A Near-Infrared Study of the NGC 7538 Star-forming Region
A Near-Infrared Study of the NGC 7538 Star-forming Region
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DOI：
10.1086/425068
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发表时间：
2004-08
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通讯作者：
D. Ojha;M. Tamura;Y. Nakajima;M. Fukagawa;K. Sugitani;C. Nagashima;T. Nagayama;T. Nagata;S. Sato;S. Vig;S. Ghosh;A. Pickles;M. Momose;K. Ogura
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作者：
D. Ojha;M. Tamura;Y. Nakajima;M. Fukagawa;K. Sugitani;C. Nagashima;T. Nagayama;T. Nagata;S. Sato;S. Vig;S. Ghosh;A. Pickles;M. Momose;K. Ogura
我们使用夏威夷大学88英寸(2.2米)望远镜和巨型米波射电望远镜(GMRT)上的天狼星，给出了亚弧秒(FWHM~0.“7)、近红外(NIR)JHKs波段图像和1280 MHz高灵敏度射电连续谱图像。近红外测量覆盖了约24角2的区域，J、H和Ks波段的10σ极限星等分别为19.5、18.4和17.3。我们的近红外图像比JHK迄今对NGC 7538恒星形成区更大区域的任何调查都要深。我们构建了JHK色图和J-H/J和H-K/K色等图来识别年轻恒星对象(YSO)并估计其质量。基于这些颜色-颜色和颜色-星等图，我们确定了与NGC 7538区域相关的丰富的YSO种群(I类和II类)。在NGC 7538附近也探测到了大量的红源(H-K和GT；2)。我们认为，这些红星很可能是主序前恒星，具有固有的颜色过剩。NGC7538中的大多数YSO是从西北向东南方向排列的，形成了一个年龄顺序：扩散的H II区(西北和最古老的H II区，大部分II类和I类源都在这里被探测到)，致密的IR核心(中心)，以及广泛的IR反射星云和红色年轻星团(东南和南部)。我们发现NGC7538的Ks波段光度函数的斜率比报道的年轻嵌入星团的典型值要小，尽管在W3主要恒星形成区也有同样低的值。根据Ks波段光度函数的斜率和Megeath及同事的分析，我们推断嵌入的恒星群是由~1Myr年龄的YSO组成的。根据前主序星模型与观测色星等图的比较，我们发现NGC7538的恒星群主要由与W3主星形成区观测到的类似的低质量前主序星组成。来自1280 MHz GMRT观测的射电连续谱图像显示，由于H II区与相邻分子云之间的相互作用，呈现出一种弧形结构。通过比较射电连续谱、分子线和近红外图像，清楚地描绘了HⅡ区和分子云之间界面的电离前沿。
We present subarcsecond (FWHM ~ 0.″7), near-infrared (NIR) JHKs-band images and a high-sensitivity radio continuum image at 1280 MHz, using SIRIUS on the University of Hawaii 88 inch (2.2 m) telescope and the Giant Metrewave Radio Telescope (GMRT). The NIR survey covers an area of ~24 arcmin2 with 10 σ limiting magnitudes of ~19.5, 18.4, and 17.3 in the J, H, and Ks bands, respectively. Our NIR images are deeper than any JHK surveys to date for the larger area of the NGC 7538 star-forming region. We construct JHK color-color and J - H/J and H - K/K color-magnitude diagrams to identify young stellar objects (YSOs) and to estimate their masses. Based on these color-color and color-magnitude diagrams, we identified a rich population of YSOs (Class I and Class II) associated with the NGC 7538 region. A large number of red sources (H - K > 2) have also been detected around NGC 7538. We argue that these red stars are most probably pre-main-sequence stars with intrinsic color excesses. Most of the YSOs in NGC 7538 are arranged from the northwest toward the southeast regions, forming a sequence in age: a diffuse H II region (northwest and oldest, where most of the Class II and Class I sources are detected), a compact IR core (center), and regions with an extensive IR reflection nebula and a cluster of red young stars (southeast and south). We find that the slope of the Ks-band luminosity function of NGC 7538 is lower than the typical values reported for young embedded clusters, although equally low values have also been reported in the W3 Main star-forming region. From the slope of the Ks-band luminosity function and the analysis by Megeath and coworkers, we infer that the embedded stellar population is composed of YSOs with an age of ~1 Myr. Based on the comparison of models of pre-main-sequence stars with the observed color-magnitude diagram, we find that the stellar population in NGC 7538 is primarily composed of low-mass pre-main-sequence stars similar to those observed in the W3 Main star-forming region. The radio continuum image from the GMRT observations at 1280 MHz shows an arc-shaped structure due to the interaction between the H II region and the adjacent molecular cloud. The ionization front at the interface between the H II region and the molecular cloud is clearly delineated by comparing the radio continuum, molecular line, and NIR images.