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Post Info TOPIC: K2-66b and K2-106b


Posts: 131433

Title: K2-106, a system containing a metal rich planet and a planet of lower density
Author: E.W. Guenther, O. Barragan, F. Dai, D. Gandolfi, T. Hirano, M. Fridlund, L. Fossati, J. Korth, J. Arraz-Prieto, D. Nespral, G. Antoniciello, H. Deeg, M. Hjorth, S. Grziwa, S. Albrecht, A.P. Hatzes, H. Rauer, S. Csizmadia, A.M.S. Smith, J. Cabrera, N. Narita, P. Arriagada, J. Burt, R.P. Butler, W.D. Cochran, J.D. Crane, Ph. Eigmueller, A. Erikson, J.A. Johnson, A. Kiilerich, D. Kubyshkina, S. Kunz, E. Palle, C.M. Persson, M. Paetzold, J. Prieto-Arranz, B. Sato, St.A. Shectman, J.K. Teske, I.B. Thompson, V. Van Eylen, G. Nowak, A. Vanderburg, J.N. Winn, R.A. Wittenmyer

Aims: Planets in the mass-range from 2 to 15 MEarth are very diverse. Some of them have very low, others very high densities.
Method: We determined the masses, radii and the densities for the two transiting planets orbiting K2-106, which have been previously found. The inner one is an ultra-short period planet with an orbital period of 0.57 days. The outer planet has orbital period of 13.3 days.
Results: The two planets have similar masses, though very different densities. For K2-106b we derive M_p=7.690.82 MEarth, Rp=1.520.16 REarth, and a high density of 12.0 -3.2+4.8 gcm-3. For K2-106c, we find 6.792.29 MEarth, R_p=2.590.27 REarth and a relatively low density of 2.4-1.1+1.6 gcm-3.
Conclusions: Since the systems contains two planets of almost the same mass, but different distances from the host star, it is an excellent laboratory to study atmospheric escape. Comparing the mass and radius of the inner planet with composition models implies that it has an iron core containing at least 50% of its mass. Such a high metal content is surprising, particularly given that the star has solar abundance. We discuss various formation scenarios for this unusual planet.

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Posts: 131433
K2-66b and K2-106b

Title: K2-66b and K2-106b: Two extremely hot sub-Neptune-size planets with high densities
Author: Evan Sinukoff, Andrew W. Howard, Erik A. Petigura, Benjamin J. Fulton, Ian J. M. Crossfield, Howard Isaacson, Erica Gonzales, Justin R. Crepp, John M. Brewer, Lea Hirsch, Lauren M. Weiss, David R. Ciardi, Joshua E. Schlieder, Bjoern Benneke, Jessie L. Christiansen, Courtney D. Dressing, Brad M. S. Hansen, Heather A. Knutson, Molly Kosiarek, John H. Livingston, Thomas P. Greene, Leslie A. Rogers, Sebastien Lepine

We report precise mass and density measurements of two extremely hot sub-Neptune-size planets from the K2 mission using radial velocities, K2 photometry, and adaptive optics imaging. K2-66 harbors a close-in sub-Neptune-sized (2.49^{+0.34}_{-0.24} earth radii) planet (K2-66b) with a mass of 21.3 3.6 earth masses. Because the star is evolving up the sub-giant branch, K2-66b receives a high level of irradiation, roughly twice the main sequence value. K2-66b may reside within the so-called "photoevaporation desert", a domain of planet size and incident flux that is almost completely devoid of planets. Its mass and radius imply that K2-66b has, at most, a meager envelope fraction (< 5%) and perhaps no envelope at all, making it one of the largest planets without a significant envelope. K2-106 hosts an ultra-short-period planet (P = 13.7 hrs) that is one of the hottest sub-Neptune-size planets discovered to date. Its radius (1.82^{+0.20}_{-0.14} earth radii) and mass (9.0 1.6 earth masses) are consistent with a rocky composition, as are all other small ultra-short-period planets with well-measured masses. K2-106 also hosts a larger, longer-period planet (Rp = 2.77^{+0.37}_{-0.23} earth radii, P = 13.3 days) with a mass less than 24.4 earth masses at 99.7% confidence. K2-66b and K2-106b probe planetary physics in extreme radiation environments. Their high densities reflect the challenge of retaining a substantial gas envelope in such extreme environments.

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