The Wavelength of Maximum Polarization in the Chamaeleon Dark Cloud

Abstract

Observational evidence for grain growth in dark clouds is provided by variations in the interstellar extinction and polarization laws, and by infrared spectroscopy (e.g. Whittet and Blades 1980). Although anomalous extinction laws indicative of biasing of the grain size distribution towards larger sizes are now well-established for regions such as Orion, Rho Oph and R CrA, the extinction law in Chamaeleon is controversial. In a recent review, Hyland et al (1982) noted that estimates of the distance to the embedded T-association vary from 110 to 215 pc dependent on the value of R = A(V)/E(B-V), the ratio of total to selective extinction. R values based on infrared photometry are often unreliable due to excess emission from circumstellar shells. This paper reports an attempt to resolve the problem by means of polarimetry, which provides an independent method of estimating R which is not hampered by such effects.