邻近年轻星团中的亚恒星天体（SONYC）：NGC1333中初始质量函数的底部
Substellar Objects in Nearby Young Clusters (SONYC): The bottom of the Initial Mass Function in NGC1333
摘要：
SONYC -邻近年轻星团中的亚恒星物体-是一个调查方案，目的是调查邻近恒星形成区域中质量低至木星几倍的亚恒星物体的频率和性质。在这里，我们提出的第一个结果，从SONYC的观测NGC 1333，一个约100万年前的星团在英仙座恒星形成复合体。我们在斯巴鲁望远镜上使用Suprime-Cam和MOIRCS仪器在四个波段（i '，z'，J，K）进行了极深的光学和近红外成像。测量范围为0.25平方度，在i波段达到24.7等的完整性极限，在J波段达到20.8等的完整性极限。我们选择了196个候选者，其颜色与年轻，质量很低的物体的颜色一样。用MOIRCS对53个天体进行了跟踪观测。我们确认了NGC 1333中的19个可能的褐矮星，其中7个以前已知。对于其中的11个，我们确认存在磁盘的基础上斯皮策/IRAC光度。棕矮星样本的有效温度范围为2500 K至3000 K，换算成质量约为0.015至0.1 Ms。为了比较，我们的测量的完整性极限转换为0.004Ms的质量极限为Av<~ 5 mag或0.008Ms的Av<~ 10 mag。与其他恒星形成区相比，NGC 1333的棕矮星相对于低质量恒星的数量要多出2-5倍。另一方面，NGC 1333缺乏行星质量的天体：根据SOrionis，ONC和Cha I的调查，NGC 1333中的行星质量天体的预期数量是8-10，但我们没有发现。我们的调查似乎已经探测到这个特殊星团中恒星形成的最小质量极限，大约在0.012-0.02Ms。如果得到证实，我们的研究结果指出，褐矮星的数量和IMF的最小质量存在显着的区域/环境差异。（节略）
英文摘要：
SONYC -- Substellar Objects in Nearby Young Clusters -- is a survey program to investigate the frequency and properties of substellar objects with masses down to a few times that of Jupiter in nearby star-forming regions. Here we present the first results from SONYC observations of NGC1333, a ~1Myr old cluster in the Perseus star-forming complex. We have carried out extremely deep optical and near-infrared imaging in four bands (i', z', J, K) using Suprime-Cam and MOIRCS instruments at the Subaru telescope. The survey covers 0.25sqdeg and reaches completeness limits of 24.7mag in the i'-band and 20.8mag in the J-band. We select 196 candidates with colors as expected for young, very low-mass objects. Follow-up multi-object spectroscopy with MOIRCS is presented for 53 objects. We confirm 19 objects as likely brown dwarfs in NGC1333, seven of them previously known. For 11 of them, we confirm the presence of disks based on Spitzer/IRAC photometry. The effective temperatures for the brown dwarf sample range from 2500K to 3000K, which translates to masses of ~0.015 to 0.1Ms. For comparison, the completeness limit of our survey translates to mass limits of 0.004Ms for Av<~5mag or 0.008Ms for Av<~ 10mag. Compared with other star-forming regions, NGC1333 shows an overabundance of brown dwarfs relative to low-mass stars, by a factor of 2-5. On the other hand, NGC1333 has a deficit of planetary-mass objects: Based on the surveys in SOrionis, the ONC and Cha I, the expected number of planetary-mass objects in NGC1333 is 8-10, but we find none. It is plausible that our survey has detected the minimum mass limit for star formation in this particular cluster, at around 0.012-0.02Ms. If confirmed, our findings point to significant regional/environmental differences in the number of brown dwarfs and the minimum mass of the IMF. (abridged)
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