The HARPS search for Earth-like planets in the habitable zone

Pepe, F.; Lovis, C.; Ségransan, D.; Benz, W.; Bouchy, F.; Dumusque, X.; Mayor, M.; Queloz, D.; Santos, N. C.; Udry, S.

doi:10.1051/0004-6361/201117055

Cited by 264 publications

(271 citation statements)

References 35 publications

(52 reference statements)

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“…As shown hereafter, this could be the case for Gl 581 c (Udry et al 2007;Mayor et al 2009;Forveille et al 2011) and HD 85512 b (Pepe et al 2011), the only two confirmed planets having masses that are compatible with a terrestrial planet (M p < ∼ 7−8 M ⊕ ; although defining such a mass limit is questionable) and that lie beyond the inner edge of the classical habitable zone but receive a moderate stellar flux, F /4 < 1000 W/m 2 . These planets lie even closer to the star that the inner edge of the limits set by Abe et al (2011) for land planets.…”

Section: Beyond the Runaway Greenhouse Limitmentioning

confidence: 89%

3D climate modeling of close-in land planets: Circulation patterns, climate moist bistability, and habitability

Leconte

Forget

Charnay

et al. 2013

A&A

242

318

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The inner edge of the classical habitable zone is often defined by the critical flux needed to trigger the runaway greenhouse instability. This 1D notion of a critical flux, however, may not be all that relevant for inhomogeneously irradiated planets, or when the water content is limited (land planets). Based on results from our 3D global climate model, we present general features of the climate and large-scale circulation on close-in terrestrial planets. We find that the circulation pattern can shift from super-rotation to stellar/anti stellar circulation when the equatorial Rossby deformation radius significantly exceeds the planetary radius, changing the redistribution properties of the atmosphere. Using analytical and numerical arguments, we also demonstrate the presence of systematic biases among mean surface temperatures and among temperature profiles predicted from either 1D or 3D simulations. After including a complete modeling of the water cycle, we further demonstrate that two stable climate regimes can exist for land planets closer than the inner edge of the classical habitable zone. One is the classical runaway state where all the water is vaporized, and the other is a collapsed state where water is captured in permanent cold traps. We identify this "moist" bistability as the result of a competition between the greenhouse effect of water vapor and its condensation on the night side or near the poles, highlighting the dynamical nature of the runaway greenhouse effect. We also present synthetic spectra showing the observable signature of these two states. Taking the example of two prototype planets in this regime, namely Gl 581 c and HD 85512 b, we argue that depending on the rate of water delivery and atmospheric escape during the life of these planets, they could accumulate a significant amount of water ice at their surface. If such a thick ice cap is present, various physical mechanisms observed on Earth (e.g., gravity driven ice flows, geothermal flux) should come into play to produce long-lived liquid water at the edge and/or bottom of the ice cap. Consequently, the habitability of planets at smaller orbital distance than the inner edge of the classical habitable zone cannot be ruled out. Transiting planets in this regime represent promising targets for upcoming exoplanet characterization observatories, such as EChO and JWST.

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Section: Beyond the Runaway Greenhouse Limitmentioning

confidence: 89%

3D climate modeling of close-in land planets: Circulation patterns, climate moist bistability, and habitability

Leconte

Forget

Charnay

et al. 2013

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“…As205a back with AS 205A. Pepe et al (2011), using high-resolution spectroscopy, published the Keplerian solutions of two orbiting planets around HD192310. The dispersion of their RV measurements, however, had a rms of only 2.6 ms −1 over a 6.5-year interval.…”

Section: Radial Velocitiesmentioning

confidence: 99%

“…Our own study detected variations in the HD192310 RV profile with a standard deviation of ≤11 ms −1 over 4 years of observations. Although it was beyond our detection limit we tried nevertheless to adjust the Keplerian solutions of Pepe et al (2011) to the variations observed. The lack of consistent fits implied that the dispersion in our RV data was instead associated with the internal uncertainty of our method.…”

Section: Radial Velocitiesmentioning

confidence: 99%

Evidence of a substellar companion around a very young T Tauri star

Almeida

Gameiro

Петров

et al. 2017

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We present results from a Near Infrared multi-epoch spectroscopic campaign to detect a young low-mass companion to a T Tauri star. AS 205A is a late-type dwarf (≈K5) of ∼ 1 M⊙ that belongs to a triple system. Independent photometric surveys discovered that AS 205A has two distinct periods (P 1 =6.78 and P 2 =24.78 days) detected in the light curve that persist over several years. Period P 1 seems to be linked to the axial-rotation of the star and is caused by the presence of cool surface spots. Period P 2 is correlated with the modulation in AS 205A brightness (V) and red color (V-R), consistent with a gravitating object within the accretion disk.We here derive precise Near Infrared radial velocities to investigate the origin of period P 2 which is predicted to correspond to a cool source in a Keplerian orbit with a semi-major axis of ∼0.17 AU positioned close to the inner disk radius of 0.14 AU. The radial velocity variations of AS 205A were found to have a period of P ≈ 24.84 days and a semi-amplitude of 1.529 kms −1 . This result closely resembles the P 2 period in past photometric observations (P ≈ 24.78 days). The analysis of the cross-correlation function bisector has shown no correlation with the radial velocity modulations, strongly suggesting that the period is not controlled by stellar rotation. Additional activity indicators should however be explored in future surveys. Taking this into account we found that the presence of a substellar companion is the explanation that best fits the results. We derived an orbital solution for AS 205A and found evidence of a m 2 sini ≃19.25 M Jup object in an orbit with moderate eccentricity of e ≃ 0.34. If confirmed with future observations, preferably using a multiwavelength survey approach, this companion could provide interesting constraints on brown dwarf and planetary formation models.

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“…The spin-orbit angle measurement may be helpful in modelling the planetary orbital evolution. The High Accuracy Radial-velocity Planet Searcher (HARPS, Mayor et al 2003), installed in 2002 on a 3.6 m telescope at the La Silla Observatory (Chile), has demonstrated a high efficiency for detecting lowmass exoplanets and for constraining their masses and orbital parameters, thanks to its sub-1 m/s RV stability (Pepe et al 2011).…”

Section: Introductionmentioning

confidence: 99%

A global analysis ofSpitzerand new HARPS data confirms the loneliness and metal-richness of GJ 436 b

Lanotte

Gillon

Demory

et al. 2014

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Context. GJ 436b is one of the few transiting warm Neptunes for which a detailed characterisation of the atmosphere is possible, whereas its non-negligible orbital eccentricity calls for further investigation. Independent analyses of several individual datasets obtained with Spitzer have led to contradicting results attributed to the different techniques used to treat the instrumental effects. Aims. We aim at investigating these previous controversial results and developing our knowledge of the system based on the full Spitzer photometry dataset combined with new Doppler measurements obtained with the HARPS spectrograph. We also want to search for additional planets. Methods. We optimise aperture photometry techniques and the photometric deconvolution algorithm DECPHOT to improve the data reduction of the Spitzer photometry spanning wavelengths from 3-24 µm. Adding the high-precision HARPS radial velocity data, we undertake a Bayesian global analysis of the system considering both instrumental and stellar effects on the flux variation.Results. We present a refined radius estimate of R P = 4.10 ± 0.16 R ⊕ , mass M P = 25.4 ± 2.1 M ⊕ , and eccentricity e = 0.162 ± 0.004 for GJ 436b. Our measured transit depths remain constant in time and wavelength, in disagreement with the results of previous studies. In addition, we find that the post-occultation flare-like structure at 3.6 µm that led to divergent results on the occultation depth measurement is spurious. We obtain occultation depths at 3.6, 5.8, and 8.0 µm that are shallower than in previous works, in particular at 3.6 µm. However, these depths still appear consistent with a metal-rich atmosphere depleted in methane and enhanced in CO/CO 2 , although perhaps less than previously thought. We could not detect a significant orbital modulation in the 8 µm phase curve. We find no evidence of a potential planetary companion, stellar activity, or a stellar spin-orbit misalignment. Conclusions. Recent theoretical models invoking high-metallicity atmospheres for warm Neptunes are a reasonable match to our results, but we encourage new modelling efforts based on our revised data. Future observations covering a wide wavelength range of GJ 436b and other Neptune-class exoplanets will further illuminate their atmosphere properties, whilst future accurate radial velocity measurements might explain the eccentricity.

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The HARPS search for Earth-like planets in the habitable zone

Cited by 264 publications

References 35 publications

3D climate modeling of close-in land planets: Circulation patterns, climate moist bistability, and habitability

3D climate modeling of close-in land planets: Circulation patterns, climate moist bistability, and habitability

Evidence of a substellar companion around a very young T Tauri star

A global analysis ofSpitzerand new HARPS data confirms the loneliness and metal-richness of GJ 436 b

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