A Chemical Composition Survey of the Iron-complex Globular Cluster NGC 6273 (M19)

作者：Johnson Christian I; Caldwell Nelson; Rich R Michael; Mateo Mario; Bailey John I III; Clarkson William I; Olszewski Edward W; Walker Matthew G

来源：Astrophysical Journal, 2017, 836(2): 168.

DOI：10.3847/1538-4357/836/2/168

• globular clusters
• general - globular clusters
• individual ( NGC 6273, M19) - stars
• abundances Supporting material
• machine-readable tables

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] greater than or similar to -1.65. The strong correlation between [La/Eu] and [Fe/H] suggests that the sprocess must have dominated the heavy element enrichment at higher metallicities. A small group of stars with low [alpha/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 omega Cen and M54.

• 出版日期2017-2-20