The ultraviolet (UV) spectral energy distributions (SEDs) of low-mass (K- and M-type) stars play a critical role in the heating and chemistry of exoplanet atmospheres, but are not observationally well-constrained. Direct observations of the intrinsic flux of the Lyα line (the dominant source of UV photons from low-mass stars) are challenging, as interstellar H i absorbs the entire line core for even the closest stars. To address the existing gap in empirical constraints on the UV flux of K and M dwarfs, the MUSCLES Hubble Space Telescope Treasury Survey has obtained UV observations of 11 nearby M and K dwarfs hosting exoplanets. This paper presents the Lyα and extreme-UV spectral reconstructions for the MUSCLES targets. Most targets are optically inactive, but all exhibit significant UV activity. We use a Markov Chain Monte Carlo technique to correct the observed Lyα profiles for interstellar absorption, and we employ empirical relations to compute the extreme-UV SED from the intrinsic Lyα flux in ~100 ? bins from 100–1170 ?. The reconstructed Lyα profiles have 300 km s?1 broad cores, while 1% of the total intrinsic Lyα flux is measured in extended wings between 300 and 1200 km s?1. The Lyα surface flux positively correlates with the Mg ii surface flux and negatively correlates with the stellar rotation period. Stars with larger Lyα surface flux also tend to have larger surface flux in ions formed at higher temperatures, but these correlations remain statistically insignificant in our sample of 11 stars. We also present H i column density measurements for 10 new sightlines through the local interstellar medium.
展开▼
机译：低质量（K型和M型）恒星的紫外线（UV）光谱能量分布（SED）在系外行星大气的加热和化学过程中起着至关重要的作用，但在观测上并没有受到很好的约束。直接观测Lyα线（来自低质量恒星的紫外线光子的主要来源）的固有通量具有挑战性，因为星际H i甚至吸收最靠近恒星的整个线核。为了解决对K和M矮星的紫外线通量的经验约束方面存在的空白，MUSBLES哈勃太空望远镜财政部调查获得了11个附近系着系外行星的M和K矮星的紫外线观测。本文介绍了肌肉目标的Lyα和极端UV光谱重建。大多数靶标是无光学活性的，但都具有明显的紫外线活性。我们使用马尔可夫链蒙特卡罗技术校正星际吸收所观测到的Lyα谱，并利用经验关系从〜100？L的固有Lyα通量计算极端UV SED。 100-1170的垃圾桶。重建的Lyα剖面具有300 km s？1的宽核，而在300至1200 km s？1之间的延伸翼中测得的总固有Lya通量的> 1％。 Lyα表面通量与Mg ii表面通量正相关，而与恒星旋转周期负相关。具有较高Lyα表面通量的恒星在较高温度下形成的离子中也往往具有较大的表面通量，但在我们的11个恒星样本中，这些相关性在统计上仍然微不足道。我们还介绍了通过当地星际介质对10条新视线进行的H i列密度测量。
展开▼
