The HARPS-N Rocky Planet Search I. HD219134b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun

Abstract

We know now from radial-velocity surveys and transit space missions that planets only a few times more massive than our Earth are frequent around solar-type stars. Fundamental questions about their formation history, physical properties, internal structure, and atmosphere composition are, however, still to be solved. We present here the detection of a system of four low-mass planets around the bright (V=5.5) and close-by (6.5 pc) star HD 219134. This is the first result of the Rocky Planet Search program with HARPS-N on the Telescopio Nazionale Galileo in La Palma. The inner planet orbits the star in 3.0937 ± 0.0004 days, on a quasi-circular orbit with a semi-major axis of 0.0382 ±0.0003 AU. Spitzer observations allowed us to detect the transit of the planet in front of the star making HD 219134 b the nearest known transiting planet to date. From the amplitude of the radial-velocity variation (2.33 ± 0.24 ms −1 ) and observed depth of the transit (359 ± 38 ppm), the planet mass and radius are estimated to be 4.46 ± 0.47 M ⊕ and 1.606 ± 0.086 R ⊕ , leading to a mean density of 5.89 ± 1.17 g cm −3 , suggesting a rocky composition. One additional planet with minimum mass of 2.67 ± 0.59 M ⊕ moves on a close-in, quasi-circular orbit with a period of 6.765±0.005 days. The third planet in the system has a period of 46.78 ± 0.16 days and a minimum mass of 8.7 ± 1.1 M ⊕ , at 0.234±0.002 AU from the star. Its eccentricity is 0.32 ± 0.14. The period of this planet is close to the rotational period of the star estimated from variations of activity indicators (42.3 ± 0.1 days). The planetary origin of the signal is, however, the preferred solution as no indication of variation at the corresponding frequency is observed for activity-sensitive parameters. Finally, a fourth additional longer-period planet of mass of 62 ± 6 M ⊕ orbits the star in 1190 days, on an eccentric orbit (e = 0.27 ± 0.11) at a distance of 2.14±0.27 AU.

The HARPS search for southern extra-solar planets. XXXVIII. Bayesian re-analysis of three systems. New super-Earths, unconfirmed signals, and magnetic cycles

“…HD1461 and HD40307 are two of only six solar-type planetary systems with at least two super-Earth companions whose mass is known to better than 50%, and they will become prime targets for the follow-up mission CHEOPS. The other systems are HD20794 (Pepe et al 2011), HD7924 (Fulton et al 2015), HD219134 (Motalebi et al 2015), and Kepler-102 (Marcy et al 2014). Except for Kepler-102, which was first discovered as a transiting candidate system, these systems required more than 100 RV measurements to be detected.…”

Precision Stellar Astrophysics in the Kepler Era

“…To test the accuracy of interferometric angular diameters, we have recently started crosscalibration efforts with the CHARA Array by revisiting stars which were observed with the Classic (H/K band) beam combiner with the higher-resolution PAVO (R band) beam combiner [101]. Figure 8 shows preliminary results for the K dwarf HD 219134, the closest transiting exoplanet known to date [102,103]. PAVO data were taken over four nights in August and September 2015 using two baselines (E2W2, W1W2), and calibrated using HD 218376 (θ = 0.304 mas), HD 225289 (θ = 0.206 mas) and HD 223386 (θ = 0.177 mas).…”

KELT-10b: the first transiting exoplanet from the KELT-South survey – a hot sub-Jupiter transiting aV= 10.7 early G-star

“…To date, over 50 papers on various properties of the exoplanet 2 have been published. Currently HD219134b (Motalebi et al 2015) is the nearest and brightest host star with a known transiting exoplanet. This system shows enormous promise for future follow-up observations, which would better constrain the system architecture and characterize the physical properties of the planet.…”