linking the formation and fate of exo-Kuiper belts within solar system analogues
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
Detailed chemical compositions of the wide binary HD 80606/80607: revised stellar properties and constraints on planet formation
Differences in the elemental abundances of planet hosting stars in binary
systems can give important clues and constraints about planet formation and
evolution. In this study we performed a high-precision, differential elemental
abundance analysis of a wide binary system, HD 80606/80607, based on
high-resolution, high signal-to-noise ratio Keck/HIRES spectra. HD 80606 is
known to host a four Jupiter mass giant planet while no planet has yet been
detected around HD 80607. We determined stellar parameters as well as
abundances for 23 elements for these two stars with extremely high precision.
Our main results are: (i) we confirmed that the two components share very
similar chemical compositions, but HD 80606 is marginally more metal-rich than
HD 80607 with an average difference of +0.013 0.002 dex ( = 0.009
dex) and (ii) there is no obvious trend between abundance differences and
condensation temperature. Assuming this binary formed from material with the
same chemical composition, it is difficult to understand how giant planet
formation could produce the present-day photospheric abundances of the elements
we measure. We can not exclude the possibility that HD 80606 might have
accreted about 2.5 to 5 material onto its surface, possibly
from a planet destabilised by the known highly-eccentric giant.Comment: 11 pages, 9 figues, accepted for publication in A&
ESPRESSO Mass determination of TOI-263b: An extreme inhabitant of the brown dwarf desert
The TESS mission has reported a wealth of new planetary systems around bright
and nearby stars amenable for detailed characterization of the planet
properties and their atmospheres. However, not all interesting TESS planets
orbit around bright host stars. TOI-263b is a validated ultra-short period
substellar object in a 0.56-day orbit around a faint (V=18.97) M3.5 dwarf star.
The substellar nature of TOI-263b was explored using multi-color photometry,
which determined a true radius of 0.87+-0.21 Rj, establishing TOI-263b's nature
ranging from an inflated Neptune to a brown dwarf. The orbital period-radius
parameter space occupied by TOI-263b is quite unique, which prompted a further
characterization of its true nature. Here, we report radial velocity
measurements of TOI-263 obtained with 3 VLT units and the ESPRESSO spectrograph
to retrieve the mass of TOI-263b. We find that TOI-263b is a brown dwarf with a
mass of 61.6+-4.0 Mj. Additionally, the orbital period of the brown dwarf is
found to be synchronized with the rotation period of the host star, and the
system is found to be relatively active, possibly revealing a star--brown dwarf
interaction. All these findings suggest that the system's formation history
might be explained via disc fragmentation and later migration to close-in
orbits. If the system is found to be unstable, TOI-263 is an excellent target
to test the migration mechanisms before the brown dwarf becomes engulfed by its
parent star.Comment: Accepted for Publication in Astronomy and Astrophysic
The Kepler-11 system: evolution of the stellar high-energy emission and {initial planetary} atmospheric mass fractions
The atmospheres of close-in planets are strongly influenced by mass loss
driven by the high-energy (X-ray and extreme ultraviolet, EUV) irradiation of
the host star, particularly during the early stages of evolution. We recently
developed a framework to exploit this connection and enable us to recover the
past evolution of the stellar high-energy emission from the present-day
properties of its planets, if the latter retains some remnants of their
primordial hydrogen-dominated atmospheres. Furthermore, the framework can also
provide constraints on planetary initial atmospheric mass fractions. The
constraints on the output parameters improve when more planets can be
simultaneously analysed. This makes the Kepler-11 system, which hosts six
planets with bulk densities between 0.66 and 2.45g cm^{-3}, an ideal target.
Our results indicate that the star has likely evolved as a slow rotator (slower
than 85\% of the stars with similar masses), corresponding to a high-energy
emission at 150 Myr of between 1-10 times that of the current Sun. We also
constrain the initial atmospheric mass fractions for the planets, obtaining a
lower limit of 4.1% for planet c, a range of 3.7-5.3% for planet d, a range of
11.1-14% for planet e, a range of 1-15.6% for planet f, and a range of 4.7-8.7%
for planet g assuming a disc dispersal time of 1 Myr. For planet b, the range
remains poorly constrained. Our framework also suggests slightly higher masses
for planets b, c, and f than have been suggested based on transit timing
variation measurements. We coupled our results with published planet atmosphere
accretion models to obtain a temperature (at 0.25 AU, the location of planet f)
and dispersal time of the protoplanetary disc of 550 K and 1 Myr, although
these results may be affected by inconsistencies in the adopted system
parameters.Comment: 8 pages, 3 figure
Post-main sequence evolution of A star debris discs
While the population of main sequence debris discs is well constrained,
little is known about debris discs around evolved stars. This paper provides a
theoretical framework considering the effects of stellar evolution on debris
discs, particularly the production and loss of dust within them. Here we repeat
a steady state model fit to disc evolution statistics for main sequence A
stars, this time using realistic grain optical properties, then evolve that
population to consider its detectability at later epochs. Our model predicts
that debris discs around giant stars are harder to detect than on the main
sequence because radiation pressure is more effective at removing small dust
around higher luminosity stars. Just 12% of first ascent giants within 100pc
are predicted to have discs detectable with Herschel at 160um. However this is
subject to the uncertain effect of sublimation on the disc, which we propose
can thus be constrained with such observations. Our model also finds that the
rapid decline in stellar luminosity results in only very young white dwarfs
having luminous discs. As such systems are on average at larger distances they
are hard to detect, but we predict that the stellar parameters most likely to
yield a disc detection are a white dwarf at 200pc with cooling age of 0.1Myr,
in line with observations of the Helix Nebula. Our model does not predict
close-in (<0.01AU) dust, as observed for some white dwarfs, however we find
that stellar wind drag leaves significant mass (~10^{-2}Msolar), in bodies up
to ~10m in diameter, inside the disc at the end of the AGB phase which may
replenish these discs
The planets around NN Serpentis : still there
We present 25 new eclipse times of the white dwarf binary NN Ser taken with the high-speed camera ULTRACAM on the William Herschel Telescope and New Technology Telescope, the RISE camera on the Liverpool Telescope and HAWK-I on the Very Large Telescope to test the two-planet model proposed to explain variations in its eclipse times measured over the last 25 yr. The planetary model survives the test with flying colours, correctly predicting a progressive lag in eclipse times of 36 s that has set in since 2010 compared to the previous 8 yr of precise times. Allowing both orbits to be eccentric, we find orbital periods of 7.9 ± 0.5 and 15.3 ± 0.3 yr, and masses of 2.3 ± 0.5 and 7.3 ± 0.3 MJ. We also find dynamically long-lived orbits consistent with the data, associated with 2:1 and 5:2 period ratios. The data scatter by 0.07 s relative to the best-fitting model, by some margin the most precise of any of the proposed eclipsing compact object planet hosts. Despite the high precision, degeneracy in the orbit fits prevents a significant measurement of a period change of the binary and of N-body effects. Finally, we point out a major flaw with a previous dynamical stability analysis of NN Ser, and by extension, with a number of analyses of similar systems
Are debris disks self-stirred?
This paper considers the evidence that debris disks are self-stirred by the
formation of Plutos. A model for the dust produced during self-stirring is
applied to statistics for A stars. As there is no significant difference
between excesses of A-stars <50Myr old, we focus on reproducing the broad
trends, the "rise and fall" of the fraction of stars with excesses. Using a
population model, we find that the statistics and trends can be reproduced with
a self-stirring model of planetesimal belts with radii distributed between
15-120AU. Disks must have this 15AU minimum radius to show a peak in disk
fraction, rather than a monotonic decline. Populations of extended disks with
fixed inner and/or outer radii fail to fit the statistics, due mainly to the
slow 70um evolution as stirring moves further out in the disk. This conclusion,
that debris disks are narrow belts, is independent of the significance of 24um
trends for young A-stars. We show that the statistics can also be reproduced
with a model in which disks are stirred by secular perturbations from a nearby
eccentric planet. Detailed imaging is therefore the best way to characterise
the stirring mechanism. From a more detailed look at beta Pictoris Moving Group
and TW Hydrae Association A-stars we find that the disk around beta Pictoris is
likely the result of secular stirring by the proposed planet at ~10AU; the
structure of the HR 4796A disk also points to sculpting by a planet. The two
other stars with disks, HR 7012 and eta Tel, possess transient hot dust, though
the outer eta Tel disk is consistent with a self-stirred origin. Planet
formation provides a natural explanation for the belt-like nature of debris
disks, with inner regions cleared by planets that may also stir the disk, and
the outer edges set by where planetesimals can form. [abridged]Comment: Accepted to MNRA
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