A HARPS-N mass for the elusive Kepler-37d: a case study in disentangling stellar activity and planetary signals

Rajpaul, Vinesh; Buchhave, Lars A.; Lacedelli, G.; Rice, Ken; Mortier, A.; Malavolta, L.; Aigrain, S.; Borsato, L.; Mayo, Andrew W.; Charbonneau, David; Damasso, M.; Dumusque, X.; Ghedina, A.; Latham, David W.; López‐Morales, Mercedes; Magazzù, A.; Micela, G.; Molinari, E.; Pepe, F.; Piotto, G.; Poretti, E.; Rowther, Sahl; Sozzetti, A.; Udry, S.; Watson, Christopher A.

doi:10.1093/mnras/stab2192

Cited by 15 publications

(9 citation statements)

References 113 publications

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“…The largest deviation from the fit is observed for Kepler-37 d. Kepler-37 is orbited by three 3 transiting small planets. Kepler-37 d is the largest planet of the system, the mass of which was very recently determined by Rajpaul et al (2021) using radial velocity (RV) observations. The authors obtained a RV based mass of 5.4±1.4 M ⊕ and a dynamical mass of ∼ 4 M ⊕ .…”

Section: Resultsmentioning

confidence: 99%

“…The authors obtained a RV based mass of 5.4±1.4 M ⊕ and a dynamical mass of ∼ 4 M ⊕ . From the low density of the planet, Rajpaul et al (2021) concluded that either Kepler-37 d is a water-world (> 25% H 2 O) or has a gaseous envelope 4 . In either case, the planet is most probably not a rocky planet consisting of only metallic core and silicate mantle.…”

Section: Resultsmentioning

confidence: 99%

“…The presence of a forth, non-transiting planet is unlikely(Rajpaul et al, 2021).4 Note, that the equilibrium temperature of Kepler-37 d is about 500K which is the coldest planet in the sample.…”

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confidence: 99%

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Composition of super-Earths, super-Mercuries, and their host stars

Adibekyan

Santos

Dorn

et al. 2021

ComBAO

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Because of their common origin, it was assumed that the composition of planet building blocks should, to a first order, correlate with stellar atmospheric composition, especially for refractory elements. In fact, information on the relative abundance of refractory and major rock-forming elements such as Fe, Mg, Si has been commonly used to improve interior estimates for terrestrial planets. Recently Adibekyan et al. (2021) presented evidence of a tight chemical link between rocky planets and their host stars. In this study we add six recently discovered exoplanets to the sample of Adibekyan et al and re-evaluate their findings in light of these new data. We confirm that i) iron-mass fraction of rocky exoplanets correlates (but not a 1:1 relationship) with the composition of their host stars, ii) on average the iron-mass fraction of planets is higher than that of the primordial f star iron , iii) super-Mercuries are formed in disks with high iron content. Based on these results we conclude that disk-chemistry and planet formation processes play an important role in the composition, formation, and evolution of super-Earths and super-Mercuries.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Composition of super-Earths, super-Mercuries, and their host stars

Adibekyan

Santos

Dorn

et al. 2021

ComBAO

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“…First, some specific observation strategies are commonly used to reduce the contribution of short-timescale activity components (Hatzes et al 2011;Dumusque et al 2011). Second, to correct for variability that evolves at the stellar rotation period (spots and plages), the most basic technique consists of fitting a model to the RV dataset (e.g., sinusoidal functions at the stellar rotation period (Boisse et al 2011), or quasi-periodic Gaussian processes (see, e.g., Aigrain et al 2012;Baluev 2011;Baluev 2013b;Rajpaul et al 2015;Jones et al 2022;Rajpaul et al 2021)). To constrain the parameters of these models, activity indicators (e.g., the S-index (Wilson 1968), logR HK (Noyes et al 1984), or the bisector span (Queloz et al 2001)) are commonly used if correlations with the RV dataset are found.…”

Section: Introductionmentioning

confidence: 99%

Semi-supervised standardized detection of extrasolar planets

Sulis

Mary

Bigot

et al. 2022

A&A

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Context. The detection of small exoplanets with the radial velocity (RV) technique is limited by various poorly known noise sources of instrumental and stellar origin. As a consequence, current detection techniques often fail to provide reliable estimates of the significance levels of detection tests in terms of false-alarm rates or p-values. Aims. We designed an RV detection procedure that provides reliable p-value estimates while accounting for the various noise sources typically affecting RV data. The method is able to incorporate ancillary information about the noise (e.g., stellar activity indicators) and specific data-or context-driven data (e.g. instrumental measurements, magnetohydrodynamical simulations of stellar convection, and simulations of meridional flows or magnetic flux emergence). Methods. The detection part of the procedure uses a detection test that is applied to a standardized periodogram. Standardization allows an autocalibration of the noise sources with partially unknown statistics (algorithm 1). The estimation of the p-value of the test output is based on dedicated Monte Carlo simulations that allow handling unknown parameters (algorithm 2). The procedure is versatile in the sense that the specific pair (periodogram and test) is chosen by the user. Ancillary or context-driven data can be used if available. Results. We demonstrate by extensive numerical experiments on synthetic and real RV data from the Sun and αCenB that the proposed method reliably allows estimating the p-values. The method also provides a way to evaluate the dependence of the estimated p-values that are attributed to a reported detection on modeling errors. It is a critical point for RV planet detection at low signal-to-noise ratio to evaluate this dependence. The python algorithms developed in this work are available on GitHub. Conclusions. Accurate estimation of p-values when unknown parameters are involved in the detection process is an important but only recently addressed question in the field of RV detection. Although this work presents a method to do this, the statistical literature discussed in this paper may trigger the development of other strategies.

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“…While some periodogram peaks genuinely describe planets, others are spurious detections resulting from stellar rotation or activity (e.g. Saar & Donahue 1997;Hatzes 2002;Desort et al 2007;Boisse et al 2011;Newton et al 2016;Suárez Mascareño et al 2017;Rajpaul et al 2021). Now that extreme precision spectrographs are on the hunt for terrestrial planets (Jurgenson et al 2016;González Hernández et al 2018;Gupta et al 2021), the need for high-performance activity diagnostics is urgent: while an earthlike planet orbiting a sunlike star yields an RV oscillation with semiamplitude K < 10 cm s −1 , that same star's expected rotational RV modulation has amplitude > 1 m s −1 (Vanderburg et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Magnitude-squared coherence: A powerful tool for disentangling Doppler planet discoveries from stellar activity

Dodson-Robinson,

Delgado,

Harrell

et al. 2022

Preprint

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If Doppler searches for earth-mass, habitable planets are to succeed, observers must be able to identify and model out stellar activity signals. Here we demonstrate how to diagnose activity signals by calculating the magnitude-squared coherence Ĉ2xy (f ) between an activity indicator time series x t and the radial velocity (RV) time series y t . Since planets only cause modulation in RV, not in activity indicators, a high value of Ĉ2xy (f ) indicates that the signal at frequency f has a stellar origin. We use Welch's method to measure coherence between activity indicators and RVs in archival observations of GJ 581, α Cen B, and GJ 3998. High RV-Hα coherence at the frequency of GJ 3998 b, and high RV-S index coherence at the frequency of GJ 3998 c, indicate that the planets may actually be stellar signals. We also replicate previous results showing that GJ 581 d and g are rotation harmonics and demonstrate that α Cen B has activity signals that are not associated with rotation. Welch's power spectrum estimates have cleaner spectral windows than Lomb-Scargle periodograms, improving our ability to estimate rotation periods. We find that the rotation period of GJ 581 is 132 days, with no evidence of differential rotation. Welch's method may yield unacceptably large bias for datasets with N < 75 observations and works best on datasets with N > 100. Tapering the time-domain data can reduce the bias of the Welch's power spectrum estimator, but observers should not apply tapers to datasets with extremely uneven observing cadence. A software package for calculating magnitudesquared coherence and Welch's power spectrum estimates is available on github.

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A HARPS-N mass for the elusive Kepler-37d: a case study in disentangling stellar activity and planetary signals

Cited by 15 publications

References 113 publications

Composition of super-Earths, super-Mercuries, and their host stars

Composition of super-Earths, super-Mercuries, and their host stars

Semi-supervised standardized detection of extrasolar planets

Magnitude-squared coherence: A powerful tool for disentangling Doppler planet discoveries from stellar activity

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