GETTING THE RED OUT: A STELLAR APPROACH TO DETERMINING SPATIAL VARIATIONS OF INTERSTELLAR DUST

By employing two dieren t spectroscopic techniques we have mapped out the variable ISM dust extinction endemic to globular cluster M4. We derive an average E(B V ) reddening of 0.33 0.01 and R = 3:4 0:4, both in good agreement with previous studies of M4. For individual stars in the most heavily reddened regions of M4, we nd E(B V ) values signican tly higher than those inferred by studies of interstellar gas | for heavily reddened regions, the gas measured in column density measurements may not completely trace the dust.