Astrophys. J., 842, 24-24 (2017/June-2)
Chemical complexity in the eu-enhanced monometallic globular NGC 5986.
JOHNSON C.I., CALDWELL N., RICH R.M., MATEO M., BAILEY III J.I., OLSZEWSKI E.W. and WALKER M.G.
Abstract (from CDS):
NGC 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 (σ = 7.44 km s–1). We derived a mean metallicity of [Fe/H] = -1.54 dex (σ = 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 (σ = 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] ∼ -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 [α/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 >=65-70 MK. However, the current data do not support burning temperatures exceeding ∼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.
© 2017. The American Astronomical Society. All rights reserved.
globular clusters: general - globular clusters: individual: NGC 5986 - stars: abundances - stars: abundances
View the reference in ADS
To bookmark this query, right click on this link: simbad:2017ApJ...842...24J and select 'bookmark this link' or equivalent in the popup menu