Semi-supervised standardized detection of extrasolar planets

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

doi:10.1051/0004-6361/202142486

Cited by 3 publications

(1 citation statement)

References 94 publications

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“…A large number of methods has been compared, to quantify detection performance [44,58] or residuals after correction without injecting planets [59]. In addition, efforts have been devoted to improve the determination of the false alarm level [37,[60][61][62][63].…”

Section: Approachesmentioning

confidence: 99%

Impact of stellar variability on exoplanet detectability and characterisation

Meunier¹

2024

Comptes Rendus. Physique

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Stellar variability has become a major issue to detect low mass planets using the radial velocity technique. I present the approaches followed to characterise the amplitude and the properties of stellar variability in radial velocity. More specifically, the approach consisting in using our knowledge of the Sun to understand better the different processes which are occuring at different scales proved to be very useful. This has been done in different ways, based on observations and models. This is crucial because it is then possible to compare disk-integrated radial velocities with actual structures on the solar surface, such as spots and plages, and with photospheric flows at different spatial scales. Many physical processes indeed affect the radial velocity measurements: they are mostly due to magnetic features (spots and plages), flows (oscillations, granulation, supergranulation, meridional flows), and to the interactions between magnetic fields and flows (inhibition of the convective blueshift in plages). I present in more detail a selection of studies aiming at characterising the impact of stellar variability, in particular the relationship between activity indicators and radial velocities, and then focusing on mass characterisation and detection performance. Finally, I briefly review the impact of stellar variability on photometric transits and astrometry, which are also affected, but to a lesser extent.Résumé. La variabilité stellaire est devenue un problème majeur pour détecter les planètes de faible masse en utilisant la méthode des vitesses radiales. Je présente les approches suivies pour caractériser l'amplitude et les propriétés de la variabilité stellaire en vitesse radiale. Plus précisément, l'approche consistant à utiliser notre connaissance du Soleil pour mieux comprendre les différents processus qui se produisent à différentes échelles s'est avérée très utile. Cela a été fait de différentes manières, sur la base d'observations et de modèles. Ceci est crucial car il est alors possible de comparer les vitesses radiales intégrées au disque avec les structures réelles de la surface solaire, telles que les taches et les plages, et avec les flux photosphériques à différentes échelles spatiales. De nombreux processus physiques affectent en effet les mesures de vitesse radiale : ils sont principalement dus aux caractéristiques magnétiques (taches et plages), aux écoulements (oscillations, granulation, supergranulation, circulation méridienne), et aux interactions entre les champs magnétiques et les écoulements (inhibition du blueshift convectif dans les plages). Je présente plus en détail une sélection d'études visant à caractériser l'impact de la variabilité stellaire, en particulier la relation entre les indicateurs d'activité et les vitesses radiales, puis je me concentre sur la caractérisation des masses et les performances de détection. Enfin, je passe brièvement en revue l'impact de la variabilité stellaire sur les transits photométriques et l'astrométrie, qui sont également affectés, mais dans une...

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Section: Approachesmentioning

confidence: 99%

Impact of stellar variability on exoplanet detectability and characterisation

Meunier¹

2024

Comptes Rendus. Physique

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Activity time series of old stars from late F to early K

Meunier,

Pous,

Sulis

et al. 2023

A&A

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Context. Stellar variability impacts radial velocities (hereafter RVs) at various timescales and therefore the detectability of exoplanets and the mass determination based on this technique. Detecting and characterising Earth-like planets in the habitable zone of solar-type stars represents an important challenge in the coming years, however. It is therefore necessary to implement systematic studies of this issue, for example to delineate the current limitations of RV techniques. Aims. A first aim of this paper is to investigate whether the targeted 10% mass uncertainty from RV follow-up of transits detected by PLATO can be reached. A second aim of this paper is to analyse and quantify Earth-like planet detectability for various spectral types. Methods. For this purpose, we implemented blind tests based on a large data set (more than 20 000) of realistic synthetic time series reproducing different phenomena leading to stellar variability such as magnetic activity patterns similar to the solar configuration as well as flows (oscillations, granulation, and supergranulation), covering F6-K4 stars and a wide range of activity levels. Results. We find that the 10% mass uncertainty for a 1 MEarth in the habitable zone of a G2 star cannot be reached, even with an improved version of the usual correction of stellar activity (here based on a non-linear relation with log R′HK and cycle phase instead of a linear correlation) and even for long-duration (10 yr) well-sampled observations. This level can be reached, however, for masses above 3 MEarth or for K4 stars alone. We quantify the maximum dispersion of the RV residuals needed to reach this 10% level, assuming the activity correction method and models do not affect the planetary signal. Several other methods, also based on a correction using log R′HK in various ways (including several denoising techniques and Gaussian processes) or photometry, were tested and do not allow a significantly improvement of this limited performance. Similarly, such low-mass planets in the habitable zone cannot be detected with a similar correction: blind tests lead to very low detection rates for 1 MEarth and to a very high level of false positives. We also studied the residuals after correction of the stellar signal, and found significant power in the periodogram at short and long timescales, corresponding to masses higher than 1 MEarth in this period range. Conclusions. We conclude that very significant and new improvements with respect to methods based on activity indicators to correct for stellar activity must be devised at all timescales to reach the objective of 10% uncertainty on the mass or to detect such planets in RV. Methods based on the correlation with activity indicators are unlikely to be sufficient.

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A low-mass sub-Neptune planet transiting the bright active star HD 73344

Sulis,

Crossfield,

Santerne

et al. 2024

A&A

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Planets with radii of between $2$ and $4 R_ closely orbiting solar-type stars are of significant importance for studying the transition from rocky to giant planets, and are prime targets for atmospheric characterization by missions such as JWST and ARIEL. Unfortunately, only a handful of examples with precise mass measurements are known to orbit bright stars. Our goal is to determine the mass of a transiting planet around the very bright F6 star HD 73344 (Vmag=6.9). This star exhibits high activity and has a rotation period that is close to the orbital period of the planet ($P_ b =15.6$ days). The transiting planet, initially a K2 candidate, is confirmed through TESS observations (TOI 5140.01). We refined its parameters using TESS data and rule out a false positive with Spitzer observations. We analyzed high-precision radial velocity (RV) data from the SOPHIE and HIRES spectrographs. We conducted separate and joint analyses of K2, TESS, SOPHIE, and HIRES data using the PASTIS software. Given the star's early type and high activity, we used a novel observing strategy, targeting the star at high cadence for two consecutive nights with SOPHIE to understand the short-term stellar variability. We modeled stellar noise with two Gaussian processes: one for rotationally modulated stellar processes, and one for short-term stellar variability. High-cadence RV observations provide better constraints on stellar variability and precise orbital parameters for the transiting planet: a radius of $R_ b R_ and a mass of $M_ b M_ (upper-limit at $3 is $<10.48 M_ oplus$) . The derived mean density suggests a sub-Neptune-type composition, but uncertainties in the planet's mass prevent a detailed characterization. In addition, we find a periodic signal in the RV data that we attribute to the signature of a nontransiting exoplanet, without totally excluding the possibility of a nonplanetary origin. This planetary candidate would have a minimum mass of about $M_ c i_ c M_ and a period of $P_ c $ days. Dynamical analyses confirm the stability of the two-planet system and provide constraints on the inclination of the candidate planet; these findings favor a near-coplanar system. While the transiting planet orbits the bright star at a short period, stellar activity prevented us from precise mass measurements despite intensive RV follow-up. Long-term RV tracking of this planet could improve this measurement, as well as our understanding of the activity of the host star. The latter will be essential if we are to characterize the atmosphere of planets around F-type stars using transmission spectroscopy.

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Semi-supervised standardized detection of extrasolar planets

Cited by 3 publications

References 94 publications

Impact of stellar variability on exoplanet detectability and characterisation

Impact of stellar variability on exoplanet detectability and characterisation

Activity time series of old stars from late F to early K

A low-mass sub-Neptune planet transiting the bright active star HD 73344

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