4,389 research outputs found
Microlensing planet detection via geosynchronous and low Earth orbit satellites
Planet detection through microlensing is usually limited by a well-known
degeneracy in the Einstein timescale , which prevents mass and distance of
the lens to be univocally determined. It has been shown that a satellite in
geosynchronous orbit could provide masses and distances for most standard
planetary events ( days) via a microlens parallax measurement.
This paper extends the analysis to shorter Einstein timescales,
day, when dealing with the case of Jupiter-mass lenses. We then study the
capabilities of a low Earth orbit satellite on even shorter timescales, days. A Fisher matrix analysis is employed to predict how the
1- error on parallax depends on and the peak magnification of the
microlensing event. It is shown that a geosynchronous satellite could detect
parallaxes for Jupiter-mass free floaters and discover planetary systems around
very low-mass brown dwarfs. Moreover, a low Earth orbit satellite could lead to
the discovery of Earth-mass free-floating planets. Limitations to these results
can be the strong requirements on the photometry, the effects of blending, and
in the case of the low orbit, the Earth's umbra.Comment: 5 pages, 3 figures. Minor language edits. Accepted for publication in
Astronomy & Astrophysic
Space based microlensing planet searches
The discovery of extra-solar planets is arguably the most exciting
development in astrophysics during the past 15 years, rivalled only by the
detection of dark energy. Two projects unite the communities of exoplanet
scientists and cosmologists: the proposed ESA M class mission EUCLID and the
large space mission WFIRST, top ranked by the Astronomy 2010 Decadal Survey
report. The later states that: "Space-based microlensing is the optimal
approach to providing a true statistical census of planetary systems in the
Galaxy, over a range of likely semi-major axes". They also add: "This census,
combined with that made by the Kepler mission, will determine how common
Earth-like planets are over a wide range of orbital parameters". We will
present a status report of the results obtained by microlensing on exoplanets
and the new objectives of the next generation of ground based wide field imager
networks. We will finally discuss the fantastic prospect offered by space based
microlensing at the horizon 2020-2025.Comment: 8 pages, Proceedings to the ROPACS meeting "Hot Planets and Cool
Stars" (Nov. 2012, Garching), invited contributio
User requirement elicitation for cross-language information retrieval
Who are the users of a cross-language retrieval system? Under what circumstances do they need to perform such multi-language searches? How will the task and the context
of use affect successful interaction with the system? Answers to these questions were explored in a user study performed as part of the design stages of Clarity, a EU
founded project on cross-language information retrieval. The findings resulted in a rethink of the planned user interface and a consequent expansion of the set of services
offered. This paper reports on the methodology and techniques used for the elicitation of user requirements as well as how these were in turn transformed into new design
solutions
User-centred interface design for cross-language information retrieval
This paper reports on the user-centered design methodology and
techniques used for the elicitation of user requirements and how these requirements informed the first phase of the user interface design for a Cross-Language Information Retrieval System. We describe a set of factors involved in analysis of the data collected and, finally discuss the implications for user interface design based on the findings
Primary transit of the planet HD189733b at 3.6 and 5.8 microns
The hot Jupiter HD 189733b was observed during its primary transit using the
Infrared Array Camera on the Spitzer Space Telescope. The transit depths were
measured simultaneously at 3.6 and 5.8 microns. Our analysis yields values of
2.356 +- 0.019 % and 2.436 +- 0.020$ % at 3.6 and 5.8 microns respectively, for
a uniform source. We estimated the contribution of the limb-darkening and
star-spot effects on the final results. We concluded that although the limb
darkening increases by ~0.02-0.03 % the transit depths, and the differential
effects between the two IRAC bands is even smaller, 0.01 %. Furthermore, the
host star is known to be an active spotted K star with observed photometric
modulation. If we adopt an extreme model of 20 % coverage with spots 1000K
cooler of the star surface, it will make the observed transits shallower by
0.19 and 0.18 %. The difference between the two bands will be only of 0.01 %,
in the opposite direction to the limb darkening correction. If the transit
depth is affected by limb darkening and spots, the differential effects between
the 3.6 and 5.8 microns bands are very small. The differential transit depths
at 3.6 and 5.8 microns and the recent one published by Knutson et al.(2007) at
8 microns are in agreement with the presence of water vapour in the upper
atmosphere of the planet. This is the companion paper to Tinetti et al.
(2007b), where the detailed atmosphere models are presented.Comment: 6 pages, 4 figures, Astrophysical Journal 675. Accepted Nov 21,
20007, to appear on March 10, 200
High-contrast imaging at small separation: impact of the optical configuration of two deformable mirrors on dark holes
The direct detection and characterization of exoplanets will be a major
scientific driver over the next decade, involving the development of very large
telescopes and requires high-contrast imaging close to the optical axis. Some
complex techniques have been developed to improve the performance at small
separations (coronagraphy, wavefront shaping, etc). In this paper, we study
some of the fundamental limitations of high contrast at the instrument design
level, for cases that use a combination of a coronagraph and two deformable
mirrors for wavefront shaping. In particular, we focus on small-separation
point-source imaging (around 1 /D). First, we analytically or
semi-analytically analysing the impact of several instrument design parameters:
actuator number, deformable mirror locations and optic aberrations (level and
frequency distribution). Second, we develop in-depth Monte Carlo simulation to
compare the performance of dark hole correction using a generic test-bed model
to test the Fresnel propagation of multiple randomly generated optics static
phase errors. We demonstrate that imaging at small separations requires large
setup and small dark hole size. The performance is sensitive to the optic
aberration amount and spatial frequencies distribution but shows a weak
dependence on actuator number or setup architecture when the dark hole is
sufficiently small (from 1 to 5 /D).Comment: 13 pages, 18 figure
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