论文标题
恒星风对近距离巨人大气的影响：逃生可能减少而不是侵蚀增加
Stellar wind effects on the atmospheres of close-in giants: a possible reduction in escape instead of increased erosion
论文作者
论文摘要
观察到高度辐照的系外行星的大气会经历流体动力学逃生。但是，由于压力很大，恒星的风可以限制行星气氛，从而减少它们的逃生。在这里，我们调查在哪些条件下，近距离巨人的大气逃逸可能会受到宿主恒星风的巨大压力。为此，我们模拟了在一系列轨道距离（[0.04，0.14] au），行星重力（[36％，87％]木星重力）和年龄（[1，6.9] gyr）处的行星中的逃生。对于这些模拟中的每一个，我们计算这些逃脱的大气的RAM压力，并将它们与预期的恒星风外部压力进行比较，以确定是否限制了给定的气氛。我们表明，尽管年轻的近距离巨人应该经历更高水平的大气逃生，但由于较高的恒星照射，恒星风在年轻人时代也更强，可能会降低年轻系外行星的逃脱。无论年龄如何，我们还发现参数空间中总是有一个区域，其中大气逃逸被限制在较高的行星重力和轨道距离处。我们研究了一些已知的系外行星的限制，发现其中几个（包括Pi Men C）的气氛应受宿主恒星的风限制，从而有可能阻止高度辐照的行星逃脱。因此，最近报道的PI MEN C缺乏氢逃生可能是由恒星风引起的。
The atmospheres of highly irradiated exoplanets are observed to undergo hydrodynamic escape. However, due to strong pressures, stellar winds can confine planetary atmospheres, reducing their escape. Here, we investigate under which conditions atmospheric escape of close-in giants could be confined by the large pressure of their host star's winds. For that, we simulate escape in planets at a range of orbital distances ([0.04, 0.14] au), planetary gravities ([36%, 87%] of Jupiter's gravity), and ages ([1, 6.9] Gyr). For each of these simulations, we calculate the ram pressure of these escaping atmospheres and compare them to the expected stellar wind external pressure to determine whether a given atmosphere is confined or not. We show that, although younger close-in giants should experience higher levels of atmospheric escape, due to higher stellar irradiation, stellar winds are also stronger at young ages, potentially reducing escape of young exoplanets. Regardless of the age, we also find that there is always a region in our parameter space where atmospheric escape is confined, preferably occurring at higher planetary gravities and orbital distances. We investigate confinement of some known exoplanets and find that the atmosphere of several of them, including pi Men c, should be confined by the winds of their host stars, thus potentially preventing escape in highly irradiated planets. Thus, the lack of hydrogen escape recently reported for pi Men c could be caused by the stellar wind.
