标题： rho Ophiuchi星云核中埋藏年轻恒星对象的中红外成像巡天 显示英文标题

标题： A Mid-Infrared Imaging Survey of Embedded Young Stellar Objects in the Rho Ophiuchi Cloud Core

摘要： 呈现了对蛇夫座ρ云年轻恒星群体的全面、全新、基于地面的中红外成像巡天的结果。数据分别使用Palomar 5米望远镜和Keck 10米望远镜上的MIRLIN和LWS仪器，在0.25角秒和0.25角秒的分辨率下获取。在172个巡天目标中，85个被检测到。在观测的22个多重系统中，15个被解析，并确定了其个体分量的流量。检测到的对象与SED光谱斜率的频率分布图表明，YSOs在平坦光谱阶段大约花费40万年时间清除其剩余的坍缩包层。在被调查的物体中有很大一部分发现了中红外变化，并且发现所有具有厚盘的SED类都发生这种变化。在所有具有厚盘的SED类中也发现了大幅度的近红外变化，似乎在较早的演化阶段发生的频率更高。尽管在通过SED类时存在一般的中红外过量和近红外覆盖趋势，但I类对象通常表现出K覆盖值>1，平坦光谱对象的K覆盖值>0.58，III类对象的K覆盖值=0，而II类对象表现出K波段覆盖值范围最宽（0-4.5）。然而，单个源在任何可以进行活跃盘吸积的SED类中所表现出的高度可变的覆盖值是显著的，并且是盘中高度时间变化的吸积活动的直接观测证据。最后，通过对具有明确有效温度和消光值的子样本中红外与近红外过量进行比较，探讨了盘清除机制。结果与从内部向外清除盘的过程一致。 显示英文摘要

摘要： Results of a comprehensive, new, ground-based mid-infrared imaging survey of the young stellar population of the Rho Ophiuchi cloud are presented. Data were acquired at the Palomar 5-m and at the Keck 10-m telescopes with the MIRLIN and LWS instruments, at 0.25 arcsec and 0.25 arcsec resolutions, respectively. Of 172 survey objects, 85 were detected. Among the 22 multiple systems observed, 15 were resolved and their individual component fluxes determined. A plot of the frequency distribution of the detected objects with SED spectral slope shows that YSOs spend ~400,000 yr in the Flat Spectrum phase, clearing out their remnant infall envelopes. Mid-infrared variability is found among a significant fraction of the surveyed objects, and is found to occur for all SED classes with optically thick disks. Large-amplitude near-infrared variability, also found for all SED classes with optically thick disks, seems to occur with somewhat higher frequency at the earlier evolutionary stages. Although a general trend of mid-infrared excess and NIR veiling exists proceeding through SED classes, with Class I objects generally exhibiting K-veilings > 1, Flat Spectrum objects with K-veilings > 0.58, and Class III objects with K-veilings =0, Class II objects exhibit the widest range of K-band veiling values, 0-4.5. However, the highly variable value of veiling that a single source can exhibit in any of the SED classes in which active disk accretion can take place is striking, and is direct observational evidence for highly time-variable accretion activity in disks. Finally, by comparing mid-infrared vs. near-infrared excesses in a subsample with well-determined effective temperatures and extinction values, disk clearing mechanisms are explored. The results are consistent with disk clearing proceeding from the inside-out.