An Earth-mass planet orbiting α Centauri B

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

doi:10.1038/nature11572

Cited by 428 publications

(481 citation statements)

References 30 publications

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“…Inspection of the RVs measured over one month indeed show some repeatability with a timescale of ~12-13 days, a sign that starspots are also inducing a large RV signal (see Extended Data Figure 3). Based on previous work 41 , we modeled the RV signal induced by spots with a primary sine function at the rotation period of the star, followed by a series of sine functions representing subharmonics of the stellar rotation. The planet-induced RV signal is modeled with a sinusoid, assuming zero eccentricity and using a linear ephemeris fixed to the best-fit orbital period and phase 6 .…”

Section: Methodsmentioning

confidence: 99%

A rocky composition for an Earth-sized exoplanet

Howard

Sanchis-Ojeda

Marcy

et al. 2013

Nature

191

157

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Planets with sizes between that of Earth (with radius R ⊕ ) and Neptune (about 4 R ⊕ ) are now known to be common around Sun-like stars 1,2,3 . Most such planets have been discovered through the transit technique, by which the planet's size can be determined from the fraction of starlight blocked by the planet as it passes in front of its star. Measuring the planet's mass-and hence its density, which is a clue to its composition-is more difficult. Planets of size 2-4 R ⊕ have proven to have a wide range of densities, implying a diversity of compositions 4,5 , but these measurements did not extend down to planets as small as Earth. Here we report Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b, which orbits its host star every 8.5 hours (ref. 6). Given a radius of 1.20 ± 0.09 R ⊕ and mass of 1.69 ± 0.41 M ⊕ , the planet's mean density of 5.3 ± 1.8 g cm -3 is similar to the Earth's, suggesting a composition of rock and iron.Kepler-78 is one of approximately 150,000 stars whose brightness was precisely measured at 30-minute intervals for four years by the NASA Kepler spacecraft 7 . This star is somewhat smaller, less massive, and younger than the Sun (Table 1). Every 8.5 hours the star's brightness declines by 0.02% as the planet Kepler-78b transits (passes in front of) the stellar disk. The planet's radius was originally measured 6 to be 1.16 !!.!" !!.!" R ⊕ . The mass could not be measured, although masses >8 M ⊕ could be ruled out because the planet's gravity would have deformed the star and produced brightness variations that were not detected.We measured the mass of Kepler-78b by tracking the line-of-sight component of the host star's motion (the radial velocity, RV) due to the gravitational force of the planet. The RV analysis is challenging not only because the signal is expected to be small (~1-3 m s -1 ) but also because the apparent Doppler shifts due to rotating starspots are much larger (~50 m s -1 peak-to-peak). Nevertheless the detection proved to be possible, thanks to the precisely known orbital period and phase of Kepler-78b that cleanly separated the timescale of spot variations (P rot ≈ 12.5 days) from the much shorter timescale of the planetary orbit (P ≈ 8.5 hours). We adopted a strategy of intensive Doppler measurements spanning 6-8 hours per night, long enough to cover nearly the entire orbit and short enough for the spot variations to be nearly frozen out.We measured RVs using optical spectra of Kepler-78 that we obtained from the High Resolution Echelle Spectrometer (HIRES) 8 on the 10-m Keck I Telescope. These Doppler shifts were computed relative to a template spectrum with a standard algorithm 9 that uses a spectrum of molecular iodine superposed on the stellar spectrum as a reference for the wavelength scale and instrumental profile of HIRES (Supplementary Table 1). Exposures lasted 15-30 minutes depending on conditions and produced RVs with 1.5-2.0 m s -1 uncertainties. The time series of RVs spans 38 days, with large velocity offsets between nights ...

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Section: Methodsmentioning

confidence: 99%

A rocky composition for an Earth-sized exoplanet

Howard

Sanchis-Ojeda

Marcy

et al. 2013

Nature

191

157

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“…Out of the methods used to detect these systems, one of the most successful for detecting planets orbiting the nearest stars is the radial velocity (RV) method, which is performed by measuring the Doppler shift of the spectral lines of a star, produced by the gravitational interaction with orbiting planets. The improvement of instrumentation, calibration techniques, and signal detection methods has made it possible to detect RV signals that conform to planets with masses approaching that of the Earth orbiting the nearest stars (Dumusque et al 2012;Anglada-Escudé et al 2014). Müller et al (2013) has shown that the pipeline of the FEROS spectrograph performs an inaccurate barycentric velocity correction, since it does not include the Earth's precession, introducing a one-year period signal with an amplitude of ∼ 62 m s −1 for τ 1 http://exoplanet.eu Ceti (a known stable star at the few m s −1 level, see Tuomi et al 2013).…”

Section: Introductionmentioning

confidence: 99%

RAFT – I. Discovery of new planetary candidates and updated orbits from archival FEROS spectra

Soto

Jenkins

Jones

2015

Monthly Notices of the Royal Astronomical Society

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A recent reanalysis of archival data has lead several authors to arrive at strikingly different conclusions for a number of planet-hosting candidate stars. In particular, some radial velocities measured using FEROS spectra have been shown to be inaccurate, throwing some doubt on the validity of a number of planet detections. Motivated by these results, we have begun the Reanalysis of Archival FEROS specTra (RAFT) program and here we discuss the first results from this work. We have reanalyzed FEROS data for the stars HD 11977, HD 47536, HD 70573, HD 110014 and HD 122430, all of which are claimed to have at least one planetary companion. We have reduced the raw data and computed the radial velocity variations of these stars, achieving a long-term precision of ∼ 10 m s −1 on the known stable star τ Ceti, and in good agreement with the residuals to our fits. We confirm the existence of planets around HD 11977, HD 47536 and HD 110014, but with different orbital parameters than those previously published. In addition, we found no evidence of the second planet candidate around HD 47536, nor any companions orbiting HD 122430 and HD 70573. Finally, we report the discovery of a second planet around HD 110014, with a minimum mass of 3.1 M Jup and a orbital period of 130 days. Analysis of activity indicators allow us to confirm the reality of our results and also to measure the impact of magnetic activity on our radial velocity measurements. These results confirm that very metal-poor stars down to [Fe/H]∼-0.7 dex, can indeed form giant planets given the right conditions.

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“…If we do find signs of Earth-mass planets orbiting our closest neighbour, then a smaller and much less costly version of Terrestrial Planet Finder could be built. Finally, we draw attention to the promising results of Dumusque et al (2012), who report the detection of an Earth-mass planet in a 3.236-day orbit around Alpha Centauri B (though this is controversial, e.g. Hatzes 2013).…”

Section: Resultsmentioning

confidence: 99%

A Campaign for the Detection of Earth-Mass Planets in the Habitable Zone of Alpha Centauri

Wittenmyer

Endl²,

Bergmann

et al. 2012

Proc. IAU

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Abstract.We review the possible formation and orbital stability of Earth-mass or super Earthmass planets around either of the stars Alpha Centauri A or B and describe a program at Mt John University Observatory using the Doppler method that aims to detect such planets. From New Zealand, we are able to observe the Alpha Centauri system year-round. This is critical in order to acquire data of sufficient quantity and phase coverage to detect the orbit of a terrestrial-mass planet in the habitable zone. Our observations are being made at high resolution (R = 70, 000) and high signal-to-noise with the Hercules vacuum echelle spectrograph attached to the 1-m McLellan telescope by a 25-m long optical fibre and using an iodine cell. We discuss the velocity precision and instrumental stability required for success and outline the progress of the observations so far. At present we are collecting about 10,000 observations of each star, A and B, per year with a typical precision of 2.5 m/s per observation.

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An Earth-mass planet orbiting α Centauri B

Cited by 428 publications

References 30 publications

A rocky composition for an Earth-sized exoplanet

A rocky composition for an Earth-sized exoplanet

RAFT – I. Discovery of new planetary candidates and updated orbits from archival FEROS spectra

A Campaign for the Detection of Earth-Mass Planets in the Habitable Zone of Alpha Centauri

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