High [Si/Mg] = 0.67 in NGC 1277 cannot be explained by standard models and suggests pair-instability supernovae from very massive early stars.
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abstract
High signal-to-noise integrated spectra of the metal-rich globular cluster 47 Tuc, spanning the H-gamma(HR) and Fe4668 line indices, have been obtained. The combination of these indices has been suggested (Jones & Worthey 1995, ApJ, 446, L31) as the best available mechanism for cleanly separating the age-metallicity degeneracy which hampers the dating of distant, unresolved, elliptical galaxies. For the first time, we apply this technique to a nearby spheroidal system, 47 Tuc, for which independent ages, based upon more established methods, exist. Such an independent test of the technique's suitability has not been attempted before, but is an essential one before its application to more distant, unresolved, stellar populations can be considered valid. Because of its weak series of Balmer lines, relative to model spectra, our results imply a spectroscopic ``age'' for 47 Tuc well in excess of 20 Gyr, at odds with the colour-magnitude diagram age of 14+/-1 Gyr. The derived metal abundance, however, is consistent with the known value. Emission ``fill-in'' of the H-gamma line as the source of the discrepancy cannot be entirely excluded by existing data, although the observational constraints are restrictive.
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HST photometry reveals radial color gradients in two ETGs that match predictions from the multiple-population scenario linking the UV upturn to second-generation stars from dissolved globular clusters.
citing papers explorer
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Chemical hints of Population III stars from silicon abundances in massive galaxies
High [Si/Mg] = 0.67 in NGC 1277 cannot be explained by standard models and suggests pair-instability supernovae from very massive early stars.
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A Colour-colour Fingerprint Links the UV Upturn in Early-type Galaxies to Second-generation Stars from Dissolved Globular Clusters
HST photometry reveals radial color gradients in two ETGs that match predictions from the multiple-population scenario linking the UV upturn to second-generation stars from dissolved globular clusters.