3D magneto-hydrodynamical simulations of stellar convective noise for improved exoplanet detection

Sulis, S.; Mary, David; Bigot, Lionel

doi:10.1051/0004-6361/201937105

Cited by 15 publications

(21 citation statements)

References 74 publications

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“…More recently, the residuals on timescales lower than one day obtained by Collier Cameron et al (2019) on solar integrated RV times series and covering the whole spectrum obtained by HARPS-N are also of the order of 0.40 m s −1 (when averaging over typically 5 min). Similar amplitudes have been obtained by Sulis et al (2020) using MHD simulations. The difference between these estimates and the results of Meunier et al (2015) may be due to some subtle effects in the centre-to-limb dependence which are not taken into account in Meunier et al (2015), but also to the fact that observations were made in a single lines which may not be representative of the whole spectrum.…”

Section: Solar Amplitudessupporting

confidence: 83%

The effects of granulation and supergranulation on Earth-mass planet detectability in the habitable zone around F6-K4 stars

Meunier

Lagrange

2020

A&A

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Context. The detectability of exoplanets and the determination of their projected mass in radial velocity are affected by stellar magnetic activity and photospheric dynamics. Among those processes, the effect of granulation, and even more so of supergranulation, has been shown to be significant in the solar case. The impact for other spectral types has not yet been characterised. Aims. Our study is aimed at quantifying the impact of these flows for other stars and estimating how such contributions affect their performance. Methods. We analysed a broad array of extended synthetic time series that model these processes to characterise the impact of these flows on exoplanet detection for main sequence stars with spectral types from F6 to K4. We focussed on Earth-mass planets orbiting within the habitable zone around those stars. We estimated the expected detection rates and detection limits, tested the tools that are typically applied to such observations, and performed blind tests. Results. We find that both granulation and supergranulation on these stars significantly affect planet mass characterisation in radial velocity when performing a follow-up of a transit detection: the uncertainties on these masses are sometimes below 20% for a 1 MEarth (for granulation alone or for low-mass stars), but they are much larger in other configurations (supergranulation, high-mass stars). For granulation and low levels of supergranulation, the detection rates are good for K and late G stars (if the number of points is large enough), but poor for more massive stars. The highest level of supergranulation leads to a very poor performance, even for K stars; this is both due to low detection rates and to high levels of false positives, even for a very dense temporal sampling over 10 yr. False positive levels estimated from standard false alarm probabilities sometimes significantly overestimate or underestimate the true level, depending on the number of points: it is, therefore, crucial to take this effect into account when analysing observations. Conclusions. We conclude that granulation and supergranulation significantly affect the performance of exoplanet detectability. Future works will focus on improving the following three aspects: decreasing the number of false positives, increasing detection rates, and improving the false alarm probability estimations from observations.

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Section: Solar Amplitudessupporting

confidence: 83%

The effects of granulation and supergranulation on Earth-mass planet detectability in the habitable zone around F6-K4 stars

Meunier

Lagrange

2020

A&A

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“…More recently, the residuals on timescales lower than one day obtained by Collier Cameron et al (2019) on solar integrated RV times series and covering the whole spectrum obtained by HARPS-N are also of the order of 0.40 m/s (when averaging over typically five minutes). Similar amplitudes have been obtained by Sulis et al (2020) using MHD simulations. The difference between these estimates and the results of Meunier et al (2015) may be due to some subtle effects in the centre-to-limb dependence which are not taken into account in Meunier et al (2015), but also to the fact that observations were made in a single lines which may not be representative of the whole spectrum.…”

Section: Solar Amplitudessupporting

confidence: 83%

The effects of granulation and supergranulation on Earth-mass planet detectability in the habitable zone around F6-K4 stars

Meunier,

Lagrange

2020

Preprint

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Context. The detectability of exoplanets and the determination of their projected mass in radial velocity are affected by stellar magnetic activity and photospheric dynamics. Among those processes, the effect of granulation, and even more so of supergranulation, has been shown to be significant in the solar case. The impact for other spectral types has not yet been characterised. Aims. Our study is aimed at quantifying the impact of these flows for other stars and estimating how such contributions affect their performance. Methods. We analysed a broad array of extended synthetic time series that model these processes to characterise the impact of these flows on exoplanet detection for main sequence stars with spectral types from F6 to K4. We focussed on Earth-mass planets orbiting within the habitable zone around those stars. We estimated the expected detection rates and detection limits, tested the tools that are typically applied to such observations, and performed blind tests. Results. We find that both granulation and supergranulation on these stars significantly affect planet mass characterisation in radial velocity when performing a follow-up of a transit detection: the uncertainties on these masses are sometimes below 20% for a 1 M Earth (for granulation alone or for low-mass stars), but they are much larger in other configurations (supergranulation, high-mass stars). For granulation and low levels of supergranulation, the detection rates are good for K and late G stars (if the number of points is large enough), but poor for more massive stars. The highest level of supergranulation leads to a very poor performance, even for K stars; this is both due to low detection rates and to high levels of false positives, even for a very dense temporal sampling over ten years. False positive levels estimated from standard false alarm probabilities sometimes significantly overestimate or underestimate the true level, depending on the number of points: it is, therefore, crucial to take this effect into account when analysing observations. Conclusions. We conclude that granulation and supergranulation significantly affect the performance of exoplanet detectability. Future works will focus on improving the following three aspects: decreasing the number of false positives, increasing detection rates, and improving the false alarm probability estimations from observations.

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“…The radial-velocity wobble induced by a small exoplanet is much smaller than stellar microvariability, therefore effects of the latter must somehow be calibrated and corrected for. Numerous authors have studied empirical correlations between various stellar activity indices and corresponding excursions in apparent radial velocity (e.g., Cegla et al 2014Cegla et al , 2019Collier Cameron et al 2020;de Beurs et al 2020;Dumusque 2016;Feng et al 2016;Haywood et al 2016;Hojjatpanah et al 2020;Kosiarek & Crossfield 2020;Lanza et al 2019;Luhn et al 2020a;Marchwinski et al 2015;Meunier et al 2010Meunier et al , 2015Meunier et al , 2017bMiklos et al 2020;Oshagh et al 2017;Sulis et al 2020a;Tayar et al 2019;Thompson et al 2020).…”

Section: The Quest For Earth-like Exoplanetsmentioning

confidence: 99%

Spatially resolved spectroscopy across stellar surfaces

Dravins

Ludwig

Freytag

2021

A&A

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Context. High-precision stellar analyses require hydrodynamic 3D modeling. Testing such models is feasible by retrieving spectral line shapes across stellar disks, using differential spectroscopy during exoplanet transits. Observations were presented in Papers I, II, and III, while Paper IV explored synthetic data at hyper-high spectral resolution for different classes of stars, identifying characteristic patterns for Fe I and Fe II lines. Aims. Anticipating future observations, the observability of patterns among photospheric lines of different strength, excitation potential and ionization level are examined from synthetic spectra, as observed at ordinary spectral resolutions and at different levels of noise. Time variability in 3D atmospheres induces changes in spectral-line parameters, some of which are correlated. An adequate calibration could identify proxies for the jitter in apparent radial velocity to enable adjustments to actual stellar radial motion. Methods. We used spectral-line patterns identified in synthetic spectra at hyper-high resolution in Paper IV from 3D models spanning Teff = 3964–6726 K (spectral types ~K8 V–F3 V) to simulate practically observable signals at different stellar disk positions at various lower spectral resolutions, down to λ/Δλ = 75 000. We also examined the center-to-limb temporal variability. Results. Recovery of spatially resolved line profiles with fitted widths and depths is shown for various noise levels, with gradual degradation at successively lower spectral resolutions. Signals during exoplanet transit are simulated. In addition to Rossiter-McLaughlin type signatures in apparent radial velocity, analogous effects are shown for line depths and widths. In a solar model, temporal variability in line profiles and apparent radial velocity shows correlations between jittering in apparent radial velocity and fluctuations in line depth. Conclusions. Spatially resolved spectroscopy using exoplanet transits is feasible for main-sequence stars. Overall line parameters of width, depth and wavelength position can be retrieved already with moderate efforts, but a very good signal-to-noise ratio is required to reveal the more subtle signatures between subgroups of spectral lines, where finer details of atmospheric structure are encoded. Fluctuations in line depth correlate with those in wavelength, and because both can be measured from the ground, searches for low-mass exoplanets should explore these to adjust apparent radial velocities to actual stellar motion.

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3D magneto-hydrodynamical simulations of stellar convective noise for improved exoplanet detection

Cited by 15 publications

References 74 publications

The effects of granulation and supergranulation on Earth-mass planet detectability in the habitable zone around F6-K4 stars

The effects of granulation and supergranulation on Earth-mass planet detectability in the habitable zone around F6-K4 stars

The effects of granulation and supergranulation on Earth-mass planet detectability in the habitable zone around F6-K4 stars

Spatially resolved spectroscopy across stellar surfaces

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