High‐Resolution Near‐Infrared Observations of the Circumstellar Disk System in the Bok Globule CB 26

Abstract

We report on results of near-infrared and optical observations ofthe millimeter disk embedded in the Bok globule CB 26. The near-infraredimages show a bipolar reflection nebula with a central extinctionlane that coincides with the millimeter disk. Imaging polarimetryof this object yielded a polarization pattern that is typical ofa young stellar object (YSO) surrounded by a large circumstellardisk and an envelope, seen almost edge-on. The strong linear polarizationin the bipolar lobes is caused by single scattering at dust grainsand reveals the location of the illuminating source that coincideswith the center of the millimeter disk. The spectral energy distributionof the YSO embedded in CB 26 resembles that of a Class I source witha luminosity of 0.5 L-.. Using the pre-main-sequence evolutionarytracks and the stellar mass inferred from the rotation curve of thedisk, we derive an age of the system of less than or equal to 10(6)yr. Halpha and {[}S II] narrowband imaging as well as optical spectroscopyrevealed a Herbig-Haro object 6.'15 northwest of CB 26 YSO 1, perfectlyaligned with the symmetry axis of the bipolar nebula. This Herbig-Haroobject (HH 494) indicates ongoing accretion and outflow activityin CB 26 YSO 1. Its excitation characteristics show that the Herbig-Haroflow is propagating into a low-density environment. We suggest thatCB 26 YSO 1 represents the transition stage between embedded protostellaraccretion disks and more evolved protoplanetary disks around T Tauristars in an undisturbed environment.