341 research outputs found
Planet formation in Binaries
Spurred by the discovery of numerous exoplanets in multiple systems, binaries
have become in recent years one of the main topics in planet formation
research. Numerous studies have investigated to what extent the presence of a
stellar companion can affect the planet formation process. Such studies have
implications that can reach beyond the sole context of binaries, as they allow
to test certain aspects of the planet formation scenario by submitting them to
extreme environments. We review here the current understanding on this complex
problem. We show in particular how each of the different stages of the
planet-formation process is affected differently by binary perturbations. We
focus especially on the intermediate stage of kilometre-sized planetesimal
accretion, which has proven to be the most sensitive to binarity and for which
the presence of some exoplanets observed in tight binaries is difficult to
explain by in-situ formation following the "standard" planet-formation
scenario. Some tentative solutions to this apparent paradox are presented. The
last part of our review presents a thorough description of the problem of
planet habitability, for which the binary environment creates a complex
situation because of the presence of two irradation sources of varying
distance.Comment: Review chapter to appear in "Planetary Exploration and Science:
Recent Advances and Applications", eds. S. Jin, N. Haghighipour, W.-H. Ip,
Springer (v2, numerous typos corrected
Conical : An extended module for computing a numerically satisfactory pair of solutions of the differential equation for conical functions
A Self-Consistent Model of the Circumstellar Debris Created by a Giant Hypervelocity Impact in the HD172555 System
Spectral modeling of the large infrared excess in the Spitzer IRS spectra of
HD 172555 suggests that there is more than 10^19 kg of sub-micron dust in the
system. Using physical arguments and constraints from observations, we rule out
the possibility of the infrared excess being created by a magma ocean planet or
a circumplanetary disk or torus. We show that the infrared excess is consistent
with a circumstellar debris disk or torus, located at approximately 6 AU, that
was created by a planetary scale hypervelocity impact. We find that radiation
pressure should remove submicron dust from the debris disk in less than one
year. However, the system's mid-infrared photometric flux, dominated by
submicron grains, has been stable within 4 percent over the last 27 years, from
IRAS (1983) to WISE (2010). Our new spectral modeling work and calculations of
the radiation pressure on fine dust in HD 172555 provide a self-consistent
explanation for this apparent contradiction. We also explore the unconfirmed
claim that 10^47 molecules of SiO vapor are needed to explain an emission
feature at 8 um in the Spitzer IRS spectrum of HD 172555. We find that unless
there are 10^48 atoms or 0.05 Earth masses of atomic Si and O vapor in the
system, SiO vapor should be destroyed by photo-dissociation in less than 0.2
years. We argue that a second plausible explanation for the 8 um feature can be
emission from solid SiO, which naturally occurs in submicron silicate "smokes"
created by quickly condensing vaporized silicate.Comment: Accepted to the Astrophysical Journa
<i>Herschel</i> observations of the debris disc around HIP 92043
Context. Typical debris discs are composed of particles ranging from several micron sized dust grains to km sized asteroidal bodies, and their infrared emission peaks at wavelengths 60-100 ÎŒm. Recent Herschel DUNES observations have identified several debris discs around nearby Sun-like stars (F, G and K spectral type) with significant excess emission only at 160 ÎŒm.
Aims. We observed HIP 92043 (110 Her, HD 173667) at far-infrared and sub-millimetre wavelengths with Herschel PACS and SPIRE. Identification of the presence of excess emission from HIP 92043 and the origin and physical properties of any excess was undertaken through analysis of its spectral energy distribution (SED) and the PACS images.
Methods. The PACS and SPIRE images were produced using the HIPE photProject map maker routine. Fluxes were measured using aperture photometry. A stellar photosphere model was scaled to optical and near infrared photometry and subtracted from the far-infared and sub-mm fluxes to determine the presence of excess emission. Source radial profiles were fitted using a 2D Gaussian and compared to a PSF model based on Herschel observations of α Boo to check for extended emission.
Results. Clear excess emission from HIP 92043 was observed at 70 and 100 ÎŒm. Marginal excess was observed at 160 and 250 ÎŒm. Analysis of the images reveals that the source is extended at 160 ÎŒm. A fit to the source SED is inconsistent with a photosphere and single temperature black body.
Conclusions. The excess emission from HIP 92043 is consistent with the presence of an unresolved circumstellar debris disc at 70 and 100 ÎŒm, with low probability of background contamination. The extended 160 ÎŒm emission may be interpreted as an additional cold component to the debris disc or as the result of background contamination along the line of sight. The nature of the 160 ÎŒm excess cannot be determined absolutely from the available data, but we favour a debris disc interpretation, drawing parallels with previously identified cold disc sources in the DUNES sample
Dynamical analysis and constraints for the HD 196885 system
The HD\,196885 system is composed of a binary star and a planet orbiting the
primary. The orbit of the binary is fully constrained by astrometry, but for
the planet the inclination with respect to the plane of the sky and the
longitude of the node are unknown. Here we perform a full analysis of the
HD\,196885 system by exploring the two free parameters of the planet and
choosing different sets of angular variables. We find that the most likely
configurations for the planet is either nearly coplanar orbits (prograde and
retrograde), or highly inclined orbits near the Lidov-Kozai equilibrium points,
i = 44^{\circ} or i = 137^{\circ} . Among coplanar orbits, the retrograde ones
appear to be less chaotic, while for the orbits near the Lidov-Kozai
equilibria, those around \omega= 270^{\circ} are more reliable, where \omega_k
is the argument of pericenter of the planet's orbit with respect to the
binary's orbit.
From the observer's point of view (plane of the sky) stable areas are
restricted to (I1, \Omega_1) \sim (65^{\circ}, 80^{\circ}),
(65^{\circ},260^{\circ}), (115^{\circ},80^{\circ}), and
(115^{\circ},260^{\circ}), where I1 is the inclination of the planet and
\Omega_1 is the longitude of ascending node.Comment: 10 pages, 7 figures. A&A Accepte
What science can do for democracy â A complexity science approach
Political scientists have conventionally assumed that achieving democracy is a one-way ratchet. Only very recently has the question of âdemocratic backslidingâ attracted any research attention. We argue that democratic instability is best understood with tools from complexity science. The explanatory power of complexity science arises from several features of complex systems. Their relevance in the context of democracy is discussed. Several policy recommendations are offered to help (re)stabilize current systems of representative democracy
Silver nanoparticle embedded copper oxide as an efficient coreâshell for the catalytic reduction of 4-nitrophenol and antibacterial activity improvement
International audienc
Can Eccentric Debris Disks Be Long-lived? A First Numerical Investigation and Application to Zeta(exp 2) Reticuli
Context. Imaging of debris disks has found evidence for both eccentric and offset disks. One hypothesis is that they provide evidence for massive perturbers, for example, planets or binary companions, which sculpt the observed structures. One such disk was recently observed in the far-IR by the Herschel Space Observatory around Zeta2 Reticuli. In contrast with previously reported systems, the disk is significantly eccentric, and the system is several Gyr old. Aims. We aim to investigate the long-term evolution of eccentric structures in debris disks caused by a perturber on an eccentric orbit around the star. We hypothesise that the observed eccentric disk around Zeta2 Reticuli might be evidence of such a scenario. If so, we are able to constrain the mass and orbit of a potential perturber, either a giant planet or a binary companion. Methods. Analytical techniques were used to predict the effects of a perturber on a debris disk. Numerical N-body simulations were used to verify these results and further investigate the observable structures that may be produced by eccentric perturbers. The long-term evolution of the disk geometry was examined, with particular application to the Zeta2 Reticuli system. In addition, synthetic images of the disk were produced for direct comparison with Herschel observations. Results. We show that an eccentric companion can produce both the observed offsets and eccentric disks. These effects are not immediate, and we characterise the timescale required for the disk to develop to an eccentric state (and any spirals to vanish). For Zeta2 Reticuli, we derive limits on the mass and orbit of the companion required to produce the observations. Synthetic images show that the pattern observed around Zeta2 Reticuli can be produced by an eccentric disk seen close to edge-on, and allow us to bring additional constraints on the disk parameters of our model (disk flux and extent). Conclusions. We conclude that eccentric planets or stellar companions can induce long-lived eccentric structures in debris disks. Observations of such eccentric structures thus provide potential evidence of the presence of such a companion in a planetary system. We considered the specific example of Zeta2 Reticuli, whose observed eccentric disk can be explained by a distant companion (at tens of AU) on an eccentric orbit (ep greater than approx. 0.3)
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