353 research outputs found
On the stratified dust distribution of the GG Tau circumbinary ring
Our objective is to study the vertical dust distribution in the circumbinary
ring of the binary system GG Tau and to search for evidence of stratification,
one of the first steps expected to occur during planet formation.
We present a simultaneous analysis of four scattered light images spanning a
range of wavelength from 800 nm to 3800 nm and compare them with (i) a
parametric prescription for the vertical dust stratification, and (ii) with the
results of SPH bi-fluid hydrodynamic calculations.
The parametric prescription and hydrodynamical calculations of stratification
both reproduce the observed brightness profiles well. These models also provide
a correct match for the observed star/ring integrated flux ratio. Another
solution with a well-mixed, but ``exotic'', dust size distribution also matches
the brightness profile ratios but fails to match the star/ring flux ratio.
These results give support to the presence of vertical stratification of the
dust in the ring of GG Tau and further predict the presence of a radial
stratification also.Comment: 9 pages, 11 figures. Accepted for publication in A&
The effect of a planet on the dust distribution in a 3D protoplanetary disk
Aims: We investigate the behaviour of dust in protoplanetary disks under the
action of gas drag in the presence of a planet. Our goal is twofold: to
determine the spatial distribution of dust depending on grain size and planet
mass, and therefore to provide a framework for interpretation of coming
observations and future studies of planetesimal growth. Method: We numerically
model the evolution of dust in a protoplanetary disk using a two-fluid (gas +
dust) Smoothed Particle Hydrodynamics (SPH) code, which is non-self-gravitating
and locally isothermal. The code follows the three dimensional distribution of
dust in a protoplanetary disk as it interacts with the gas via aerodynamic
drag. In this work, we present the evolution of a minimum mass solar nebula
(MMSN) disk comprising 1% dust by mass in the presence of an embedded planet.
We run a series of simulations which vary the grain size and planetary mass to
see how they affect the resulting disk structure. Results: We find that gap
formation is much more rapid and striking in the dust layer than in the gaseous
disk and that a system with a given stellar, disk and planetary mass will have
a completely different appearance depending on the grain size. For low mass
planets in our MMSN disk, a gap can open in the dust disk while not in the gas
disk. We also note that dust accumulates at the external edge of the planetary
gap and speculate that the presence of a planet in the disk may enhance the
formation of a second planet by facilitating the growth of planetesimals in
this high density region.Comment: 13 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
Planet gaps in the dust layer of 3D protoplanetary disks. II. Observability with ALMA
[Abridged] Aims: We provide predictions for ALMA observations of planet gaps
that account for the specific spatial distribution of dust that results from
consistent gas+dust dynamics. Methods: In a previous work, we ran full 3D,
two-fluid Smoothed Particle Hydrodynamics (SPH) simulations of a planet
embedded in a gas+dust T Tauri disk for different planet masses and grain
sizes. In this work, the resulting dust distributions are passed to the Monte
Carlo radiative transfer code MCFOST to construct synthetic images in the ALMA
wavebands. We then use the ALMA simulator to produce images that include
thermal and phase noise for a range of angular resolutions, wavelengths, and
integration times, as well as for different inclinations, declinations and
distances. We also produce images which assume that gas and dust are well mixed
with a gas-to-dust ratio of 100 to compare with previous ALMA predictions, all
made under this hypothesis. Results: Our findings clearly demonstrate the
importance of correctly incorporating the dust dynamics. We show that the gap
carved by a 1 M_J planet orbiting at 40 AU is visible with a much higher
contrast than the well-mixed assumption would predict. In the case of a 5 M_J
planet, we clearly see a deficit in dust emission in the inner disk, and point
out the risk of interpreting the resulting image as that of a transition disk
with an inner hole if observed in unfavorable conditions. Planet signatures are
fainter in more distant disks but declination or inclination to the
line-of-sight have little effect on ALMA's ability to resolve the gaps.
Conclusions: ALMA has the potential to see signposts of planets in disks of
nearby star-forming regions. We present optimized observing parameters to
detect them in the case of 1 and 5 M_J planets on 40 AU orbits.Comment: 15 pages, 21 figures, accepted by Astronomy & Astrophysics, a higher
resolution version of the paper is available at
http://www-obs.univ-lyon1.fr/labo/perso/jean-francois.gonzalez/Papers/Gaps_ALMA.pd
Wave Forcing of Saturn's Equatorial Oscillation
Ground-based measurements and Cassini data from CIRS thermal-infrared spectra and radio-occultation soundings have characterized the spatial structure and temporal behavior of a 15-year equatorial oscillation in Saturn's stratosphere. The equatorial region displays a vertical pattern of alternating warm and cold anomalies and, concomitantly, easterly and westerly winds relative to the cloud-top winds, with a peak-to-peak amplitude of 200 m/s. Comparison of the Cassini data over a four-year period has established that the pattern of mean zonal winds and temperatures descends at a rate of roughly I scale height over 4 years. This behavior is reminiscent of the equatorial oscillations in Earth's middle atmosphere. Here the zonal-mean spatial structure and descending pattern are driven by the absorption of vertically propagating waves. The maximum excursions in the pattern of easterly and westerly winds is determined by the limits of the zonal phase velocities of the waves. Here we report on the characterization of the waves seen in the temperature profiles retrieved from the Cassini radio-occultation soundings. The equatorial profiles exhibit a complex pattern of wavelike structure with dimensions one pressure scale height and smaller. We combine a spectral decomposition with a WKBJ analysis, where the vertical wavelength is assumed to vary slowly with the ambient static stability and doppler-shifted phase velocity of the wave. Use of the temperature and zonal wind maps from CIRS makes this approach viable. On Earth, the wave forcing associated with the equatorial oscillations generates secondary meridional circulations that affect the mean flow and planetary wave ducting well away from the equator. This may relate to the triggering of the recently reported mid-latitude storms on Saturn
Equatorial Oscillations in Jupiter's and Saturn's Atmospheres
Equatorial oscillations in the zonal-mean temperatures and zonal winds have been well documented in Earth's middle atmosphere. A growing body of evidence from ground-based and Cassini spacecraft observations indicates that such phenomena also occur in the stratospheres of Jupiter and Saturn. Earth-based midinfrared measurements spanning several decades have established that the equatorial stratospheric temperatures on Jupiter vary with a cycle of 4-5 years and on Saturn with a cycle of approximately 15 years. Spectra obtained by the Composite Infrared Spectrometer (CIRS) during the Cassini swingby at the end of 2000, with much better vertical resolution than the ground-based data, indicated a series of vertically stacked warm and cold anomalics at Jupiter's equator; a similar structurc was seen at Saturn's equator in CIRS limb measurements made in 2005, in the early phase of Cassini's orbital tour. The thermal wind equation implied similar patterns of mean zonal winds increasing and decreasing with altitude. On Saturn the peak-to-pcak amplitude of this variation was nearly 200 meters per second. The alternating vertical pattern of wanner and colder cquatorial tcmperatures and easterly and westerly tendencies of the zonal winds is seen in Earth's equatorial oscillations, where the pattern descends with time, The Cassini Jupiter and early Saturn observations were snapshots within a limited time interval, and they did not show the temporal evolution of the spatial patterns. However, more recent Saturn observations by CIRS (2010) and Cassini radio-occultation soundings (2009-2010) have provided an opportunity to follow the change of the temperature-zonal wind pattern, and they suggest there is descent, at a rate of roughly one scale height over four years. On Earth, the observed descent in the zonal-mean structure is associated with the absorption of a combination of vertically propagating waves with easlerly and westerly phase velocities. The peak-to-peak zonal wind amplitude in the oscillation pattern and the rate of descent constrain the absorbed wave flux of zonal momentum. On Saturn this is approximately 0.05 square meters per square seconds, which is comparable to if not greater than that associated with the terrestrial oscillations. We discuss possible candidates for the absorbed waves on Saturn. On Earth the wave forcing of the equatorial oscillation generales secondary circulations that can affcct the temperature and wind structure at latitudes well away from the equator, and we discuss possible evidence of that on Saturn
Gap Formation in the Dust Layer of 3D Protoplanetary Disks
We numerically model the evolution of dust in a protoplanetary disk using a
two-phase (gas+dust) Smoothed Particle Hydrodynamics (SPH) code, which is
non-self-gravitating and locally isothermal. The code follows the three
dimensional distribution of dust in a protoplanetary disk as it interacts with
the gas via aerodynamic drag. In this work, we present the evolution of a disk
comprising 1% dust by mass in the presence of an embedded planet for two
different disk configurations: a small, minimum mass solar nebular (MMSN) disk
and a larger, more massive Classical T Tauri star (CTTS) disk. We then vary the
grain size and planetary mass to see how they effect the resulting disk
structure. We find that gap formation is much more rapid and striking in the
dust layer than in the gaseous disk and that a system with a given stellar,
disk and planetary mass will have a different appearance depending on the grain
size and that such differences will be detectable in the millimetre domain with
ALMA. For low mass planets in our MMSN models, a gap can open in the dust disk
while not in the gas disk. We also note that dust accumulates at the external
edge of the planetary gap and speculate that the presence of a planet in the
disk may facilitate the growth of planetesimals in this high density region.Comment: 5 page, 4 figures. Accepted for publication in Astrophysics & Space
Scienc
Hubbard band or oxygen vacancy states in the correlated electron metal SrVO?
We study the effect of oxygen vacancies on the electronic structure of the
model strongly correlated metal SrVO. By means of angle-resolved
photoemission (ARPES) synchrotron experiments, we investigate the systematic
effect of the UV dose on the measured spectra. We observe the onset of a
spurious dose-dependent prominent peak at an energy range were the lower
Hubbard band has been previously reported in this compound, raising questions
on its previous interpretation. By a careful analysis of the dose dependent
effects we succeed in disentangling the contributions coming from the oxygen
vacancy states and from the lower Hubbard band. We obtain the intrinsic ARPES
spectrum for the zero-vacancy limit, where a clear signal of a lower Hubbard
band remains. We support our study by means of state-of-the-art ab initio
calculations that include correlation effects and the presence of oxygen
vacancies. Our results underscore the relevance of potential spurious states
affecting ARPES experiments in correlated metals, which are associated to the
ubiquitous oxygen vacancies as extensively reported in the context of a
two-dimensional electron gas (2DEG) at the surface of insulating
transition metal oxides.Comment: Manuscript + Supplemental Material, 12 pages, 9 figure
Detection of CO and HCN in Pluto's atmosphere with ALMA
Observations of the Pluto-Charon system, acquired with the ALMA
interferometer on June 12-13, 2015, have yielded a detection of the CO(3-2) and
HCN(4-3) rotational transitions from Pluto, providing a strong confirmation of
the presence of CO, and the first observation of HCN, in Pluto's atmosphere.
The CO and HCN lines probe Pluto's atmosphere up to ~450 km and ~900 km
altitude, respectively. The CO detection yields (i) a much improved
determination of the CO mole fraction, as 515+/-40 ppm for a 12 ubar surface
pressure (ii) clear evidence for a well-marked temperature decrease (i.e.,
mesosphere) above the 30-50 km stratopause and a best-determined temperature of
70+/-2 K at 300 km, in agreement with recent inferences from New Horizons /
Alice solar occultation data. The HCN line shape implies a high abundance of
this species in the upper atmosphere, with a mole fraction >1.5x10-5 above 450
km and a value of 4x10-5 near 800 km. The large HCN abundance and the cold
upper atmosphere imply supersaturation of HCN to a degree (7-8 orders of
magnitude) hitherto unseen in planetary atmospheres, probably due to the slow
kinetics of condensation at the low pressure and temperature conditions of
Pluto's upper atmosphere. HCN is also present in the bottom ~100 km of the
atmosphere, with a 10-8 - 10-7 mole fraction; this implies either HCN
saturation or undersaturation there, depending on the precise stratopause
temperature. The HCN column is (1.6+/-0.4)x10^14 cm-2, suggesting a
surface-referred net production rate of ~2x10^7 cm-2s-1. Although HCN
rotational line cooling affects Pluto's atmosphere heat budget, the amounts
determined in this study are insufficient to explain the well-marked mesosphere
and upper atmosphere's ~70 K temperature. We finally report an upper limit on
the HC3N column density (< 2x10^13 cm-2) and on the HC15N / HC14N ratio (<
1/125).Comment: Revised version. Icarus, in press, Oct. 11, 2016. 57 pages, including
13 figures and 4 table
On the pressure of collisionless particle fluids. The case of solids settling in disks
Aims. Collections of dust, grains, and planetesimals are often treated as a
pressureless fluid. We study the validity of neglecting the pressure of such a
fluid by computing it exactly for the case of particles settling in a disk.
Methods. We solve a modified collisionless Boltzmann equation for the particles
and compute the corresponding moments of the phase space distribution: density,
momentum, and pressure. Results. We find that whenever the Stokes number,
defined as the ratio of the gas drag timescale to the orbital timescale, is
more than 1/2, the particle fluid cannot be considered as pressureless. While
we show it only in the simple case of particles settling in a laminar disk,
this property is likely to remain true for most flows, including turbulent
flows.Comment: Accepted for publication as a research note in Astronomy and
Astrophysics. Language edite
OPA quantification of amino groups at the surface of Lipidic NanoCapsules (LNCs) for ligand coupling improvement
Lipidic NanoCapsules (LNCs) were prepared via an emulsion phase inversion method. Nanoparticles with hydrodynamic diameter of 25, 50 and 100nm were easily obtained. Their surfaces are covered with short PEG chains (PEG 660) which are not bearing any chemical reactivities. Thus, in order to overcome this handicap towards post-functionalization possibilities, post-insertion of DSPE-PEG2000 amino (DSPA) can be employed. In order to characterize the insertion step, we have developed a chemical assay for the quantification of amino group inside the PEG shell of LNCs. Subsequently, the post-insertion yield was found to be comprised between 60 and 90% whatever the hydrodynamic diameter of the LNCs is. By means of simple calculations, the density of amino group is estimated to be closed to 0.2 and 1.2molecules/nm(2). The formulation of LNCs and their controlled functionalization represent an interesting system for the development of bionanoconjugates in a short and effective process
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