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Project Progress

Planet Detection Algorithms: Velusamy leads the effort for efficient planet signal extraction from Terrestrial Planet Finder Interferometer (TPF-I) data using a priori instrumental and astrophysical information. This Point Process Algorithm (PPA), has been developed by Velusamy, Marsh and Brent, and uses a Bayesian technique to extract planetary signals from simulated data for the TPF-I X-array design. The system being observed is represented as a set of points in a suitably defined state space, thus providing a natural way of incorporating prior knowledge. Spatial covariance of the exozodi can be incorporated, helping to mitigate against false detections. Data at multiple wavelengths are used simultaneously, taking into account possible spectral variations of the planetary signals. Previous approaches to planet detection for TPF-I have relied on the potentially non-robust identification of peaks in a “dirty” image, usually a correlation map. Tests with synthetic data suggest that the PPA is more efficient for planet detection and provides greater sensitivity than does the standard approach (correlation map + CLEAN). PPA will be a useful tool for optimizing the design of TPF-I and for extracting the spectral characteristics of planetary signals.

Extrasolar Planet Detection and Characterization: Velusamy and collaborators have combined Caltech Submillimeter Observatory 350 & 450 μm data with Spitzer 70 μm images, and modeling techniques to obtain new results about the unseen planet and the dust grains in debris disk around Vega. They show that different grain populations are trapped in the mean motion resonances of a Neptune-mass planet orbiting at a radial distance of 65 AU from the star. The 4:3 resonance is populated by the mm-sized grains while the 2:1(u) resonance contains cm-sized grains. We attribute this to the differing collision history of planetesimals in different resonances. Our detection of the 4:3 resonance resolves an ambiguity in the location and orbital direction of the unseen planet.

Bailey and collaborators reported several new planets resulting from the Anglo-Australian Planet Search, including a 2:1 resonant system orbiting HD73526, and two high-eccentricity planets (HD187085 and HD20782). Bailey and collaborators also carried out high precision (parts per million level) polarimetry of the Tau Boo hot Jupiter system. They did not detect polarized scattered light from the planet, thereby setting significant limits on the nature of scatterers in the planet’s atmosphere.