文章基本信息

标题：K2-146: Discovery of Planet c, Precise Masses from Transit Timing, and Observed Precession
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作者：Aaron Hamann ; Benjamin T. Montet ; Daniel C. Fabrycky 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2019
卷号：158
期号：3
页码：1-18
DOI：10.3847/1538-3881/ab32e3
语种：English
出版社：American Institute of Physics
摘要：K2-146 is a mid-M dwarf (M å = 0.331± 0.009M e ; R å = 0.330± 0.010R e ), observed in Campaigns 5, 16, and 18 of the K2 mission. In Campaign 5 data, a single planet was discovered with an orbital period of 2.6days and large transit timing variations due to an unknown perturber. Here, we analyze data from Campaigns 16 and 18, detecting the transits of a second planet, c, with an orbital period of 4.0days, librating in a 3:2 resonance with planet b. Large, anticorrelated timing variations of both planets exist due to their resonant perturbations. The planets have a mutual inclination of 2°.40±0°.25, which torqued planet c more closely into our line of sight. Planet c was grazing in Campaign 5 and thus missed in previous searches; it is fully transiting in Campaigns 16 and 18, and its transit depth is three times larger. We improve the stellar properties using data from Gaia DR2, and use dynamical fits to find that both planets are sub-Neptunes: their masses are 5.77±0.18 and 7.50±0.23M ⊕ , and their radii are 2.04±0.06 and 2.19±0.07 R ⊕ , respectively. These mass constraints set the precision record for small exoplanets (a few gas giants have comparable relative precision). These planets lie in the photoevaporation valley when viewed in Radius–Period space, but due to the low-luminosity M-dwarf host star, they lie among the atmosphere-bearing planets when viewed in Radius–Irradiation space. This, along with their densities being 60–80% that of Earth, suggests that they may both have retained a substantial gaseous envelope.
关键词：planets and satellites: detection;planets and satellites: dynamical evolution and stability;planets and satellites: individual (EPIC 211924657, K2-146)