Planets less massive than about 10
M
Earth
are expected to have no massive H–He atmosphere and a cometary composition (∼50% rocks, 50% water, by mass) provided they formed beyond the snowline of ...protoplanetary disks. Due to inward migration, such planets could be found at any distance between their formation site and the star. If migration stops within the habitable zone, this may produce a new kind of planets, called
ocean-planets. Ocean-planets typically consist in a silicate core, surrounded by a thick ice mantle, itself covered by a 100 km-deep ocean. The possible existence of ocean-planets raises important astrobiological questions: Can life originate on such body, in the absence of continent and ocean–silicate interfaces? What would be the nature of the atmosphere and the geochemical cycles? In this work, we address the fate of
hot ocean-planets produced when migration ends at a closer distance. In this case the liquid/gas interface can disappear, and the hot H
2O envelope is made of a supercritical fluid. Although we do not expect these bodies to harbor life, their detection and identification as water-rich planets would give us insight as to the abundance of hot and, by extrapolation, cool ocean-planets. The water reservoir of these planets seems to be weakly affected by gravitational escape, provided that they are located beyond some minimum distance, e.g. 0.04 AU for a 5-Earth-mass planet around a Sun-like star. The swelling of their water atmospheres by the high stellar flux is expected not to significantly increase the planets' radii. We have studied the possibility of detecting and characterizing these hot ocean-planets by measuring their mean densities using transit missions in space—CoRoT (CNES) and
Kepler (NASA)—in combination with Doppler velocimetry from the ground—HARPS (ESO) and possible future instruments. We have determined the domain in the stellar magnitude, orbital distance plane where discrimination between ocean-planets and rocky planets is possible with these instruments. The brightest stars of the mission target lists and the planets closest to their stars are the most favorable cases. Full advantage of high precision photometry by CoRoT, and particularly
Kepler, can be obtained only if a new generation of Doppler instruments is built.
Context. Nulling interferometry has been suggested as the underlying principle for the Darwin and TPF-I exoplanet research missions. Aims. There are constraints both on the mean value of the nulling ...ratio, and on its stability. Instrument instability noise is most detrimental to the stability of the nulling performance. Methods. We applied a modified version of the classical dithering technique to the optical path difference in the scientific beam. Results. Using only this method, we repeatedly stabilised the dark fringe for several hours. This method alone sufficed to remove the $1/f$ component of the noise in our setup for periods of 10 min, typically. These results indicate that performance stability may be maintained throughout the long-duration data acquisitions typical of exoplanet spectroscopy. Conclusions. We suggest that further study of possible stabilisation strategies should be an integral part of Darwin/TPF-I research and development.
Résumé Quand La N.R.F. se crée en 1909, la poésie française est animée par un double courant, de liberté créatrice et de « renaissances ». Elle cherche une « modernité » qui échapperait à la fois à ...l'éphémère des modes et à l'académisme. C'est Henri Ghéon qui définit le plus précisément ce « classicisme moderne ». La plupart des collaborateurs de La N.R.F. sont proches de cette position. Apollinaire, Picasso, Braque sont méconnus. La revue reste étrangère au futurisme, au cubisme. Alors que l'avant-garde donne de plus en plus de place à la poésie, La N.R.F. lui en accorde peu ; elle multiplie les mises en garde et les conseils de prudence. Malgré des efforts d'ouverture, elle est passée à côté de l'avant-garde.
GOLF in-flight commissioning and calibration was carried out during the first four months, most of which represented the cruise phase of SOHO towards its final L1 orbit. The initial performance of ...GOLF is shown to be within the design specification, for the entire instrument as well as for the separate sub-systems. Malfunctioning of the polarising mechanisms after 3 to 4 months operation has led to the adoption of an unplanned operating sequence in which these mechanisms are no longer used. This mode, which measures only the blue wing of the solar sodium lines, detracts little from the detection and frequency measurements of global oscillations, but does make more difficult the absolute velocity calibration, which is currently of the order of 20%. Data continuity in the new mode is extremely high and the instrument is producing exceptionally noise-free p-mode spectra. The data set is particularly well suited to the study of effects due to the excitation mechanism of the modes, leading to temporal variations in their amplitudes. The g modes have not yet been detected in this limited data set. In the present mode of operation, there are no indications of any degradation which would limit the use of GOLF for up to 6 years or more.
Sur la prosodie de "Gravitations" Décaudin, Michel
Revue d'histoire littéraire de la France,
01/1982, Volume:
82, Issue:
1
Journal Article
Peer reviewed
Supervielle laisse, dit-il, son poème " lui-même faire son choix " en matière de prosodie, dans un esprit non de " mépris " , mais d' " assouplissement de la technique " . L'étude de Gravitations ...montre que cette incitation du texte suscite sans doute une certaine indétermination (par exemple dans la présence ou l'absence de rimes), mais qu'elle s'organise aussi selon des structures récurrentes, où apparaît particulièrement le vers de sept syllabes. Une lecture qui accepte l'élision et le langage parlé ramène fréquemment le vers libre, voire le verset, à ce type de structures, comme en une texture où, de temps en temps, une maille est sautée, ou doublée. Une indétermination analogue préside à la succession des strophes : il n'est pas rare qu'une série régulière soit interrompue par une strophe non conforme.
En 1909, dans un mouvement de rapprochement sans lendemain avec Jules Romains et les poètes de l'Abbaye, Apollinaire évoque l'existence d'un groupe qui se serait organisé en 1903-1904 autour de sa ...revue Le Festin d'Ésope. L'examen des neuf numéros publiés montre que les relations amicales ont joué plus que les affinités esthétiques dans le choix des collaborateurs. S'il est vrai qu'Apollinaire et Salmon, dans une moindre mesure Hertz et Nau représentent une tendance de la poésie à venir, il n'y a pas eu pour autant de groupe cohérent du Festin d'Ésope.
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