Astron. Astrophys. 324, L5-L8 (1997)

1. Introduction

The Chamaeleon I cloud is the most obscured region of the Chamaeleon dust-molecular complex. An extinction map of this cloud has been drawn out by Gregorio Hetem et al. (1988) using star counts on ESO(B) plates. It shows a maximum of , and the extinction profile across the cloud centre shows an abrupt growth between 2 and 6 , followed by a plateau at the peak of extinction which looks like a saturation. As stars become too scarce, optical counts can no longer be used to derive the extinction accurately. Near infrared (1-2 ) star counts are more appropriate to probe regions where since an extinction of 10 visual magnitudes drops to only 3 magnitudes in the J band at 1.25 . Massive star counts in the near infrared are made possible for the first time thanks to the large scale near infrared survey, DENIS, currently in progress (Epchtein, 1997). The aim of this paper is to investigate in detail the extinction toward the Cham I cloud using this new wealth of data.

The Cham I dark cloud is located at and its current distance estimate is 140 pc (Whittet et al, 1987). Its high galactic latitude implies a small number density of background stars which limits the spatial resolution of the extinction estimation, but, on the other hand, the probability of crossing several clouds on the line of sight is low.

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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