标题： BOSS超冷矮星I：M型和L型矮星的颜色与磁场活动 显示英文标题

标题： BOSS Ultracool Dwarfs I: Colors and Magnetic Activity of M and L dwarfs

摘要： 我们展示了斯隆数字巡天（SDSS）第十次数据发布（DR10）中的超冷矮星（M7-L8）的颜色和活动性。我们将以前的SDSS M型和L型矮星样本与通过重子振荡光谱巡天（BOSS）获得的新数据相结合，生成了包含11820个M7-L8矮星的BOSS超冷矮星（BUD）样本。通过结合SDSS数据与两微米全天巡天（2MASS）和广域红外巡天探测器（WISE）任务的测光数据，我们根据光谱类型给出了从$i-z$到$W2-W3$的超冷矮星颜色，并扩展了SDSS-2MASS-WISE颜色区域以包括超冷矮星。$i-z$、$i-J$和$z-J$颜色为M7-L3矮星提供了光谱类型的最佳指示。我们还通过H$\alpha$发射的存在及其强度来研究超冷矮星的色球活动性。活跃矮星的比例在整个M型光谱序列中上升，直到L0时达到90%的$\sim$。 活跃矮星的比例随后在L5光谱型时下降到50%；在BUD样本中的晚L型矮星没有观测到H$\alpha$发射。 活跃的L0-L5矮星比例比之前观测到的要高得多。 活动强度从M7到L3随着光谱型的变化而减弱，之后数据没有显示出明确的趋势。 利用一维色球模型，我们探讨了与M0-L7矮星的H$\alpha$观测结果一致的填充因子和色球温度结构范围。 M型矮星的色球具有相似且平滑变化的温度和表面覆盖范围，而L型矮星的色球较冷且填充因子较小。 显示英文摘要

摘要： We present the colors and activity of ultracool (M7-L8) dwarfs from the Tenth Data Release of the Sloan Digital Sky Survey (SDSS). We combine previous samples of SDSS M and L dwarfs with new data obtained from the Baryon Oscillation Sky Survey (BOSS) to produce the BOSS Ultracool Dwarf (BUD) sample of 11820 M7-L8 dwarfs. By combining SDSS data with photometry from the Two Micron All Sky Survey and the Wide-Field Infrared Sky Explorer mission, we present ultracool dwarf colors from $i-z$ to $W2-W3$ as a function of spectral type, and extend the SDSS-2MASS-WISE color locus to include ultracool dwarfs. The $i-z$, $i-J$, and $z-J$ colors provide the best indication of spectral type for M7-L3 dwarfs. We also examine ultracool dwarf chromospheric activity through the presence and strength of H$\alpha$ emission. The fraction of active dwarfs rises through the M spectral sequence until it reaches $\sim$90% at spectral type L0. The fraction of active dwarfs then declines to 50% at spectral type L5; no H$\alpha$ emission is observed in the late-L dwarfs in the BUD sample. The fraction of active L0-L5 dwarfs is much higher than previously observed. The strength of activity declines with spectral type from M7 through L3, after which the data do not show a clear trend. Using one-dimensional chromosphere models, we explore the range of filling factors and chromospheric temperature structures that are consistent with H$\alpha$ observations of M0-L7 dwarfs. M dwarf chromospheres have a similar, smoothly varying range of temperature and surface coverage while L dwarf chromospheres are cooler and have smaller filling factors.