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Abstract: We report first results from the Anglo-Australian Telescope Rocky PlanetSearch - an intensive, high-precision Doppler planet search targeting low-massexoplanets in contiguous 48 night observing blocks. On this run we targeted 24bright, nearby and intrinsically stable Sun-like stars selected from theAnglo-Australian Planet Search-s main sample. These observations have alreadydetected one low-mass planet reported elsewhere HD16417b, and here wereconfirm the detection of HD4308b. Further, we have Monte-Carlo simulated thedata from this run on a star-by-star basis to produce robust detectionconstraints. These simulations demonstrate clear differences in the exoplanetdetectability functions from star to star due to differences in sampling, dataquality and intrinsic stellar stability. They reinforce the importance ofstar-by-star simulation when interpreting the data from Doppler planetsearches. The simulations indicate that for some of our target stars we aresensitive to close-orbiting planets as small as a few Earth masses. The twolow-mass planets present in our 24 star sample indicate that the exoplanetminimum mass function at low masses is likely to be a flat alpha ~ -1 fordN-dM proportional to M^alpha and that between 15+-10% at alpha=-0.3 and48+-34% at alpha=-1.3 of stars host planets with orbital periods of lessthan 16 days and minimum masses greater than 3 Mearth.

Author: S.J. O'Toole, H.R.A. Jones, C.G. Tinney, R.P. Butler, G.W. Marcy, B. Carter, J. Bailey, R.A. Wittenmyer


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