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Chromospheres of metal-deficient field giantsObservations of the 2800-A Mg II line have been obtained with IUE for a sample of 10 metal-deficient field giant stars to search for chromospheric emission and signatures of mass loss, as well as to establish the level of chromospheric radiative energy losses from these stars. Mg II emission is probably present in all stars. High-resolution spectra of three of the brightest giants show asymmetric Mg II profiles which indicate a differentially expanding atmosphere, signaling the presence of outward mass motions. Surprisingly, the stellar surface fluxes in the Mg II lines are commensurate with the values found for disk giant stars (population I) of similar color. In spite of substantially depleted Mg abundances in the target stars (by factors of 10-100 relative to the solar abundance), the radiative losses implied by the Mg II fluxes, and possibly the chromospheric heating mechanism, appear to be reasonably independent of metallicity and age.
Document ID
19900044378
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Dupree, A. K.
(Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Hartmann, L.
(Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Smith, Graeme H.
(Mount Stromlo and Siding Spring Observatories Canberra, Australia)
Date Acquired
August 14, 2013
Publication Date
April 20, 1990
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 353
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
90A31433
Funding Number(s)
CONTRACT_GRANT: NAG5-87
Distribution Limits
Public
Copyright
Other

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