2004PASP..116..819S

We present the results of a search for near-IR chromospheric He I absorption in 10 metal-poor red giants using high-resolution spectra obtained with NIRSPEC on Keck II. Four of these red giants are in the field, and six are in the globular cluster M13. Two of the field stars and one of the cluster stars show evidence for He I absorption that is consistent with chromospheric outflow velocities ranging from 30 to 140 km/s. If identified with a wind, the velocity found in the M13 red giant IV-15 (30 km/s) is comparable to the escape velocity of the cluster core, suggesting that such winds may be effective in clearing out the interstellar medium of globular clusters. Absorption is confined to stars with T_eff≳4600 K and M_Vfainter than -1.5. Since previous studies have found Hα and Ca II K₂emission line profiles indicative of winds in metal-poor giants brighter than this limit, the mechanism responsible for He I absorption in metal-poor red giants apparently operates less effectively in the cooler and brighter stars. On the other hand, the He I line extends the detection of mass outflows further down the giant branch of metal-poor stars than the Hα observations.