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Title: RUBIDIUM ABUNDANCES IN THE GLOBULAR CLUSTERS NGC 6752, NGC 1904, AND NGC 104 (47 Tuc)

Large star-to-star variations of the abundances of proton-capture elements, such as Na and O, in globular clusters (GCs) are interpreted as the effect of internal pollution resulting from the presence of multiple stellar populations. To better constrain this scenario, we investigate the abundance distribution of the heavy element rubidium (Rb) in NGC 6752, NGC 1904, and NGC 104 (47 Tuc). Combining the results from our sample with those in the literature, we found that Rb exhibits no star-to-star variations, regardless of cluster metallicity, with the possible intriguing, although very uncertain, exception of the metal-rich bulge cluster NGC 6388. If no star-to-star variations can be confirmed for all GCs, this finding implies that the stellar source of the proton-capture element variations must not have produced significant amounts of Rb. This element is observed to be enhanced at extremely high levels in intermediate-mass asymptotic giant branch (IM-AGB) stars in the Magellanic Clouds (i.e., at a metallicity similar to 47 Tuc and NGC 6388). This fact may present a challenge to this popular candidate polluter, unless the mass range of the observed IM-AGB stars does not participate in the formation of the second-generation stars in GCs. A number of possible solutions are availablemore » to resolve this conundrum, including the fact that the Magellanic Cloud observations are very uncertain and may need to be revised. The fast rotating massive stars scenario would not face this potential problem as the slow mechanical winds of these stars during their main-sequence phase do not carry any Rb enhancements; however, these candidates face even bigger issues such as the production of Li and the close overlap with core-collapse supernova timescales. Observations of Sr, Rb, and Zr in metal-rich clusters such as NGC 6388 and NGC 6441 are sorely needed to clarify the situation.« less
Authors:
 [1] ; ;  [2] ; ;  [3] ; ;  [4] ;  [5]
  1. Department of Physics and Astronomy, Macquarie University, Balaclava Road, North Ryde, NSW 2109 (Australia)
  2. Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Building 28, Clayton, VIC 3800 (Australia)
  3. INAF Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
  4. INAF Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, I-35122 Padova (Italy)
  5. INAF Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio (Italy)
Publication Date:
OSTI Identifier:
22270743
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 776; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; ASYMPTOTIC SOLUTIONS; CAPTURE; ELEMENT ABUNDANCE; LITHIUM; MAGELLANIC CLOUDS; MAIN SEQUENCE STARS; MASS; OXYGEN; PROTONS; SODIUM; STAR CLUSTERS; STELLAR WINDS; STRONTIUM; SUPERNOVAE; VARIATIONS