The Frequency of Low-mass Exoplanets

TL;DR

This study reports initial findings from a high-precision Doppler survey targeting low-mass exoplanets around Sun-like stars, revealing detection sensitivities, confirming known planets, and estimating the prevalence of such planets.

Contribution

It introduces star-by-star Monte Carlo simulations to assess detection limits and estimates the occurrence rate of low-mass, short-period exoplanets.

Findings

Detected one new low-mass planet and confirmed another.

Sensitivity to planets as small as a few Earth masses for some stars.

Estimated that 15-48% of stars host close-in low-mass planets.

Abstract

We report first results from the Anglo-Australian Telescope Rocky Planet Search - an intensive, high-precision Doppler planet search targeting low-mass exoplanets in contiguous 48 night observing blocks. On this run we targeted 24 bright, nearby and intrinsically stable Sun-like stars selected from the Anglo-Australian Planet Search's main sample. These observations have already detected one low-mass planet reported elsewhere (HD16417b), and here we reconfirm the detection of HD4308b. Further, we have Monte-Carlo simulated the data from this run on a star-by-star basis to produce robust detection constraints. These simulations demonstrate clear differences in the exoplanet detectability functions from star to star due to differences in sampling, data quality and intrinsic stellar stability. They reinforce the importance of star-by-star simulation when interpreting the data from Doppler planet searches. The simulations indicate that for some of our target stars we are sensitive to close-orbiting planets as small as a few Earth masses. The two low-mass planets present in our 24 star sample indicate that the exoplanet minimum mass function at low masses is likely to be a flat alpha ~ -1 (for dN/dM proportional to M^alpha) and that between 15+/-10% (at alpha=-0.3) and 48+/-34% (at alpha=-1.3) of stars host planets with orbital periods of less than 16 days and minimum masses greater than 3 Mearth.