40 research outputs found
Beam dynamics studies in SPIRAL II LINAC
ACCInternational audienceThe proposed LINAG driver for the SPIRAL 2 project aims to accelerate a 5-mA D+ beam up to 20 A.MeV and 1-mA beam for q/A=1/3 up to 14.5 A.MeV. It is acontinuous wave regime (cw), designed for maximum efficiency in the transmission of intense beams. It consists of an injector (two ECR sources + a Radio Frequency Quadrupole) followed by a superconducting section based on an array of independently phased cavities. This paper presents beams dynamics studies associated to the LINAG driver. End-to-end simulations (low-energy beam lines, RFQ, medium-energy beam line, SC linac) are shown
Spectropolarimetric observations of the transiting planetary system of the K dwarf HD 189733
With a Jupiter-mass planet orbiting at a distance of only 0.031 AU, the
active K2 dwarf HD 189733 is a potential candidate in which to study the
magnetospheric interactions of a cool star with its recently-discovered
close-orbiting giant planet. We decided to explore the strength and topology of
the large-scale magnetosphere of HD 189733, as a future benchmark for
quantitative studies for models of the star/planet magnetic interactions. To
this end, we used ESPaDOnS, the new generation spectropolarimeter at the
Canada-France-Hawaii 3.6m telescope, to look for Zeeman circular polarisation
signatures in the line profiles of HD 189733 in 2006 June and August. Zeeman
signatures in the line profiles of HD 189733 are clearly detected in all
spectra, demonstrating that a field is indeed present at the surface of the
star. The Zeeman signatures are not modulated with the planet's orbital period
but apparently vary with the stellar rotation cycle. The reconstructed
large-scale magnetic field, whose strength reaches a few tens of G, is
significantly more complex than that of the Sun; it involves in particular a
significant toroidal component and contributions from magnetic multipoles of
order up to 5. The CaII H & K lines clearly feature core emission, whose
intensity is apparently varying mostly with rotation phase. Our data suggest
that the photosphere and magnetic field of HD 189733 are sheared by a
significant amount of differential rotation. Our initial study confirms that HD
189733 is an optimal target for investigating activity enhancements induced by
closely orbiting planets. More data are needed, densely covering both the
orbital and rotation cycles, to investigate whether and how much the planet
contributes to the overall activity level of HD 189733.Comment: Accepted in Astronomy and Astrophysics, 12 page
Defining and cataloging exoplanets: The exoplanet.eu database
We describe an online database for extra-solar planetary-mass candidates,
updated regularly as new data are available. We first discuss criteria for the
inclusion of objects in the catalog: "definition" of a planet and several
aspects of the confidence level of planet candidates. {\bf We are led to point
out the conflict between sharpness of belonging or not to a catalogue and
fuzziness of the confidence level.} We then describe the different tables of
extra-solar planetary systems, including unconfirmed candidates (which will
ultimately be confirmed, or not, by direct imaging). It also provides online
tools: histogrammes of planet and host star data, cross-correlations between
these parameters and some VO services. Future evolutions of the database are
presented.Comment: Accepted in Astronomy and Astrophysics (revised version
Low-Rank Network Decomposition Reveals Structural Characteristics Of Small-World Networks
Small-world networks occur naturally throughout biological, technological, and social systems. With their prevalence, it is particularly important to prudently identify small-world networks and further characterize their unique connection structure with respect to network function. In this work we develop a formalism for classifying networks and identifying small-world structure using a decomposition of network connectivity matrices into low-rank and sparse components, corresponding to connections within clusters of highly connected nodes and sparse interconnections between clusters, respectively. We show that the network decomposition is independent of node indexing and define associated bounded measures of connectivity structure, which provide insight into the clustering and regularity of network connections. While many existing network characterizations rely on constructing benchmark networks for comparison or fail to describe the structural properties of relatively densely connected networks, our classification relies only on the intrinsic network structure and is quite robust with respect to changes in connection density, producing stable results across network realizations. Using this framework, we analyze several real-world networks and reveal new structural properties, which are often indiscernible by previously established characterizations of network connectivity
Discovery of a weak magnetic field in the photosphere of the single giant Pollux
Aims: We observe the nearby, weakly-active single giant, Pollux, in order to
directly study and infer the nature of its magnetic field. Methods: We used the
new generation spectropolarimeters ESPaDOnS and NARVAL to observe and detect
circular polarization within the photospheric absorption lines of Pollux. Our
observations span 18 months from 2007-2009. We treated the spectropolarimetric
data using the Least-Squares Deconvolution method to create high
signal-to-noise ratio mean Stokes V profiles. We also measured the classical
activity indicator S-index for the Ca H&K lines, and the stellar radial
velocity (RV). Results: We have unambiguously detected a weak Stokes V signal
in the spectral lines of Pollux, and measured the related surface-averaged
longitudinal magnetic field Bl. The longitudinal field averaged over the span
of the observations is below one gauss. Our data suggest variations of the
longitudinal magnetic field, but no significant variation of the S-index. We
observe variations of RV which are qualitatively consistent with the published
ephemeris for a proposed exoplanet orbiting Pollux. The observed variations of
Bl appear to mimic those of RV, but additional data for this relationship to be
established. Using evolutionary models including the effects of rotation, we
derive the mass of Pollux and we discuss its evolutionary status and the origin
of its magnetic field. Conclusions: This work presents the first direct
detection of the magnetic field of Pollux, and demonstrates that ESPaDOnS and
NARVAL are capable of obtaining sub-G measurements of the surface-averaged
longitudinal magnetic field of giant stars, and of directly studying the
relationships between magnetic activity, stellar evolution and planet hosting
of these stars.Comment: 8 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
SPIRAL II Project (electron option) - Preliminary Design Study
This document presents a Preliminary Design Study (PDS) of the electron option of the SPIRAL II project
EXODAT: A VO-Compliant Database for Exoplanetary Systems
International audienceThe EXODAT project aims to provide the information needed for the selection of the best targets and preparation of the statistical analysis for exoplanet searches. The COROT exoplanet mission will continuously observe a set of selected stars for 150 days to discover planetary transits. At the end of the mission in 2010, EXODAT will be the first exoplanet database with physical characteristics of parent stars and of their planets. EXODAT currently contains 10 million stars over 100 square degrees centered on two main regions (RA=6h50m Dec=0\deg, RA=18h50 Dec=0\deg). COROT team members can access: astrometry; broad-band photometry from UBVRi, 2MASS, USNO-A2 and DENIS; stellar parameters such as spectral type, luminosity class and reddening; and a subset of moderate resolution spectra with the derived stellar parameters T_\eff\, log g, [M/H], rotation velocity and binarity. Light curves and planet properties will be available after the mission's launch
The LASCO-ARTEMIS Catalog links to the virtual Observatory using SiTools
International audienceThe LASCO-C2 coronagraph aboard the SOHO solar observatory has been providing a continuous flow of coronal images for the past ten years. Synoptic maps have been built from these images and offer a view of the temporal evolution of the solar corona and Coronal Mass Ejections (CMEs). We present the LASCO-ARTEMIS (Automatic Recognition of Transient Events and Marseille Inventory from Synoptic maps) database. Data have been released using a new automated method of detection of CMEs based on an adaptive filtering and segmentation. Time of appearance, position angle, angular extent and average velocity are released via the SiTools environment and their Virtual Observatory (VO) SVA (Services á Valeur Ajoutée)