MEDI: An instrument for direct-detection of massive extrasolar planets

We have developed an instrument, MEDI (Massive Exoplanet Differential Imager), that takes advantage of a unique method of starlight rejection, simultaneous differential imaging, in order to directly image massive planets around nearby stars. Using this technique we expect to achieve suppression of starlight to the photon-noise limit, which means that increased exposure time will translate into higher sensitivities. This is in contrast to past sequential and two-color simultaneous studies that reach a sensitivity floor due to speckle-noise limitations. MEDI is currently installed in ARIES, the infrared camera that will be commissioned at the newly refurbished 6.5m MMT in January 2003, with the world's first adaptive secondary. This should allow us to take Nyquist sampled, diffraction-limited images in the near-IR. The adaptive secondary will also give us unprecedented throughput while minimizing the thermal background and providing a smooth PSF. Based on lab results, we expect to be able to detect objects 10⁶ times fainter than their primaries at 0.5″ separations in 2 hours, limited only by photon noise. This suggests that we will be sensitive to objects with masses as small as ∼ 5 M_Jupiter at separations of greater than ∼ 5 AU for G2 V stars that are ∼ 300 Myr old and within about 10 pc. Therefore, we will probe a unique search space compared with current radial velocity methods, which are so far restricted to close-in (< 6 AU) orbits.