Astrophys. J., 836, 168-168 (2017/February-3)
A chemical composition survey of the iron-complex globular cluster NGC 6273 (M19).
JOHNSON C.I., CALDWELL N., RICH R.M., MATEO M., BAILEY III J.I., CLARKSON W.I., OLSZEWSKI E.W. and WALKER M.G.
Abstract (from CDS):
Recent observations have shown that a growing number of the most massive Galactic globular clusters contain multiple populations of stars with different [Fe/H] and neutron-capture element abundances. NGC 6273 has only recently been recognized as a member of this "iron-complex" cluster class, and we provide here a chemical and kinematic analysis of >300 red giant branch and asymptotic giant branch member stars using high-resolution spectra obtained with the Magellan-M2FS and VLT-FLAMES instruments. Multiple lines of evidence indicate that NGC 6273 possesses an intrinsic metallicity spread that ranges from about [Fe/H] = -2 to -1 dex, and may include at least three populations with different [Fe/H] values. The three populations identified here contain separate first (Na/Al-poor) and second (Na/Al-rich) generation stars, but a Mg-Al anti-correlation may only be present in stars with [Fe/H] >= -1.65. The strong correlation between [La/Eu] and [Fe/H] suggests that the s-process must have dominated the heavy element enrichment at higher metallicities. A small group of stars with low [α/Fe] is identified and may have been accreted from a former surrounding field star population. The cluster's large abundance variations are coupled with a complex, extended, and multimodal blue horizontal branch (HB). The HB morphology and chemical abundances suggest that NGC 6273 may have an origin that is similar to ω Cen and M54.
© 2017. The American Astronomical Society. All rights reserved.
globular clusters: general - globular clusters: individual: (NGC 6273, M19) - stars: abundances - stars: abundances
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<Available at CDS (J/ApJ/836/168): table1.dat table2.dat table3.dat table4.dat table5.dat table6.dat table7.dat>
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