He I λ10830 Absorption in Metal-Poor Red Giants: Probing Fast Chromospheric Outflows

Details He I λ10830 Absorption in Metal-Poor Red Giants: Probing Fast Chromospheric Outflows He I λ10830 Absorption in Metal-Poor Red Giants: Probing Fast Chromospheric Outflows

Sep 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004pasp..116..819s&link_type=abstract

The Publications of the Astronomical Society of the Pacific, Volume 116, Issue 823, pp. 819-825.

Astronomy and Astrophysics

Astronomy

14

Stars: Chromospheres, Stars: Population Ii, Stars: Winds, Outflows

Scientific paper

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-1. If identified with a wind, the velocity found in the M13 red giant IV-15 (30 km s-1) 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 Teff>~4600 K and MV fainter than -1.5. Since previous studies have found Hα and Ca II K2 emission 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.
Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

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