Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.8204f&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #82.04; Bulletin of the American Astronomical Society, Vol. 24, p.1256
Other
Scientific paper
Analysis of spectra from the Hopkins Ultraviolet Telescope (HUT) suggests Extreme-Horizontal-Branch (EHB) stars and AGB-Manque stars as the dominant contributors to the far-UV rising branch in the most metal-rich galaxies (NGC1399 in particular), while in less-metal-rich galaxies (the bulge of M31 in particular), Post-Asymptotic-Giant-Branch (PAGB) stars may be significant contributors. If these inferences from the far-UV HUT data are correct, there are interesting implications for the stellar populations in elliptical galaxies at other wavelengths. In metal rich galaxies that show the strongest far-UV upturns, it is possible that the low-mass stars that produce the UV emission never reach the tip of the AGB. In this case both planetary nebulae and stars at the tip of the AGB represent only the low-metallicity tail of the full metallicity distribution in giant ellipticals; in galaxies of lower metallicity, these stars sample the population closer to the peak of the metallicity distribution. This scenario produces the following testable predictions: 1) The number of planetary nebula (PN) per unit V-band luminosity should decrease with increasing metallicity; 2) in metal-rich systems such as elliptical galaxies and spiral bulges, the metal abundances of PN should be below the mean galaxian metal abundance deduced from optical absorption lines; 3) the number of luminous AGB stars per unit V-band luminosity should decrease with increasing metallicity; 4) in metal-rich systems the metallicities of stars near the tip of the AGB should be lower in the mean than the metallicities of RGB or main-sequence stars. We examine available data and find that many of these consequences are consistent with, if not actually required by, the observations. We discuss implications of these findings for the cosmic distance scale derived from planetary nebulae and surface-brightness fluctuations.
Davidsen Arthur F.
Ferguson Henry C.
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