Planet Hunters. VII. Discovery of a New Low-mass, Low-density Planet (PH3 C) Orbiting Kepler-289 With Mass Measurements of Two Additional Planets (PH3 B and D) (The Astrophysical Journal, 2014)

• Eric Agol

Full Citation:
Schmitt, J. R., Agol, E., Deck, K. M., Rogers, L. A., Gazak, J. Z., Fischer, D. A., Wang, J., Holman, M. J., Jek, K. J., Margossian, C., Omohundro, M. R., Winarski, T., Brewer, J. M., Giguere, M. J., Lintott, C., Lynn, S., Parrish, M., Schawinski, K., Schwamb, M. E., … Smith, A. M. (2014). Planet Hunters. Vii. Discovery of a New Low-mass, Low-density Planet (PH3 C) Orbiting Kepler-289 With Mass Measurements of Two Additional Planets (PH3 B and D). The Astrophysical Journal, 795(2), 167. https://doi.org/10.1088/0004-637x/795/2/167

Abstract:
We report the discovery of one newly confirmed planet (P = 66.06 days, R P = 2.68 ± 0.17 R ⊕) and mass determinations of two previously validated Kepler planets, Kepler-289 b (P = 34.55 days, R P = 2.15 ± 0.10 R ⊕) and Kepler-289-c (P = 125.85 days, R P = 11.59 ± 0.10 R ⊕), through their transit timing variations (TTVs). We also exclude the possibility that these three planets reside in a 1:2:4 Laplace resonance. The outer planet has very deep (~1.3%), high signal-to-noise transits, which puts extremely tight constraints on its host star's stellar properties via Kepler's Third Law. The star PH3 is a young (~1 Gyr as determined by isochrones and gyrochronology), Sun-like star with M * = 1.08 ± 0.02 M ☉, R * = 1.00 ± 0.02 R ☉, and T eff = 5990 ± 38 K. The middle planet's large TTV amplitude (~5 hr) resulted either in non-detections or inaccurate detections in previous searches. A strong chopping signal, a shorter period sinusoid in the TTVs, allows us to break the mass-eccentricity degeneracy and uniquely determine the masses of the inner, middle, and outer planets to be M = 7.3 ± 6.8 M ⊕, 4.0 ± 0.9M ⊕, and M = 132 ± 17 M ⊕, which we designate PH3 b, c, and d, respectively. Furthermore, the middle planet, PH3 c, has a relatively low density, ρ = 1.2 ± 0.3 g cm–3 for a planet of its mass, requiring a substantial H/He atmosphere of $2.1^{+0.8}_{-0.3}\%$ by mass, and joins a growing population of low-mass, low-density planets.

URL:
https://iopscience.iop.org/article/10.1088/0004-637X/795/2/167/meta

VPL Research Tasks:
Task E: The Observer