AAS 201st Meeting, January, 2003
Session 117. Delta Scuti and Pulsating Friends
Poster, Thursday, January 9, 2003, 9:20am-4:00pm, Exhibit Hall AB

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[117.13U] Pulsations in Metal-Deficient Field Giants

E. Alicea-Muñoz (U Puerto Rico at Mayagüez Campus), A. K. Dupree (Harvard-Smithsonian CfA)

Emission wings in H-\alpha profiles generally occur in spectra of the luminous metal-deficient field giants and in red giants in globular clusters. Asymmetries and variability of this emission have hinted that pulsating motions may be present in the chromospheres of these stars. Pulsation could lead to atmospheric extension and facilitate the mass loss necessary to explain morphology of the red giant branch in globular clusters.

Eight metal deficient field giant stars (HD 6833, HD 29574, HD103036, HD 110184, HD 110281, HD 122563, HD 165195, HD 232078) were observed through the Synoptic Series Observing Program at the McMath-Pierce Telescope at NSO during most of 1995. Nine to 49 spectra, at a resolution of 43000 were obtained of each target, with the average number being 25. These spectra represent the first spectroscopic time series of chromospheric emission for metal deficient objects. The majority of giants exhibit variable H\alpha emission, generally changing in a systematic way. For several giants, a periodicity of ~50 days was detected in the asymmetry of the H-\alpha wings. Because radiative transfer considerations and modeling suggest the relative strengths of the short and long wavelength emission represent mass motions in the chromosphere, these stars give evidence for periodic pulsation. In several stars, such motions are found also in the velocity variation of the H-\alpha core. The most metal rich star in the sample (HD 6833; [Fe/H]=--0.9) and also the least luminous does not exhibit variability in H\alpha whereas more metal-deficient objects (more luminous) generally show periodic motions. Thus pulsation appears to be present in the most luminous objects, and can contribute to mass loss needed for evolutionary considerations.

This work was supported in part by NSF grant AST-9731923 to the SAO Summer Intern program.

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