Speaker
Description
Radial-velocity (RV) of stars in statistically well-defined samples have been monitored for decades in search for extra-solar planets. Depending on the achieved precision these surveys are sensitive to giant planets on orbits out to several AUs or on low-mass planets on orbits with periods smaller than typically a few tens of days. A special attention will be brought in the presentation to multi-planet systems found in these surveys. For solar-type stars, we will give a work in progress update of the results obtained with the Coralie planet search survey ongoing since 1998 (27 years) and recall the main findings for small-mass planets around these stars within the suite of HARPS Large Programs that ran between 2003 and 2016. The findings for giant planets will also be compared with the very recent results of a parallel survey of giant stars with masses between 1.2 and ~ 4 Msun monitored for about 15 years now with the Coralie spectrograph. For the sample of more massive stars, the occurrence rate of giant planets as well as their typical mass seem to be higher than for the solar-type stars. The fraction of multi-planet systems vs single planet systems is similar in both surveys but with a much higher fraction of them being close to a commensurability in the giant star sample. In particular a significant part of them show period ratios below 2 (between 1.2 and 1.7). We have to be extra-careful here in interpreting this results as the latter feature might be i) the result of the planet formation process in disks more massive than the typical ones around solar-type stars, or ii) it can also be due to the “pollution” of the sample by intrinsic stellar effects in giant stars mimicking the RV variation induced by a planet. The latter possibility is also supported by a dozen of still to be explained cases for which the RV variation is accompanied by the variation of the FWHM of the spectral lines with the exact same period. More work on better understanding giant star intrinsic variation is required before releasing the ~ 60 planet candidates in this sample and use them for the determination of occurrence rate and statistical properties of planets around stars more massive than the Sun.