S

11-inch f/10 Celestron

The MICROFUN collaboration has announced 3 planetary candidates: OGLE-2005-BLG-071, OGLE-2005-BLG-169 and OGLE-2006-BLG-109 (www. astronomy.ohio-state.edu/~microfun/).

8.1.4.2 Observation from Space

The Microlensing Planet Finder Mission (MPF)

The MPF mission concept (Fig. 8.13) is an American project dedicated to the search for extrasolar planets by the microlensing method. The efficiency of the microlensing method, and thus the number of planetary candidates, depends strongly on both source and lens stellar-field density. The microlensing effect occurs specifically when source and lens are aligned. Detection from the ground is thus limited by the angular resolution achievable, taking into account the effects of atmospheric turbulence (about 1 arcsec). Planets are effectively detectable when they create a high-magnification event (when the planet is close to the Einstein ring i.e. 2-3 AU from the star).

Compared to ground-based observations, space surveys allow a higher angular resolution (to the diffraction limit of the telescope), and the lack of atmospheric turbulence allows a better determination of photometric variations and thus a higher sensitivity (Fig. 8.14), particularly towards closer objects (with distances of less than 1 AU).

Technically speaking, the MPF (Fig. 8.13) concept is a 1.1-m TMA telescope (Three Mirror Anastigmat). This optical configuration enables observation of a field of 0.65 square degrees. The focal plane is filled by a 145 Mpixel focal-plane array made of a HgCdTe detector, allowing observation in three spectral

Fig. 8.13 Schematic diagram of the Microlensing Planet Finder satellite (see the text for description) (after Bennett et al., 2007)
Fig. 8.14 Sensitivity of space-based microlensing event detection compared with several other methods (ground-based microlensing, radial velocimetry, space-based astrometry and transit detection) (after Bennett et al., 2007)

bands from 600 to 1700 nm at an angular resolution of 0.24 arcsec per pixel. This design should lead to a photometric accuracy of better than 1 per cent at magnitude J=20.5.

Such performance will permit the detection of both planetary systems (star + planets) and free-floating objects. The sensitivity to each type of objects is given in Fig. 8.15.

The EUCLID Mission (Formerly Named DUNE)

The EUCLID mission is the result of the merger of the DUNE and SPACE mission concepts proposed to ESA in answer to its call for 'Cosmic Vision' proposals, and pre-selected for A-phase studies. The main goal of EUCLID is concerned with cosmology. The aim of EUCLID is to search for dark energy by gravitational shear. In its previous version (DUNE), EUCLID's method of observation mode was a complete survey of the sky including, thanks to the proposed observational strategy, a 3 month-survey of the galactic plane, which would have allowed a search for extrasolar planets by microlensing. The sensitivity of EUCLID in the detection of extrasolar planets is comparable with that of MPF. At present, a complete revision of the initial instrumental concept (DUNE) is under way, so there is little point in describing it in detail. Among visible and near-infrared photometric wide-field imaging and

Fig. 8.15 Sensitivity of MPF to several type of planetary objects, (left) in the case of planetary systems with a parent star, (right) free-floating objects (after Bennett et al., 2007)

spectroscopic instruments, the visible camera appears to be the instrument that is most suitable for this task.

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