Observed Properties of Exoplanets: Masses, Orbits, and Metallicities

Abstract

We review the observed properties of exoplanets found by the Doppler technique which has revealed 152 exoplanets to date. We focus on our ongoing 18-year survey of 1330 FGKM type stars at Lick, Keck, and the Anglo-Australian Telescopes carried out with a uniform Doppler precision of 3 m/s. The 104 planets detected in our survey have masses as low as 15 M_Earth orbiting between 0.03 and 5.5 AU. The mass distribution rises toward the lowest detectable masses as dN/dM is proportional to M^-1.1. Nearly all giant planets orbiting within 2 AU of all FGK stars within 30 pc have now been discovered. The distribution of semi-major axes rises from 0.3 -- 3.0 AU (in bins of Delta log a), but remains unknown for larger orbits. Extrapolation suggests that 12% of the FGK stars harbor exoplanets within 20 AU. The median orbital eccentricity is <e>=0.25 (excluding those tidally circularized), lower than previously measured . Planets orbiting beyond 3 AU continue to exhibit non-zero eccentricity, suggesting that the circular orbits of giant planets in our Solar System are unusual. The occurrence rate of ``hot Jupiters'' within 0.1 AU is 1.2$\pm$0.3 %. The probability of occurrence of planets varies as the square of the stellar metal abundance, $P \propto N^2_Fe, ranging from $<$3% for stars of subsolar metallicity to 25% for stars with [Fe/H] > +0.3. Nearly 14% of planet-bearing stars harbor multiple-planet systems, occasionally locked in resonances. Kepler and Corot should measure the occurrence of earth-sized planets. The Space Interferometry Mission (SIM) will detect planets with masses as low as 3 M_ Earth orbiting within 2 AU of nearby stars and will measure masses, orbits and multiplicity. These candidate rocky planets will motivate spectroscopic follow-up by the ``Terrestrial Planet Finder'' and Darwin.}Comment: Nishinomiya-Yukawa Symposiu

Exoplanet Observations

“…data from recent discoveries and its statistics are consistent with the results from volume-limited [15] and magnitude-limited [16] surveys. We include only objects with 0.3M Jup < M < 20M Jup and which were discovered from radial velocity surveys.…”

“…Assuming 300 M dwarfs have been surveyed for Hot Jupiters [17], no detection implies a 1σ upper limit to their frequency of 0.4%. In contrast, the frequency of Hot Jupiters around FGK-type stars is 1.2% ± 0.2% [16].…”

Circumstellar disks and planets

“…Hot Jupiters accompany around one Solar-type star in 200 (Gould et al, 2006;Howard et al, 2010). At larger orbital distances, gas giants get more common as the orbit get wider, reaching a frequency of about 5 % of solar-type stars out to radii of 2-3 AU (Marcy et al, 2005). As radial-velocity surveys do not seem to have reached the mode of the gas giant frequency distribution yet, the actual frequency including Jupiter analogues could be comparable or much higher.…”

Exoplanets: The tip of the iceberg?

“…The results of this computation are show in Fig. 3 in which we also plotted the observationally determined probability as given by Marcy et al (2005).…”