Optical polarimetry, high–resolution spectroscopy and IR analysis of the Chamaeleon I dark cloud

Abstract

We present optical polarimetry and high res- olution spectroscopy of a sample of stars toward the Chamaeleon I dark cloud. We use our polarimetry which includes 33 stars to study the wavelength dependence of the degree and position angle of polarization. From ts to the normalized wavelength dependence of interstellar polarization, we derive estimates of Max ranging from 4500 A to 6700 A, and PMax ranging from 3 to 8%. The values ofMax were found to be well correlated with the IRAS 100 m intensity, whilePMax was found to increase with EB V. High resolution spectra of the Ca II, CH, and CH + lines were obtained for 10 stars, which show two compo- nents of Ca II in absorption at 3.0 <v LSR < 5k m s 1 , andvLSR= 3.0 km s 1 and a single strong molecular CH absorption component at 3.0 <v LSR < 5.0 km s 1 . From our data we found, by interpretation of the vari- ous correlations between the polarimetry, photometry and IRAS fluxes, the following: the probable presence of shocked molecular gas; a warm molecular CH component; small dust grains at the edges of the cloud, and larger grains in the central parts, which are causing the polarization. Our results provide a consistent picture of the gas and dust content in the Cha I region, where larger grains, re- sponsible of the starlight polarization, exist in the center of the cloud, surrounded by envelopes of warmer molecular and atomic material.