太阳活动随时间的演变及其对行星大气的影响。II。鲸鱼座kappa^1，当地球上出现生命时，它是太阳的类似物
Evolution of the solar activity over time and effects on planetary atmospheres. II. kappa^1 Ceti, an analog of the Sun when life arose on Earth
摘要：
地球大气层的早期演化和生命的起源发生在地球的物理条件与现在的状态完全不同的时候。太阳辐射输入在高能光谱域中大大增强，为了详细模拟早期行星大气，需要了解太阳辐射输入。我们对邻近恒星kap^1 Cet的大气参数、演化状态和高能通量进行了研究，之前认为该恒星具有类似于早期太阳的性质。大气参数来自Fe I和Fe II的激发/电离平衡，轮廓拟合的H α和光谱能量分布。紫外辐照度来自FUSE和HST数据，绝对色球通量来自Halalpha线芯。通过仔细的光谱分析和对不同方法的比较，我们提出了kap^1 Cet的以下大气参数：Teff = 5665+/-30 K（H α剖面和能量分布），log g = 4.49+/-0.05 dex（演化和光谱）和[Fe/H] = +0.10+/-0.05 dex（Fe II谱线）。kap^1 Cet的紫外辐射特性表明，在210 ~ 300 nm之间，它的辐射通量比现在的太阳低35%左右，在170 nm处与太阳相当，在110 ~ 140 nm之间，它的辐射通量至少比太阳高2-7倍。使用几种指标可以确定kap^1 Cet的年龄在~0.4-0.8 Gyr之间，对理论HR图的分析表明质量约为1.04 Msun。因此，这颗恒星与地球上生命出现时的太阳非常相似，火星被认为已经失去了液态水的表面。光化学模型表明，增强的紫外线辐射导致的光解速率显着增加，与那些通常假设的早期地球。我们的研究结果表明，早期行星大气的化学成分的可靠计算需要考虑到更强的太阳光离解紫外线照射。
英文摘要：
The early evolution of Earth's atmosphere and the origin of life took place at a time when physical conditions at the Earth where radically different from its present state. The radiative input from the Sun was much enhanced in the high-energy spectral domain, and in order to model early planetary atmospheres in detail, a knowledge of the solar radiative input is needed. We present an investigation of the atmospheric parameters, state of evolution and high-energy fluxes of the nearby star kap^1 Cet, previously thought to have properties resembling those of the early Sun. Atmospheric parameters were derived from the excitation/ionization equilibrium of Fe I and Fe II, profile fitting of Halpha and the spectral energy distribution. The UV irradiance was derived from FUSE and HST data, and the absolute chromospheric flux from the Halpha line core. From careful spectral analysis and the comparison of different methods we propose for kap^1 Cet the following atmospheric parameters: Teff = 5665+/-30 K (Halpha profile and energy distribution), log g = 4.49+/-0.05 dex (evolutionary and spectroscopic) and [Fe/H] = +0.10+/-0.05 dex (Fe II lines). The UV radiative properties of kap^1 Cet indicate that its flux is some 35% lower than the current Sun's between 210 and 300 nm, it matches the Sun's at 170 nm and increases to at least 2-7 times higher than the Sun's between 110 and 140 nm. The use of several indicators ascribes an age to kap^1 Cet in the interval ~0.4-0.8 Gyr and the analysis of the theoretical HR diagram suggests a mass ~1.04 Msun. This star is thus a very close analog of the Sun when life arose on Earth and Mars is thought to have lost its surface bodies of liquid water. Photochemical models indicate that the enhanced UV emission leads to a significant increase in photodissociation rates compared with those commonly assumed of the early Earth. Our results show that reliable calculations of the chemical composition of early planetary atmospheres need to account for the stronger solar photodissociating UV irradiation.
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