标题： 近发现观测星际彗星3I/ATLAS与美国国家红外望远镜设施 显示英文标题

标题： Near-Discovery Observations of Interstellar Comet 3I/ATLAS with the NASA Infrared Telescope Facility

摘要： 星际天体是围绕其他恒星形成但尚未聚集成为系外行星就被弹出的彗星和小行星。 因此，它们提供了一个罕见的机会，可以将太阳系行星的构建块与其他恒星系统的进行比较。 第三个星际天体，3I/ATLAS，是这个群体中最新、最亮、可能最大且最快的成员。 我们报告了在2025年7月3日和4日用美国宇航局红外望远镜设施对3I/ATLAS进行的观测，就在其发现后的几天内。 在r'-波段成像中使用'Opihi，我们没有看到明显的光变曲线变化，并得出g'-i'颜色为1.06±0.11，这与D.Z. Seligman等人（2025）和C. Opitom（2025）最近的研究在光谱斜率上是一致的。 我们用SpeX获得了3I/ATLAS的第一个近红外（NIR）反射光谱。 可见光颜色和NIR光谱显示线性、红色的可见光斜率，在0.7到1.1$\mu{m}$之间斜率稍低，而在更长波长处则为中性或略微蓝色的斜率。 建模3I反射率的挑战可能表明，这颗彗星具有复杂的颗粒尺寸分布、与太阳系彗星不同的颗粒组成，或者两者皆有。 与2I/Borisov一样，3I/ATLAS的晕中没有明显的水冰迹象。 更接近近日点的观测将有助于阐明3I是否比预期含有较少的水，或者星际天体可能以不同于太阳系彗星的方式保留和释放它们的冰。 显示英文摘要

摘要： Interstellar Objects are comets and asteroids that formed around other stars but were ejected before they could accrete into exoplanets. They therefore represent a rare opportunity to compare the building blocks of planets in the Solar System to those in other stellar systems. The third Interstellar Object, 3I/ATLAS, is the newest, brightest, potentially largest, and fastest member of this population. We report observations of 3I/ATLAS taken on 2025 July 3 and 4 with the NASA Infrared Telescope Facility just days after its discovery. In r'-band imaging with 'Opihi, we see no obvious lightcurve variability and derive a g'-i' color of 1.06+/-0.11 which is consistent in spectral slope to recent work by D.Z. Seligman et al. (2025) and C. Opitom (2025). We obtained the first near-infrared (NIR) reflectance spectrum of 3I/ATLAS with SpeX. The visible color and NIR spectrum show a linear, red visible slope, a somewhat less red slope between 0.7 and 1.1 $\mu{m}$, and a neutral or slightly blue slope at longer wavelengths. Challenges in modeling the reflectivity of 3I may indicate that this comet has a complex grain size distribution, grain compositions unlike Solar system comets, or both. Like 2I/Borisov, there are no obvious signatures of water ice in the coma of 3I/ATLAS. Observations closer to perihelion will help elucidate whether 3I has less water than anticipated or whether the Interstellar Objects might retain and release their ices somewhat differently than Solar System comets do.