The Giant Star Ca II Ionization Problem: Mass Loss Revisited

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 first time, the flux from the photoionizing radiation field shortward of 1045Â. We present a FUSE 912-1185Â spectroscopic survey of evolved late-K and M stars; including the M giants α Cet (M1.5 III), γ Cru (M3.5 III), β Gru (M4.5 III), and R Dor (M8e III). Using FUSE spectra of α Tau (K5 III), supplemented with partial redistribution calculations of H Ly-α and Ly-β, together with UV and radio data, we present a study of α Tau's wind ionization balance and derive new constraints which place the mass-loss rate significantly below that suggested by the Reimers formula.