EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars
EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars
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围绕活跃恒星运行的太阳系外巨行星上的 EUV 驱动的电离层和电子传输
DOI：
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
R. Yelle
中科院分区：
文献类型：
--
作者：
J. Chadney;M. Galand;T. Koskinen;S. Miller;J. Sanz;Y. Unruh;R. Yelle
太阳系外巨行星（EGP）上层大气的组成和结构受到其宿主恒星从软X射线到极紫外线的高能光谱的影响。这种发射取决于星星的活动水平，而这主要取决于它的年龄。我们专注于EGPs轨道K-和M-矮星的不同年龄。这些恒星的XUV光谱是使用日冕模型构建的。这些光谱用于驱动热层模型和电离层模型，提供中性和离子种类的密度。电离包括通过光电离和电子碰撞过程。我们发现，EGP电离层在所有的轨道距离考虑和周围的所有恒星选择的长寿命H$^+$离子占主导地位。此外，在H$_2$基本上不离解的上层大气中，行星的电离层底部有一层H$_3^+$是主要离子。对于快速旋转的行星，短寿命的H$_3^+$的密度经历显著的日变化，最大值由恒星X射线通量驱动。相比之下，寿命较长的H$^+$的密度显示出非常小的昼夜变化，其大小由恒星EUV通量的水平驱动。在高大气层的EGP中，H$_2$在强恒星光照下离解，H$_3^+$峰被推到同层顶以下的高度，在那里，该离子可能通过与重物质的反应而被破坏。与不包括电子碰撞电离的模型相比，包含二次电离过程在低于主EUV电离峰的高度处产生显著增强的离子和电子密度。我们估计了H$3 ^+$的红外辐射，虽然在H/H$2 $/He大气中，这些辐射在靠近更活跃恒星的行星上更大，但它们仍然显得太低，无法用现有的天文台检测到。
The composition and structure of the upper atmospheres of Extrasolar Giant Planets (EGPs) are affected by the high-energy spectrum of their host stars from soft X-rays to EUV. This emission depends on the activity level of the star, which is primarily determined by its age. We focus upon EGPs orbiting K- and M-dwarf stars of different ages. XUV spectra for these stars are constructed using a coronal model. These spectra are used to drive both a thermospheric model and an ionospheric model, providing densities of neutral and ion species. Ionisation is included through photo-ionisation and electron-impact processes. We find that EGP ionospheres at all orbital distances considered and around all stars selected are dominated by the long-lived H$^+$ ion. In addition, planets with upper atmospheres where H$_2$ is not substantially dissociated have a layer in which H$_3^+$ is the major ion at the base of the ionosphere. For fast-rotating planets, densities of short-lived H$_3^+$ undergo significant diurnal variations, with the maximum value being driven by the stellar X-ray flux. In contrast, densities of longer-lived H$^+$ show very little day/night variability and the magnitude is driven by the level of stellar EUV flux. The H$_3^+$ peak in EGPs with upper atmospheres where H$_2$ is dissociated under strong stellar illumination is pushed to altitudes below the homopause, where this ion is likely to be destroyed through reactions with heavy species. The inclusion of secondary ionisation processes produces significantly enhanced ion and electron densities at altitudes below the main EUV ionisation peak, as compared to models that do not include electron-impact ionisation. We estimate infrared emissions from H$_3^+$, and while, in an H/H$_2$/He atmosphere, these are larger from planets orbiting close to more active stars, they still appear too low to be detected with current observatories.
影响因子：
64.8
作者：
G. Hallinan;S. P. Littlefair;G. Cotter;S. Bourke;L. K. Harding;J. Pineda;R. P. Butler;A. Golden;G. Basri;J. Doyle;M. Kao;S. Berdyugina;A. Kuznetsov;M. Rupen;A. Antonova
通讯作者：
G. Hallinan;S. P. Littlefair;G. Cotter;S. Bourke;L. K. Harding;J. Pineda;R. P. Butler;A. Golden;G. Basri;J. Doyle;M. Kao;S. Berdyugina;A. Kuznetsov;M. Rupen;A. Antonova
太阳系外巨行星大气的电离
DOI：
10.1088/0004-637x/722/1/178
发表时间：
2010
期刊：
The Astrophysical Journal
影响因子：
--
作者：
Koskinen T
通讯作者：
Koskinen T