26 research outputs found
The Earth as an extrasolar transiting planet - II: HARPS and UVES detection of water vapor, biogenic O, and O
The atmospheric composition of transiting exoplanets can be characterized
during transit by spectroscopy. For the transit of an Earth twin, models
predict that biogenic and should be detectable, as well as water
vapour, a molecule linked to habitability as we know it on Earth. The aim is to
measure the Earth radius versus wavelength - or the atmosphere
thickness - at the highest spectral resolution available to fully
characterize the signature of Earth seen as a transiting exoplanet. We present
observations of the Moon eclipse of 21-12-2010. Seen from the Moon, the Earth
eclipses the Sun and opens access to the Earth atmosphere transmission
spectrum. We used HARPS and UVES spectrographs to take penumbra and umbra
high-resolution spectra from 3100 to 10400 Ang. A change of the quantity of
water vapour above the telescope compromised the quality of the UVES data. We
corrected for this effect in the data processing. We analyzed the data by 3
different methods. The 1st method is based on the analysis of pairs of penumbra
spectra. The 2nd makes use of a single penumbra spectrum, and the 3rd of all
penumbra and umbra spectra. Profiles are obtained with the three
methods for both instruments. The 1st method gives the best result, in
agreement with a model. The second method seems to be more sensitive to the
Doppler shift of solar spectral lines with respect to the telluric lines. The
3rd method makes use of umbra spectra which bias the result, but it can be
corrected for this a posteriori from results with the first method. The 3
methods clearly show the spectral signature of the Rayleigh scattering in the
Earth atmosphere and the bands of HO, O, and O. Sodium is detected.
Assuming no atmospheric perturbations, we show that the E-ELT is theoretically
able to detect the A-band in 8~h of integration for an Earth twin at
10pc.Comment: Final version accepted for publication in A&A - 21 pages, 27 figures.
Abstract above slightly shortened wrt the original. The ArXiv version has low
resolution figures, but a version with full resolution figures is available
here:
http://www.obs-hp.fr/~larnold/publi_to_download/eclipse2010_AA_v5_final.pd
The Earth as an extrasolar transiting planet: Earth's atmospheric composition and thickness revealed by Lunar eclipse observations
An important goal within the quest for detecting an Earth-like extrasolar
planet, will be to identify atmospheric gaseous bio-signatures. Observations of
the light transmitted through the Earth's atmosphere, as for an extrasolar
planet, will be the first step for future comparisons. We have completed
observations of the Earth during a Lunar eclipse, a unique situation similar to
that of a transiting planet. We aim at showing what species could be detected
in its atmosphere at optical wavelengths, where a lot of photons are available
in the masked stellar light. We present observations of the 2008 August 16 Moon
eclipse performed with the SOPHIE spectrograph at the Observatoire de
Haute-Provence. Locating the spectrograph fibers in the penumbra of the
eclipse, the Moon irradiance is then a mix of direct, unabsorbed Sun light and
solar light that has passed through the Earth's limb. This mixture essentially
reproduces what is recorded during the transit of an extrasolar planet. We
report here the clear detection of several Earth atmospheric compounds in the
transmission spectra, such as ozone, molecular oxygen, and neutral sodium as
well as molecular nitrogen and oxygen through the Rayleigh signature. Moreover,
we present a method that allows us to derive the thickness of the atmosphere
versus the wavelength for penumbra eclipse observations. We quantitatively
evaluate the altitude at which the atmosphere becomes transparent for important
species like molecular oxygen and ozone, two species thought to be tightly
linked to the presence of life. The molecular detections presented here are an
encouraging first attempt, necessary to better prepare for the future of
extremely-large telescopes and transiting Earth-like planets. Instruments like
SOPHIE will be mandatory when characterizing the atmospheres of transiting
Earth-like planets from the ground and searching for bio-marker signatures.Comment: 15 pages, 14 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
Gas–Solid Chromatography on Organic Crystals
THE full potential of gas–solid chromatography has not yet been revealed. Theoretically it could be used to obtain much greater selectivity and higher efficiency than gas–liquid chromatography1–4. So far the characteristics required of an adsorbent have limited the use of gas–solid chromatography
MEASUREMENT OF THERMODYNAMIC EQUILIBRIA BY CHROMATOGRAPHY
International audienceAfter a brief recall of the chromatographic principles, the different applications of gas chromatographic measurements of thermodynamic equilibria were reviewed. Gas and liquid chromatographies are now well known and elegant methods for measuring the physicochemical properties and phase equilibrium thermodynamic constants. Although fundamentally a dynamical method and mostly known as a powerful separation technique, chromatography can be schematized by a succession of equilibria of a chemical species partitioning between a mobile phase and a fixed liquid or solid stationary phase. It can be operated in either infinite dilution or finite concentration conditions and permits to collect a large number of data for calculating molecular interactions for solutes which are either rare or available at the trace level. Gas chromatography permits the measurement of gas adsorption isotherms, gas-liquid equilibria, molecular diffusion and interaction virials. The modelization of successive partition equilibria occuring in the chromatographic column leads to rather simple expressio is of differential enthalpy, entropy, free energy of adsorption or solution, variation of heat capacity, complexation constant, second virial coefficients, gas-solid and gas-liquid isotherms and also binary or ternary equilibria. The possibilities of High Performance-Liquid Chromatography to investigate adsorption from solutions and chemical equilibria are also discussed
Gas Solid Chromatography Measurements of the Change in the Heat Capacity during Adsorption on Graphitized Thermal Carbon Black
Gas chromatography is widely used to measure the thermodynamic functions of adsorption on the homogeneous surface of graphitized thermal carbon black in the region where Henry\u27s adsorption law is valid. A high-precision instrument with computer data acquisition measures the isosteric heat of adsorption and the change of the heat capacity during adsorption. The method is used to study the adsorption of benzene and n-pentane on different graphitized thermal carbon black samples. The data are directly comparable with the values calculated from statistical thermodynamics on graphite since it is shown that adsorbateadsorbate interactions are negligible and that the behavior of the bulk gas phase is nearly ideal. The results obtained for benzene could be compared with the molar heat capacity of adsorbed benzene measured by calorimetric methods and extrapolated at zero surface coverage. With n-pentane, however, the gas solid chromatographic method is unique, as extrapolation of calorimetric measurements is impossible because of strong adsorbate-adsorbate interactions at relatively low surface coverage
Gas-solid and gas-liquid chromatography using porous layer open tube columns made with graphitized thermal carbon black
International audienceThe preparation of porous-layer open-tubular columns for gas—liquid chromatography with graphitized thermal carbon black as a solid support and a polar stationary phase is described. The application of these columns is demonstrated by an example.The reaction products from two oxidation reactions for the production of synthetic citral have been analysed by combined gas chromatography—mass spectrometry. About 30 trace substances rsulting from redox reaction and cyclization of the starting materials were found
Analyse par chromatographie des constituants minoritaires de l'atmosphere
Action concertee: Variations climatiques naturelles ou provoqueesSIGLEAvailable from Centre de Documentation Scientifique et Technique, CNRS, 26 rue Boyer, 75971 Paris Cedex 20 (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Adsorption kinetics of β-lactoglobulin on a polyclonal immunochromatographic support
β-Lactoglobulin is one of the main components of whey proteins. Among other reasons, its allergenicity makes its
determination in hypoallergenic foods and bio-pharmaceutical products necessary. Immunoaffinity chromatography is a
widely accepted technique for purification and analysis of proteins. Knowledge of the apparent kinetics of the adsorption of
b-lactoglobulin onto the anti-b-lactoglobulin immunochromatographic column is important to optimize the analytical
process. High-performance frontal affinity chromatography was used to study the apparent kinetics of the adsorption process.
Langmuir and bi-Langmuir kinetic models, assuming one and two kinds of binding sites, respectively, were used to
characterize the adsorption kinetics of b-lactoglobulin B on a polyclonal immunoadsorbent. Very good fits were obtained
with the bi-Langmuir model for two different concentrations of b-lactoglobulin and this allowed us to calculate the apparent
adsorption rate constants and the column capacities for both kinds of sites. Experimental results indicate the possibility that
the adsorption process is not irreversible. The values of the apparent dissociation rate constants leading to the best fit were
estimated and the affinity constants were calculated. Ó 2002 Elsevier Science B.V. All rights reserved.A.P. acknowledges the Spanish Ministry of Sci-ence and Technology for a predoctoral grant. This work has been supported by CICYT (project AGL2000-1480). Collaboration between our labora-tories has been possible thanks to French–Spanish Cooperation between CNRS and CSIC (project 7954, 2000).Peer reviewe
Frontal analysis for characterizing the adsorption-desorption behavior of beta-lactoglobulin on immunoadsorbents
High-performance frontal affinity chromatography was employed to study the adsorption–desorption kinetics characterizing the retention of
Beta-lactoglobulin (Beta-LG) onto polyclonal anti-Beta-lactoglobulin (anti-Beta-LG) chromatographic supports. The adsorption and desorption processes were
studied by analyzing two different elution fronts separated by a relatively long rinsing step. The method consists in performing two successive frontal
injections of the protein. In between, the column was rinsed with a given volume of mobile phase (buffer alone). During this rinsing stage, a partial
desorption may occur and a novel amount of protein could be adsorbed in the second frontal injection step. The whole process (first adsorption,
possible desorption, and second adsorption) was simulated by a numerical procedure, in which the column was divided into a large number of slices.
A model based on bi-Langmuir type kinetics was used to describe the adsorption of the protein on the support. The model assumes a non-uniform
adsorbent with two types of binding sites. At equilibrium the adsorption isotherm is of the bi-Langmuir type. A global adsorption effect was
considered which includes the effective binding process and the mass transfer resistances due to the transport to the binding site. Therefore, the
column capacity and the kinetic parameters of the model (apparent adsorption and desorption rate constants) were determined from the best fit of
the first and second adsorption fronts to the experimental ones. The other parameters of the model are the saturation capacities for the adsorption on
each type of sites. The equilibrium affinity constants were estimated in a single experiment from the ratio of the apparent adsorption and desorption
rate constants. The high values found (around 108 M−1) reveal a strong interaction of -LG with the immunoadsorbent. Kinetic measurements
were carried out at different flow rates. Both the apparent adsorption and desorption kinetics were faster at larger flow rates, indicating an important
contribution of the mass transfer resistance in the stagnant fluid at the particle boundary. However, as expected, close values were found for the
resulting equilibrium constants calculated from the ratio of the apparent adsorption and desorption rate constant determined at various flow rates.A.P. acknowledges Spanish Ministry of Science and Tech-
nology for a predoctoral grant. This work has been supported
by Spanish CICYT (Project TIC2003-01906) and Foundation
Ramon Areces. Collaboration between laboratories has been
possible thanks to French-Spanish Cooperation between CNRS
and CSIC.Peer reviewe