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Gas compression and likely triggered star formation in the infrared bubble N107

Research in Astronomy and Astrophysics 2018年第10期18卷 49-64页

作者： Hao Li Jin-Zeng Li Jing-Hua Yuan Ya-Fang Huang Zhi-Yuan Ren National Astronomical Observatories Chinese Academy of Sciences School of Astronomy and Space Science University of Chinese Academy of Sciences

The expansion of HII regions can regulate the evolution of their natal clouds and the star for-mation therein. Infrared dust bubbles, which are frequently associated with HII regions, are ideal labora-tories to test whether impulse（s） driven by the expanding bubbles enhances or suppresses star-formation. In this work, we present a comprehensive study of a 20-pc scale infrared bubble N107 to reveal the com- pression of the neutral gas and associated star-forming activities. We obtain column density （NH2） and dust temperature （Tdust） maps via fitting modified blackbodies to multi-band far-infrared Herschel data. The shell structure can be recognized on the column density map. The molecular gas along the rim of N107 fragments into 94 dense clumps at an angular resolution of 18＂. Besides, based on the GLIMPSE point source catalog, we have identified 228 young stellar objects （YSOs） which are categorized into 55 Class I objects, 127 Class II objects and 46 transition disks （TDs）. The 94 clumps and 55 Class I type YSOs are mainly distributed along the shell, which may suggest triggered star formation exists in N107. In addition, analysis of NH2 probability density functions （PDFs） helps us reveal the condition of natal clouds. The two lognormal profiles of PDFs suggest that the surrounding molecular gas has been compressed due to expansion of the bubble. This compression may trigger the star formation process. Moreover, we find the shape of the PDFs changed after removing the background. Taken together, this big bubble seems to compress the surrounding gas and strongly regulate star formation therein.

关键词： ISM HII regions - ISM clouds - stars formation - ISM structure - methods observational

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New open cluster candidates discovered in the XSTPS-GAC survey

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Research in Astronomy and Astrophysics 2018年第3期18卷 77-90页

作者： Jin-Cheng Guo Hua-Wei Zhang Hui-Hua Zhang Xiao-Wei Liu Hai-Bo Yuan Yang Huang Song Wang Li Chen Hai-Bin Zhao Ji-Feng Liu Bing-Qiu Chen Mao-Sheng Xiang Zhi-Jia Tian Zhi-Ying Huo Chun Wang Department of Astronomy Peking University Kavli Institute for Astronomy and Astrophysics Peking University Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of Sciences South-Western Institute for Astronomy Research Yunnan University Department of Astronomy Beijing Normal University Shanghai Astronomical Observatory Chinese Academy of Sciences Purple Mountain Observatory Chinese Academy of Sciences

The Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center（XSTPS-GAC）is a photometric sky survey that covers nearly 6000 deg^2 towards the Galactic Anti-center（GAC） in the g,r,i bands. Half of its survey field is located on the Galactic Anti-center disk,which makes XSTPSGAC highly suitable to search for new open clusters in the GAC region. In this paper,we report new open cluster candidates discovered in this survey,as well as properties of these open cluster candidates,such as age,distance and reddening,derived by isochrone fitting in the color-magnitude diagram（CMD）.These open cluster candidates are stellar density peaks detected in the star density maps by applying the method from Koposov et al. Each candidate is inspected in terms of its true color image composed from three XSTPS-GAC band images. Then its CMD is checked,in order to identify whether the central region stars have a clear isochrone-like trend differing from background stars. The parameters derived from isochrone fitting for these candidates are mainly based on three band photometry of ***,when these new candidates are able to be seen clearly in 2 MASS data,their parameters are also derived based on the 2 MASS（J-H,J） CMD. There are a total of 320 known open clusters rediscovered and 24 new open cluster candidates discovered in this work. Furthermore,the parameters of these new candidates,as well as another 11 previously known open clusters,are properly determined for the first time.

关键词： open clusters and associations general - Galaxy structure - methods data analysis

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