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Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES
- Source :
- Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, EDP Sciences, 2019, 621, pp.A49. ⟨10.1051/0004-6361/201833995⟩
- Publication Year :
- 2019
- Publisher :
- EDP Sciences, 2019.
-
Abstract
- 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 $\sim 9$ 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 to be related to stellar activity than to being planetary. Here we conduct a detailed re-analysis of all available RV time-series, including a set of 31 previously unpublished HARPS measurements, to investigate the effects of time-sampling and of simultaneous modelling of planetary + activity signals on the existence and origin of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. By this analysis, we reconcile the conflicting HARPS and CARMENES results and measure precise and self-consistent planet masses of $m_{p,b} = 8.63 \pm 1.35$ and $m_{p,c}\sin{i_c}=5.62 \pm 0.84$ M$_{\oplus}$. This work, along with the previously published RV papers on the K2-18 planetary system, highlight the importance of understanding one's time-sampling and of simultaneous planet + stochastic activity modelling, particularly when searching for sub-Neptune-sized planets with radial velocities.<br />19 pages, 10 figures (including 9 interactive figures when viewed in Adobe Acrobat), accepted for publication in Astronomy & Astrophysics
- Subjects :
- planets and satellites: detection
010504 meteorology & atmospheric sciences
FOS: Physical sciences
Astrophysics
01 natural sciences
Signal
fundamental parameters -planets and satellites
Planet
radial velocities -planets and satellites
techniques: radial velocities
0103 physical sciences
individual
planets and satellites: fundamental parameters
010303 astronomy & astrophysics
Spectrograph
0105 earth and related environmental sciences
Earth and Planetary Astrophysics (astro-ph.EP)
Physics
K2-18
Super-Earth
Astronomy and Astrophysics
planets and satellites: individual: K2-18
Planetary system
data analysis -planets and satellites
methods: data analysis
Radial velocity
detectionmethods
Wavelength
[SDU]Sciences of the Universe [physics]
13. Climate action
Space and Planetary Science
techniques
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Astrophysics - Earth and Planetary Astrophysics
Subjects
Details
- ISSN :
- 14320746 and 00046361
- Volume :
- 621
- Database :
- OpenAIRE
- Journal :
- Astronomy & Astrophysics
- Accession number :
- edsair.doi.dedup.....8169671e4588874af0ed68057e870984