89 research outputs found
PSF reconstruction for NAOS-CONICA
Adaptive optics (AO) allows one to derive the point spread function (PSF)
simultaneously to the science image, which is a major advantage in
post-processing tasks such as astrometry/photometry or deconvolution. Based on
the algorithm of \citet{veran97}, PSF reconstruction has been developed for
four different AO systems so far: PUEO, ALFA, Lick-AO and Altair. A similar
effort is undertaken for NAOS/VLT in a collaboration between the group PHASE
(Onera and Observatoire de Paris/LESIA) and ESO. In this paper, we first
introduce two new algorithms that prevent the use of the so-called "
functions" to: (1) avoid the storage of a large amount of data (for both new
algorithms), (2) shorten the PSF reconstruction computation time (for one of
the two) and (3) provide an estimation of the PSF variability (for the other
one). We then identify and explain issues in the exploitation of real-time
Shack-Hartmann (SH) data for PSF reconstruction, emphasising the large impact
of thresholding in the accuracy of the phase residual estimation. Finally, we
present the data provided by the NAOS real-time computer (RTC) to reconstruct
PSF ({\em (1)} the data presently available, {\em (2)} two NAOS software
modifications that would provide new data to increase the accuracy of the PSF
reconstruction and {\em (3)} the tests of these modifications) and the PSF
reconstruction algorithms we are developing for NAOS on that basis.Comment: 12 pages & 13 figures. To be published in the proceedings of the SPIE
conference Advances in Adaptive Optics - Astronomical Telescopes &
Instrumentation, 24-31 May 2006, Orland
Influence of ethylene on sucrose accumulation in grape berry
Grape ripening is thought to be ethylene independent. However, Cabernet Sauvignon berries that were treated with 1-methylcyclopropene (1-MCP), a specific inhibitor of ethylene receptors, accumulated less sucrose over the following three weeks than did controls. This was associated with a decreased RNA accumulation of two sucrose transporters (SUC11 and SUC12), whose expression is triggered at the veraison stage when grape berries start to accumulate sugars. These observations were performed over two consecutive years. This preliminary study suggests that the role of ethylene in grape ripening needs to be reconsidered and that it could be related to sugar accumulation
LBT/LUCIFER Observations of the z~2 Lensed Galaxy J0900+2234
We present rest-frame optical images and spectra of the gravitationally
lensed, star-forming galaxy J0900+2234 (z=2.03). The observations were
performed with the newly commissioned LUCIFER1 near-infrared instrument mounted
on the Large Binocular Telescope (LBT). We fit lens models to the rest-frame
optical images and find the galaxy has an intrinsic effective radius of 7.4 kpc
with a lens magnification factor of about 5 for the A and B components. We also
discovered a new arc belonging to another lensed high-z source galaxy, which
makes this lens system a potential double Einstein ring system. Using the high
S/N rest-frame optical spectra covering H+K band, we detected Hbeta, OIII,
Halpha, NII and SII emission lines. Detailed physical properties of this high-z
galaxy were derived. The extinction towards the ionized HII regions (E_g(B-V))
is computed from the flux ratio of Halpha and Hbeta and appears to be much
higher than that towards stellar continuum (E_s(B-V)), derived from the optical
and NIR broad band photometry fitting. The metallicity was estimated using N2
and O3N2 indices. It is in the range of 1/5-1/3 solar abundance, which is much
lower than the typical z~2 star-forming galaxies. From the flux ratio of SII
6717 and 6732, we found that the electron number density of the HII regions in
the high-z galaxy were >1000 cm^-3, consistent with other z~2 galaxies but much
higher than that in local HII regions. The star-formation rate was estimated
via the Halpha luminosity, after correction for the lens magnification, to be
about 365\pm69 Msun/yr. Combining the FWHM of Halpha emission lines and the
half-light radius, we found the dynamical mass of the lensed galaxy is
5.8\pm0.9x10^10 Msun. The gas mass is 5.1\pm1.1x10^10~Msun from the H\alpha
flux surface density by using global Kennicutt-Schmidt Law, indicating a very
high gas fraction of 0.79\pm0.19 in J0900+2234.Comment: 11 pages, 6 figures accepted by ApJ, revised based on referee repor
Polychromatic guide star: feasibility study
International audienceAdaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D; program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS
Polychromatic guide star: feasibility study
International audienceAdaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D; program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS
NEAR: New Earths in the Alpha Cen Region (bringing VISIR as a "visiting instrument" to ESO-VLT-UT4)
By adding a dedicated coronagraph, ESO in collaboration with the Breakthrough Initiatives, modifies the Very Large Telescope mid-IR imager (VISIR) to further boost the high dynamic range imaging capability this instru- ment has. After the VISIR upgrade in 2012, where coronagraphic masks were first added to VISIR, it became evident that coronagraphy at a ground-based 8m-class telescope critically needs adaptive optics, even at wavelengths as long as 10μm. For VISIR, a work-horse observatory facility instrument in normal operations, this is ”easiest” achieved by bringing VISIR as a visiting instrument to the ESO-VLT-UT4 having an adaptive M2. This “visit” enables a meaningful search for Earth-like planets in the habitable zone around both α-Cen1,2. Meaningful here means, achieving a contrast of ≈ 10^(-6) within ≈ 0.8arcsec from the star while maintaining basically the normal sensitivity of VISIR. This should allow to detect a planet twice the diameter of Earth. Key components will be a diffractive coronagraphic mask, the annular groove phase mask (AGPM), optimized for the most sensitive spectral band-pass in the N-band, complemented by a sophisticated apodizer at the level of the Lyot stop. For VISIR noise filtering based on fast chopping is required. A novel internal chopper system will be integrated into the cryostat. This chopper is based on the standard technique from early radio astronomy, conceived by the microwave pioneer Robert Dicke in 1946, which was instrumental for the discovery of the 3K radio background
Impact du stress hydrique sur la qualité de la vendange : l'exemple des flavonoïdes
Ce numéro d'Innovations Agronomiques comprend les articles correspondant aux présentations du colloque « Viticulture et stress hydrique » qui s'est tenu à Montpellier le 17 juin 2014.Wine quality depends strongly on the composition of the grapes from which they are produced. Flavonoids are secondary plant metabolites that directly affect the quality, being involved in their color and stability of this color, and astringency. As many metabolites, their synthesis in the berry may vary depending on environmental conditions, especially water status of the plant. We will present the structures and properties of these flavonoids, how they are synthesized in the berry and how water stress can alter their synthesis in the berry and the composition at harvest.La qualité des vins dépend étroitement de la composition des raisins dont ils sont issus. Les flavonoïdes sont des métabolites secondaires de la plante influant directement sur cette qualité, impliqués notamment dans leur couleur et la stabilité de cette couleur, et leur astringence. Comme de nombreux métabolites, leur synthèse dans la baie peut varier en fonction des conditions environnementales, et en particulier de l’état hydrique de la plante. Nous présenterons les structures et propriétés de ces flavonoïdes, comment ils sont synthétisés dans la baie et comment un stress hydrique peut modifier leur synthèse dans la baie et la composition de la vendange
Biosynthesis and chemistry of proanthocyanidin and anthocyanin, from grapes to wine
Biosynthesis and chemistry of proanthocyanidin and anthocyanin, from grapes to wine. Macrowine 201
Fruit nutritional quality : Polyphenols
Fruit nutritional quality : Polyphenol
BAHD or SCPL acyltransferase? What a dilemma for acylation in the world of plant phenolic compounds
Phenolic compounds are secondary metabolites involved in several plant growth and development processes, including resistance to biotic and abiotic stresses. The biosynthetic pathways leading to the vast diversity of plant phenolic products often include an acylation step, with phenolic compounds being the donor or acceptor molecules. To date, two acyltransferase families using phenolic compounds as acceptor or donor molecules have been described, with each using a different 'energy-rich' acyl donor. BAHD-acyltransferases, named after the first four biochemically characterized enzymes of the group, use acyl-CoA thioesters as donor molecules, whereas SCPL (Serine CarboxyPeptidase Like)-acyltransferases use 1-O-beta-glucose esters. Here, common and divergent specifications found in the literature for both enzyme families were analyzed to answer the following questions. Are both acyltransferases involved in the synthesis of the same molecule (or same group of molecules)? Are both acyltransferases recruited in the same plant? How does the subcellular localization of these enzymes impact metabolite trafficking in plant cells
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