The HARPS search for southern extra-solar planets

Delisle, J.-B.; Ségransan, D.; Dumusque, X.; Díaz, R. F.; Bouchy, F.; Lovis, C.; Pepe, F.; Udry, S.; Alonso, R.; Benz, W.; Coffinet, A.; Cameron, A. Collier; Deleuil, M.; Figueira, P.; Gillon, M.; Curto, G. Lo; Mayor, M.; Mordasini, C.; Motalebi, F.; Moutou, C.; Pollacco, D.; Pompei, E.; Queloz, D.; Santos, N. C.; Wyttenbach, A.

doi:10.1051/0004-6361/201732529

Cited by 60 publications

(76 citation statements)

References 39 publications

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“…For planet b, the prior T c was set in accordance with TESS data. The convergence was checked by computing the number of effective samples in each parameter chain as in Delisle et al (2018). We find that each chain has at least 18 000 effective samples, which indicates convergence of the chain.…”

Section: E1 Mcmcmentioning

confidence: 99%

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The SOPHIE search for northern extrasolar planets

Hara

Bouchy

Stalport

et al. 2020

A&A

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Aims. Since 2011, the SOPHIE spectrograph has been used to search for Neptunes and super-Earths in the northern hemisphere. As part of this observational program, 290 radial velocity measurements of the 6.4 V magnitude star HD 158259 were obtained. Additionally, TESS photometric measurements of this target are available. We present an analysis of the SOPHIE data and compare our results with the output of the TESS pipeline. Methods. The radial velocity data, ancillary spectroscopic indices, and ground-based photometric measurements were analyzed with classical and ℓ1 periodograms. The stellar activity was modeled as a correlated Gaussian noise and its impact on the planet detection was measured with a new technique. Results. The SOPHIE data support the detection of five planets, each with m sin i ≈ 6 M⊕, orbiting HD 158259 in 3.4, 5.2, 7.9, 12, and 17.4 days. Though a planetary origin is strongly favored, the 17.4 d signal is classified as a planet candidate due to a slightly lower statistical significance and to its proximity to the expected stellar rotation period. The data also present low frequency variations, most likely originating from a magnetic cycle and instrument systematics. Furthermore, the TESS pipeline reports a significant signal at 2.17 days corresponding to a planet of radius ≈1.2 R⊕. A compatible signal is seen in the radial velocities, which confirms the detection of an additional planet and yields a ≈2 M⊕ mass estimate. Conclusions. We find a system of five planets and a strong candidate near a 3:2 mean motion resonance chain orbiting HD 158259. The planets are found to be outside of the two and three body resonances.

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Section: E1 Mcmcmentioning

confidence: 99%

“…Near resonant, compact systems are detectable by radial velocity (RV), as demonstrated by follow up observations of transits (Lopez et al 2019). However, such detections with only RV are rare: HD 40307 (Mayor et al 2009) and HD 215152 (Delisle et al 2018) both have three planets near 2:1 -2:1 and 5:3 -3:2 configurations, respectively.…”

Section: Introductionmentioning

confidence: 99%

The SOPHIE search for northern extrasolar planets

Hara

Bouchy

Stalport

et al. 2020

A&A

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“…In addition, using statistical techniques like Gaussian Processes (e.g. Haywood et al 2014;Rajpaul et al 2015;Jones et al 2017;Delisle et al 2018) or Moving Average (e.g. Tuomi et al 2013) can mitigate to a certain level the impact of the red noise induced by stellar activity.…”

Section: Introductionmentioning

confidence: 99%

“…Finally fitting the RVs with the long-term trend observed in the log(R HK ) activity index reduces the impact of solar-like magnetic cycle on the RVs (e.g. Dumusque et al 2011cDumusque et al , 2012Delisle et al 2018). Although these different techniques have been applied on several RV data set and have been able to detect interesting planetary systems, it seems that nowadays we are facing the obstacle of stellar activity, which is extremely difficult to overcome.…”

Section: Introductionmentioning

confidence: 99%

Measuring precise radial velocities on individual spectral lines

Dumusque

2018

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Context. Stellar activity is the main limitation to the detection of an Earth-twin using the radial-velocity (RV) technique. Despite many efforts in trying to mitigate the effect of stellar activity using empirical and statistical techniques, it seems that we are facing an obstacle that will be extremely difficult to overcome using current techniques. Aims. In this paper, we investigate a novel approach to derive precise RVs considering the wealth of information present in high-resolution spectra. Methods. This new method consists of building a master spectrum from all available observations and measure the RVs of each individual spectral line in a spectrum relative to this master. When analysing several spectra, the final product of this approach is the RVs of each individual line as a function of time. Results. We demonstrate on three stars intensively observed with HARPS that our new method gives RVs that are extremely similar to the one derived from the HARPS data reduction software. Our new approach to derive RVs demonstrates that the non-stability of daily HARPS wavelength solution induces night-to-night RV offsets with an standard deviation of 0.4 m s−1, and we propose a solution to correct for this systematic. Finally, and this is probably the most astrophysically relevant result of this paper, we demonstrate that some spectral lines are strongly affected by stellar activity while others are not. By measuring the RVs on two carefully selected subsample of spectral lines, we demonstrate that we can boost by a factor of two or mitigate by a factor of 1.6 the red noise induced by stellar activity in the 2010 RV measurements of α Cen B. Conclusions. By measuring the RVs of each spectral line, we are able to reach the same RV precision as other approved techniques. In addition, this new approach allows us to demonstrate that each spectral line is differently affected by stellar activity. Preliminary results show that studying in details the behaviour of each spectral line is probably the key to overcome the obstacle of stellar activity.

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“…1, 100, 000 samples are computed, the first fourth being the burn-in phase. The algorithm is an adaptive Metropolis algorithm as in Delisle et al (2018), and the convergence is checked by calculating the effective number of independent samples (see Delisle et al (2018), Appendix A).…”

Section: Incorrect Covariance: Simulationsmentioning

confidence: 99%

Bias and robustness of eccentricity estimates from radial velocity data

Hara

Boué

Laskar

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Eccentricity is a parameter of particular interest as it is an informative indicator of the past of planetary systems. It is however not always clear whether the eccentricity fitted on radial velocity data is real or if it is an artefact of an inappropriate modelling. In this work, we address this question in two steps: we first assume that the model used for inference is correct and present interesting features of classical estimators. Secondly, we study whether the eccentricity estimates are to be trusted when the data contain incorrectly modelled signals, such as missed planetary companions, non Gaussian noises, correlated noises with unknown covariance, etc. Our main conclusion is that data analysis via posterior distributions, with a model including a free error term gives reliable results provided two conditions. First, convergence of the numerical methods needs to be ascertained. Secondly, the noise power spectrum should not have a particularly strong peak at the semi period of the planet of interest. As a consequence, it is difficult to determine if the signal of an apparently eccentric planet might be due to another inner companion in 2:1 mean motion resonance. We study the use of Bayes factors to disentangle these cases. Finally, we suggest methods to check if there are hints of an incorrect model in the residuals. We show on simulated data the performance of our methods and comment on the eccentricities of Proxima b and 55 Cnc f.

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The HARPS search for southern extra-solar planets

Cited by 60 publications

References 39 publications

The SOPHIE search for northern extrasolar planets

The SOPHIE search for northern extrasolar planets

Measuring precise radial velocities on individual spectral lines

Bias and robustness of eccentricity estimates from radial velocity data

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