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

¹ Osservatorio Astronomico di Capodimonte, Via Moiariello, 16, I–80131 Napoli, Italy
² ITESRE/C.N.R. Bologna, Italy
³ Pomona College, Department of Physics and Astronomy, Claremont, CA, U.S.A.
⁴ Nordic Optical Telescope, Apartado 474, E-38700 Sta. Cruz de La Palma, Canarias, Spain

Send offprint request to: E. Covino

Received: 21 March 1996
Accepted: 2 July 1996

Abstract

We present optical polarimetry and high resolution 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 fits to the normalized wavelength dependence of interstellar polarization, we derive estimates of ranging from 4500 Å to 6700 Å, and P_Max ranging from 3 to 8%. The values of were found to be well correlated with the IRAS 100 μm intensity, while P_Max was found to increase with E_B-V.
High resolution spectra of the Ca II, CH, and CH⁺ lines were obtained for 10 stars, which show two components of Ca II in absorption at 3.0 < 5 km , and v_LSR= -3.0 km and a single strong molecular CH absorption component at 3.0 < v_LSR < 5.0 km .
From our data we found, by interpretation of the various 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, responsible of the starlight polarization, exist in the center of the cloud, surrounded by envelopes of warmer molecular and atomic material.