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: Research - peer-reviewArticle

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Abstract

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.

LanguageEnglish (US)
Article number168
JournalAstrophysical Journal
Volume836
Issue number2
DOIs
StatePublished - Feb 20 2017

Fingerprint

globular clusters
chemical composition
iron
stars
chemical
metallicity
kinematics
analysis
star distribution
heavy elements
chemical analysis
neutrons
high resolution

Keywords

  • 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

Cite this

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

A Chemical Composition Survey of the Iron-complex Globular Cluster NGC 6273 (M19). / Johnson, Christian I.; Caldwell, Nelson; Rich, R. Michael; Mateo, Mario; Bailey, John I.; Clarkson, William I.; Olszewski, Edward W.; Walker, Matthew G.

In: Astrophysical Journal, Vol. 836, No. 2, 168, 20.02.2017.

Research output: Research - peer-reviewArticle

Johnson, CI, Caldwell, N, Rich, RM, Mateo, M, Bailey, JI, Clarkson, WI, Olszewski, EW & Walker, MG 2017, 'A Chemical Composition Survey of the Iron-complex Globular Cluster NGC 6273 (M19)' Astrophysical Journal, vol 836, no. 2, 168. DOI: 10.3847/1538-4357/836/2/168
Johnson CI, Caldwell N, Rich RM, Mateo M, Bailey JI, Clarkson WI et al. A Chemical Composition Survey of the Iron-complex Globular Cluster NGC 6273 (M19). Astrophysical Journal. 2017 Feb 20;836(2). 168. Available from, DOI: 10.3847/1538-4357/836/2/168
Johnson, Christian I. ; Caldwell, Nelson ; Rich, R. Michael ; Mateo, Mario ; Bailey, John I. ; Clarkson, William I. ; Olszewski, Edward W. ; Walker, Matthew G./ A Chemical Composition Survey of the Iron-complex Globular Cluster NGC 6273 (M19). In: Astrophysical Journal. 2017 ; Vol. 836, No. 2.
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