A SPECTROSCOPIC ANALYSIS OF THE GALACTIC GLOBULAR CLUSTER NGC 6273 (M19)

A combined effort utilizing spectroscopy and photometry has revealed the existence of a new globular cluster class. These "anomalous" clusters, which we refer to as "iron-complex" clusters, are differentiated from normal clusters by exhibiting large ([gap]0.10 dex) intrinsic meta...

Full description

Saved in:
Bibliographic Details
Published in:The Astronomical journal 2015-08, Vol.150 (2), p.1-21
Main Authors: Johnson, Christian I, Rich, R Michael, Pilachowski, Catherine A, Caldwell, Nelson, Mateo, Mario, Bailey, John I, Crane, Jeffrey D
Format: Article
Language:English
Subjects:
ALUMINIUM
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
CLAYS
Clusters
ELEMENT ABUNDANCE
Globular clusters
HYDROGEN
IRON
IRON COMPLEXES
LANTHANUM
METALLICITY
PHOTOMETRY
Populations
RADIAL VELOCITY
RESOLUTION
S PROCESS
SODIUM
STAR CLUSTERS
STARS
TELESCOPES
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:A combined effort utilizing spectroscopy and photometry has revealed the existence of a new globular cluster class. These "anomalous" clusters, which we refer to as "iron-complex" clusters, are differentiated from normal clusters by exhibiting large ([gap]0.10 dex) intrinsic metallicity dispersions, complex sub-giant branches, and correlated [Fe/H] and s-process enhancements. In order to further investigate this phenomenon, we have measured radial velocities and chemical abundances for red giant branch stars in the massive, but scarcely studied, globular cluster NGC 6273. The velocities and abundances were determined using high resolution (R ~ 27,000) spectra obtained with the Michigan/Magellan Fiber System (M2FS) and MSpec spectrograph on the Magellan-Clay 6.5 m telescope at Las Campanas Observatory. We find that NGC 6273 has an average heliocentric radial velocity of +144.49 km s super(-1) ([sigma] = 9.64 km s super(-1)) and an extended metallicity distribution ([Fe/H] = -1.80 to -1.30) composed of at least two distinct stellar populations. Although the two dominant populations have similar [Na/Fe], [Al/Fe], and [ alpha /Fe] abundance patterns, the more metal-rich stars exhibit significant [La/Fe] enhancements. The [La/Eu] data indicate that the increase in [La/Fe] is due to almost pure s-process enrichment. A third more metal-rich population with low [X/Fe] ratios may also be present. Therefore, NGC 6273 joins clusters such as omega Centauri, M2, M22, and NGC 5286 as a new class of ironcomplex clusters exhibiting complicated star formation histories.
ISSN:1538-3881
0004-6256
1538-3881
DOI:10.1088/0004-6256/150/2/63