1,175 research outputs found
Water in Comet 2/2003 K4 (LINEAR) with Spitzer
We present sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR)
obtained on 16 July 2004 (r_{h} = 1.760 AU, Delta_{Spitzer} = 1.409 AU, phase
angle 35.4 degrees) with the Spitzer Space Telescope. The nu_{2} vibrational
band of water is detected with a high signal-to-noise ratio (> 50). Model
fitting to the best spectrum yields a water ortho-to-para ratio of 2.47 +/-
0.27, which corresponds to a spin temperature of 28.5^{+6.5}_{-3.5} K. Spectra
acquired at different offset positions show that the rotational temperature
decreases with increasing distance from the nucleus, which is consistent with
evolution from thermal to fluorescence equilibrium. The inferred water
production rate is (2.43 +/- 0.25) \times 10^{29} molec. s^{-1}. The spectra do
not show any evidence for emission from PAHs and carbonate minerals, in
contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp).
However, residual emission is observed near 7.3 micron the origin of which
remains unidentified.Comment: 33 pages, including 11 figures, 2 tables, ApJ 2007 accepte
Observations of OH in comet Levy with the Nancay radio telescope
Due to extremely favorable excitation conditions, comet Levy (1990c) exhibited in August-September 1990 the strongest OH 18-cm signal ever recorded in a comet at the Nancay radio telescope. This unique opportunity was used to measure the OH satellite lines at 1612 and 1721 MHz, to perform extensive mapping of the OH radio emission and to make a sensitive evaluation of the cometary magnetic field, of the H2O outflow velocity and of the OH production rate
Interferometric mapping of the 3.3-mm continuum emission of comet 17P/Holmes after its 2007 outburst
Comet 17P/Holmes underwent a dramatic outburst in October 2007, caused by the
sudden fragmentation of its nucleus and the production of a large quantity of
grains scattering sunlight. We report on 90 GHz continuum observations carried
out with the IRAM Plateau de Bure interferometer on 27.1 and 28.2 October 2007
UT, i.e., 4-5 days after the outburst. These observations probed the thermal
radiation of large dust particles, and therefore provide the best constraints
on the mass in the ejecta debris. The thermal emission of the debris was
modelled and coupled to a time-dependent description of their expansion after
the outburst. The analysis was performed in the Fourier plane. Visibilities
were computed for the two observing dates and compared to the data to measure
their velocity and mass. Optical data and 250-GHz continuum measurements
published in the literature were used to further constrain the dust kinematics
and size distribution. Two distinct dust components in terms of kinematic
properties are identified in the data. The large-velocity component, with
typical velocities V0 of 50-100 m/s for 1 mm particles, displays a steep size
distribution with a size index estimated to q = -3.7 (\pm0.1), assuming a
minimum grain size of 0.1 \mum. It corresponds to the fast expanding shell
observed in optical images. The slowly-moving "core" component (V0 = 7-9 m/s)
detected near the nucleus has a size index |q| < 3.4 and contains a higher
proportion of large particles than the shell. The dust mass in the core is in
the range 0.1-1 that of the shell. Using optical constants pertaining to porous
grains (50% porosity) made of astronomical silicates mixed with water ice (48%
in mass), the total dust mass Mdust injected by the outburst is estimated to
4-14 x 10**11 kg, corresponding to 3-9% the nucleus mass.Comment: 15 pages with 11 figures and 7 tables. Accepted for publication in
Astronomy & Astrophysic
SĂ©lection participative et adaptation locale
The use of organic seeds has been compulsory since 2005 for practicing organic farming. Despite the efforts made by seed companies, applications are not yet fully satisfied in quantity and diversity. Producers of Bio Loire Ocean made the bet to develop a research program on this issue. How to set up and select specific varieties for their territories and production systems? Choice was made to work with varieties populations because of their plasticity and diversity. With the help of INRA SAD, a local participatory breeding work was initiated on many vegetable crops including leading species in the region (carrot, salad) and other species for diversification (parsnips, tomatoes,...). The results are encouraging and the producers wish to pursue and develop specific selection on their farms in order to have organic varieties adapted to their pedoclimatic and socio-economic environments. Like the partnership established with AGROCAMPUS OUEST and the network Carotte et autres Daucus, we wish to promote the genetic diversity of crop varieties and meet the needs of producers and consumers.
Our program will grow in the coming years, involving and combining the skills and expertise of researchers, producers and multipliers for an overall, coherent and sustainable organic vegetable seed industry in the region of Pays de Loire
A Coupled Euler-Lagrange CFD Modelling of Droplets-To-Film
In this paper, a droplet to film interaction model technique is presented. In the proposed approach, the liquid and gas continua are modelled using an enhanced Volume of Fluid (VoF) technique while the droplets are tracked using a Lagrangian framework and are coupled to the Eulerian phases using source terms. The eventual target application is an aeroengine bearing chamber in which oil is found as droplets, shed from the bearings, splashing on impact, separated from wall surfaces at obstacles or simply re-entrained, and as a continuum oil film coating the bearing chamber outer walls which it also cools. In finite volume CFD techniques, a prohibitively large number of cells would be required to describe the details of the droplet impact phenomenon. Based on published correlations, the splashing droplets are created and tracked as Lagrangian particles. The flowing film and the gas continua are handled with an enhanced Volume of Fluid technique
Nitrogen isotopic ratios in Barnard 1: a consistent study of the N2H+, NH3, CN, HCN and HNC isotopologues
The 15N isotopologue abundance ratio measured today in different bodies of
the solar system is thought to be connected to 15N-fractionation effects that
would have occured in the protosolar nebula. The present study aims at putting
constraints on the degree of 15N-fractionation that occurs during the
prestellar phase, through observations of D, 13C and 15N-substituted
isotopologues towards B1b. Both molecules from the nitrogen hydride family,
i.e. N2H+ and NH3, and from the nitrile family, i.e. HCN, HNC and CN, are
considered in the analysis. As a first step, we model the continuum emission in
order to derive the physical structure of the cloud, i.e. gas temperature and
H2 density. These parameters are subsequently used as an input in a non-local
radiative transfer model to infer the radial abundances profiles of the various
molecules. Our modeling shows that all the molecules are affected by depletion
onto dust grains, in the region that encompasses the B1-bS and B1-bN cores.
While high levels of deuterium fractionation are derived, we conclude that no
fractionation occurs in the case of the nitrogen chemistry. Independently of
the chemical family, the molecular abundances are consistent with 14N/15N~300,
a value representative of the elemental atomic abundances of the parental gas.
The inefficiency of the 15N-fractionation effects in the B1b region can be
linked to the relatively high gas temperature ~17K which is representative of
the innermost part of the cloud. Since this region shows signs of depletion
onto dust grains, we can not exclude the possibility that the molecules were
previously enriched in 15N, earlier in the B1b history, and that such an
enrichment could have been incorporated into the ice mantles. It is thus
necessary to repeat this kind of study in colder sources to test such a
possibility.Comment: accepted in A&
A Review of H2CO 6cm Masers in the Galaxy
We present a review of the field of formaldehyde (H2CO) 6cm masers in the
Galaxy. Previous to our ongoing work, H2CO 6cm masers had been detected in the
Galaxy only toward three regions: NGC7538 IRS1, Sgr B2, and G29.96-0.02.
Current efforts by our group using the Very Large Array, Arecibo, and the Green
Bank Telescope have resulted in the detection of four new H2CO 6cm maser
regions. We discuss the characteristics of the known H2CO masers and the
association of H2CO 6cm masers with very young regions of massive star
formation. We also review the current ideas on the pumping mechanism for H2CO
6cm masers.Comment: 10 pages, 5 figures, IAU Symposium 242: Astrophysical Masers and
their Environment
Rift Valley Fever during Rainy Seasons, Madagascar, 2008 and 2009
The virus reemerged during an outbreak in Madagascar in 2008
Water in Comets 71P/Clark and C/2004 B1 (LINEAR) with Spitzer
We present 5.5 to 7.6 micron spectra of comets 71P/Clark (2006 May 27.56 UT,
r_h = 1.57 AU pre-perihelion) and C/2004 B1 (LINEAR) (2005 October 15.22 UT,
r_h = 2.21 AU pre-perihelion and 2006 May 16.22 UT, r_h = 2.06 AU
post-perihelion) obtained with the Spitzer Space Telescope. The nu_2
vibrational band of water is detected with a signal-to-noise ratio of 11 to 50.
Fitting the spectra using a fluorescence model of water emission yields a water
rotational temperature of < 18 K for 71P/Clark and approximately less than or
equivalent to 14 +/- 2 K (pre-perihelion) and 23 +/- 4 K (post-perihelion) for
C/2004 B1 (LINEAR). The water ortho-to-para ratio in C/2004 B1 (LINEAR) is
measured to be 2.31 +/- 0.18, which corresponds to a spin temperature of
26^{+3}_{-2} K. Water production rates are derived. The agreement between the
water model and the measurements is good, as previously found for Spitzer
spectra of C/2003 K4 (LINEAR). The Spitzer spectra of these three comets do not
show any evidence for emission from PAHs and carbonate minerals, in contrast to
results reported for comets 9P/Tempel~1 and C/1995 O1 (Hale-Bopp).Comment: 16 pages, 1 table, 7 figures, ApJ accepted 200
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