The Giant Star Ca II Ionization Problem: Mass Loss Revisited

Abstract

Pioneering studies of winds from non-coronal evolved late- type stars were plagued by uncertainties in the Ca ionization balance which severely limited the accuracy of derived mass-loss rates. Here we re-examine the Ca II ionization balance in these stellar winds using FUSE spectra which reveal, for the rst time, the ux from the photoionizing radiation eld shortward of 1045A. We present a FUSE 912-1185A spec- troscopic survey of evolved late-K and M stars; including the M giants Cet (M1.5 III), Cru (M3.5 III), Gru (M4.5 III), and RDor (M8e III). Using FUSE spectra of Tau (K5 III), supplemented with partial redistribution calculations of H Ly- and Ly- , together with UV and radio data, we present a study of Tau's wind ionization balance and derive new constraints which place the mass-loss rate signi cantly below that suggested by the Reimers formula.