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Paper: The Mass Function Below the Substellar Limit
Volume: 154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop
Page: 77
Authors: Mayor, M.; Udry, S.; Queloz, D.
Abstract: During the last 13 years, the radial velocity monitoring of about 570 G and K dwarfs in the solar vicinity has permitted an almost complete census of the spectroscopic binaries. These detections, combined with discoveries from recent high-precision radial velocity surveys (OHP, Lick, McDonald), are already sufficient to describe some characteristics of the mass function f(m_2) below the substellar limit. This function is shown to be moderately rising for m_2 going down to about ten Jupiter masses (M_Jup). An impressive peak of the function is observed below 5 M_Jup. We can compare this characteristic of the mass function with a discontinuity of the orbital eccentricities (e) of substellar companions also observed at about 10 M_Jup. We can note that: - The two discontinuities observed for f(m_2) and for the (log m_2,e) distribution take place at similar masses. This correspondence strongly suggests two different formation mechanisms for objects below 5-7 M_Jup and above 7 M_Jup. - The low-mass tail of spectroscopic binaries exists down below 10 M_Jup. The distribution of orbital eccentricities on the domain of brown dwarfs is similar to the distribution of ordinary spectroscopic binaries. - The upper limit for the mass of giant planets seems close to 5 M_Jup and the lightest brown dwarfs could have masses as low as 5 to 10 M_Jup.
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