EDP Sciences
Free access
Volume 401, Number 1, April I 2003
Page(s) 185 - 192
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021914

A&A 401, 185-192 (2003)
DOI: 10.1051/0004-6361:20021914

Near-infrared imaging of the star forming region S87

Yuxi Chen1, Xing-Wu Zheng1, Yongqiang Yao2, Ji Yang2 and Shuji Sato3

1  Department of Astronomy, Nanjing University, Nanjing 210093, PR China
2  Purple Mountain Observatory, Chinese Academy of Science, 2 Beijing Xi Lu, Nanjing 210008, PR China
3  Department of Astrophysics, School of Science, Nagoya University, Chikusa-ku, Nagoya 464-01, Japan

(Received 26 November 2001 / Accepted 26 August 2002 )

Near-infrared images of the star forming region S87 in the $JHK^\prime$ broad-band filters and H 2 v=1-0 S $\left(
1\right) $ narrow-band filter are presented. In the eastern part of the region, the S87E nebula shows a quite complex structure. In the optically thin southern part of the nebula, there is an elongated cavity in the direction aligned with the blue-shifted molecular outflow. A subcluster of twelve young near-infrared sources has been detected in the optically thick northern part of the nebula, where a cone-shaped opaque patch is seen. In the $90\arcsec\times 90\arcsec$ region around S87E, we detected 111 sources with $m_{K^\prime}>15.2~$mag. From analysis of the $JHK^\prime$ colors of the stars inside S87E, we find that after adjusting for background contamination, more than 40% of all the sources associated with the cluster display infrared excesses. This high fraction of infrared excess sources, along with the evidence of molecular outflow activity near the cluster, suggests that the S87E cluster is very young(~ $3{-}4 \times 10^6$ yr). We construct the differential $K^\prime$ luminosity function for S87E and find the overall shape and structure are somewhat different to that of other young clusters. Besides a common turnover at 14 mag, there is a prominent peak and still more cluster members with luminosities fainter than 14th magnitude at  $K^\prime$ band. Five H 2 regions were also discovered and three of them are associated with the S87E nebula. nfrared: stars - ISM: individual: S87 - ISM: reflection nebulae - stars: formation

Offprint request: Xing-Wu Zheng, xwzheng@nju.edu.cn

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