INFRARED POLARIMETRY OF STAR-FORMING REGIONS - THE SERPENS CLOUD CORE

We present the results of near infrared (JHK) direct and polarimetric imaging of the Serpens cloud core. We detected approximately 200 stars with completeness limits of J=15.5 mag, H=14.75 mag, and K=14.0 mag i n a 92.4 arcmin(2) region. Although the sources with near-infrared exc ess distinguished from JHK colors are distributed over the entire regi on surveyed, there is a concentration toward the SE core. The lower li mit of the visual extinction toward the cloud core is estimated to be 24 mag from the absence of the field stars. The polarization of 12 com pact sources was measured; 10 sources are young stellar objects, one i s a background star candidate, and the other is unidentified. The pola rization of the young stellar object (YSO) is most likely due to scatt ering in the associated nebulae; their position angles are therefore p erpendicular to the extension of the nebula associated with each YSO. In contrast, the polarization of the background star candidate CK2 is about 40 degrees. Our results do not support the previously suggested model that the magnetic field runs in a NW-SE direction. The color and polarization patterns suggest that the bright near-infrared reflectio n nebula in the core is mainly composed of two parts, one illuminated by SVS 2 (the Serpens Reflection Nebula, SRN), and the other by the in frared bright star SVS 20. The appearance of SRN changed between 1991 and 1992. Both surface brightness and polarization patterns in SRN are interpreted as results of the interaction between the outflow and the circumstellar material around SVS 2, showing the inhomogeneity of the surrounding cloud density. (C) 1997 American Astronomical Society.