Chromospheres of two red giants in NGC 6752
1990; IOP Publishing; Volume: 361; Linguagem: Inglês
10.1086/185815
ISSN1538-4357
AutoresA. K. Dupree, G. M. Harper, Lee Hartmann, Carole Jordan, A. W. Rodgers, Graeme H. Smith,
Tópico(s)Geological and Geophysical Studies
Resumoview Abstract Citations (21) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Chromospheres of Two Red Giants in NGC 6752 Dupree, A. K. ; Harper, G. M. ; Hartmann, L. ; Jordan, Carole ; Rodgers, A. W. ; Smith, Graeme H. Abstract Two red giant stars, A31 and A59, in the globular cluster NGC 6752 exhibit Mg II (2800 A) emission with surface fluxes comparable to those observed among metal-deficient halo field giants, and among low-activity Population I giants. Optical echelle spectra of these cluster giants reveal emission in the core of the Ca II K (3933.7 A) line, and in the wing of the H-alpha (6562.8 A) profile. Asymmetries exist both in the emission profiles and the line cores. These observations demonstrate unequivocally the existence of chromospheres among old halo population giants, and the presence of mass outflow in their atmospheres. Maintenance of a relatively constant level of chromospheric activity on the red giant branch contrasts with the decay of magnetic dynamo activity exhibited by dwarf stars and younger giants. A purely hydrodynamic phenomenon may be responsible for heating the outer atmospheres of these stars, enhancing chromospheric emission, thus extending the atmospheres and facilitating mass loss. Publication: The Astrophysical Journal Pub Date: September 1990 DOI: 10.1086/185815 Bibcode: 1990ApJ...361L...9D Keywords: Chromosphere; Globular Clusters; Red Giant Stars; Emission Spectra; H Alpha Line; Metallicity; Stellar Evolution; Ultraviolet Spectra; Astrophysics; CLUSTERS: GLOBULAR; STARS: CHROMOSPHERES; STARS: MASS LOSS; STARS: POPULATION II; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (3) MAST (1) INES (1)
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