Near-infrared imaging of the star forming region S87

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

Corresponding author: Xing-Wu Zheng, xwzheng@nju.edu.cn

Received: 26 November 2001
Accepted: 26 August 2002

Abstract

Near-infrared images of the star forming region S87 in the broad-band filters and H₂ 1–0 S 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 region around S87E, we detected 111 sources with mag. From analysis of the 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(~ yr). We construct the differential 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  band. Five H₂ regions were also discovered and three of them are associated with the S87E nebula. nfrared: stars – ISM: individual: S87 – ISM: reflection nebulae – stars: formation