Chemical Complexity in the Eu-enhanced Monometallic Globular NGC 5986
AuthorJohnson, Christian I.
Rich, R. Michael
Bailey III, John I.
Olszewski, Edward W.
Walker, Matthew G.
AffiliationUniv Arizona, Steward Observ
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationChemical Complexity in the Eu-enhanced Monometallic Globular NGC 5986 2017, 842 (1):24 The Astrophysical Journal
JournalThe Astrophysical Journal
Rights© 2017. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at email@example.com.
AbstractNGC 5986 is a poorly studied but relatively massive Galactic globular cluster that shares several physical and morphological characteristics with "iron-complex" clusters known to exhibit significant metallicity and heavy-element dispersions. In order to determine whether NGC 5986 joins the iron-complex cluster class, we investigated the chemical composition of 25 red giant branch and asymptotic giant branch cluster stars using high-resolution spectra obtained with the Magellan-M2FS instrument. Cluster membership was verified using a combination of radial velocity and [Fe/H] measurements, and we found the cluster to have a mean heliocentric radial velocity of +99.76 km s(-1) (sigma = 7.44 km s(-1)). We derived a mean metallicity of [Fe/H] = -1.54 dex (sigma = 0.08 dex), but the cluster's small dispersion in [Fe/H] and low [La/Eu] abundance preclude it from being an iron-complex cluster. NGC 5986 has <[Eu/Fe]> = +0.76 dex (sigma = 0.08 dex), which is among the highest ratios detected in a Galactic cluster, but the small [Eu/Fe] dispersion is puzzling because such high values near [Fe/H] similar to -1.5 are typically only found in dwarf galaxies exhibiting large [Eu/Fe] variations. NGC 5986 exhibits classical globular cluster characteristics, such as uniformly enhanced [alpha/Fe] ratios, a small dispersion in Fe-peak abundances, and (anti) correlated light-element variations. Similar to NGC 2808, we find evidence that NGC 5986 may host at least four to five populations with distinct light-element compositions, and the presence of a clear Mg-Al anticorrelation along with an Al-Si correlation suggests that the cluster gas experienced processing at temperatures. greater than or similar to 65-70 MK. However, the current data do not support burning temperatures exceeding similar to 100 MK. We find some evidence that the first-and second-generation stars in NGC 5986 may be fully spatially mixed, which could indicate that the cluster has lost a significant fraction of its original mass.
VersionFinal published version
SponsorsNational Aeronautics and Space Administration; Clay Fellowship; National Science Foundation [AST-0923160, AST-1312997, AST-1313045, AST-1412999, AST-1413755, AST-1313006]