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The Far Ultraviolet M-dwarf Evolution Survey. I. The Rotational Evolution of High-energy EmissionsThis research is based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 526555.
The Astrophysical Journal ( IF 4.9 ) Pub Date : 2021-04-23 , DOI: 10.3847/1538-4357/abe8d7
J. Sebastian Pineda 1 , Allison Youngblood 1, 2 , Kevin France 1
Affiliation  

M-dwarf stars are prime targets for exoplanet searches because of their close proximity and favorable properties for both planet detection and characterization. However, the potential habitability and atmospheric characterization of these exoplanetary systems depends critically on the history of high-energy stellar radiation from X-rays to NUV, which drive atmospheric mass loss and photochemistry in the planetary atmospheres. With the Far Ultraviolet M-dwarf Evolution Survey, we have assessed the evolution of the FUV radiation, specifically eight prominent emission lines, including Lyα, of M-dwarf stars with stellar rotation period and age. We demonstrate tight power-law correlations between the spectroscopic FUV features, and measure the intrinsic scatter of the quiescent FUV emissions. The luminosity evolution with rotation of these spectroscopic features is well-described by a broken power law, saturated for fast rotators, and decays with increasing Rossby number, with a typical power-law slope of −2, although likely shallower for Lyα. Our regression fits enable FUV emission-line luminosity estimates relative to bolometric from known rotation periods to within ∼0.3 dex, across eight distinct UV emission lines, with possible trends in the fit parameters as a function of source layer in the stellar atmosphere. Our detailed analysis of the UV luminosity evolution with age further shows that habitable-zone planets orbiting lower-mass stars experience much greater high-energy radiative exposure relative the same planets orbiting more massive hosts. Around early- to mid-M dwarfs, these exoplanets, at field ages, accumulate up to 10–20 more EUV energy, relative to modern Earth. Moreover, the bulk of this UV exposure likely takes place within the first Gyr of the stellar lifetime.



中文翻译:

远紫外线 M 矮星进化调查。I. 高能辐射的旋转演化本研究基于 NASA/ESA 哈勃太空望远镜的观测结果,该望远镜来自太空望远镜科学研究所,该研究所由天文学研究大学协会运营,根据NASA 合同 NAS 526555。

M 矮星是系外行星搜索的主要目标,因为它们距离很近,并且具有有利于行星探测和表征的特性。然而,这些系外行星系统的潜在宜居性和大气特征在很大程度上取决于从 X 射线到 NUV 的高能恒星辐射的历史,这些辐射驱动了行星大气中的大气质量损失和光化学。通过远紫外 M 矮星演化调查,我们评估了 FUV 辐射的演化,特别是 8 条突出的发射线,包括 Ly α,具有恒星自转周期和年龄的 M 矮星。我们证明了光谱 FUV 特征之间的紧密幂律相关性,并测量了静态 FUV 发射的内在散射。随着这些光谱特征旋转的光度演化可以用不规则的幂律很好地描述,对于快速旋转器来说是饱和的,并且随着罗斯比数的增加而衰减,具有典型的幂律斜率 -2,尽管对于 Ly α可能更浅. 我们的回归拟合使得 FUV 发射线光度估计值相对于从已知旋转周期到约 0.3 dex 内的热辐射,跨越 8 条不同的 UV 发射线,拟合参数的可能趋势作为恒星大气中源层的函数。我们对紫外线光度随年龄演变的详细分析进一步表明,相对于围绕更大质量宿主运行的相同行星,围绕质量较低恒星运行的宜居带行星经历了更大的高能辐射暴露。相对于现代地球,在早期到中期 M 矮星附近,这些系外行星在野外年龄积累了多达 10-20 倍的 EUV 能量。此外,大部分紫外线照射可能发生在恒星生命周期的第一个 Gyr 内。

更新日期:2021-04-23
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