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Post Info TOPIC: WASP-47
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WASP-47 Planetary System
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Title: Mass Constraints of the WASP-47 Planetary System from Radial Velocities
Author: Evan Sinukoff, Andrew W. Howard, Erik A. Petigura, Benjamin J. Fulton, Howard Isaacson, Lauren M. Weiss, John M. Brewer, Brad M. S. Hansen, Lea Hirsch, Jessie L. Christiansen, Justin R. Crepp, Ian J. M. Crossfield, Joshua E. Schlieder, David R. Ciardi, Charles A. Beichman, Heather A. Knutson, Bjoern Benneke, Courtney D. Dressing, John H. Livingston, Katherine M. Deck, Sebastien Lepine, Leslie A. Rogers

We report precise radial velocity (RV) measurements of WASP-47, a G star that hosts three transiting planets in close proximity (a hot Jupiter, a super-Earth and a Neptune-sized planet) and a non-transiting planet at 1.4 AU. Through a joint analysis of previously published RVs and our own Keck-HIRES RVs, we significantly improve the planet mass and bulk density measurements. For the super-Earth WASP-47e (P = 0.79 days), we measure a mass of 9.11 ± 1.17 Earth masses, and a bulk density of 7.63 ± 1.90 g cm^-3, consistent with a rocky composition. For the hot Jupiter WASP-47b (P = 4.2 days), we measure a mass of 356 ± 12 Earth masses (1.12 ± 0.04 MJup) and constrain its eccentricity to <0.021 at 3-sigma confidence. For the Neptune-size planet WASP-47d (P = 9.0 days), we measure a mass of 12.75 ± 2.70 Earth masses, and a bulk density of 1.36 ± 0.42 g cm^-3, suggesting it has a thick H/He envelope. For the outer non-transiting planet, we measure a minimum mass of 411 ± 18 Earth masses (1.29 ± 0.06 MJup), an orbital period of 595.7 ± 5.0 days, and an orbital eccentricity of 0.27 ± 0.04. Our new measurements are consistent with but 2-4 X more precise than previous mass measurements.

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RE: WASP-47
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Title: A low stellar obliquity for WASP-47, a compact multiplanet system with a hot Jupiter and an ultra-short period planet
Author: Roberto Sanchis-Ojeda, Joshua N. Winn, Fei Dai, Andrew W. Howard, Howard Isaacson, Geoffrey W. Marcy, Erik Petigura, Evan Sinukoff, Lauren Weiss, Simon Albrecht, Teruyuki Hirano, Leslie Rogers

We have detected the Rossiter-Mclaughlin effect during a transit of WASP-47b, the only known hot Jupiter with close planetary companions. By combining our spectroscopic observations with Kepler photometry, we show that the projected stellar obliquity is lambda=0°±24°. We can firmly exclude a retrograde orbit for WASP-47b, and rule out strongly misaligned prograde orbits. Low obliquities have also been found for most of the other compact multiplanet systems that have been investigated. The Kepler-56 system, with two close-in gas giants transiting their subgiant host star with an obliquity of at least 45°, remains the only clear counterexample.

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Blobrana


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Title: WASP-47: A Hot Jupiter System with Two Additional Planets Discovered by K2
Author: Juliette C. Becker, Andrew Vanderburg, Fred C. Adams, Saul A. Rappaport, Hans Martin Schwengeler

Using new data from the K2 mission, we show that WASP-47, a previously known hot Jupiter host, also hosts two additional transiting planets: a Neptune-sized outer planet and a super-Earth inner companion. We measure planetary properties from the K2 light curve and detect transit timing variations, confirming the planetary nature of the outer planet. We performed a large number of numerical simulations to study the dynamical stability of the system and to find the theoretically expected transit timing variations (TTVs). The theoretically predicted TTVs are in good agreement with those observed, and we use the TTVs to determine the masses of two planets, and place a limit on the third. The WASP-47 planetary system is important because companion planets can both be inferred by TTVs and are also detected directly through transit observations. The depth of the hot Jupiter's transits make ground-based TTV measurements possible, and the brightness of the host star makes it amenable for precise radial velocity measurements. The system serves as a Rosetta Stone for understanding TTVs as a planet detection technique.

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