502 research outputs found
Formation and evolution of planetary systems: the impact of high angular resolution optical techniques
The direct images of giant extrasolar planets recently obtained around
several main sequence stars represent a major step in the study of planetary
systems. These high-dynamic range images are among the most striking results
obtained by the current generation of high angular resolution instruments,
which will be superseded by a new generation of instruments in the coming
years. It is therefore an appropriate time to review the contributions of high
angular resolution visible/infrared techniques to the rapidly growing field of
extrasolar planetary science. During the last 20 years, the advent of the
Hubble Space Telescope, of adaptive optics on 4- to 10-m class ground-based
telescopes, and of long-baseline infrared stellar interferometry has opened a
new viewpoint on the formation and evolution of planetary systems. By spatially
resolving the optically thick circumstellar discs of gas and dust where planets
are forming, these instruments have considerably improved our models of early
circumstellar environments and have thereby provided new constraints on planet
formation theories. High angular resolution techniques are also directly
tracing the mechanisms governing the early evolution of planetary embryos and
the dispersal of optically thick material around young stars. Finally, mature
planetary systems are being studied with an unprecedented accuracy thanks to
single-pupil imaging and interferometry, precisely locating dust populations
and putting into light a whole new family of long-period giant extrasolar
planets.Comment: 71 pages, published in Astronomy and Astrophysics Review, online at
http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s00159-009-0028-
Darwin—an experimental astronomy mission to search for extrasolar planets
International audience; As a response to ESA call for mission concepts for its Cosmic Vision 2015–2025 plan, we propose a mission called Darwin. Its primary goal is the study of terrestrial extrasolar planets and the search for life on them. In this paper, we describe different characteristics of the instrument
Post-coronagraphic tip-tilt sensing for vortex phase masks: the QACITS technique
Small inner working angle coronagraphs, like the vortex phase mask, are
essential to exploit the full potential of ground-based telescopes in the
context of exoplanet detection and characterization. However, the drawback of
this attractive feature is a high sensitivity to pointing errors, which
degrades the performance of the coronagraph. We propose a tip-tilt retrieval
technique based on the analysis of the final coronagraphic image, hereafter
called Quadrant Analysis of Coronagraphic Images for Tip-tilt Sensing (QACITS).
Under the assumption of small phase aberrations, we show that the behaviour of
the vortex phase mask can be simply described from the entrance pupil to the
Lyot stop plane by Zernike polynomials. This convenient formalism is used to
establish the theoretical basis of the QACITS technique. Simulations have been
performed to demonstrate the validity and limits of the technique, including
the case of a centrally obstructed pupil. The QACITS technique principle is
further validated by experimental results in the case of an unobstructed
circular aperture. The typical configuration of the Keck telescope (24% central
obstruction) has been simulated with additional high order aberrations. In
these conditions, our simulations show that the QACITS technique is still
adapted to centrally obstructed pupils and performs tip-tilt retrieval with a
precision of {\lambda}/D when wavefront errors amount to
{\lambda}/14 rms and {\lambda}/D for {\lambda}/70 rms errors (with
{\lambda} the wavelength and D the pupil diameter). The implementation of the
QACITS technique is based on the analysis of the scientific image and does not
require any modification of the original setup. Current facilities equipped
with a vortex phase mask can thus directly benefit from this technique to
improve the contrast performance close to the axis.Comment: 12 pages, 15 figures, accepted for publication in A&
VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy Orbital architecture analysis with PyAstrOFit
HR8799 is orbited by at least four giant planets, making it a prime target
for the recently commissioned Spectro-Polarimetric High-contrast Exoplanet
REsearch (VLT/SPHERE). As such, it was observed on five consecutive nights
during the SPHERE science verification in December 2014. We aim to take full
advantage of the SPHERE capabilities to derive accurate astrometric
measurements based on H-band images acquired with the Infra-Red Dual-band
Imaging and Spectroscopy (IRDIS) subsystem, and to explore the ultimate
astrometric performance of SPHERE in this observing mode. We also aim to
present a detailed analysis of the orbital parameters for the four planets. We
report the astrometric positions for epoch 2014.93 with an accuracy down to 2.0
mas, mainly limited by the astrometric calibration of IRDIS. For each planet,
we derive the posterior probability density functions for the six Keplerian
elements and identify sets of highly probable orbits. For planet d, there is
clear evidence for nonzero eccentricity (), without completely
excluding solutions with smaller eccentricities. The three other planets are
consistent with circular orbits, although their probability distributions
spread beyond , and show a peak at for planet e. The
four planets have consistent inclinations of about with respect to the
sky plane, but the confidence intervals for the longitude of ascending node are
disjoint for planets b and c, and we find tentative evidence for
non-coplanarity between planets b and c at the level.Comment: 23 pages, 14 figure
Prospects for mid-infrared imaging of rocky exoplanets
The mid-infrared domain offers interesting perspectives for the direct imaging and characterization of rocky exoplanets, thanks to a reduced star/planet flux ratio (a few millions) compared to the visible/near-infrared range (a few billions), and thanks to a wealth of relevant molecular signatures such as water, carbon dioxide, methane, or ozone. Resolving nearby planetary systems in the mid-infrared, and in particular the habitable zone around nearby stars, requires however to use telescopes larger than the current generation of 10-m class telescopes. In this talk, I will review the currently on-going efforts to tackle this challenge. I will first briefly review the NEAR project, which aimed to demonstrate the power of mid-infrared high-contrast imaging on the 8-m Very Large Telescope, targeting our nearest neighbor alpha Centauri. I will then describe the goals and expected performance of METIS, the mid-infrared imager of the future 38-m European Extremely Large Telescope. I will finally discuss the status and perspectives of the LIFE project, a mid-infrared space interferometer dedicated to the study of temperate, rocky exoplanets, preselected within the ESA Voyage 2050 large mission themes.EPIC; NNEx
STIM map: detection map for exoplanets imaging beyond asymptotic Gaussian residual speckle noise
Direct imaging of exoplanets is a challenging task as it requires to reach a
high contrast at very close separation to the star. Today, the main limitation
in the high-contrast images is the quasi-static speckles that are created by
residual instrumental aberrations. They have the same angular size as planetary
companions and are often brighter, hence hindering our capability to detect
exoplanets. Dedicated observation strategies and signal processing techniques
are necessary to disentangle these speckles from planetary signals. The output
of these methods is a detection map in which the value of each pixel is related
to a probability of presence of a planetary signal. The detection map found in
the literature relies on the assumption that the residual noise is Gaussian.
However, this is known to lead to higher false positive rates, especially close
to the star. In this paper, we re-visit the notion of detection map by
analyzing the speckle noise distribution, namely the Modified Rician
distribution. We use non-asymptotic analysis of the sum of random variables to
show that the tail of the distribution of the residual noise decays as an
exponential distribution, hence explaining the high false detection rate
obtained with the Gaussian assumption. From this analysis, we introduce a novel
time domain detection map and we demonstrate its capabilities and the relevance
of our approach through experiments on real data. We also provide an empirical
rule to determine detection threshold providing a good trade off between true
positive and false positive rates for exoplanet detection
The STAR contribution to ELT/METIS
I will focus on how STAR is currently contributing to the METIS project, the perspectives for becoming a formal partner in the METIS collaboration, and how this could benefit all STAR astronomers
Configurations and Modulation Schemes Trade-off
During the preliminary phase A of the Ground-based European Nulling Interferometer Experiment (GENIE), a number of interferometric configurations have been studied, in the cases of exozodiacal cloud and hot Jupiter detection. Their expected performances have been computed in light of the measured or expected performances of the VLTI subsystems. A simple Bracewell nulling interferometer, formed of two Unit Telescopes and working in the L’ or N bands, has been identified as a good candidate configuration for exozodiacal cloud detection. External or internal chopping, fringe tracking and intensity matching will be critical issues for this configuration. In the case of hot Jupiter detection, a double Bracewell with internal modulation in the L’ band seems well appropriate, and should allow to carry out low resolution spectroscopy on a few bright exoplanets. The basic assumptions and computations which have lead to these candidate configurations are described in this paper
Multi-Aperture Imaging of Extrasolar Planetary Systems
In this paper, we review the various ways in which an infrared stellar interferometer can be used to perform direct detection of extrasolar planetary systems. We first review the techniques based on classical stellar interferometry, where (complex) visibilities are measured, and then describe how higher dynamic ranges can be achieved with nulling interferometry. The application of nulling interferometry to the study of exozodiacal discs and extrasolar planets is then discussed and illustrated with a few examples
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