论文标题
重新审视的K2-3系统：测试光蒸发和核心驱动的质量损失，三个小行星横跨半径谷
The K2-3 system revisited: testing photoevaporation and core-powered mass loss with three small planets spanning the radius valley
论文作者
论文摘要
旋转的多行星系统对小星球形成和进化的理论提供了宝贵的测试。 K2-3是一个早期的M矮人，在0.07-0.20 au的距离处托有三个小型系外行星（1.5-2.0地球半径）。我们使用HST/COS和XMM-Newton测量K2-3的高能谱，并使用以经验驱动的Ly-Alpha和极端紫外线的估计值。我们使用exofastv2共同拟合径向速度，传输和SED数据。这将K2-3行星半径限制为4％的不确定性，而K2-3b和C的质量分别将其质量限制在13％和30％上。在RV测量中未检测到K2-3D。 K2-3b和C与岩石岩心一致，这些岩石岩心被太阳组成信封（质量分数为0.36％和0.07％），H2O信封（55％和16％）或两者的混合物。但是，基于K2-3的高能量输出和估计的年龄，K2-3B和C不太可能保留太阳能组成氛围。我们将行星参数和高能恒星光谱传递给大气模型。将高能光谱上下拨动10倍拨打10倍，导致痕量分子丰度的显着变化，但在传输光谱方面可检测到的水平并不能产生显着变化。尽管K2-3行星跨越了小行星半径谷，但观察到的系统体系结构不能通过光蒸发或核心驱动的质量损失轻松解释。相反，我们提出的是1）K2-3行星全都富含挥发性，K2-3D的密度低于典型的超级地点，/或2）K2-3行星体系结构是由更多随机过程（例如行星形成，行星迁移和影响侵蚀）产生的。
Multi-planet systems orbiting M dwarfs provide valuable tests of theories of small planet formation and evolution. K2-3 is an early M dwarf hosting three small exoplanets (1.5-2.0 Earth radii) at distances of 0.07-0.20 AU. We measure the high-energy spectrum of K2-3 with HST/COS and XMM-Newton, and use empirically-driven estimates of Ly-alpha and extreme ultraviolet flux. We use EXOFASTv2 to jointly fit radial velocity, transit, and SED data. This constrains the K2-3 planet radii to 4% uncertainty and the masses of K2-3b and c to 13% and 30%, respectively; K2-3d is not detected in RV measurements. K2-3b and c are consistent with rocky cores surrounded by solar composition envelopes (mass fractions of 0.36% and 0.07%), H2O envelopes (55% and 16%), or a mixture of both. However, based on the high-energy output and estimated age of K2-3, it is unlikely that K2-3b and c retain solar composition atmospheres. We pass the planet parameters and high-energy stellar spectrum to atmospheric models. Dialing the high-energy spectrum up and down by a factor of 10 produces significant changes in trace molecule abundances, but not at a level detectable with transmission spectroscopy. Though the K2-3 planets span the small planet radius valley, the observed system architecture cannot be readily explained by photoevaporation or core-powered mass loss. We instead propose 1) the K2-3 planets are all volatile-rich, with K2-3d having a lower density than typical of super-Earths, and/or 2) the K2-3 planet architecture results from more stochastic processes such as planet formation, planet migration, and impact erosion.
