2019A&A...621A..49C -
Astronomy and Astrophysics, volume 621A, 49-49 (2019/1-1)
Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES.
CLOUTIER R., ASTUDILLO-DEFRU N., DOYON R., BONFILS X., ALMENARA J.-M., BOUCHY F., DELFOSSE X., FORVEILLE T., LOVIS C., MAYOR M., MENOU K., MURGAS F., PEPE F., SANTOS N.C., UDRY S. and WUNSCHE A.
Abstract (from CDS):
In an earlier campaign to characterize the mass of the transiting temperate super-Earth K2-18b with HARPS, a second, non-transiting planet was posited to exist in the system at ∼9-days. Further radial velocity follow-up with the CARMENES spectrograph visible channel revealed a much weaker signal at 9-days, which also appeared to vary chromatically and temporally, leading to the conclusion that the origin of the 9-day signal was more likely related to stellar activity than to a planetary presence. Here we conduct a detailed reanalysis of all available RV time-series - including a set of 31 previously unpublished HARPS measurements - to investigate the effects of time-sampling and of simultaneous modelling of planetary plus activity signals on the existence and origin of the curious 9-day signal. We conclude that the 9-day signal is real and was initially seen to be suppressed in the CARMENES data due to a small number of anomalous measurements, although the exact cause of these anomalies remains unknown. Investigation of the signal's evolution in time with wavelength and detailed model comparison reveals that the 9-day signal is most likely planetary in nature. Using this analysis, we reconcile the conflicting HARPS and CARMENES results and measure precise and self-consistent planet masses of mp,b=8.63±1.35 and mp,c sinic=5.62±0.84 Earth masses. This work, along with the previously published RV papers on the K2-18 planetary system, highlights the importance of understanding the time-sampling and of modelling the simultaneous planet plus stochastic activity, particularly when searching for sub-Neptune-sized planets with radial velocities.
Abstract Copyright:
© ESO 2019
Journal keyword(s):
techniques: radial velocities - planets and satellites: fundamental parameters - planets and satellites: detection - methods: data analysis - planets and satellites: individual: K2-18
VizieR on-line data:
<Available at CDS (J/A+A/621/A49): tablea1.dat>
Simbad objects:
6
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