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

Christian I. Johnson, Nelson Caldwell, R. Michael Rich, Mario Mateo, John I. Bailey, William I. Clarkson, Edward W. Olszewski, Matthew G. Walker

Research output: Contribution to journalArticle

17 Scopus citations


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.

Original languageEnglish (US)
Article number168
JournalAstrophysical Journal
Issue number2
StatePublished - Feb 20 2017


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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Johnson, C. I., Caldwell, N., Rich, R. M., Mateo, M., Bailey, J. I., Clarkson, W. I., Olszewski, E. W., & Walker, M. G. (2017). A Chemical Composition Survey of the Iron-complex Globular Cluster NGC 6273 (M19). Astrophysical Journal, 836(2), [168]. https://doi.org/10.3847/1538-4357/836/2/168