Near-infrared polarimetric and spectrometric study of the massive star-forming region S87

¹ Purple Mountain Observatory, Chinese Academy of Sciences, 2 Beijing Westroad, Nanjing 210008, PR China e-mail: xpchen@pmo.ac.cn
² National Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, PR China e-mail: yqyao@bao.ac.cn; [jiyang;zbjiang]@pmo.ac.cn
³ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka 181, Japan e-mail: ishii@optik.mtk.nao.ac.jp

Received: 10 May 2004
Accepted: 30 July 2004

Abstract

We present JHK' imaging polarimetry for the massive star-forming region S87, and K-band spectrometry from 2.0 to 2.35 μm for several infrared sources in the region. The polarimetric patterns of S87E reveal a deeply embedded source (DES-S87) associated with reflection nebulosities. Exciting OH maser and 1.3 mm dust continuum emission, the DES-S87 is suggested to be the youngest star in S87 and the driving source of bipolar CO outflow in the region. A blue cavity is discovered in the [ J-K'] color image, to the southwest of DES. Radial dependence of polarization degrees in the cavity could be fitted to the slab model of outflows at an inclination of ~60° out of the plane of the sky (Minchin et al. [CITE]b). The nebular complex of S87E can be divided into three area. The North nebula, exhibiting a bipolar structure, may represent a bipolar outflow in the northwest-southeast direction. The southwest nebula traces the blueshifted CO outflow and corresponds to the cavity structure discovered in the [ J-K'] color image. The nebular structure of S87E suggests a quadrupolar outflow driven by DES-S87. A well-defined centrosymmetric pattern is found in the nebula of S87W with high degrees of polarization, which indicates single scattering off small dust grains in the reflection nebula. The polarimetric vectors around NIRS A show a polarization disk feature oriented in the southeast-northwest direction. Strong Brγ emission and H₂ emissions are found in the K-band spectra, indicating the presences of strong stellar wind, envelope/disk, shocked gas, and high-density PDRs in the circumstellar environment of S87E and S87W. According to the K-band spectrum, the mass of DES-S87E is estimated to be 20 .