The Chamaeleon I dark cloud (
, 
)
is one of the nearest active star
formation regions (
). Thanks to its proximity
and relatively high galactic latitude (
), this
cloud is well suited for investigating the composition, magnetic field
geometry and IR emission of a star forming cloud.
Observations of the Chamaeleon region were reviewed by
Schwartz (1991), who provides a particularly complete account of the
determination of the stellar content, extinction and distance toward
the complex. The Cha I cloud was initially discovered to harbour an
unusual number of H
emitting stars (Henize 1954), and recent
observations have determined that there are more than 100 association
members (Prusti et al. 1991; Gauvin & Strom 1992;
Hartigan 1993).
Additional Young Stellar Object (YSO) members of Chamaeleon have been
found from both X-ray emission from pointed ROSAT observations
(Feigelson et al. 1993; Zinnecker et al. 1996) and deep IRAS
(Assendorp
et al. 1990) and 
m observations of selected fields (Jones et al.
1985; Prusti et al. 1994). The consensus is that there are between 70
and 300 YSOs in Chamaeleon, in a cloud which is approximately 4
degrees across and has a mass of 700 to 1030 solar masses. Toriseva
& Mattila (1985) have estimated the dust to gas ratio in the cloud
to be about 0.02 by mass. We should note that the inferred star
formation efficiency of the Chamaeleon cloud is between 10% and 30%
which is remarkably high.
While the stellar content of the Chamaeleon region is fairly well
known, much uncertainty exists regarding the large scale structure of
the ISM in the region. Early studies of extinction and distance to the
cloud (Grasdalen et al. 1975; Thé et al. 1986) provided very different
estimates of 
, and distance 
pc). More recently, photometric observations (Franco
1991) suggest that the Chamaeleon region is contained in a sheet like
cloud at 140 pc, which extends over several degrees on the sky into
the constellation Musca. The maximum extinction in the Cha I cloud is
thought to be in the range 
, and the reddening
of field stars from Vrba and Rydgren (1984) behind the cloud ranges
from 
, which completely samples the
expected extinction in the Cha I cloud.
In this work we concentrate on the interstellar medium around the Chamaeleon I association, by combining new optical polarimetry and optical spectroscopy of atomic and molecular absorption features with IR data.
Recent work on the polarimetry of the Chamaeleon region has also been published (Whittet et al. 1994; McGregor et al. 1994) as has a comparison between IR and UV emission and extinction (Boulanger et al. 1994). Our work seeks to provide a unified approach in which the different observations provide a complementary picture about the interrelations between dust and gas in the Chamaeleon cloud.
Where possible we will analyze the connections between the observed
optical polarization, IR emission and optical absorption lines for the
stars in the Chamaeleon region. Photometry suggests a very low foreground
reddening (
is reported by Whittet et al. 1987,
and an even smaller value of 
is found by Franco 1991),
which insures that optical absorption lines and the polarization
of background stars of moderate distances are due to the Cha I dark
cloud, and are not significantly affected by foreground absorption.
Table 1: Stellar parameters
