3,662 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
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
Determination of the Hubble Constant Using a Two-Parameter Luminosity Correction for Type Ia Supernovae
In this paper, we make a comprehensive determination of the Hubble constant
by using two parameters - the B-V color and the rate of decline - to simultaneously standardize the luminosities of all nearby
Cepheid-calibrated type Ia supernovae (SNe Ia) and those of a larger, more
distant sample of 29 SNe Ia. Each group is treated in as similar a manner as
possible in order to avoid systematic effects. A simultaneous
minimization yields a standardized absolute luminosity of the
Cepheid-calibrated supernovae as well as the Hubble constant obtained from the
more distant sample. We find and a standardized
absolute magnitude of -19.46. The sensitivity of to a metallicity
dependence of the Cepheid-determined distances is investigated. The total
uncertainty , dominated by uncertainties in the primary Cepheid
distance indicator, is estimated to be 5 km/s Mpc^{-1}.Comment: To appear in Ap
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