CEMP星HE 1005-1439中子俘获元素天体物理来源的研究

HE1005-1439是一颗金属丰度极低(Fe/H]～-3.0)的碳增丰贫金属星(Carbon Enhanced Metal-Poor,CEMP),该星的s-过程元素显著超丰(Ba/Fe]=1.16±0.31,Pb/Fe]=1.98±0.19),而r-过程元素温和超丰(Eu/Fe]=0.46±0.22),使用单一的s-过程模型和i-过程模型均不能拟合该星中子俘获丰度分布.采用丰度分解的方法探究该星化学元素的天体物理来源可有助于理解CEMP星的形成和化学演化.利用s-过程和r-过程的混合模型对其中子俘获元素的丰度分布进行拟合,发现该星的中子俘获元素主要来源于低质量低金属丰度AGB伴星的s-过程核合成,而r-过程核合成也有贡献.

Analysis and Design of Starlink-like Satellite Constellation

Satellite constellations are widely used for communication, navigation and Earth observation purposes. They provide good ground coverages and serve better for these needs. Of all the configurations, the Walker constellation is extensively applied in many navigation satellite systems and some low Earth orbit communication constellations, since it can be easily designed and has good coverage. Despite of these advantages, the satellites in Walker constellation generally have different ground tracks. When multiple Walker constellations are to be coordinated, in terms that the orbital planes precess synchronously with the same satellite mean motion $\Omega_1$, the semi-major axes of these Walker constellations would be significantly different even when the orbital inclinations differ by a small amount. The Space Exploration Corp (SpaceX) claimed a new constellation design in a patent for their multi-shell Starlink satellite constellation. Constellation shells with different inclinations have small altitude differences, which facilitates regulatory approval and deployment. Satellites in the same shell can also be easily designed to share the same ground track. Although they claimed these features in the patent, SpaceX shared little technical details regarding how to design these constellations. Here in this paper, we analyze the features of the Starlink constellation and try to find a practical approach to design a Starlink-like constellation, as well as how to determine the rules for inter-satellite links within the constellation.