Infrared spectroscopy of dust in the Taurus dark clouds: ice and silicates

Abstract

Low-resolution spectra of the 3 micron water-ice features of 22 stars and the 10 micron silicate dust features of 16 stars are presented for stars in the direction of the extensive dark cloud complex in Taurus, including both dust-embedded objects and background field stars seen through the cloud. A very close linear correlation is found between the peak optical depth in the 3 micron feature and visual extinction, A(v), for field stars. The detection of ice in all cases where A(v) exceeds a threshold value of 3.3 + or - 0.1 mag serves as a basis for models of volatile mantle growth on grains in the dark cloud environment. The silicate feature is poorly correlated with A(v), and its relative weakness per unit A(v) in the spectra of field stars with strong ice bands may reflect the dilution of silicates as a fraction of total grain mass as mantles accrete in the dark cloud.