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A&A Supplement series, Vol. 122, April I 1997, 95-109

Received March 21; accepted July 2, 1996

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

E. Covinotex2html_wrap1873 - E. Palazzitex2html_wrap1875 - B.E. Penprasetex2html_wrap1877 - H.E. Schwarztex2html_wrap1879 - L. Terranegratex2html_wrap1881

Send offprint request: E. Covino

tex2html_wrap1883  Osservatorio Astronomico di Capodimonte, Via Moiariello, 16, I-80131 Napoli, Italy
tex2html_wrap1885  ITESRE/C.N.R. Bologna, Italy
tex2html_wrap1887  Pomona College, Department of Physics and Astronomy, Claremont, CA, U.S.A.
tex2html_wrap1889  Nordic Optical Telescope, Apartado 474, E-38700 Sta. Cruz de La Palma, Canarias, Spain


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 tex2html_wrap_inline1829 ranging from 4500 Å to 6700 Å, and tex2html_wrap_inline1831 ranging from 3 to 8%. The values of tex2html_wrap_inline1833 were found to be well correlated with the IRAS 100 tex2html_wrap_inline1835m intensity, while tex2html_wrap_inline1837 was found to increase with tex2html_wrap_inline1839.

High resolution spectra of the Ca II, CH, and CHtex2html_wrap_inline1841 lines were obtained for 10 stars, which show two components of Ca II in absorption at 3.0 tex2html_wrap_inline1843 < 5 km tex2html_wrap_inline1847, and tex2html_wrap_inline1849= -3.0 km tex2html_wrap_inline1853 and a single strong molecular CH absorption component at 3.0 < tex2html_wrap_inline1857 < 5.0 km tex2html_wrap_inline1861.

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.

keywords: ISM: chamacleon clouds; dust, extinction; atoms; molecules -- polarization -- infrared: ISM: continuum

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