A 1.9 Earth Radius Rocky Planet and the Discovery of a Non-Transiting Planet in the Kepler-20 System*

Buchhave, Lars A.; Dressing, Courtney D.; Dumusque, X.; Rice, Ken; Vanderburg, Andrew; Mortier, A.; López‐Morales, Mercedes; Lopez, Eric; Lundkvist, M.; Kjeldsen, H.; Affer, L.; Bonomo, A. S.; Charbonneau, David; Cameron, A. Collier; Cosentino, R.; Figueira, P.; Fiorenzano, A. F. Martínez; Harutyunyan, A.; Haywood, R. D.; Johnson, John Asher; Latham, David W.; Lovis, C.; Malavolta, L.; Mayor, M.; Micela, G.; Molinari, E.; Motalebi, F.; Nascimbeni, V.; Pepe, F.; Phillips, David F.; Piotto, G.; Pollacco, D.; Queloz, D.; Sasselov, Dimitar; Ségransan, D.; Sozzetti, A.; Udry, S.; Watson, Chris

doi:10.3847/0004-6256/152/6/160

Cited by 98 publications

(102 citation statements)

References 63 publications

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“…We base the 5% metric on the range of uncertainties produced by LC estimates of P rot , used as priors in RV fits (e.g. López-Morales et al 2016;Buchhave et al 2016;Dai et al 2017).…”

Section: Investigation Of Simulated Rv Periodogramsmentioning

confidence: 99%

Exoplanet Imitators: A Test of Stellar Activity Behavior in Radial Velocity Signals

Nava

López‐Morales

Haywood

et al. 2019

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Accurately modeling effects from stellar activity is a key step in detecting radial velocity signals of low-mass and long-period exoplanets. Radial velocities from stellar activity are dominated by magnetic active regions that move in and out of sight as the star rotates, producing signals with timescales related to the stellar rotation period. Methods to characterize radial velocity periodograms assume that peaks from magnetic active regions will typically occur at the stellar rotation period or a related harmonic. However, with surface features unevenly spaced and evolving over time, signals from magnetic activity are not perfectly periodic, and the effectiveness of characterizing them with sine curves is unconfirmed. With a series of simulations, we perform the first test of common assumptions about signals from magnetic active regions in radial velocity periodograms. We simulate radial velocities with quasi-periodic signals that account for evolution and migration of magnetic surface features. As test cases, we apply our analysis to two exoplanet hosts, Kepler-20 and K2-131. Simulating observing schedules and uncertainties of real radial velocity surveys, we find that magnetic active regions commonly produce maximum periodogram peaks at spurious periods unrelated to the stellar rotation period: 81% and 72% of peaks, respectively for K2-131 and Kepler-20. These unexpected peaks can potentially lead to inaccuracies in derived planet masses. We also find that these spurious peaks can sometimes survive multiple seasons of observation, imitating signals typically attributed to exoplanet companions.

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“…We base the 5% metric on the range of uncertainties produced by LC estimates of P rot , used as priors in RV fits (e.g. López-Morales et al 2016;Buchhave et al 2016;Dai et al 2017).…”

Section: Investigation Of Simulated Rv Periodogramsmentioning

confidence: 99%

Exoplanet Imitators: A Test of Stellar Activity Behavior in Radial Velocity Signals

Nava

López‐Morales

Haywood

et al. 2019

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“…Theoretically, given the small scatter in chemical abundances of stars in the solar neighborhood, rocky planet radii should not change much more than 2% due to differences in compositions (Grasset et al 2009), while WASP-47 e's radius is 7% larger than an Earth-like planet with the same mass. Moreover, observations of small, likely rocky planets near their host stars have shown that rocky exoplanets tend to have compositions consistent with that of the Earth (Dressing et al 2015;Buchhave et al 2016). It is unclear how a planet of this size, around a star of such high metallicity/iron content, could avoid accumulating any substantial amount of iron.…”

Section: Constraints On the Composition Of Wasp-47 Ementioning

confidence: 99%

Precise Masses in the WASP-47 System

Vanderburg

Becker

Buchhave

et al. 2017

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We present precise radial velocity observations of WASP-47, a star known to host a hot Jupiter, a distant Jovian companion, and, uniquely, two additional transiting planets in short-period orbits: a super-Earth in a ≈19 hr orbit, and a Neptune in a ≈9 day orbit. We analyze our observations from the HARPS-N spectrograph along with previously published data to measure the most precise planet masses yet for this system. When combined with new stellar parameters and reanalyzed transit photometry, our mass measurements place strong constraints on the compositions of the two small planets. We find that, unlike most other ultra-short-period planets, the inner planet, WASP-47 e, has a mass (6.83 ± 0.66 Å M ) and a radius (1.810 ± 0.027 Å R ) that are inconsistent with an Earth-like composition. Instead, WASP-47 e likely has a volatile-rich envelope surrounding an Earth-like core and mantle. We also perform a dynamical analysis to constrain the orbital inclination of WASP-47 c, the outer Jovian planet. This planet likely orbits close to the plane of the inner three planets, suggesting a quiet dynamical history for the system. Our dynamical constraints also imply that WASP-47 c is much more likely to transit than a geometric calculation would suggest. We calculate a transit probability for WASP-47 c of about 10%, more than an order of magnitude larger than the geometric transit probability of 0.6%.

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“…Furthermore, RV measurements are being used to follow up planets discovered by the transit method to determine the bulk densities of transiting planets and to look for more non-transiting planets in the system (see for example Buchhave et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Stacked Bayesian general Lomb-Scargle periodogram: Identifying stellar activity signals

Mortier

Cameron

2017

A&A

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Context. Distinguishing between a signal induced by either stellar activity or a planet is currently the main challenge in radial velocity searches for low-mass exoplanets. Even when the presence of a transiting planet and hence its period are known, stellar activity can be the main barrier to measuring the correct amplitude of the radial velocity signal. Several tools are being used to help understand which signals come from stellar activity in the data. Aims. We aim to present a new tool that can be used for the purpose of identifying periodicities caused by stellar activity, and show how it can be used to track the signal-to-noise ratio (SNR) of the detection over time. The tool is based on the principle that stellar activity signals are variable and incoherent. Methods. We calculate the Bayesian general Lomb-Scargle periodogram for subsets of data and by adding one extra data point we track what happens to the presence and significance of periodicities in the data. Publicly available datasets from HARPS and HARPS-N were used for this purpose. Additionally, we analysed a synthetic dataset that we created with SOAP2.0 to simulate pure stellar activity and a mixture of stellar activity and a planet. Results. We find that this tool can easily be used to identify unstable and incoherent signals, such as those introduced by stellar activity. The SNR of the detection grows approximately as the square root of the number of data points, in the case of a stable signal. This can then be used to make decisions on whether it is useful to keep observing a specific object. The tool is relatively fast and easy to use, and thus lends itself perfectly to a quick analysis of the data.

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A 1.9 Earth Radius Rocky Planet and the Discovery of a Non-Transiting Planet in the Kepler-20 System*

Cited by 98 publications

References 63 publications

Exoplanet Imitators: A Test of Stellar Activity Behavior in Radial Velocity Signals

Exoplanet Imitators: A Test of Stellar Activity Behavior in Radial Velocity Signals

Precise Masses in the WASP-47 System

Stacked Bayesian general Lomb-Scargle periodogram: Identifying stellar activity signals

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