472 research outputs found
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
Hdo And SO2 Thermal Mapping On Venus: Evidence For Strong SO2 Variability
We have been using the TEXES high-resolution imaging spectrometer at the NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over the disk of Venus. Observations took place on January 10-12, 2012. The diameter of Venus was 13 arcsec, with an illumination factor of 80%. Data were recorded in the 1344-1370 cm(-1) range (around 7.35 mu m) with a spectral resolving power of 80 000 and a spatial resolution of about 1.5 arcsec. In this spectral range, the emission of Venus comes from above the cloud top (z = 60-80 km). Four HDO lines and tens of SO2 lines have been identified in our spectra. Mixing ratios have been estimated from HDO/CO2 and SO2/CO2 line depth ratios, using weak neighboring transitions of comparable depths. The HDO maps, recorded on Jan. 10 and Jan. 12, are globally uniform with no significant variation between the two dates. A slight enhancement of the HDO mixing ratio toward the limb might be interpreted as a possible increase of the D/H ratio with height above the cloud level. The mean H2O mixing ratio is found to be 1.5 +/-0.75 ppm, assuming a D/H ratio of 0.0312 (i.e. 200 times the terrestrial value) over the cloud deck. The SO2 maps, recorded each night from Jan. 10 to Jan. 12, show strong variations over the disk of Venus, by a factor as high as 5 to 10. In addition, the position of the maximum SO2 mixing ratio strongly varies on a timescale of 24 h. The maximum SO2 mixing ratio ranges between 75 +/-25 ppb and 125 +/-50 ppb between Jan. 10 and Jan. 12. The high variability of sulfur dioxide is probably a consequence of its very short photochemical lifetime.NASA NNX-08AE38A, NNX08AW33G S03NSF AST-0607312, AST-0708074Astronom
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HDO And SO2 Thermal Mapping On Venus II. The So2 Spatial Distribution Above And Within The Clouds
Sulfur dioxide and water vapor, two key species of Venus photochemistry, are known to exhibit significant spatial and temporal variations above the cloud top. In particular, ground-based thermal imaging spectroscopy at high spectral resolution, achieved on Venus in January 2012, has shown evidence for strong SO2 variations on timescales shorter than a day. We have continued our observing campaign using the TEXES high-resolution imaging spectrometer at the NASA InfraRed Telescope Facility to map sulfur dioxide over the disk of Venus at two different wavelengths, 7 mu m (already used in the previous study) and 19 mu m. The 7 mu m radiation probes the top of the H2SO4 cloud, while the 19 mu m radiation probes a few kilometers below within the cloud. Observations took place on October 4 and 5, 2012. Both HDO and SO2 lines are identified in our 7-mu m spectra and SO2 is also easily identified at 19 mu m. The CO2 lines at 7 and 19 mu m are used to infer the thermal structure. An isothermal/inversion layer is present at high latitudes (above 60 N and S) in the polar collars, which was not detected in October 2012. The enhancement of the polar collar in October 2012 is probably due to the fact that the morning terminator is observed, while the January data probed the evening terminator. As observed in our previous run, the HDO map is relatively uniform over the disk of Venus, with a mean mixing ratio of about 1 ppm. In contrast, the SO2 maps at 19 mu m show intensity variations by a factor of about 2 over the disk within the cloud, less patchy than observed at the cloud top at 7 mu m. In addition, the SO2 maps seem to indicate significant temporal changes within an hour. There is evidence for a cutoff in the SO2 vertical distribution above the cloud top, also previously observed by SPICAV/SOIR aboard Venus Express and predicted by photochemical models.NASA NNX-08AE38AIRTF AST-0607312, AST-0708074Astronom
Dust evolution in protoplanetary disks
We investigate the behaviour of dust in protoplanetary disks under the action
of gas drag using our 3D, two-fluid (gas+dust) SPH code. We present the
evolution of the dust spatial distribution in global simulations of planetless
disks as well as of disks containing an already formed planet. The resulting
dust structures vary strongly with particle size and planetary gaps are much
sharper than in the gas phase, making them easier to detect with ALMA than
anticipated. We also find that there is a range of masses where a planet can
open a gap in the dust layer whereas it doesn't in the gas disk. Our dust
distributions are fed to the radiative transfer code MCFOST to compute
synthetic images, in order to derive constraints on the settling and growth of
dust grains in observed disks.Comment: 6 pages, 5 figures, to appear in the Proceedings of IAU Symp. 249:
Exoplanets: Detection, Formation and Dynamics (Suzhou, China
Predicting Dust Distribution in Protoplanetary Discs
We present the results of three-dimensional numerical simulations that
include the effects of hydrodynamical forces and gas drag upon an evolving
dusty gas disk. We briefly describe a new parallel, two phase numerical code
based upon the smoothed particle hydrodynamics (SPH) technique in which the gas
and dust phases are represented by two distinct types of particles. We use the
code to follow the dynamical evolution of a population of grains in a gaseous
protoplanetary disk in order to understand the distribution of grains of
different sizes within the disk. Our ``grains'' range from metre to
submillimetre in size.Comment: 2 pages, LaTeX with 1 ps figure embedded, using newpasp.sty
(supplied). To appear in the proceedings of the XIXth IAP colloquium
"Extrasolar Planets: Today and Tomorrow" held in Paris, France, 2003, June 30
-- July 4, ASP Conf. Se
Investigation of laser ablated ZnO thin films grown with Zn metal target: a structural study
High quality ZnO thin films were gown using the pulsed laser deposition
technique on (0001) AlO substrates in an oxidizing atmosphere, using a
Zn metallic target. We varied the growth conditions such as the deposition
temperature and the oxygen pressure. First, using a battery of techniques such
as x-rays diffraction, Rutherford Backscattering spectroscopy and atomic force
microscopy, we evaluated the structural quality, the stress and the degree of
epitaxy of the films. Second, the relations between the deposition conditions
and the structural properties, that are directly related to the nature of the
thin films, are discussed qualitatively. Finally, a number of issues on how to
get good-quality ZnO films are addressed.Comment: To be published in Jour. Appl. Phys. (15 August 2004
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
Structural and magnetic properties of a series of low doped ZnCoO thin films deposited from Zn and Co metal targets on (0001) AlO substrates
We report on the synthesis of low doping ZnCoO () thin
films on (0001)-AlO substrates. The films were prepared in an oxidizing
atmosphere, using the pulsed laser deposition technique starting from Zn and Co
metallic targets. We first studied the influence of the strains of ZnO and
their stuctural properties. Second, we have investigated the structural and the
magnetic properties of the ZnCoO films. We show that at low doping,
the lattice parameters and the magnetization of the ZnCoO films
depend strongly on the Co concentration.Comment: to be published in Journal Applied Physics (June 2004) as a
proceeding of the MMM/Intermag Conferenc
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