An Earth-sized exoplanet with a Mercury-like composition

Santerne, A.; Brugger, B.; Armstrong, David J.; Adibekyan, V.; Lillo-Box, J.; Gosselin, H.; Aguichine, Artyom; Almenara, J. M.; Barrado, D.; Barros, S. C. C.; Bayliss, Daniel; Boisse, I.; Bonomo, A. S.; Bouchy, F.; Brown, D. J. A.; Deleuil, M.; Delgado-Mena, E.; Demangeon, O.; Díaz, R. F.; Doyle, A. P.; Dumusque, X.; Faedi, F.; Faria, J. P.; Figueira, P.; Foxell, Emma; Giles, H.; Hébrard, G.; Hojjatpanah, S.; Hobson, Mélissa J.; Jackman, James A. G.; King, George W.; Kirk, James; Lam, K. W. F.; Ligi, R.; Lovis, C.; Louden, Tom; McCormac, J.; Mousis, O.; Neal, J. J.; Osborn, H.; Pepe, F.; Pollacco, D.; Santos, N. C.; Sousa, S. G.; Udry, S.; Vigan, A.

doi:10.1038/s41550-018-0420-5

Cited by 97 publications

(63 citation statements)

References 75 publications

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“…However, a more efficient way to deal with activity effects could be to schedule RV observations of specific systems in ways that optimize the sampling of both the magnetic activity and exoplanet signals, so both can be more easily extracted from the data. Early attempts to do this have proven successful (López-Morales et al 2016;Barros et al 2017;Santerne et al 2018). As more precise and stable RV instruments become available, collaboration between those instruments will be necessary to achieve better coverage of stellar activity cycles.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

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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“…Similarly to previous studies (Osborn et al 2017;Barros et al 2017;Santerne et al 2018;Lam et al 2018), we used the bayesian software PASTIS (Díaz et al 2014;Santerne et al 2015) to jointly analyse the HARPS radial velocities, the K2 light curve and the spectral energy distribution (SED). For the SED, we used the magnitudes in optical from the APASS survey and in near-infrared from the 2MASS and AllWISE surveys (Henden et al 2015;Munari et al 2014;Cutri & et al 2014).…”

Section: Pastis Analysismentioning

confidence: 99%

Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

Lopez

Barros

Santerne

et al. 2019

A&A

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The detection of low-mass transiting exoplanets in multiple systems brings new constraints to planetary formation and evolution processes and challenges the current planet formation theories. Nevertheless, only a mere fraction of the small planets detected by Kepler and K2 have precise mass measurements, which are mandatory to constrain their composition. We aim to characterise the planets that orbit the relatively bright star K2-138. This system is dynamically particular as it presents the longest chain known to date of planets close to the 3:2 resonance. We obtained 215 HARPS spectra from which we derived the radial-velocity variations of K2-138. Via a joint Bayesian analysis of both the K2 photometry and HARPS radial-velocities (RVs), we constrained the parameters of the six planets in orbit. The masses of the four inner planets, from b to e, are 3.1, 6.3, 7.9, and 13.0 M ⊕ with a precision of 34%, 20%, 18%, and 15%, respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8 g cm −3 , ranging from Earth to Neptune-like values. For planets f and g, we report upper limits. Finally, we predict transit timing variations of the order two to six minutes from the masses derived. Given its peculiar dynamics, K2-138 is an ideal target for transit timing variation (TTV) measurements from space with the upcoming CHaracterizing ExOPlanet Satellite (CHEOPS) to study this highly-packed system and compare TTV and RV masses.

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“…2. Error bars on the FWHM and BIS values have been taken as twice those of the RV ones (Santerne et al 2018). A positive trend is clearly visible for the RVs, with no counterparts in the stellar activity indicators, pointing out the presence of an outer companion.…”

Section: Harps-n Spectroscopymentioning

confidence: 99%

“…These planets orbit with extremely short periods (P ≤ 1 d), are smaller than about 2R ⊕ and appear to have compositions similar to that of the Earth (Winn et al 2018). There is also evidence that some of them might have iron-rich compositions (e.g., Santerne et al 2018). The origin of this sub-population of planets is still unclear.…”

Section: Introductionmentioning

confidence: 99%

An ultra-short period rocky super-Earth orbiting the G2-star HD 80653

Frustagli

Poretti

Milbourne

et al. 2020

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Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653≡EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet (R b = 1.613 ± 0.071 R ⊕ ) transiting the star on a short-period orbit (P b = 0.719573 ± 0.000021 d). From our radial velocity measurements, we constrained the mass of HD 80653 b to M b = 5.60 ± 0.43 M ⊕ . We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of R ⋆ = 1.22 ± 0.01 R ⊙ and mass of M ⋆ = 1.18 ± 0.04 M ⊙ , suggesting that HD 80653 has an age of 2.7 ± 1.2 Gyr. The bulk density (ρ b = 7.4 ± 1.1 g cm −3 ) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1±3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at T ∼ 3480 K.

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An Earth-sized exoplanet with a Mercury-like composition

Cited by 97 publications

References 75 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

Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

An ultra-short period rocky super-Earth orbiting the G2-star HD 80653

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