HAZMAT. VII. The Evolution of Ultraviolet Emission with Age and Rotation for Early M Dwarf Stars
R. O. Parke Loyd, Evgenya L. Shkolnik, Adam C. Schneider, Tyler Richey-Yowell, James A. G. Jackman, Sarah Peacock, Travis S. Barman, Isabella Pagano, Victoria S. Meadows
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accepted to The Astronomical Journal, 25 pages, 9 figures | v2 accidental trackchanges toggled off | v3 typo fixes, more precise language on activity decline
The ultraviolet (UV) emission from the most numerous stars in the universe, M dwarfs, impacts the formation, chemistry, atmospheric stability, and surface habitability of their planets. We have analyzed the spectral evolution of UV emission from M0-M2.5 (0.3-0.6 Msun) stars as a function of age, rotation, and Rossby number, using Hubble Space Telescope observations of Tucana Horologium (40 Myr), Hyades (650 Myr), and field (2-9 Gyr) objects. The quiescent surface flux of their C II, C III, C IV, He II, N V, Si III, and Si IV emission lines, formed in the stellar transition region, remains elevated at a constant level for 240 $\pm$ 30 Myr before declining by 2.1 orders of magnitude to an age of 10 Gyr. Mg II and far-UV pseudocontinuum emission, formed in the stellar chromosphere, exhibit more gradual evolution with age, declining by 1.3 and 1.7 orders of magnitude, respectively. The youngest stars exhibit a scatter of 0.1 dex in far-UV line and pseudocontinuum flux attributable only to rotational modulation, long-term activity cycles, or an unknown source of variability. Saturation-decay fits to these data can predict an M0-M2.5 star's quiescent emission in UV lines and the far-UV pseudocontinuum with an accuracy of roughly 0.2-0.3 dex, the most accurate means presently available. Predictions of UV emission will be useful for studying exoplanetary atmospheric evolution, the destruction and abiotic production of biologically relevant molecules, and interpreting infrared and optical planetary spectra measured with observatories like the James Webb Space Telescope.
HAZMAT. VIII. A Spectroscopic Analysis of the Ultraviolet Evolution of K Stars: Additional Evidence for K Dwarf Rotational Stalling in the First Gigayear
发现和描述宜居带行星的努力主要集中在类太阳恒星和M矮星上。然而，K星在这两种选择之间提供了一个相对未被探索的有吸引力的折衷方案。了解这些恒星周围的紫外线（UV）环境对于我们了解它们的行星至关重要，因为UV可以极大地改变行星大气层的光化学。在这里，我们提出了近紫外和远紫外\textit{Hubble Space Telescope}的宇宙起源光谱仪观测39 K恒星在三个不同的年龄：40百万年，650百万年，和$\approx$ 5 Gyr。我们发现，K星（0.6 - 0.8 M $_{\odot}$）的紫外线通量保持不变超过650百万年前下降了一个数量级的字段年龄。这与早期M星（0.3 - 0.6 M $_{\odot}$）不同，后者在几百万年后就开始衰退。然而，K星的自转-紫外线活动关系与早期M星几乎相同。这些结果可能是最近报道的K矮星的自旋下降失速效应的结果，其中K星的自旋下降在其旋转周期达到$\approx$ 10 d时停止超过Gyr，而不是G星经历的连续自旋下降。这些结果意味着围绕K型矮星运行的系外行星可能会经历比想象中更强的紫外线环境，削弱了K型恒星作为潜在的“超级宜居”行星宿主的可能性。
An Analysis of the Shapes of Interstellar Extinction Curves. VII. Milky Way Spectrophotometric Optical-through-Ultraviolet Extinction and Its R-Dependence
Post-common envelope binaries from SDSS - VII: A catalogue of white dwarf-main sequence binaries
我们提出了一个目录的1602白矮星主序星（WDMS）的光谱斯隆数字巡天数据发布6（SDSS DR 6）。其中，我们确定440作为新的WDMS二进制文件。我们从拟合所有127万个DR 6光谱的模板中选择WDMS二进制候选者，使用$χ^{2}$和信噪比中的组合约束。此外，我们使用星系演化探测器（GALEX）和UKIRT红外巡天（UKIDSS）的大小搜索的对象，其中两个组件之一占主导地位的SDSS光谱。我们使用分解/拟合技术来测量有效温度，表面重力，质量和距离的白矮星，以及光谱类型和距离的同伴在我们的目录。从这些恒星参数的分布和密度图，然后被用来研究的一般性质和选择效应的WDMS双星SDSS。我们还利用SDSS-GALEX-UKIDSS星等研究了WDMS双星在紫外到红外色空间的分布，以及它们的白矮星有效温度和伴星光谱类型。我们表明，WDMS双星可以非常有效地从单一的主序星和白矮星分离时，使用组合的紫外，光学和红外颜色选择。最后，我们还提供了径向速度为1068系统测量的\Lines{Na}{I}{8183.27,8194.81}吸收双峰和/或H $α$发射线。在具有多个SDSS光谱的系统中，我们发现了五个新的系统表现出显着的径向速度变化，将其确定为后共同包络二进制候选人。
Stellar laboratories. IX. New Se V, Sr IV - VII, Te VI, and I VI oscillator strengths and the Se, Sr, Te, and I abundances in the hot white dwarfs G191-B2B and RE 0503-289
Stellar laboratories. VII. New Kr IV - VII oscillator strengths and an improved spectral analysis of the hot, hydrogen-deficient DO-type white dwarf RE0503-289
Stellar laboratories. VIII. New Zr IV - VII, Xe IV - V, and Xe VII oscillator strengths and the Al, Zr, and Xe abundances in the hot white dwarfs G191-B2B and RE0503-289
