GJ 328, 649 and 849 HARPS-N observations

We identify a new short-period, low-mass planet orbiting GJ 328, GJ 328 c, with P_c_=241.8^+1.3^_-1.7_d and M_c_sini=21.4^+3.4^_-3.2_M_{Earth}_. We moreover identify and model the chromospheric activity signals and rotation periods of GJ 649 and GJ 849, around which no additional planet is found. Then, taking into account also planetary system around the previously analysed low-mass star BD-11 4672, we derive an estimate of the frequencies of inner planets in such systems.

In particular, f(SN|CJ)=0.25^+0.58^_-0.07_ for mini-Neptunes (10M_{Earth}_<Msini<30M_{Earth}_, P<150d), marginally larger than f(SN). For lower mass planets (Msini<10M_{Earth}_) instead f(SN|CJ)<0.69, which is compatible with f(SN). In light of the newly detected mini-Neptune, we find tentative evidence of a positive correlation between the presence of long-period giant planets and that of inner low-mass planets, f(SN|CJ)>f(SN).

This might indicate that cold Jupiters have an opposite influence in the formation of inner sub-Neptunes around late-type dwarfs as opposed to their solar-type counterparts, boosting the formation of mini-Neptunes instead of impeding it.