2,022 research outputs found
Detection of CO in Triton's atmosphere and the nature of surface-atmosphere interactions
Triton possesses a thin atmosphere, primarily composed of nitrogen, sustained
by the sublimation of surface ices. The goal is to determine the composition of
Triton's atmosphere and to constrain the nature of surface-atmosphere
interactions. We perform high-resolution spectroscopic observations in the
2.32-2.37 m range, using CRIRES at the VLT. From this first spectroscopic
detection of Triton's atmosphere in the infrared, we report (i) the first
observation of gaseous methane since its discovery in the ultraviolet by
Voyager in 1989 and (ii) the first ever detection of gaseous CO in the
satellite. The CO atmospheric abundance is remarkably similar to its surface
abundance, and appears to be controlled by a thin, CO-enriched, surface veneer
resulting from seasonal transport and/or atmospheric escape. The CH partial
pressure is several times larger than inferred from Voyager. This confirms that
Triton's atmosphere is seasonally variable and is best interpreted by the
warming of CH-rich icy grains as Triton passed southern summer solstice in
2000. The presence of CO in Triton's atmosphere also affects its temperature,
photochemistry and ionospheric composition. An improved upper limit on CO in
Pluto's atmosphere is also reported.Comment: 11 pages, including 4 figures and 2 on-line figures Astronomy and
Astrophysics, in press (accepted March 13, 2010
Exploring the spatial, temporal, and vertical distribution of methane in Pluto's atmosphere
High-resolution spectra of Pluto in the 1.66 um region, recorded with the
VLT/CRIRES instrument in 2008 (2 spectra) and 2012 (5 spectra), are analyzed to
constrain the spatial and vertical distribution of methane in Pluto's
atmosphere and to search for mid-term (4 year) variability. A sensitivity study
to model assumptions (temperature structure, surface pressure, Pluto's radius)
is performed. Results indicate that (i) no variation of the CH4 atmospheric
content (column-density or mixing ratio) with Pluto rotational phase is present
in excess of 20 % (ii) CH4 column densities show at most marginal variations
between 2008 and 2012, with a best guess estimate of a ~20 % decrease over this
time frame. As stellar occultations indicate that Pluto's surface pressure has
continued to increase over this period, this implies a concomitant decrease of
the methane mixing ratio (iii) the data do not show evidence for an
altitude-varying methane distribution; in particular, they imply a roughly
uniform mixing ratio in at least the first 22-27 km of the atmosphere, and high
concentrations of low-temperature methane near the surface can be ruled out.
Our results are also best consistent with a relatively large (> 1180 km) Pluto
radius. Comparison with predictions from a recently developed global climate
model GCM indicates that these features are best explained if the source of
methane occurs in regional-scale CH4 ice deposits, including both low latitudes
and high Northern latitudes, evidence for which is present from the rotational
and secular evolution of the near-IR features due to CH4 ice. Our "best guess"
predictions for the New Horizons encounter in 2015 are: a 1184 km radius, a 17
ubar surface pressure, and a 0.44 % CH4 mixing ratio with negligible
longitudinal variations.Comment: 21 pages, 6 figure
Bescherming en beheer van het Schelde-estuarium
The ecological quality ofthe Scheldt has been strongly affected by deepening, reclaiming and polluting the water of the river. The use of national instruments of protection has unsufficiently contributed to the recovery of the estuarium. Field managers of nature-areas have succesfully taken the negative effects of the other functions as starting point into their management. The program for compensation of lost nature on behalf of the recent deepening will be evaluated next year, and adapted if necessary. The European directives for nature, water and fishery become more and more important. They play a big role in the long term vision for the Scheldt-estuarium
A flexible data architecture to automate collection of (near) real-time methane sensor data at commercial dairy farms
To reduce methane emissions from the animal production domain, a large intensive research programme has been started in 2018 by the Dutch Ministry of Agriculture, Nature and Food. Part of this programme involves continuous monitoring of methane, by means of sensor measurements, both at the barn and ..
The Color Distribution in the Edgeworth-Kuiper Belt
We have started since 1997 the Meudon Multicolor Survey of Outer Solar System
Objects with the aim of collecting a large and homogeneous set of color data
for Trans-Neptunian and Centaurs objects [...] We have a combined sample of 52
B-R color measurements for 8 Centaurs, 22 Classicals, 13 Plutinos, 8 Scattered
objects and 1 object with unidentified dynamical class. This dataset is the
largest single and homogeneous published dataset to date [...]. A strong
(color) correlation with mean excitation velocity points toward a space
weathering/impact origin for the color diversity. However, thorough modeling of
the collisional/dynamical environment in the Edgeworth-Kuiper belt needs to be
done in order to confirm this scenario. We found also that the Classical TNOs
consist in the superposition of two distinct populations: the dynamically Cold
Classical TNOs (red colors, low i, small sizes) and the dynamically Hot
Classical TNOs (diverse colors, moderate and high i, larger sizes). [...] Our
specific observation strategy [...] permitted us to highlight a few objects
suspected to have true compositional and/or texture variation on their
surfaces. These are 1998 HK151, 1999 DF9, 1999 OY3, 2000 GP183, 2000 OK67, and
2001 KA77 and should be prime targets for further observations [...]. Our
survey has also highlighted 1998 SN165 whose colors and dynamical properties
puts it in a new dynamical class distinct from the Classicals, its previously
assigned dynamical class.Comment: Accepted for publication in Astronomical Journal (38 pages, inc. 11
figures
Determining the environmental effects of indirect subsidies: A methodological approach with an application to the Netherlands
Automated sampling and analysis in research product synthesis
The information obtained about relevant reaction parameters can be
greatly increased by monitoring concentration changes during a
reaction. To achieve this goal, a fully automated system was
designed which handles both sampling and analysis. The sampling
system takes samples at predefined intervals, and also performs a
number of tasks such as dilution, neutralization, filtration and
analysis
Chemical and physical properties of the variegated Pluto and Charon surfaces
International audienceWe present new photometric and spectroscopic observations of the Pluto-Charon system carried out at the VLT-ESO (Chile) with two 8-meter telescopes equipped with the FORS2, ISAAC and SINFONI instruments. The spectra were obtained in the 0.6-2.45μm range with a spectral resolution from 300 to 1500. The SINFONI data were obtained using Adaptive Optics, allowing a complete separation of the two bodies. We derive both objects' magnitudes in the near infrared and convert them into albedo values. These first near infrared photometric data allow to adjust the different parts of Pluto's spectrum, provided by the three instruments. We run spectral models in order to give chemical and physical constraints on the surface of Pluto and Charon. We discuss the dilution properties of the methane ice and its implications on Pluto's surface. The heterogeneities of the pure and diluted methane ice on Pluto's surface is also investigated. The high signal-to-noise level of the data and our analyses may support the presence of ethane ice on the surface of Pluto, which is one of the main products of the methane irradiation and photolysis. The analyses of the spectra of Charon suggest that the water ice is almost completely in its crystalline form and that the ammonia compound is hydrated on the surface of this satellite
Reconstructing fossil sub-structures of the Galactic disk: clues from abundance patterns of old open clusters and moving groups
The long term goal of large-scale chemical tagging is to use stellar
elemental abundances as a tracer of dispersed substructures of the Galactic
disk. The identification of such lost stellar aggregates and the exploration of
their chemical properties will be key in understanding the formation and
evolution of the disk. Present day stellar structures such as open clusters and
moving groups are the ideal testing grounds for the viability of chemical
tagging, as they are believed to be the remnants of the original larger
starforming aggregates. Until recently, high accuracy elemental abundance
studies of open clusters and moving groups having been lacking in the
literature. In this paper we examine recent high resolution abundance studies
of open clusters to explore the various abundance trends and reasses the
prospects of large-scale chemical tagging.Comment: Accepted for publication in the Publications of the Astronomical
Society of Australi
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