MUSCLES与Mega-MUSCLES HST Treasury巡天项目观测到的邻近低质量系外行星宿主星的冕X射线辐射
Coronal X-Ray Emission from Nearby, Low-Mass, Exoplanet Host Stars Observed by the MUSCLES and Mega-MUSCLES HST Treasury Survey Projects
AI总结：
本文利用钱德拉、XMM-牛顿和斯威夫特天文台观测MUSCLES与Mega-MUSCLES巡天样本中低质量系外行星宿主星的冕X射线辐射，测量其光度和耀发变率，为恒星EUV光谱建模提供关键约束。
摘要：
系外行星宿主星的高能X射线和紫外（UV）辐射场在控制系外行星的大气条件和潜在宜居性方面起着至关重要的作用。MUSCLES和Mega-MUSCLES哈勃空间望远镜（HST）Treasury项目已对晚型（K和M光谱型）系外行星宿主星的X射线/紫外辐射开展了大规模巡天。这些样本主要由相对年老、“不活跃”的低质量恒星组成。本文介绍了利用钱德拉X射线天文台、XMM-牛顿天文台和尼尔·格雷尔斯·斯威夫特天文台对这些恒星的冕发射进行X射线观测所得的结果。这些恒星有效地采样了低质量恒星在广泛质量和年龄范围内的冕活动。绝大多数恒星（23颗中的21颗）被探测到，并测量了它们的X射线光度。在这些观测期间，大多数完全对流（M ≤ 0.35 M⊙）恒星探测到短时耀发变率，但质量较大的M矮星未探测到。尽管存在这一差异，这两组M矮星的平均X射线光度相似，质量较大的（0.35 M⊙ ≤ M ≤ 0.6 M⊙）M矮星约为5 × 10^26 erg s^-1，而年龄大于1 Gyr的完全对流恒星约为2 × 10^26 erg s^-1。较年轻的完全对流M矮星的X射线光度在3至6 × 10^27 erg s^-1之间。冕X射线光谱已得到表征，并提供了对恒星EUV光谱建模至关重要的信息。
英文摘要：
The high energy X-ray and ultraviolet (UV) radiation fields of exoplanet host stars play a crucial role in controlling the atmospheric conditions and the potential habitability of exoplanets. Major surveys of the X-ray/UV emissions from late-type (K and M spectral type) exoplanet hosts have been conducted by the MUSCLES and Mega-MUSCLES Hubble Space Telescope (HST) Treasury programs. These samples primarily consist of relatively old, ``inactive'', low mass stars. In this paper we present results from X-ray observations of the coronal emission from these stars obtained using the Chandra X-ray Observatory, the XMM-Newton Observatory, and the Neil Gehrels Swift Observatory. The stars effectively sample the coronal activity of low-mass stars at a wide range of masses and ages. The vast majority (21 of 23) of the stars are detected and their X-ray luminosities measured. Short-term flaring variability is detected for most of the fully-convective (M $\leq$ 0.35 M$_{\odot}$) stars but not for the more massive M dwarfs during these observations. Despite this difference, the mean X-ray luminosities for these two sets of M dwarfs are similar with more massive (0.35 M$_{\odot}$ $\leq$ M $\leq$ 0.6 M$_{\odot}$) M dwarfs at $\sim$5 $\times$ 10$^{26}$ erg s$^{-1}$ compared to $\sim$2 $\times$ 10$^{26}$ erg s$^{-1}$ for fully-convective stars older than 1 Gyr. Younger, fully-convective M dwarfs have X-ray luminosities between 3 and 6 $\times$ 10$^{27}$ erg s$^{-1}$.The coronal X-ray spectra have been characterized and provide important information that is vital for the modeling of the stellar EUV spectra.
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