标题： Y型矮星：发现太阳邻域中最冷的亚恒星天体的挑战 显示英文标题

标题： Y Dwarfs: The Challenge of Discovering the Coldest Substellar Population in the Solar Neighborhood

摘要： 恒星在银河系中以广泛的质量形成。 如果质量低于太阳的7%，那么该物体不会热到足以进行稳定的氢燃烧。 这些亚恒星天体被称为褐矮星。 在红外波长的天空图中已经发现了大量褐矮星。 然而，截至2017年4月，只发现了24个足够冷的天体被归类为“Y型褐矮星”：这些天体的大气温度低于500 K（或200°C，400°F），且质量仅为木星的5至20倍。 目前已知最冷的Y型褐矮星是在2014年发现的，其温度接近冰点，质量约为5个木星质量，并且距离太阳只有2秒差距。 这些小而寒冷的天体非常暗淡，难以发现。 本章描述了Y型褐矮星的发现和特征。 要找到更多这种极冷的类行星褐矮星，将需要一项尚未计划的太空任务，在约5微米波长下绘制大面积天空的地图。 显示英文摘要

摘要： Stars form in the Galaxy with a wide range in mass. If the mass is below 7% of the Sun's, then the object does not become hot enough for stable hydrogen burning. These substellar objects are called brown dwarfs. Maps of the sky at infrared wavelengths have found large numbers of brown dwarfs. However only 24 objects have been found (as of April 2017) that are cold enough to be classified as "Y dwarfs": these have atmospheres that are cooler than 500 K (or 200 C, 400 F) and have masses only 5 - 20 times that of Jupiter. The coolest Y dwarf currently known, discovered in 2014, has a temperature around freezing, has a mass of about 5 Jupiter masses, and is only 2 pc away from the Sun. These small and cold objects are faint and difficult to find. This chapter describes the discovery and characterization of the Y dwarfs. Finding more of these very cold planet-like brown dwarfs will require an as-yet unplanned space mission mapping large areas of sky at wavelengths around 5 microns.