Dust production is explored around 14 metal-poor ( [ Fe/H ] = –1.91 to –0.98 ) giant stars in the Galactic globular cluster \omega Centauri using new Spitzer IRS spectra .
This sample includes the cluster ’ s post-AGB and carbon stars and is thus the first representative spectral study of dust production in a metal-poor ( [ Fe/H ] < -1 ) population .
Only the more metal rich stars V6 and V17 ( [ Fe/H ] = –1.08 , –1.06 ) exhibit silicate emission , while the five other stars with mid-infrared excess show only a featureless continuum which we argue is caused by metallic iron dust grains .
We examine the metallicity of V42 , and find it is likely part of the metal-rich population ( [ Fe/H ] \sim –0.8 ) .
Aside from the post-AGB star V1 , we find no star from the cluster ’ s bulk , metal-poor ( [ Fe/H ] < -1.5 ) population — including the carbon stars — to be producing detectable amounts of dust .
We compare the dust production to the stars ’ H \alpha line profiles obtained at the Magellan/Clay telescope at Las Campanas Observatory , finding pulsation shocking in the strongest pulsators ( V6 , V17 and V42 ) , but evidence of outflow in all other stars .
We conclude that the onset of dust production does not signify a fundamental change in the material leaving the star .
Our data add to a growing body of evidence that metallic iron dominates dust production in metal-poor , oxygen-rich stars , but that dust is probably not the primary accelerant of winds in this mass-metallicity regime .