9,487 research outputs found
High-contrast imaging of Sirius~A with VLT/SPHERE: Looking for giant planets down to one astronomical unit
Sirius has always attracted a lot of scientific interest, especially after
the discovery of a companion white dwarf at the end of the 19th century. Very
early on, the existence of a potential third body was put forward to explain
some of the observed properties of the system. We present new coronagraphic
observations obtained with VLT/SPHERE that explore, for the very first time,
the innermost regions of the system down to 0.2" (0.5 AU) from Sirius A. Our
observations cover the near-infrared from 0.95 to 2.3 m and they offer the
best on-sky contrast ever reached at these angular separations. After detailing
the steps of our SPHERE/IRDIFS data analysis, we present a robust method to
derive detection limits for multi-spectral data from high-contrast imagers and
spectrographs. In terms of raw performance, we report contrasts of 14.3 mag at
0.2", ~16.3 mag in the 0.4-1.0" range and down to 19 mag at 3.7". In physical
units, our observations are sensitive to giant planets down to 11 at
0.5 AU, 6-7 in the 1-2 AU range and ~4 at 10 AU. Despite
the exceptional sensitivity of our observations, we do not report the detection
of additional companions around Sirius A. Using a Monte Carlo orbital analysis,
we show that we can reject, with about 50% probability, the existence of an 8
planet orbiting at 1 AU. In addition to the results presented in the
paper, we provide our SPHERE/IFS data reduction pipeline at
http://people.lam.fr/vigan.arthur/ under the MIT license.Comment: 16 pages, 10 figures, accepted for publication in MNRA
04081 Abstracts Collection -- Theory of Evolutionary Algorithms
From 15.02.04 to 20.02.04, the Dagstuhl Seminar 04081 ``Theory of Evolutionary Algorithms\u27\u27 was held in the International Conference and Research Center (IBFI),
Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Astrometry and Exoplanets: the Gaia Era, and Beyond
The wealth of information in the Gaia catalogue of exoplanets will constitute
a fundamental contribution to several hot topics of the astrophysics of
planetary systems. I briefly review the potential impact of Gaia micro-arsec
astrometry in several areas of exoplanet science, discuss what key follow-up
observations might be required as a complement to Gaia data, and shed some
light on the role of next generation astrometric facilities in the arena of
planetary systems.Comment: 6 pages, 1 figure. Proceedings of the final ELSA Conference 'Gaia: at
the frontiers of astrometry', Sevres (France), 7-11 June 2010. To appear in
EAS Publication Series, EDP Science
Apodization in high-contrast long-slit spectroscopy. Closer, deeper, fainter, cooler
The spectroscopy of faint planetary-mass companions to nearby stars is one of
the main challenges that new-generation high-contrast spectro-imagers are going
to face. In a previous work we presented a long slit coronagraph (LSC), for
which the presence of a slit in the coronagraphic focal plane induces a complex
distribution of energy in the Lyot pupil-plane that cannot be easily masked
with a binary Lyot stop. To alleviate this concern, we propose to use a pupil
apodization to suppress diffraction, creating an apodized long slit coronagraph
(ALSC). After describing how the apodization is optimized, we demonstrate its
advantages with respect to the CLC in the context of SPHERE/IRDIS long slit
spectroscopy (LSS) mode at low-resolution with a 0.12" slit and 0.18"
coronagraphic mask. We perform different sets of simulations with and without
aberrations, and with and without a slit to demonstrate that the apodization is
a more appropriate concept for LSS, at the expense of a significantly reduced
throughput (37%) compared to the LSC. Then we perform detailed end-to-end
simulations of the LSC and the ALSC that include realistic levels of
aberrations to obtain datasets representing 1h of integration time on stars of
spectral types A0 to M0 located at 10 pc. We insert spectra of planetary
companions at different effective temperatures (Teff) and surface gravities
(log g) into the data at angular separations of 0.3" to 1.5" and with contrast
ratios from 6 to 18 mag. Using the SD method to subtract the speckles, we show
that the ALSC brings a gain in sensitivity of up to 3 mag at 0.3" with respect
to the LSC, which leads to a much better spectral extraction below 0.5". In
terms of Teff, we demonstrate that at small angular separations the limit with
the ALSC is always lower by at least 100K, inducing an increase of sensitivity
of a factor up to 1.8 in objects' masses at young ages. [Abridged]Comment: 15 pages, 17 figures. Accepted for publication in A&
Sequential Parameter Optimization
We provide a comprehensive, effective and very efficient methodology for the design and experimental analysis of algorithms.
We rely on modern statistical techniques for tuning and understanding algorithms
from an experimental perspective. Therefore, we make use of the sequential parameter optimization (SPO) method that has been successfully applied as a tuning procedure to numerous heuristics for practical and theoretical
optimization problems.
Two case studies, which illustrate the applicability of SPO to algorithm tuning
and model selection, are presented
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